Abstract:
In Bangladesh, use of burnt clay brick masonry as infill material for
exterior wall and interior partition wall in high-rise building frame is very
common. The frame-infill system is used throughout the world only for
architectural needs or aesthetic reasons. Present code of practice does not
include provision of taking into consideration the effect of infil!. It can be
understood that if the effect of infill is taken into account in the analysis and
design of frame, the resulting structures may be significantly economic.
This study has been undertaken to investigate the elastic behavior of
R.C high-rise frame with brick masonry infill subjected to lateral load. In
this investigation a 20-storied building with a lift core has been taken as a
reference structure. Finite element package (ANSYS 5.4) has been used for
two dimensional and three dimensional analysis of this building. Two
dimensional beam element has been used in modeling 2-D frame and beam
element in space has been used to model the 3-D frame. To model roof Slab
and Lift Core, elastic shell element was used. The infill panel in reinforced
concrete frame has been modeled in two different ways. In one way, the
panel is modeled as a homogeneous continuum considering perfect bond
between the frame element and the masonry. Secondly, an equivalent strut
is used to simulate the separation of infill panel from the surrounding frame
due to bond failure. A number of different cases have been considered for this finite
element study, these are (i) Bare frame (ii) Infill as equivalent strut (iii) Infill
as homogeneous continuum (iv) Infill as homogeneous continuum with
opening (v) Infill as homogeneous continuum with opening & soft story at
ground floor. In this study masonry infills are provided along the windward
direction and no out-of-plane infills are provided in the analysis. Lateral
loads (wind load) at different levels of the building have been calculated
according to the method specified in the Bangladesh National Building Code
(BNBC,1993).
A comparative study has been performed using results of the finite
element analysis for different cases. In all cases, deflection, bending
moment, shear force and axial force for columns and beams have been
studied. From the study it is observed that the stiffness of frames will be
significantly increased when masonry infill panels are considered for
stiffness computation. From this finite element study, it is found that due to
the presence of infill, the moment, shear, and axial force in the columns and
beams of the building frame reduces quite significantly. This study indicates
that an economy in building design can be achieved if the composition
action between building frame and infill panel can be fully utilized.
