- Email: [email protected]
Behavior of connections between square CFST columns and H-section steel beams
Journal of Constructional Steel Research 145 (2018) 10–27
Contents lists available at ScienceDirect
Journal of Constructional Steel Research
Behavior of connections between square CFST columns and H-section steel beams Bin-yang Li a,b, Yuan-Long Yang a,b,⁎, Yohchia-Frank Chen a,b, Wei Cheng c, Lin-Bo Zhang a,b a b c
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Ministry of Education), Chongqing University, Chongqing 400045, China School of Civil Engineering, Chongqing University, Chongqing 400045, China Huanqiu Contracting & Engineering Corp. (Guangzhou) CO., LTD, Guangzhou 510000, China
a r t i c l e
i n f o
Article history: Received 25 August 2017 Received in revised form 20 January 2018 Accepted 6 February 2018 Available online xxxx Keywords: Beam-column connection Square concrete filled steel tube Finite element model Static behavior Seismic behavior
a b s t r a c t Three large-scale connections between square concrete-filled steel tubular (CFST) columns and H-section steel beams were tested. The specimens include one connection with continuous flange under static load and two connections with continuous flange and vertical anchor respectively under seismic loads. The static properties of strength and ductility are calculated for static connection based on load-displacement curves, while the seismic properties of strength, ductility, stiffness degradation and energy dissipation are calculated for seismic connections based on hysteretic load-displacement curves. Combining the mechanical properties, experimental phenomena and strain development, beam hinge failure mode can be identified for all specimens. The measured beam strengths of specimens are compared with those predicted by the current AISC-360, EC4 and GB500172003 codes. The study results show that all connections are reliable. A finite element model (FEM), developed and verified with the experimental results, is used to perform parametric analysis. Furthermore, design suggestions are presented. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction The structures with concrete-filled steel tubular (CFST) columns have been widely used for several decades due to their excellent strength, ductility and constructional convenience [1–3]. The most important component of a CFST frame structure is the beam-column connection [4,5]. The seismic behavior of connection has great influence on the reliability of a building. Because of the popularity of structures with CFST columns in applications, many researches on the behavior of connections between CFST columns and steel beams have been reported in the past three decades. In the process of research and engineering, various connection details have been developed. Details can be generalized into two broad categories: connections that attach to the face of the steel tube only, and connections that use elements embedded into the concrete core. Connections to the face of the steel tube include, for example, connections with stiffening rings [6–8] and connections with vertical stiffeners [9,10], etc. Conclusions from these studies showed these connection details exhibited good seismic performance. However, restricted by column size, these connection details are not applicable to large-section columns (far more ⁎ Corresponding author at: Key Laboratory of New Technology for Construction of Cities in Mountain Area (Ministry of Education), Chongqing University, Chongqing 400045, China. E-mail address: [email protected] (Y.-L. Yang).
https://doi.org/10.1016/j.jcsr.2018.02.005 0143-974X/© 2017 Elsevier Ltd. All rights reserved.
larger than beam sections) located at the lower floors of high-rise buildings. Connections with embedded elements include, for example, through bolting with end plates [11–14] and continuous structural steel components through the column [15–18]. The test data indicated that embedding connection components into the concrete core could alleviate high shear demand on the tube wall, which may improve the seismic performance of the connections. Experimental researches above on CFST connections showed that the behavior of connections has varied significantly depending on details of connections. In the 1990s, Schneider and Alostaz [19,20] investigated various details of connections between circular CFST columns and H-section beams by FEM method and experiments. Results showed that the connection detail which beam passed through column provided the best cyclic strength and ductility. Additional tests and further theoretical analysis were performed by Elremaily and Azizinamini [21,22]. To investigate cyclic behavior of various details of connections between square CFST column and H-section beams, Chang-Hoon Kang et al. [23] tested eight interior connections with external T-stiffeners in 2001. Results showed that types of internal penetrated elements (re-bar or bent plate) had similar effect on connection performance. In 2004, four types of connections details (interior diaphragms, exterior extended, structural tees and split tees) were tested by J. M. Ricles et al. [24]. The result indicated that moment resisting connection details can be economically designed that enable more than 0.045 rad of inelastic story drift angle to be developed under cyclic loading.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
From the beginning of 21th century, researchers began to pay attention to the performance of connections with slab [25,26]. In 2007, two interior and two exterior joints were tested by Chin-Tung Cheng et al. [27] to evaluate the composite effect of steel beam and floor slab commonly used in Taiwan in practice. Results showed the composite effect of floor slab and beam was significant under sagging moment. In contrast, the flexural strength of composite beams under hogging moment was only slightly increased. According to the former researches, the CFST columns with high strength, can significantly reduce the column sections and are widely applied at lower floors of high-rise buildings. In this case, the column sections are much larger than beam sections. A 468-metre high-rise building (T2 tower of Chongqing Shuion project in Fig. 1), located at Chongqing city of China, adopted large section CFST columns. Connection details of continuous flange between square CFST columns and Hsection beams were used at floor L50 to L66. The cross-section of column and beam are 1550 × 38 and H800 × 250 × 14 × 26, respectively. To investigate the actual behavior of connections with large columns and small beams, these connections are used as prototype to design specimens in this paper. The floor slab, of which the influence on the connection behavior is very important, is not taken into consideration in the first-step experiment in this paper. The research about the effect of floor slab will be conducted by the authors and the results will be published in the future. This paper presents an in-depth study on the static and seismic behaviors of large-scale connections between square CFST columns and H-section steel beams. Two types of connections with embedded elements (continuous flange and vertical anchor) are compared and studied. The strength, ductility and other mechanical properties of specimens are analyzed in the experiments. A further parametric
11
study is conducted with FEM to investigate the following parameters: (1) thickness of continuous flange tf; (2) width of continuous flange bf; (3) thickness of horizontal plate th; (4) thickness of vertical anchor tv; (5) depth of vertical anchors da; (6) width of horizontal plate and vertical anchor bh. Based on the parametric analysis, some design suggestions are presented to achieve better cost effectiveness in actual engineering structures. 2. Experimental design 2.1. Details of specimens Based on the real connections of T2 tower of Chongqing Shuison project, a total of three square CFST column to H-section steel beam connection specimens were tested. The specimens include one static connection with continuous flanges (JS-1 in Fig. 2) and two seismic connections respectively with continuous flanges and vertical anchors (JD-1 and JD-2 in Fig. 3). More detailed information of the test specimens including the dimensions and locations of strain gauges are respectively given in Figs. 2, 3 and Table 1. Before assembling the column tubes, embedded elements were fillet welded to steel plates. The continuous flange in the JS-1 and JD-1 specimens and horizontal plates in the JD-2 specimen, welded at the same height with the beam flanges, can be deemed as extension of beam flanges. After assembling steel tube, the H-section beams were fillet welded to the steel tube. Large reduced scale was adopted for static and seismic connections within the limit of experiment devices (Table 1). For JS-1, the axial compression ratio n of column is 0.31. For JD-1 and JD-2, the axial compression ratio n of columns is 0.33. Steel ratio α of CFST column is about 10%. The measured steel and concrete material properties of the specimens are listed in Table 2. The compressive cylinder strength of concrete fc,k was converted from compressive cubic strength of concrete fcu,k based on Chinese concrete code (GB50010-2010) [28]. 2.2. Experimental set-up and measuring apparatus The experimental set-up and locations of measuring apparatus for static loading test are shown in Figs. 4, and 5. A 10,000 kN hydraulic compression machine was used to apply a constant axial compressive load. Two 2000 kN hydraulic jacks were located at the ends of the beams to apply upward shear loads. To prevent out-of-plane displacement at beams' ends, lateral supports were arranged on both sides of the beams. Four displacement sensors (LVDTs) were placed on each surface of column to measure its vertical shortening. Two LVDTs were placed at both ends of the beams to measure the vertical displacements. Inclinometers were arranged on the beam flanges to measuring their rotation angles. The experimental set-up and locations of measuring apparatus for the seismic loading test are shown in Figs. 6 and 7. The ends of beams were pinned to vertical rigid trusses whose another ends were pinned to ground. Constant vertical compressive load and cyclic horizontal load (or displacement) were applied at the top of columns. The cyclic loading scheme, according to the Chinese code (JGJ/T 101-2015) [29], is shown in Fig. 8. This loading system considers second-order effect of vertical compressive load on the top of column, which is similar to that in actual frame structures. Similar to static system, LVDTs are used to measure the horizontal displacement of column. And inclinometers are used to measure the rotation angels of beams and column. 3. Static behavior of CFST column to H-section connection 3.1. Failure mode of specimen JS-1
Fig. 1. T2 tower of Chongqing Shuion project.
The failure mode of specimen JS-1 is shown in Fig. 9. When loading to 300 kN (corresponding displacement was 5.14 mm to beam 1 and
12
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 2. Dimensions and arrangement of strain gauges of JS-1. Note: The length of beam (760 mm) is the distance from tube surface to the center of loading area at the beam end.
12.32 mm to beam 2), data of strain gauges showed that beam flanges reached yield strain. Since then, the force control loading program was replaced by displacement control. The loading process was finally stopped at maximum beam displacement of 35 mm, and the corresponding average rotation angle of beams reached about 0.045 rad (in Fig. 9a), which was large enough for engineering application. Because lateral supports could not fully prevent the torsion of beams, especially when the torsional imperfection of beams existed, the final torsional angles of beams reached about 2° (beam 1) and 6° (beam 2) (in Fig. 10). Moreover, influenced by beam torsion, local buckling occurred at the web of beam 2 (in Fig. 9b), which led the ultimate load of beam 2
about 15% lower than that of beam 1. Meanwhile, there was no obvious phenomenon on column tube during the whole test. Taking these aspects into consideration, the failure mode of JS-1 can be identified as beam-hinge failure.
3.2. Load-deformation curve of specimen JS-1 The load-displacement curves and moment-rotation curves of beams in JS-1 are shown in Fig. 11. Accordingly, the mechanical properties of JS-1 are listed in Table 3.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
13
Fig. 3. Dimensions and locations of strain gauges of JD-1 and JD-2. Note: The length of beam (1300 mm) is the distance from tube surface to the center of loading area at the beam end.
