Analysis of Sluice Gates of Hydroelectric Power Stations

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Figure 2. Vertical section of inlet pipe of power plant

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Figure 3. Typical representative of sluice gate - basic dimensions

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Figure 4. View to sluice gates

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Figure 5. Deformation of flange and poor weld

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After sand blasting of structure the visual control of welds or measurement of dimensions can be realized. Further, quality of welds can be accomplished by the defectoscopy methods. The main aim of this control is detection of possible cracks in welds.

Figure 6. Corrosion of sluice gate structure

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Because the structure works under water in severe corrosion conditions, the measurements of wall thicknesses have to be realized for cover sheets, webs, flanges and reinforcement ribs in order to use these dimensions in analytical and numerical computations. The measurement can be accomplished e.g. by ultrasound apparatus TG-400. Attention has to be devoted also to the stress concentrators that can be sources of initial failures and from the point of view of safety they are critical part of structure. For the detection of actual state of structure it is often necessary to provide measurement of cover plate surface evenness. The measurement is realized by robotic geodetic station Trible VX Spatial Total Station 305 while the quick valve or sluice gates are in vertical position.

3. Numerical Computations

The computation of strength is based on numerical procedures, but in case of simple structures the analytical methods are applied too. The computation comes out from fact that sluice gate is loaded during operation by water pressure pand it is simply supported in locationsH andB Figure 7. Typical computational schema represents loading of single rib by pressure of water in depth h. Accordingly, continual loading qis acting on single rib (Figure 7b) and on the basis of classical theory normal shear and equivalent stresses in the structure are computed.

Figure 7. Computational scheme of one rib of sluice gate

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Besides of strength conditions the profiles have to be checked (even there are compact cross-sections) for shear stability of walls according to part 6.7.3 of Standard STN 73 1401 and also transverse reinforcements have to be checked.

Computation by the finite element method is the most important numerical treatment and one example of meshed model is given in Figure 8. It represents mesh of shell finite elements for which characteristic field of equivalent von Mises stresses on bottom part of shells are given in Figure 9.

Figure 8. Mesh of shell finite elements

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Figure 9. Field of equivalent stresses on bottom sides of supporting member

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In order to provide investigation of stresses in the area of stress concentrators it is necessary to model whole closing equipment. During years different computational models of various sluice gates were used based on shells as well as volume elements. Examples of such computations are given in next figures. In Figure 10 are shown deformation fields and in Figure 11 the fields of equivalent stresses for two different structures.

Figure 10. Field of deformations for bottom sluice gate on inlet

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Figure 11. Fields of von Mises equivalent stresses on quick valve of different type

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4. Experimental Measurements

Knowledge of actual state of structure is based on the following measurements ^[2]:

- measurement of residual stresses,

- strain gage measurements of time-dependent stress changes during operational loading of structure.

4.1. Residual Stresses

The most important method of measurement of residual stresses in the structure is the hole drilling method. The method is nowadays a standard method of measurement ^[1]. Despite of fact that the residual stresses frequently occur in the structure and they significantly influence their reliability, only very small attention is devoted to their measurement. Consideration of quantitative levels of residual stresses is still one of the forgotten parts of structural designing which is regrettable.

Figure 12. Measurement of residual stresses by system RS 200

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The precision of hole drilling method depends mainly on following factors:

Ÿ strain gages and their installation,

Ÿ centering of drilling tool and hole drilling,

Ÿ apparatus for deformation measurement,

Ÿ knowledge of material properties of tested part.

Positioning of strain gages in rosette has been proposed and developed by Micro-Measurements and HBM especially for the measurement of residual stresses. Rosettes are equipped by centering signs for positioning of drilling tool in the centre of strain gage circle. This is a critical operation on which the precision of whole measurement depends. The most effective and appropriate equipment for the measurement in terrain is a portable static strain gage apparatus Model P-3 charged by battery, or apparatus RS 200 Figure 12. In laboratory conditions is very suitable to use automatic system connected with computer, e.g. Measurements Group System 4000, or SPIDER 8. Special off-line computer program is also suitable for using with System 4000. Program automatically provides procedures connected with computation of residual stress magnitudes in accordance with ASTM E 837-01. In the standard is recommended to drill the hole by small increments together with registering measured deformations and depth of drilled hole after each increment.

4.2. Determination of Operation Loading

By the strain gage measurement are analyzed also time-dependent charts of strains in the most loaded locations of hatching equipment ^{[6, 7]}. For the joining of strain-gages with measurement apparatus are used shield cables. Measurement chain consist of strain-gage apparatus SPIDER 8 and notebook. On the sluice gate are applied strain-gages symmetrically to the vertical axis, Figure 13. Detail of strain-gage application is given in Figure 14. Two strain gages are used in order to avoid possible error of one strain gage due to relatively high water pressure and during manipulation with sluice gates by crane before realization of measurement.

Figure 13. Insulated strain gages on sluice gate before measurement

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Figure 14. Detail of applied strain-gages

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