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The requirement for casting (or cutting) holes in reinforced concrete beams for services etc is a common one. Practical guidance is given in Concrete Advice No. 01, The provision of holes in reinforced concrete beams and in the BSRIA/Concrete Society publication Services integration with concrete buildings. (Note that copies of Concrete Advice Sheets can be downloaded from the Members´ area of the Concrete Society web site.)
Circular holes are preferable as square holes can induce stress concentrations, increasing the risk of cracking. Long rectangular holes are not recommended as they can significantly affect the structural performance of the member. Also, holes should be located away from points of high bending moment or shear. All holes, apart from very small ones, should be ‘framed’ by links and longitudinal steel. Guidance on the provision of reinforcement is given in the Institution of Structural Engineers/Concrete Society Manual Standard method of detailing structural concrete. In general the hole diameter (or dimension in the direction considered) should not exceed 25% of the relevant section. Even holes of this size may significantly affect the design of heavily loaded beams.
Acknowledgement: The Concrete Society
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