ALGOR AROUND THE WORLD - Zimbabwe

Algor Software Helps Engineer to Design Arch Dams

Mr. Laxman used Algor software to analyze and optimize the Mtshabezi Dam, shown here under construction, as well as the Silverstroom Dam. Analyses revealed zones of high compressive stress. Higher strength concrete was used in these areas to compensate.

Mr. Manoj Laxman, an engineer at the Department of Water Development in Zimbabwe, designs dams with the aid of Algor. One of his latest projects is the proposed Silverstroom Dam, a 74 meter high, double curvature concrete arch dam.

The dam will be located in Mashonaland Central Province, 115 kilometers north of Harare. The reservoir will be capable of storing 140 million cubic meters of water and will provide 33.3 million cubic meters of water annually to supply the town of Centenary and to irrigate export crops such as soya, citrus and tobacco.

Mr. Manoj Laxman is a designer for the Department of Water Development in Zimbabwe. He uses Algor software to design and analyze dams.

Modeling and Preliminary Analysis

Mr. Laxman modeled the dam in Superdraw II based on previous designs. The final design was determined through several cycles of layout, linear static stress analysis, evaluation and improvement. In this case it took only four such cycles to arrive at the optimum solution.

The results of the preliminary analyses indicated that the angle of the curve was too high. Three adjustments were necessary before the compression and deflection results were satisfactory. The improved shape of the fourth model not only made it stronger, but also thinner than the second model.

The second model of the Silverstroom Dam. This model is displaced. The gray lines indicate the undisplaced position.

A Crackerjack Analysis

The fourth model was then tested further. Mr. Laxman carried out a cracked model analysis. The model had been created three elements deep to allow a crack to be added either one- or two-thirds through the thickness of the wall. Cracks were modeled in high tension zones and analyses were performed. Additional cracks were added until all excessive tensile stresses were eliminated. The compressive stresses in the model were then checked to ensure that they did not exceed the design strength. "

The hide element option became very useful when observing stresses in the model," said Mr. Laxman. "The stresses in the Vogt elements, which were used to simulate foundation displacement during loading, are meaningless compared to the foundation displacement. Therefore, it is essential to hide the Vogt elements when observing the stresses to ensure visualization of the meaningful elements."

About Algor

"A significant advantage in using the Algor finite element system for arch dam analysis is the great detail received from the results," said Mr. Laxman. "The designer is therefore able to converge on an optimum solution in fewer trials, i.e., in four trials using Algor, compared with fifty trials using traditional means. "

Another advantage of the Algor program is the tremendous confidence you gain in the design due to the powerful visualization capabilities such as the 3-D displaced model facility which is an essential feature in the design of arch dams. "

The 3-D displacements and stresses give a much better understanding of the behavior of arch dams compared to traditional programs. An ideal displacement is one in which we get a perfect shortening of the arch during loading with no unsymmetric effects and no unnecessarily induced bending moments. This leads to a better stress distribution in the dam. "

By observing the magnified 3-D displacements, it is easily possible to assess whether the angle of the log spiral curve is correct, too large, or too small. It is mainly the deflected shape that guides me toward the optimal solution."

Looking to the Future

Mr. Laxman plans to use Algor on small and large projects in and around Zimbabwe. He intends to incorporate nonlinear analysis and the use of gap elements in future models. He is also working on automating the cracking process. Algor will be used to analyze the proposed Gwai-Shangani Dam, a cylindrical gravity arch dam with a maximum height of 63 meters, which will supply the future water demands for the city of Bulawayo.

This is the final model of the Silverstroom Dam in Zimbabwe.