Thirteen specimens were experimentally tested under single midspan concentrated loads
to study the shear behavior of lightweight concrete (LWC) and normal weight concrete
(NWC) deep beams with web openings. In this research, the term LWC refers to the concrete
obtained by partially replacing aggregate by polystyrene foam balls not the concrete
containing lightweight aggregate. This resulted in a weight reduction of LWC beams in this
research by approximately 30% compared to NWC compartments. The studied variables
were the dimensions and location of openings, transverse reinforcement ratio, and shear
span to depth ratio (a/d). It was found that the overall shear behavior and failure mode for
LWC deep beams are comparable to those of the NWC specimens. This is very promising
and encouraging to build lighter deep beams of similar structural behaviour as that of NWC
deep beams. Dimensions of the openings have a significant effect on the behaviour of
failure and shear strength of LWC and NWC deep beams. It was found that increasing the
depth of the opening from 20 % to 40 % of the beam depth led to a reduction in the ultimate
load by up to 46.4 %. Finite element modelling of the test beams was carried out to verify
numerical results versus experimental work and both were very well correlated. In
addition, a parametric study was conducted to assess the effect of internal stiffening around
openings in deep beams. The maximum enhancement in the shear capacity was
approximately 30 % for beams, internally strengthened by additional reinforcement on
the perimeter of openings compared to the beams without any reinforcement around the
openings. Strut-and-Tie model (STM) was carried out as a rational approach to predict the
shear behaviour of studied beams. It was found that STM underestimates the shear of the
studied beams compared to experimental results for different tested beams but the
agreement between both of them was acceptable. It is recommended that the depth of
opening should not exceed 20 % of the depth of the deep beam and if the depth of opening is
more than that or lies in the shear span it is highly recommended to strengthen the opening
internally by additional reinforcement around its perimeter. |
