Effectiveness of the Buckling Restrained Brace in Steel Moment Frames in Afghanistan

Abstract

Abstract
This paper studies the seismic response behavior and seismic performance of unbraced Steel
Moment Frame Structure designed for seismicity of Kabul province and then it is assumed that
same design is subjected to the seismicity of Badakhshan province of Afghanistan by Time
History Analysis method. The validity of the concept of eliminating the compression buckling
failure mode of Buckling Restrained Brace by encasing it over its length in a steel tube filled
with concrete leading to similar performance under compression and tension is investigated
from the result of Nonlinear Dynamic Time History Response Analysis. Recent developments
have caused population growth concentrated in major cities of Afghanistan, building owners
and engineers have no option other than going for vertical building structures. As Afghanistan
is located in a seismically active zone, these structures are subjected to collapse or large lateral
displacements due to strong earthquake ground motions. Afghanistan has newly adopted
standards for the design of steel structures, but there is no steel building designed with a BRB
system yet in the country. Therefore, in this research, an unbraced steel office building is
designed for Kabul city by Afghan Structural Code (ASC), and also it is assumed to be
constructed in Badakhshan province with the highest seismic hazard in the country. Two
patterns of BRBs with varying core cross-section areas have been used in order to find the
optimum cross-section area. Dynamic Eugene value analysis and nonlinear dynamic response
analysis are carried out to determine the dynamic characteristics and seismic performance.
For response analysis, artificially simulated ground accelerations of Badakhshan and Kabul
provinces, which have the phases of recorded Seismic waves of (El Centro NS) are adopted to
the response spectrum prescribed by Afghan Structural Code. From the result of response
analysis, it is concluded that the response of the special moment frame structure in terms of
maximum story drift angle is within the code limitation in Kabul province and more than the
code limitation for Badakhshan province. With employing Buckling Restrained Braces in
Badakhshan province, the energy dissipation and damage prevention capacity of unbraced
frame is greatly improved and the response of the frame braced with-BRB is mostly within the
allowable range of the Afghan Structural Code.