Behaviour and push out test of concrete dowel connectors for longitudinal shear in shallow hollow composite beams

The shear transferring mechanisms of shallow-hollow composite beams with concrete slab cast in place are different with conventional headed shear studs and have not been investigated previously. In this study, the behavior and push-out test of concrete dowel connectors for longitudinal shear in shallow-hollow composite beams are described.

Journal of Science and Technology in Civil Engineering NUCE 2018 12 (5): 1–9 BEHAVIOUR AND PUSH-OUT TEST OF CONCRETE DOWEL CONNECTORS FOR LONGITUDINAL SHEAR IN SHALLOW-HOLLOW COMPOSITE BEAMS Han Ngoc Duca,∗, Vu Anh Tuana , Nguyen Tuan Datb a Faculty of Building and Industrial Construction, National University of Civil Engineering, 55 Giai Phong road, Hai Ba Trung district, Hanoi, Vietnam b Consultancy Company Limited of University of Civil Engineering, 55 Giai Phong road, Hai Ba Trung district, Hanoi, Vietnam Article history: Received 23 July 2018, Revised 25 August 2018, Accepted 29 August 2018 Abstract The shear transferring mechanisms of shallow-hollow composite beams with concrete slab cast in place are different with conventional headed shear studs and have not been investigated previously In this study, the behavior and push-out test of concrete dowel connectors for longitudinal shear in shallow-hollow composite beams are described The theory prediction for concrete dowel connectors without tie-bars adopted in this study was based on EN 1992-1-1 and EN 1994-1-1 Push-out tests of three specimens were conducted and the results were compared with theory prediction and published formula to identify longitudinal shear resistance The failure of specimens and the ultimate failure load values of push-out test were proved that the behavior of concrete dowel in shallow-hollow composite beams was not under pure shear stress Keywords: steel-concrete composite beam; shallow-hollow composite beam; concrete dowel connectors; longitudinal shear resistance; shallow floor structure https://doi.org/10.31814/stce.nuce2018-12(5)-01 c 2018 National University of Civil Engineering Introduction In recent years, the increasing demands on composite floor-beams systems in steel building have led to the development of steel and concrete structures Although steel and concrete composite beams have outstanding advantages in comparison with concrete or steel beam such as bigger moment resistance strength, higher stiffness, shorter and more effective in construction manner [1], it still has some weaknesses such as low fire resistance, large beam-floor structure height, more cost for headedshear stud connectors Hence, many types of shallow floor as Slimflor, Slimdek Asymmetric Slimflor Beam [2], Delta beam [3] and Ultra Shallow Floor Beam with precast concrete slab [4] are developed to overcome such problems Typically, these steel sections of innovative composite beams are partial embedded in concrete slab to increase the fire resistance, the structure height will be reduced and concrete dowel connectors play a role as headed-shear studs in conventional composite beams In Vietnam, the shallow-hollow floors composite structures are new type of composite beam in building construction The steel section of the composite shallow-hollow beam is fabricated by welding trapezoidal-hollow section with flat or U-shaped steel plate together Along the web of ∗ Corresponding author E-mail address: duchn@nuce.edu.vn (Duc, H N.) composite beam in building construction The steel section of the composite shallowhollow beam is fabricated by welding trapezoidal-hollow section with flat or U-shaped steel plate together Along the web of trapezoidal-hollow section, the circular openings are perforated The profiled steel decking is supported by the flat flange plate, creating a Duc, H N et al / Journal of Science and Technology in Civil Engineering shallow-hollow floor construction system, as illustrated in Fig.1 The overall floor depth trapezoidal-hollow circular embedded openings are in perforated The moment profiled steel decking of is supwill be reduced section, by steelthesection slab The resistance the ported by the flat flange plate, creating a shallow-hollow floor construction system, as illustrated in composite beams could be optimized by sizes and shape of the steel parts The circular Fig The overall floor depth will be reduced by steel section embedded in slab The moment resisweb openings provide passage for the concrete and reinforcing tie-bars to create the tance of the composite beams could be optimized by sizes and shape of the steel parts The circular concrete dowel shearpassage connectors resisting longitudinal sheartoatcreate the steel and concrete web openings provide for theBy concrete and reinforcing tie-bars the concrete dowel to interface, the composite section act as single The hollow steelinterface, section