Experimental investigation on the structural response of T, T-block and T-Perfobond shear connectors at elevated temperatures

Engineering Structures 75 (2014) 299–314

Contents lists available at ScienceDirect

Engineering Structures journal homepage: www.elsevier.com/locate/engstruct

Experimental investigation on the structural response of T, T-block and T-Perfobond shear connectors at elevated temperatures João Paulo C. Rodrigues ⇑, Luis Laím ISISE – Institute for Sustainability and Innovation in Structural Engineering, University of Coimbra, Portugal

a r t i c l e

i n f o

Article history: Received 3 February 2014 Revised 4 June 2014 Accepted 10 June 2014

Keywords: Composite structures T T-block T-Perfobond connectors Elevated temperatures Push-out tests Shear resistance

a b s t r a c t The structural performance of different connectors at ambient temperature is already known in contrast to the structural response of some connectors at high temperatures. An example of this is the T, T-block and T-Perfobond connectors. This paper reports a research study on the structural behaviour of T, T-block and T-Perfobond shear connectors under fire conditions for assessing the connector shear resistance, its ductility and collapse modes at elevated temperatures. The main purpose of this research was to investigate the influence of the number of holes in the connector, the presence of transversal reinforcement bars passing through these holes, the connector arrangement and the connector height, among others, on the structural performance of the connector at different levels of elevated temperature. It was also compared the behaviour of these connectors at ambient and elevated temperatures. Finally, the experimental results were compared with the predictions from available analytical models, taking into account changes in the shear strength of the T, T-block and T-Perfobond connectors at elevated temperatures. The results of this research showed mainly that the shear resistance capacity at elevated temperatures of these connectors depends extremely on their shape in relation to the steel beam. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction The use of composite members in buildings is a solution that is under continuous development, and so it will remain a challenge for the next few years. The use of composite members accounts for the contribution of different materials, enabling a composite action between them. One of the most popular and extensively used solutions is the composite beam: the steel girder absorbs the tension stresses and the reinforced concrete slab sustains most of the compressive stresses [1]. To achieve this structural behaviour in a composite beam, it is well known that shear transfer between the steel profile and the concrete deck has to be provided, in other words, a composite action can be obtained by reducing or preventing the relative displacement of concrete and steel sections at their interface. This composite action is usually assured by shear connectors. The strength and stiffness of a composite beam depends on the degree of composite action between the concrete deck and the steel profile. It must be remembered that the chemical bond effect between ⇑ Corresponding author. Address: Departamento de Engenharia Civil, Universidade de Coimbra, Rua Luís Reis Santos, Pólo II da Universidade, 3030-788 Coimbra, Portugal. Tel.: +351 239797237; fax: +351 239797123. E-mail address: [email protected] (J.P.C. Rodrigues). http://dx.doi.org/10.1016/j.engstruct.2014.06.016 0141-0296/Ó 2014 Elsevier Ltd. All rights reserved.

the concrete and the steel does not account for much of the total shear resistance and due to the difficulty of calculating this bond effect, this one is often ignored. Hence, the degree of composite action is related to the geometrical and mechanical properties of the shear connectors and the concrete slab. It is up to the shear connectors to resist the horizontal shear and vertical uplift forces generated in beams, ensuring that the two different materials that constitute the composite beam behave as a single unit. Nowadays, several types of shear connectors are available such as Stud [2], Crestbond [3], Perfobond [4], T-Perfobond [5] and T connectors [6], among others. The Stud or Nelson connector is the most widely used and known shear connector due to a high degree of automation in workshop or construction site. However, it can cause cracks in the concrete slab and experience fatigue under service loading conditions, and its resistance is somewhat limited, comparing with other types of connectors, especially in applications where a discrete distribution of the connectors is needed, for example in precast concrete decks or in strengthening, repairing or even retrofitting existing structures taking the maximum advantage of the steel and concrete composite action. Therefore, some other alternative shear connectors that have higher shear capacity, ductility, and fatigue resistance have been proposed to substitute for stud connectors. This is the case of the Perfobond connector, which was developed in the eighties by the

300

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

Nomenclature Af1 Af2

Ah Atr D P PT,20°C PT,t PT-P,20°C PT-P,t PRk Ptest P0 test Ph

front bearing area of the shear connector front bearing area of the shear connector amplified at an inclination rate of 1:5 to the rear surface of adjacent connector total area of holes in the connector total area of transversal steel reinforcement bars passing through the connector holes hole diameter in the connector applied load on the specimen or load-carrying capacity of the specimen ultimate load-carrying capacity of the specimen with T connector at ambient temperature ultimate load-carrying capacity of the specimen with T connector at time t ultimate load-carrying capacity of the specimen with Tblock or T-Perfobond connector at ambient temperature ultimate load-carrying capacity of the specimen with Tblock or T-Perfobond connector at time t characteristic value of the load-carrying capacity of the specimen ultimate load-carrying capacity of the specimen estimated maximum load-carrying capacity of the specimen ultimate load-carrying capacity of the specimen at elevated temperature h

German company Leonhardt, Andrä and Partners for the design of the third bridge over the Caroni River, in Venezuela [7]. Its development was based in the need of a system that involved only elastic deformations under service loads, with some specific bond behaviour. Whereas the Stud connectors have a shank and a head that contributes to the shear transfer and prevents the uplift, the Perfobond connectors are formed by a rectangular steel plate with holes drilled on it, and is welded to the beam flange. Therefore, its shear resistance capacity depends mainly on the shear resistance of the concrete dowel in the connector hole (horizontal and vertical shear), the shear resistance of the transverse rebars in the connector holes and the concrete end-bearing resistance [8]. In the recent past, several authors have studied the behaviour of the Perfobond connectors at ambient temperature, namely by the evaluation of results from push-out tests or by the development of numerical models. It was concluded that their structural response is influenced by several geometrical properties such as the number of holes, the height, length and thickness of the steel plate, the concrete compressive strength, and the percentage of transverse steel reinforcement present in the concrete slab. Reference is made to the studies of Machácek and Studnicka [9], Cândido-Martins et al. [1], Valente and Cruz [8], Vianna et al. [10,11]. In addition, some analytical models were proposed to predict the resistance of Perfobond shear connectors. The most relevant models were proposed by Al-Darzi et al. [12], Marecek et al. [13] and Oguejiofor and Hosain [14]. On the other hand, with the goal of improving the shear resistance of the Perfobond connector, Vianna et al. [10] presented other connector, called T-Perfobond. The main difference between the Perfobond and T-Perfobond connectors is the presence of a flange, providing a further anchorage to the system, acting as a block. This is why they are also known as T-shape block type connectors. However, a careful choice of flange thickness is required to achieve an adequate balance between the overall resistance and ductility. Another advantage of using this type of connector may

