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SUMMARYThe viability of most analytical approaches developed to predict the inelastic response of Reinforced Concrete (RC) structures requires the load-deformation relationship to have a positive slope. In many realistic cases the slope is not positive. When this happens, most analytical approaches consider the maximum point as the failure point or use unrealistic material laws, e.g., the assumption of a positive slope when it really is negative. Hence, there is a need to develop a new analytical approach which recognizes loaddeflection relationships which have ascending and descending branches. A method based on the impulse momentum principle and the resistance force (IMR) of an RC structure is developed. The resistance force vector {R(t)} is used in place of the stiffness approach. The material non-linearity of RC systems can be elegantly accounted for in the (R(t)} vector. An examination of numerical properties of the IMR method shows that stability and convergence are dependent on a time step length ratio. Applications of the IMR method which predict the inelastic seismic response of RC structures are performed.

A framing system considered for a shallow-floor building to be used in seismic zones has wide shallow beams with sufficient stirrups. Two-way slab design is used for this system. This shallow-floor system is likely to have good ductile behavior as the beams deform inelastically. The lateral resisting system is designed with a 'strong column-weak beam' ductile frame configuration so that the hinging zones occur within the beams away from the face of the column. The beams will be substantially wider than the columns. The joint and hinge regions must have sufficient tie and stirrup reinforcement. P-delta effects should be considered but are not serious when drifts are controlled. The survivability of the ductile shallow-floor building under moderate earthquakes is studied. The serviceability, e.g., story drift, of the building is of concern. The usual case is that the building is likely to satisfy code requirements for base shear resistance and corresponding story drift limitation. Contrary to code prediction, the performance under a moderate earthquake often yields large story drifts which may severely damage the non-structural systems.