Shoji Nakazawa

A Trial for Seismic Fragility Evaluation of a Large Lattice Dome Supported by Buckling Restrained Braces

A trial to evaluate the seismic fragility of a large dome supported by buckling restrained braces is performed and discussed in comparison with a dome supported by ordinary braces of tension-active capability. In order to evaluate the fragility depending on an adopted bracing system, the damage burdened to the dome structure due to earthquakes is calculated and interpreted as total fragility in terms of assumed seismic intensity varying from small to large earthquakes. The procedure for calculating the total fragility utilizes a simple event tree modelling, where the total fragility is counted considering the damage intensity to structural members, non-structural walls and ceilings. Based on a simple calculation, an example is illustrated to see how the buckling restrained braces are effective or not effective as an anti-seismic reinforcement method.

Estimation of Buckling Loads of Elliptic Paraboloidal Single Layer Lattice Domes under Vertical Loads

The present paper presents an effective evaluation method for elasto-plastic buckling loads of elliptic paraboloidal lattice domes for roof on a rectangular plan. The roofs are assumed as three way of single layer with a pin-support or a simple-support at all peripheries on a rectangular plan. The buckling loads are evaluated using a simple procedure adopting a linear buckling analysis, a knockdown factor for imperfection sensitivity, and column buckling strength for axial forces in terms of a generalized slenderness proposed in ordinary recommendations.

Free-form reticulated shell structures searched for maximum buckling strength

In this paper, a scheme of shape optimization is proposed for maximum buckling strength of free-form steel reticulated shells. In order to discuss the effectiveness of objective functions with respect to maximizing buckling strength, several different optimizations are applied to shallow steel single layer reticulated shells targeting rigidly jointed tubular members. The objective functions to be compared are linear buckling load, strain energy, initial yield load, and elasto-plastic buckling strength evaluated based on Modified Dunkerley Formula. With respect to obtained free-forms based on the four optimization schemes, both of their elastic buckling and elasto-plastic buckling behaviour are investigated and compared considering geometrical imperfections. As a result, it is concluded that the first and fourth optimization methods are effective from a viewpoint of buckling strength. And the relation between generalized slenderness ratio and appropriate objective function applied in buckling strength maxi...

ESTIMATION OF DYNAMIC DUCTILITY INDEX OF BRACES IN LONGITUDINAL DIRECTION OF SPORT HALLS BASED ON ENERGY BALANCE RESPONSE

The present paper discusses on a dynamic seismic performance index of structure, d Is, and a dynamic ductility index, d F, of a brace installed in the longitudinal direction of sport halls. Based on the result of the elasto-plasitc dynamic analysis depending on various input levels, d F and d Is are re-studied. As numerical parameters, a yield base shear coefficient of braces of substructure, Cy , and a capacity limit deformation of braces as well as hysteresis types are considered, and their effects on d F and d Is are investigated. Furthermore, the method of estimation for d F is proposed using an absorbed energy principle, and the validity of the proposal method is proven by comparing the responses of the dynamic response analysis with those based on the proposed method.