| In this study, the cracking behaviour of RC panels under a two-way loading condition is investigated analytically and experimentally. A modified FE bond layer model is introduced and shown to be much simpler to define, and yet, more accurate than perfect bond or link element bond models. FE analysis suggests a bi-linear curve for approximating the distribution of bond stresses at stabilized cracking. Several FE parametric studies are performed on a one-way tension member to obtain peak shear bond stresses, concrete tensile stresses due to internal restrained shrinkage, splitting tensile stresses caused by radial bond stresses, and the reduction in bond strength caused by longitudinal splitting cracks. The FE analysis of flexural beams suggests a new factor for estimation of the depth of effective tension area, which is defined through FE parametric study. In the experimental phase, three medium-scale RC panels are subjected to direct tension in one direction and bending in the perpendicular direction. The collected data consist of applied loads, steel and concrete stresses, crack propagation sequence, crack pattern, crack width, total elongation, and leakage observations. The crack pattern is mainly influenced by the shape of reinforcement mesh due to the presence of splitting tensile stresses. The formation of diagonal cracks depends on principal stresses that can be influenced by reinforcement ratio, ratio of loads in two directions, and clear concrete cover to bar diameter ratio. The bond strength is significantly weakened by the formation of orthogonal cracks along reinforcing bars. The crack width is increased under repeated loading especially at the first cycle. Residual crack widths remain in place even after complete unloading. Observations indicate that the water leakage is influenced by the crack width gradient. Finally, it is shown that one-way crack prediction models underestimate the crack width of two-way panels. A new set of analytical equations is developed for the prediction of cracking load, minimum and maximum spacing of cracks, and maximum crack width in a two-way panel. These equations are shown to predict the cracking behaviour of the tested panels more accurately than any other previously proposed model. |
