A Self-Learning Manual - Institution of Engineers Mauritius

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A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU To aid in providing adequate resistance to the overturning moment by the berthing load, the soil resistance above bedrock contributes to stabilizing moment. For commonly adopted marine piling type, i.e. driven steel tubular piles with reinforced concrete infill, driven piles can at most be founded on top of rockhead surface. In case the rockhead level is shallow, then the little soil cover may result in insufficient lateral resistance to the berthing load. 3. Why are high and narrow beams not desirable in concrete piers? (P2) Based on past experience in other countries (Carl A. Thoresen (1988)), high and narrow beams after several years of construction showed signs of serious deterioration at the bottom of the beams. However, the deterioration of pier slabs was not significant when compared with that of the deep beams. The main reason to account for this is due to the close proximity of the deep beams to the sea level. To avoid these problems, either beamless slab or wide with shallow beams are normally designed. 4. Shall a layer of wearing course or additional thickness be designed on the surface of piers? (P2) In the design of piers, consideration should be given to the effect of wearing action caused by passengers, other traffics and even sometimes vehicles. In maritime environment, the durability and integrity of concrete is detrimental to the servicing life of piers because it acts an essential barrier to chloride attack. However, in view of these gradual wear and tear generated by the loading traffic, some forms of surface protection should be provided on top of pier surface like wearing course or additional increase in concrete cover. 5. In mooring of vessels, wire ropes or fibre ropes are commonly used for tying the vessels to mooring system. It is not recommended to use them together in mooring. Why? Mooring lines are provided by vessel while the shore provides the mooring points. Wire ropes provide a more rigid mooring system than fibre ropes. When a high degree elastically is required, fibre ropes would be a better choice. The mixed usage of wire ropes and fibre ropes is not recommended 170
A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU because of the uneven tensioning of ropes. Owing to different material properties associated with wire ropes and fibre ropes, it is almost impossible to allocate uniform tension on both types of wires. As a result, there is possible occurrence of overloading in some ropes. 6. What is the difference in design philosophy between flexible dolphin and rigid dolphin? (D1) (A) Rigid dolphin The impact energy of vessel is absorbed mainly by fender. As such, the dolphin itself is designed as a rigid structure with a group of piles. The piles serve to transfer the reaction force from fender system to the foundation soils. The design of rigid fender is similar to other structures and the strength and stiffness of rigid dolphin should be sufficient to withstand berthing forces without causing excessive deformations. (B) Flexible dolphin The impact energy of vessel is absorbed by lateral deflection of piles. The dolphin itself performs both the functions of fender and berthing structure. Flexible dolphin is particular suitable in deep water region because the energy absorption capacity is a function of pile length. The pile stiffness could not be designed to be too low because large deflection of pile may occur so that the pile may touch the jetty or the vessel may touch the pile. On the other hand, pile stiffness could not be designed to be too high because of potential yielding of piles or vessel’s hull. 7. What is the difference between breasting dolphin and mooring dolphin? (D2) A dolphin is an isolated marine structure for berthing and mooring of vessels. It is not uncommon that the combination of dolphins with piers could drastically reduce the size of piers. Dolphins are generally divided into two types, namely breasting dolphins and mooring dolphins. Breasting dolphins serves the following purposes: (i) Assist in berthing of vessels by taking up some berthing loads. (ii) Keep the vessel from pressing against the pier structure. (iii) Serve as mooring points to restrict the longitudinal movement of the berthing vessel. 171
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A Self-Learning Manual - Institution of Engineers Mauritius

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