Effect of Shrinkage on Short-Term Deflection of Reinforced Concrete Beams and Slabs


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Title: Effect of Shrinkage on Short-Term Deflection of Reinforced Concrete Beams and Slabs

Author(s): P.H. Bischoff and R.D. Johnson

Publication: Special Publication

Volume: 246


Appears on pages(s): 167-180

Keywords: deflection; reinforced concrete beam; shrinkage; stiffness; tension stiffening

Date: 9/1/2007

This paper investigates the influence of shrinkage on tension stiffening in flexure and subsequent effect on short-term deflection in beams and slabs. While shrinkage is typically thought of as being a long-term effect, it can also have a significant effect on the initial short-term response (particularly for beams tested in the laboratory that are used to develop and validate theoretical models for predicting deflection). Shrinkage that takes place before the beam is loaded is locked into the member response, having the effect of reducing the cracking moment (caused by tensile stresses that develop in the concrete from restraint to shrinkage by the reinforcement) and causing a shift in the bare bar response of the cracked transformed section. The lower cracking moment and shift in the cracked member response both work together to increase the immediate (short-term) deflection of a member loaded in flexure. Neglecting this influence leads to a perception of reduced levels of tension stiffening and also affects comparison of theoretical deflection models with experimental results.