Papers by Author: Yan Gang Zhao

Abstract: Ductile frame structures are generally designed with column over-design factors (COF) to assure plastic hinges occurring in all beams and avoid unpreferable failure modes. In order to avoid story mechanisms of frame structure constructed with elastic-plastic materials, target COF has been investigated where the relative occurrence probability of most likely story mechanism is limited within a specific tolerance. In the present paper, the concept of basic and optimum column over-design factor for avoiding story mechanism are proposed and the value of them for multi-span multi-story ductile frames are presented based on a comprehensive investigation on the occurrence order of story mechanisms. The basic COF is defined as the critical value that the preferable failure mode and unpreferable failure mode are with the same failure probability, and it is the low limit assuring the entire beam-hinging pattern prior to story mechanisms. For a structure designed with a COF less than basic COF, the plastic hinges are easier to occur in partial stories to form story mechanism. The optimum COF is the most effective and economy COF to enhance the safety of structure, and it is resulted from the shift of priority of plastic hinges in different stories. The relationships between the basic and optimum COF with calculation parameters are also analyzed in this paper.

Abstract: In ultimate asseismic design of ductile frame structures, plastic deformation and plastic hinge are generally permitted, and some preferred failure modes are often selected. It is an important problem that whether the designed structure collapses according to the designed failure mode, because of the large uncertainties included in external loads and member strength. In this paper, an identification procedure of failure modes for frame structures is developed, and the likely collapse modes of frame structures under uncertain load and member strength are investigated under assumption of normal distributed and non-normal distributed external loads and member strength. It is found that the occurrence order of likely collapse mode is much influenced by the distribution of the random variables. The occurrence order of collapse modes for column over designed structures are investigated and it is found that the increase of column over-design factor can effectively avoid the story collapse mode in probabilistic means.

Abstract: Analysis of dynamic behavior of soil-structure interaction (SSI) is a complicated problem due to the complexities of soil behaviors and dynamic analysis. It is difficult to solve SSI with analytical methods. However, numerical methods with highly developed computer technique are efficient. Based on the advanced nonlinear finite element analysis software MSC.Marc, SSI on loess ground is studied. An approach for the application of MSC.Marc in SSI analysis is presented and an example is given. Hyperbolic soil constitutive relationship and viscous boundary conditions are adopted in the soil model. Moreover, contact between the embedded columns and the adjacent soil is considered. Response spectrum analysis of the result is carried out. Some conclusions about the seismic response of soil-structure system under different soil stiffness and different soil-layer thickness conditions are given. A new way of analyzing SSI for loess ground is provided.

Abstract: This paper focuses on an experimental investigation and theoretical analysis of different types of RC shear wall with the profile steel braces in two side columns and diagonal profile steel braces of walls subjected to applied repeated cyclic loads. Fifteen RC shear walls with different shear span ratio are tested and their aseismic charactertics are studied. The effect of profile steel bracings on failure property, bearing capacity, ductility and hysteretical characteristic of shear wall is investigated based on experimental results. It is shown that adding the profile steel braces on the boundary column and inner of walls can obviously enhance the ultimate strength of specimens and improve their aseismic characteristics. Finally, the mechanical model of the shear wall is presented and the formulae for calculating the load-carrying capacity are developed. Numerical analyses indicate that the theoretical results agree well with those from experiments.