Experimental Behavior of Steel-Concrete Composite Girders with UHPC-Grout Strip Shear Connection
Experimental Behavior of Steel-Concrete Composite Girders with UHPC-Grout Strip Shear Connection
He, Zhi-Qi;Ou, Changxue;Tian, Fei;Liu, Zhao
2021-04-24 00:00:00
buildings Article Experimental Behavior of Steel-Concrete Composite Girders with UHPC-Grout Strip Shear Connection 1 , 1 2 1 Zhi-Qi He * , Changxue Ou , Fei Tian and Zhao Liu Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing 211189, China; changxue_ou@163.com (C.O.); mr.liuzhao@seu.edu.cn (Z.L.) Key Laboratory of Large-Span Bridge Construction Technology of Ministry of Communications, CCCC Second Harbour Engineering Company Ltd., Wuhan 430040, China; shec_tianfei@foxmail.com * Correspondence: z.he@seu.edu.cn Abstract: This paper develops a new type of shear connection for steel-concrete composite bridges using Ultra-High Performance Concrete (UHPC) as the connection grout. The UHPC-grout strip shear connection is fabricated by preforming a roughened slot in the concrete deck slab, welding an embossed steel rib longitudinally to the upper flange of the steel girder, and casting the strip void between the slot and the steel rib with UHPC grout. The structural performance of the new connection was validated by two sets of experimental tests, including push-out testing of shear connectors and static and fatigue testing of composite beams. The results of push-out testing indicate that the UHPC-grout strip shear connection exhibits a significant improvement of ductility, ultimate capacity, and fatigue performance. The interface shear strength of the UHPC-grout strip connection is beyond 15 MPa, which is about three times that of the strip connection using traditional cementitious grouts. The ultimate capacity of the connection is dominated by the interface failure between the embossed steel and the UHPC grout. The results of composite-beam testing indicate that full composite action Citation: He, Z.-Q.; Ou, C.; Tian, F.; is developed between the precast decks and the steel beams, and the composite action remained Liu, Z. Experimental Behavior of intact after testing for two million load cycles. Finally, the trail design of a prototype bridge shows Steel-Concrete Composite Girders that this new connection has the potential to meet the requirements for horizontal shear. with UHPC-Grout Strip Shear Connection. Buildings 2021, 11, 182. Keywords: composite bridge; precast deck; shear connection; strip connection; UHPC https://doi.org/10.3390/ buildings11050182 Academic Editor: Eva O.L. Lantsoght 1. Introduction In recent years, a prefabricated steel–concrete composite bridge system has been used Received: 31 March 2021 increasingly in new constructions. A typical system is the full-depth deck panel system Accepted: 21 April 2021 shown in Figure 1. Shear stud clusters embedded in shear pockets are applied to create Published: 24 April 2021 composite action between precast decks and steel girders. The shear pockets are filled with field-cast cementitious grouts to generate the composite action. This innovative solution al- Publisher’s Note: MDPI stays neutral lows shorter time for the construction, while extending the service life of bridge decks [1,2]. with regard to jurisdictional claims in Significant advances have been made to study the composite action between steel girders published maps and institutional affil- and precast decks when large clusters of studs are utilized [3–7]. Meanwhile, there are iations. some potential problems with the use of clustered studs such as the shear connection [3,8], which include deck uplift, nonuniform distribution of horizontal shear along the interface, and local bearing failure of concrete in the shear pockets. Potential solutions to these problems would be the use of innovative detailing and/or advanced materials. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Buildings 2021, 11, 182. https://doi.org/10.3390/buildings11050182 https://www.mdpi.com/journal/buildings Buildings 2021, 11, x FOR PEER REVIEW 2 of 19 Buildings 2021, 11, x FOR PEER REVIEW 2 of 19 Buildings 2021, 11, 182 2 of 19 Figure 1. Schematic of full-depth precast concrete deck panel system. Figure 1. Figure 1. Sche Schematic matic of of fu full-depth ll-depth precast precast con concr crete d ete deck eck pan panel el sy system. stem. One potential solution is the use of strip or distributed connections, rather than point connections. They offer the advantage of minimizing the risk of local failures. Among var- One potential solution is the use of strip or distributed connections, rather than One potential solution is the use of strip or distributed connections, rather than point ious types of strip connections, one promising detailing is the “connection by adhesion, point connections. They offer the advantage of minimizing the risk of local failures. connections. They offer the advantage of minimizing the risk of local failures. Among var- interlocking and friction,” which is first presented and studied by EPFL in Switzerland Among various types of strip connections, one promising detailing is the “connection ious types of strip connections, one promising detailing is the “connection by adhesion, [9]. This innovative connection (Figure 2a) consists of a precast deck fabricated with a by adhesion, interlocking and friction,” which is first presented and studied by EPFL in interlocking and friction,” which is first presented and studied by EPFL in Switzerland roughened slot in the lower part and an embossed steel rib welded longitudinally to the Switzerland [9]. This innovative connection (Figure 2a) consists of a precast deck fabricated [9]. This innovative connection (Figure 2a) consists of a precast deck fabricated with a upper flange of the steel girder. The channel void under the precast panel is injected with with a roughened slot in the lower part and an embossed steel rib welded longitudinally to roughened slot in the lower part and an embossed steel rib welded longitudinally to the cement grout. As shown in Figure 2b, the horizontal shear resistance of the connection is the upper flange of the steel girder. The channel void under the precast panel is injected upper flange of the steel girder. The channel void under the precast panel is injected with controlled by two interfaces: the grout-concrete interface (interface 1), and the steel-grout with cement grout. As shown in Figure 2b, the horizontal shear resistance of the connection cement grout. As shown in Figure 2b, the horizontal shear resistance of the connection is interface (interface 2). Papastergiou and Lebet [10] conducted several improvements to is controlled by two interfaces: the grout-concrete interface (interface 1), and the steel-grout controlled by two interfaces: the grout-concrete interface (interface 1), and the steel-grout this type of connection, including the absence of a bonding layer on the upper flange to interface (interface 2). Papastergiou and Lebet [10] conducted several improvements to interface (interface 2). Papastergiou and Lebet [10] conducted several improvements to improve the brittle behavior of the connection, the presence of circular holes in the steel this type of connection, including the absence of a bonding layer on the upper flange this type of connection, including the absence of a bonding layer on the upper flange to rib to generate a “dowel effect” [11], and the use of high-performance mortar as the injec- to improve the brittle behavior of the connection, the presence of circular holes in the improve the brittle behavior of the connection, the presence of circular holes in the steel tion [12]. The connection by adhesion, interlocking, and friction offers an alternative solu- steel rib to generate a “dowel effect” [11], and the use of high-performance mortar as the rib to generate a “dowel effect” [11], and the use of high-performance mortar as the injec- tion for the accelerated construction of steel–concrete composite bridges. However, pre- injection [12]. The connection by adhesion, interlocking, and friction offers an alternative tion [12]. The connection by adhesion, interlocking, and friction offers an alternative solu- vious studies conducted by Thomann and Lebet [13] and Papastergiou [14] pointed out solution for the accelerated construction of steel–concrete composite bridges. However, tion for the accelerated construction of steel–concrete composite bridges. However, pre- that this connection usually exhibits less ductile behavior in comparison with the shear previous studies conducted by Thomann and Lebet [13] and