The vertical shear load of beams kept increasing constantly from yield point to the completion of test and the rotational angles of steel beams were largely developed (0.0464 rad for beam 1 and 0.0468 rad for beam 2), revealing good ductility of specimen. The comparison of vertical loads of steel beams between experiment and codes AISC 360-2010, BS EN 1993-1-1:2005 and GB50017-2003 are given in Table 4. Because of strain hardening, the experimental ultimate vertical loads are approximately 25%, 34% and 24% higher than that of AISC 360-2010 [30], BS EN 1993-1-1:2005 [31] and GB 50017-2003 [32], respectively. In addition, the experimental peak vertical loads are
13% higher than calculated plastic flexural capacity. Analysis above reveals the failure mode of JS-1 is beam plastic hinge and continuous flange is reliable enough to allow beam achieve calculated plastic moment. This illustrates continuous flange is a kind of practical connection for composite structure. 3.3. Strain of specimen The elastic-plastic analysis method is adopted to analyze the stress of the steel component. According to this method, the stress along the
Table 1 Detailed parameters of experimental specimens. Specimen
Embedded element
Reduced scale
Tube section
α (%)
Beam section
n
N (kN)
JS-1 JD-1
Continuous flange Continuous flange
775 × 20 400 × 10
11.2 10.8
H400 × 125 × 8 × 14 H320 × 100 × 6 × 10
0.31 0.33
8000 2000
JD-2
Vertical anchor
1:2 Column section (1:4) Beam section (1:2.5) Column section (1:4) Beam section (1:2.5)
400 × 10
10.8
H320 × 100 × 6 × 10
0.34
2200
Notes: (i) α = steel ratio of CFST column section; (ii) N = axial compressive load; (iii) n = N/(Asfy + Acfc,k) = axial compression ratio of columns; As = area of steel tube; fy = yield strength of steel tube; Ac = area of concrete; fc,k = compressive cylinder strength of concrete.
14
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Table 2 Material properties of steel and concrete. Specimen
JS-1
JD-1
JD-2
Steel
Concrete
Components
Thickness (mm)
fy (MPa)
fu (MPa)
fcu,k (MPa)
fc,k (MPa)
Tube Flange Web Continuous flange Tube Flange Web Continuous flange Tube Flange Web Horizontal plate Vertical anchor
20.08 13.64 7.52 13.64 9.82 9.82 5.90 13.85 9.82 9.82 5.90 13.85 13.85
276.1 275.2 279.5 275.2 246.3 246.3 284.4 255.6 246.3 246.3 284.4 255.6 255.6
434.2 450.2 419.5 450.2 401.0 401.0 416.8 412.7 401.0 401.0 416.8 412.7 412.7
25.2
16.8
23.4
15.6
27.2
18.2
Fig. 5. Diagram of static measurement.
Notes: (i) fy = yield strength of steel tube; (ii) fu = ultimate strength of steel tube; (iii) fcu, k = compressive cubic strength of concrete.
thickness is small and can be neglected. Therefore, the steel plate can be treated as a plane-stress problem. Von Mises yield criterion is thus employed to describe the yielding behavior of the steel. Fig. 12 illustrates the analysis results of JS-1, in which σv and σh are longitudinal stress and transverse stress of the steel plates respectively and σz is the equivalent stress determined from the following equation pffiffiffiqffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 ðσ v −σ h Þ2 þ σ 2v þ σ 2h σz ¼ 2
The confinement for concrete provided by steel tube is a kind of passive confinement after lateral concrete expansion emerged. For the compression ratio of the column is only 0.31, the lateral concrete expansion is relatively small during the elastic stage. Therefore, the influence of confinement for the concrete is not considered in the mechanical behavior of the specimen in this experiment.
4. Seismic behavior of CFST column to H-section connection ð1Þ
In Fig. 12(a) and (b), the average stress along the beams length all reached the yield point. (The yield stress of flange and web are 275.2 MPa and 279.5 MPa respectively). Since then, the growth rate of equivalent stress at mid-height of web was accelerated and reached yield stress (S23-2 in Fig. 2a). The stress-load curves of continuous flanges are shown in Fig. 12(c). The stress of continuous flange in tension (S41-1, 4, 6) all reached the yield point, while that in compression (S42-5) didn't reach the yield point. Analyzing the stress of S41-1, 4 and 6, the stress of region near tube was comparatively higher. This is attributed to the friction between concrete and plate, which reduced the tension strain inside tube.
4.1. Failure mode of specimen 4.1.1. Specimen JD-1 The failure mode of JD-1 is shown in Fig. 13. When horizontal load just entered descending stage, loading device began to irregularly shake due to impurities in hydraulic oil. In order to ensure safety, the test terminated. It took about one week for repairing devices. When test terminated, the story drift ratio reached about 2.4%, and the horizontal load of column felt to 96.8% of peak load. Local buckling of steel beam and fracture of welds were not detected during test. Removing the tube after test, concrete crack was not detected in the joint panel zone (in Fig. 13a). While, some slight vertical cracks were found above beam top flange (in Fig. 13b). This phenomenon may be attributed to the bending moment at column end. The beams' flanges reached yield
Fig. 4. Static loading program.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
15
Fig. 6. Seismic loading program.
point at the story drift ratio of approximately 0.91%. Considering the stress of beam flanges and phenomenon within the joint zone, the failure mode of JD-1 can be identified as beam-hinge failure. 4.1.2. Specimen JD-2 The failure mode of JD-2 is shown in Figs. 14 and 15. The strain of beams' flanges reached yield strain at the story drift ratio of 0.9%. When the story drift ratio reached about 2%, due to slip of continuous flange and slight punching shear deformation of concrete, a drum deformation of steel tube with 3 mm pull-out displacement was detected (in Fig. 14). The area of drum deformation is about 70 mm in vertical direction of steel tube. The pull out displacement increased to about 10 mm when drift ratio reached 2.7%. Slight welding cracks were detected at the end of beam flanges when test terminated (in Fig. 15a). By removing steel tube, similar to JD-1, concrete crack at joint panel zone was not detected (in Fig. 15c). While, concrete cracks were detected over the top beam flanges (in Fig. 15b). These cracks may be attributed to slight punching shear failure. Considering the phenomenon of joint panel zone and beam flanges, the failure mode of JD-2 can be identified as beam-hinge failure. 4.2. Load-deformation curve of specimen The horizontal load-displacement hysteresis curves of the specimens are shown in Fig. 16. Due to the slip of continuous flange [33],
pinch effect of the hysteresis behavior was obvious for JD-1. While the vertical anchor can significantly decrease the pinch effect.
4.3. Strength, ductility and energy dissipation Fig. 17 gives the skeleton curves of specimens. The mechanical properties of the specimens are listed in Table 5, which calculated based on Figs. 15 and 16. The moment of beams of JD-2 is a little higher than that of JD-1. While, the horizontal load of column of JD2 are lower than that of JD-1, due to higher axial load ratio of JD-2. Compare with design codes, the vertical loads of beam increase to approximately 1.2 times of predictions of AISC 360-2010 [30], BS EN 1993-1-1:2005 [31] and GB 50017-2003 [32]. The experimental vertical loads of beams are approximately 15% higher than that corresponding to calculated plastic flexural capacity. Considering all phenomenon above, failure mode of JD-1 and JD-2 can be identified as beam plastic hinge. Both continuous flange and vertical anchor are practical for composite structures. For the ductility analysis, there are normally two ways to define the ductility of a structure or member. One way is to use the ductility coefficients μp at the peak load, which is given by
μ p ¼ Δp =Δy
ð2Þ
16
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 7. Diagram of seismic measurement. Note: (i) H = distance between the center of column hinges; (ii) Before axial loading, vertical rigid trusses is not attached to beam ends.
The other is to calculate the ductility coefficient μu at the ultimate stage, which can be obtained from μ u ¼ Δu =Δy
ð3Þ
The results for the ductility are presented in Table 5. Both specimens show good ductile post-peak load behavior. Because of vertical anchor, the ductility coefficient of JD-2 is larger than that of JD-1. Unfortunately, due to the device problem, the test of JD-1 stopped before dropping to 85% of peak strength. Therefore, the data Δu of JD-1 was not available. For the displacement capacity, the elastic inter-story drift ratios are approximately to 1.0%, which satisfy the demand of 1/550 from Chinese concrete code (GB50010-2010) [28]. The energy dissipation capacity is another important factor to assess a structure's seismic performance. In this paper, equivalent viscous damping coefficient factor ξeq is calculated by
Fig. 8. Horizontal loading scheme of column.
ξeq ¼
S1 2πðS2 þ S3 Þ
ð4Þ
Fig. 9. Failure mode of JS-1.
Fig. 10. Torsional angle of beams.
in Fig. 18b. Combined with the hysteresis loops, both JD-1 and JD-2 have good capacity of energy dissipation. The connection specimen JD-2 has better energy dissipation capacity than specimen JD-1.
Table 3 The mechanical properties of JS-1. Beam number Vy (kN) 1 2
Vu (kN)
My Mu Δy Δu θy (kN∙m) (kN∙m) (mm) (mm) (rad)
300.3 406.6 242.3 240.4 347.4 190.3
303.2 259.0
5.1 7.2
33.95 35.04
θp (rad)
4.4. Stiffness of specimens
0.0065 0.0464 0.008 0.0468
Secant stiffness is used to assess the stiffness degradation of the connections. The secant stiffness of a member with different loading cycles at each load step can be expressed as
Notes: (i) Vy = vertical yield load of steel beam; (ii) Vp = vertical ultimate load of steel beam; (iii) My = Vy × L = yield moment at the fixed ends of beam; L = length of beam; (iv) Mu = Vu × L = ultimate moment at the fixed ends of beam; (v) Δy = displacement at the loading ends of beam corresponding to Vy; (vi) Δu = displacement at the loading ends of beam corresponding to Vu; (vii) θy = Δy/L = average rotational angle of beam corresponding to Δy; (viii) θu = Δu/L = average rotational angle of beam corresponding to Δu.
