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Can a concrete structure be completely free of expansion joints and contraction joints?

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Consider that the concrete structure is not subject to the problem of differential settlement.

For contraction joints, it may be possible to design a concrete structure without any contraction joints. By using sufficient steel reinforcement to spread evenly the crack width over the span length of the structure, it may achieve the requirement of minimum crack width and cause no adverse impact to the aesthetics of the structure. However, it follows that the amount of reinforcement required is higher than that when with sufficient contraction joints.

For expansion joints, the consequence of not providing such joints may be difficult to cater for. For example, a concrete structure has the coefficient of thermal expansion of 9×106 /sup>o
C and a Young’s modulus of 34.5kN/mmsup>2 With an increase of temperature of 20sup>oC and it is restricted to free
expansion, then the structure is subject to an axial stress of 6.21MPa. If the structure is very slender (e.g. concrete carriageway), buckling may occur.

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Therefore, the structure has to be designed to take up these thermal stresses if expansion joints are not provided. However, for water retaining structures, most of them are not affected by weather conditions because they are insulated from the water they contain internally and soil backfill that surround them. Therefore, it is expected that a smaller amount of thermal movement will occur when compared with normal exposed concrete structure. Consequently, expansion joints may be omitted in this case with the view that the compressive stress induced by thermal expansion toughens the structure to limit the development of tensile stress.

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.

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Comments
  • Bennett April 2, 2015 at 9:18 am

    Please, in answering some of this basic questions, do well to refer us to applicable standards/codes. Thank you very much

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