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The longitudinal shear behaviour of a new steel sheeting profile for composite floor slabs
Journal of Constructional Steel Research 49 (1999) 117–128
The longitudinal shear behaviour of a new steel sheeting profile for composite floor slabs Pentti Ma¨kela¨inen*, Ye Sun Laboratory of Steel Structures, Helsinki University of Technology, P.O.Box 2100, FIN-02015 HUT, Helsinki, Finland Received 27 April 1998; accepted 5 May 1998
Abstract Longitudinal shear failure is the most common failure-type in composite slabs. In this paper, the shear-connection behaviour of composite slabs with a particular profiled steel sheeting having a depth of 153 mm is experimentally studied. Twenty-seven push-out test specimens of different shapes, sizes, locations of embossments and different steel sheeting thicknesses are carried out in two test series. The embossments are first rolled onto the profiled sheeting, then every embossment is punched through along one side. It is found that the shear-connection behaviour of composite slabs is significantly affected by the depth of embossments. For the profiled steel sheeting with penetrated embossments, the reduction of Young’s modulus caused by the penetrated embossments is an important factor that affects the determination of the depth and width of the embossments. Finally, a new type of profiled steel sheeting, which can offer longitudinal shear strength in composite slabs up to 0.6 N/mm2, is proposed for further research. 1998 Elsevier Science Ltd. All rights reserved. Keywords: Steel-concrete composite slabs; Steel sheeting; Longitudinal shear
Nomenclature
max S S1
shear stress maximum shear stress end slip end slip corresponding to max
* Corresponding author. Tel.: + 358-94513780; Fax: + 358-94515019; E-mail: [email protected] 0143-974X/98/$—see front matter 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 3 - 9 7 4 X ( 9 8 ) 0 0 2 1 1 - 9
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1. Introduction Composite slabs consisting of profiled steel sheeting and concrete blocks are widely used in buildings nowadays. The profiled steel sheeting acts as a permanent formwork during the concrete casting and as tensile reinforcement after the concrete has hardened. There are three possible failure-types in composite slabs: flexural failure, longitudinal shear failure and vertical shear failure. The longitudinal shear failure is the most common failure type [1,2]. Therefore, the efficiency of the composite slabs depends on the composite action between these two materials. To achieve the desired composite action, shearing forces have to be transferred between the concrete slab and the steel sheeting. This is usually accomplished by the mechanical interlocking devices rolled onto the surface of the steel sheeting. So far the most effective and most common used shear-connecting device is the pressed embossment on the profiled steel surface [3–5]. Embossments are usually made in shapes of circular spot, chevron or bar at different angles to the shear force axis. The embossments may be pressed onto the webs or flanges. The efficiency of the composite action of steel sheeting in composite slabs is obtained from the test information. The method used for measuring the shear resistance can be either a full-scale test or a small-scale test. Small-scale tests have been widely used for obtaining the shear resistance at the interface between the concrete and steel-sheeting profile. Small-scale tests usually give the shear resistance by pushing out the concrete block horizontally or pulling off the steel sheet vertically [6– 8]. It is shown that the small-scale test is a very effective way to develop a new type of profiled steel sheeting. The design of composite slabs is currently based on the test information for a particular steel-sheeting profile. One type of steel-sheeting profile, RAN153 with a depth of 153 mm is modified by cold-rolling and punching the penetrated embossments onto the surface and is then tested in the Laboratory of Steel Structures at Helsinki University of Technology to investigate the longitudinal shear behaviour of the composite slabs [4,9,10].
2. Experimental programme 2.1. Specimen description The small-scale specimens consisting of steel-sheeting profile and concrete block were cast in the sheeting. The sheeting had a width of 400 mm and length of 300 mm. Each concrete block covered one rib with a width of 280 mm. The concrete block was 300 mm long and 280 mm thick. The steel-sheeting surface was well cleaned before casting the concrete. Twenty-seven small-scale specimens were made in all, twenty-one of them were made in Test Series I and six in Test Series II. The steel sheeting profile used in all specimens of Test Series I was of type RAN153 (1 mm), only the embossments on the steel sheeting were different. The embossment shape of Test Series II is based on the optimization of the embossment shapes of Test Series I. The embossment shape of the specimens in Test Series II was the
P. Ma¨kela¨inen, Y. Sun / Journal of Constructional Steel Research 49 (1999) 117–128
Fig. 1.
