コンクリートはり部材断面の曲げ終局限界点に関する研究 : (その1) 各種終局域指標点と提案する曲げ終局限界点の存在メカニズム

抄録

Successful evaluation of deformation capacity of concrete flexural members and techniques to make the members ductile are essential to seismic design methods based on energy absorption capacity of concrete structures. Design index points and equations, however, to calculate ultimate deformation capacity of the members are not established, so that, ductility of the members and the structures is not utilized in current seismic design methods. The object of this investigation is to propose and present distinctly a new ultimate limit index point in the softening branch of moment-curvature relation for more reasonable and effective estimation of ductility of partially prestressed concrete beams as general concrete flexural members. Following conclusions are obtained from the investigation. (1) Mechanism of existence of two ultimate limit index points proposed herein, i.e. points Lc and Lp, are explained physically. The point Lc, which is caused by strain softening characteristics of concrete, is defined as that at which the maximum total tensile force occured in prestressed and ordinary reinforcements (T) (=total compression force in concrete (C)) takes place in a flexural section, i.e. [C=T] max., or at which strain in the tendon reaches the maximum value. The point Lp is defined as that at which fracture of tendons occures. (2) The points Lc and Lp are very useful to evaluate the deformation capacity taking account for falling behavior of the moment-curvature relations of concrete flexural members because those two points always appear sufficiently in the stage of large deformation after the maximum moment which is differed from other limit index points in ultimate state proposed previously.