•The composite beam-column assemblies with unequal span ratios are tested.•The contribution coefficients of two-bay beams are proposed in this paper.•The composite effect and unequal height-span ...ratio of two-bay beams are analyzed.
To investigate the collapse performance of composite beam-column assemblies consisting of three columns and two beams with unequal spans under an internal column removal scenario, static loading tests with either unequal spans (1.4:1 or 0.6:1) or an equal span (1:1) were conducted. Experimental results, including the load-displacement responses, failure modes, internal force development and resistance mechanism, are discussed in detail. Besides, the contributions of different resistance mechanisms to the total resistance of the two-bay beams are quantitatively separated, which include the flexural resistance and catenary resistance of two-bay beams. In addition, finite element models of three specimens are validated based on the test results. Furthermore, the numerical models are used to illustrate the effect of the composite effect and unequal height-span ratio of two-bay beams on the collapse-resistant performance of the assembly. The results showed that the concrete slabs contributed to an increased collapse resistance of the composite beam-column assemblies. Decreasing the beam span resulted in a larger resistance under both mechanisms, whereas increasing the beam height increased the resistance under the flexural mechanism but contributed little to that under the catenary mechanism.
•A restrained steel-concrete composite beam was examined using ABAQUS.•Catenary action is affected by span, axial restraint, and load ratio.•The span of the composite beam affects the failure mode of ...the beam.
The actions of a restrained steel-concrete composite beam exposed to fire are investigated using the finite element software ABAQUS. A parametric study is performed to examine the influence of axial restraint stiffness, beam slenderness, load level, and axial restraint location. The fire scenario is also examined, and two fires are considered including an ASTM E119 standard fire and a design natural fire. Validation of both the heat transfer and structural analyses are presented to establish confidence in the results. The validation sheds new light on the macro-modeling of composite beams comprised of beam and shell elements. Specifically, the reference of the beam elements should be positioned at the geometric centroid of the end-connection when an axial-restraint is present. The study shows that the length of the beam heavily influences the fire response of a restrained composite beam. Composite beams with short spans tend to fail in the compressive beam-column stage, while composite beams with longer spans tend to fail in the tensile catenary stage. Furthermore, conditions that are favorable for inducing catenary action include longer beam spans, increased axial restraint stiffness, increased load level, and positioning of the axial restraint near the top of the beam. Finally, the results show that, for a beam of length L, catenary action is generally developed after the deflection limit of L/20 is reached, demonstrating that care should be used when using this deflection limit to evaluate the fire resistance of restrained composite beams.
•Replacing NSC by UHPC in the hogging moment region of steel-concrete composite beams was studied.•The flexural responses of steel-UHPC composite beams with welded stud and high strength bolt ...connectors were compared.•The crack resistance and flexural capacity were improved in steel-UHPC composite beams.•The theoretical formulas of flexural capacity of steel-UHPC composite beams under hogging moment were constructed.
Using ultra-high performance concrete (UHPC) in the hogging moment regions of composite beams might significantly enhance their cracking and flexural performance. In the present paper, the flexural test was performed on steel-UHPC composite beams with stud connectors (SU-S) and bolt connectors (SU-B) at the interface. Crack resistance, ultimate flexural capacity, failure modes, and deformation characteristics of SU-S and SU-B under hogging moment were investigated. The test results showed that steel-UHPC composite beams exhibited excellent cracking and flexural performance under the hogging moment. As compared to the steel-normal strength concrete (NSC) composite beam (SC-S), cracking load and ultimate flexural capacity of steel-UHPC composite beams increased by around 340% and 26%, respectively. Moreover, the length and width of cracks in the UHPC flange plate developed slowly with load. Many short and small cracks were observed, having a close spacing in the UHPC flange plate. However, ductility and rotation capacity of both SU-S and SU-B under the hogging moment were smaller than those of SC-S. Due to the bolts’ slip in SU-B, the tensile stress in the UHPC flange plate was reduced, resulting in higher crack resistance and rotation capacity than SU-S, while its flexural stiffness and ultimate flexural capacity were slightly smaller than those of SU-S. Finally, theoretical formulas were proposed for calculation of the slip moment, moment at crack width of 0.05 mm and ultimate moment of the steel-UHPC composite beams under the hogging moment. The test results verify the applicability of these formulas to predict flexural capacity of the steel-UHPC composite beams.
