Influence of Localized Beam Cracking Representation on Nonlinear Seismic Performance of RC Moment Frames

Cracking in reinforced concrete (RC) members is a key mechanism governing stiffness degradation and seismic response of structural systems. This study examines the influence of different beam-cracking modeling approaches on the nonlinear seismic behavior of RC moment-resisting frames. Three RC frames with ۳, ۶, and ۹ stories are analyzed under three modeling schemes: (۱) uncracked elastic model, (۲) code-based effective stiffness reduction model, and (۳) localized cracking model distributed along beam elements. In the localized formulation, stiffness degradation is defined in a position-dependent manner, allowing non-uniform reduction along the member length to better represent crack concentration in plastic hinge regions and mid-span zones. This overcomes a major limitation of conventional effective stiffness methods, which assume uniform stiffness reduction and cannot capture spatial damage distribution. Nonlinear static (pushover) and nonlinear time-history analyses are performed using Imperial Valley, Duzce, and Northridge ground motions within a nonlinear analysis framework. Results show that cracking representation significantly affects seismic response. Considering cracking reduces initial stiffness, increases fundamental period, and decreases base shear capacity. In the code-based model, base shear capacity decreases by up to ۳۲%, while roof displacement increases by ۲۱%, ۲۶%, and ۸% for the ۳-, ۶-, and ۹-story frames, respectively. The localized cracking model yields responses between the uncracked and code-based models and consistently predicts lower displacements than the latter. Crack distribution also significantly influences bending moments, plastic hinge formation, and energy dissipation. Overall, the localized cracking model provides an improved representation of stiffness degradation effects and a practical simplified framework for nonlinear seismic assessment of RC frames.

کلیدواژه ها:

Reinforced concrete cracking ، Localized stiffness reduction ، seismic performance ، Nonlinear static analysis ، Nonlinear dynamic analysis