COMPUTER AIDED DESIGN OF ARCH-GRAVITY DAMS

Abstract

An arch-gravity dam is basically a gravity dam with some curvature imparted to it in plan, so that in addition to transferring the water load by gravity action, some portion is also transferred by arch action to the abutments. Normally, for a narrow valley, arch dams are preferred, which transfer the major portion of the water load by arch action to the abutments. But, sometimes, the abutment foundation is found to be weak to resist this arch load. In such cases, the arch dam is made of a thicker cross section so that a significant portion of the water load is transferred by gravity action, thereby causing relief at the abutments. Thus, arch-gravity dams can be an effective solution In such situations. The structural action of an arch-gravity dam is similar to an arch dam, and hence can be analysed as such. At present, there are several methods. available for the analysis of arch-gravity dams. This study has adopted the trial load method utilizing the crown cantilever analysis technique, The trial load method finds, by trial, the proportion of the total water loading that is transmitted by the arch and gravity actions separately. This method has been found satisfactory in the preliminary analysis and design of arch-gravity dams. For the detailed design, finite element techniques can be used at the final stage. Most of the previous trial load analysis were done by trial and error method, In this dissertation, an attempt has been made towards a matrix formulation of the problem. It has been formulated in the form of a set of linear simultaneous equations, easily programmable on a computer. The solution of these equations directly gives the load division taking place between the arch and cantilever elements. Thus the solution is obtained in a single operation, and the trial and error process eliminated. The problem has been subdivided into the following steps: 1. Crown cantilever analysis 2. Arch analysis 3. Formulation of the compatibility equations and determination of load distribution. 4. Stress analysis. For each of these topics, computer programs have been developed in FORTRAN 77. These programs can be run on personal computers. Using these programs, an arch-gravity dam has been analysed. The results from this analysis gives the load distribution that. is taking place between the arch and the cantilever elements. The program_output-also gives the deflected shape of the crown cantilever. To verify these programs, a thin arch section was also analysed. The results showed a behaviour similar to that of arch dams, greater transfer of load taking place to the arch elements as compared to the cantilever elements. Finally, stress analysis of the arch-gravity dam has been carried out, the stresses being calculated at the arch and at the abutments. The results from this analysis can be used to evaluate the safety of the adopted section. If the stresses exceed the permissible limits, the section is modified accordingly and rechecked by repetition of the analysis procedure. The final design is the outcome of a series of such iterative analysis and design procedures.