Civil Insight: A Technical Magazine Volume 3 | Page 46

Karki G. and Bhatt M.R.
Civil Insight (2019) 45-50
designed to have a relatively higher strength than that of a beam, which is known as strong column-weak
beam concept. The concept has been adopted for a long time for seismic design of structures. In countries
like Nepal, the seismic design shall be done intensively, since the structures are always in a threat of
collapsing due to high seismic force.
The strong column-weak beam concept is explained in Fig. 1 with moment equations, as expressed in Eqn
(1) and Eqn (2).
Fig. 1. Strong column-weak beam provision
For strong column-weak beam concept,
σ … ൒ ȗ σ „ ሺͳሻ
and σ … ൌ …–  ൅  …„ ƒ†σ „ ൌ „Ž  ൅  „” ሺʹሻ
where  … = Moment capacity of column,  „ = Moment capacity of beam,  …– = Moment capacity of column
at the top,  …„ = Moment capacity of column at the bottom,  „Ž = Moment capacity of beam at left,  „” =
Moment capacity of beam at right,  = Multiplication factor
2) Methodology
Two buildings, one 3-storied and other 9-storied, were modeled to represent a lower-rise and medium-rise
building. The models of the buildings are shown in Fig. 2.
The grades of concrete and steel were taken M20 and Fe415 respectively, and the bay dimension was kept
3.5m in both X and Y directions. The story height was kept 3m. A slab having a thickness of 127mm was
taken, which also acts as a diaphragm to the model. SAP2000 (SAP2000, 2018) was used for modeling and
analysis approaches.
Moreover, response spectrum analysis was done for fixing beam rebar and column size. From the response
spectrum analysis, beam rebar was selected. MATLAB (MATLAB, 2015) coding was done to calculate
rebar size of the column for a particular cof, then different columns are modeled for different joints to satisfy
particular column overdesign factor. Default auto hinge P-M2-M3 and M3 were assigned to both ends of
the column and the beam. The numerical value of hinge length was taken as 5% of the length of the
respective beam or column. Further, static pushover analysis was carried out to obtain collapse mechanism
as per ATC-40.
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