Guideline for QCVN xxxx : 2013/BXD

8.Hydromechanical equipments

8.1 General requirements 8.1.1.

-Hydromechanical equipment is applied to mainly hydraulic gates and steel penstocks.

-The following matters are required for designing hydromechanical equipment;

i)The equipment must be safe against anticipated loads.

ii)The equipment must be economical.

iii)The equipment must be easy for maintenance.

iv)The equipment must affect minimum to the environment.

8.1.2.

As the specific procedure regarding determination of loads acting on the equipment depends on stipulations in each design standard, the clarifications of major loads are as follows:

1. Valve and gate

(1) Hydrostatic pressure

- Hydrostatic pressure is a pressure which acts by static fluid. In case of designing valve and gate at a hydropower plant, thehydrostatic pressure is of subtracted by the pressure under the minimum water level of downstream side from the pressure underthe maximum water level. The brief illustration of hydrostatic pressure is shown in Fig.8.1.

Fig.8.1 Hydrostatic pressure

(2) Hydrodynamic pressure

- Hydrodynamic pressure acts to the valve and gate as the pressure createdby the water flow in a reservoir during discharging from the gate.

(3) Own weight, inertia force

- Own weight acts to the valve and gate, and inertia force of the gate leaf acts when gate stops.

(4) Seepage pressure of water

- Seepage pressure acts from bedrock to outside of the gate guide which has box-shape structure such as bonnet type gate guide, because the gate guide blocks the water passing between outside and inside of the gate guide.

(5) Buoyancy

- When a valve or a gate locates under water, buoyancy acts to submerged part of the structure.

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(6) Wave pressure

- Wave pressure acts to the gate leaf from the reservoir due to wind or earthquake.

(7) Friction force

- Friction force acts between seal material and seal plate of the gate guide, bearing part of the gate leaf and bearing plate of the gate guide and so forthwhen the gate is moving. The brief illustration of friction force is shown in Fig.8.2.

Friction force at seal part and bearing part when gate is moving upward

Fig.8.2 Friction force

(8) Silt deposit pressure

- If silt sedimentation is anticipated, silt deposit pressure acts to the gate leaf in addition to hydrostatic pressure.

(9) Operating force (tension force of lifting cable, friction force of supporting device for radial gate, force of elevating gear)

- Tension force acts to a gate leaf from the gate hoist via wire rope, and friction force acts to the trunnion part of the gate arms of radial gate as the operating force when the gate is moving. The brief illustration of operating force is shown in Fig.8.3.

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Tension force

Tension force

Friction force at trunnion part when gate is moving upward

Fig.8.3 Operating force

(10) Wind pressure, air pressure

- Wind pressure acts to the structure, and it is affected by strength of wind and the projected dimension of the structure.

(11) Impact pressure of floating object and ships

-Impact pressure acts when floating object such as driftwood or ships collide the gate leaf. (12) Assembling loads, thermal expansion load

-Temporary loads act during fabricating and installing such as hang at temporary hook, liquid pressure by casting concrete and so forth, and temperature change induces thermal expansion load to the structure.

(13)Testing loads

-In some cases, inspections and/or tests are conducted under severer conditions than anticipated load in actual operation. Testing load is the load during inspections and tests.

(14)Air vacuum force in case of closing gate

-Vacuuming force pulls a gate leaf toward downstream with flowing water in case of some layout of the structure. The brief illustration of air vacuum force in case of closing gate is shown in Fig.8.4.

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Water level

Fig.8.4 Air vacuum force in case of closing gate

(15) Water hammer pressure

- When the turbines are shut off, inertia force of the flowing water disperses as the water hammer pressure to submerged structures including the gate leaf.

(16) Forces at the lifting gear in case of stuck gate

- When each side of wire rope which is connected to the gate leaf is hanged unequally, the gate leaf may be seized by the gate guide. In this case, the gate hoist may reach to the maximum torque as the forces at the lifting gear in case of stuck gate. The brief illustration of forces at lifting gear in case of stuck gate is shown in Fig.8.5.

Forces at lifting gear in case of stuck gate

Seized by the gate guide when gate leaf is hanged unequally

Fig.8.5 Forces at lifting gear in case of stuck gate

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(17) Earthquake force

- Earthquake force consists of hydrodynamic force of reservoir and inertia force of the equipment. The brief illustration of earthquake force is shown in Fig.8.6.

Inertia force of equipment

Water level

Hydrodynamic force of reservoir

Fig.8.6 Earthquake force

2.Penstock

(1)Longitudinal force caused by the changes of pipeline diameters at bend elbow and at the butt end of expansion joints

- If the diameter of a penstock is narrowed down including part of dimension change at the expansion joint, longitudinal force occurs. The brief illustration of longitudinal force caused by changes of pipeline

is shown in Fig.8.7, and the brief illustration of longitudinal force caused by changes of pipeline direction at bend section is shown in Fig.8.8.

