Crack analysis of reinforced concrete two-way slabs

Hossin, Mohamed A. A. (2007) Crack analysis of reinforced concrete two-way slabs. Masters thesis, Memorial University of Newfoundland.

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Abstract

Offshore structures are exposed to harsh environmental conditions, including the structure's existence in the splash zone as well as exposure to seawater and sea spray. The design of offshore structures is controlled by mandatory design codes to ensure structural safety and integrity. The main objective of this study is to investigate the cracking criteria for offshore structures and develop a rational numerical model in order to predict crack width and spacing of high strength concrete under flexural sustained service loads. -- An experimental investigation is designed to study the cracking behaviour of high strength concrete plates. Eight two-way reinforced concrete specimens with different thick concrete cover and bar spacing were tested in the structural laboratory at Memorial University of Newfoundland under flexural loading. The tests specimens are divided into three groups. The first two groups are heavily reinforced and designed to fail under punching shear mode. The first group (Series I) is designed to investigate the effect of concrete cover on the crack width and crack spacing. The second group (Series II) is designed to investigate the effect of bar spacing on the crack width and crack spacing. The third group (Series III) is designed to investigate the effect of different modes of failure on the crack width and crack spacing for two-way reinforced concrete slabs. The structural behaviour of the test slabs with regards to deformations, strains, crack patterns, crack width and mode of failure was examined. -- It has been found that the effect of increasing concrete cover from 30 mm to 60 mm of (Series I) increases the crack spacing by 38%. The crack spacing of (Series II) was increased by 28%, when the bar spacing increased from 1 50 to 250 mm. The test results revealed that the relation of the crack width versus steel strain can be represented by a straight line up to a limiting steel strain of 0.001 to 0.0015 for most of the test slabs. This strain value corresponds to a reinforcement stress equal to 200 MPa to 250 MPa (0.50-0.63fy). -- The theoretical investigation includes two phases. The first phase is evaluating the suitability of the existing crack width and crack spacing expressions for structures with large concrete covers. The experimental test results of all test slabs confirmed the recommendation of an existing equation. The second phase includes the development of a numerical crack analysis model based on tension chord method. The developed proposed expression to calculate the crack width is based on the modified assumption of the tension chord method. A second model was recommended based on the fracture energy principles to estimate the crack width. The modified assumptions deal with estimating the tensile strength, bond strength and the active tension concrete area. The newly developed expressions provided good results for high strength thick concrete cross sections with large concrete cover.

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