Ki ¼
Where S1 is the area of the hysteresis loop ABCDA, S2 is the area of the triangle OBF and S3 is the area of the triangle ODE (in Fig. 18a). The relationship between ξeq and inter-story displacement Δ is shown
jþF i j þ j−F i j jþX i j þ j−X i j
ð5Þ
where +Fi (−Fi) is the positive (negative) peak load at the i loading cycle, and +Xi (−Xi) is the corresponding positive (negative) displacement. The degradation of the secant stiffness for all the specimens is
Table 4 The comparison of strengths between experiment and codes. Beam number
VAISC (kN)
VBS (kN)
VGB (kN)
Vyf (kN)
Vpf (kN)
Myf (kN)
Mpf (kN)
1 2
301.1
281.2
303.7
289.2
334.6
219.8
254.3
Beam number
Vy (kN) 300.3 240.4
Vp (kN) 406.6 347.4
Vp/VAISC
Vp/VBS
Vp/VGB
Vp/Vpf
1 2
1.35 1.15
1.25 (Average)
1.45 1.23
1.34 (Average)
1.34 1.14
1.24 (Average)
1.21 1.04
1.13 (Average)
Notes: (i) VAISC = vertical design load calculated according to AISC 360-2010 (LRFD) [30]; (ii) VBS = vertical design load calculated according to BS EN 1993-1-1:2005 [31]; (iii) VGB = vertical design load calculated according to GB50017-2003 [32].
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
19
Fig. 13. The failure mode of specimen JD-1.
plotted in Fig. 19. With the increase of the displacement at different load steps, the stiffness of the specimens is approximately linearly reduced. Compared to JD-1, the stiffness of JD-2 during elastic stage is
approximately 10% higher than that of JD-2. But this difference between tow specimens can be ignored during plastic stage due to the same failure mode of beam plastic hinge.
Fig. 14. Drum deformation of steel tube near beam flanges.
Fig. 15. Experimental phenomenon of JD-1.
20
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 16. Horizontal load-displcement hysteresis curves.
Fig. 17. The skeleton of load-displacement and moment-rotation curves of JD-1, 2.
The classification of joint according to Eurocode 3 Part 1–8 is shown in Fig. 20. Quantitatively, the relationship between M/Mp and Φ/Φp is used to classify the stiffness of joint. Mp and Φp are the plastic moment and plastic rotation angle of steel beam. Φp can be obtained from Φp ¼ Mp Lp =ðEIn Þ
ð6Þ
where Lp is beam span (twice the beam length L of the specimen); In is the moment of inertia of beam section; M is the moment of steel beam which is calculated by shear force V multiplied beam L; Φ, the rotation angle within plastic hinge of steel beam, can be calculated with data of inclinometers on two sides of plastic hinge. As shown in Fig. 20, the curves of JD-1 and JD-2 near or slightly above the boundary line between semi-rigid joint and rigid joint. Therefore both the continuous flange and vertical anchor can achieve rigid joint. 4.5. Strain of specimen The Stress development of JD-1 is shown in Fig. 21. The absolute value of stress is calculated based on the strain data from gauges and material property. In positive direction, the top flange reached yield stress at 28 kN, which was earlier than bottom flange at 65 kN. The flanges reached yield stress simultaneously at −35 kN in negative direction. Instead, the stress of joint tube kept in elastic stage during all test
Table 5 The mechanical properties of JD-1 and 2. Specimen
Fy (kN) Fp (kN) Δy/H (%) Δp/H (%) Δu/H (%) μp μu VAISC (kN) VBS (kN) VGB (kN) Vy (kN) Vp (kN) Vyf (kN) Vpf (kN) Myf (kN∙m) Mpf (kN∙m) Vp/VAISC Vp/VBS Vp/VGB Vy/Vyf Vp/Vpf
JD-1
JD-2
Positive direction
Negative direction
Positive direction
Negative direction
129.3 138.9 1.1 1.3 – 1.18 – 78.1 86.8 75.3 88.3 99.5 71.7 86.8 93.3
145.6 152.3 1.4 1.9 – 1.37 –
123.6 128.4 1.0 1.6 2.5 1.54 2.40
113.1 136.9 0.9 1.8 2.0 2.01 2.59
85.8 97.3
87.3 108.9
76.5 103.1
1.25 1.12 1.29 1.20 1.12
1.39 1.25 1.45 1.22 1.25
1.32 1.19 1.37 1.07 1.19
112.9 1.27 1.15 1.32 1.23 1.15
Notes: (i) Fy = horizontal yield load of column; (ii) Fp = horizontal peak load of column; (iii) Δy = yield displacement of column; (iv) Δu = displacement corresponding to a 15% degradation from the peak load.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
21
0.4
ξeq
0.3 0.2 0.1
JD-1 JD-2
0.0 10
a Typical hysteresis loop
20
30
40
Δ (mm)
50
60
b Equivalent viscous damping coefficient ξeq curves.
Fig. 18. a Typical hysteresis loop. b Equivalent viscous damping coefficient ξeq curves.
(in Fig. 21b). Similar with JD-1, confinement of tube is not considered for JD-1 and 2 either. The stress development agrees with the beamhinge failure mode discussed above. The stress development of JD-2 is shown in Fig. 22. Similar to JD-1, both flanges reached yield stress, while the stress of joint tube kept in elastic stage. 5. Finite element modeling 5.1. General A FEM with ABAQUS software is established in the following to simulate specimens with continuous flange (JS-1 and JD-1) and specimen with vertical anchor (JD-2). The FEM is verified by the experimental results. Furthermore, a parametric study is performed and accordingly some design suggestions were presented.
Fig. 19. Secant stiffness of JD-1 and JD-2.
5.1.1. Materials An elastic-plastic model consisting of five stages is used to describe the mechanical behavior of steel material [34]. A concrete damage plasticity model in ABAQUS software is used to describe
Fig. 20. Classification of joints. Note: The blue line are boundary lines of joint type. A area represents nominal pinned joint; B area represents semi-rigid joint; C area represents rigid joint. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
22
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 21. The stress of JD-1. Notes: (i) V = shear force of beam; (ii) F = horizontal load of column; (iii) Stress is in the direction of length of beams.
concrete material. The confined effect for concrete, which is considered in damage plasticity model but insufficient for experimental CFST columns. So it is modified by increasing peak strain and transforming descending branch of input stress-strain curve according to Li [35] and Zhou [36].
5.1.2. Element type, interaction and boundary conditions The steel tube, beam flange, beam web and embedded elements (continuous flange, horizontal plate and vertical anchor) are modelled using a 4-node general-purpose shell element S4R with reduced integration, hourglass control and membrane strains. The concrete is modelled using an 8-node linear brick solid element C3D8R with reduced integration and hourglass control. A surface-to-surface contact interaction is applied to describe the interaction between steel tube and concrete of the column, by specifying a hard contact property in the normal direction and a friction property in the tangential direction (friction coefficient is chosen as 0.6 [37]. A value of 0.6 MPa is used as the maximum surface bond stress in the Coulomb friction model [36]. The interaction allows separation of the concrete and steel tube after tube's local buckling. Besides, a merge property is used to simulate interaction between steel tube, beams and embedded elements.
For JS-1 and JD-1, the interaction between continuous flange and concrete is ignored in order to simulate the interface slip between them. For JD-2, same interaction modeling is adopted between horizontal plate and concrete, while the embedded constraint is applied between the vertical anchors and concrete. The boundary condition and loading program in the finite element model are simulated completely according to those in the experiments. 5.2. Verifications The shear load V-vertical displacement D curve obtained from FEM is compared with that from experiment in Fig. 23(a). Generally good agreement in elastic stiffness, bearing capacity and ductility is shown between the experimental and predicted results. The plastic strain distribution based on the FEM for specimen JS-1 is shown in Fig. 23(b). It can be seen that the large plastic strain is distributed mainly at the beam end connected to column, coinciding with the failure mode observed from experiment. The comparisons of load- displacement skeleton curves of FEM and experiments are shown in Fig. 25. F is the horizontal load at the top of column; Δ is the displacement at the top of column and V is the vertical shear load at the end of beam. Approximately good agreement is achieved in stiffness and bearing capacity.
Fig. 22. The stress of JD-2.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
23
500
V(kN)
400 300 200 JS-1 (beam 1) FEM
100 0
0
10
20 D(mm)
30
40
(a) Load-displacement of JS-1
(b) Plastic strain distribution of JS-1
Fig. 23. (a) Load-displacement of JS-1. (b) Plastic strain distribution of JS-1.
The strain and stress distributions for JD-1 and JD-2 are shown in Fig. 24. Plastic hinges are observed in FEM which coincide with the failure modes in the experiments (Fig. 24a, b). The continuous flange and horizontal plate in tension all reach yield stress, while those in compression reach yield stress only in the region near steel tube (Fig. 24c). Similar phenomenon is detected in JD-2, the Mises stress of vertical anchors in tension all reach yield stress, while the stress of those in compression is relatively lower than yield stress (Fig. 24d). The distribution of
principal compressive stress in concrete within joint panel zone reveals an obvious strut-tie mechanism in both JD-1 and JD-2 (Fig. 24(e), (f)). Besides, concrete between vertical anchor and steel tube is compressed by vertical anchor (Fig. 24f), due to the tension force transferred from beam. Considering the above analysis, the transmission of tension force from beam depends mostly on embedded anchor and continuous flange. While the transmission of compression force depends mainly on the concrete within joint panel zone.
Fig. 24. Comparison of load-displacement skeleton curves of FEM and experiments.
