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In the construction of pump troughs for accommodation of screw pumps, what is the construction method to ensure close contact between the screw pumps and the pump trough?

In the construction of screw pump troughs, trapezoidal-shaped troughs are usually formed by using normal formwork. In order to enhance close contact between screw pumps and troughs, upon lifting the screw pumps into the troughs screeding works is carried out. Screw pumps are set to rotate and screeds are placed between the gap of screw pumps’ blade and trapezoidal-shaped troughs during the rotating action of screw pumps. After the screed sets, it serves to prevent leakage of water during the pumping operation of screw pumps.

corbel beam

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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In the design of corbel beams in a pumping station, why are shear links designed in the top 2/3 of the section? What is the general advice on the design?

Corbel beams are defined as z/d<0.6 where z is the distance of bearing load to the beams’ fixed end (or called shear span) and d is depth of beams. The design philosophy is based on strut and tie system. To establish the design model, it is firstly assumed the failure surface, i.e. shear cracks extending to 2/3 of depth of beam. Experiment results verified that the failure cracks extended only to 2/3 of beam while the remaining 1/3 depth of concrete contributed as concrete strut to provide compressive strut force to the bearing loading. Horizontal links are normally provided to corbel beams because experimental results indicated that horizontal links were more effective than vertical links when shear span/depth is less than 0.6. For shear span/depth>0.6, it should be not considered as corbel beams but as cantilevers.

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In designing corbel beams, care should be taken to avoid bearing load to extend beyond the straight portion of tie bars, otherwise the corners of corbel beams are likely to shear off. Reference is made to L. A. Clark (1983).

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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What is the difference among cement plaster, cement render and cement screed? Under what situations should each of the above be used?

The purpose of plastering, rendering and screeding is to create a smooth, flat surface to receive finishes like paint, wallpaper etc.

Plastering is the intermediately coating of building materials to be applied on the internal facade of concrete walls or blockwalls. Rendering is the intermediate coating for external walls only. Screeding is the coating laid on floors to receive finishes like tiles, carpet, and marble.

Hence, these terms differ basically from the locations at which they are applied. Due to different locations of application of plasterwork, the proportion of material component for plaster and render is different. For example:

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(i) Cement plaster
Undercoat- cement:lime:sand (by volume) = 1:4:16
Finishing coat – cement:lime:sand = 1:12:30

(ii) Cement render

Undercoat- cement:lime:sand (by volume) = 1:2:6
Finishing coat – cement:lime:sand = 1:3:6

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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In pumping stations one of the choices for the material of water tanks is fibre-reinforced plastic (FRP). What are the advantages associated with this kind of material?

There are two main advantages for FRP water tanks:

(i) It possesses high strength to weight ratio and this leads to the ease of site handling.

(ii) It is highly resistant to corrosion and thus it is more durable than steel water tank.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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What are the components of a waterproofing system in the roof of a typical pumping station?

In the design of a waterproofing system at the roof of a pumping station, normally the following components are:

(i) Above the structural finish level of the concrete roof, a screed of uniform thickness is applied to provide a smooth surface for the application of waterproofing membrane. (Screed of varying thickness can also be designed on the roof to create a slope for drainage.) The screed used for providing a surface for membrane should be thin and possess good adhesion to the substrate. Moreover, the screed aids in the thermal insulation of the roof.

(ii) Above the screed, waterproofing membrane is provided to ensure watertightness of the roof.

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(iii) An insulation board may be placed on top of waterproof membrane for thermal insulation. In cold weather condition where the loss of heat at the roof is significant, the insulation board helps to reduce these losses. On the contrary, in summer the roof is heated up by direct sunlight and the insulation layer reduces the temperature rise inside the pumping station.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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