Search Results (8)

Steel–concrete composite beams offer significant advantages in long-span, heavy-load, and prefabricated construction; however, the concrete slabs are prone to tensile cracking under negative bending moments. To enhance cracking resistance, uplift-restricted and slip-permitted (URSP) perfobond rib (PBL) connectors were adopted with a cast-in-place high-performance concrete (HPC) topping. Five composite beam-steel column joint specimens were tested under quasi-static cyclic loading. The test variables included connector type, cast-in-place concrete type, and reinforcement grade. In addition, refined numerical simulations were conducted on the test specimens. Both test and numerical results show that: (1) The combined application of URSP-PBL connectors and HPC enhanced the cracking resistance of the composite beam, with the initial cracking load and corresponding cracking displacement increased by approximately 50% compared with the control specimen. (2) The ultimate flexural capacity of the composite beams under negative moments showed limited sensitivity to the type of cast-in-place concrete topping and the reinforcement grade within the tested range. (3) The use of URSP-PBL connectors improved the flexural stiffness of the composite beams. (4) The URSP-PBL specimens showed good energy dissipation capacity under cyclic loading, which was further improved with the addition of HPC in the topping. Within the tested range, the reinforcement grade showed limited influence on this performance. This study provides a scientific basis for the crack control design and engineering application of long-span composite beams. Full article

An innovative form of steel–concrete composite beam, the steel–coarse aggregate reactive powder concrete (CA-RPC) composite beam with uplift-restricted and slip-permitted (URSP) connectors, is introduced in this paper. The aim is to enhance the cracking resistance under negative bending moments, which is a difficult problem for traditional composite beams, and to make the cost lower than using ordinary reactive powder concrete (RPC). An experimental investigation of the behavior of six specimens of simply supported steel–CA-RPC composite beams with URSP connectors under negative bending moments is presented in this paper. The test results validated that the cracking load of steel–CA-RPC composite beams could be approximately three times that of the ordinary steel–concrete composite beams while the bearing capacity and stiffness are almost the same. A numerical model, using the concrete damaged plasticity (CDP) model to simulate the behavior of the CA-RPC material, was proposed and successfully calculated the overall load–displacement relationship of the composite beams with sufficient accuracy compared with the experimental results, and the distribution of cracks and the failure mode of the beams could also be captured by this model. Furthermore, a parametric analysis was carried out to find out how the application of prestress, CA-RPC, and URSP connectors could affect the cracking resistance of the composite beams, and the results indicated that using CA-RPC and prestress made the main contributions and that the usage of URSP could boost the effect of the other two factors. The plastic resistance moment of the beams was also compared with the calculation results using the methods introduced in Eurocode 4, and it was proved that the calculation results were lower than the experimental results by approximately 10%, which meant that the method was reliable for this kind of composite beam. Full article

Uplift-restricted and slip-permitted (URSP) connectors have been demonstrated to effectively enhance the anti-cracking performance of RC slabs in negative moment areas. While their efficacy is recognized, studies of composite frames utilizing URSP connectors remain scarce, limiting their application in construction. This research undertakes a numerical analysis of the seismic performance of steel–concrete composite frames that employ URSP connectors. The influence of key design parameters on seismic behavior is scrutinized. Leveraging prior tests on composite frames with URSP connectors carried out by the authors’ group, a sophisticated three-dimensional FEM model is crafted. This model, built using the ABAQUS software (2016), accounts for the intricate mechanical behaviors of shear connectors. The fidelity of the FEM model is validated through a juxtaposition of numerical and test outcomes, assessing strain distribution, damage patterns, and load–displacement curves. This numerical model serves as a basis for the study, exploring the impacts of three crucial design parameters on structural seismic performance. The findings suggest that the arrangement length of URSP connectors should be constrained to less than half of the frame beam’s span to optimize mechanical performance during seismic events. Additionally, enhancing both the flange thickness and the steel beam’s height is recommended to further bolster structural integrity. Full article

To improve the cracking resistance of a concrete slab in the hogging moment region, a new concept called uplift-restricted and slip-permitted (URSP) connection technology has been proposed. Several studies have been conducted on URSP connectors, but investigations into the time-varying evolution behaviors of composite beams with URSP connectors are still lacking. In this paper, three types of elaborate finite element models of composite girders with differentiated connectors and different construction methods were established. Simulation of the concrete shrinkage and creep effect was realized using a user subroutine based on an improved rate-type formulation. The performances of the composite girders in three schemes were analyzed and compared in both the construction and service stages. The results demonstrated that the URSP connection technique can effectively increase the prestressing efficiency and decrease the tensile stress of the concrete induced by dead loads and vehicle loads. With an increasing service time, the concrete shrinkage effect will enhance the advantage of the URSP connection technique, and the creep effect will reduce this advantage. Finally, parametric analyses were conducted, and a value of 0.2 is recommended for the URSP length ratio to promote practical applications. Full article