24
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
5.3. Parametric study Based on the FEM, parametric analysis method is used to investigate the influences of six main parameters on the strength of connections. When the parametric studies are taken on a certain parameter, other parameters are identical to those of JD-1 and JD-2. The parameters include: (1) thickness of continuous flange tf (8 mm, 10 mm, 12 mm, 14 mm, 18 mm, 22 mm); (2) width of continuous flange bf (100 mm, 125 mm, 150 mm, 175 mm); (3) thickness of horizontal plate th (8 mm, 10 mm, 14 mm, 18 mm); (4) thickness of vertical anchor tv (8 mm, 10 mm, 14 mm, 18 mm); (5) the anchoring depth da (90 mm,
120 mm, 150 mm, 180 mm); (6) width of horizontal plate and vertical anchor bh (125 mm, 150 mm, 175 mm, 200 mm). The results of parametric studies are shown in Fig. 26. The parameters tf, th and da have significant effect on the strength of specimens. The strength for tf = 1.8tb is about 1.60 times of that for tf = 0.8tb. The strength for th = 1.4tb is about 1.17 times of that for th = 0.8tb. And the strength for da = 1.5wb is about 1.20 times of that for da = 0.9wb. When these parameters reach their critical values, the strength increases almost stop. And these critical values are suggested as reference values for preliminary design (Table 6). Meanwhile, the influences of wf, tv and wh are slight on the strength of specimens.
Fig. 25. The strain and stress distributions for JD-1 and JD-2.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
25
Fig. 25 (continued).
6. Conclusion This paper investigates both static and seismic behavior of two type of connections between square CFST columns and steel beams. Both experimental and numerical approaches were used to obtain the following conclusion: 1. Static failure mode of connection between CFST columns and steel beams is plastic hinges of steel beams. The continuous flange guarantees plastic yielding of steel beam and effectively transfers internal forces of steel beam to joint panel zone under static loading. 2. Seismic failure mode of connections with continuous flanges or vertical anchors is both plastic hinges of steel beams. Good seismic performance can be expected in these connections. The experimental
value of beam strength is about 1.2 times of value calculated from AISC 360-2010 [30], BS EC 1993-1-1:2005 [31] and GB 50017-2003 [32]. These two types of connections are thus expected to be adoptable in practical building structures. 3. FEM is established and agrees well with the experimental results. Parametric analysis was conducted with FEM to obtain the following design suggestions: (a) thickness of continuous flange (tf) is suggest to be 1.4–1.8 times of thickness of beam flange (tb); (b) width of continuous flange (wf) is suggested to be 1.25 times of width of beam flange (wb); (c) thickness of horizontal plate (th) and thickness of vertical anchor (tv) is suggested to be 1.4 times of thickness of beam flange (tb); (d) depth of vertical anchor (da) and width of horizontal plate and vertical anchor (wh) is suggested to be 1.5 times of width of beam flange (wb).
26
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 26. Parametric studies. Notes: (i) tb = the thickness of beam flange; (ii) wb = the width of beam flange.
Acknowledgements This research is supported by the National Key Research and Development Program of China (Grant No. 2016YFC0701200, 2017YFC0703805), Research and Development Project of Ministry of
Housing and Urban-Rural Development (Grant No. 2014-K2-010) and the Fundamental Research Funds for the Central Universities (Grant No. 106112014CDJZR200001, 106112017CDJXY200010).
References Table 6 The suggested value for parameters. Type of connection
Parameters
Specimen's value
Suggested value
Continuous flange
tf wf th tv da wh
1.4tb 1.0wb 1.4tb 1.4tb 1.5wb 1.5wb
1.4tb to 1.8tb 1.25wb 1.4tb 1.4tb 1.5wb 1.5wb
Vertical anchor
[1] Y.S. Du, Z.H. Chen, J.Y.R. Liew, M.X. Xiong, Rectangular concrete-filled steel tubular beam-columns using high-strength steel: experiments and design, J. Constr. Steel Res. 131 (2017) 1–18. [2] Y.C. Tang, L.J. Li, W.X. Feng, F. Liu, B. Liao, Seismic performance of recycled aggregate concrete–filled steel tube columns, J. Constr. Steel Res. (2017) 112–124. [3] J.P. Liu, X.H. Zhou, S.M. Zhang, Seismic behavior of square CFT beam-columns under biaxial bending moment, J. Constr. Steel Res. 64 (12) (2008) 1473–1482. [4] A.H. Varma, J.M. Ricles, R. Sause, L.W. Lu, Seismic behavior and modeling of highstrength composite concrete-filled steel tube (CFT) beam–columns, J. Constr. Steel Res. 58 (5–8) (2002) 725–758.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27 [5] L.Y. Wu, L.L. Chung, S.F. Tsai, T.J. Shen, G.L. Huang, Seismic behavior of bolted beamto-column connections for concrete filled steel tube, J. Constr. Steel Res. 61 (10) (2005) 1387–1410. [6] J.W. Park, S.M. Kang, S.C. Yang, Experimental studies of wide flange beam to square concrete-filled tube column joints with stiffening plates around the column, J. Struct. Eng. 131 (12) (2005) 1866–1876. [7] W.D. Wang, L.H. Han, B. Uy, Experimental behaviour of steel reduced beam section to concrete-filled circular hollow section column connections, J. Constr. Steel Res. 64 (5) (2008) 493–504. [8] W.D. Wang, L.H. Han, X.L. Zhao, Analytical behavior of frames with steel beams to concrete-filled steel tubular column, J. Constr. Steel Res. 65 (3) (2009) 497–508. [9] J. Kimura, J. Chung, C. Matsui, S. Choi, Structural characteristics of H-shaped beamto-square tube column connection with vertical stiffeners, Int. J. Steel Struct. 5 (2) (2005) 109–117. [10] K.J. Shin, Y.J. Kim, Y.S. Oh, Seismic behaviour of composite concrete-filled tube column-to-beam moment connections, J. Constr. Steel Res. 64 (1) (2008) 118–127. [11] L.Y. Wu, L.L. Chung, et al., Seismic behavior of bidirectional bolted connections for CFT columns and H-beams, Eng. Struct. 29 (3) (2007) 395–407. [12] H. Yao, H. Goldsworthy, E. Gad, Experimental and numerical investigation of the tensile behavior of blind-bolted T-stub connections to concrete-filled circular columns, J. Struct. Eng. 134 (2) (2008) 198–208. [13] X. Li, Y. Xiao, Y.T. Wu, Seismic behavior of exterior connections with steel beams bolted to CFT columns, J. Constr. Steel Res. 65 (7) (2009) 1438–1446. [14] J.F. Wang, L.H. Han, B. Uy, Behaviour of flush end plate joints to concrete-filled steel tubular columns, J. Constr. Steel Res. 65 (4) (2009) 925–939. [15] Y. Qin, Z.H. Chen, B. Rong, Component-based mechanical models for axially-loaded through-diaphragm connections to concrete-filled RHS columns, J. Constr. Steel Res. 102( (2014) 150–163. [16] Y. Qin, Z.H. Chen, B. Rong, Component-based mechanical models for concrete-filled RHS connections with diaphragms under bending moment, Adv. Struct. Eng. 18 (8) (2015) 1241–1256. [17] I. Nishiyama, T. Fujimoto, T. Fukumoto, K. Yoshioka, Inelastic force-deformation response of joint shear panels in beam-column moment connections to concretefilled tubes, J. Struct. Eng. 130 (2) (2004) 244–252. [18] L. Wu, Z.H. Chen, B. Rong, L. Song, Panel zone behavior of diaphragm-through connection between concrete-filled steel tubular columns and steel beams, Adv. Struct. Eng. 2016 (2016) 19.4. [19] Y.M. Alostaz, S.P. Schneider, Analytical behavior of connections to concrete-filled steel tubes, J. Constr. Steel Res. 40 (2) (1996) 95–127.
27
[20] S.P. Schneider, Y.M. Alostaz, Experimental behavior of connections to concrete-filled steel tubes, J. Constr. Steel Res. 45 (3) (1998) 321–352. [21] A. Elremaily, A. Azizinamini, Experimental behavior of steel beam to CFT column connections, J. Constr. Steel Res. 57 (10) (2001) 1099–1119. [22] A. Elremaily, A. Azizinamini, Design provisions for connections between steel beams and concrete filled tube columns, J. Constr. Steel Res. 57 (9) (2001) 971–995. [23] C.H. Kang, K.J. Shin, et al., Hysteresis behavior of CFT column to H-beam connections with external T-stiffeners and penetrated elements, Eng. Struct. 23 (9) (2001) 1194–1201. [24] J.M. Ricles, S.W. Peng, L.W. Lu, Seismic behavior of composite concrete filled steel tube column-wide flange beam moment connections, J. Struct. Eng. 130 (2) (2004) 223–232. [25] J.G. Nie, K. Qin, C.S. Cai, Seismic behavior of connections composed of CFSSTCs and steel-concrete composite beams-experimental study, J. Constr. Steel Res. 64 (10) (2008) 1178–1191. [26] L.H. Han, W. Li, Seismic performance of CFST column to steel beam joint with RC slab: experiments, J. Constr. Steel Res. 66 (11) (2010) 1374–1386. [27] C.T. Cheng, C.F. Chan, L.L. Chung, Seismic behavior of steel beams and CFT column moment-resisting connections with floor slabs, J. Constr. Steel Res. 63 (11) (2007) 1479–1493. [28] GB50010-2010 Code for Design of Concrete Structures2010 (in Chinese). [29] JGJ/T 101-2015 Specification for Seismic Test of Buildings2015 (in Chinese). [30] AISC, 360-2010 Specification for Structural Steel Buildings, 2010. [31] BS EN 1993-1-1:2005 Design of Steel Structures – Part 1–1: General Rules and Rules for Buildings2005. [32] GB 50017-2003 Code For Design of Steel Structures2003 (in Chinese). [33] Y.M. Alostaz, S.P. Schneider, Connections to Concrete-filled Steel Tubes, University of Illinois, Urbana, USA, 1997. [34] L.H. Han, X.L. Zhao, Z. Tao, Tests and mechanics model for concrete filled SHS stub columns, columns and beam-columns, Steel Compos. Struct. 1 (1) (2001) 51–74. [35] B. Li, R. Park, H. Tanaka, Stress-strain behavior of high strength concrete confined by ultra high and normal strength transverse reinforcements, ACI Struct. J. 98.3 (2001) 395–406. [36] X.H. Zhou, B. Yan, J.P. Liu, Behavior of square tubed steel reinforced-concrete (SRC) columns under eccentric compression, Thin-Walled Struct. 91( (2015) 129–138. [37] L.H. Han, G.H. Yao, Z. Tao, Performance of concrete-filled thin-walled steel tubes under pure torsion, Thin-Walled Struct. 45 (1) (2007) 24–36.
