Zhongxian Li

An effective model for analysis of reinforced concrete members and structures under blast loading

The traditional fiber beam model has been widely used in the seismic analysis of reinforced concrete members and structures. However, the inability to capture shear failure restricts its application to blast loadings. In this article, a numerical model that considers both rate-dependent shear behavior and damage effect is proposed based on the traditional fiber beam element. This is achieved using the modified compression-field theory with a concrete damage model and bilinear steel model in the principal directions. Meanwhile, a condensed three-dimensional stress–strain relation from the isotropic hardening plasticity model is implemented to simulate longitudinal reinforcement bars, as large shear strain would be produced under severe blast loads. The proposed model is validated by comparing the numerical and test results. The high-fidelity physics-based finite element model, validated by the same experiment, is also used in the study to prove the efficiency of the proposed model. Case studies of a reinforced concrete beam and a six-story reinforced concrete frame structure subjected to blast loads are then carried out. The results indicate that the proposed model is reliable compared with the high-fidelity physics-based model. In addition to the accuracy, comparisons of the computational time show an excellent performance with respect to the efficiency of the proposed model.

Dynamic response of monolithic and sandwich structures subjected to impulsive and impact loadings

Monolithic and sandwich structures have been widely used as energy absorption structures in military and civil engineering. This article reviews theoretical analyses of monolithic beams and plates subjected to static loading, impulsive loading and impact by a mass systematically. Experimental data collected from the literatures are compared with these theoretical results. In addition, the critical impulses for the failure of the monolithic structures are also reviewed. Furthermore, sandwich structures under quasi-static, low-velocity impact, high-velocity impact and blast loading, as well as their failure modes, are also summarized. The research methodology involves experimental investigations, theoretical analyses and numerical simulations.

Equivalent Seismic Performance Optimization of Steel Structures Based on Nonlinear Damage Analysis

An equivalent seismic performance optimization (ESPO) method is proposed in this article based on nonlinear seismic damage analysis, where the constraints and the fitness function of the optimization problem are expressed as the seismic performance index combined with the importance coefficient and the damage index. Two prototype buildings, a 9-story building with steel frame and a 15-story building with steel frame plus steel plate shear wall are optimized using the ESPO method, and the building seismic performance is obtained through incremental dynamic analysis. The analysis results show that the global seismic performance of the optimized building has obviously improved while the building self-weight has been reduced significantly.

Numerical Study on Nonlinear Semiactive Control of Steel-Concrete Hybrid Structures Using MR Dampers

Controlling the damage process, avoiding the global collapse, and increasing the seismic safety of the super high-rise building structures are of great significance to the casualties’ reduction and seismic losses mitigation. In this paper, a semiactive control platform based on magnetorheological (MR) dampers comprising the Bouc-Wen model, the semi-active control law, and the shear wall damage criteria and steel damage material model is developed in LS-DYNA program, based on the data transferring between the main program and the control platform; it can realize the purpose of integrated modeling, analysis, and design of the nonlinear semi-active control system. The nonlinear seismic control effectiveness is verified by the numerical example of a 15-story steel-concrete hybrid structure; the results indicate that the control platform and the numerical method are stable and fast, the relative displacement, shear force, and damage of the steel-concrete structure are largely reduced using the optimal designed MR dampers, and the deformations and shear forces of the concrete tube and frame are better consorted by the control devices.

Energy-Based Modal Pushover Procedure for Asymmetric Structures

Energy-based seismic evaluations of structures can give clear illustrations of seismic demands made upon structures. This paper presents a 3-dimensional energy-based modal pushover analysis (3D EMPA) method with equivalent three degree of freedom (ETDOF) system and equal-displacement rule. The lateral-rotational coupled effect on structures asymmetric in plan is considered using the energy-based modal pushover analysis (EMPA), which is more robust than the traditional Modal Pushover Analysis (MPA) procedure. The proposed procedure was validated against a nonlinear time history analysis of a 5-storey structure. The results show that the method is able to take higher mode effects into account and that the instability of capacity spectra will be avoided. The maximum deformation obtained from EMPA shows good agreement with a nonlinear time history analysis results of the original system. The proposed EMPA procedure appears to be reliable and effective for evaluating the seismic response of asymmetric-plan structures.

Displacement-dependent nonlinear damping model in steel buildings with bolted joints

The stick–slip phenomenon is commonly found at structural connections in steel buildings. It is a major damping mechanism in a structure with bolted joints and makes a significant contribution to the total structural damping. This article reviews the stick–slip damping model of an elastic single-degree-of-freedom system with one stick–slip component. It is observed that the damping ratios of the system with the stick–slip mechanism first quickly increase when experiencing a very small displacement and then slowly decrease. After the number of activated slip surfaces is assumed to be a linear function related to the structural displacement, the equivalent damping ratios of a structural system with numerous stick–slip components are derived. However, this displacement-dependent damping model is very difficult to be used for a structural dynamic analysis due to its inherent complexity. Therefore, a new displacement-dependent damping model for a structural dynamic analysis is proposed based on the viscous damping. A high-rise steel moment resisting frame with bolted joints subjected to an earthquake ground motion is taken as an example to verify the proposed method.