ABSTRACT
The limit state design procedure of reinforced concrete elements has undergone major revision in recent times with more emphasis toward a performance-based engineering approach. This design approach demands a thorough understanding of axial force-bending moment (P-M) yield interaction of elements, for moment-resistant reinforced concrete (RC) frames under seismic loads, in particular. Current design methodologies, both recommended by international codes and employed by practicing engineers, include desirable features of ultimate strength and working stress procedures as well ensure a ductile response. In this chapter, detailed mathematical modeling of P-M yield interaction of RC rectangular beams based on Eurocode currently in prevalence is presented; six subdomains defining the boundary of P-M yield interaction are classified. A complete set of analytical expressions is proposed and also illustrated through relevant examples. Results obtained for the failure interaction curve of RC rectangular sections under P-M yield interaction show that by adopting Eurocode strain limits, the boundary curve is divided into two main parts, namely, (1) tension failure with weak reinforcement resulting in yielding of steel and (2) compression failure with strong reinforcement resulting in crushing of concrete. The curves are given in analytical form for every feasible coupling of bending moment and axial force. Advantageous use of the proposed P-M interaction for nonlinear seismic analysis is demonstrated in the subsequent chapters; also the developed boundary of different subdomains is verified for a plastic flow rule. With the help of the presented mathematical model and proposed expressions for P-M yield interaction, the designing of new structures and assessment of existing RC structures can be performed with better understanding and improved accuracy.