To verify the effectiveness of uplift-restricted and slip-permitted (URSP) connectors in alleviating crack formation in the negative-moment region of steel-concrete composite beams (SCCBs) and improve the engineering adaptability of URSP connectors, this paper proposes a modified uplift-restricted and slip-permitted (MURSP) connector. Static load tests and theoretical analysis were conducted on two overhanging beams with MURSP connectors and ordinary studs to analyze the influence of different stud forms on the deflection, crack, and slip of SCCBs in the negative-moment region. Finally, a nonlinear finite element modeling method for MURSP-type steel-concrete composite beams was developed, and a finite element model was established. The results showed that the use of MURSP connectors could effectively alleviate the concrete cracking problem in the negative-moment zone of SCCBs. Compared with the common stud SCCB, the crack load of the MURSP-type SCCB was higher, the maximum crack width was lower, and the crack distribution was more uniform; however, the overall flexural stiffness of the overhanging beam with MURSP connectors was reduced by 3.08%. The interface slip of the overhanging beam with the MURSP connectors increased suddenly in the initial stage of loading, whereas the increase was more gradual in the later stage. The SCCB model established in this study was in good agreement with the results of experimental beams. The finite element analysis results showed that the ordinary stud and MURSP connector exhibited different stress and deformation states in the negative-moment region of SCCBs, and the deformation states changed from bending type to shear type. Full article

The uplift-restricted and slip-permitted (URSP) connector is a new type of connector used in steel–concrete composite structures that has been proven to improve the structural performance of negative moment regions. Since this connector changes the interface restraint between the slab and steel beam, there is an imperative to study the seismic performance of steel–concrete composite frame systems with this new type of connector. In this study, the dynamic behavior of composite frame structures with URSP connectors under seismic loads was numerically investigated. First, a beam–shell mixed model was used and complex interfaces of different connectors were considered while establishing a numerical model to conduct elasto–plastic time history analysis under various seismic loads. This numerical model was validated with the frame sub-assemblage experimental results of quasi-static cyclic tests. Second, the model analysis results of structures with URSP connectors were obtained and compared with those of traditional structures. Third, dynamic response results including roof displacement, inter-story displacement, and the distribution and failure modes of plastic hinges were analyzed and compared. The comparisons indicated that the arrangement of full-span URSP connectors had a non-negligible influence on the dynamic behavior of the systems. The arrangement increased the maximum inter-story displacement by 31.5% and induced adverse effects in certain cases, which is not suggested in the application of URSP connectors. The partial arrangement of URSP connectors had little influence on the dynamic behavior of the systems, and the frame systems still showed a good seismic performance, which was the same as the traditional composite structural system. These findings may promote the application of URSP connectors in composite structures. Full article

Due to the strong interface effect of continuous steel–concrete composite beams with conventional shear connectors, the efficiency of applying pre-stress in the negative moment zone is greatly reduced, which leads to a difficulty of anti-cracking design in the negative moment zone of pre-stressed steel–concrete composite box girder. In order to study the feasibility and the working mechanism of improving the crack resistance of continuous steel–concrete composite bridges by releasing the interfacial slip effect within the negative bending moment region, two groups of model tests were carried out in the paper. Two steel–concrete composite beams were used for model test, one of them using the conventional stud shear connectors, another one using the new shear connectors, named uplift-restricted and slip-permitted shear connectors. The results show that, compared with the composite beam with conventional shear studs, the composite beams with uplift-restricted and slip-permitted shear connectors have a higher pre-stress application efficiency, and the new connector could release the interface slip, which can make the tensile stress distribution in concrete slab more uniform within the negative moment zone, thus increasing the cracking load of concrete slab and reducing the subsequent crack width effectively. This study is helpful to understand the relationship between the interface slip and the anti-crack characteristics in negative moment zones, and a new anti-crack design method is proposed for the design of continuous composite girder. Full article

Tensile stresses and cracks in concrete slabs induced by a hogging moment have always been a disadvantage of steel-concrete composite structures and key issue of concern in the design of such structures. To reduce the tensile stress and control the crack width of the reinforced concrete (RC) slab, a new type of connector, called the uplift-restricted and slip-permitted (URSP) connector has been proposed and successfully applied in the area subjected to a negative bending moment in steel-concrete composite bridges. The feasibility of the URSP connector in steel-concrete composite frame buildings is investigated in this study based on a comprehensive parametric analysis. The effects of URSP connectors on the cracking behavior, as well as the stiffness and strength of composite frames, are systematically analyzed using an elaborate finite element model, which resembles a typical composite beam-column joint subjected to both lateral loads and vertical loads. In addition, an optimized arrangement length of URSP connectors is proposed for practical design. The research findings indicate that the application of URSP connectors greatly improves the crack resistance of RC slabs without an obvious reduction of the ultimate capacity and lateral stiffness of the composite frame. It is recommended that the distribution length of URSP connectors at each beam end should be 20–25% of the frame beam length. Full article