istheexposed shear connectors By resisting longitudinal shear atunit the steel and concrete composite sectionheat act as unit The hollowconcrete steel section exposed direct section heat in fire not only direct in single fire while not only part isinside the tohollow butwhile also the slab concrete part inside the hollow section but also the slab behaves as “heat sink”, so the fire resistance behaves as “heat sink”, so the fire resistance can be archived [1] can be archived [1] Figure Cross-section of drawingof of the composite beam beam Figure Cross-section of drawing theshallow-hollow shallow-hollow composite The studies based on EN 1992-1-1 [5]; EN 1994-1-1 [6] presented in this paper have provided The studies based onof EN 1992-1-1 EN 1994-1-1 [6] presented in this paper information on the behavior concrete dowel [5]; connectors in shallow-hollow composite beams A have onofthe connectors in shallowseries provided of push-outinformation tests consisting threebehavior full-scaleof testconcrete specimensdowel were performed to investigate the shear connection under the direct longitudinal shear force hollow composite beams A series of push-out tests consisting of three full-scale test specimens were performed to investigate the shear connection under the direct Longitudinal shear resistance of shallow-hollow composite beams longitudinal shear force One of the most important characteristics of shallow floor composite structures is identify the shear connection level Theresistance behavior ofof longitudinal shear hascomposite been mentioned in many articles since Longitudinal shear shallow-hollow beams 2004 Peltonen S and Leskelăa M V pointed out the shear behavior of shallow floor structures with precast concrete slab [7] Huo B Y and D’Mello C A implemented the push-out test and published One of the most important characteristics of shallow floor composite structures is the shear mechanism on composite shallow cellular floor beams in 2013 [8] The longitudinal force identify the shear connection level The behavior of longitudinal shear has been transferring mechanism, load bearing capacity and failure behavior of the shear connections under dimentioned in many articles since 2004 Peltonen S and Leskelä M V pointed out the rect longitudinal shear forces were investigated by numerical simulation in 2017 [9, 10] However, the behavior of shallow-hollow composite beams with concrete slab cast in place still has not mentioned The longitudinal shear resistance of shallow-hollow composite beam depends on shear resistance of concrete dowels with or without tie-bars along the beam and friction (bond) force at outer interface of hollow steel section and concrete slab The tie-bars arrangement in concrete dowel are excluded in this study 2.1 Shear resistance of concrete members by design code EN 1992-1-1 In EN 1992-1-1 [5], shear resistance of concrete members without reinforcement is mentioned relying on shear failure of reinforced concrete beams Shear force in a concrete beam causes cracks Duc, H N et al / Journal of Science and Technology in Civil Engineering on incline planes near the support where magnitude of shear force is high The cracks are formed by principle tensile stress and compressive stresses of the same magnitude as the shear stress and inclined 45◦ to the neutral axis An accurate analysis for shear strength is impossible because of complex state of stress and many mechanisms of concrete material The problem has been solved by testing beams of the type normally used in practice Simplified equation to determine the shear strength of concrete members was provided in design code [5] as: VRd,c = max k1 σcp bw d; (vmin + k1 σcp )bw d (1) σcp = NEd /Ac < 0.2 fcd (MPa) (2) vmin = 0.035k3/2 fck 1/2 k =1+ (3) 200/d ≤ 2.0 where bw is the smallest width of the cross section in the tensile area (mm); d is the height of member under shear force (mm); NEd is the axial force in the cross-section due to loading, the influence of imposed deformation on NEd may be ignored; Ac is the area of concrete section (mm2 ); fck is the cylinder strength of concrete at 28 days (MPa); The recommended value for k1 is 0.15 2.2 Interface bond resistance between steel and concrete The friction resistance between steel and concrete material is normally calculated as contact shear strength τRd by area of interface as shown in following formula: VRd, f = τRd A (4) The shear strength provided in Table [6] for outer surface of steel section contact with the concrete is unpainted and free from oil, grease and loose scale or rust Table Design contact shear strength Type of cross section τRd (N/mm2 ) Completely concrete encased steel sections Concrete filled circular hollow sections Concrete filled rectangular hollow sections Flanges of partially encased sections Web of partially encased sections 0.30 0.55 0.40 0.20 0.00 These values τRd given in