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Abstract

The thesis describes a study of the effects of lateral restraint on the bond behaviour of reinforcement bars. Bond performance of three types of deformed bars, namely Torbar, Hybar and Square-twisted bars has been investigated experimentally both under varying levels of lateral tension release and lateral compression. The tests included different values of concrete cover to the reinforcement bars and the study of the bond behaviour of top and bottom cast reinforcement bars under lateral compression.

Ultimate bond stress and critical bond stress defined as at the serviceability limit state are shown to increase progressively with cover and the square-root of the lateral compression, the cover affecting the ultimate bond stress more significantly than the lateral pressure. However, a limiting cover of 3*5 bar diameters and a lateral compression of about 25 per cent of the compressive strength of concrete are shown to give the maximum bond resistance. The bursting effects of lateral compression are suggested to affect the bond performance of reinforcement bars under lateral compression. Torbar and Hybar are shown to develop higher ultimate bond resistance under lateral compression than the Square-twisted bars. Top cast bars are demonstrated to be inferior in bond resistance than bottom cast bars.

Ultimate bond stress and critical bond stress are shown to decrease with decreasing cover and increasing lateral tension release. Complete loss of bond is suggested at a tension release of about ^250 micro- strains. A limiting cover of 3.5 bar diameters is shown to offer the maximum bond resistance. Torbar and Hybar are again demonstrated to perform better under tension release than Square-twisted bar.

The interactive behaviour of cover with either lateral tension release or lateral compression has been studied and relationships between bond stress, concrete cover and lateral restraint have been formulated based on the experimental results, both at ultimate and serviceability limit states. A theoretical model for the bond behaviour of reinforce- ment bars under lateral compression at serviceability limit state has been proposed and verified with the experimental results. The safety factors under lateral tension release and lateral compression are examined based on the provisions for bond design in the current Code of Practice C.P. 110.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Communication & Creativity > School of Communication & Creativity Doctoral Theses School of Science & Technology > Engineering Doctoral Theses

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