P20°C b fck fy h l lc n re t tsc tc wc d du hC hS

l r

ultimate load-carrying capacity of the specimen at ambient temperature total width of the connector flange characteristic compressive cylinder strength of concrete at 28 ambient temperature yield strength of the steel rebars at ambient temperature connector height connector length concrete slab length number of holes in the connector steel reinforcement bar diameter exposure time to fire shear connector thickness concrete slab thickness concrete slab width relative displacement between the short steel beam and the concrete slab slip capacity of the connector concrete temperature steel temperature sample mean value sample standard deviation

also be dictated by the fact that it may be produced with ordinary laminated I or H sections, saving material and labour. Concrete block resistance was also found in their studies [11] to be of much greater importance than the resistances related to the holes and to the reinforcement bars. In fact, connectors with and without holes and steel reinforcement bars passing through the holes, showed limited gains in resistance for the investigated specimens range. Furthermore, other type of connector, known as T connector, evolved from the observation by Oguejiofor [4]. The load capacity of these connectors are very similar to that of the oscillating perfobond strip, however, the ductility of the T-connectors is much larger [15], and by its shape could prevent vertical separation between steel-section and concrete. When used in concrete with fibres, lightweight concrete or a higher strength concrete, there is a notable increase in the load capacity and ductility of this type of connector [16]. As a result of the relatively small area of its cross-section, the bearing stress on the front of the T is very high and consequently local concrete crushing may occur, meaning a quasi-plastic performance [17]. In spite of the relatively large number of studies on connectors at ambient temperature, very few studies were performed on the behaviour of these structural elements at elevated temperatures. Reference may be done to the works of Choi et al. [18], Mirza and Uy [19] and Zhao and Kruppa [20] on the behaviour of Stud connectors and to the study of Rodrigues and Laím [21] on the behaviour of Perfobond connectors in case of fire. From this last work, it could be observed that the shear resistance increased significantly with the number of holes for 30 min of standard fire conditions in relation to other periods (60 and 90 min). It was noted that the presence of reinforcing bars passing through the connector holes and the presence of two connectors placed side by side had a significant contribution to the resistance of the connections at ambient temperature in contrast to what was observed at high temperatures. This may have meant that the larger the amount of steel in the connection is the greater the damage in the connection resistance is.

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

This paper therefore intends to fill the knowledge gap in this almost unexplored field and bring a better understanding about these issues. So, this paper is mainly aimed at the structural behaviour of T, T-block and T-Perfobond shear connectors at elevated temperatures, based on the results of a large programme of experimental tests. This study was founded by several modified push-out tests to provide information concerning the general behaviour and suitability for practical applications of T, T-block and T-Perfobond connectors in case of fire. The experimental programme was conducted in accordance with the specifications of EN1994-1-1 (2005), annex B [22], changing some features in order that the tests at elevated temperatures were enabled. The number of holes in the shear connector, the presence of transversal reinforcement bars passing through these holes, the connector arrangement and the connector height, among others, were the main parameters investigated in this study for evaluating the influence of these variables on the structural response of this type of connectors at different levels of elevated temperatures. The experimental results are presented and discussed, focusing on the T and T-block structural performance in terms of shear transfer capacity, ductility and collapse modes. Furthermore, as reference, some modified push-out tests at ambient temperature were also carried out for comparison, especially the failure modes of the corresponding connectors. Finally, the experimental results were still compared with the predictions from available analytical models, taking into account changes in the shear strength of the T, T-block and T-Perfobond connectors at elevated temperatures, in order to establish their accuracy and applicability. 2. Experimental tests 2.1. Specimens The fabrication of the test specimens were based on the standard push-out test suggested in the EN1994-1-1 (2005), annex B [22]. This type of specimens quite often consists of a short steel beam held in a vertical position by two identical reinforced concrete slabs. The concrete slabs are attached to the beam flanges by the shear connectors. However, in this study, one of the concrete slabs of the standard specimen was removed with the purpose of applying the thermal action at one side of the short beam. This resulted in specimens for modified push-out tests at high temperatures where their geometry is represented in Fig. 1. The reinforced concrete slab was 600 mm wide, 650 mm long and 150 or 200 mm thick depending on the connector height. This one was reinforced both on its top and bottom with 10 mm diameter continuous steel bars, with a spacing about 150 mm in both directions and reinforcement layers and, finally, with a concrete cover about 25 mm, as established in EN1994-1-1, annex B [22].

Fig. 1. Test specimen for the modified push-out tests at high temperatures.

301

All specimens presented a similar concrete compressive strength of approximately 28 MPa, obtained from cubes at 28 days old and so corresponding to a C20/25 class according to EN 206-1 [23]. In what concerns to the steel beam attached to the concrete slab, a HEA200 profile was adopted, as it is one of the most used on beams on composite steel and concrete construction. Regarding the shear connector, the present work focuses on T, T-block and T-perfobond connectors (Figs. 2 and 3) with different heights (100 and 150 mm), number of holes (0, 1 and 3 holes for the 100 mm height connectors and 3 and 6 holes for the 150 mm height connectors), amounts of transversal reinforcement bars passing through these holes (no bars and bars with 12 mm in diameter) and arrangements. Therefore, several connector dimensions, including length, thickness, hole diameter, and hole spacing were fixed for all specimens. Additionally, the dimensions of the concrete slab, the diameter of the transverse rebars and the mechanical properties of all different materials were also fixed. All connectors were 240 mm long and 15 mm thick and their holes were 30 mm in diameter and 70 mm away from each other in relation to their centres. The geometrical characteristics of the tested specimens are summarised in Table 1. The rebars in the concrete slab were made of A500 steel (relation between the characteristic values of the tensile and yield strength higher or equal to 1.05, according to EN 1992-1.1 [24]) and the beams and shear connectors respectively of S275 steel (with a nominal yield strength of 275 MPa and a tensile strength of 430 MPa, according to EN19931.1 [25]) and S355 steel (with a nominal yield strength of 355 MPa and a tensile strength of 510 MPa, according to EN19931.1 [25]). From Table 1 and Fig. 4, where the geometry of different connectors assembled in test specimens are illustrated, it can be mentioned that the reference T_1h_12re_100tall corresponds to a T connector (T) with 100 mm of height (100tall), with one hole (1h) and a 12 mm diameter rebar passing through its hole (12re). On the other hand, in the case of the references T-block_100tall, T-P_6h_0re_150tall and T-block_100tall_In, T-block and T-P means respectively a T-shape block type connector and a T-Perfobond type connector, 150tall stands for the connector height (150 mm) and In indicates that the position of the shear connector was changing by 180° in relation to other connectors, in other words, the connector flange is at the top instead of its flange is at the bottom. In these tests the bearing into the concrete is provided firstly by the connector web. Note that when there are no holes in the T-Perfobond connector, this one turns into a T-block connector. 2.2. Test set-up A detail of the specimen’s instrumentation and the experimental test set-up for modified push-out tests at ambient and elevated temperatures is illustrated in Fig. 5. Therefore, one of the concrete slabs of the standard specimen was replaced (1) by the electric furnace (2) that applied the thermal action, and a restraining structure (3) was built to re-establish the symmetry of the loading and to keep the specimen in position during the tests. A neoprene sheet was placed below the specimen in order to absorb any imperfections present at the concrete bottom face and to reduce friction. The furnace available in the Laboratory was 1500 mm long  1000 mm tall  750 mm wide in internal dimensions and capable to heat up to 1200 °C and follow fire curves with different heating rates. The loading was applied by a 1 MN servo-controlled hydraulic actuator (4), which was hung on a two-dimensional reaction frame (5), which consisted of two HEB500 columns and a HEB600 beam of class S355 steel. Data acquisition system was assured by a data logger and the applied loads were measured by the actuator load cell, while the relative displacement between the short steel beam

