تاريخ مجلس الدراسات العليا

2023-02-05

اسم الطالب

خولة خالد حسن الجعار

ملخص الرسالة

U-boot slab system is a procedure used to construct two-way slabs and forming an I-Shaped section in both directions. In this research light weight concrete was used in the first stage to form lower flange, then normal concrete was used to form the web and top flange. Four slabs with dimensions (1.58 x 0.7 x 0.25) m were casted and cured for 28 days. The first slab was casted with normal concrete only (NC), the second with light weight and normal concrete without shear links (LN-NSL), the third slab was made by light weight concrete and normal concrete with shear links (LN-SL) also the fourth slab as well. The results showed that the ultimate load of the normal weight concrete was larger than that for the one that combined between lightweight concrete and normal concrete by a percent of 27.7%, it was also more brittle than it. It could be explained due to the inhomogeneous between the two concrete layers and the reduction of the modulus of elasticity in light weight concrete, this is resolved by adding a shear link where the result of the experimental work showed that the ultimate load for (LN-SL) is larger than that for (LN-NSL) and (NC). The use of lightweight concrete together with normal-weight concrete was very effective, it increased the value of load that the slab can carry by 35.5% more than the normal concrete, in one condition, and its required to take into account to the inhomogeneous between the concrete layers. The heat was responsible for reducing the amount of the ultimate force that the slab could carry by a percent of 14.8%, also the heating resulted in reducing the ductility factor by a percent of 50.1% and brought the specimen to a more brittle altitude. For all slabs, the usual shear failure mechanisms comprised abrupt failure close to the support and the formation of a massive diagonal main fracture. Cracks appeared as flexural fractures at the mid-region and diagonal-web shear cracks close to the support before to collapse. The bonding between the rebar and the lightweight concrete is reduced by a factor ranging from 1.3 to 1.45, as established by the ACI requirement for concrete bonding and development length.