| Summary: | Thesis (Ph.D.)--Memorial University of Newfoundland, 2002. Engineering and Applied Science Bibliography: leaves 231-245 Strengthening of existing concrete structural elements is a viable means for improving the performance of such elements. Plenty of strengthening-related research work on beams and columns has been conducted. However, research work related to two-way slab strengthening is very scarce. Hence, there are academic and industrial needs to investigate such an issue experimentally and theoretically. This thesis is an attempt to fill the need for an experimental and theoretical research work on the punching shear and flexural strengthening of two-way slab system. -- The experimental phase of this research work includes testing of three groups of specimens. The first and second groups are composed of specimens strengthened using steel plates and steel bolts. The specimens of the first group are loaded centrally omV The second group of specimens is loaded centrally combined with lateral static or cyclic moment. The specimens of the third group are loaded centrally and strengthened with either Carbon Fibre Reinforced Polymer (CFRP) strips or Glass Fibre Reinforced Polymer (GFRP) laminates. -- The first group of specimens is used to develop and optimize a strengthening technique using the integration of steel plates and steel bolts. The effectiveness of four different configurations of steel plates and steel bolts are evaluated. The steel plates are assumed to act as horizontal flexural reinforcement representing an equivalent concrete drop panel. Moreover, the steel bolts are designed to act as vertical shear reinforcement, to transfer the horizontal forces between steel plates and concrete slab, and to confine the concrete between the steel plates. An average increase in the load capacity of 50% is achieved over that of the unstrengthened specimens. -- The second group of specimens is intended to evaluate the performance of recommended steel strengthening technique for specimens subjected to static or cyclic moments. The ultimate load capacity is increased by an average of 122% for specimens subjected to static moment compared to the unstrengthened specimens. For the specimens subjected to cyclic moment, the lateral drift is increased by 76% compared to the unstrengthened specimens. -- The third group includes specimens strengthened using CFRP strips and GFRP laminates for flexural-strengthening. In addition, This group includes specimens strengthened with CFRP strips and steel bolts for punching-shear strengthening. Utilizing CFRP strips and GFRP laminates contribute to an average increase of the flexural capacity of two-way slabs by an average of 36% compared to that of the unstrengthened specimens. However, a small average increase within 9% is achieved for the CFRP punching shear-strengthening. -- The theoretical work is composed of two parts: mechanical model and Finite Element Analysis (FEA). In the first part, a mechanical model is developed to analyze centrally loaded two-way slabs strengthened using steel plates. A concrete model that considers the biaxial state of stress of concrete as well as the confinement effect of steel plates is introduced. An iterative incremental mechanical model is used to determine the load carrying capacity and to evaluate the deformation characteristics of strengthened slabs at each load increment until failure. -- In the finite element analysis part, a full bond assumption is made between the concrete and both reinforcing steel bars and the strengthening FRP material. The comparison between the FEA and the experimental results showed an acceptable agreement. A tension-stiffening model is recommended for the concrete constitutive model taking into consideration the effect of strengthening material on the concrete behaviour in tension. In addition a regression equation based on the statistical approach of the Response Surface Methodology is recommended. The tension stiffening model is useful as an input in finite element packages and useful for classical approaches. In addition, The regression design equations can be used to provide simple design guide for engineers to predict the ultimate load carrying capacity of CFRP and GFRP strengthened two-way slabs.
|
|---|