Table for completely concrete encased steel section apply to section with a minimum concrete cover of 40 mm For greater concrete cover and adequate reinforcement, higher values of τRd may be used Unless verified by test, for completely encased sections, the increased value of βc may be used With βc given by: βc = + 0.02cz (1 − 40/cz ) ≤ 2.5 (5) where cz is the nominal value of concrete cover in mm In this research the given values in Table were used to estimate shear bond strength between steel and concrete of composite specimens Duc, H N et al / Journal of Science and Technology in Civil Engineering 2.3 Analytical study of previous experimental test A similar configuration of shear connectors relying on shear strength of perfobond rib shear connections has been investigated by Ahn et al [11] A series of push-out test including 24 specimens were conducted to obtain a calculation design method of shear resistance for the shear connection The proposed design shear resistance of the shear connector is given by: Q = 2.76h sc t sc fck + 1.06Atr fy + 3.32nπ(d/2)2 fck (N) (6) where Atr is the area of the transverse rebars in the rib holes (mm2 ); fy is the yield strength of the transverse rebar (MPa); n is the number of rib holes; h sc is the height of the rib; d is the diameter of the rib (mm) and t sc is the thickness of the rib (mm) If the reinforcement is omitted, the web thickness is thin then in this study the shear strength of perfobond rib shear connections could be rewritten as: Q = 3.32nπ(d/2)2 fck (N) (7) Push-out test 3.1 Test specimen The push-out test aimed to identify the shear resistance of concrete infill only shear connector, so the test specimens consisted of a steel hollow section and concrete slab without any reinforcement There were three opening holes in each web of the steel beams Concrete infilled the hollow section of steel beam passed through the web opening to form the shear connection subjected to longitudinal shear force There were three similar composite beams including two de-bonding specimens with greased and one nature bond specimen The designed shape with dimensions of steel part and specimen is shown in Fig Figure Figure Dimensions and ofpush-out push-out specimens Dimensions andshape shape of testtest specimens The steel section of the test was a short4 trapezoidal hollow section with 550mm in length Three couple of 70mm circular openings were perforated on the web post The trapezoidal section was used to investigate shear connections in some innovative composite beams which are embedded in concrete slabs The steel beams are fabricated Duc, H N et al / Journal of Science and Technology in Civil Engineering The steel section of the test was a short trapezoidal hollow section with 550 mm in length Three couple of 70 mm circular openings were perforated on the web post The trapezoidal section was used to investigate shear connections in some innovative composite beams which are embedded in concrete slabs The steel beams are fabricated by SS400 steel material follow EN 1993-1-1 [12] that have 245 MPa yield strength; 400 MPa ultimate strength The total depth of the steel beams was 114 mm, and the total width was 220 mm The concrete slabs in the push-out test used concrete grade C25/30 following [5] specification The overall width of concrete slabs was 420 mm The concrete cover of trapezoidal hollow section was 40 mm which is similar to actual working conditions The concrete batch of each specimen was extracted to unit test that was conducted to test concrete compressive strength Two of three steel beams were applied with greased to prevent the development of the bond between concrete and steel and then, they were put in formwork for concreting All the push out test specimens were casted in the laboratory LAS-XD 125 of National University of Civil Engineering Some pictures of construction of composite specimens are shown in Fig Time for concrete hardening was 28 days After concrete hardening, three specimens were marked as Table Figure 3: Formwork finishing the specimens Figure Formworkand and finishing of theof specimens Table 2.Table Name ofofspecimens their features Name specimens andand their features No Feature Feature TN-C1-G 70 mm Circularhole, hole, un-bond Circular un1 TN-C1-G 7070mm TN-C2-G mm Circular hole, un-bond bond TN-C3-F 70 mm Circular hole, friction Circular hole, un2 TN-C2-G 70 mm bond 3.2 Test set up and procedures Circular hole, TN-C3-F 70 mm Test specimens were put into a rig 200-ton capacity vertically Basedfriction on prediction of failure 3.2 No Specimens Specimens Holediameter diameter Hole load, a hydraulic jack 50 ton was used to apply load There were four linear variable differential transformers (LVDTs) attached in steel part and concrete part to measure slip These loaded jacks and Test setwere up and procedures LVDTs connected to a data logger which wrote and saved