Intak’s work is lowering thereservoir level to prevent dams from damaging during a catastrophic failurelike earthquakes.
Lowering process decreases the hydrostatic loads at the baseof intakes. So, understanding the dynamic behavior of a dam intake tower isquite important. The complexity in this kind of structures is the presence ofwater around and inside the tower and axisymmetric geometry. In addition, soilwhere is found at the base of intake tower has significant effects on thedynamic response of towers. Other parameters which affect the behavior ofintake towers during an earthquake such as depth of submergence(H0/H),wall thickness(t), the ratio outside radius(r0) to height(H) oftower are taken into consideration to obtain their effects on the dynamicbehavior of intake towers.
But, all these parameters are out of this review’sscope except soil-structure interaction is involved. In this study, the dynamicbehavior of cylindrical intake towers is investigated. A 3D model is modeled tostudy the dynamic behavior of towers and incorporate the effects of thewater-structure and soil-structure interaction. The finite element method isused to model the intake tower with 61m height. Three different submergencelevels are taken for inside and surrounding water; H0/H = 0.5, H0/H= 1.
0, and no water condition, where H0 is the level of water bothinside and outside. Hydrodynamic masses were added according to the concept ofGoyal and Chopra (1989). An equation has been adopted to add hydrodynamicmasses taking water as an incompressible fluid: Ms(z) = m s(z) + m0(z) + mi(z),where the mass of an intake tower m s(z) has a qualitative cross-section with two axes of symmetry is changed by the virtual mass M s(z),m0(z): added hydrodynamic mass represents the effect of outsidewater, mi(z): added hydrodynamic mass represents the effect ofinside water. Soil- structure interaction is represented by block elements havemedium to hard stiffness.
Sap2000 software is used to model the block elements.SSI affects the dynamic behavior of the intake towers. Different submergenceconditions are applied on intake tower models with soil. Model analysis iscarried out by using Eigenvector method. In analysis process, 12 natural modeshave been considered because these modes provide an excellent shrewdness intodynamic behavior of the structure. The time periods are obtained and comparedfor the same model with fixed base.
Response spectrum analysis was carried outto study the effects of soil structure interaction on the dynamic behavior ofintake tower with soil. Response reduction factor and importance factor wasused 5 and 1.5, respectively. We can see from the obtained results that timeperiods and displacements at the top are increased because of the presence ofsoil under the intake towers. Soil’s presence decreases bending moment due toincreased flexibility.
Shear forces at the base are much greater for model withflexible base. Finally, when flexibility of soil is increased, the fundamentaltime-period increases also.