119
Dimensions (in mm) of the RAN153 sheeting and cross-section of the test specimen.
same, but the steel sheeting thickness was different. The nominal geometric crosssectional dimensions of the RAN153 sheeting and the test specimen cross-section are shown in Fig. 1. Reinforcement bars (see Fig. 1.) were placed in the concrete blocks in order to avoid failure in the concrete rather than the longitudinal slip failure. The reinforcement bars have no connection with the steel sheeting [6]. 2.2. Push-out test set-up The push-out test set-up consisted of two layer frames as shown in Fig. 2. The bottom layer was a fixed frame and the upper frame could move smoothly in the horizontal direction. The steel-sheeting profile was attached to the fixed frame with 10 M8 bolts and the fixed frame was screwed to the ground to prevent horizontal movement [7,11,12]. The horizontal load was placed symmetrically with respect to the longitudinal axis of the concrete blocks. The horizontal load was generated by an actuator with a 50 kN capacity. The load was transferred to the movable frame and then through two pieces of steel to the concrete block. These two steel pieces with a square section of 40 × 40 mm and a thickness of 5 mm were adhered to every specimen at a height corresponding to the middle of the web of the steel sheeting. Three displacement transducers (LVDT) were used for measuring the slips. Two
Fig. 2. Push-out test set-up.
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of them (stroke 10 mm) measured the slip occurring on the bottom of the concrete block. The third one (stroke 10 mm) measured the slip that occurred at the top of the concrete block. Two transducers (stroke 5 mm) were used for measuring the uplift of the concrete block. 2.3. Material properties The material properties of the steel sheeting were determined from 9 coupon tests according to the EN-SFS 10 002-1 standard for both test series. The mean values obtained for the yield stress and the modulus of elasticity of the steel sheet were 396 N/mm2 and 200 kN/mm2, respectively. The compression strength of the concrete was determined by the cylinder compression test according to the DIN 1048 Part 1 standard, and the mean value obtained for compression strength was 37 N/mm2. 2.4. Embossments 2.4.1. Test Series I There were two categories of embossments in Test Series I: Straight penetrated embossment and V-shaped penetrated embossment. The straight penetrated embossments differed in length, depth and position in the web. Embossments HD5, HD6 and HD7 were rolled onto the middle part of the web. Embossments HD8 were rolled onto the corner of the web. The V-shaped embossments were named as VD2S and VD2O. The only difference between profile RAN153-VD2O and profile RAN153-VD2S was the orientation of embossments: the embossments on both webs of profile RAN153-VD2O had an opposite orientation towards the applied load, and the ones of profile RAN153-VD2S had the same orientation towards the applied load. The detailed information about these embossments is shown in Fig. 3 and the design values of the embossments are shown in Table 1. 2.4.2. Test Series II The shape of the embossments in Test Series II was based on that of RAN153HD6 and is shown in Fig. 4. There were two types of specimens, T10-HD6 and T09-HD6. These two types of specimens had the same embossments on the profiled steel sheeting but different sheeting thicknesses. The thickness of the profiled steel sheeting for T10-HD6 was 1 mm and for T09-HD6 was 0.9 mm. 2.5. Testing programme Eurocode 4 (1990) ([1]) requires that three tests should be carried out on nominal identical specimens. Therefore, a total of 21 push-out tests (Test Series I) were carried out according to the classification of Table 1 and Fig. 3. Seven different embossment types were tested: RAN153-HD5, RAN153-HD6, RAN153-HD7-S, RAN153-HD7-O, RAN153-HD8, RAN153-VD2-S and RAN153-VD2-O. Compared with Test Series I, Test Series II had wider and deeper actual emboss-
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Fig. 3.
121
The shapes of embossments in Test Series I.
Table 1 Dimensions of penetrated embossments Profile Embossment length (mm) depth (mm)
RAN153 HD5 45 2.5
HD6 45 3
HD7 52 3
HD8 25 2.5
VD2 45 2.5
ments on the profiled steel sheeting. In total 6 test specimens were tested, three for T10-HD6 and three for T09-HD6.
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Fig. 4.
The shape of embossments in Test Series II.
3. Test results Fig. 5 shows the typical shear stress-end slip curve obtained from a push-out test. Ultimate longitudinal shear resistance is the most important characteristic of the sheeting and it is designed to be obtained from the recorded horizontal force of the push-out test. The distribution of the longitudinal shear stress is assumed to be uniform along the shear span and it is calculated from the horizontal force divided by the projected contact area of the profiled steel sheeting and concrete. This area is 280 × 300 mm2. The stiffness of the profiled steel sheeting is represented by the secant slip modulus. The ductility is defined as the slip between two points on the shear stress-end slip curve corresponding to the stress level of 0.85max in Fig. 5. The secant slip modulus is defined as the tangent of the line from the zero point to the left point at the 0.85max stress level. For these particular profiled steel sheetings with penetrated embossments, the general observations made during testing are as follows: 앫 the slip was nearly zero even though the load was up to 80% of the maximum load.
Fig. 5. Typical shear stress-slip curve recorded in a push-out test.
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Fig. 6.
123
Results of the RAN153-HD6 separation (Test Series I).
