Investigating effects of boundary conditions on the evaluation of R-factor of un-braced steel frames

Abstract EN

Design of Structures to resist seismic load depends on the theory of dissipation in elastic of energy that already exists in response modification factor ‘‘R-factor’’.

The main problem in codes gives a constant value for R-factor, since change in boundary conditions of building change in behavior of steel frame structures and that effect on R-factor.

This study is an attempt to assess overstrength, ductility and response modification factor of un-braced steel frames under change in boundary conditions as change in the direction of strong axis of column and support type beside to variation in story and bay number to be 9 frame and each frame has 8 different boundary conditions as sum of 72 case for analysis.

These frames were analyzed by using nonlinear static ‘‘pushover’’ analysis using SAP2000 program.

As a result of this study R-factor does not has a constant value, when change in boundary conditions R-factor directly changes, minimum value of 8 boundary conditions is close to the code value that is mean the code is more conservative and give a large factor of safety.

Ductility reduction factor increases with increasing number of story for all boundary conditions, but overstrength has different rule.

Response modification factor, overstrength factor and ductility reduction factor decrease when fundamentals period increasing for the studied frames.