302

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

Fig. 2. Connector geometry for the modified push-out tests (dimensions in mm): (a) T_ih_ire_100tall; (b) T-block_100tall and T-P_ih_ire_100tall; and (c) T-P_ih_ire_150tall.

and the concrete slab were measured by linear variable displacement transducers (LVDT) (6). In order to register any slip of the specimen with the base, two LVDT were still mounted (7). The LVDT readings, together with the load measurements, were able to provide the force–slip curves for all studied shear connectors. 2.3. Test plan The experimental tests on this type of shear connectors were conducted in the Laboratory of Testing Materials and Structures (LEME) of the University of Coimbra, in Portugal. The experimental programme consisted of 44 modified push-out tests, 11 of which were performed at ambient temperature and 33 at elevated temperatures. Eleven different modified push-out tests at ambient temperature, in specimens made with the connectors referred in Table 1, were conducted to assess the reference force–slip curves, failure modes, ultimate load-carrying and slip capacity of the specimens. Eleven modified push-out tests at elevated temperatures, per each temperature level tested, were also conducted to assess the force–slip

Fig. 3. Scheme of the T (a) and T-block (b) connectors welded in the steel profile.

Table 1 Geometrical characteristics for the modified push-out specimens. Specimen

Concrete slab tc (mm)

T_0h_0re_100tall T_1h_0re_100tall T_3h_0re_100tall T_1h_12re_100tall T-block_100tall T-P_1h_0re_100tall T-P_3h_0re_100tall T-P_1h_12re_100tall T-block_100tall_In T-P_3h_0re_150tall T-P_6h_0re_150tall

Shear connector wc (mm)

lc (mm)

tsc (mm)

h (mm)

l (mm)

D (mm)

re (mm)

– – 30 12 150

100 600

650

15

– 240

– 30 12

200

150

– 30

–

n 0 1 3 1 0 1 3 1 0 3 6

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

303

Fig. 4. Detailing of the modified push-out specimens (dimensions in mm): (a) T_1h_12re_100tall; (b) T-block_100tall; and (c) T-P_6h_0re_150tall.

curves, failure modes, ultimate load-carrying and slip capacity of the specimens, as well as the temperature distribution in the shear connector when this one reached its failure load. It was intended to test the same type of specimens that were used for ambient temperature tests, but under elevated temperatures. The temperature levels tested were 840, 950 and 1005 °C (furnace temperatures), corresponding to 30, 60 and 90 min of the ISO 834 fire curve, respectively. 2.4. Test procedure 2.4.1. Ambient temperature tests These experimental tests were loaded in two stages according to EN1994-1-1, annex B [22]. At the first stage a cyclic loading between 5% and 30% of the expected ultimate load-carrying

capacity was applied under load control in 25 cycles and at a rate of 1 kN/s. The ultimate load-carrying capacity was predicted from the study of Vianna et al. [11] for standard push-out specimens made with the same type of connectors of the ones tested in the present study (Table 2). This cyclic loading intended to simulate the serviceability state of the specimens when inserted in a real building structure. At the second stage the specimens were also subjected to a vertical load, which produced shear loading along the interface between the concrete slab and the beam flange, under displacement control and at a rate of 0.01 mm/s until the relative displacement between the short steel beam and the concrete slab was very large (where the load in the unload stage was equal at least to 80% of the peak load).

304

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314 Table 3 Values of the cyclic loading for the elevated temperature tests. Specimen

5% Ptest (kN)

30% Ptest (kN)

T_0h_0re_100tall T_1h_0re_100tall T_3h_0re_100tall T_1h_12re_100tall T-block_100tall T-P_1h_0re_100tall T-P_3h_0re_100tall T-P_1h_12re_100tall T-block_100tall_In T-P_3h_0re_150tall T-P_6h_0re_150tall

26.7 29.0 32.6 34.7 37.9 35.9 36.4 38.2 40.4 56.3 54.2

159.8 174.2 195.2 208.4 227.1 215.5 218.2 229.3 242.8 337.9 326.1

and hS10 (Fig. 6) were welded to steel connector plate, whereas thermocouples hC1, hC2, and hC3 (Figs. 6 and 7) were embedded in the concrete. The thermocouples hC1, hC2 and hC3 allowed to measure the temperatures in concrete at different depths (near the concrete slab surfaces, about 20 mm away, and in the middle of the slab), as well as the thermocouples hS1 and hS2 in the steel connector (Fig. 7), for instance. The thermocouples were also employed in order to evaluate the temperature evolution both in the connector flange and in the connector web. Fig. 5. Test set-up for modified push-out tests.