Contents lists available at ScienceDirect
Journal of Constructional Steel Research
Behavior of connections between square CFST columns and H-section steel beams Bin-yang Li a,b, Yuan-Long Yang a,b,⁎, Yohchia-Frank Chen a,b, Wei Cheng c, Lin-Bo Zhang a,b a b c
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Ministry of Education), Chongqing University, Chongqing 400045, China School of Civil Engineering, Chongqing University, Chongqing 400045, China Huanqiu Contracting & Engineering Corp. (Guangzhou) CO., LTD, Guangzhou 510000, China
a r t i c l e
i n f o
Article history: Received 25 August 2017 Received in revised form 20 January 2018 Accepted 6 February 2018 Available online xxxx Keywords: Beam-column connection Square concrete filled steel tube Finite element model Static behavior Seismic behavior
a b s t r a c t Three large-scale connections between square concrete-filled steel tubular (CFST) columns and H-section steel beams were tested. The specimens include one connection with continuous flange under static load and two connections with continuous flange and vertical anchor respectively under seismic loads. The static properties of strength and ductility are calculated for static connection based on load-displacement curves, while the seismic properties of strength, ductility, stiffness degradation and energy dissipation are calculated for seismic connections based on hysteretic load-displacement curves. Combining the mechanical properties, experimental phenomena and strain development, beam hinge failure mode can be identified for all specimens. The measured beam strengths of specimens are compared with those predicted by the current AISC-360, EC4 and GB500172003 codes. The study results show that all connections are reliable. A finite element model (FEM), developed and verified with the experimental results, is used to perform parametric analysis. Furthermore, design suggestions are presented. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction The structures with concrete-filled steel tubular (CFST) columns have been widely used for several decades due to their excellent strength, ductility and constructional convenience [1–3]. The most important component of a CFST frame structure is the beam-column connection [4,5]. The seismic behavior of connection has great influence on the reliability of a building. Because of the popularity of structures with CFST columns in applications, many researches on the behavior of connections between CFST columns and steel beams have been reported in the past three decades. In the process of research and engineering, various connection details have been developed. Details can be generalized into two broad categories: connections that attach to the face of the steel tube only, and connections that use elements embedded into the concrete core. Connections to the face of the steel tube include, for example, connections with stiffening rings [6–8] and connections with vertical stiffeners [9,10], etc. Conclusions from these studies showed these connection details exhibited good seismic performance. However, restricted by column size, these connection details are not applicable to large-section columns (far more ⁎ Corresponding author at: Key Laboratory of New Technology for Construction of Cities in Mountain Area (Ministry of Education), Chongqing University, Chongqing 400045, China. E-mail address: [email protected] (Y.-L. Yang).
https://doi.org/10.1016/j.jcsr.2018.02.005 0143-974X/© 2017 Elsevier Ltd. All rights reserved.
larger than beam sections) located at the lower floors of high-rise buildings. Connections with embedded elements include, for example, through bolting with end plates [11–14] and continuous structural steel components through the column [15–18]. The test data indicated that embedding connection components into the concrete core could alleviate high shear demand on the tube wall, which may improve the seismic performance of the connections. Experimental researches above on CFST connections showed that the behavior of connections has varied significantly depending on details of connections. In the 1990s, Schneider and Alostaz [19,20] investigated various details of connections between circular CFST columns and H-section beams by FEM method and experiments. Results showed that the connection detail which beam passed through column provided the best cyclic strength and ductility. Additional tests and further theoretical analysis were performed by Elremaily and Azizinamini [21,22]. To investigate cyclic behavior of various details of connections between square CFST column and H-section beams, Chang-Hoon Kang et al. [23] tested eight interior connections with external T-stiffeners in 2001. Results showed that types of internal penetrated elements (re-bar or bent plate) had similar effect on connection performance. In 2004, four types of connections details (interior diaphragms, exterior extended, structural tees and split tees) were tested by J. M. Ricles et al. [24]. The result indicated that moment resisting connection details can be economically designed that enable more than 0.045 rad of inelastic story drift angle to be developed under cyclic loading.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
From the beginning of 21th century, researchers began to pay attention to the performance of connections with slab [25,26]. In 2007, two interior and two exterior joints were tested by Chin-Tung Cheng et al. [27] to evaluate the composite effect of steel beam and floor slab commonly used in Taiwan in practice. Results showed the composite effect of floor slab and beam was significant under sagging moment. In contrast, the flexural strength of composite beams under hogging moment was only slightly increased. According to the former researches, the CFST columns with high strength, can significantly reduce the column sections and are widely applied at lower floors of high-rise buildings. In this case, the column sections are much larger than beam sections. A 468-metre high-rise building (T2 tower of Chongqing Shuion project in Fig. 1), located at Chongqing city of China, adopted large section CFST columns. Connection details of continuous flange between square CFST columns and Hsection beams were used at floor L50 to L66. The cross-section of column and beam are 1550 × 38 and H800 × 250 × 14 × 26, respectively. To investigate the actual behavior of connections with large columns and small beams, these connections are used as prototype to design specimens in this paper. The floor slab, of which the influence on the connection behavior is very important, is not taken into consideration in the first-step experiment in this paper. The research about the effect of floor slab will be conducted by the authors and the results will be published in the future. This paper presents an in-depth study on the static and seismic behaviors of large-scale connections between square CFST columns and H-section steel beams. Two types of connections with embedded elements (continuous flange and vertical anchor) are compared and studied. The strength, ductility and other mechanical properties of specimens are analyzed in the experiments. A further parametric
11
study is conducted with FEM to investigate the following parameters: (1) thickness of continuous flange tf; (2) width of continuous flange bf; (3) thickness of horizontal plate th; (4) thickness of vertical anchor tv; (5) depth of vertical anchors da; (6) width of horizontal plate and vertical anchor bh. Based on the parametric analysis, some design suggestions are presented to achieve better cost effectiveness in actual engineering structures. 2. Experimental design 2.1. Details of specimens Based on the real connections of T2 tower of Chongqing Shuison project, a total of three square CFST column to H-section steel beam connection specimens were tested. The specimens include one static connection with continuous flanges (JS-1 in Fig. 2) and two seismic connections respectively with continuous flanges and vertical anchors (JD-1 and JD-2 in Fig. 3). More detailed information of the test specimens including the dimensions and locations of strain gauges are respectively given in Figs. 2, 3 and Table 1. Before assembling the column tubes, embedded elements were fillet welded to steel plates. The continuous flange in the JS-1 and JD-1 specimens and horizontal plates in the JD-2 specimen, welded at the same height with the beam flanges, can be deemed as extension of beam flanges. After assembling steel tube, the H-section beams were fillet welded to the steel tube. Large reduced scale was adopted for static and seismic connections within the limit of experiment devices (Table 1). For JS-1, the axial compression ratio n of column is 0.31. For JD-1 and JD-2, the axial compression ratio n of columns is 0.33. Steel ratio α of CFST column is about 10%. The measured steel and concrete material properties of the specimens are listed in Table 2. The compressive cylinder strength of concrete fc,k was converted from compressive cubic strength of concrete fcu,k based on Chinese concrete code (GB50010-2010) [28]. 2.2. Experimental set-up and measuring apparatus The experimental set-up and locations of measuring apparatus for static loading test are shown in Figs. 4, and 5. A 10,000 kN hydraulic compression machine was used to apply a constant axial compressive load. Two 2000 kN hydraulic jacks were located at the ends of the beams to apply upward shear loads. To prevent out-of-plane displacement at beams' ends, lateral supports were arranged on both sides of the beams. Four displacement sensors (LVDTs) were placed on each surface of column to measure its vertical shortening. Two LVDTs were placed at both ends of the beams to measure the vertical displacements. Inclinometers were arranged on the beam flanges to measuring their rotation angles. The experimental set-up and locations of measuring apparatus for the seismic loading test are shown in Figs. 6 and 7. The ends of beams were pinned to vertical rigid trusses whose another ends were pinned to ground. Constant vertical compressive load and cyclic horizontal load (or displacement) were applied at the top of columns. The cyclic loading scheme, according to the Chinese code (JGJ/T 101-2015) [29], is shown in Fig. 8. This loading system considers second-order effect of vertical compressive load on the top of column, which is similar to that in actual frame structures. Similar to static system, LVDTs are used to measure the horizontal displacement of column. And inclinometers are used to measure the rotation angels of beams and column. 3. Static behavior of CFST column to H-section connection 3.1. Failure mode of specimen JS-1
Fig. 1. T2 tower of Chongqing Shuion project.
The failure mode of specimen JS-1 is shown in Fig. 9. When loading to 300 kN (corresponding displacement was 5.14 mm to beam 1 and
12
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 2. Dimensions and arrangement of strain gauges of JS-1. Note: The length of beam (760 mm) is the distance from tube surface to the center of loading area at the beam end.
12.32 mm to beam 2), data of strain gauges showed that beam flanges reached yield strain. Since then, the force control loading program was replaced by displacement control. The loading process was finally stopped at maximum beam displacement of 35 mm, and the corresponding average rotation angle of beams reached about 0.045 rad (in Fig. 9a), which was large enough for engineering application. Because lateral supports could not fully prevent the torsion of beams, especially when the torsional imperfection of beams existed, the final torsional angles of beams reached about 2° (beam 1) and 6° (beam 2) (in Fig. 10). Moreover, influenced by beam torsion, local buckling occurred at the web of beam 2 (in Fig. 9b), which led the ultimate load of beam 2
about 15% lower than that of beam 1. Meanwhile, there was no obvious phenomenon on column tube during the whole test. Taking these aspects into consideration, the failure mode of JS-1 can be identified as beam-hinge failure.
3.2. Load-deformation curve of specimen JS-1 The load-displacement curves and moment-rotation curves of beams in JS-1 are shown in Fig. 11. Accordingly, the mechanical properties of JS-1 are listed in Table 3.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
13
Fig. 3. Dimensions and locations of strain gauges of JD-1 and JD-2. Note: The length of beam (1300 mm) is the distance from tube surface to the center of loading area at the beam end.
