Influence of shrinkage strains on the cracking of reinforced concrete beams

The development of strains in the tensile reinforcement of a reinforced concrete beam, obtained from flexural tests using strain gauged reinforcement, is discussed and the consequences of loss of strain compatibility, together with plane sections no longer remaining plane, are highlighted. These are contrasted with assumptions made in practical design and some resulting mismatches are flagged. The effect of internally restrained shrinkage on strain distributions across both uncracked and cracked sections is discussed and it is shown that the reinforcement is in compression, even for the cracked situation. Experimental evidence is presented to support the latter assertion. Results of this work demonstrate that it can be appropriate to add part of the shrinkage strain to the cracking strain resulting from mechanical loads. A revision to the crack width expression 7.8 in Eurocode 2, which currently ignores this effect, is proposed and discussed.