Stiffness Reduction Factor for Flat Slab Structures under Lateral Loads

Effective beam width model (EBWM) has been widely used for predicting lateral drifts and slab moments in flat slab structures under lateral loads. As the slab moment due to lateral loads increases, slab stiffness decreases due to crack formation. The accuracy of the EBWM strongly depends on how the reduced slab stiffness is estimated. For this purpose, this study developed equations for calculating slab stiffness reduction factor (β) by conducting nonlinear regression analysis using stiffness reduction factors estimated from collected test results. The slab stiffness reduction factor (β) is defined as a ratio of reduced slab stiffness due to crack formation to the stiffness of the uncracked slab section. For verifying the proposed equation, the lateral stiffness of two slab–column connection specimens tested by the writers was compared with the lateral stiffness calculated using the EBWM with the proposed stiffness reduction factor. Further, two flat plate specimens having two continuous spans were also considered for verifying the proposed equations for β.