Papastergiou [14] pointed vious studies conducted by Thomann and Lebet [13] and Papastergiou [14] pointed out studs. out that this connection usually exhibits less ductile behavior in comparison with the that this connection usually exhibits less ductile behavior in comparison with the shear shear studs. studs. Precast deck Precast deck Interface 1 Grout (UHPC) Interface 2 Interface 1 Embossed Grout steel plate (UHPC) Interface 2 Embossed steel plate Flange of steel girder Flange of steel girder (a) (b) Figure 2. Schematic of strip shear connection: (a) general view; (b) interface details. Figure 2. Schematic of strip shear connection: (a) general view; (b) interface details. (a) (b) Figure 2. Schematic of strip shear connection: (a) general view; (b) interface details. Another potential solution would be the utilization of high-performance materials such as Ultra-High Performance Concrete (UHPC) to ensure improved performance in the Buildings 2021, 11, 182 3 of 19 shear connections. UHPC-class materials typically exhibit compressive strengths beyond 120 MPa and tensile strengths above 5 MPa [15]. UHPC has been successfully applied in composite connections between precast concrete slabs and steel girders [16–19]. Recently, Haber et al. [20] proposed two new deck-to-girder composite connections employing UHPC, referred to as the UHPC shear lug connection and the rebar dowel connection. Both connection details exhibited good ultimate capacity and excellent ductility. The objective of this paper is to develop an enhanced strip connection using UHPC as the connection grout. UHPC has better durability and mechanical properties over traditional cementitious grouts. Compared with existing strip connections using cement grout, the UHPC-grout strip shear connection allows for a significant improvement of ductility, ultimate capacity, and durability. 2. Experimental Program Three sets of experiments were conducted to study the structural performance and constructability of UHPC-grout strip shear connections: (1) push-out tests of shear con- nectors; (2) static tests of composite beams; and (3) fatigue tests of composite beams. The experimental work is described in the following sections. 2.1. UHPC-Class Grout The UHPC-class grout applied in this study is a commercially available product in China, which is composed of Portland cement, fine sand, silica fume, high active admixture, superplasticizer, steel fibers, and water. Table 1 shows the composition of this material. With regard to the steel fibers, the volumetric percentage is 1.5%, and the nominal length and diameter are13 mm and 0.2 mm, respectively. The average compressive strength of this UHPC-class grout is 125.6 MPa after 28 days of curing. Specimens were cured at ambient laboratory temperatures (25 C 2 C). The compressive strength is obtained from uniaxial compression tests on 150 150 150 mm cubic specimens. More details about the mix and properties of this UHPC-grout material are available in the report by He et al. [21]. Table 1. Relative weight ratios to cement in the mix design. Silica High Active Cement Fine Sand Superplasticizer Steel Fiber Water Fume Admixture 1.0 1.1 0.25 0.28 0.05 0.22 0.2 2.2. Push-Out Testing of Shear Connectors Three identical push-out test specimens were fabricated, as shown in Figure 3. Each specimen is assembled by two precast concrete blocks and a steel connector. The void in the connection is filled with UHPC-class grout. The concrete blocks are made of C50 concrete. The steel connector consists of a steel plate in which two embossed steel plates are welded. The surface of the inner rib of the concrete block was roughened by sand-blasting with at least 3 mm roughness at about 40 mm spacing. The embossed steel plate was roughed by 45 oriented grooves. These grooves are 2 mm deep and 10 mm wide. Circular holes (d = 50 mm) spaced at 150 mm were drilled in the embossed steel plate to generate a “dowel effect” that improves the shear strength of the connector. The above roughness treatments are the same as the specimens tested by Diógenes et al. [11]. Buildings 2021, 11, x FOR PEER REVIEW 4 of 19 Buildings 2021, 11, x FOR PEER REVIEW 4 of 19 Buildings 2021, 11, 182 4 of 19 (a) (b) (c) Figure 3. General details of push-out specimens (dimensions in mm): (a) elevation view; (b) plane view; (c) roughness (a) (b) (c) treatment. Figure 3. General details of push-out specimens (dimensions in mm): (a) elevation view; (b) plane view; (c) roughness Figure 3. General details of push-out specimens (dimensions in mm): (a) elevation view; (b) plane view; (c) roughness treatment. treatment. 2.3. Static and Fatigue Testing of Composite Beams 2.3. Static and Fatigue Testing of Composite Beams 2.3.1. Specimen Design 2.3. Static and Fatigue Testing of Composite Beams 2.3.1. Specimen Design Three identical specimens were fabricated to investigate the static and fatigue behav- 2.3.1. Specimen Design Three identical specimens were fabricated to investigate the static and fatigue behavior ior of composite girders with UHPC-grout strip shear connections. Beam 1 and Beam 2 of composite Three identic gira ders l spec with imens UHPC-gr were fabr outic strip ated to shear invest connections. igate the stat Beam ic and 1 and fatig Beam ue behav- 2 were were loaded statically to failure, and Beam 3 was exposed to two million cycles of fatigue ior of compo loaded staticall site girders y to failur with UHPC-grout e, and Beam 3 wasstrip sh exposed ear connectio to two million ns. Be cycles am 1 ofand Beam fatigue loads. 2 loads. were lo Figur adede s4 tat shows ically t the o fa general ilure, and Be details am of 3 w thea composite s exposed t beam o two mi specimens. llion cycEach les ofspecimen fatigue Figure 4 shows the general details of the composite beam specimens. Each specimen has a length of 4000 mm and a height of 400 mm. The precast deck slab is 4 m long 0.5 m loads. has a length of 4000 mm and a height of 400 mm. The precast deck slab is 4 m long × 0.5 wide 0.15 m thick. The steel girder is welded by three 12-mm-thick plates of Grade Q235 Figure 4 shows the general details of the composite beam specimens. Each specimen m wide × 0.15 m thick. The steel girder is welded by three 12-mm-thick plates of Grade steel. The size of the longitudinal grouting channel in the concrete slab is 90 mm 120 mm, has a length of 4000 mm and a height of 400 mm. The precast deck slab is 4 m long × 0.5 Q235 steel. The size of the longitudinal grouting channel in the concrete slab is 90 mm × and the grouting pockets have a size of 100 100 mm and a spacing of 1000 mm. The m wide × 0.15 m thick. The steel girder is welded by three 12-mm-thick plates of Grade 120 mm, and the grouting pockets have a size of 100 × 100 mm and a spacing of 1000 mm. roughness treatments to the embossed steel plates and the grouting channel are the same Q235 steel. The size of the longitudinal grouting channel in the concrete slab is 90 mm × The roughness treatments to the embossed steel plates and the grouting channel are the as the push-out tests. The material properties of the concrete slab and the UHPC-grout are 120 mm, and the grouting pockets have a size of 100 × 100 mm and a spacing of 1000 mm. same as the push-out tests. The material properties of the concrete slab and the UHPC- also the same as the push-out tests, as listed in Table 2. The roughness treatments to the embossed steel plates and the grouting channel are the grout are also the same as the push-out tests, as listed in Table 2. same as the push-out tests. The material properties of the concrete slab and the UHPC- grout are also the same as the push-out tests, as listed in Table 2. (a) (b) (a) (b) (c) (d) Figure 4. General details of composite beam specimens (dimensions in mm): (a) elevation view; (b) cross section (c) plane Figure 4. General details of composite beam specimens (dimensions in mm): (a) elevation view; (b) cross section (c) plane (c) (d) view; (d) beam segment. view; (d) beam segment. Figure 4. General details of composite beam specimens (dimensions in mm): (a) elevation view; (b) cross section (c) plane view; (d) beam segment. Buildings 2021, 11, 182 5 of 19 Buildings 2021, 11, x FOR PEER REVIEW 5 of 19 Table 2. Material properties for composite beam specimens. Table 2. Material properties for composite beam specimens. Component Material Grade Material Properties Component Material Grade Material Properties Steel plate Q235B fy = 250 MPa Steel plate Q235B f = 250 MPa Concrete slab Concrete slab C50 C50 f ’ = 57.8 MPa fc’(28 = 57 days) .8 MPa (28 days) Grout UHPC f ’ = 125.6 MPa (28 days) Grout UHPC fc’ = 125.6 MPa (28 days) Mild steel rebar HRB400 f = 415 MPa Mild steel rebar HRB400 fy = 415 MPa Note: f is the yield strength of steel; f ’ is the cylinder compressive strength of concrete. y c Note: fy is the yield strength of steel; fc’ is the cylinder compressive strength of concrete. Figure 5 shows the fabrication process of the composite beam specimens. After the Figure 5 shows the fabrication process of the composite beam specimens. After the precast concrete slab was installed on the steel girder, the interface between them was precast concrete slab was installed on the steel girder, the interface between them was filled filled with the UHPC-grout through the pockets preformed in the precast slab. with the UHPC-grout through the pockets preformed in the precast slab. (a) (b) (c) (d) Figure 5. Fabrication of composite beam specimens: (a) welding of embossed steel plate; (b) casting of precast slab; (c) Figure 5. Fabrication of composite beam specimens: (a) welding of embossed steel plate; (b) casting sand-blasting; (d) grouting from pockets. of precast slab; (c) sand-blasting; (d) grouting from pockets. 