•Steel–precast UHPC composite beam performs better than conventional counterpart.•Composite beam shows similar load–slip relationship to push-out test with connector fracture.•Rigid plastic analysis ...models are proposed to predict the flexural capacity.
Two types of steel–precast ultra-high-performance concrete (UHPC) composite beams were investigated in this study, which can be vastly used in accelerated bridge construction (ABC). One of them contains full-depth slabs with stud shear connectors embedded in shear pockets, while the remaining one adopts demountable slabs with high-strength friction-grip bolts (HSFGBs). Four-point bending tests were conducted on six large-scale composite beams to investigate the interfacial shear and flexural performance of such innovative types of steel–precast UHPC composite structures. The failure modes, vertical deflection, horizontal interfacial slip and the stain distribution at mid-span cross-section were investigated. The experimental results indicated that the cracking patterns and failure modes of the composite beams were highly dependent on the slab concrete types and the degrees of shear connection. The composite beams adopting UHPC slabs achieved larger cracking resistance and higher ultimate strength than those containing normal-strength concrete slabs and favorable ductility. Similar trends were also presented by the composite beams with large degrees of shear connection. The composite beams with HSFGBs showed enhanced load capacities and larger vertical deflections and horizontal interface slips at peak load than those adopting stud shear connectors. Additionally, the composite beams that failed in shear connector fractures presented shear resistance–interface slip relationships comparable to their push-out counterparts. Finally, theoretical formulas based on rigid plastic analysis were proposed for predicting the flexural capacity of both types of composite beams.
•Two types of composite beam slabs produce different crack patterns.•The composite beam to undergo retraction in a reverse arch shape when the fire stops.•Local buckling occurred in the lower flange ...and web under the end of the steel beam.•The welds at both ends of the laminated-slab composite beam were cracked.•A calculation method of axial force of composite beam is proposed.
To study the fire resistance of different types of composite beams in integral structures, transient state tests were performed on two-span composite beams (one span is a monolithic composite beam with a laminated slab and the other span is a composite beam with a cast-in-place slab) with rigid beam-to-column connections. The temperature distribution, displacement changes, and failure modes of the two types of composite beams were evaluated in tests mimicking the entire process of a real fire disaster. The following results were obtained in this study. Under the influence of fire, cracks of different patterns were formed on different types of composite beams. When the heating was stopped, the temperature of the steel beam experienced a sudden and sharp drop, whereas the temperature of the concrete slab rose within a short period of time. These behaviours cause the composite beam to undergo retraction in a reverse arch shape during deformation. Severe buckling occurred in the lower flange under the two ends of the steel beam as well as the web of the steel beam. During the test, the welds at both ends of the laminated-slab composite beam were cracked, whereas those at both ends of the composite beam with a cast-in-place slab remained undamaged. Finally, a method for calculating the axial force of the composite beam that considers the constraints at the beam ends is proposed in this study. The calculation results are in good agreement with the experimental test results.
•Partial composite beams were fabricated and tested statically.•The use of precast concrete (PC) deck enhances the moment capacity and stiffness of the composite beam.•The ductility of steel block ...shear connector is similar to the shear stud group.•The composite beam with PC deck makes good use of the current design theory and standard.
This study aims to investigate the static behavior of a simply-supported assembled monolithic steel-concrete composite beam (SCCB). A total of ten composite beams were tested considering the parameters of shear connection degree, reserved hole shape, concrete deck width, and deck casting method. Based on the test results, failure mode, stiffness, ductility, and moment capacity were obtained and are discussed in this paper. Compared to the conventional SCCBs with wide flange beams and headed shear connectors, the composite beam considered in this study has favorable flexural performance, while reducing the excessive cost and potential construction challenge due to the use of precast concrete (PC) deck. The flexural behavior of the new assembled monolithic SCCBs was investigated through the one-point bending tests on the ten specimens. The study results indicate that: (1) The assembled monolithic SCCB with shear stud group (SSG) or steel block shear connector (SBSC) has higher moment capacity and ductility, with the ductility factor ranging from 3.4 to 6.8; (2) the higher the degree of shear connection, the greater the moment capacity; (3) the SBSC has higher moment capacity and stiffness and is suggested for practical use for better welding quality and convenient construction; (4) the nonlinear calculation formula specified in GB50017-2017 (Code for Design of Steel Structures) predicts more accurate ultimate moment strength for the composite beams with partial shear connection than Eurocode 4, in comparison with the experimental results; (5) the SCCB with PC deck shows respective 50% and 174% higher elastic stiffness when using SSG and SBSC, compared to the SCCB with cast-in-place concrete (CIPC) deck.