data of load and slip in each second Some pictures of test were set up are Test specimens putshown intoina Fig rig 4.200-ton capacity vertically Based on prediction of failure load, a hydraulic jack 50ton was5 used to apply load There were four linear variable differential transformers (LVDTs) attached in steel part and concrete part to measure slip These loaded jacks and LVDTs were connected to a data logger which wrote variable differential transformers (LVDTs) attached in steel part and concrete part to measure slip These loaded jacks and LVDTs were connected to a data logger which wrote and saved data of load and slip in each second Some pictures of test set up are shown in Fig.4 Duc, H N et al / Journal of Science and Technology in Civil Engineering The push-out test was carried out following specification Appendix B [6] The load were first applied increments up to 40% of the expected failure load Subsequent load increments then were imposed such that failure does not occur in less than 15 minutes Thepush-out push-outtest testwas was carried out following specification Appendix B [6] [6] The load The carried following specification Appendix B [6] [6] The loadload out following specification Appendix B The Thepush-out push-out testwas was carried out following specification Appendix B The [6] The load The test carried out following specification Appendix B load continuously during loading Longitudinal slip between steel and out concrete was measured were first applied increments up to 40% of the expected failure load Subsequent load were first applied increments up to 40% of the expected failure load Subsequent load werefirst firstapplied applied increments up to 40% of expected failure Subsequent were first applied increments up to 40% of the expected failure load Subsequent load were increments toload 40% of displacements thethe expected failure load.load Subsequent load load After failure of specimens, dataupof and were collected automatically increments then were imposed such that failure does not occur in less than 15 minutes increments then were imposed such that failure does not occur in less than 15 minutes increments then were imposed such that failure does not occur in less than 15 minutes increments thenwere wereimposed imposed such failure does occur in less 15 minutes increments such thatthat failure does notnot occur in less thanthan 15 minutes and analysisthen later measured continuously during loading Longitudinal slipbetween betweensteel steel and concrete was Figure 4.concrete Push-out test set up Figure Push-out test set up measured continuously during loading Longitudinal slip and was measured continuously during loading Longitudinalslip slipbetween between steel and concrete measured continuously during loading Longitudinal slip between steel and concrete was measured continuously during loading Longitudinal steel and concrete waswas After failure of specimens, data of load and displacements were collected automatically After failure of specimens, data of load and displacements were collected automatically After failure ofspecimens, specimens, data load displacements were collected automatically After failure specimens, data of load and displacements were collected After failure ofof data of of load andand displacements were collected The push-out test was carried out following specification Appendix B [6] Theautomatically loadautomatically were first 3.3 Test result and analysis later and analysis later and analysis later and analysis later.up to 40% of the expected failure load Subsequent load increments then were applied increments and analysis later Aftersuchthree tests does havenotconducted, of specimen failure steel are imposed that failure occur in less some than 15 pictures minutes Longitudinal slip between 3.3 Test result andTest concrete was loading of specimens, load and demonstrated in measured Table 3; continuously the ultimateduring failure loadAfter and failure maximum relativedata slipofof three 3.3 3.3 Testresult result 3.3 Test result 3.3 Test result displacements were collected and analysis later pictures of specimen failure After three tests automatically have conducted, some are After have some pictures of of specimen failure are are After three tests have conducted, some pictures specimen failure specimens arethree listedtests intests Table conducted, After three have conducted,some somepictures pictures of specimen failure are After three tests have conducted, of specimen failure are demonstrated in Table 3; the ultimate failure load maximum relative slip of three three demonstrated ultimate failure load andand maximum relative slip slip of three three demonstrated inTable Table3; 3;the the ultimate failure load and maximum relative of 3.3 Test resultin demonstrated Table ultimate failure load and maximum relative slip of three demonstrated inin Table 3;3; thethe ultimate