앫 there was a very small amount of vertical separation between the concrete block and steel sheeting. 앫 the maximum load was reached just before failure and the failure behaviour was brittle. 앫 after failure, the concrete block was lifted away from the sheeting at both ends with rather large end slip. 앫 the concrete block was complete except for the parts of embossments. 앫 after a test, the depth of the end-opening embossment was deeper than the one before the test. 앫 no plastic deformations were observed in the profiled steel sheeting. The test results of RAN153-HD6 and T10-HD6 are shown in Fig. 6 and Fig. 7, respectively. The average results of all the push-out tests are listed in Table 2. Vertical separation between concrete block and profiled steel sheeting was measured by two displacement transducers. From Table 2, it can be seen that the vertical separation of Test Series I (Fig. 8) is smaller than that of Test Series II (Fig. 9).
Fig. 7.
Results of the T10-HD6 push-out test (Test Series II).
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Table 2 Average results of push-out tests Test series
Specimen Shear stress Slip Ductility Secant Embossment depth max(N/mm2) corresponding (mm) slip (mm) modulus to max S1 (mm) (N/mm2/mm) RAN153-
I
II
HD5 HD6 HD7O HD7S HD8 VD2S VD2O T10-HD6 T09-HD6
0.313 0.638 0.470 0.610 0.319 0.528 0.511 0.519 0.395
0.980 0,228 0,221 0,170 1,061 0,226 0,297 0.093 0.072
0.650 0.819 0.690 0.315 0.343 0.710 0.440 0.539 0.604
0.83 3.99 5.53 6.31 2.41 5.07 2.56 8.31 6.35
Before test 1.43 2.31 1.62 1.92 1.90 1.76 1.98 3.22 2.93
Fig. 8.
Results of vertical separation (Test Series I).
Fig. 9.
Results of vertical separation (Test Series II).
Vertical separation (mm)
After test 1.46 2.46 1.72 2.05 2.03 1.80 2.04 3.72 3.56
0.409 0.686 0.812 0.698 0.834 0.467 0.823 1.250 1.053
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The sheeting RAN153-HD6 has the smallest amount of vertical separation, which was 0.326 mm.
4. Discussion of the test results
4.1. Effects of the embossment depth 4.1.1. Test Series I The test results show that the depth of the embossments has a significant effect on the longitudinal shear behaviour of the steel sheeting profiles. The penetrated embossments can improve the shear resistance greatly since the concrete permeates into the small hole of the embossment. The RAN153-HD6 profile has the highest shear strength among all the test specimens, the average shear stress can be up to 0.638 N/mm2. The main reason is that RAN153-HD6 has the deepest embossments. The embossments on RAN153-HD5 and RAN153-HD6 were the same except for the depth: the depth for HD6 was 2.31 mm and for HD5, 1.43 mm. The shear stress for RAN153-HD6 sheeting was more than twice that of RAN153-HD5 sheeting. As shown in Fig. 10, the deeper the embossment the higher the shear stress value if other characteristics of the embossments were roughly the same. 4.1.2. Test Series II The purpose of testing the specimens in Test Series II is to try to improve the ultimate shear stress and ductility with deeper and wider embossments. The embossments in Test Series II have wider and deeper end-holes than those in Test Series I. The average depth of the straight penetrated embossments in T10-HD6 (Test Series II) was approximately 39% deeper than that in RAN153-HD6 (Test Series I). How-
Fig. 10. Effects of embossment-depth.
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ever, this increase in embossment depth didn’t contribute to any increase in the ultimate shear stress. The main reason for it is the different Young’s Modulus of the embossements’ part of the profiled steel sheeting. The Young’s Modulus of the embossments’ part of the sheeting cannot be tested in our laboratory. The Young’s Modulus of the embossments’ part in T10-HD6 must be lower than that for RAN153HD6 due to the wider and deeper end-holes in the embossments. This test result confirmed the test results of Veljkovic, [5], who reported that the pressed embossments reduce the effective yield strength and Young’s Modulus to about 47% of the original values of the flat sheet, according to his test specimens. 4.2. Effects of embossment shape The depth of embossments varied from one specimen to another since the embossments were manually rolled onto the steel-sheeting profiles. Therefore it is difficult to compare the test results of different embossment-types. The profile with a Vshaped embossment may have better shear resistance behaviour with deeper embossments. However, it can be seen from the test results that there is no big difference between the straight shape embossments and the V-shaped embossments. 4.3. Effects of embossment length The embossment length is a very influential factor for the shear resistance. This was proved by the results of RAN153-HD8, which had the shortest embossments (25 mm). The shear stress of RAN153-HD8 was rather low (0.319 N/mm2) even though the depth of the embossment was 19 mm. However, when the embossments had a certain length, the influence was not significant when increasing the length. The specimen groups RAN153-HD7 and RAN153-VD2 may have higher shear strength with deeper embossments, but the inclined straight embossments and Vshape embossments may cause difficulties for the manufacturer in the production line. 4.4. Effects of the thickness of the profiled steel sheeting The effects of the thickness of the profiled steel sheeting are illustrated by the test results of T10-HD6 and T09-HD6. These two type specimens have the same embossments but different sheeting thickness. The sheeting thickness of T10-HD6 is 1 mm and that of T09-HD6 is 0.9 mm. The shear stress of T09-HD6 is only 76% of that of T10-HD6 due to the 10% reduction in sheeting thickness. The secant slip modulus of T10-HD6 is almost 30% higher than that of T09-HD6. This means that the sheeting thickness has a significant effect on the stiffness of the tested specimen. 4.5. Ductility In Eurocode 4, the behaviour of composite slabs is defined as ductile if the failure load exceeds the load causing the first recorded end slip (0.5 mm defined as an initial end slip) by more than 10%. Otherwise it is defined as brittle.
