Reinforced concrete

Reinforced concrete - The University of Hong Kong...

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1 The University of Hong Kong Department of Civil Engineering Theory and Design of Structures I Reinforced Concrete Design Scope Rectangular singly and doubly reinforced beams Elastic design Limit state design concepts; material strength and loading Flexural strength and shear strength of beams; one-way slabs References 1. BS8110: 1985, Structural use of concrete – Part 3: Design charts for singly reinforced beams, doubly reinforced beams and rectangular columns, British Standard Institution, London, 1985. 2. BS8110: 1997, Structural use of concrete – Part 1: Code of practice for design and construction, British Standard Institution, London, 1997. 3. Code of practice for structural use of concrete 2004, second edition, Buildings Department, Hong Kong, 2008. 4. Design of structural elements: concrete, steelwork, masonry and timber design to British standards and Eurocodes, 2nd ed., C. Arya, Spon Press, London, 2003. 5. Reinforced concrete design, 5th ed., W.H. Mosley, J.H. Bungey and R. Hulse, Macmillan Press, Basingstoke, 1999. 6. Reinforced concrete designer’s handbook, 10th ed., C.E. Reynolds and J.C. Steedman, E. & F.N. Spon, London, 1988. 7. Reinforced concrete design to BS8110: simply explained, A.H. Allen, E. & F.N. Spon, London, 1988. 8. Structural design in concrete to BS8110, L.H. Martin, P.C.L. Croxton and J.A. Purkiss, Edward Arnold, London, 1989. Introduction A plain concrete beam cannot support much loading because of the low tensile strength. The introduction of steel tension reinforcement can effectively strengthen a concrete beam. In a reinforced concrete (RC) beam, the concrete carries compression while the steel reinforcement mainly carries tension. Figure 1(a) Plain concrete beam under loading. f c f c b d Z = b d 2 / 6 Figure 1(b) Reinforced concrete beam under loading. Section (cracked) C T a M = C a = T a
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2 Properties of steel The stress is proportional to the strain up to the yield point. At the yield point, steel becomes plastic and the stress remains practically constant while the strain increases. Finally owing to work hardening, there is another increase in stress but not in proportion to strain. Properties of concrete It has no clearly defined yield point. Nor is stress ever proportional to strain exactly. However, that portion of the stress-strain curve below 1/3 of the ultimate strength is very nearly a straight line and is assumed to be so. Beyond 1/3 of the ultimate strength, the concrete is in the elasto-plastic state, and the stress is no longer proportional to strain. Methods of design The following methods of design are available: 1. Based on elastic theory (elastic theory method in CP114 and previous Hong Kong codes) 2. Based on ultimate load (load factor method in CP114 and previous Hong Kong codes) 3. Based on limit states design philosophy (BS8110, CP110 and present Hong Kong concrete code) Elastic method When the elastic method is adopted, the structural members are reinforced so that at working load, the maximum stress in the concrete is a certain fraction of the cube strength and the maximum stress in the steel is a certain fraction of the yield stress.
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Reinforced concrete - The University of Hong Kong...

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