2.5. Results and discussion

Table 2 Values of the cyclic loading for the ambient temperature tests. Specimen

5% P0 test (kN)

30% P0 test (kN)

T_0h_0re_100tall T_1h_0re_100tall T_3h_0re_100tall T_1h_12re_100tall T-block_100tall T-P_1h_0re_100tall T-P_3h_0re_100tall T-P_1h_12re_100tall T-block_100tall_In T-P_3h_0re_150tall T-P_6h_0re_150tall

11.1 11.5 11.9 15.5 26.0 26.0 26.0 26.0 26.0 33.0 33.8

66.8 69.1 71.4 93.0 156.0 156.0 156.0 156.0 156.0 197.7 202.8

2.4.2. Elevated temperature tests In the same way of the ambient temperature tests, firstly a cyclic loading was applied in 25 cycles at a rate of 1 kN/s ranging from 5% to 30% of the failure load obtained from the respective tests carried out at ambient temperature in this research work (Table 3). Secondly, the specimens were heated up to the target temperature following the heating rate of the ISO 834 fire curve [26]. As already mentioned the target temperatures for the ultimate shear strength tests of the specimens were 840, 950 and 1005 °C in the furnace, corresponding to 30, 60 and 90 min of the ISO 834 fire curve, respectively. Finally, when the temperature in the furnace reached the desired level, the specimens were loaded at a rate of 0.01 mm/s until the relative displacement between the short steel beam and the concrete slab was very large, as well as at the ambient temperature tests. During the application of this load the furnace temperature was kept constant. As shown in Fig. 5, the thermal action was applied by a modular electric furnace (2) and followed nearly the ISO 834 fire curve, as it has already been mentioned. Type K (chromel–alumel) thermocouple probes were used to measure the temperatures in the furnace and cable thermocouples of the same type were used to measure the temperature in the specimens at different depths, as illustrated in Figs. 6 and 7. Thermocouples hS1, hS2, hS3, hS4, hS5, hS6, hS7, hS8, hS9

2.5.1. Ambient temperature tests Figs. 8 and 9 present the force–slip curves for the modified push-out tests with T, T-block and T-Perfobond connectors at ambient temperature, from which it can be assessed the ultimate and the characteristic value of the load capacity of the specimens, Ptest and PRk, and their slip capacity, du, (Fig. 10) respectively, as recommended by EN1994–1-1, annex B [22]. The slip capacity of the connector, du, should be taken as the highest measured value at the level of the characteristic load, PRk, which should be 90% of the maximum load-carrying capacity of the specimen, Ptest. Table 4 summarises the values obtained for these parameters. Hence, a comparative analysis of the different types of shear connectors in terms of their resistance, ductility and failure modes is described ahead in this paper. It may be concluded that an increase of the slab thickness from 150 to 200 mm leads to an increase of approximately 55% in the connector characteristic resistance, PRk (from 654.6 kN of the specimen T-P_3h_0re_100tall to 1013 kN of the specimen T-P_3h_0re_150tall), and still to a higher increase in the slip capacity, du (from 14.40 to 26.67 mm, respectively). Furthermore, it was observed that an increase in the number of connector holes slightly enhanced the connector load-carrying capacity. This relative gain was higher for the specimens with T connector than for the specimens with T-Perfobond connector. It can be seen in Table 4 that the characteristic value of the load-carrying capacity for the specimens T_0h_0re_100tall, T_1h_0re_100tall and T_3h_0re_100tall was respectively of 479.9, 523.1 and 586.2 kN, whereas for the specimens T-block_100tall, T-P_1h_0re_100tall and T-P_3h_0re_100tall was respectively of 633.3, 646.5 and 654.6 kN. This means that one more hole in the T connector may lead to an increase in the connector characteristic resistance, PRk, of about 8%, whereas for T-Perfobond connectors that increase may be just about 1%. On the other hand, adding steel reinforcement in the holes of the shear connectors may also slightly improve the connector characteristic resistance, PRk, from 523.1 to 625.0 kN for the T connector (an increase of about 19%) and from 646.5 to 687.7 kN for the T-Perfobond connector (an increase of about 6%). Fig. 9 also shows some differences in the connection behaviour between the specimens T-block_100tall

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

305

Fig. 6. Location of the thermocouples in the specimens with T connector: (a) overall view; (b) yz-plane view; (c) xy-plane view and xz-plane view.

Fig. 7. Location of the thermocouples in the specimens with T-block or T-Perfobond connector: (a) overall view; (b) yz-plane view; (c) xy-plane view and xz-plane view.

Fig. 8. Force–slip curves of the specimens with T connector at ambient temperature.

Fig. 9. Force–slip curves of the specimens with T-block or T-Perfobond connector at ambient temperature.

306

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

these parameters had a higher effect on the stiffness of the connection between the concrete deck and the steel beam. The stiffness of the specimens T-block_100tall, T-P_3h_0re_100tall and T-P_1h_0re_100tall was respectively of 48, 60 and 62 kN/mm, for instance. Another main feature of these connectors was that their ductility was much lower than the one observed in the T connectors, in contrast to the shear resistance. Note that, some specimens (T-block_100tall, T-P_1h_0re_100tall and T-P_3h_0re_100tall) with T-block or T-Perfobond connector reached its failure load during the initial linear loading stage, not presenting a satisfactory ductility for the connection between the two elements (beam and slab).

Fig. 10. Determination of slip capacity du.

Table 4 Results of the modified push-out tests at ambient temperature. Specimen

Ptest (kN)

PRk (kN)

du (mm)

T_0h_0re_100tall T_1h_0re_100tall T_3h_0re_100tall T_1h_12re_100tall T-block_100tall T-P_1h_0re_100tall T-P_3h_0re_100tall T-P_1h_12re_100tall T-block_100tall_In T-P_3h_0re_150tall T-P_6h_0re_150tall

533.3 581.2 651.3 694.4 703.7 718.4 727.3 764.1 828.8 1126 1087

479.9 523.1 586.2 625.0 633.3 646.5 654.6 687.7 745.9 1013 978.4

22.12 24.56 24.36 24.75 16.43 16.95 14.40 15.08 18.43 26.67 29.62

and T-block_100tall_In (connector arrangement). In the specimen T-block_100tall_In the contribution of the connector web is higher than in the specimen T-block_100tall. This resulted in an 18% increase of the connector characteristic resistance, Prk, and in an approximately 2.0 mm increase of the slip capacity, du. It is quite interesting to observe that the changes in the uplift magnitude due to the number of holes and the presence of reinforcement bars in the holes were more significant in the specimens with T connector than in the specimens with T-Perfobond connector. This suggests that the behaviour of the T-Perfobond shear connectors was governed essentially by the flange geometry and not by the web dimensions or number and size of holes, as also concluded by Vianna et al. [10,11] and Neves et al. [27]. However,