2.3.2. Test Set-Up 2.3. and 2. Te Instr st Set umentation -Up and Instrumentation Figure 6 shows the experimental set-up used for both the static and fatigue tests of Figure 6 shows the experimental set-up used for both the static and fatigue tests of the composite beam models. The tests were performed with a four-point flexural loading the composite beam models. The tests were performed with a four-point flexural loading configuration. During the static tests for Beam 1 and Beam 2, loading was applied in in- configuration. During the static tests for Beam 1 and Beam 2, loading was applied in crements of approximately 20 kN prior to the yielding of the steel girder. After that, load- increments of approximately 20 kN prior to the yielding of the steel girder. After that, ing was continued in displacement control at a speed of 2 mm per stage. Beam 3 was loading was continued in displacement control at a speed of 2 mm per stage. Beam 3 exposed to 2,000,000 cycles of cyclic loads at 3 Hz. The maximum and minimum cyclic was exposed to 2,000,000 cycles of cyclic loads at 3 Hz. The maximum and minimum loads were respectively 0.3Pu and 0.5Pu, where Pu is the ultimate failure load of the com- cyclic loads were respectively 0.3P and 0.5P , where P is the ultimate failure load of the u u u posite beam. composite beam. As shown in Figure 6, strain gauges were used to monitor the normal strains on critical sections and linear variable displacement transducers (LVDTs) were installed to measure the vertical deflections of the composite beam models. Mechanical dial indicators were installed along the beam for monitoring the steel-concrete interlayer load-slip relationship. Buildings 2021, 11, x FOR PEER REVIEW 6 of 19 Buildings 2021, 11, 182 6 of 19 Buildings 2021, 11, x FOR PEER REVIEW 6 of 19 Figure 6. Test set-up and instrumentation of composite beam specimens. As shown in Figure 6, strain gauges were used to monitor the normal strains on crit- ical sections and linear variable displacement transducers (LVDTs) were installed to meas- ure the vertical deflections of the composite beam models. Mechanical dial indicators were installed along the beam for monitoring the steel-concrete interlayer load-slip relation- ship. Figure 6. Test set-up and instrumentation of composite beam specimens. Figure 6. Test set-up and instrumentation of composite beam specimens. 3. Results and Discussions 3. Results and Discussions As shown in Figure 6, strain gauges were used to monitor the normal strains on crit- 3.1. Push-Out Testing of Shear Connectors 3.1. Push-Out Testing of Shear Connectors ical sections and linear variable displacement transducers (LVDTs) were installed to meas- Accor Accordi ding ng to the previ to the previous ous study of study of Papaster Papast giou ergiou and and Lebet Lebet [10], t [10], therehar ere are two e two primary pri- ure the vertical deflections of the composite beam models. Mechanical dial indicators were types mary types o of failurfe failure for the fo embossed r the embossed steel-cement steel-cement grout interfac grout interface: bearing e: befailur aring failure e and shear and installed along the beam for monitoring the steel-concrete interlayer load-slip relation- failur shear e. failure In the . In the current push-o current push-out tests, ut tests, three three spec specimensimens all all failed faile along d alon the embossed g the embossed steel- ship. UHPC-gr steel-UHPC out-grout interfac interface (Interface e (Inter 2). face Obvious 2). Obvi relative ous relative slip occurr slip occ ed between urred betwee the embossed n the em- steel bossed stee plate and l plate an the UHPC-gr d the UHPC-grout out (Figur (Figur e 7), while e 7), w no hile no ob obviousvio cracks us cracks appear aped peared in the in 3. Results and Discussions specimens. the specimens. 3.1. Push-Out Testing of Shear Connectors According to the previous study of Papastergiou and Lebet [10], there are two pri- mary types of failure for the embossed steel-cement grout interface: bearing failure and shear failure. In the current push-out tests, three specimens all failed along the embossed steel-UHPC-grout interface (Interface 2). Obvious relative slip occurred between the em- bossed steel plate and the UHPC-grout (Figure 7), while no obvious cracks appeared in the specimens. Figure 7. Slip between embossed steel plate and UHPC grout. Figure 7. Slip between embossed steel plate and UHPC grout. Figure 8 shows the shear stress–slip curves of the push-out tests. All specimens ex- Figure 8 shows the shear stress–slip curves of the push-out tests. All specimens hibited similar load-slip behavior. The slip was primarily from the interface between the exhibited similar load-slip behavior. The slip was primarily from the interface between embossed steel rib and the UHPC grout. The ultimate shear resistance of the UHPC-grout the embossed steel rib and the UHPC grout. The ultimate shear resistance of the UHPC- grout strip shear connection (t ) is 15 MPa, and the residual frictional resistance (t ) is u fr roughly 9 MPa. Figure 8 also shows the typical load-slip behavior of the specimens tested by Diógenes et al. [11], which were grouted by High-Performance Mortar (HPM) with Figure 7. Slip between embossed steel plate and UHPC grout. an average compressive strength of 80 MPa. As can be seen, the use of UHPC as the Figure 8 shows the shear stress–slip curves of the push-out tests. All specimens ex- connection grout exhibited a significant increase in ultimate shear resistance compared hibited similar load-slip behavior. The slip was primarily from the interface between the embossed steel rib and the UHPC grout. The ultimate shear resistance of the UHPC-grout Buildings 2021, 11, x FOR PEER REVIEW 7 of 19 Buildings 2021, 11, x FOR PEER REVIEW 7 of 19 strip shear connection (τu) is 15 MPa, and the residual frictional resistance (τfr) is roughly 9 MPa. Figure 8 also shows the typical load-slip behavior of the specimens tested by Diógenes et al. [11], which were grouted by High-Performance Mortar (HPM) with an strip shear connection (τu) is 15 MPa, and the residual frictional resistance (τfr) is roughly average compressive strength of 80 MPa. As can be seen, the use of UHPC as the connec- 9 MPa. Figure 8 also shows the typical load-slip behavior of the specimens tested by Buildings 2021, 11, 182 7 of 19 tion grout exhibited a significant increase in ultimate shear resistance compared to HPM, Diógenes et al. [11], which were grouted by High-Performance Mortar (HPM) with an mainly attributing to the better mechanical properties of UHPC over traditional cementi- average compressive strength of 80 MPa. As can be seen, the use of UHPC as the connec- tious grouts. tion grout exhibited a significant increase in ultimate shear resistance compared to HPM, mainly attributing to the better mechanical properties of UHPC over traditional cementi- to HPM, mainly attributing to the better mechanical properties of UHPC over traditional tious grouts. cementitious grouts. Specimens of this study 14 fr Specimens of this study fr Specimen P11-RP by Diógenes et al. (2015) 2 Specimen P11-RP by Diógenes et al. (2015) 3.0 00.5 1.0 1.5 2.0 2.5 Slip (mm) 1.5 2.0 2.5 3.0 00.5 1.0 Figure 8. Comparison of shear stress–slip behaviors of the specimen tested by Diógenes et al. [11] Slip (mm) and the ones tested in this study. Figure 8. Comparison of shear stress–slip behaviors of the specimen tested by Diógenes et al. [11] Figure 8. Comparison of shear stress–slip behaviors of the specimen tested by Diógenes et al. [11] 3.2. Static Testing of Composite Beam 1 and Beam 2 and the ones tested in this study. and the ones tested in this study. 