The vertical shear load of beams kept increasing constantly from yield point to the completion of test and the rotational angles of steel beams were largely developed (0.0464 rad for beam 1 and 0.0468 rad for beam 2), revealing good ductility of specimen. The comparison of vertical loads of steel beams between experiment and codes AISC 360-2010, BS EN 1993-1-1:2005 and GB50017-2003 are given in Table 4. Because of strain hardening, the experimental ultimate vertical loads are approximately 25%, 34% and 24% higher than that of AISC 360-2010 [30], BS EN 1993-1-1:2005 [31] and GB 50017-2003 [32], respectively. In addition, the experimental peak vertical loads are
13% higher than calculated plastic flexural capacity. Analysis above reveals the failure mode of JS-1 is beam plastic hinge and continuous flange is reliable enough to allow beam achieve calculated plastic moment. This illustrates continuous flange is a kind of practical connection for composite structure. 3.3. Strain of specimen The elastic-plastic analysis method is adopted to analyze the stress of the steel component. According to this method, the stress along the
Table 1 Detailed parameters of experimental specimens. Specimen
Embedded element
Reduced scale
Tube section
α (%)
Beam section
n
N (kN)
JS-1 JD-1
Continuous flange Continuous flange
775 × 20 400 × 10
11.2 10.8
H400 × 125 × 8 × 14 H320 × 100 × 6 × 10
0.31 0.33
8000 2000
JD-2
Vertical anchor
1:2 Column section (1:4) Beam section (1:2.5) Column section (1:4) Beam section (1:2.5)
400 × 10
10.8
H320 × 100 × 6 × 10
0.34
2200
Notes: (i) α = steel ratio of CFST column section; (ii) N = axial compressive load; (iii) n = N/(Asfy + Acfc,k) = axial compression ratio of columns; As = area of steel tube; fy = yield strength of steel tube; Ac = area of concrete; fc,k = compressive cylinder strength of concrete.
14
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Table 2 Material properties of steel and concrete. Specimen
JS-1
JD-1
JD-2
Steel
Concrete
Components
Thickness (mm)
fy (MPa)
fu (MPa)
fcu,k (MPa)
fc,k (MPa)
Tube Flange Web Continuous flange Tube Flange Web Continuous flange Tube Flange Web Horizontal plate Vertical anchor
20.08 13.64 7.52 13.64 9.82 9.82 5.90 13.85 9.82 9.82 5.90 13.85 13.85
276.1 275.2 279.5 275.2 246.3 246.3 284.4 255.6 246.3 246.3 284.4 255.6 255.6
434.2 450.2 419.5 450.2 401.0 401.0 416.8 412.7 401.0 401.0 416.8 412.7 412.7
25.2
16.8
23.4
15.6
27.2
18.2
Fig. 5. Diagram of static measurement.
Notes: (i) fy = yield strength of steel tube; (ii) fu = ultimate strength of steel tube; (iii) fcu, k = compressive cubic strength of concrete.
thickness is small and can be neglected. Therefore, the steel plate can be treated as a plane-stress problem. Von Mises yield criterion is thus employed to describe the yielding behavior of the steel. Fig. 12 illustrates the analysis results of JS-1, in which σv and σh are longitudinal stress and transverse stress of the steel plates respectively and σz is the equivalent stress determined from the following equation pffiffiffiqffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 ðσ v −σ h Þ2 þ σ 2v þ σ 2h σz ¼ 2
The confinement for concrete provided by steel tube is a kind of passive confinement after lateral concrete expansion emerged. For the compression ratio of the column is only 0.31, the lateral concrete expansion is relatively small during the elastic stage. Therefore, the influence of confinement for the concrete is not considered in the mechanical behavior of the specimen in this experiment.
4. Seismic behavior of CFST column to H-section connection ð1Þ
In Fig. 12(a) and (b), the average stress along the beams length all reached the yield point. (The yield stress of flange and web are 275.2 MPa and 279.5 MPa respectively). Since then, the growth rate of equivalent stress at mid-height of web was accelerated and reached yield stress (S23-2 in Fig. 2a). The stress-load curves of continuous flanges are shown in Fig. 12(c). The stress of continuous flange in tension (S41-1, 4, 6) all reached the yield point, while that in compression (S42-5) didn't reach the yield point. Analyzing the stress of S41-1, 4 and 6, the stress of region near tube was comparatively higher. This is attributed to the friction between concrete and plate, which reduced the tension strain inside tube.
4.1. Failure mode of specimen 4.1.1. Specimen JD-1 The failure mode of JD-1 is shown in Fig. 13. When horizontal load just entered descending stage, loading device began to irregularly shake due to impurities in hydraulic oil. In order to ensure safety, the test terminated. It took about one week for repairing devices. When test terminated, the story drift ratio reached about 2.4%, and the horizontal load of column felt to 96.8% of peak load. Local buckling of steel beam and fracture of welds were not detected during test. Removing the tube after test, concrete crack was not detected in the joint panel zone (in Fig. 13a). While, some slight vertical cracks were found above beam top flange (in Fig. 13b). This phenomenon may be attributed to the bending moment at column end. The beams' flanges reached yield
Fig. 4. Static loading program.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
15
Fig. 6. Seismic loading program.
point at the story drift ratio of approximately 0.91%. Considering the stress of beam flanges and phenomenon within the joint zone, the failure mode of JD-1 can be identified as beam-hinge failure. 4.1.2. Specimen JD-2 The failure mode of JD-2 is shown in Figs. 14 and 15. The strain of beams' flanges reached yield strain at the story drift ratio of 0.9%. When the story drift ratio reached about 2%, due to slip of continuous flange and slight punching shear deformation of concrete, a drum deformation of steel tube with 3 mm pull-out displacement was detected (in Fig. 14). The area of drum deformation is about 70 mm in vertical direction of steel tube. The pull out displacement increased to about 10 mm when drift ratio reached 2.7%. Slight welding cracks were detected at the end of beam flanges when test terminated (in Fig. 15a). By removing steel tube, similar to JD-1, concrete crack at joint panel zone was not detected (in Fig. 15c). While, concrete cracks were detected over the top beam flanges (in Fig. 15b). These cracks may be attributed to slight punching shear failure. Considering the phenomenon of joint panel zone and beam flanges, the failure mode of JD-2 can be identified as beam-hinge failure. 4.2. Load-deformation curve of specimen The horizontal load-displacement hysteresis curves of the specimens are shown in Fig. 16. Due to the slip of continuous flange [33],
pinch effect of the hysteresis behavior was obvious for JD-1. While the vertical anchor can significantly decrease the pinch effect.
4.3. Strength, ductility and energy dissipation Fig. 17 gives the skeleton curves of specimens. The mechanical properties of the specimens are listed in Table 5, which calculated based on Figs. 15 and 16. The moment of beams of JD-2 is a little higher than that of JD-1. While, the horizontal load of column of JD2 are lower than that of JD-1, due to higher axial load ratio of JD-2. Compare with design codes, the vertical loads of beam increase to approximately 1.2 times of predictions of AISC 360-2010 [30], BS EN 1993-1-1:2005 [31] and GB 50017-2003 [32]. The experimental vertical loads of beams are approximately 15% higher than that corresponding to calculated plastic flexural capacity. Considering all phenomenon above, failure mode of JD-1 and JD-2 can be identified as beam plastic hinge. Both continuous flange and vertical anchor are practical for composite structures. For the ductility analysis, there are normally two ways to define the ductility of a structure or member. One way is to use the ductility coefficients μp at the peak load, which is given by
μ p ¼ Δp =Δy
ð2Þ
16
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 7. Diagram of seismic measurement. Note: (i) H = distance between the center of column hinges; (ii) Before axial loading, vertical rigid trusses is not attached to beam ends.
The other is to calculate the ductility coefficient μu at the ultimate stage, which can be obtained from μ u ¼ Δu =Δy
ð3Þ
The results for the ductility are presented in Table 5. Both specimens show good ductile post-peak load behavior. Because of vertical anchor, the ductility coefficient of JD-2 is larger than that of JD-1. Unfortunately, due to the device problem, the test of JD-1 stopped before dropping to 85% of peak strength. Therefore, the data Δu of JD-1 was not available. For the displacement capacity, the elastic inter-story drift ratios are approximately to 1.0%, which satisfy the demand of 1/550 from Chinese concrete code (GB50010-2010) [28]. The energy dissipation capacity is another important factor to assess a structure's seismic performance. In this paper, equivalent viscous damping coefficient factor ξeq is calculated by
Fig. 8. Horizontal loading scheme of column.
ξeq ¼
S1 2πðS2 þ S3 Þ
ð4Þ
Fig. 9. Failure mode of JS-1.
Fig. 10. Torsional angle of beams.
in Fig. 18b. Combined with the hysteresis loops, both JD-1 and JD-2 have good capacity of energy dissipation. The connection specimen JD-2 has better energy dissipation capacity than specimen JD-1.
Table 3 The mechanical properties of JS-1. Beam number Vy (kN) 1 2
Vu (kN)
My Mu Δy Δu θy (kN∙m) (kN∙m) (mm) (mm) (rad)
300.3 406.6 242.3 240.4 347.4 190.3
303.2 259.0
5.1 7.2
33.95 35.04
θp (rad)
4.4. Stiffness of specimens
0.0065 0.0464 0.008 0.0468
Secant stiffness is used to assess the stiffness degradation of the connections. The secant stiffness of a member with different loading cycles at each load step can be expressed as
Notes: (i) Vy = vertical yield load of steel beam; (ii) Vp = vertical ultimate load of steel beam; (iii) My = Vy × L = yield moment at the fixed ends of beam; L = length of beam; (iv) Mu = Vu × L = ultimate moment at the fixed ends of beam; (v) Δy = displacement at the loading ends of beam corresponding to Vy; (vi) Δu = displacement at the loading ends of beam corresponding to Vu; (vii) θy = Δy/L = average rotational angle of beam corresponding to Δy; (viii) θu = Δu/L = average rotational angle of beam corresponding to Δu.