2.5.2. Elevated temperature tests 2.5.2.1. Temperature distribution. Figs. 11 and 12 show an example of the evolution of temperature in specimens with T (Fig. 11) and T-block or T-Perfobond (Fig. 12) connectors as a function of time and for the temperature level of 950 °C, corresponding to 60 min of the ISO 834 fire curve. It can be observed that those temperatures were recorded during 90 min, because after the furnace reached the desired level of temperature the specimen was loaded at a rate of 0.01 mm/s and, consequently, during this period the temperature in the specimen continued to increase, due to heat transfer by conduction. The furnace temperature exhibited a small delay in relation to the ISO 834 fire curve because the initial minutes of the curve are very difficult to reproduce with the electric furnace and this becomes worse for larger furnaces (high initial thermal inertia). This evolution of temperatures inside the furnace over time was nearly the same in all elevated temperatures tests, meaning that the tests are comparable. Each measuring point in the shear connector was used for assessing an average temperature on the bottom and top of the respective connector, so that the thermal gradient across it could be recorded. From Fig. 11, it can be seen that the mean temperature on the bottom of the connector T_0h_0re_100tall for 60 min of heating was about 448 °C (hS1 and hS2) and on the top about 148 °C (hS3, hS4, hS5, hS6, hS7, hS8, hS9 and hS10). On the other hand, from Fig. 12, it can be observed that the temperature on the bottom of the connector T-block_100tall_In for 60 min of heating was about 439 °C (hS1, hS3 and hS5) and on the top about 235 °C (hS2, hS4 and hS6). The temperature in the concrete around the connector ranged approximately from 300 °C (hC1) to 100 °C (hC2) for the specimen T_0h_0re_100tall (Fig. 11) and from 400 to 100 °C for the specimen T-block_100tall_In (Fig. 12).

Fig. 11. Evolution of temperature in the test specimen T_0h_0re_100tall as a function of time for the temperature level of 950 °C (60 min of ISO 834 fire curve).

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

307

Fig. 12. Evolution of temperature in the test specimen T-block_100tall_In as a function of time for the temperature level of 950 °C (60 min of ISO 834 fire curve).

Taking all thermal results from this investigation into account, it can be concluded that the temperature on the bottom of the T_nh_0re_100tall connectors was, on average, about 185, 450 and 510 °C for 30, 60 and 90 min of heating, respectively; and on the top about 55, 150 and 170 °C. Besides, the temperature on the bottom of the T-P_nh_0re_100tall connectors was, on average, about 220, 475 and 575 °C for 30, 60 and 90 min of heating, respectively; and on the top about 100, 235 and 370 °C. And, finally, the temperature on the bottom of the T-P_nh_0re_150tall connectors was, on average, about 140, 300 and 470 °C for 30, 60 and 90 min of heating, respectively; and on the top about 55, 110 and 150 °C. Regarding the temperature in the concrete slab, when this one was 150 mm thick, the temperature near the concrete surface exposed to fire was about 300, 450 and 600 °C for 30, 60 and 90 min of heating, respectively; whereas the temperature in the middle of the thickness was about 80, 120 and 160 °C. On the other hand, when

the concrete slab was 200 mm thick, the temperature in the middle of the thickness was about 70, 100 and 120 °C, respectively for 30, 60 and 90 min of heating. To conclude, it is important to emphasize that the temperature in the T connectors is slightly lower than in the T-block or T-Perfobond connectors and significantly lower when its height is strongly increased. Note that these differences increased with increasing exposure time to fire. 2.5.2.2. Reduction of the shear resistance. Figs. 13 and 14 present the force–slip curves for the modified push-out tests with T, T-block and T-Perfobond connectors at different levels of temperature. The same way that the ambient temperature tests these curves allow the assessment of the ultimate and characteristic value of the load capacity of the connectors, Ptest and PRk, and their slip capacity, du, respectively, as recommended by EN1994-1-1, annex B [22]. Table 5 summarises the values obtained for these parameters.

Fig. 13. Force–slip curves of the specimens with T connector at elevated temperatures: (a) 30, (b) 60 and (c) 90 min of the ISO 834 fire curve.

308

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

The main conclusions to be drawn were that the high temperatures adversely affected the resistance and stiffness of the connections and that the effect of number of holes and the presence of reinforcement bars in the holes were less significant in the specimens than at ambient temperature, as it can be seen ahead in this paper. For example, at 840, 950 and 1005 °C (30, 60 and 90 min of the ISO 834 fire curve, respectively) the stiffness of the specimen T-P_1h_0re_100tall was respectively of 55, 48 and 39 kN/mm. In Fig. 15 it can be also observed the influence of the high temperatures in the ultimate load-carrying capacity of the connectors in relation to the ones obtained at ambient temperature. It is important to stress that the connectors with a higher height (T-P_3h_0re_150tall and T-P_6h_0re_150tall) presented a higher reduction in the shear resistance, in contrast to the connector T_0h_0re_100tall, where the reduction was only of 12%, 34% and 69% for 30, 60 and 90 min of the ISO 834 fire curve, respectively (Fig. 15a). Note that the ultimate load-carrying capacity of the connector T-P_3h_0re_150tall decreased about 43%, 71% and 83% for the same levels of temperature, respectively (Fig. 15b). It is obvious to observe that the reduction factors of the characteristic resistance (Ph/P20°C) for the specimens with T connector were generally higher than the respective reduction factors for the specimens with T-block or T-Perfobond connector, since the T connector is better protected against the high temperatures. This also means that the connector temperature may be more relevant to its shear resistance than the concrete temperature. Another important point to note is that the reduction factors of the characteristic resistance (Ph/P20°C) for the specimens with T connector had the same tendency in contrast to the specimens with T-Perfobond connector. For those specimens the standard deviations of the results were always less than 0.05. However, the higher the temperature is, the smaller the influence of the studied variables is on the ultimate load-carrying capacity of the T-Perfobond connectors, since the relations between the respective connector shear resistances at elevated and ambient temperatures were closing each other for the different levels of testing temperatures, as it can clearly be seen

by the standard deviations of the results (Fig. 15b). The ultimate load-carrying capacity of these connectors, in relation to the ambient temperature, dropped between 14% and 43%, 42% and 71% and between 69% and 83% at 840, 950 and 1005 °C, respectively. Thus, for these cases, it can be concluded that the type of connector is not so important for 90 min as for 30 min of the ISO 834 fire curve. For 30 and 60 min the relations between the respective connector shear resistance at elevated and ambient temperatures had a great range (Fig. 15b). Lastly, it can still be seen from Table 5 that the connections between the short steel beams and the concrete slabs at 1005 °C (90 min of the ISO 834 fire curve) were much more ductile than the ones at others temperatures. At this temperature the slip capacity, du, was almost always larger than 20 mm and, in some cases, was higher than 30 mm. As well as at ambient temperature, for 30 min of the ISO 834 fire curve some specimens (T-block_100tall, T-P_1h_0re_100tall, T-P_3h_0re_100tall, TP_1h_12re_100tall and T-block_100tall_In) with T-block or T-Perfobond connector reached its failure load during the initial linear loading stage, perhaps not presenting enough ductility for the connection between the two elements (beam and slab). 2.5.2.3. Effect of number of holes, reinforcement bars, connector arrangement and connector height. Fig. 16 also provides a general idea of how the number of connector holes affects the shear resistance of the specimens for different levels of temperature tested. For a clear visualization of these results it was plotted their trend as well. It can be observed that the shear resistance increased with increasing the number of holes for almost all levels of temperature, except for the specimens with T-Perfobond connector and for 60 min of heating. However, the enhancement of the shear resistance due to holes in the connectors was mostly lower for high temperatures in relation to ambient temperature. From these results, it may also be concluded that the concrete has an important role to play in the ultimate load-carrying capacity of connectors more exposed to fire (T-block and T-perfobond connectors). In addition, the enhancement of the connector characteristic

Fig. 14. Force–slip curves of the specimens with T-block or T-Perfobond connector at elevated temperatures: (a) 30, (b) 60 and (c) 90 min of the ISO 834 fire curve.