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For the steel-sheeting profiles with penetrated embossments, the end slip corresponding to the maximum horizontal force of all the test specimens is around 0.25 mm except for RAN153-HD8. The behaviour of specimen RAN153-HD8 is just near to the limit of the ductility requirement: some specimens even had a ductile behaviour. The behaviour of other tested specimens is definitely brittle. Since the partial shear-connection method should be applied only for composite slabs with ductile behaviour, the m–k method can only be used for all the tested types, except for profile RAN153-HD8. 4.6. Vertical separation In composite slabs, concrete blocks and steel-sheeting profile have different curvature when they deform. Different deflections of these two parts result in vertical separation between them. If a composite slab is subjected to bending, vertical forces between concrete and steel sheeting occur due to the fact that the two components are forced to the same curvature. The shear resistance at the steel–concrete interface should provide the resistance to horizontal slip and as well as to vertical separation. Therefore, the mechanical interlocking forces can be split into two components. The first one is in the longitudinal direction and the second one is in the vertical direction. The vertical forces are likely to be rather small compared to the longitudinal forces. Since the penetrated embossments in the steel sheeting can provide enough resistance against the separation, the vertical separation is very small in those test specimens. 4.7. Optimizing the steel sheeting profiles Maximum shear resistance obtained from push-out tests is the most important characteristic of the shear transfer, but when optimizing the steel-sheeting profiles, many other characteristics, such as the end slip, the stiffness, the ductility and the vertical separation must also be taken into account. Based on the above discussions, the steel sheeting profile RAN153-HD6, which offers quite high longitudinal shear resistance (0.638 N/mm2), low vertical separation and simple manufacturing technology, is chosen for further study.
5. Conclusions From the test results, it can be seen that the longitudinal shear resistance of the test specimens is significantly affected by the depth of the embossments. For a particular steel sheeting profile, the depth of embossments has more effect on the shear resistance behaviour compared with the length and the shape of embossments. The deeper the embossments the higher the shear stress value if other characteristics of the embossment were roughly the same. The Young’s Modulus of the embossments’ part of the profiled steel sheeting determines the depth and the width of the penetrated embossments [5]. Based on the test results, the suggested depth for penetrated embossments is 2.5 mm for all the eight embossment types. The vertical separation
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was very small in the tested specimens and the reason is that the penetrated embossments in the steel sheeting can provide enough resistance against the separation [13]. The steel sheeting profiles with penetrated embossments offer high shear resistance, but the behaviour of the tested specimens was brittle except for RAN153-HD8. Specimen RAN153-HD8 had better ductile behaviour but the lowest shear resistance. Specimen RAN153-HD6 is suggested for further research. Composite floor slabs consisting of steel sheeting profile RAN153-HD6 must be designed by the m–k method due to the brittle longitudinal shear behaviour.
Acknowledgement The financial support of the company Rautaruukki Oy for this research work given through the TEKES (Technology Development Centre of Finland) research project “Time and Cost Effective Composite Floor” is gratefully acknowledged.
