Analyses Of Dynamic Performances And Low-Cycle Fatigue Behavior Of Concentrically Two-Story X-Braced Frames

Interacting system of concentrically braced and moment resisting frames is one of the commonly used dual systems resisting lateral forces. It is widely used in tall buildings as an effective and economic seismic structure system. While this system is considered inadequately in design, it may suffer extensive damage under strong ground motion during the seldomly occurred earthquakes. If we employ chevron braced or V-braced members in the structure, will cause rather large unbalanced force on the frame beam intersected with braced members under the strong earthquake and will cause large quantity of steel in use. How-ever,the adoption of two-story X-braced members can avoid these shortcomin-gs. Therefore , according to the comprehensive consideration of the anti-earthquake design, various performance of two-story X-braced frames will be analyzed and studied mainly in the paper.The slenderness ratio and the manner in checking bearing capacity of the bra-cing member are key factors to the seismic performance of this system. Our nati-onal codes are keeping being strict hard on the slenderness ratio limitations of br-acing members, and they strengthen the bracing members in checking their be-aring capacity. This measure may lead to larger seismic response. Experimental researches also indicate that the smaller slenderness ratio,the shorter fatigue lif-e for the bracing member.Influences on structure caused by variation of slenderness ratios of bracing members have been analyzed in full in the paper. In addition,the performance of the structures with strengthened bracing members and those with unstrengthe-ned bracing members have been analyzed coarsely.Concerning bracing members'fatigue resistance under strong earthquake, structures whose bracing members'slenderness ratios is different have been com-pared and analyzed. We find that fatigue damage of bracing members will decr-ease quickly if bracing members'slenderness ratios increase,decrease when the height of the floor of bracing member increases. Fatigue damage of bracing members may be increase suddenly in a few floors.Finally, stiffness, acceleration of the top floor, displacement and shear of structure models with hinged bracing members is compared to those of structure models with rigidly jointed bracing members through static and dynamic analys-es of twenty-four-floor models. The results discover that there no difference bet-ween stiffness of structures hinged with bracing members and that of those join-ted ridigly with bracing members in the elastic stage. However,not only the latter mod-els'stiffness is larger than the former,but also their dynamic perform-ance is different in the plastic stage.