Vincent T. H. CHU

For more than 2 metres, it is commonly defined as high level fall in which most injuries are resulted from. However, there is an increasing trend that there has been similar number of injuries from low level falls (i.e. less than 2 metres) and from high level falls. As such, some countries have deleted the “2 metre rule” as the definition of falling at height. Instead, it is newly defined as working at a place from which a person could be injured by falling from it, regardless of whether it is above, at or below ground level without stating the level of fall.

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.

The main principle of safety helmet is to protect workers against impact by falling objects or struck by swinging object by energy absorption. Upon hitting by an object, the helmet dissipates some of the energy in the following mechanisms:

(i) Stretching of harness inside the helmet;
(ii) Partial damage of outer shell of helmet.

The remaining energy is then evenly spread around the head to reduce the hitting stress on worker’s head.

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.

In construction contracts, if a contractor fails to perform the works, the employer would suffer from severe financial loss and therefore some forms of protection has to be established in the contract.

For surety bond, the contractor obtains a guarantee from a third party i.e. a bank or an insurance company, which in return for a fee, agrees to undertake the financial responsibility for the performance of contractor’s obligations. This third party will pay to the employer in case there is a contractor’s default.

For security, a sum of money is deposited in the employer’s account and upon satisfactory fulfillment of contractor’s obligations, the sum will be released to the contractor.

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.

Design life means the minimum duration a structure is expected to last. The longer is the design life; the higher is the cost of a project. Therefore, in choosing the design life for a structure, engineers should consider the design life which generates a economical project without sacrificing the required function.

In selection of return period of certain design conditions, winds, waves, etc., one should consider the consequences of exceedance. In fact, there are normally no extreme maximum values of these design conditions and its selection is based on the probability of exceedance which is related to return period.

Therefore, design life may not be equal to return period of design conditions because their selections are based on different considerations.

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.

The purpose of third party insurance is to protect contractors from bankruptcy in case there are severe accidents happened to the third party due to the construction work. Therefore, in government contracts, contractors are requested contractually to procure third party insurance from the commencement of contract until the end of Maintenance Period. If contractors have the financial capability to handle the claims due to accidents to third party, the client is not bound to include this requirement in the contract.

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.

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.

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.

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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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.

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.

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.

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.

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.

(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.

(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.