Background and Objective: Progressive collapse resistance of the steel moment-frame with composite floor slabs can be assessed by sudden column loss scenarios. In order to investigate the progressive collapse-resistant capacity of the steel moment-frame with composite floor slabs, a simplified approach based on the theory of membrane action and energy equilibrium principle is presented, which assessed the behaviour of progressive collapse resistance of this frame subjected to the removal of a penultimate column via the static and dynamic analysis. Mateial and Method: The residual vertical bearing capacity model considering of the membrane action and tie force (TF) method of composite floor slabs is developed to evaluate the force mechanism of the composite floor slabs. An energy-based theoretical framework is proposed for calculating the maximum allowable dynamic demands based on the nonlinear static Pulldown analysis, which is used to explore the relationship between of dynamic and static response in the progressive collapse process. Furthermore, the finite element software SAP2000 is used to calculate the numerical example to verify the reliability of this simplified approach. Results: The results show that the composite floor slabs significantly improve the structural progressive collapse-resistant ability and this simplified approach evaluates the progressive collapse resistance of the whole structure effectively. Conclusion: The existence of the floor can increase the ductility of the structure, and increase the progressive collapse-resistant ability. The appropriate value of the DIF depends on the ductility and amount of inelastic action the structure would experience during the column removal scenario.

The optimal strut-and-tie models (STMs) of two typical irregular concrete deep beams were constructed using evolutionary structural optimization and compared with those of previous studies. The reinforced concrete deep beam specimens were cast according to the reinforcement designs guided by different STMs. Eight irregular concrete deep beam specimens were experimentally investigated under stepped loading, and the differences in the amount of steel used, the load-carrying capacity, and the failure pattern of the different specimens were analyzed. The results show that the optimal STMs proposed in this study have significant advantages in terms of cost-effectiveness and can simultaneously ensure the load-carrying capacity, delay the crack propagation of irregular concrete deep beams, and reduce the amount of steel used in structural members. Therefore, they have an important engineering application value for the reinforcement design of irregular concrete deep beams.

A static loading test was carried out on a 1/3‐scale concrete‐filled square steel tubular column‐steel beam frame (CFSTSBF) specimen with 2 spans to study its progressive collapse behaviors under the middle column failure scenario using the alternate load path method and to examine the failure mode and load transfer and main resistance mechanisms of the residual structure. Then, theoretical models of the specimen, involving the whole collapse process, were developed, and the resistance and deformation relationships of each model were calculated and validated with test results. The results indicated that the specimen collapse process includes the elastoplastic stage, plastic stage, transfer stage, and catenary stage, the beam mechanism and catenary mechanism were the principal mechanisms for the structure against progressive collapse, and catenary action can significantly strengthen structural resistance. The modified theoretical models with higher practical accuracy could be used to assess structural performances against progressive collapse.

To study the interfacial bond‐slip performance of concrete‐filled square steel tubes (CFSSTs), taking the core concrete strength, slenderness ratio, and width‐to‐thickness ratio as the influencing factors; 9 specimens were designed with 3 factors and 3 levels for the orthogonal test method. In addition, different from the above 9 specimens, one specimen without rust removal was designed for the purpose of comparison. Based on the bond stress distribution and deformation coordination relationships between the specimens during the push‐out tests, a theoretical formula for calculating the relative slip of a CFSST was deduced. The results show that with the increase of load, the relative slip at the loading ends was earlier than that at the free ends of the specimens; the interfacial bond failure and relative slip gradually developed from the two ends towards the centre of the specimens; the increase of the bond stress in the middle part was faster than that at the ends of the specimens. The order of these factors from main to secondary is the presence of rust in the inner wall of the square steel tube, the slenderness ratio, the core concrete strength, and the width‐to‐thickness ratio.

In order to assess the seismic performance of damaged reinforced concrete (RC) frame strengthened with carbon fiber reinforced polymers (CFRP) sheets, two experimental specimens with identical reinforcement ratio and geometric dimensions were designed following Chinese code for seismic design of buildings. Experimental specimens consist of a reference (undamaged) RC frame, namely, KJ-1, and an earthquake-damaged RC frame strengthened with CFRP sheets, namely, KJ-2. A pseudostatic test was conducted on the two specimens to simulate moderate earthquake damage. The strengthening effects of CFRP sheets on damaged RC frame were discussed in terms of hysteretic curve, skeleton curve, stiffness degradation, and ductility. In addition, numerical method based on fiber model method was utilized to analyze the seismic performance of KJ-1 and KJ-2 and it is compared with the experimental result. Both the results confirm that the method of exterior bonding CFRP sheets on the damaged RC frame has restored the seismic performance such as bearing capacity, stiffness, and ductility to its original undamaged level, and some of the seismic performance of the damaged RC frame strengthened with CFRP sheets is even better than the undamaged one, which proves that the method has significant effect in strengthening postearthquake-damaged RC frames.

In order to investigate the seismic performance of reinforced concrete frame with unequal span, a specimen was tested under low-cyclic loading and the seismic performance of this frame was analyzed based on fiber element method using software OpenSees. Hysteretic curves, skeleton curves, ductility, stiffness degradation and energy dissipating capacity of the frame are compared and analyzed. The experimental and simulate results demonstrate that this frame has a poor seismic performance. Thus, it is suggested that the seismic strengthening criteria of unequal-span frame structure should be raised and the existing buildings of this structure should be retrofitted.