Structural Behavior of Weirs with One Bottom Circular Opening

Weirs are important hydraulic structures which are widely used for various purposes. Recently, the need for irrigation water increased due to the expansion of agriculture areas, and hence a need to increase the discharge capacity of canals evolved. In canals with weir systems, as in Fayoum region in Egypt, water distribution to sub-channels depends on their upstream water head (i.e. any change in water levels will reflect on the water distribution to sub-channels). Moreover, changes in the flow affect the water levels over weirs and consequently the backwater curves in their upstream. Hence, to increase the discharges, weirs should be reconstructed to ensure that the water levels over sub-channels' intakes would provide the required flows. As this would be very costly; it was decided to study, from hydraulic and structural points of view, the possibility of making openings in weirs, to increase the discharge running through them.
Aims: This research studies the structural behavior of the rectangular Fayoum standard type weirs, with one bottom circular opening at their middle. The main goals of this research is to predict the maximum tensile, maximum compressive, maximum shear stresses on the weir body to evaluate the feasibility of constructing a bottom circular opening in the middle of the existing weirs to increase the flow.
Methodology: The research is based on numerical analysis of weirs with various dimensions using ANSYS Fluent and ANSYS Mechanical applying Fluid Structure Interaction techniques. Results of the model were validated with the experimental results of previous studies. The research results were used to develop regression equations between weir dimensions, opening diameters and flow discharge with maximum tensile stress, σt-max, maximum compressive stress, σc-max, maximum shear stress,τmax, and maximum deformation,δmax, occurring to the weir body.
Results: There are clear correlations between the stresses on the weir, including maximum tensile, maximum shear and maximum compressive stresses, and the dimensions of the weir and its opening diameter. Hence, the multiple regression analysis was applied to predict the maximum stresses and the maximum deformation based on the dimensions of the weir, the pipe diameter and the discharge passing in the channel.
Conclusion: Four formulae were developed to predict the values of maximum tensile stress, maximum shear stress, maximum compressive stress, and maximum deformation around circular openings in Fayoum type weirs. By comparing the stresses values with the allowable strength of concrete, the maximum allowable opening diameter could be determined for each case.