3.2.1. Load-Deflection Relationship and Failure Mode 3.2. Static Testing of Composite Beam 1 and Beam 2 3.2. Static Testing of Composite Beam 1 and Beam 2 Figure 9 shows the load-deflection curves at the midspan obtained from the static 3.2.1. Load-Deflection Relationship and Failure Mode tests. Both composite beams behaved in a linear elastic manner until the supporting steel 3.2.1. Load-Deflection Relationship and Failure Mode Figure 9 shows the load-deflection curves at the midspan obtained from the static tests. beam started to yield at a strain of 1250 με. Simultaneously, cracks began to appear on the Figure 9 shows the load-deflection curves at the midspan obtained from the static Both composite beams behaved in a linear elastic manner until the supporting steel beam precast concrete slab at the locations of loading plates. The final collapse of the composite tests. Both composite beams behaved in a linear elastic manner until the supporting steel started to yield at a strain of 1250 ". Simultaneously, cracks began to appear on the precast beams was caused by the failure of the shear connection, where vertical cracks were ob- beam started to yield at a strain of 1250 με. Simultaneously, cracks began to appear on the concrete slab at the locations of loading plates. The final collapse of the composite beams served at the beam ends. The ultimate loads of Beam 1 and Beam 2 are 845 kN and 810 precast concrete slab at the locations of loading plates. The final collapse of the composite was caused by the failure of the shear connection, where vertical cracks were observed kN, respectively. The ultimate midspan deflection is above 20 mm (i.e., l0/180, where l0 is beams was caused by the failure of the shear connection, where vertical cracks were ob- at the beam ends. The ultimate loads of Beam 1 and Beam 2 are 845 kN and 810 kN, the span length), indicating that the structural performance of the beam is ductile (Figure served at the beam ends. The ultimate loads of Beam 1 and Beam 2 are 845 kN and 810 respectively. The ultimate midspan deflection is above 20 mm (i.e., l /180, where l is the 0 0 10). kN, respectively. The ultimate midspan deflection is above 20 mm (i.e., l0/180, where l0 is span length), indicating that the structural performance of the beam is ductile (Figure 10). the span length), indicating that the structural performance of the beam is ductile (Figure 10). (a) (b) Figure 9. Static testing results of Beam 1 and Beam 2: (a) load-deflection curves; (b) failure mode. Figure 9. Static testing results of Beam 1 and Beam 2: (a) load-deflection curves; (b) failure mode. (a) (b) Figure 9. Static testing results of Beam 1 and Beam 2: (a) load-deflection curves; (b) failure mode. Shear stress (MPa) Shear stress (MPa) Buildings 2021, 11, 182 8 of 19 Buildings 2021, 11, x FOR PEER REVIEW 8 of 19 Buildings 2021, 11, x FOR PEER REVIEW 8 of 19 Figure 10. Deformation capacity of Beam 2 at failure. Figure 10. Deformation capacity of Beam 2 at failure. Figure 10. Deformation capacity of Beam 2 at failure. 3.2.2. Composite Action 3.2.2. Composite Action 3.2.2. Composite Action Fig Figur ure 11 sho e 11 shows ws the the longitudinal longitudinal st strain rain di distributions stributions over over the beam depth at mid- the beam depth at mid-span Figure 11 shows the longitudinal strain distributions over the beam depth at mid- spa for n Beam for Beam 1. 1. As expected, As expected, the pla the plane-section ne-secti assumption on assumpt isiwell on issatisfied well satiin sfied the in elastic the el stage. astic span for Beam 1. As expected, the plane-section assumption is well satisfied in the elastic stage. Although inconsistencies can be seen in the plastic stage, it can be observed that Although inconsistencies can be seen in the plastic stage, it can be observed that effective stage. Although inconsistencies can be seen in the plastic stage, it can be observed that effect composite ive com action positwas e actdeveloped ion was deve between loped bet thew deck een the dec slab and k the slab steel and the girder steel g up to irder failur up e. effective composite action was developed between the deck slab and the steel girder up to failure. A As can be seen s can be from seen Figu fr rom Figure e 11, the theor 11, the etical theoreti location cal lof oca the tion of neutral the neutral axis is close axis ito s clthat ose to failure. As can be seen from Figure 11, the theoretical location of the neutral axis is close identified from the test results. Once again, it can be concluded that an effective composite to that identified from the test results. Once again, it can be concluded that an effective to that identified from the test results. Once again, it can be concluded that an effective action was developed between the precast slab and the steel girder. When the load is composite action was developed between the precast slab and the steel girder. When the composite action was developed between the precast slab and the steel girder. When the increased to 800 kN, the longitudinal strain distribution over the mid-span section is not load is increased to 800 kN, the longitudinal strain distribution over the mid-span section load is increased to 800 kN, the longitudinal strain distribution over the mid-span section linear. This indicates that interface slippage occurred between the precast slab and the is not linear. This indicates that interface slippage occurred between the precast slab and is not linear. This indicates that interface slippage occurred between the precast slab and supporting steel girder. the supporting steel girder. the supporting steel girder. 200kN 400kN 200kN 400kN 600kN 800kN 600kN 800kN N.A. at failure (theoretical) N.A. at failure (theoretical) 200 N.A. in elastic stage (theoretical) N.A. in elastic stage (theoretical) 0 6000 -2000 2000 4000 0 6000 -2000 2000 4000 Strain (με) Strain (με) Figure 11. Longitudinal strain distributions over mid-span section of Beam 1. Figure 11. Longitudinal strain distributions over mid-span section of Beam 1. Figure 11. Longitudinal strain distributions over mid-span section of Beam 1. 3.2.3. Load–Slip Relationship 3.2.3. Load–Slip Relationship 3.2.3. Load–Slip Relationship Figure 12 shows the load–slip relationships obtained for the test specimens. The slip Figure 12 shows the load–slip relationships obtained for the test specimens. The slip Figure 12 shows the load–slip relationships obtained for the test specimens. The slip between the concrete and steel was measured by mechanical dial indicators along the beam. between the concrete and steel was measured by mechanical dial indicators along the between the concrete and steel was measured by mechanical dial indicators along the At failure, a maximum slip of 0.5 mm was observed, which is identical to the result of the beam. At failure, a maximum slip of 0.5 mm was observed, which is identical to the result beam. At failure, a maximum slip of 0.5 mm was observed, which is identical to the result Height (mm) Height (mm) 316 mm 316 mm 250 mm 150 mm 250 mm 150 mm Buildings 2021, 11, x FOR PEER REVIEW 9 of 19 Buildings 2021, 11, 182 9 of 19 of the push-out specimens shown in Figure 8. The steel–concrete interfaces with the max- push-out specimens shown in Figure 8. The steel–concrete interfaces with the maximum imum slip were in the middle of the shear spans. As the applied load increased, the max- slip were in the middle of the shear spans. As the applied load increased, the maximum imum slip increased nonlinearly. slip increased nonlinearly. P/2 P/2 3600 mm 0.6 800 kN 600 kN 0.5 200 kN 100 kN 0.4 0.3 0.2 0.1 mm 0 600 1200 1800 2400 3000 3600 -0.1 (a) 0.5 800 kN 600 kN 0.4 200 kN 100 kN 0.3 0.2 0.1 mm 0 600 1200 1800 2400 3000 3600 (b) Figure 12. Interface slip at different loading stages: (a) results of Beam 1; (b) results of Beam 2. Figure 12. Interface slip at different loading stages: (a) results of Beam 1; (b) results of Beam 2. 