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 16. What are the functions of different reinforcement in a typical pile cap? (FD11) Loads from columns transferring to pile cap induce tensile forces at the bottom of the cap. For instance, by using truss analogy to analyze a pile cap sitting on two piles with a column at the centre of the pile cap, the tensile force at the bottom is proportional to the pile spacing and is inversely proportional to depth of pile cap. The bottom reinforcement is designed to resist the tensile stressed generated from loads in columns. Side reinforcement may not be necessary in pile cap (L.A. Clark (1983)). In fact, the primary aim of the side reinforcement is to control cracking. However, as most pile caps are hidden from view and it is considered not necessary to provide side reinforcement to pile caps based on aesthetic reason. Sometimes, reinforcement may be designed at the top of pile caps which serve as compression reinforcement. This type of reinforcement is required in case there is a limitation on the depth of pile caps. Similarly shear reinforcement is introduced to the pile caps in case there is a restriction to the depth of pile caps. L. A. Clark (1983) Concrete Bridge Design to BS5400 Construction Press, Longman Group Limited pp.94 17. What are the head details of H-piles under compression and subject to bending moment? (FD11) For steel sections referred to in BS5950, universal bearing pile is characterized by having equal flange and web thickness while universal column has different flange and web thickness. Universal columns can also be used as bearing piles. In the design of the head details of H-piles, there are three typical cases to be considered, namely compression piles, tension piles and piles with bending moment at the head in addition to tension or compression. The design of these piles recommended by G. M. Cornfield (1968) is listed below: (i) Compression piles For this type of piles, H-piles should be embedded 150mm in concrete pile 230
A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU caps and it is not necessary to use any dowels and capping plates in their connection. (ii) Tension piles A number of hook-ended bars are welded to the top of H-piles. (iii) Piles with bending moment at their head (tension or compression) The depth of embedment of piles into pile caps is substantially increased and loads are transferred by horizontal bars welded to piles’ flanges. Fig. Different arrangement of pile head details 18. It is not necessary to design nominal reinforcement to piles. Is it true? In BS8110 and BS5400 Pt.4, they require the provision of nominal reinforcement for columns. However, for pile design the requirement of nominal reinforcement may not be necessary. Firstly, as piles are located underground, the occurrence of unexpected loads to piles is seldom. Secondly, shear failure of piles is considered not critical to the structure due to severe collision. Moreover, the failure of piles by buckling due to fire is unlikely because fire is rarely ignited underground. 231
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A Self-Learning Manual - Institution of Engineers Mauritius

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