Xudong Zhi

Study on the effect of ground motion direction on the response of engineering structure

Due to the randomness of earthquake wave magnitude and direction, and the uncertain direction of strong axis and weak axis in the construction of engineering structures, the effect of the direction of ground motion on a structure are studied herein. Ground motion records usually contain three vertical ground motion data, which are obtained by sensors arranged in accordance with the EW (East -West) direction, NS (South- North) direction and perpendicular to the surface (z) direction, referring to the construction standard of seismic stations. The seismic records in the EW and NS directions are converted to Cartesian coordinates in accordance with the rotation of θ = 0°−180°, and consequently, a countless group of new ground motion time histories are obtained. Then, the characteristics of the ground motion time history and response spectrum of each group were studied, resulting in the following observations: (1) the peak and phase of ground motion are changed with the rotation of direction θ, so that the direction θ of the maximum peak ground motion can be determined; (2) response spectrum values of each group of ground motions change along with the direction θ, and their peak, predominant period and declining curve are also different as the changes occur; then, the angle θ in the direction of the maximum peak value or the widest predominant period can be determined; and (3) the seismic response of structures with different directions of ground motion inputs has been analyzed under the same earthquake record, and the results show the difference. For some ground motion records, such as the Taft seismic wave, these differences are significant. Next, the Lushan middle school gymnasium structure was analyzed and the calculation was checked using the proposed method, where the internal force of the upper space truss varied from 25% to 28%. The research results presented herein can be used for reference in choosing the ground motion when checking the actual damage to structures following earthquakes and explaining the seismic damage. Meanwhile, it also provides a reference value for research into the most severe ground motion.

Damage evaluation of square steel tubes at material and component levels based on a cyclic loading experiment

Circular and square steel tubes are two of the most commonly used members in the construction industry in China. Material damage and its accumulation cannot be neglected when structures undergo obvious deformation and material plasticity during severe earthquakes. In another published paper, a material damage constitutive model for Q235 steel was derived, and some of its parameters were defined based on a cyclic test. This article focuses on developing a normalized constitutive model at the material level and a damage model at the component level for square steel tubes based on experimentally derived results. First, the material damage behavior of 10 square steel tubes under five cyclic load schemes was investigated. The material damage and its accumulation at the material level were defined using a user-defined material sub-routine (UMAT) in the finite element software Abaqus. Next, the parameters in the constitutive model were calibrated by the fitting degree between the test result and numerical result. Furthermore, based on the experimental and numerical data, a damage model combined with deformation and energy was developed at the component level to evaluate the overall damage behavior of the specimens. Finally, the parameters in the damage model were calibrated based on the responses of the specimens at the time of collapse. The effect of material damage behavior and the accumulation of damage were found to significantly reduce the collapse load of specimens, which must be considered in the theoretical analysis and design process. The constitutive model and damage model developed in this article can be used to quantify the degree of damage of the material and components of structures under earthquake loads.

Simplified design method and seismic performance of space trusses with consideration of the influence of the stiffness of their lower supporting columns

Static and dynamic force performance of two types of space truss structures i.e. square pyramid space truss (SPST) and diagonal on square pyramid space truss (DSPST), are studied to determine the effect of stiffness of their lower supporting members. A simplified model for the supporting columns and the equivalent spring mass system are presented. Furthermore, the feasibility of the simplified model is demonstrated through theoretical analysis and examples of comparative analysis of the simplified model with the entire model. Meanwhile, from the elastic analysis under frequently occurring earthquakes and elasto-plastic analysis under seldom occurring earthquakes subjected to TAFT and EL-Centro seismic oscillation it is shown that the simplified method can be encompassed in the results from the normal model. It also showed good agreement between the two methods, as well as greatly improved the computational efficiency. This study verified that the dynamic effect of the supporting structures was under considered in space truss design in the past. The method proposed in the paper has important significance for other space truss structures.

Seismic resistance effect of BRB on the single-layer reticulated dome

This paper presents research on seismic resistance effect of BRB on the single-layer reticulated dome and its substructure. The analytical method of tracing the full-range dynamic responses of the structures is adopted to compare the seismic response of whole structure with three kinds of braces and describe the mechanism of BRBs seismic reducing effect; Through the parametric analysis, this paper investigates the influence of BRB with different core area and yield stress on displacement, development of plastic deformation and critical load of whole structure. Its concluded that BRB can effectively improve structures anti-seismic performance.