References [1] Eurocode 4, Design of Composite Steel and Concrete Structures, Part 1, General Rules and Rules for Buildings, Revised Draft, 1990. [2] Wright HD, Evans HR. A review of composite slab design, in Proceedings of the Tenth International Specialty Conference on Cold-Formed Steel Structures, St. Louis, Missouri, USA, 1990:27–47. [3] Cheng JJR, Yam MCH, Davison EB. Behaviour and failure mechanism of composite slabs, in Proceedings of the Twelfth International Specialty Conference on Cold-Formed Steel Structures, St. Louis, Missouri, USA, 1994:361–81. [4] Siren M. A modified composite slim floor slab with minimum propping, Master thesis, Laboratory of Steel Structures, Helsinki University of Technology, 1997. [5] Veljkovic M. Behaviour and resistance of composite slabs, experiments and finite element analysis, Doctoral Thesis, Luleå, Sweden, Division of Steel Structures, Luleå University of Technology, 1996. [6] An L, Cederwall K. Composite slabs analyzed by block bending test, in Proceedings of the Eleventh International Specialty Conference on Cold-Formed Steel Structures, St. Louis, Missouri, USA, 1992:268–82. [7] Patrick M, Poh KW. Controlled test for composite slab design parameters, IABSE Symposium on Mixed Structures, Including New Materials, Brussels, 1990:227–31. [8] Daniels BJ. Shear-bond pull-out tests for cold formed steel composite slabs, Ecole Polytechnic Federale De Lausanne (Publication ICOM 194), 1988. [9] Ma¨kela¨inen P, Sun Y. Optimization of the cross-section of a new steel sheeting profile for longspan composite slabs, in Proceedings of the 5th International Conference, Modern Building Materials, Structures and Techniques, Vilnius, Lithuania, vol. 2, 1997:5–10. [10] Yu WW. Cold-Formed Steel Design. A Wiley-Interscience Publication, John Wiley and Sons, Inc., New York, 1985. [11] Patrick M, Bridge R. Review of concepts concerning bond of steel decking, Proceedings of the Twelfth International Specialty Conference on Cold-Formed Steel Structures, St. Louis, Missouri, USA, 1994:335–59. [12] Patrick M. A new partial shear connection strength model for composite slabs, Steel Construction Journal, Australian Institute of Steel Construction, vol. 24, No. 3, August 1990:2–17. [13] Wright HD, Veljkovic M. Towards a numerical procedure for composite slab assessment, in Proceedings of the Thirteenth International Specialty Conference on Cold-Formed Steel Structures, St. Louis, Missouri, USA, 1996:415–35.
The longitudinal shear behaviour of a new steel sheeting profile for composite floor slabs Pentti Ma¨kela¨inen*, Ye Sun Laboratory of Steel Structures, Helsinki University of Technology, P.O.Box 2100, FIN-02015 HUT, Helsinki, Finland Received 27 April 1998; accepted 5 May 1998
Abstract Longitudinal shear failure is the most common failure-type in composite slabs. In this paper, the shear-connection behaviour of composite slabs with a particular profiled steel sheeting having a depth of 153 mm is experimentally studied. Twenty-seven push-out test specimens of different shapes, sizes, locations of embossments and different steel sheeting thicknesses are carried out in two test series. The embossments are first rolled onto the profiled sheeting, then every embossment is punched through along one side. It is found that the shear-connection behaviour of composite slabs is significantly affected by the depth of embossments. For the profiled steel sheeting with penetrated embossments, the reduction of Young’s modulus caused by the penetrated embossments is an important factor that affects the determination of the depth and width of the embossments. Finally, a new type of profiled steel sheeting, which can offer longitudinal shear strength in composite slabs up to 0.6 N/mm2, is proposed for further research. 1998 Elsevier Science Ltd. All rights reserved. Keywords: Steel-concrete composite slabs; Steel sheeting; Longitudinal shear
Nomenclature
max S S1
shear stress maximum shear stress end slip end slip corresponding to max
* Corresponding author. Tel.: + 358-94513780; Fax: + 358-94515019; E-mail: [email protected] 0143-974X/98/$—see front matter 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 3 - 9 7 4 X ( 9 8 ) 0 0 2 1 1 - 9
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1. Introduction Composite slabs consisting of profiled steel sheeting and concrete blocks are widely used in buildings nowadays. The profiled steel sheeting acts as a permanent formwork during the concrete casting and as tensile reinforcement after the concrete has hardened. There are three possible failure-types in composite slabs: flexural failure, longitudinal shear failure and vertical shear failure. The longitudinal shear failure is the most common failure type [1,2]. Therefore, the efficiency of the composite slabs depends on the composite action between these two materials. To achieve the desired composite action, shearing forces have to be transferred between the concrete slab and the steel sheeting. This is usually accomplished by the mechanical interlocking devices rolled onto the surface of the steel sheeting. So far the most effective and most common used shear-connecting device is the pressed embossment on the profiled steel surface [3–5]. Embossments are usually made in shapes of circular spot, chevron or bar at different angles to the shear force axis. The embossments may be pressed onto the webs or flanges. The efficiency of the composite action of steel sheeting in composite slabs is obtained from the test information. The method used for measuring the shear resistance can be either a full-scale test or a small-scale test. Small-scale tests have been widely used for obtaining the shear resistance at the interface between the concrete and steel-sheeting profile. Small-scale tests usually give the shear resistance by pushing out the concrete block horizontally or pulling off the steel sheet vertically [6– 8]. It is shown that the small-scale test is a very effective way to develop a new type of profiled steel sheeting. The design of composite slabs is currently based on the test information for a particular steel-sheeting profile. One type of steel-sheeting profile, RAN153 with a depth of 153 mm is modified by cold-rolling and punching the penetrated embossments onto the surface and is then tested in the Laboratory of Steel Structures at Helsinki University of Technology to investigate the longitudinal shear behaviour of the composite slabs [4,9,10].
