Roof and Floor Slabs Assembled with Precast Concrete

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Title: Roof and Floor Slabs Assembled with Precast Concrete

Author(s): B. Venkateswarlu, Jeganathan Shanmugasundaram, and Vadivelu Shanmugam

Publication: Journal Proceedings

Volume: 79

Issue: 1

Appears on pages(s): 50-55

Keywords: concrete slabs; cracking (fracturing); deflection; flexural strength; floors; hollow core slabs; joints (junctions); keys and keyways; loads (forces); moments; precast concrete; roofs; shear stresses; stiffness; two-way slabs.

Date: 1/1/1982

Abstract:
Roof and floor slabs constructed by jointing the precast concrete cored units with shear keys resist higher load intensities and show fewer deflections than the individual units due to transfer of loads through the shear keys. The extent of two-way distribution of loads in these slabs depends on their aspect ratios and torsional to flexural stiffness ratios. Full-scale tests showed that for a uniformly loaded, two- way slab with an aspect ratio of 1.1, the cracking load and the load at 0.1 mm crack width were 67 and 30 percent, respectively, more than in the case of the individual unit. The maximum deflection of the two-way slab under a service load of 4000 N/m2 [Pa] (82 psf) was found to be 83 percent less than in the case of the individual unit, and this difference increased to 260 percent at cracking load. The slabs constructed with precast concrete units have been analyzed as orthotropic slabs with zero flexural stiffness perpendicular to the line of joints; expressions for deflections, moments, and shear force have been derived. Coefficients to compute the maximum values of deflections, moments, and shear force for uniformly loaded, simply supported slabs with different aspect ratios and with different torsional to flexural stiffness ratios are presented. The deflections predicted from theoretical analysis of the slab under test agreed very closely with the test results up to cracking load. Beyond cracking load, the deflections computed using postcracking stiffnesses were found to be slightly more than the measured values.