3.3. Fatigue Testing of Composite Beam 3 3.3. Fatigue Testing of Composite Beam 3 Beam 3 was tested with a cyclic loading followed by a static test to failure. The cyclic Beam 3 was tested with a cyclic loading followed by a static test to failure. The cyclic loading corresponds to a variation of 0.3P to 0.5P , where P is the ultimate load capacity u u u loading corresponds to a variation of 0.3Pu to 0.5Pu, where Pu is the ultimate load capacity of composite Beams 1 and 2. of composite Beams 1 and 2. Figure 13 shows the distributions of longitudinal strain over the beam depth at the Figure 13 shows the distributions of longitudinal strain over the beam depth at the mid-span after a specified number of load cycles. As can be seen, the composite action mid-span after a specified number of load cycles. As can be seen, the composite action remained intact after testing for 2 million load cycles. After the cyclic load tests, Beam 3 remained intact after testing for 2 million load cycles. After the cyclic load tests, Beam 3 was loaded to failure. Figure 14 shows the load-defection curve of Beam 3, together with was loaded to failure. Figure 14 shows the load-defection curve of Beam 3, together with the curves of Beam 1 and Beam 2. As can be seen, the fatigue loading has no damage effect the curves of Beam 1 and Beam 2. As can be seen, the fatigue loading has no damage effect on the structural performance of the composite beam. on the structural performance of the composite beam. Slip (mm) Slip (mm) Buildings 2021, 11, x FOR PEER REVIEW 10 of 19 Buildings 2021, 11, x FOR PEER REVIEW 10 of 19 Buildings 2021, 11, 182 10 of 19 100 kN 100 kN 200 kN 200 kN 300 kN 300 kN 400 kN 400 kN -400-200 0 200 400 600 800 -400-200 0 200 400 600 800 -400-200 0 200 400 600 800 -400-200 0 200 400 600 800 -400-200 0 200 400 600 800 -400-200 0 200 400 600 800 -400-200 0 200 400 600 800 -400-200 0 200 400 600 800 Strain (με) Strain (με) Strain (με) Strain (με) Strain (με) Strain (με) Strain (με) Strain (με) 0.25M cycles 1M cycles 1.5M cycles 2M cycles 0.25M cycles 1M cycles 1.5M cycles 2M cycles Figure 13. Longitudinal strain distributions over mid-span section of Beam 3. Figure 13. Longitudinal strain distributions over mid-span section of Beam 3. Figure 13. Longitudinal strain distributions over mid-span section of Beam 3. Beam failure Beam 1 Beam failure 1000 Beam 1 Beam 2 Beam 2 Beam 3 Beam 3 Slab cracking Slab cracking Steel yielding 400 Steel yielding Beam 3 Beam 3 0.04M cycles 0.04M cycles 200 0.6M cycles 0.6M cycles 1.2M cycles 1.2M cycles 2.0M cycles 2.0M cycles 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Deflection (mm) Deflection (mm) Figure 14. Figure 14.Loa Load-deflection d-deflection cu curves rves of of com composite posite beam beams. s. Figure 14. Load-deflection curves of composite beams. 4. Theoretical Analysis and Comparison 4. Theoretical Analysis and Comparison 4. Theoretical Analysis and Comparison 4.1. Evaluation of the Degree of Shear Connection 4.1. Evaluation of the Degree of Shear Connection 4.1. Evaluation of the Degree of Shear Connection Composite beams are classified as fully composite and partially composite based on Composite beams are classified as fully composite and partially composite based on Composite beams are classified as fully composite and partially composite based on the degree of shear connection [22]. In the plastic approach adopted by the AASHTO and the degree of shear connection [22]. In the plastic approach adopted by the AASHTO and the degree of shear connection [22]. In the plastic approach adopted by the AASHTO and AISC specifications, it is assumed that the horizontal shear is distributed evenly along the AISC specifications, it is assumed that the horizontal shear is distributed evenly along the AISC specifications, it is assumed that the horizontal shear is distributed evenly along the interface (Figure 15). To develop a full interaction, the required horizontal shear (V ) along interface (Figure 15). To develop a full interaction, the required horizontal shear (Vh ) * interface (Figure 15). To develop a full interaction, the required horizontal shear (Vh ) the interface between the concrete slab and the steel beam shall be: along the interface between the concrete slab and the steel beam shall be: along the interface between the concrete slab and the steel beam shall be: V = min {A f , 0.85A f ’}, (1) h * s y c c Vh = mi * n {Asfy, 0.85Acfc’}, (1) Vh = min {Asfy, 0.85Acfc’}, (1) where A is the area of the steel beam; f is the yield strength of the steel beam; f ’ is the where As is the area of the steel beam; fy is the yield strength of the steel beam; fc’ is the s y c where As is the area of the steel beam; fy is the yield strength of the steel beam; fc’ is the compressive strength of the concrete; and A is the effective area of the concrete slab. compressive strength of the concrete; and Acc is the effective area of the concrete slab. compressive strength of the concrete; and Ac is the effective area of the concrete slab. Load (kN) Load (kN) Buildings Buildings 2021 2021 , 11 , 11 , 182 , x FOR PEER REVIEW 11 11 of of 19 19 Shear span, a Concrete slab N =0.85A f c c c V = min(N , N ) h s c Steel beam N =A f s s y max Uniform distribution avg Actual distribution Steel-concrete interface Figure 15. Distribution of horizontal shear stresses along steel–concrete interface. Figure 15. Distribution of horizontal shear stresses along steel–concrete interface. Meanwhile, the actual shear force (V ) provided by the UHPC-grout strip shear Meanwhile, the actual shear force (Vh) provided by the UHPC-grout strip shear con- connection along the shear span is given as: nection along the shear span is given as: V = 2h a t , (2) p v u Vh = 2hp·av·τu, (2) where τu is the interface shear strength of the UHPC-grout strip shear connection, which where t is the interface shear strength of the UHPC-grout strip shear connection, which can be taken as 15 MPa according to the pull-out tests; hp is the height of the embossed can be taken as 15 MPa according to the pull-out tests; h is the height of the embossed steel steel p plate; late; an andd aavis is the the length length of of the the shear shear span. span. The degree of shear connection is defined as: The degree of shear connection is defined as: η = V* h/Vh. (3) h = V /V . (3) h h If η is greater than or equal to 1, the beam is said to be a “full composite beam.” If h is greater than or equal to 1, the beam is said to be a “full composite beam.” Otherwise, the beam is said to be a “partially composite beam.” For the composite beams Otherwise, the beam is said to be a “partially composite beam.” For the composite beams * −3 −3 tested in this study, Vh is calculated as min{7512 × 250 × 10 , 0.85 × 66,000 × 57.8 × 10 } = * 3 tested in this study, V is calculated as min{7512 250 10 , 0.85 66,000 57.8 min{1878, 3243} = 1878 kN, and Vh is calculated as 2 × 0.06 × 1.2 × 15 × 103 = 2160 kN. 10 } = min{1878, 3243} = 1878 kN, and V is calculated as 2 0.06 1.2 15 103 = Therefore, the degree of shear connection is η = 2160/1878 = 1.15, which indicates that the 2160 kN. Therefore, the degree of shear connection is h = 2160/1878 = 1.15, which indicates tested beams are “full composite.” that the tested beams are “full composite.” In the tests, all three beams exhibited a sudden loss of load capacity due to the failure In the tests, all three beams exhibited a sudden loss of load capacity due to the failure of the shear connection. As shown in Figure 15, the actual distribution of horizontal shear of the shear connection. As shown in Figure 15, the actual distribution of horizontal shear stresses along the interface slightly deviates from the uniform-distribution assumption in stresses along the interface slightly deviates from the uniform-distribution assumption in the plastic analysis. The maximum shear stress is roughly 15% larger than the average the plastic analysis. The maximum shear stress is roughly 15% larger than the average value. This provides a reasonable explanation for the failure mode of the tested beams. value. This provides a reasonable explanation for the failure mode of the tested beams. 