الفهرس 
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Abstract
Weirs are important hydraulic structures which are widely used for many purposes. Recently, due to the expansions of agriculture areas, the need for irrigation water increased, and hence there is a need to increase the discharge capacity of canals. 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 disturb water distribution to sub-channels along it). Also, changes of the flowed discharge affect water levels over weirs and consequently affect the back water curves upstream them. Hence, to increase the discharges, weirs should be reconstructed to guarantee water levels over sub-channels’ intakes. That will be very costly which gave great importance to study the possibility of making openings in weirs, to increase the discharge passing through them, hydraulically and structurally.
This thesis aims to study the structural behavior of rectangular weirs, Fayoum standard type, with one bottom circular opening at their middle. The main goal of this research is to predict the maximum tensile, the maximum compressive, and the maximum shear stresses on the weir body to know the possibility of introducing a bottom circular opening in the middle of the existing weirs.
The thesis work is based on numerical analysis of weirs with different dimensions using ANSYS Fluent and ANSYS Mechanical applying Fluid Structure Interaction techniques. Results of the model were validated with experimental results from previous studies. The research results were used to develop regression equations between weir dimensions, opening diameter and flow discharge with the maximum tensile stress, the maximum compressive stress, the maximum shear stress, and the maximum deformation, occurring on weir body.
It was found that, there are clear correlations between stresses on the weir, including maximum tensile, maximum shear and maximum compressive stresses, and 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.
from the results of structural model, four formulae were developed to predict the values of the maximum tensile stress, the maximum shear stress, the maximum compressive stress, and the maximum deformation around circular openings in Fayoum type weirs. By comparing stresses values with the allowable strength of concrete, the allowable opening diameter could be determined for each case.