Effect of Early Age Loading on Time-Dependent Deflection and Shrinkage Restraint Cracking of Slabs with Low Reinforcement Ratios

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Title: Effect of Early Age Loading on Time-Dependent Deflection and Shrinkage Restraint Cracking of Slabs with Low Reinforcement Ratios

Author(s): J.I. Lee, A. Scanlon, and M.A. Scanlon

Publication: Special Publication

Volume: 246

Issue:

Appears on pages(s): 149-166

Keywords: creep; deflection; early-age; experiment; reinforced concrete; shrinkage; slab; time-dependent

Date: 9/1/2007

Abstract:
This paper describes laboratory tests on nine simply supported one-way reinforced concrete members subjected to immediate live load and sustained load. The specimens are 12 ft (3.66 m) long supported on an 11 ft. (3.35 m) span, 12 in. (304.8 mm) wide, and 5 in. (127 mm) deep with two #3 bars at an effective depth of 4 in. (101.6 mm) providing a reinforcement ratio of 0.0046. The specimens were moist cured for up to seven days. Three specimens each were removed from the forms and subjected to immediate live load at three days, seven days, and twenty eight days followed by sustained load due to self weight. Each specimen was subjected to immediate full live load again after six months. Applied load and mid-span deflections were recorded under immediate live load and sustained load. The test results demonstrate the effect of shrinkage restraint provided by embedded bars on the flexural cracking of the specimens under applied load, as well as effects of early age loading on time-dependent response. Calculated deflections based on effective moment of inertia for immediate deflection and long time multipliers for time-dependent deflection are compared with measured deflections.