4.2. Evaluation of Plastic Resistance Moment 4.2. Evaluation of Plastic Resistance Moment For a full composite beam, the plastic resistance moment of the composite cross-sec- For a full composite beam, the plastic resistance moment of the composite cross-section tion can be calculated based on the sectional analysis by CEN [23]. The calculation result can be calculated based on the sectional analysis by CEN [23]. The calculation result in in Figure 16 shows that the plastic neutral axis of the cross-section lies in the concrete slab. Figure 16 shows that the plastic neutral axis of the cross-section lies in the concrete slab. The depth of the neutral axis is given as: The depth of the neutral axis is given as: x = Asfy/0.85bfc’ = 83.9 mm, (4) x = A f /0.85bf ’ = 83.9 mm, (4) s y c where As is the area of the steel beam and the embossed steel plate and b is the effective where A is the area of the steel beam and the embossed steel plate and b is the effective width of the concrete slab. width of the concrete slab. Buildings 2021, 11, x FOR PEER REVIEW 12 of 19 Buildings 2021, 11, 182 12 of 19 Buildings 2021, 11, x FOR PEER REVIEW 12 of 19 0.85f 0.85f ' 0.85xbf N.A. 0.85xbf N.A. A f s y A f s y Figure 16. Sectional analysis for plastic resistance moment. Figure 16. Sectional analysis for plastic resistance moment. Figure 16. Sectional analysis for plastic resistance moment. Therefore, the plastic resistance moment of the composite cross-section is obtained as: Therefore, the plastic resistance moment of the composite cross-section is obtained as: Therefore, the plastic resistance moment of the composite cross-section is obtained Mu = Asfy(h − hs/2 − x/2) = 480 kN·m, (5) as: M = A f (h h /2 x/2) = 480 kNm, (5) u s y s where h is the overall height of the composite beam and hs is the height of the steel beam. Mu = Asfy(h − hs/2 − x/2) = 480 kN·m, (5) where h is the overall height of the composite beam and h is the height of the steel beam. In the tests of Beam 1 and Beam 2, the experimental s moment strengths are 507 kN·m where h is the overall height of the composite beam and hs is the height of the steel beam. In the tests of Beam 1 and Beam 2, the experimental moment strengths are 507 kNm and 489 kN·m, which are slightly higher than the above prediction (i.e., 480 kN·m). In the tests of Beam 1 and Beam 2, the experimental moment strengths are 507 kN·m and 489 kNm, which are slightly higher than the above prediction (i.e., 480 kNm). and 489 kN·m, which are slightly higher than the above prediction (i.e., 480 kN·m). 5. Finite Element Modelling 5. Finite Element Modelling 5.1. Finite Element Model 5. Finite Element Modelling 5.1. Finite Element Model Three-dimensional stress analysis was conducted using the software ANSYS (Release 5.1. Finite Element Model Three-dimensional stress analysis was conducted using the software ANSYS (Release 10.0). Figure 17 shows the finite element (FE) model, in which the concrete was modelled 10.0). Figure 17 shows the finite element (FE) model, in which the concrete was modelled by Three-dimensional stress analysis was conducted using the software ANSYS (Release by eight-node solid elements (SOLID 65); steel girder and steel rib were modelled by four- eight-node solid elements (SOLID 65); steel girder and steel rib were modelled by four-node 10.0). Figure 17 shows the finite element (FE) model, in which the concrete was modelled node shell elements (SHELL 43); and UHPC grouting shear connections were modelled shell elements (SHELL 43); and UHPC grouting shear connections were modelled by spring by eight-node solid elements (SOLID 65); steel girder and steel rib were modelled by four- by spring elements (COMBIN 39). The constitutive relationship of concrete and steel were elements (COMBIN 39). The constitutive relationship of concrete and steel were adopt as node shell elements (SHELL 43); and UHPC grouting shear connections were modelled adopt as shown in Figure 18a,b. The shear stress–slip constitutive relationship of UHPC shown in Figure 18a,b. The shear stress–slip constitutive relationship of UHPC grouting by spring elements (COMBIN 39). The constitutive relationship of concrete and steel were grouting material (Figure 18c) was adopted from the direct shear tests by Thomann et al. material (Figure 18c) was adopted from the direct shear tests by Thomann et al. [13] and adopt as shown in Figure 18a,b. The shear stress–slip constitutive relationship of UHPC [13] and Papastergiou [14]. Papastergiou [14]. grouting material (Figure 18c) was adopted from the direct shear tests by Thomann et al. [13] and Papastergiou [14]. concrete slab concrete slab combin 39 combin 39 steel girder (a) (b) steel girder Figure 17. Three-dimensional FE model of composite beam: (a) general view of the FE model; (b) simulation of shear Figure 17. Three-dimensional FE model of composite beam: (a) general view of the FE model; (b) simulation of shear (a) (b) connections. connections. Figure 17. Three-dimensional FE model of composite beam: (a) general view of the FE model; (b) simulation of shear connections. h c h c z Buildings 2021, 11, x FOR PEER REVIEW 13 of 19 Buildings 2021, 11, x FOR PEER REVIEW 13 of 19 Buildings 2021, 11, 182 13 of 19 50 200 1600 40 200 0 0 0 1 2 3 4 5 6 7 8 0 0.001 0.002 0.003 0.004 0 0 0.002 0.004 0.006 0.008 0 1 2 3 4 5 6 7 8 0 0.001 0.002 0.003 0.004 0 0.002 0.004 0.006 0.008 Slip (mm) Slip (mm) (a) (b) (c) (a) (b) (c) Figure 18. Constitutive relationship: (a) concrete; (b) steel; (c) UHPC grouted shear connection. Figure 18. Constitutive relationship: (a) concrete; (b) steel; (c) UHPC grouted shear connection. Figure 18. Constitutive relationship: (a) concrete; (b) steel; (c) UHPC grouted shear connection. 5.2. Comparisons between FEA and Test Results 5.2. Comparisons between FEA and Test Results 5.2. Comparisons between FEA and Test Results Figure 19a shows the load-deflection relationship curves of test beams and FE simu- Figure 19a shows the load-deflection relationship curves of test beams and FE simu- Figure 19a shows the load-deflection relationship curves of test beams and FE simu- lation and Figure 19b gives the distribution of interface slip at the load of 800 kN. In the lation and Figure 19b gives the distribution of interface slip at the load of 800 kN. In the lation and Figure 19b gives the distribution of interface slip at the load of 800 kN. In the elastic and plastic stage, the load-deflection curve of the finite element simulation is in elastic and plastic stage, the load-deflection curve of the finite element simulation is in elastic and plastic stage, the load-deflection curve of the finite element simulation is in good agreement with that of test results, which shows that the shear behavior of compo- good agreement with that of test results, which shows that the shear behavior of compo- good agreement with that of test results, which shows that the shear behavior of composite site beams with UHPC grouting material can be well simulated. The maximum relative site beams with UHPC grouting material can be well simulated. The maximum relative beams with UHPC grouting material can be well simulated. The maximum relative slip of slip of Beam 1, Beam 2 and FE modelling are 0.53 mm, 0.44 mm, and 0.46 mm respectively, slip of Beam 1, Beam 2 and FE modelling are 0.53 mm, 0.44 mm, and 0.46 mm respectively, Beam 1, Beam 2 and FE modelling are 0.53 mm, 0.44 mm, and 0.46 mm respectively, with a with a high degree of coincidence. The maximum slip occurs at approximate 800 mm with a high degree of coincidence. The maximum slip occurs at approximate 800 mm high degree of coincidence. The maximum slip occurs at approximate 800 mm away from away from the bearing instead of at loading points or at the bearing. This could possibly away from the bearing instead of at loading points or at the bearing. This could possibly the bearing instead of at loading points or at the bearing. This could possibly be because be because the complex stress condition makes the slip stiffness of loading points or at the be because the complex stress condition makes the slip stiffness of loading points or at the the complex stress condition makes the slip stiffness of loading points or at the bearing bearing increase. bearing increase. increase. 