Abstract: Open ground storey with floating columns is a typical feature in the modern multistory constructions in urban India. Such features are very much undesirable in buildings built in seismically active areas. The present study proposes a feasible solution to mitigate the effects caused due to non-uniformity of stiffness and discontinuity in load path and to simultaneously hold the functional use of the open storey particularly under the floating column, through a combination of various lateral strengthening systems. An investigation is performed on an example building with nine different analytical models to bring out the importance of recognising the presence of open ground storey and floating columns. Two separate analyses on various models of the building namely, the equivalent static analysis and the response spectrum analysis as per IS: 1893-2002 were performed. Various measures such as incorporation of Chevron bracings and shear walls, strengthening the columns in the open ground storey, and their different combinations were examined. The analysis shows that, in comparison to two short ones separated by interconnecting beams, the structural walls are most effective when placed at the periphery of the buildings and used as one long structural wall. Further, it can be shown that the force transfer from floating columns becomes less horizontal when the Chevron Bracings are placed just below them, thereby reducing the shear forces in the beams on which the floating column rests.
Abstract: Building code-related literature provides
recommendations on normalizing approaches to the calculation of
the dynamic properties of structures. Most building codes make a
distinction among types of structural systems, construction material,
and configuration through a numerical coefficient in the
expression for the fundamental period. The period is then used in
normalized response spectra to compute base shear. The typical
parameter used in simplified code formulas for the fundamental
period is overall building height raised to a power determined from
analytical and experimental results. However, reinforced concrete
buildings which constitute the majority of built space in less
developed countries pose additional challenges to the ones built with
homogeneous material such as steel, or with concrete under stricter
quality control. In the present paper, the particularities of reinforced
concrete buildings are explored and related to current methods of
equivalent static analysis. A comparative study is presented between
the Uniform Building Code, commonly used for buildings within
and outside the USA, and data from the Middle East used to model
151 reinforced concrete buildings of varying number of bays, number
of floors, overall building height, and individual story height. The
fundamental period was calculated using eigenvalue matrix
computation. The results were also used in a separate regression
analysis where the computed period serves as dependent variable,
while five building properties serve as independent variables. The
statistical analysis shed light on important parameters that simplified
code formulas need to account for including individual story height,
overall building height, floor plan, number of bays, and concrete
properties. Such inclusions are important for reinforced concrete
buildings of special conditions due to the level of concrete damage,
aging, or materials quality control during construction.
Overall results of the present analysis show that simplified code
formulas for fundamental period and base shear may be applied but
they require revisions to account for multiple parameters. The
conclusion above is confirmed by the analytical model where
fundamental periods were computed using numerical techniques and
eigenvalue solutions. This recommendation is particularly relevant
to code upgrades in less developed countries where it is customary to
adopt, and mildly adapt international codes.
We also note the necessity of further research using empirical data
from buildings in Lebanon that were subjected to severe damage due
to impulse loading or accelerated aging. However, we excluded this
study from the present paper and left it for future research as it has its
own peculiarities and requires a different type of analysis.
Abstract: As the world move to the accomplishment of Performance Based Engineering philosophies in seismic design of Civil Engineering structures, new seismic design provisions require Structural Engineers to perform both static and dynamic analysis for the design of structures. While Linear Equivalent Static Analysis is performed for regular buildings up to 90m height in zone I and II, Dynamic Analysis should be performed for regular and irregular buildings in zone IV and V. Dynamic Analysis can take the form of a dynamic Time History Analysis or a linear Response Spectrum Analysis. In present study, Multi-storey irregular buildings with 20 stories have been modeled using software packages ETABS and SAP 2000 v.15 for seismic zone V in India. This paper also deals with the effect of the variation of the building height on the structural response of the shear wall building. Dynamic responses of building under actual earthquakes, EL-CENTRO 1949 and CHI-CHI Taiwan 1999 have been investigated. This paper highlights the accuracy and exactness of Time History analysis in comparison with the most commonly adopted Response Spectrum Analysis and Equivalent Static Analysis.