Abstract:
Sway of reinforced concrete (RC) frames subjected to lateral load is an
important design parameter from serviceability point of view. A reasonably
accurate determination of sway still lags proper guideline. The widely
followed code of American Concrete Institute (ACI)as well as Bangladesh
National Building Code (BNBC)does not provide any specific guideline in
this regard. These codes only suggest the use of eff~ctivemoment of inertia
in plane frame idealization of RC frames using linear frame members and
homogenous material properties. Such approximation of RC frames may be
considered as over simplification by present day standards with the
availability of versatile computational techniques. Thus there is scope of
investigation and improvement of the methods for sway estimation.
In this thesis an investigation based on finite element (FE) modeling of RC
frame is carried out to study the sway behaviour of RC frame. In the FE
modeling the heterogeneity of RC is maintained by separate modeling of
concrete, steel and bond-slip mechanism using different elements. Thus the
RC frame is modeled as two-dimensional plane stress problem in which
bending as well as shear deformations are included. Flexural cracks are also
incorporated. Thus developing a finite element model that is closer to reality,
an extensive investigation is performed under various parametric conditions
to determine the deformation and sway characteristics of RC frames.
The investigation is based on two models. The first model consists of two
columns and a beam representing an exterior joint of a RC frame.
Investigation of deformation characteristics of this frame by FE modeling as
well as ACI guideline established the fact that ACI method differs from the
FE analysis in terms of deflections calculated. The second FE model was a
simple portal frame subjected to a lateral load. The same frame was analyzed
according to ACI guideline and the results are compared with those of FE
analysis. From the comparison, different parameters, which influence the
sway, are identified. It was observed that in most of the cases ACI method
tends to overestimate the sway by considerable amount, establishing the fact
that there is scope of modification in the ACI guideline.
In the last phase of the work investigation was carried out to identify
possible areas of modification in the ACI formula and proposals have been
made for calculation of effective moment of inertia using which more
reasonable estimation of sway can be made. Finally the performance of the
proposals are checked through an example.