0.6 FEA 0.6 FEA FEA Beam 1 FEA Beam 1 Beam 1 Beam 1 Beam 2 0.5 Beam 2 Beam 2 0.5 800 Beam 2 0.4 0.4 0.3 0.3 0.2 0.2 0.1 0.1 0 0 0 0 0 5 10 15 20 25 1000 2000 3000 4000 0 5 10 15 20 25 1000 2000 3000 4000 Deflection (mm) Longitudinal position (mm) Deflection (mm) Longitudinal position (mm) (a) (b) (a) (b) Figure 19. Comparison of test and FE results: (a) load-deflection relationship; (b) interface slip of steel and concrete at a Figure 19. Comparison of test and FE results: (a) load-deflection relationship; (b) interface slip of steel and concrete at a Figure 19. Comparison of test and FE results: (a) load-deflection relationship; (b) interface slip of steel and concrete at a load of 800 kN. load of 800 kN. load of 800 kN. Figure 20 shows the comparison of strain distribution of FE simulation and test re- Figure 20 shows the comparison of strain distribution of FE simulation and test results. Figure 20 shows the comparison of strain distribution of FE simulation and test re- sults. During the loading process, the experimental and theoretical variation of strain During the loading process, the experimental and theoretical variation of strain agree well sults. During the loading process, the experimental and theoretical variation of strain with agree wel each other l with ea at both ch other the top at both the top of the concrete sl of the concrete slab and the bottom ab and t ofhthe e bottom of steel girder the steel . agree well with each other at both the top of the concrete slab and the bottom of the steel girder. girder. σ (MPa) σ (MPa) Load (kN) Load (kN) σ(MPa) σ(MPa) Slip (mm) Slip (mm) Shear force (kN/m) Shear force (kN/m) Buildings 2021, 11, x FOR PEER REVIEW 14 of 19 Buildings 2021, 11, 182 14 of 19 1000 1000 FEA FEA Beam 1 Beam 1 Beam 2 Beam 2 800 800 600 600 400 400 200 200 0 0 0 1000 4000 6000 -1500 -1000 -500 -2000 Strain (με) Strain (με) (a) (b) 400 400 FEA FEA Beam 2 Beam 2 -2000 0 2000 4000 6000 -200 -100 0 100 200 300 400 Strain (με) Strain (με) (c) (d) Figure 20. Comparison of strain: (a) strain at the bottom of the steel beam; (b) strain at the top of the concrete slab; (c) Figure 20. Comparison of strain: (a) strain at the bottom of the steel beam; (b) strain at the top of the concrete slab; (c) strain strain distribution on sections at the load of 200 kN; (d) strain distribution on sections at the load of 800 kN. distribution on sections at the load of 200 kN; (d) strain distribution on sections at the load of 800 kN. 6. Design of a Prototype Bridge 6. Design of a Prototype Bridge To facilitate future applications in bridge engineering, a trial design of a steel-con- To facilitate future applications in bridge engineering, a trial design of a steel-concrete crete composite bridge using the UHPC-grout strip shear connection is presented here. composite bridge using the UHPC-grout strip shear connection is presented here. The The prototype bridge is designed in accordance with AASHTO [24]. prototype bridge is designed in accordance with AASHTO [24]. 6.1. Details of the Prototype Bridge 6.1. Details of the Prototype Bridge As As illustr illustrated ated in in Figur Figure 21 e 21, , the the prototype prototype bridge bridhas ge ha a simply-supported s a simply-supported s span p of an 35 of m 35 m with a 12.4 m wide deck. The bridge carries two standard 3.75 m traffic lanes and a 3.4 with a 12.4 m wide deck. The bridge carries two standard 3.75 m traffic lanes and a 3.4 m m wide urgency parking strip. Precast panels 2–3 m wide are transversely connected by wide urgency parking strip. Precast panels 2–3 m wide are transversely connected by prpreformed eformed shear shear key key joints. jointsThe . The str struct uctural ural stee steel used l used for fothe r the main main beams, beams stif , stfeners iffenerand s and crcross b oss bracing racing conforms conform to s t ASTM o ASTM A709 A7 Grade 09 Grade 345.34 The 5. T deck he deck conc concrete has rete a has minimum a minim 28u day m 28 compressive strength of 40 MPa. The UHPC-grout has a minimum 28 day compressive day compressive strength of 40 MPa. The UHPC-grout has a minimum 28 day compres- str siv ength e strengt of 120 h of MPa, 120 and MPa, 1.5% and 1 high-str .5% high ength -strsteel ength st fibers eel fib by e volume. rs by volume. Height (mm) Force (kN) Height (mm) Force (kN) Buildings 2021, 11, x FOR PEER REVIEW 15 of 19 Buildings 2021, 11, 182 15 of 19 Buildings 2021, 11, x FOR PEER REVIEW 15 of 19 Figure 21. Schematic of the prototype bridge. Figure 21. Schematic of the prototype bridge. Figure 21. Schematic of the prototype bridge. Figure 22 shows typical cross-sections for the composite bridge at midspan and sup- Figure 22 shows typical cross-sections for the composite bridge at midspan and Figure 22 shows typical cross-sections for the composite bridge at midspan and sup- port. The superstructure consists of four steel I-girders with a full-depth precast concrete support. The superstructure consists of four steel I-girders with a full-depth precast port. The superstructure consists of four steel I-girders with a full-depth precast concrete deck. The deck is 380 mm thick above the main beams and 220 mm thick at its center. The concrete deck. The deck is 380 mm thick above the main beams and 220 mm thick at its deck. The deck is 380 mm thick above the main beams and 220 mm thick at its center. The steel girders are 1.6 m deep and are spaced at 3.2 m center to center. center. The steel girders are 1.6 m deep and are spaced at 3.2 m center to center. steel girders are 1.6 m deep and are spaced at 3.2 m center to center. ½ Midspan ½ Support ½ Midspan ½ Support 2% 2% 2% 2% t = 22 t = 22 t = 16 t = 16 t = 34 t = 34 1400 3200 3200 3200 1400 1400 3200 3200 3200 1400 Figure 22. Typical cross sections at midspan and support (dimensions in mm). Figure 22. Typical cross sections at midspan and support (dimensions in mm). Figure 22. Typical cross sections at midspan and support (dimensions in mm). Figure 23 shows the details of the UHPC-grout strip shear connection. The grouting Figure 23 shows the details of the UHPC-grout strip shear connection. The grouting Figure 23 shows the details of the UHPC-grout strip shear connection. The grouting channel pre-formed in the slab has a trapezoidal-shaped cross-section. The depth of the channel pre-formed in the slab has a trapezoidal-shaped cross-section. The depth of channel pre-formed in the slab has a trapezoidal-shaped cross-section. The depth of the grouting channel is 120 mm. The embossed steel plate for the shear connection has a thick- the grouting channel is 120 mm. The embossed steel plate for the shear connection has grouting channel is 120 mm. The embossed steel plate for the shear connection has a thick- ness of 12 mm and a depth of 115 mm. It is roughed by 45° oriented grooves (2 mm deep a thickness of 12 mm and a depth of 115 mm. It is roughed by 45 oriented grooves ness of 12 mm and a depth of 115 mm. It is roughed by 45° oriented grooves (2 mm deep and (2 mm 40 m deep m wand ide) and 40 mm is dri wide) lled w and ith cis ircdrilled ular hole with s (40 cir m cular m diam holes eter(40 and mm 150 m diameter m spacing and ). and 40 mm wide) and is drilled with circular holes (40 mm diameter and 150 mm spacing). 150 mm spacing). Grouting pocket Grouting pocket 3200 3200 3200 1400 3200 12 3200 400 3200 1400 (a) (a) 1600 320 1600 320 750 1500 750 750 1500 750 3000 Buildings 2021, 11, x FOR PEER REVIEW 15 of 19 Figure 21. Schematic of the prototype bridge. Figure 22 shows typical cross-sections for the composite bridge at midspan and sup- port. The superstructure consists of four steel I-girders with a full-depth precast concrete deck. The deck is 380 mm thick above the main beams and 220 mm thick at its center. The steel girders are 1.6 m deep and are spaced at 3.2 m center to center. ½ Midspan ½ Support 2% 2% t = 22 t = 16 t = 34 1000 1000 1400 3200 3200 3200 1400 Figure 22. Typical cross sections at midspan and support (dimensions in mm). Figure 23 shows the details of the UHPC-grout strip shear connection. The grouting channel pre-formed in the slab has a trapezoidal-shaped cross-section. The depth of the grouting channel is 120 mm. The embossed steel plate for the shear connection has a thick- Buildings 2021, 11, 182 16 of 19 ness of 12 mm and a depth of 115 mm. It is roughed by 45° oriented grooves (2 mm deep and 40 mm wide) and is drilled with circular holes (40 mm diameter and 150 mm spacing). Grouting pocket 3200 3200 3200 1400 Buildings 2021, 11, x FOR PEER REVIEW 16 of 19 (a) 120 120 340 340 340 340 (b) (c) t = 12 2-mm deep groove d=40 d=40 d=40 150 150 (d) Figure 23. Details of the UHPC grout strip shear connection (dimensions in mm): (a) plane view of Figure 23. Details of the UHPC grout strip shear connection (dimensions in mm): (a) plane view precast deck panel; (b) details of grouting channel; (c) details of grouting pocket; (d) details of of precast deck panel; (b) details of grouting channel; (c) details of grouting pocket; (d) details of embossed steel plate. embossed steel plate. 