2. Experimental programme 2.1. Specimen description The small-scale specimens consisting of steel-sheeting profile and concrete block were cast in the sheeting. The sheeting had a width of 400 mm and length of 300 mm. Each concrete block covered one rib with a width of 280 mm. The concrete block was 300 mm long and 280 mm thick. The steel-sheeting surface was well cleaned before casting the concrete. Twenty-seven small-scale specimens were made in all, twenty-one of them were made in Test Series I and six in Test Series II. The steel sheeting profile used in all specimens of Test Series I was of type RAN153 (1 mm), only the embossments on the steel sheeting were different. The embossment shape of Test Series II is based on the optimization of the embossment shapes of Test Series I. The embossment shape of the specimens in Test Series II was the
P. Ma¨kela¨inen, Y. Sun / Journal of Constructional Steel Research 49 (1999) 117–128
Fig. 1.
119
Dimensions (in mm) of the RAN153 sheeting and cross-section of the test specimen.
same, but the steel sheeting thickness was different. The nominal geometric crosssectional dimensions of the RAN153 sheeting and the test specimen cross-section are shown in Fig. 1. Reinforcement bars (see Fig. 1.) were placed in the concrete blocks in order to avoid failure in the concrete rather than the longitudinal slip failure. The reinforcement bars have no connection with the steel sheeting [6]. 2.2. Push-out test set-up The push-out test set-up consisted of two layer frames as shown in Fig. 2. The bottom layer was a fixed frame and the upper frame could move smoothly in the horizontal direction. The steel-sheeting profile was attached to the fixed frame with 10 M8 bolts and the fixed frame was screwed to the ground to prevent horizontal movement [7,11,12]. The horizontal load was placed symmetrically with respect to the longitudinal axis of the concrete blocks. The horizontal load was generated by an actuator with a 50 kN capacity. The load was transferred to the movable frame and then through two pieces of steel to the concrete block. These two steel pieces with a square section of 40 × 40 mm and a thickness of 5 mm were adhered to every specimen at a height corresponding to the middle of the web of the steel sheeting. Three displacement transducers (LVDT) were used for measuring the slips. Two
Fig. 2. Push-out test set-up.
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of them (stroke 10 mm) measured the slip occurring on the bottom of the concrete block. The third one (stroke 10 mm) measured the slip that occurred at the top of the concrete block. Two transducers (stroke 5 mm) were used for measuring the uplift of the concrete block. 2.3. Material properties The material properties of the steel sheeting were determined from 9 coupon tests according to the EN-SFS 10 002-1 standard for both test series. The mean values obtained for the yield stress and the modulus of elasticity of the steel sheet were 396 N/mm2 and 200 kN/mm2, respectively. The compression strength of the concrete was determined by the cylinder compression test according to the DIN 1048 Part 1 standard, and the mean value obtained for compression strength was 37 N/mm2. 2.4. Embossments 2.4.1. Test Series I There were two categories of embossments in Test Series I: Straight penetrated embossment and V-shaped penetrated embossment. The straight penetrated embossments differed in length, depth and position in the web. Embossments HD5, HD6 and HD7 were rolled onto the middle part of the web. Embossments HD8 were rolled onto the corner of the web. The V-shaped embossments were named as VD2S and VD2O. The only difference between profile RAN153-VD2O and profile RAN153-VD2S was the orientation of embossments: the embossments on both webs of profile RAN153-VD2O had an opposite orientation towards the applied load, and the ones of profile RAN153-VD2S had the same orientation towards the applied load. The detailed information about these embossments is shown in Fig. 3 and the design values of the embossments are shown in Table 1. 2.4.2. Test Series II The shape of the embossments in Test Series II was based on that of RAN153HD6 and is shown in Fig. 4. There were two types of specimens, T10-HD6 and T09-HD6. These two types of specimens had the same embossments on the profiled steel sheeting but different sheeting thicknesses. The thickness of the profiled steel sheeting for T10-HD6 was 1 mm and for T09-HD6 was 0.9 mm. 2.5. Testing programme Eurocode 4 (1990) ([1]) requires that three tests should be carried out on nominal identical specimens. Therefore, a total of 21 push-out tests (Test Series I) were carried out according to the classification of Table 1 and Fig. 3. Seven different embossment types were tested: RAN153-HD5, RAN153-HD6, RAN153-HD7-S, RAN153-HD7-O, RAN153-HD8, RAN153-VD2-S and RAN153-VD2-O. Compared with Test Series I, Test Series II had wider and deeper actual emboss-
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Fig. 3.
121
The shapes of embossments in Test Series I.
Table 1 Dimensions of penetrated embossments Profile Embossment length (mm) depth (mm)
RAN153 HD5 45 2.5
HD6 45 3
HD7 52 3
HD8 25 2.5
VD2 45 2.5
ments on the profiled steel sheeting. In total 6 test specimens were tested, three for T10-HD6 and three for T09-HD6.
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Fig. 4.
The shape of embossments in Test Series II.