•Cyclic behaviour of steel-concrete composite connection is experimentally investigated.•Steel-concrete composite connections have high ductility and energy dissipating capacity.•Three different ...modes of failure were observed in the steel-concrete composite connections.•The strength deterioration in cyclic loading is much higher than that in monotonic loading.•Increasing the diameter and strength of the shear connector resulted in an increase in the hysteretic loop area.
An experimental study of the cyclic behaviour of steel-concrete composite connections using mechanical shear connectors subjected to a low-cycle high-amplitude loading regime is presented in this study. The ductility, strength degradation and absorbed energy which characterise the performance of a mechanical shear connector under cyclic loading conditions in steel-concrete composite connections are assessed. Nine steel-concrete composite connection specimens were designed and tested in order to investigate the cyclic behaviour of the proposed composite connections, and to elucidate the structural behaviour of the demountable bolt shear connectors between the precast concrete panels and steel beams. In addition, three monotonic tests on steel-concrete composite connection were conducted to evaluate the yield slip, yield load, ultimate slip, and ultimate shear strength capacity. The size of the bolted shear connector and the strength of the bolted shear connectors are the main variables in this study. The preparation and construction of the specimens, the testing procedure, the test set-up, and the instrumentation used are described and the results of the monotonic and cyclic tests are reported in detail.
•The end-restraint effect in composite beam with URSP connectors is proposed for the first time, and the mechanism of force transfer of URSP composite beams is revealed.•The actual performance of the ...new type of connectors is investigated using beam tests.•Successfully verified the effectiveness of URSP technology for crack resistance in the negative moment zone of the composite beam.•The key mechanical properties of composite beam with URSP connectors are discussed in depth.
The uplift-restricted and slip-permitted (URSP) connector technology is a new composite technology which achieves the purpose of reducing the tensile stress in concrete slab by releasing part of the composite action in the negative moment region. In this paper, it is found that arranging URSP connectors in continuous composite beams has an end-restraint effect, which has a significant impact on the force transfer mechanism of URSP composite beams. Previous studies on URSP technology seldom mention similar constraint effects, which cannot accurately reveal the mechanical behavior of URSP composite beams. In order to properly consider the influence brought by the end-restraint effect, this study uses continuous composite beams to carry out experimental research. Three two-span continuous composite specimens are fabricated and tested in this research. Six aspects of performance are compared and analyzed in detail, including ① cracking load, ② crack distribution and development pattern, ③ interfacial slip behavior, ④ deformation and stiffness, ⑤ internal force redistribution, and ⑥ strain distribution. It is found that the URSP connector can realize the release of part of the composite action, and has a significant effect on the crack control in the negative moment region. Meanwhile, the application of URSP connectors has little effect on the stiffness, bearing capacity and strain of steel beam.
•Static and fatigue behavior of RC-UHTCC beams is investigated using a four-point bending test.•With an increase in thickness of UHTCC, the fatigue life and mid-span deflection of RC-UHTCC beam ...increase.•A simplified method is introduced to model the fatigue performance of RC-UHTCC beam.•UHTCC layer can lower the tensile stress, strain localization and stress concentration of the longitudinal reinforcements.
The static and fatigue performance of reinforced concrete beams strengthened by strain-hardening fiber-reinforced cementitious composite is investigated. Two series of strengthened beam specimens are prepared with different thicknesses of the enhancement layer (40 mm and 50 mm), and three fatigue stress levels (0.9, 0.8, and 0.7) are tested. The fatigue life, mid-span deflection, and crack mode of the tested specimens are analyzed. Emphasis is placed on the fatigue response of the strain-hardening fiber-reinforced cementitious composite layer and longitudinal reinforcements. A simplified method is proposed to model the fatigue performance of the composite beam. The mechanism of the fatigue enhancement of the strengthened beam compared to a conventional reinforced concrete beam is as follows: (1) the enhancement layer physically contributes by taking part of the stress in the tension zone, and (2) the enhancement layer can lower the strain localization and stress concentration of the longitudinal reinforcements. Several methods for further improvement in the fatigue performance of reinforced concrete beams are suggested.
