Time-Dependent Deflection and Cracking of Reinforced Concrete Flat Slabs


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Title: Time-Dependent Deflection and Cracking of Reinforced Concrete Flat Slabs

Author(s): R. I. Gilbert

Publication: Special Publication

Volume: 203


Appears on pages(s): 157-178

Keywords: cracking; creep; deflection; flat slabs; laboratory tests; reinforced concrete; restraint; serviceability; service loads; shrinkage; structural behavior; time-dependent behavior

Date: 8/1/2001

An experimental program of long-term testing of large-scale reinforced concrete flat slab structures is described and the results from the first series of tests on five continuous flat slab specimens are presented. Each specimen was subjected to sustained service loads for periods up to 500 days and the deflection, extent of cracking and column loads were monitored throughout. The measured long-term deflection is many times the initial short-term deflection, due primarily to the loss of stiffness associated with time-dependent cracking under the combined influences of transverse load and drying shrinkage. This effect is not accounted for in the current code approaches for deflection calculation and control. Recently proposed procedures to improve deflection calculation (1) are evaluated against the test results and good agreement between the measured and calculated deflections is obtained.