failure load and maximum relative slip of specimens are listed in Table specimens are in Table specimens arelisted listed in Table specimens are listed Table specimens are listed inin Table 4 Table Failure of of thespecimen specimens After three tests have conducted, some pictures failure are demonstrated in Table 3; the ultimate failure load and maximum relative slip of three specimens are listed in Table No Specimens Steel partof of Concrete part Table Failure the specimens Table Failure the specimens Table Failure of the specimens Table of specimens Table 3 Failure specimens Table Failure Failureof of the the the specimens No Specimens Steel part Concrete part No Specimens Steel part Concrete partpart No Specimens Specimens Steel Concrete part No Specimens Steel part Concrete part Specimens Steel partpart Concrete part NoNo Steel part Concrete TN-C1-G 11111 TN-C1-G TN-C1-G TN-C1-G TN-C1-G 2 222 TN-C2-G TN-C2-G TN-C2-G TN-C2-G TN-C2-G TN-C2-G 3333 TN-C3-F TN-C3-F TN-C3-F TN-C3-F TN-C3-F 33 TN-C1-G TN-C1-G TN-C2-G TN-C3-F TN-C3-F Table Ultimate failure load and maximum value of the specimens Table4 4.Ultimate Ultimate failure load maximum slip value of the specimens Table failure load and maximum slipslip value of the the specimens value of Table 4.4 Ultimate failure load andand maximum slip Table Ultimate failure load and maximum slip value of specimens the specimens Maximum Ultimate failure Maximum Ultimate failure Maximum Ultimate failure Hole Ultimate failure Maximum Ultimate failure Maximum Hole Hole Slip No Specimens load Hole Hole Hole No Specimens load SlipSlip No Specimens load Duc, H N et al / Journal of Science and Technology in Civil Engineering Table Ultimate failure load and maximum slip value of the specimens No Specimens Hole diameter Ultimate failure load (kN) Maximum Slip (µm) TN-C1-G TN-C2-G TN-C3-F 70 mm 70 mm 70 mm 176.6 141.3 160.6 805 665 905 A load-slip curve was drawn from the result of data logger These curves illustrate the characteristic behavior of the shear connection in response to direct longitudinal shear force Three graphs corresponding to three specimens are shown in Fig Figure Load-slip curve Figure Load-slip curve It is worth notetest thatresult test result the concrete in trapezoidal It is worth to notetothat shownshown that thethat concrete filled infilled trapezoidal space ofspace the steel of the steel have notand been and still filled in hollow section beams have not beams been damaged stilldamaged filled in hollow section Analysis of test result Analysis of test result datadata During the test, were ruptured suddenlysuddenly with no warning or ductileordeformation During thethree test,specimens three specimens were ruptured with no warning ductile Thedeformation failure modeThe of shear connection could be confirmed that was brittle failure for de-bonding failure mode of shear connection could be confirmed that was brittle specimen specimen with maximum displacement weremaximum approximate mm whichwere is much failureand for bonded de-bonding specimen and bonded specimen with displacement smaller than required slip in [6] for ductile connector mm approximate 1mm which is much smaller than required slip in [6] for ductile connector After doing unit test, characteristic strength of concrete was obtained to determine ultimate failure 6mm load The mean value of concrete cubic specimen and cylinder specimen were 33.4 and 26.7 MPa, After doing unit test, characteristic strength of concrete was obtained to determine respectively Based on the detail dimension of test specimens and Eqs (1) to (7) the ultimate failure ultimate failure load The mean value of concrete cubic specimen and cylinder specimen load of the specimen has been calculated Those values were compared to mean value of ultimate were 33.4 and 26.7 MPa, Based on the failure load obtaining from test respectively result as shown in Table detail dimension of test specimens and Eq (1) to Eq (6) the ultimate failure load of the specimen been Those While calculation of shear resistance by Eq (1) given much lower has value thancalculated test result with nearly values were compared to mean value of ultimate failure load obtaining from test result as 2.5 times, Eq (7) slightly overestimate shear resistance of the concrete dowel with 16% shown in Table of test specimen, the stress state of concrete dowel is illustrated in Fig The Based on the failure flat surface of concrete could be seen, so the shear connectors have been cut by shear stress along the Table Comparison of ultimate failure loads steel beam length Eq (1) Eq (6) Prediction of shear strength (kN) 60.6 191 Test result (kN) Ratio (Test/prediction) 159.5 263% 84% Duc, H N et al / Journal of Science and Technology in Civil Engineering Table Comparison of ultimate failure loads Based on Prediction shear failure of strength test specimen, the state of Ratio concrete dowel