A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
4. Why is tension anchorage length generally longer than
compression anchorage length? (SR3)
Tension anchorage length of steel reinforcement in concrete depends on
bond strength. When steel reinforcement is anchored to concrete and is
subjected to compressive forces, the resistance is provided by the bond
strength between concrete and steel and the bearing pressure at the
reinforcement end. Tension lap length is generally longer than compression
lap length. In some design codes, instead of permitting the use of bearing
pressure at reinforcement ends, the allowable ultimate bond stress is
increased when calculating compression anchorage length.
5. Why does lap length generally greater than anchorage length?
(SR3)
In some structural codes, the lap length of reinforcement is simplified to be
a certain percentage (e.g. 25%) higher than the anchorage length. This
requirement is to cater for stress concentrations at the end of lap bars. A
smaller load when compared with the load to pull out an anchored bar in
concrete triggers the splitting of concrete along the bar because of the
effect of stress concentration. A higher value of lap length is adopted in
design code to provide for this phenomenon.
6. Does longitudinal steel serve as an enhancement of shear
strength?
In addition to shear resistance provided by shear reinforcement, shear
forces in a concrete section is also resisted by concrete compression force
(compressive forces enhances higher shear strength), dowel actions and
aggregate interlocking. The presence of longitudinal steel contributes to
the enhancement of shear strength of concrete section in the following
ways [46]:
(i) The dowelling action performed by longitudinal reinforcement directly
contributes significantly to the shear capacity.
(ii) The provision of longitudinal reinforcement also indirectly controls the
crack widths of concrete section which consequently affects the degree
of interlock between aggregates.
7. Why are longer tension lap lengths designed at the corners and at
the top of concrete structures? (SR3)
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