Code Provisions to Contain Floor Flexibility in RC Buildings Under Earthquake Shaking

Code Provisions to Contain Floor Flexibility in RC Buildings Under Earthquake Shaking—An Elastic Study

Tamizharasi, G. / Harshit, M. S.

Typically, floor diaphragms of RC buildings with a long and narrow plan or poor plan geometry, large openings, and inadequate vertical lateral load-resisting elements exhibit huge in-plane flexibility; which leads to unforeseen drift patterns and force distribution among structural elements. Building code provisions independently define rigid diaphragm by placing upper limits on (i) the plan aspect ratio, (ii) the percentage area of openings, and (iii) the relative diaphragm displacements, with additional remarks on plan geometry. Therefore, this study aims to understand the combined effects of these parameters and check the applicability of these provisions given in building codes. Thus, parameters influencing floor flexibility are identified based on relative diaphragm displacements. Equivalent Static Analysis ESA is conducted on the spectrum of rectangular building configurations consisting of RC Moment Frame and RC Structural Wall buildings having: (a) rectangular plan geometry, (b) slab with openings, (c) structural walls located at the periphery, and (d) varying height, respectively. Results agree with Linear Time History Analysis THA. Floor diaphragms of buildings with RC Frames are always rigid and those with RC structural walls (located especially at edges) show significant in-plane floor deformation under earthquake shaking. Also, defining rigid floor diaphragm solely based on plan aspect ratio, the percentage area of openings and relative diaphragm displacements may not ensure diaphragm to behave rigidly; the relative diaphragm displacements exceed the prescribed limits even if the plan aspect ratio or percentage area of opening is within the limits, especially in buildings with structural walls located at the periphery. Building code provisions (like India) must revise the criteria by satisfying all three conditions collectively. For a fixed relative diaphragm displacement, upper limits are placed on the plan aspect ratio and percentage area of the opening.