Behavior of concentric flat plate-column assemblies exposed to ambient and high temperature conditions

Flat plate-column connection is one of structural joint that is widely used worldwide, because of its low cost compared to other slab types. However, this type of connection is under significant risk of brittleness in punching shear failure, which is incompetently understood as the flexural behavior. The problem is aggravated when the structure exposed to high temperature. One of the commonly suggested solutions to the minimize the brittleness effect of the punching shear is using fibrous concrete. The shear failure of the slab-column connection under fire conditions depends mainly on the degradation of the material properties in addition to the indirect structural effect. This thesis aims to investigate the behavior of flat plate-column assembly, made from plain and fibrous concrete under ambient and fire conditions. The experimental work is divided into two main stages. In the first stage, twenty one slabs made from ECC of different types of synthetic fibers (NM, PVA, and PP) were compared with slabs made from plain concrete and steel fiber reinforced concrete. Moreover, in three other slabs, the critical D-zone was poured with ECC-NM, while plain concrete was used outside the zone. The results showed that the addition of steel fiber provides high improvement in the slab behavior. Therefore, the steel fiber reinforced concrete was used in the second stage. Twenty slabs were constructed and tested to investigate the residual punching shear strength of high-strength steel-fiber reinforced concrete flat plates after exposure to high temperatures. Four levels of high temperatures of 150, 300, 450, and 550 °C were adopted and three fiber contents of 0.75, 1, and 1.25% by volume of concrete were used. The experimental results were discussed and compared with results from previous works and existing formulas of some international codes of practice. In addition, regression formulas based on the current research's experimental results were suggested. Although extensive literature is available on the punching shear strength of fibrous concrete at ambient conditions, to the best of the authors' knowledge, there is no experimental work on the residual punching shear strength of steel-fiber reinforced concrete after high temperature exposure. Finally, the heat transfer and the mechanical behavior of the specimens in the second stage were simulated in sequentially analysis process using the general purposes finite element software ABAQUS 6.14-1. Key Words: Slab, Punching shear, Fire, Steel fiber, Flat plate - column connection