Fig.8.7 Longitudinal force causing by changes of pipeline diameters

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Fig.8.8 Longitudinal force causing by changes of pipeline direction at bend section

(2) Water pressure acting on the pipe shell, including water hammer

- Water pressure acting on the pipe shell consists of hydrostatic pressure, pressure rise due to water hammering and water rising due to surging. The maximum value is hydrostatic pressplureswater hammering at the lower part of the penstock. However, hydrostatic pressure plus surging is severer at the upper part of the penstock generally. The brief illustration of water pressure acting on pipe shell is shown

in Fig.8.9.

Water hammering

Water rising due to surging

Hydrostatic pressure

Fig.8.9 Water pressure acting on pipe shell

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(3)Water pressure acting on the guard valve in the pipe

-Water pressure acting on the guard valve consists of hydrostatic pressure, pressure rise due to water hammering and water rising due to surging. The maximum value is hydrostatic pressplureswater

hammering, if the guard valve locates at the lower part of the penstock.However, hydrostatic pressure plus surging is severer at the upper part of the penstock generally.

(4) Own weight of pipe shell and water, which is fully stored in a pipe

- Own weight of pipe shell and water inside the pipe shell act to the exposed pipe of a penstock. The maximum forces occur when the pipe shell is filled with water. The brief illustration of own weight of pipe shell and water is shown in Fig.8.10.

Own weight of pipe shell and water

Fig.8.10 Own weight of pipe shell and water

(5) Friction force between steel pipe and intermediate abutments, between water and pipe shell, friction force inside expansion joints

- When penstock is moving along longitudinal direction by temperature change, longitudinal friction force acts at the sliding part such as intermediate abutments and between packing and pipe shell of the expansion joint.

(6) Centrifugal force caused by the movement of water through bend elbow

- At bend section of a penstock, centrifugal force acts by inertial action of flowing water.

(7) Deformation force caused by the influencesof environmental temperature and internal water pressure to the un-sectional pipe

- In case that there are not any adjustment devices such as expansion joint, the forces caused by temperature change or water pressure to the un-sectional pipe and so on act to the pipe shell directly.

(8) Rock pressure on anchors and intermediate abutments

- The underground part of anchor block and intermediate abutments may be actedby pressures due to displacements of surrounding rocks, especiallywhen the penstock is located at inclined part. The penstock may be actedby rock pressure due to the movement of the anchor blocks and intermediate abutments. The brief illustration of rock pressure on intermediate abutments is shown in Fig.8.11

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Intermediate abutments

Rock pressure

Fig.8.11 Rock pressure on intermediate abutments

(9) Forces caused by the uneven settlement of anchors and intermediate abutments

- Displacement such as uneven settlement of bedrock induces pressures to the anchors and intermediate abutments. The brief illustration of forces caused by uneven settlement of intermediate abutments is shown in Fig.8.12.

Bending moment due to unsettlement of intermediate abutments

Uneven settlement of intermediate abutments

Forces causing by uneven settlement of intermediate abutments

Fig.8.12 Forces causing by uneven settlement of intermediate abutments

(10) Rock pressure acting on embedded pipe sections

- Rock pressure or earth load acts as an external pressure to the embedded part of the penstock. (11) Decree of vacuum being generated in the pipeline in case of empty pipe

- Vacuum pressure acts on the pipe shell of a penstock along circumferential direction during dewatering when the penstock is long enough or the air is supplied by air valve which moves by pressure difference.

(12) Wind force

- Wind force acts to the structure, and it is affected by strength of wind and the projected dimension of the structure.

(13) Force generating from hydraulic test

- In some cases, inspections and/or tests are conducted under severer conditions than anticipated load in actual operation. Testing load is the load during inspections and tests.

(14) Forces being generated during the construction of concrete parts

- Liquid pressure acts to the embedded part of the penstock during lining concrete, grout concrete or

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anchor concrete is consolidating.

(15) Forces causing by earthquake and other geologic factors

- Inertia force which is induced by earthquake acts to the anchors of a penstock.

In many technical standards regarding designing hydromechanical equipment, correcting bearing force such as correcting allowable stress according to sort of load is stipulated. If the load act temporarily during earthquake, installation and so on, or the load actsto limited part of structures for example part of

pipe shell of penstocks which is seized rigidly by reinforcement members, the considerable load combination and/or the bearing force such as allowable stress is corrected. Thus, utmost attention must be

paid to the sort of load to be classified properly at design.

3. Load combination

The following classifications shown in Tables 8.1 and 8.2 are only examples. Specific procedure for selecting loads must obey the technical standard which is used at the design project by project.

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8.1.3. Result of calculation at design and behavior of actual equipmentmust be corresponded. Thus behavior of the equipment must be confirmed by visual inspections and/or measurements. Confirmation methods are measuring deflections of members, measuring stresses of members, conducting visual inspection to check deformations and so forth.

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