is of shear (kN) Test stress result (kN) (Test/prediction) illustrated in Fig.6 The flat surface of concrete could be seen, so the shear263% connectors Eq (1) 60.6 159.5 have been along the steel beam length Eq (7)cut by shear stress191.0 84% Stress state concrete dowel Figure Figure 6: Stress state of ofconcrete dowel Conclusion Conclusion In order to investigate behavior of concrete dowel shear connectors for longitudinal In order to investigate behavior of concrete dowel shear connectors for longitudinal shear in shear in shallow-hollow composite beams, the experimental test presented brittle failure shallow-hollow composite beams, the experimental test presented brittle failure mode of the conThe failure of specimens andload the values ultimate failure load values mode of the connectors nectors The failure of specimens and the ultimate failure of push-out test are provedofthat push-out test are proved that the of concrete dowel in is shallow-hollow composite the behavior of concrete dowel in behavior shallow-hollow composite beams not under pure shear stress So, beams is notinunder pure shear stress So,only theshear stressstress in the shear connectors werebutnot only the stress the shear connectors were not along the steel beam length also possible compressive stress of concrete in slab From this study, future research may be prepared properly shear stress along the steel beam length but also possible compressive stress of concrete to develop shear resistance this type properly of shear connection in slab Fromcalculation this study,method futureforresearch may beofprepared to develop calculation method for shear resistance of this type of shear connection Acknowledgements Acknowledgements The study presented in this paper was financially supported by National University of Civil EngiThe study presented in this paper wasThe financially supported by National University neering through Grant 149-2017/KHXD-TĐ financial support is greatly appreciated of Civil Engineering through Grant 149-2017/KHXD-T! The financial support is greatly appreciated References [1] Tuan, V A (2017) Steel-concrete composite structure: Slabs, beams and columns for buildings Con- References struction Published House, Vietnam [2] Tata Europe Limited (2012) Slimdeck manual Structure: Slabs, Beams and Columns Tuan, V.Steel A (2017) Steel-Concrete Composite [3] Peikko Group (2007) DELTABeam composite beam for Buildings Construction Published House, Vietnam [4] Rackham, J W., Hick, S., Newman, G M (2006) SCI-P342: Design of asymmetric slimflor beams with Slimdeck Manual (2012) Tata Steel Europe Limited precast concrete slabs Steel Construction Institude DELTABeam Composite beam (2007) Peikko Group Rackham, J W, Hick, S., Newman, G M, (2006), SCI-P342: Design of asymmetric slimflor beams with precast concrete slabs, Steel Construction Institude Duc, H N et al / Journal of Science and Technology in Civil Engineering [5] EN 1992-1-1 (2004) Eurocode 2: Design of concrete structures, part 1.1: General rules and rules for building [6] EN 1994-1-1 (2004) Eurocode 4: Design of steel and concrete composite structures, part 1.1: General rules and rules for building [7] Peltonen, S., Leskelăa, M V (2006) Connection behaviour of a concrete dowel in a circular web hole of a steel beam In Fifth International Conference on Composite Construction in Steel and Concrete, 544–552 [8] Huo, B Y., D’Mello, C A (2013) Push-out tests and analytical study of shear transfer mechanisms in composite shallow cellular floor beams Journal of Constructional Steel Research, 88:191–205 [9] Limazie, T., Chen, S (2017) Effective shear connection for shallow cellular composite floor beams Journal of Constructional Steel Research, 128:772–788 [10] Hosseinpour, E., Baharom, S., Badaruzzaman, W H W., Al Zand, A W (2018) Push-out test on the web opening shear connector for a slim-floor steel beam: Experimental and analytical study Engineering Structures, 163:137–152 [11] Ahn, J H., Lee, C G., Won, J H., Kim, S H (2010) Shear resistance of the perfobond-rib shear connector depending on concrete strength and rib arrangement Journal of Constructional Steel Research, 66(10):1295–1307 [12] EN 1993-1-1 (2005) Eurocode 3: Design of steel structures, part 1.1: General rules and rules for building ... behavior concrete dowel [5]; connectors in shallow- hollow composite beams A have onofthe connectors in shallowseries provided of push- outinformation tests consisting threebehavior full-scaleof testconcrete... connectors for longitudinal In order to investigate behavior of concrete dowel shear connectors for longitudinal shear in shear in shallow- hollow composite beams, the experimental test presented... failure of specimens and the ultimate failure of push- out test are provedofthat push- out test are proved that the of concrete dowel in is shallow- hollow composite the behavior of concrete dowel in