Abstract:
Bangladesh is situated in a seismically active region. Part of the country extended
from Sylhet to Chittagong is in the high seismic zone whereas Dhaka lies in the
moderate seismic zone. Major metropolitan cities of our country are under serious
threat because of inadequacies in design and construction of structures. A lot of
multistoried buildings have already been built in order to fulfill the ever increasing
demand of urban population. Bangladesh National Building Code (BNBC) proposes
equivalent static load method to design the buildings; however a seismic event will
result in damaged structure, performance of which cannot be evaluated from a static
analysis. Pushover analysis, a comparatively simplified nonlinear method involving
certain approximations and simplifications, is capable of predicting the damage extent
due to a seismic event. ATC-40 and FEMA-356 propose the pushover analysis
method in detail. In this thesis, an attempt has been made to demonstrate the validity
and efficiency of pushover analysis method of ATC-40 as incorporated in ETABS,
SAP2000 and SeismoStruct software. Performance of building frames designed as per
BNBC has also been evaluated against targeted performance levels for serviceability,
design and maximum earthquakes. Nonlinear time history analysis, although
complicated and time consuming, is a more rigorous method of modeling seismic
response of a structure. Both linear and nonlinear time history analyses have been
validated against published results using SAP2000 and SeismoStruct. The work also
studied the effectiveness of pushover analysis in comparison to more rigorous
nonlinear time history analysis with particular emphasis on the load pattern employed
in pushover analysis. Different load patterns have been used in pushover analysis and
uniform load pattern has been found to give better capacity curves that compare well
with nonlinear time history analysis. Performances have also been evaluated for 2D
frames designed according to BNBC using nonlinear time history. Well-known EL
Centro and Kobe earthquakes have suitably been scaled as per required Z value for
use in the analysis. A comparison of linear and nonlinear time history analyses have
been carried out to demonstrate the damage extent caused during an earthquake.
Similar pushover analyses carried out on 3-D six and twelve story building designed
according to BNBC show that they easily satisfy the ATC-40 local and global seismic
requirements. A building which is designed only for gravity load failed to satisfy the
requirements for serviceability and maximum earthquakes.