Ki ¼
Where S1 is the area of the hysteresis loop ABCDA, S2 is the area of the triangle OBF and S3 is the area of the triangle ODE (in Fig. 18a). The relationship between ξeq and inter-story displacement Δ is shown
jþF i j þ j−F i j jþX i j þ j−X i j
ð5Þ
where +Fi (−Fi) is the positive (negative) peak load at the i loading cycle, and +Xi (−Xi) is the corresponding positive (negative) displacement. The degradation of the secant stiffness for all the specimens is
Table 4 The comparison of strengths between experiment and codes. Beam number
VAISC (kN)
VBS (kN)
VGB (kN)
Vyf (kN)
Vpf (kN)
Myf (kN)
Mpf (kN)
1 2
301.1
281.2
303.7
289.2
334.6
219.8
254.3
Beam number
Vy (kN) 300.3 240.4
Vp (kN) 406.6 347.4
Vp/VAISC
Vp/VBS
Vp/VGB
Vp/Vpf
1 2
1.35 1.15
1.25 (Average)
1.45 1.23
1.34 (Average)
1.34 1.14
1.24 (Average)
1.21 1.04
1.13 (Average)
Notes: (i) VAISC = vertical design load calculated according to AISC 360-2010 (LRFD) [30]; (ii) VBS = vertical design load calculated according to BS EN 1993-1-1:2005 [31]; (iii) VGB = vertical design load calculated according to GB50017-2003 [32].
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
19
Fig. 13. The failure mode of specimen JD-1.
plotted in Fig. 19. With the increase of the displacement at different load steps, the stiffness of the specimens is approximately linearly reduced. Compared to JD-1, the stiffness of JD-2 during elastic stage is
approximately 10% higher than that of JD-2. But this difference between tow specimens can be ignored during plastic stage due to the same failure mode of beam plastic hinge.
Fig. 14. Drum deformation of steel tube near beam flanges.
Fig. 15. Experimental phenomenon of JD-1.
20
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 16. Horizontal load-displcement hysteresis curves.
Fig. 17. The skeleton of load-displacement and moment-rotation curves of JD-1, 2.
The classification of joint according to Eurocode 3 Part 1–8 is shown in Fig. 20. Quantitatively, the relationship between M/Mp and Φ/Φp is used to classify the stiffness of joint. Mp and Φp are the plastic moment and plastic rotation angle of steel beam. Φp can be obtained from Φp ¼ Mp Lp =ðEIn Þ
ð6Þ
where Lp is beam span (twice the beam length L of the specimen); In is the moment of inertia of beam section; M is the moment of steel beam which is calculated by shear force V multiplied beam L; Φ, the rotation angle within plastic hinge of steel beam, can be calculated with data of inclinometers on two sides of plastic hinge. As shown in Fig. 20, the curves of JD-1 and JD-2 near or slightly above the boundary line between semi-rigid joint and rigid joint. Therefore both the continuous flange and vertical anchor can achieve rigid joint. 4.5. Strain of specimen The Stress development of JD-1 is shown in Fig. 21. The absolute value of stress is calculated based on the strain data from gauges and material property. In positive direction, the top flange reached yield stress at 28 kN, which was earlier than bottom flange at 65 kN. The flanges reached yield stress simultaneously at −35 kN in negative direction. Instead, the stress of joint tube kept in elastic stage during all test
Table 5 The mechanical properties of JD-1 and 2. Specimen
Fy (kN) Fp (kN) Δy/H (%) Δp/H (%) Δu/H (%) μp μu VAISC (kN) VBS (kN) VGB (kN) Vy (kN) Vp (kN) Vyf (kN) Vpf (kN) Myf (kN∙m) Mpf (kN∙m) Vp/VAISC Vp/VBS Vp/VGB Vy/Vyf Vp/Vpf
JD-1
JD-2
Positive direction
Negative direction
Positive direction
Negative direction
129.3 138.9 1.1 1.3 – 1.18 – 78.1 86.8 75.3 88.3 99.5 71.7 86.8 93.3
145.6 152.3 1.4 1.9 – 1.37 –
123.6 128.4 1.0 1.6 2.5 1.54 2.40
113.1 136.9 0.9 1.8 2.0 2.01 2.59
85.8 97.3
87.3 108.9
76.5 103.1
1.25 1.12 1.29 1.20 1.12
1.39 1.25 1.45 1.22 1.25
1.32 1.19 1.37 1.07 1.19
112.9 1.27 1.15 1.32 1.23 1.15
Notes: (i) Fy = horizontal yield load of column; (ii) Fp = horizontal peak load of column; (iii) Δy = yield displacement of column; (iv) Δu = displacement corresponding to a 15% degradation from the peak load.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
21
0.4
ξeq
0.3 0.2 0.1
JD-1 JD-2
0.0 10
a Typical hysteresis loop
20
30
40
Δ (mm)
50
60
b Equivalent viscous damping coefficient ξeq curves.
Fig. 18. a Typical hysteresis loop. b Equivalent viscous damping coefficient ξeq curves.
(in Fig. 21b). Similar with JD-1, confinement of tube is not considered for JD-1 and 2 either. The stress development agrees with the beamhinge failure mode discussed above. The stress development of JD-2 is shown in Fig. 22. Similar to JD-1, both flanges reached yield stress, while the stress of joint tube kept in elastic stage. 5. Finite element modeling 5.1. General A FEM with ABAQUS software is established in the following to simulate specimens with continuous flange (JS-1 and JD-1) and specimen with vertical anchor (JD-2). The FEM is verified by the experimental results. Furthermore, a parametric study is performed and accordingly some design suggestions were presented.
Fig. 19. Secant stiffness of JD-1 and JD-2.
5.1.1. Materials An elastic-plastic model consisting of five stages is used to describe the mechanical behavior of steel material [34]. A concrete damage plasticity model in ABAQUS software is used to describe
Fig. 20. Classification of joints. Note: The blue line are boundary lines of joint type. A area represents nominal pinned joint; B area represents semi-rigid joint; C area represents rigid joint. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
22
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 21. The stress of JD-1. Notes: (i) V = shear force of beam; (ii) F = horizontal load of column; (iii) Stress is in the direction of length of beams.
concrete material. The confined effect for concrete, which is considered in damage plasticity model but insufficient for experimental CFST columns. So it is modified by increasing peak strain and transforming descending branch of input stress-strain curve according to Li [35] and Zhou [36].
5.1.2. Element type, interaction and boundary conditions The steel tube, beam flange, beam web and embedded elements (continuous flange, horizontal plate and vertical anchor) are modelled using a 4-node general-purpose shell element S4R with reduced integration, hourglass control and membrane strains. The concrete is modelled using an 8-node linear brick solid element C3D8R with reduced integration and hourglass control. A surface-to-surface contact interaction is applied to describe the interaction between steel tube and concrete of the column, by specifying a hard contact property in the normal direction and a friction property in the tangential direction (friction coefficient is chosen as 0.6 [37]. A value of 0.6 MPa is used as the maximum surface bond stress in the Coulomb friction model [36]. The interaction allows separation of the concrete and steel tube after tube's local buckling. Besides, a merge property is used to simulate interaction between steel tube, beams and embedded elements.
For JS-1 and JD-1, the interaction between continuous flange and concrete is ignored in order to simulate the interface slip between them. For JD-2, same interaction modeling is adopted between horizontal plate and concrete, while the embedded constraint is applied between the vertical anchors and concrete. The boundary condition and loading program in the finite element model are simulated completely according to those in the experiments. 5.2. Verifications The shear load V-vertical displacement D curve obtained from FEM is compared with that from experiment in Fig. 23(a). Generally good agreement in elastic stiffness, bearing capacity and ductility is shown between the experimental and predicted results. The plastic strain distribution based on the FEM for specimen JS-1 is shown in Fig. 23(b). It can be seen that the large plastic strain is distributed mainly at the beam end connected to column, coinciding with the failure mode observed from experiment. The comparisons of load- displacement skeleton curves of FEM and experiments are shown in Fig. 25. F is the horizontal load at the top of column; Δ is the displacement at the top of column and V is the vertical shear load at the end of beam. Approximately good agreement is achieved in stiffness and bearing capacity.
Fig. 22. The stress of JD-2.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
23
500
V(kN)
400 300 200 JS-1 (beam 1) FEM
100 0
0
10
20 D(mm)
30
40
(a) Load-displacement of JS-1
(b) Plastic strain distribution of JS-1
Fig. 23. (a) Load-displacement of JS-1. (b) Plastic strain distribution of JS-1.
The strain and stress distributions for JD-1 and JD-2 are shown in Fig. 24. Plastic hinges are observed in FEM which coincide with the failure modes in the experiments (Fig. 24a, b). The continuous flange and horizontal plate in tension all reach yield stress, while those in compression reach yield stress only in the region near steel tube (Fig. 24c). Similar phenomenon is detected in JD-2, the Mises stress of vertical anchors in tension all reach yield stress, while the stress of those in compression is relatively lower than yield stress (Fig. 24d). The distribution of
principal compressive stress in concrete within joint panel zone reveals an obvious strut-tie mechanism in both JD-1 and JD-2 (Fig. 24(e), (f)). Besides, concrete between vertical anchor and steel tube is compressed by vertical anchor (Fig. 24f), due to the tension force transferred from beam. Considering the above analysis, the transmission of tension force from beam depends mostly on embedded anchor and continuous flange. While the transmission of compression force depends mainly on the concrete within joint panel zone.
Fig. 24. Comparison of load-displacement skeleton curves of FEM and experiments.
24
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
5.3. Parametric study Based on the FEM, parametric analysis method is used to investigate the influences of six main parameters on the strength of connections. When the parametric studies are taken on a certain parameter, other parameters are identical to those of JD-1 and JD-2. The parameters include: (1) thickness of continuous flange tf (8 mm, 10 mm, 12 mm, 14 mm, 18 mm, 22 mm); (2) width of continuous flange bf (100 mm, 125 mm, 150 mm, 175 mm); (3) thickness of horizontal plate th (8 mm, 10 mm, 14 mm, 18 mm); (4) thickness of vertical anchor tv (8 mm, 10 mm, 14 mm, 18 mm); (5) the anchoring depth da (90 mm,
120 mm, 150 mm, 180 mm); (6) width of horizontal plate and vertical anchor bh (125 mm, 150 mm, 175 mm, 200 mm). The results of parametric studies are shown in Fig. 26. The parameters tf, th and da have significant effect on the strength of specimens. The strength for tf = 1.8tb is about 1.60 times of that for tf = 0.8tb. The strength for th = 1.4tb is about 1.17 times of that for th = 0.8tb. And the strength for da = 1.5wb is about 1.20 times of that for da = 0.9wb. When these parameters reach their critical values, the strength increases almost stop. And these critical values are suggested as reference values for preliminary design (Table 6). Meanwhile, the influences of wf, tv and wh are slight on the strength of specimens.
