Report - PEER - University of California, Berkeley

their assigned strength, without affecting the initially assumed stiffness, a quiteunrealistic assumption not only for steel structures but also for reinforced concreteones. Since in fact stiffness varies with assigned strength the design becomesiterative. However, this interrelation makes it possible to reduce eccentricity byjudiciously assigning the reinforcement ratios. Procedures aiming at finding thestrength distribution among the lateral force resisting elements that would minimizetwist are described in section 3.2.3.1 Shear Demand on Torsionally Flexible 10-Storey Wall Structure: A CaseStudyThe studied torsionally flexible mono-symmetric 4-wall 10-storey system is shownschematically in Fig.2. The wall properties are given in Table 1. The stiffnesseccentricity = 25.6% of width. Storey weight = 3000kN. This structure was excited by10 of the 20 SAC 10/50 Los Angeles records with 5% Rayleigh damping in the 1stand 4th modes. Cyclic pushover analyses with inverted triangular loading and with apoint load located so as to account for base shear amplification due to higher vibrationmodes were also carried out. Finally, 1-storey 2-DOF models having the same massand 1st two natural periods as the full structure were also excited by the sameensemble of records.Figure 2. Monosymmetric 10-storey 4-wall model.374