3. Test results Fig. 5 shows the typical shear stress-end slip curve obtained from a push-out test. Ultimate longitudinal shear resistance is the most important characteristic of the sheeting and it is designed to be obtained from the recorded horizontal force of the push-out test. The distribution of the longitudinal shear stress is assumed to be uniform along the shear span and it is calculated from the horizontal force divided by the projected contact area of the profiled steel sheeting and concrete. This area is 280 × 300 mm2. The stiffness of the profiled steel sheeting is represented by the secant slip modulus. The ductility is defined as the slip between two points on the shear stress-end slip curve corresponding to the stress level of 0.85max in Fig. 5. The secant slip modulus is defined as the tangent of the line from the zero point to the left point at the 0.85max stress level. For these particular profiled steel sheetings with penetrated embossments, the general observations made during testing are as follows: 앫 the slip was nearly zero even though the load was up to 80% of the maximum load.
Fig. 5. Typical shear stress-slip curve recorded in a push-out test.
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Fig. 6.
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Results of the RAN153-HD6 separation (Test Series I).
앫 there was a very small amount of vertical separation between the concrete block and steel sheeting. 앫 the maximum load was reached just before failure and the failure behaviour was brittle. 앫 after failure, the concrete block was lifted away from the sheeting at both ends with rather large end slip. 앫 the concrete block was complete except for the parts of embossments. 앫 after a test, the depth of the end-opening embossment was deeper than the one before the test. 앫 no plastic deformations were observed in the profiled steel sheeting. The test results of RAN153-HD6 and T10-HD6 are shown in Fig. 6 and Fig. 7, respectively. The average results of all the push-out tests are listed in Table 2. Vertical separation between concrete block and profiled steel sheeting was measured by two displacement transducers. From Table 2, it can be seen that the vertical separation of Test Series I (Fig. 8) is smaller than that of Test Series II (Fig. 9).
Fig. 7.
Results of the T10-HD6 push-out test (Test Series II).
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Table 2 Average results of push-out tests Test series
Specimen Shear stress Slip Ductility Secant Embossment depth max(N/mm2) corresponding (mm) slip (mm) modulus to max S1 (mm) (N/mm2/mm) RAN153-
I
II
HD5 HD6 HD7O HD7S HD8 VD2S VD2O T10-HD6 T09-HD6
0.313 0.638 0.470 0.610 0.319 0.528 0.511 0.519 0.395
0.980 0,228 0,221 0,170 1,061 0,226 0,297 0.093 0.072
0.650 0.819 0.690 0.315 0.343 0.710 0.440 0.539 0.604
0.83 3.99 5.53 6.31 2.41 5.07 2.56 8.31 6.35
Before test 1.43 2.31 1.62 1.92 1.90 1.76 1.98 3.22 2.93
Fig. 8.
Results of vertical separation (Test Series I).
Fig. 9.
Results of vertical separation (Test Series II).
Vertical separation (mm)
After test 1.46 2.46 1.72 2.05 2.03 1.80 2.04 3.72 3.56
0.409 0.686 0.812 0.698 0.834 0.467 0.823 1.250 1.053
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The sheeting RAN153-HD6 has the smallest amount of vertical separation, which was 0.326 mm.
4. Discussion of the test results
4.1. Effects of the embossment depth 4.1.1. Test Series I The test results show that the depth of the embossments has a significant effect on the longitudinal shear behaviour of the steel sheeting profiles. The penetrated embossments can improve the shear resistance greatly since the concrete permeates into the small hole of the embossment. The RAN153-HD6 profile has the highest shear strength among all the test specimens, the average shear stress can be up to 0.638 N/mm2. The main reason is that RAN153-HD6 has the deepest embossments. The embossments on RAN153-HD5 and RAN153-HD6 were the same except for the depth: the depth for HD6 was 2.31 mm and for HD5, 1.43 mm. The shear stress for RAN153-HD6 sheeting was more than twice that of RAN153-HD5 sheeting. As shown in Fig. 10, the deeper the embossment the higher the shear stress value if other characteristics of the embossments were roughly the same. 4.1.2. Test Series II The purpose of testing the specimens in Test Series II is to try to improve the ultimate shear stress and ductility with deeper and wider embossments. The embossments in Test Series II have wider and deeper end-holes than those in Test Series I. The average depth of the straight penetrated embossments in T10-HD6 (Test Series II) was approximately 39% deeper than that in RAN153-HD6 (Test Series I). How-
Fig. 10. Effects of embossment-depth.