309

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314 Table 5 Results of the modified push-out tests at elevated temperatures. Specimen

Time of the ISO 834 fire curve 30 min

T_0h_0re_100tall T_1h_0re_100tall T_3h_0re_100tall T_1h_12re_100tall T-block_100tall T-P_1h_0re_100tall T-P_3h_0re_100tall T-P_1h_12re_100tall T-block_100tall_In T-P_3h_0re_150tall T-P_6h_0re_150tall

60 min

90 min

Ptest (kN)

PRk (kN)

du (mm)

Ptest (kN)

PRk (kN)

du (mm)

Ptest (kN)

PRk (kN)

du (mm)

470.7 488.5 518.9 609.5 465.4 568.8 545.8 491.4 711.9 642.5 614.8

423.6 439.7 467.0 548.5 418.8 511.9 491.2 442.2 640.7 578.2 553.3

12.55 16.63 15.76 18.40 9.32 11.86 9.37 8.07 14.39 16.50 15.67

351.2 365.6 428.8 424.3 381.6 336.9 294.2 312.3 481.7 328.6 347.5

316.1 329.1 385.9 381.9 343.4 303.2 264.8 281.0 433.5 295.8 312.7

19.90 13.99 15.82 16.08 11.78 10.50 10.61 12.42 14.45 11.45 11.86

164.2 166.0 195.3 178.2 157.5 159.2 171.7 159.9 253.2 187.8 184.7

147.8 149.4 175.8 160.4 141.8 143.3 154.5 143.9 227.9 169.0 166.2

31.55 34.03 23.17 27.73 27.75 38.51 39.95 37.51 14.57 15.89 19.75

Fig. 15. Relative values of the ultimate load-carrying capacity of the specimens with T (a), T-block or T-Perfobond (b) connector at elevated temperatures h.

resistance, due to the increase of its height, decreased as the period of heating increased. For instance, an increase of the slab thickness from 150 mm (specimen T-P_3h_0re_100tall) to 200 mm (specimen T-P_3h_0re_150tall) led to an increase of approximately 18%, 12% and 9% in the connector characteristic resistance, PRk, for 30, 60 and 90 min of the ISO 834 fire curve, respectively (Table 5). As well as at ambient temperature, the contribution of adding steel reinforcement in the holes of the T shear connectors is more significant than in the holes of the T-Perfobond connectors. At high temperatures, adding steel reinforcement may even induce negative effect on the shear resistance of these last connectors. Note that, the steel reinforcement in the hole of the T shear connector led to an increase in the connector characteristic resistance, PRk, of about 25%, 16% and 7% for 30, 60 and 90 min of the ISO 834

fire curve, respectively, whereas for T-Perfobond connectors the resistance decreased respectively about 14%, 7% and 0%. On the other hand, when the position of the connector was inverted (from specimen T-block_100tall to the specimen T-block_100tall_In), the gain in resistance was much higher at elevated temperatures than at ambient temperature. This may be due to the fact that the degree of tension in concrete is lower in the specimen T-block_100tall_In than in the specimen T-block_100tall, in contrast to the degree of compression. 3. Proposal of simple design models The behaviour at high temperatures of the connectors used in this study was rarely studied before by other authors. However,

310

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

Fig. 16. Effect of the number of connector holes on the ultimate load-carrying capacity of the specimens with T (a) or T-Perfobond (b) connector at different times of the ISO 834 fire curve.

were on the safe side and secondly it was intended that the errors of the proposal decreased with increasing temperature since in a fire scenario the risk to human life decreases with increasing fire time due to the collapse of the structure. It is quite interesting to observe that the reduction factors for the calculation of the ultimate load-carrying capacity of specimens with T-Perfobond connector at elevated temperatures (Eq. (4)) depend on the exposure time to fire, the shear resistance of the concrete dowel in the connector holes, the shear resistance of the transverse rebars in the connector holes and on the height of the connector in contrast to the model used for estimating the connector resistance at ambient temperature (Eq. (1)). On the contrary, as Eq. (3) already takes those parameters into account in the connector resistance at ambient temperature, the reduction factors for the calculation of the ultimate load-carrying capacity of specimens with T connector at elevated temperatures only depend on the exposure time to fire (Eq. (5)). Note that these reduction factors were affected by the exposure time to fire, and were not by the temperature neither in the concrete nor in the steel, because the temperature distribution in the specimen was never uniform. Finally, this approach may be criticisable as it is stated from results of only one test per each combination of test parameters, however these equations might be useful to provide a quick and easy first estimation of the structural response of T, T-block and T-Perfobond shear connectors under fire conditions.

PT-P;20 C ¼ gAf 1 fck ; Eurocode 4 [28], in 1992, proposed an equation (Eq. (1)) to calculate the resistance of a block connector at ambient temperature and due to its similarities with the T-block and T-Perfobond connectors, this equation was used to predict the resistance of the these types of connectors, like other researchers in the same field did [10,11,27]. It is worth noting that this model neglects the contribution from the holes and reinforcement bars, but as it was mentioned in Section 2.5.1 of this paper, those parameters did not have much influence on the resistance of T-Perfobond connectors at ambient temperature. On the other hand, the analytical model (Eq. (2)) for the resistance prediction of Perfobond shear connectors proposed by Oguejiofor and Hosain [14] was used for the T connectors at ambient temperature because, in this case, the shear resistance of both types of connectors (Perfobond and T connectors) depends significantly on the bearing concrete resistance at the shear connector face, the steel reinforcement bars in the concrete slab, and the concrete cylinders in shear that are formed through the shear connector’s holes. It is obvious that in this equation the cross-section perimeter of the connector was used instead of its height, as shown in Eq. (3). The comparison between the experimental and analytical results at ambient temperature obtained from Eqs. (1) and (3) are illustrated in Figs. 17 and 18, respectively. These models led to a significant underestimation of the actual load, with an error between 45% and 52% for the T-block and T-Perfobond connectors and approximately of 51% for the T connectors. However, it must be pointed out that the estimated values were obtained considering for the concrete cylinder (20 MPa) and not the cube (28 MPa) compressive strength at 28 days old, as suggested by the Eurocode [22]. Otherwise these errors would be extensively lower (about 30%). Besides, the actual resistance of concrete and composite steel and concrete structures is commonly much higher than the predicted value. Regarding the analytical models for the resistance prediction of these connectors at elevated temperatures, the authors propose an approach based on the previously mentioned models (Eqs. (1) and (3)) affected by reduction factors (Eqs. (4) and (5)). The presented proposal was firstly obtained taking into account that the values

