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If the contractor is liable for defective works for 12 years with contract under seal (6 years with contract not under seal), then what is the significance of Maintenance Period?

Defective works constitute a breach of contract in accordance with Limitation Ordinance (Cap. 347).

An action founded on simple contract (not under seal) shall not be brought after expiration of 6 years while an action founded with contract under seal shall not be brought after expiration of 12 years. For construction works, the date of counting these actions should be the date of substantial completion.

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To answer the above question, one should note that under the contractual requirement, the contractor during Maintenance Period has the right to rectify the defects and the employer has also the right to request the contractor to make good defective work. However, after the expiry of Maintenance Period, in case of any arising of defects, the employer has to employ others to rectify these works and bring the action to court to claim the contractor for the costs associated.

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.

What are the functions of different components of paint?

For normal paint application, there are mainly three main components of paint, namely primer, undercoat and finishing coat.

Primer: This is the first layer of a typical painting system and it is used to inhabit corrosion and provide a good bond for subsequent coats.

Undercoat: This component acts as a barrier to corrosion agents and even out irregularities of bonding surface. It also serves to hide the underlying background and prevent the details and colour of the area of application to affect the designed colour and finishing details of paint.

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Finishing coat: This is the final layer of a typical painting system and it protects the underlying layers from the effect of adverse weather conditions (e.g. sunlight) and to provide the designed properties of paint like colour, impermeability, wearing resistance, etc.

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.

Filed under Building | 1 Comment

What is the difference between working stress approach and limit state approach?

For working stress approach, service loads are used in the whole design and the strength of material is not utilized in the full extent. In this method of design, stresses acting on structural members are calculated based on elastic method and they are designed not to exceed certain allowable values. In fact, the whole structure during the lifespan may only experience loading stresses far below the ultimate state and that is the reason why this method is called working stress approach. Under such scenario, the most economical design can hardly be obtained by using working stress approach which is now commonly used in the design of temporary works.

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For limit state approach, for each material and load, a partial safety factor is assigned individually depending on the material properties and load properties. Therefore, each element of load and material properties is accurately assessed resulting in a more refined and accurate analysis of the structure. In this connection, the material strength can be utilized to its maximum value during its lifespan and loads can be assessed with reasonable probability of occurrence. Limit state approach is commonly used for the majority of reinforced concrete design because it ensures the utilization of material strength with the lowest construction cost input.

Filed under Steelworks | 1 Comment

Why are voids filled with lightweight infilling material in raft foundation of pumping stations?

To reduce the dead load and hence to reduce the settlement of pumping stations, the voids inside the raft foundations are filled with light material. If instead concrete is placed inside these voids, it poses severe thermal cracking problem and drastically increases loads to pumping stations. The use of general fill is also not desirable because its self-weight is comparable to that of concrete. On the contrary, if these voids are left vacant, water may penetrate into these voids during future operation and increases the dead load of pumping stations during its normal operation. Therefore, lightweight infill material, which is non-water-absorbing and non-biodegradable, is designed inside these voids to avoid ingress of water and to reduce the dead load of the structure.

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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.

Filed under Hydraulics | 0 Comments

Given a 1m high staircase resting on solid concrete, would it be adequate to design nominal reinforcement for the staircase?

For the design of staircase, there are three main scenarios:

(i) Stairs spans longitudinally
This kind of stairs refers to stairs spanning between landings only without any side supports. In this case, the staircase should be designed as a beam between two end supports (i.e. landing) and the main reinforcement is provided at the bottom of staircase slabs.

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(ii) Stairs spanning transversely
This kind of staircase is supported by sidewalls only and it may also be supported by stringer beams. For the case of sidewalls, it acts as a cantilever beam and the main reinforcement are provided the top surface of slab. For the case of staircase supported sideways by both sidewall and stringer beam, it should be designed transversely with end supports as sidewall and stringer beam and reinforcement is provided at the bottom of the staircase.
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(iii) Stairs resting on solid support
For stairs resting on solid supports, only nominal steel reinforcement is provided to control thermal and shrinkage cracking.

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.