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ever, this increase in embossment depth didn’t contribute to any increase in the ultimate shear stress. The main reason for it is the different Young’s Modulus of the embossements’ part of the profiled steel sheeting. The Young’s Modulus of the embossments’ part of the sheeting cannot be tested in our laboratory. The Young’s Modulus of the embossments’ part in T10-HD6 must be lower than that for RAN153HD6 due to the wider and deeper end-holes in the embossments. This test result confirmed the test results of Veljkovic, [5], who reported that the pressed embossments reduce the effective yield strength and Young’s Modulus to about 47% of the original values of the flat sheet, according to his test specimens. 4.2. Effects of embossment shape The depth of embossments varied from one specimen to another since the embossments were manually rolled onto the steel-sheeting profiles. Therefore it is difficult to compare the test results of different embossment-types. The profile with a Vshaped embossment may have better shear resistance behaviour with deeper embossments. However, it can be seen from the test results that there is no big difference between the straight shape embossments and the V-shaped embossments. 4.3. Effects of embossment length The embossment length is a very influential factor for the shear resistance. This was proved by the results of RAN153-HD8, which had the shortest embossments (25 mm). The shear stress of RAN153-HD8 was rather low (0.319 N/mm2) even though the depth of the embossment was 19 mm. However, when the embossments had a certain length, the influence was not significant when increasing the length. The specimen groups RAN153-HD7 and RAN153-VD2 may have higher shear strength with deeper embossments, but the inclined straight embossments and Vshape embossments may cause difficulties for the manufacturer in the production line. 4.4. Effects of the thickness of the profiled steel sheeting The effects of the thickness of the profiled steel sheeting are illustrated by the test results of T10-HD6 and T09-HD6. These two type specimens have the same embossments but different sheeting thickness. The sheeting thickness of T10-HD6 is 1 mm and that of T09-HD6 is 0.9 mm. The shear stress of T09-HD6 is only 76% of that of T10-HD6 due to the 10% reduction in sheeting thickness. The secant slip modulus of T10-HD6 is almost 30% higher than that of T09-HD6. This means that the sheeting thickness has a significant effect on the stiffness of the tested specimen. 4.5. Ductility In Eurocode 4, the behaviour of composite slabs is defined as ductile if the failure load exceeds the load causing the first recorded end slip (0.5 mm defined as an initial end slip) by more than 10%. Otherwise it is defined as brittle.
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For the steel-sheeting profiles with penetrated embossments, the end slip corresponding to the maximum horizontal force of all the test specimens is around 0.25 mm except for RAN153-HD8. The behaviour of specimen RAN153-HD8 is just near to the limit of the ductility requirement: some specimens even had a ductile behaviour. The behaviour of other tested specimens is definitely brittle. Since the partial shear-connection method should be applied only for composite slabs with ductile behaviour, the m–k method can only be used for all the tested types, except for profile RAN153-HD8. 4.6. Vertical separation In composite slabs, concrete blocks and steel-sheeting profile have different curvature when they deform. Different deflections of these two parts result in vertical separation between them. If a composite slab is subjected to bending, vertical forces between concrete and steel sheeting occur due to the fact that the two components are forced to the same curvature. The shear resistance at the steel–concrete interface should provide the resistance to horizontal slip and as well as to vertical separation. Therefore, the mechanical interlocking forces can be split into two components. The first one is in the longitudinal direction and the second one is in the vertical direction. The vertical forces are likely to be rather small compared to the longitudinal forces. Since the penetrated embossments in the steel sheeting can provide enough resistance against the separation, the vertical separation is very small in those test specimens. 4.7. Optimizing the steel sheeting profiles Maximum shear resistance obtained from push-out tests is the most important characteristic of the shear transfer, but when optimizing the steel-sheeting profiles, many other characteristics, such as the end slip, the stiffness, the ductility and the vertical separation must also be taken into account. Based on the above discussions, the steel sheeting profile RAN153-HD6, which offers quite high longitudinal shear resistance (0.638 N/mm2), low vertical separation and simple manufacturing technology, is chosen for further study.
5. Conclusions From the test results, it can be seen that the longitudinal shear resistance of the test specimens is significantly affected by the depth of the embossments. For a particular steel sheeting profile, the depth of embossments has more effect on the shear resistance behaviour compared with the length and the shape of embossments. The deeper the embossments the higher the shear stress value if other characteristics of the embossment were roughly the same. The Young’s Modulus of the embossments’ part of the profiled steel sheeting determines the depth and the width of the penetrated embossments [5]. Based on the test results, the suggested depth for penetrated embossments is 2.5 mm for all the eight embossment types. The vertical separation
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was very small in the tested specimens and the reason is that the penetrated embossments in the steel sheeting can provide enough resistance against the separation [13]. The steel sheeting profiles with penetrated embossments offer high shear resistance, but the behaviour of the tested specimens was brittle except for RAN153-HD8. Specimen RAN153-HD8 had better ductile behaviour but the lowest shear resistance. Specimen RAN153-HD6 is suggested for further research. Composite floor slabs consisting of steel sheeting profile RAN153-HD6 must be designed by the m–k method due to the brittle longitudinal shear behaviour.
Acknowledgement The financial support of the company Rautaruukki Oy for this research work given through the TEKES (Technology Development Centre of Finland) research project “Time and Cost Effective Composite Floor” is gratefully acknowledged.
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