Mass Distribution Of Structure Research Articles

A mode contribution ratio method for seismic analysis of large-span spatial structures

The structural forms of large-span spatial structures can be characterized by the dense distribution of their natural frequencies, and their vibration subjected to seismic loads is three-dimensional. There are many modes that contribute to the seismic response. The high-order modes typically dominate. The mode superposition dynamic analysis method used for seismic design of spatial structures requires a criterion to determine the dominant modes. The criterion for tall buildings is not applicable for spatial structures; instead, we have proposed the mode contribution ratio method for the selection of the dominant modes of spatial structures subjected to seismic loads. A set of 18 typical cases of different single-layer spherical lattice shells was used to verify the validity of this method. The following conclusions can be drawn: First, the method for combining the first thirty modes to calculate the seismic responses specified in the Technical Specification for Space Frame Structures is not accurate and is not applicable to spatial structures. Second, the mode contribution ratio method can be used to choose the dominant modes of spatial structures. Third, the mode contribution ratio is physically different from the effective mass ratio. Especially when the structural mass distribution is uneven, the two ratios are different, and the mode contribution ratio is more precise in calculation of the seismic responses of spatial structures.

Estimation of Tension Force in Short Hangers Using Added Mass Method

For short hangers, the influence of flexural rigidities and boundary conditions on tension measuring cannot be neglected. But there has no effective method to precisely calculate hanger tension considering the two parameters. This paper proposes the Added Mass Method (AMM) to simultaneously identify the tension, flexural rigidity and boundary condition of short hangers. In this method, the effect of mass distribution of structure on natural frequencies has been studied to add extra calculation conditions for establishing the eigenvalue equation set. The method of Genetic Algorithm (GA) with adaptive crossover and mutation rate is used to solve the equation set quickly. The results provides that the AMM is a high-accurate field testing technology in tension measurement for short hanger of arch bridge.

強震を受ける2層鋼構造建物で塑性変形が卓越する層を予測する方法

The objective of this paper is to establish criteria using which one can predict the story where plastic drift dominates in two-story steel building under strong ground motion. The dynamic response analyses were conducted for Elasto-Plastic and Rigid-Plastic models. The following conclusions are obtained for the response of Rigid-Plastic model. 1) If the shear coefficient of the 2nd story exceeds the base shear coefficient, the plastic drift occurs only in the 1st story. 2) Otherwise, the plastic drift occurs also in the 2nd story. The story of which plastic drift dominates can be predicted considering the story shear coefficient, the peak ground acceleration and the mass distribution of structure as shown in Fig. 12. Similar conclusions are obtained for Elasto-Plastic model if the story shear coefficients are small enough.