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Abstract:
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A significant number of short-to-mid height RC buildings with wide beams have been constructed in areas of
moderate seismicity of Spain, mainly for housing and administrative use. The buildings have a framed structure
with one-way slabs; the wide beams constitute the distinctive characteristic, their depth being equal to that of the
rest of the slab, thus providing a flat lower surface, convenient for construction and the layout of facilities.
Seismic behavior in the direction of the wide beams appears to be deficient because of: (i) low lateral strength,
mainly because of the small effective depth of the beams, (ii) inherent low ductility of the wide beams, generated
by high amount of reinforcement, (iii) the big strut compressive forces developed inside the column-beam
connections due to the low height of the beams, and (iv) the fact that the wide beams are wider than the columns,
meaning that the contribution of the outer zones to the resistance of the beam-column joints is unreliable because
there is no torsion reinforcement. In the orthogonal direction, the behavior is worse since the only members of
the slabs that contribute to the lateral resistance are the joists and the façade beams. Moreover, these buildings
were designed with codes that did not include ductility requirements and required only a low lateral resistance;
indeed, in many cases, seismic action was not considered at all. Consequently, the seismic capacity of these
structures is not reliable. The objective of this research is to assess numerically this capability, whereas further
research will aim to propose retrofit strategies. The research approach consists of: (i) selecting a number of 3-
story and 6-story buildings that represent the vast majority of the existing ones and (ii) evaluating their
vulnerability through three types of analyses, namely: code-type, push-over and nonlinear dynamic analysis.
Given the low lateral resistance of the main frames, the cooperation of the masonry infill walls is accounted for;
for each representative building, three wall densities are considered. The results of the analyses show that the
buildings in question exhibit inadequate seismic behavior in most of the examined situations. In general, the
relative performance is less deficient for target drift CP (Collapse Prevention) than for IO (Immediate
Occupancy). Since these buildings are selected to be representative of the vast majority of buildings with wide
beams that were constructed in Spain without accounting for any seismic consideration, our conclusions can be
extrapolated to a broader scenario. |