Fig. 25. The strain and stress distributions for JD-1 and JD-2.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
25
Fig. 25 (continued).
6. Conclusion This paper investigates both static and seismic behavior of two type of connections between square CFST columns and steel beams. Both experimental and numerical approaches were used to obtain the following conclusion: 1. Static failure mode of connection between CFST columns and steel beams is plastic hinges of steel beams. The continuous flange guarantees plastic yielding of steel beam and effectively transfers internal forces of steel beam to joint panel zone under static loading. 2. Seismic failure mode of connections with continuous flanges or vertical anchors is both plastic hinges of steel beams. Good seismic performance can be expected in these connections. The experimental
value of beam strength is about 1.2 times of value calculated from AISC 360-2010 [30], BS EC 1993-1-1:2005 [31] and GB 50017-2003 [32]. These two types of connections are thus expected to be adoptable in practical building structures. 3. FEM is established and agrees well with the experimental results. Parametric analysis was conducted with FEM to obtain the following design suggestions: (a) thickness of continuous flange (tf) is suggest to be 1.4–1.8 times of thickness of beam flange (tb); (b) width of continuous flange (wf) is suggested to be 1.25 times of width of beam flange (wb); (c) thickness of horizontal plate (th) and thickness of vertical anchor (tv) is suggested to be 1.4 times of thickness of beam flange (tb); (d) depth of vertical anchor (da) and width of horizontal plate and vertical anchor (wh) is suggested to be 1.5 times of width of beam flange (wb).
26
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27
Fig. 26. Parametric studies. Notes: (i) tb = the thickness of beam flange; (ii) wb = the width of beam flange.
Acknowledgements This research is supported by the National Key Research and Development Program of China (Grant No. 2016YFC0701200, 2017YFC0703805), Research and Development Project of Ministry of
Housing and Urban-Rural Development (Grant No. 2014-K2-010) and the Fundamental Research Funds for the Central Universities (Grant No. 106112014CDJZR200001, 106112017CDJXY200010).
References Table 6 The suggested value for parameters. Type of connection
Parameters
Specimen's value
Suggested value
Continuous flange
tf wf th tv da wh
1.4tb 1.0wb 1.4tb 1.4tb 1.5wb 1.5wb
1.4tb to 1.8tb 1.25wb 1.4tb 1.4tb 1.5wb 1.5wb
Vertical anchor
[1] Y.S. Du, Z.H. Chen, J.Y.R. Liew, M.X. Xiong, Rectangular concrete-filled steel tubular beam-columns using high-strength steel: experiments and design, J. Constr. Steel Res. 131 (2017) 1–18. [2] Y.C. Tang, L.J. Li, W.X. Feng, F. Liu, B. Liao, Seismic performance of recycled aggregate concrete–filled steel tube columns, J. Constr. Steel Res. (2017) 112–124. [3] J.P. Liu, X.H. Zhou, S.M. Zhang, Seismic behavior of square CFT beam-columns under biaxial bending moment, J. Constr. Steel Res. 64 (12) (2008) 1473–1482. [4] A.H. Varma, J.M. Ricles, R. Sause, L.W. Lu, Seismic behavior and modeling of highstrength composite concrete-filled steel tube (CFT) beam–columns, J. Constr. Steel Res. 58 (5–8) (2002) 725–758.
B. Li et al. / Journal of Constructional Steel Research 145 (2018) 10–27 [5] L.Y. Wu, L.L. Chung, S.F. Tsai, T.J. Shen, G.L. Huang, Seismic behavior of bolted beamto-column connections for concrete filled steel tube, J. Constr. Steel Res. 61 (10) (2005) 1387–1410. [6] J.W. Park, S.M. Kang, S.C. Yang, Experimental studies of wide flange beam to square concrete-filled tube column joints with stiffening plates around the column, J. Struct. Eng. 131 (12) (2005) 1866–1876. [7] W.D. Wang, L.H. Han, B. Uy, Experimental behaviour of steel reduced beam section to concrete-filled circular hollow section column connections, J. Constr. Steel Res. 64 (5) (2008) 493–504. [8] W.D. Wang, L.H. Han, X.L. Zhao, Analytical behavior of frames with steel beams to concrete-filled steel tubular column, J. Constr. Steel Res. 65 (3) (2009) 497–508. [9] J. Kimura, J. Chung, C. Matsui, S. Choi, Structural characteristics of H-shaped beamto-square tube column connection with vertical stiffeners, Int. J. Steel Struct. 5 (2) (2005) 109–117. [10] K.J. Shin, Y.J. Kim, Y.S. Oh, Seismic behaviour of composite concrete-filled tube column-to-beam moment connections, J. Constr. Steel Res. 64 (1) (2008) 118–127. [11] L.Y. Wu, L.L. Chung, et al., Seismic behavior of bidirectional bolted connections for CFT columns and H-beams, Eng. Struct. 29 (3) (2007) 395–407. [12] H. Yao, H. Goldsworthy, E. Gad, Experimental and numerical investigation of the tensile behavior of blind-bolted T-stub connections to concrete-filled circular columns, J. Struct. Eng. 134 (2) (2008) 198–208. [13] X. Li, Y. Xiao, Y.T. Wu, Seismic behavior of exterior connections with steel beams bolted to CFT columns, J. Constr. Steel Res. 65 (7) (2009) 1438–1446. [14] J.F. Wang, L.H. Han, B. Uy, Behaviour of flush end plate joints to concrete-filled steel tubular columns, J. Constr. Steel Res. 65 (4) (2009) 925–939. [15] Y. Qin, Z.H. Chen, B. Rong, Component-based mechanical models for axially-loaded through-diaphragm connections to concrete-filled RHS columns, J. Constr. Steel Res. 102( (2014) 150–163. [16] Y. Qin, Z.H. Chen, B. Rong, Component-based mechanical models for concrete-filled RHS connections with diaphragms under bending moment, Adv. Struct. Eng. 18 (8) (2015) 1241–1256. [17] I. Nishiyama, T. Fujimoto, T. Fukumoto, K. Yoshioka, Inelastic force-deformation response of joint shear panels in beam-column moment connections to concretefilled tubes, J. Struct. Eng. 130 (2) (2004) 244–252. [18] L. Wu, Z.H. Chen, B. Rong, L. Song, Panel zone behavior of diaphragm-through connection between concrete-filled steel tubular columns and steel beams, Adv. Struct. Eng. 2016 (2016) 19.4. [19] Y.M. Alostaz, S.P. Schneider, Analytical behavior of connections to concrete-filled steel tubes, J. Constr. Steel Res. 40 (2) (1996) 95–127.
27
[20] S.P. Schneider, Y.M. Alostaz, Experimental behavior of connections to concrete-filled steel tubes, J. Constr. Steel Res. 45 (3) (1998) 321–352. [21] A. Elremaily, A. Azizinamini, Experimental behavior of steel beam to CFT column connections, J. Constr. Steel Res. 57 (10) (2001) 1099–1119. [22] A. Elremaily, A. Azizinamini, Design provisions for connections between steel beams and concrete filled tube columns, J. Constr. Steel Res. 57 (9) (2001) 971–995. [23] C.H. Kang, K.J. Shin, et al., Hysteresis behavior of CFT column to H-beam connections with external T-stiffeners and penetrated elements, Eng. Struct. 23 (9) (2001) 1194–1201. [24] J.M. Ricles, S.W. Peng, L.W. Lu, Seismic behavior of composite concrete filled steel tube column-wide flange beam moment connections, J. Struct. Eng. 130 (2) (2004) 223–232. [25] J.G. Nie, K. Qin, C.S. Cai, Seismic behavior of connections composed of CFSSTCs and steel-concrete composite beams-experimental study, J. Constr. Steel Res. 64 (10) (2008) 1178–1191. [26] L.H. Han, W. Li, Seismic performance of CFST column to steel beam joint with RC slab: experiments, J. Constr. Steel Res. 66 (11) (2010) 1374–1386. [27] C.T. Cheng, C.F. Chan, L.L. Chung, Seismic behavior of steel beams and CFT column moment-resisting connections with floor slabs, J. Constr. Steel Res. 63 (11) (2007) 1479–1493. [28] GB50010-2010 Code for Design of Concrete Structures2010 (in Chinese). [29] JGJ/T 101-2015 Specification for Seismic Test of Buildings2015 (in Chinese). [30] AISC, 360-2010 Specification for Structural Steel Buildings, 2010. [31] BS EN 1993-1-1:2005 Design of Steel Structures – Part 1–1: General Rules and Rules for Buildings2005. [32] GB 50017-2003 Code For Design of Steel Structures2003 (in Chinese). [33] Y.M. Alostaz, S.P. Schneider, Connections to Concrete-filled Steel Tubes, University of Illinois, Urbana, USA, 1997. [34] L.H. Han, X.L. Zhao, Z. Tao, Tests and mechanics model for concrete filled SHS stub columns, columns and beam-columns, Steel Compos. Struct. 1 (1) (2001) 51–74. [35] B. Li, R. Park, H. Tanaka, Stress-strain behavior of high strength concrete confined by ultra high and normal strength transverse reinforcements, ACI Struct. J. 98.3 (2001) 395–406. [36] X.H. Zhou, B. Yan, J.P. Liu, Behavior of square tubed steel reinforced-concrete (SRC) columns under eccentric compression, Thin-Walled Struct. 91( (2015) 129–138. [37] L.H. Han, G.H. Yao, Z. Tao, Performance of concrete-filled thin-walled steel tubes under pure torsion, Thin-Walled Struct. 45 (1) (2007) 24–36.