where g ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Af 2 =Af 1 6 2:5

PT;20 C ¼ 4:5  h  t sc  fck þ 0:91  Atr  fy þ 3:31  n  D2 

ð1Þ pffiffiffiffiffi fck

PT;20 C ¼ 4:5  ððh  t sc Þ þ bÞ  tsc  fck þ 0:91  Atr  fy þ 3:31  n pffiffiffiffiffi  D2 fck

ð2Þ

ð3Þ

PT-P;t ¼ P T-P;20 C  ½1  ð6:5  103  t þ 1:65  107  Ah  t þ 6:19  106  Atr  t þ 2:2  105  ðh  100Þ  tÞ PT;t ¼ PT;20 C  ½1  ð5:2  103  tÞ

ð4Þ ð5Þ

where Af1 is the front bearing area of the shear connector (mm2), Af2 is the front bearing area of the shear connector amplified at an inclination rate of 1:5 to the rear surface of adjacent connector (mm2), Ah is the total area of holes in the connector (mm2), Atr is the total area of transversal steel reinforcement bars passing through the connector holes (mm2), D is the hole diameter in the connector (mm), PT-P,20°C and PT-P,t are respectively the ultimate load-carrying capacity of the specimen with T-block or T-Perfobond connector at ambient temperature and at time t (kN), PT,20°C and PT,t are respectively the ultimate load-carrying capacity of the specimen with T connector at ambient temperature and at time t (kN), b is the total width of the connector flange (mm), fck is the characteristic compressive cylinder strength of concrete (MPa) and fy is the yield strength of the steel reinforcement bars (MPa) both at ambient temperature, h is the connector height (mm), t is the exposure time to fire (min) and tsc is the shear connector thickness (mm). 4. Failure mode analysis 4.1. Ambient temperature tests The failure modes were similar for all ambient temperature tests with identical connectors, in spite of the fact that the first cracks have been similar in both kinds of specimens. Hence, firstly, it was observed a longitudinal crack along the concrete slab’s inner side at the lower side, from the connector’s end edge to the bottom of

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

311

Fig. 17. Comparison of experimental and analytical results for the T-block and T-Perfobond shear connectors: (a) T-block_100tall; (b) T-P_1h_0re_100tall; (c) TP_3h_0re_100tall; (d) T-P_1h_12re_100tall; (e) T-P_3h_0re_150tall; and (f) T-P_6h_0re_150tall.

the concrete slab, moving forward and growing thicker while the loading was increasing up to their maximum (Figs. 19 and 20a). Other cracks, at a 45° angle, also appeared, (i) from the bottom of the connector and growing forward for the specimens with T-Perfobond connector (Fig. 20a) and (ii) from the middle of the connector and growing downward for the specimens with T connector (Fig. 19b). At the end, some detachment of concrete occurred in the specimens (Fig. 20b). It is important to stress that this type of cracks was more severe in specimens reinforced with rebars passing through the holes and became much more extensive in specimens with T connector (Fig. 19c). This may be explained by the fact that these types of specimens can mobilise larger areas of reinforced concrete slab and lead to extensive concrete degradation.

4.2. Elevated temperature tests In these tests failure cannot be followed from its onset to its final stage, since the specimen was placed inside the electrical furnace. Therefore, the report conclusions result from the specimen observation after the test completion. As well as the tests at ambient temperature, an identical failure configuration was found for all specimens under fire conditions for 30 min (Fig. 21). For higher exposure times, it seems that there is an extensive yielding of the connectors, as it can also be concluded from Figs. 13 and 14. In addition, the steel beam presented the typical failure configuration of a steel section tested under fire conditions, with some instability resulting from the steel properties degradation, as shown by

312

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

Fig. 18. Comparison of experimental and analytical results for the T shear connectors: (a) T_0h_0re_100tall; (b) T_1h_0re_100tall; (c) T_3h_0re_100tall; and (d) T_1h_12re_100tall.

Fig. 19. Failure mode for specimens with T connector at ambient temperature: (a) T_3h_0re_100tall; (b) T_1h_0re_100tall; and (c) T_1h_12re_100tall.

Fig. 20. Failure mode for specimens with T-block or T-Perfobond connector at ambient temperature: (a) T-P_3h_0re_100tall; and (b) T-block_100tall.

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

313

Fig. 21. Failure mode for the specimen T-P_1h_0re_100tall tested at elevated temperature (30 min of the ISO 834 fire curve).

Fig. 22. Failure mode for the specimens T-P_1h_0re_100tall (a) and T-block_100tall_In (b) tested at elevated temperature (90 min of the ISO 834 fire curve), one (a) and three (b) days after the fire test.

Fig. 23. Specimens after test.

Fig. 22a. It is believed that this phenomenon occurred at latter stages of the test after the uplift of the connector. Several specimens after test can be seen in Fig. 23, which also shows some detachment of pieces of concrete on the specimen face subjected to fire (Fig. 22b), caused by the concrete spalling.

