Provision of strength of hydrostation trash racks

Conclusions

• 1. The replacement of welding of bars to the horizontal beams and of the intermediate grates by round ties itself did not worsen the working conditions of rack bars. But the conditions are markedly worsened as a consequence of not fastening the intermediate ties in their direction.

• 2. One intermediate tie does not increase the first natural frequency of the unit in its plane, it even reduces it slightly. The placement of two intermediate ties increase the first natural frequency of the unit by no more than 40%.

• 3. To avoid fatigue breaks of the bars, a decrease of the first natural frequency of the units in water to the level (St/d)v_max and of the frequency of vibration of the mass of the intake cannot be allowed.

• 4. It is necessary to experimentally determine the value of the Strouhal number St for the bar profiles being used and to study the conditions of occurrence of self-excited vibrations of bars with a streamlined profile. It would be best of all to use for this purpose one of the intakes of some hydrpstations which is adpated for a rapid change of rack units being tested and for a change in the flow velocity in sufficiently wide limits. During the tests the bar profile, diameter of the support ties, and diameter and arrangement of the intermediate ties should be varied.

• 5. Since the damages of bars by cracks have a pronounced fatigue character, when manufacturing racks it is necessary to use welded joints with gradual transitions to the base metal, without allowing poor penetration, undercuts, craters, and lowering of the standards of performing the works.