6.2. Dema 6.2. Demand nd for Interface for Interface Shear Shear Accordin Accor g to ding AASHTO [24], the n to AASHTO [24], the omin nominal al horizontal sh horizontal ear shear (Vh ) betw (V ) een the mid-span between the mid-span and the support shall be taken as: and the support shall be taken as: Vh = min {Asfy, 0.85Acfc’} = 24,807 kN, (6) V = min {A f , 0.85A f ’} = 24,807 kN, (6) h s y c c where As is the area of the steel beam (71,904 mm ); fy is the yield strength of the steel beam where A is the area of the steel beam (71,904 mm ); f is the yield strength of the steel beam s y (345 MPa); fc’ is the compressive strength of the concrete (40 MPa); and Ac is the effective (345 MPa); f ’ is the compressive strength of the concrete (40 MPa); and A is the effective c c area of the concrete slab (0.832 m ). area of the concrete slab (0.832 m ). The nominal shear resistance (Vh ) provided by the UHPC-grout strip shear connec- The nominal shear resistance (V ) provided by the UHPC-grout strip shear connection tion along the shear span is given as: along the shear span is given as: Vh = Vn·l0/2 = 31,500 kN, (7) V = V l /2 = 31,500 kN, (7) h n 0 where Vn is the nominal shear resistance of the UHPC grout strip shear connection, which can be wher taken as 1800 kN/m e V is the nominal accord shear ing resistance to composit of the e be UHPC am test grs; out anstrip d l0 is the shearspan connection, length. which Therefore, the degree of shear connection is: can be taken as 1800 kN/m according to composite beam tests; and l is the span length. Therefore, the degree of shear connection is: η = Vh/Vh = 1.27. (8) h = V /V = 1.27. (8) The above result shows that the UHPC grou h t strip shear connection h has the potential to meet the requirements for horizontal shear in the design of a real bridge. The above result shows that the UHPC grout strip shear connection has the potential to meet the requirements for horizontal shear in the design of a real bridge. 6.3. Construction Process Figure 24 shows the major construction stages of the prototype bridge, including (1) 6.3. Construction Process erection of steel girders and cross frames; (2) erection of precast deck panels; (3) field cast- Figure 24 shows the major construction stages of the prototype bridge, including ing of panel-to-panel joints; (4) grouting of UHPC to the connection channel; and (5) cast- (1) erection of steel girders and cross frames; (2) erection of precast deck panels; (3) field ing of deck surfacing layer. 1600 320 160 220 750 1500 750 380 Buildings 2021, 11, 182 17 of 19 Buildings 2021, 11, x FOR PEER REVIEW 17 of 19 casting of panel-to-panel joints; (4) grouting of UHPC to the connection channel; and (5) casting of deck surfacing layer. Figure 24. Major construction stages of the prototype bridge. Figure 24. Major construction stages of the prototype bridge. 6.4. Discussio 6.4. Discussions ns The trail design of the prototype bridge shows that the UHPC-grout strip shear The trail design of the prototype bridge shows that the UHPC-grout strip shear con- connection has the potential to be used in accelerated bridge construction. It is believed nection has the potential to be used in accelerated bridge construction. It is believed that that the UHPC-grout strip shear connection is a promising option for the design of steel– the UHPC-grout strip shear connection is a promising option for the design of steel–con- concrete composite bridges. However, more research should be carried out, especially in crete composite bridges. However, more research should be carried out, especially in re- relation to fatigue behavior under vehicular loading and the response under long-term lation to fatigue behavior under vehicular loading and the response under long-term load- loading. ing. 7. Conclusions 7. Conclusions An enhanced strip shear connection using UHPC as the grout has been developed An enhanced strip shear connection using UHPC as the grout has been developed for the prefabricated steel–concrete composite bridge system. Push-out tests of shear for the prefabricated steel–concrete composite bridge system. Push-out tests of shear con- connectors and static and fatigue tests of composite beams were conducted to validate the nectors and static and fatigue tests of composite beams were conducted to validate the performance of the new connection. The following conclusions can be drawn: performance of the new connection. The following conclusions can be drawn: 1. Based on the push-out testing, the ultimate capacity of the shear connection was 1. Based on the push-out testing, the ultimate capacity of the shear connection was dominated by the interface failure between the embossed steel and the UHPC grout. dominated by the interface failure between the embossed steel and the UHPC The interface shear strength of the UHPC grout strip shear connection could be as grout. The interface shear strength of the UHPC grout strip shear connection could high as 15 MPa. The use of UHPC as the connection grout exhibited a significant be as high as 15 MPa. The use of UHPC as the connection grout exhibited a signifi- increase in capacity compared to HPM. cant increase in capacity compared to HPM. 2. Based on the static testing of composite beams, the UHPC-grout strip shear connection 2. Based on the static testing of composite beams, the UHPC-grout strip shear connec- exhibited good interface shear performance. Full composite action was developed tion exhibited good interface shear performance. Full composite action was devel- between the precast panels and steel beams in the composite beams. oped between the precast panels and steel beams in the composite beams. 3. Based on the fatigue testing of a composite beam, the composite action remained intact 3. Based on the fatigue testing of a composite beam, the composite action remained after testing for two million load cycles, and the fatigue loading had no damaging intact after testing for two million load cycles, and the fatigue loading had no dam- effect on the structural performance of the composite beam. aging effect on the structural performance of the composite beam. 4. Both the experimental tests and theoretical calculations showed that a full interaction 4. Both the experimental tests and theoretical calculations showed that a full interac- could be developed between the precast panels and steel beams. The ultimate capacity tion could be developed between the precast panels and steel beams. The ultimate of the composite beam using the UHPC grout strip shear connection could be well capacity of the composite beam using the UHPC grout strip shear connection could predicted by the plastic approach. In the tests of Beam 1 and Beam 2, the experimental be well predicted by the plastic approach. In the tests of Beam 1 and Beam 2, the moment strengths are 507 kNm and 489 kNm, respectively, which are close to the experimental moment strengths are 507 kN·m and 489 kN·m, respectively, which theoretical moment strength of 480 kNm predicted by the plastic approach. are close to the theoretical moment strength of 480 kN·m predicted by the plastic 5. The trail design of the prototype bridge shows that the UHPC grout strip shear approach. connection has the potential to be used in accelerated bridge construction. Calculation 5. The trail design of the prototype bridge shows that the UHPC grout strip shear con- results indicate that this novel connection has the potential to meet the requirements nection has the potential to be used in accelerated bridge construction. Calculation for horizontal shear in the design of a real bridge. results indicate that this novel connection has the potential to meet the require- ments for horizontal shear in the design of a real bridge. Author Contributions: Conceptualization, Z.-Q.H.; methodology, Z.-Q.H.; software, C.O.; valida- tion, Z.-Q.H. and F.T.; formal analysis, Z.-Q.H.; investigation, Z.-Q.H. and C.O.; resources, Z.L.; data Buildings 2021, 11, 182 18 of 19 Author Contributions: Conceptualization, Z.-Q.H.; methodology, Z.-Q.H.; software, C.O.; validation, Z.-Q.H. and F.T.; formal analysis, Z.-Q.H.; investigation, Z.-Q.H. and C.O.; resources, Z.L.; data curation, C.O. and F.T.; writing—original draft preparation, Z.-Q.H.; writing—review and editing, Z.- Q.H. and Z.L.; visualization, F.T.; supervision, Z.L.; project administration, Z.L.; funding acquisition, Z.-Q.H. and Z.L. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the National Key R&D Program of China, grant num- ber 2019YFE0119800; the National Natural Science Foundation of China, grant number U1934205 and 51778137; and the Outstanding Youth Foundation of Jiangsu Province, China, grant number BK20180063. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The authors confirm that the data supporting the findings of this study are available within the article. Conflicts of Interest: The authors declare no conflict of interest. References 1. Shim, C.S.; Lee, P.G.; Chang, S.P. Design of shear connection in composite steel and concrete bridges with precast decks. J. Constr. Steel Res. 2001, 57, 203–219. [CrossRef] 2. Issa, M.A.; Patton, T.A.; Abdalla, H.A.; Yousif, A.A.; Issa, M.A. Composite behavior of shear connections in full-depth precast concrete bridge deck panels on steel stringers. PCI J. 2003, 48, 76–89. [CrossRef] 3. 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