5. Conclusions This paper presented and discussed the results of an experimental investigation into the shear strength of T, T-block and T-Perfobond connectors at elevated temperatures. A total of forty-four modified push-out tests were conducted under different

temperature levels, focusing on the connector resistance and its slip capacity. The main investigated variables were the number of holes in the shear connectors and the presence of transversal steel reinforcement bars passing through these holes, the connector arrangement and the connector height. Additionally, the experimental results at ambient temperature were still compared with the predictions from available analytical models and a new proposal for the calculation of their resistance at elevated temperatures was presented. The results of this research study showed that all those parameters have a different role to play in the ultimate load-carrying capacity of the connectors, depending strongly on their type (T or T-Perfobond connectors) and temperature. In general, it seems that those parameters are more effective in the T connectors than in the T-block or T-Perfobond connectors at ambient temperature in contrast to at elevated temperatures. In relation to the ambient temperature tests, it was shown that adding more holes to the connector increases the resistance and that for each added hole the mean gain of resistance was around 8% for the T connectors and just 1% for the T-Perfobond connectors. By comparing the reinforced and unreinforced connections, it was observed that adding transversal steel reinforcement bars increased the connector characteristic resistance by 19% for the T connectors and just 6% for the T-Perfobond connectors. On the other hand, an increase of the T-Perfobond connector height by 50% led to a greater resistance enhancement than the resistance related to the holes and to the reinforcement bars, increasing it by approximately 55%. From the results of the tests at elevated temperatures it may be concluded that these temperatures adversely affect the connector load-carrying capacity. It was observed that the connections made of T-Perfobond connectors with 150 mm height presented the

314

João Paulo C. Rodrigues, L. Laím / Engineering Structures 75 (2014) 299–314

worst behaviour in fire (the highest reduction in shear resistance) and, in opposition, the T connectors (T_0h_0re_100tall) presented the best one in general. The enhancement of the connector shear resistance due to holes in the connectors and to the reinforcement bars was mostly lower for high temperatures (especially when exposed to a standard fire during 60 or 90 min) than at ambient temperature. Finally, the analytical models available in the literature for the resistance prediction of T, T-block and T-Perfobond shear connectors at ambient temperature provided conservative results, with an average difference of approximately 50%. However, the reduction factors proposed by the authors in order to reduce their resistance with increasing temperature seems to provide safe and reasonable estimations of the connector’s strength at high temperatures, which might be a good help/contribution for fire structural designs.

References [1] Cândido-Martins JPS, Costa Neves LF, Vellasco PCGS. Experimental evaluation of the structural response of Perfobond shear connectors. Eng Struct 2010;32:1976–85. [2] Li AN, Cederwall K. Push-out tests on studs in high strength and normal strength concrete. J Constr Steel Res 1996;36(1):15–29. [3] Veríssimo GS, Oliveira AFN, Fakury RH, Rodrigues FC, Paes JLR, Valente MIB, et al. Assessment of the behaviour of a Crestbond connector for composite steel-concrete structures. In: Proceedings of the congress on numerical methods in engineering; 2007. [in Portuguese]. [4] Oguejiofor EC, Hosain MU. Numerical analysis of push-out specimens with perfobond rib connectors. Comput Struct 1997;62(4):617–24. [5] Vianna JC. Assessment of the structural behaviour of Perfobond and TPerfobond connectors for composite beams. Ph.D. thesis in Civil Engineering, Pontifical Catholic University of Rio de Janeiro (PUC-RIO), Brazil; 2009, 300p. [in Portuguese]. [6] Valente MIB. Experimental studies on shear connection systems in steel and lightweight concrete composite bridges. Ph.D. thesis in Civil Engineering, University of Minho, Portugal; 2007, 427p. [7] Leonhardt F, Andrä W, Andrä HP, Harre W. New advantageous shear connection for composite structures with high fatigue strength. Beton Stahlbetonbau 1987;62(12):325–31 [in German]. [8] Valente MIB, Cruz PJS. Experimental analysis of the Perfobond shear connection between steel and lightweight concrete. J Constr Steel Res 2004;60:465–79. [9] Machácek J, Studnicka J. Perfobond shear connector. Steel Compos Struct 2002;2(1):51–66.

[10] Vianna JC, Costa Neves LF, Vellasco PCGS, Andrade SAL. Structural behavior of T-Perfobond shear connectors in composite girders: an experimental approach. Eng Struct 2008;30:2381–91. [11] Vianna JC, Costa Neves LF, Vellasco PCGS, Andrade SAL. Experimental assessment of Perfobond and T-Perfobond shear connectors’ structural response. J Constr Steel Res 2009;65:408–21. [12] Al-Darzi SYK, Chen AR, Liu YQ. Development of new hole shape of Perfobond shear connectors, parametric study. In: Proceedings of the 2nd international symposium on connection between steel & conrete, University of Stuttgart; 2007, p. 1401–13. [13] Marecek J, Samec J, Studnicka J. Numerical analysis of perfobond shear connectors. In: Proceedings of the 4th international conference on advanced engineering design; 2004. [14] Oguejiofor EC, Hosain MU. A parametric study of Perfobond rib shear connectors. Can J Civ Eng 1994;21:614–25. [15] Garcia AR, Arrizabalaga EM. Design of composite beams using light steel sections. Universitat Politècnica de Catalunya, Escola Tècnica Superior d’Enginyers de Camins; 2004. 109 p. [16] Shariati A, RamliSulong NH, MeldiSuhatril, Shariati M. Various types of shear connectors in composite structures: a review. Int J Phys Sci 2012;7(22):2876–90. [17] Galjaard HJC, Walraven JC. Behaviour of different types of shear connectors for steel–concrete structures. Struct Eng, Mech Comput 2001;1:385–92. [18] Choi S, Han S, Kim S, Nadjai A, Ali F, Choi JA. Performance of shear Studs in fire. In: International conference applications of structural fire engineering, Prague; 2009. P. 490–5. [19] Mirza O, Uy B. Behaviour of headed Stud shear connectors for composite steel– concrete beams at elevated temperatures. J Constr Steel Res 2009;65:662–74. [20] Zhao B, Kruppa J. Experimental and numerical investigation of fire behavior of steel and concrete composite beams. In: Proceedings of the engineering foundation conference, New York, USA; 1996. [21] Rodrigues JPC, Laím L. Behaviour of Perfobond shear connectors at high temperatures. Eng Struct 2011;33:2744–53. [22] EN 1994-1-1 – Design of composite steel and concrete structures – general rules and rules for buildings. European Committee for Standardization (CEN), Brussels, Belgium; 2005. [23] EN 206-1 – Concrete. Specification, performance, production and conformity. European Committee for Standardization (CEN), Brussels, Belgium; 2000. [24] EN1992-1.1 – Design of concrete structures. General rules and rules for buildings. European Committee for Standardization (CEN), Brussels, Belgium; 2004. [25] EN1993-1.1 – Design of steel structures. General rules and rules for buildings. European Committee for Standardization (CEN), Brussels, Belgium; 2004. [26] ISO 834-1: Fire resistance tests – elements of building construction, Part 1: general requirements. International Organization for Standardization (ISO), Genève, Switzerland, 1999. [27] Neves LFC, Figueiredo JP, Vellasco PCG, Vianna JC. Perforated shear connectors on composite girders under monotonic loading: an experimental approach. Eng Struct 2013;56:721–37. [28] pr ENV 1994-1-1 – Design of composite steel and concrete structures – general rules and rules for buildings. European Committee for Standardization (CEN), Brussels, Belgium; 1992.