Unified Procedures for Predicting the Deflection and Centroidal Axis Location of Partially Cracked Nonprestressed and Prestressed Concrete Members

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Title: Unified Procedures for Predicting the Deflection and Centroidal Axis Location of Partially Cracked Nonprestressed and Prestressed Concrete Members

Author(s): Dan E. Branson and Heinrich Trost

Publication: Journal Proceedings

Volume: 79

Issue: 2

Appears on pages(s): 119-130

Keywords: beams (supports): cnckiag (fracturing); creep properties: cyclic loads: deflection; flexural strength; loads (forces); modulus of elasticity; moments of inertia; prestressed concrete: reinforced concrete: structural members;bonded prestressing.

Date: 3/1/1982

Abstract:
A unified I-effective procedure for predicting the short-time deflection of cracked nonprestressed and prestressed concrete members is formulated. The procedure also lends itself to a simple method for estimating the time-dependent effects on deflection of creep and cracking under a limited number of Ioading cycles. Experimental and computed results were compared for four full-size beams, two under two-cycle short-time ioading and two under a few hours time-dependent two- and four-cycle loading. The agreement was found to be satisfactory to quite good. One nonprestressed, one bonded prestressed, and two unbonded prestressed concrete beams were tested. In addition, one of the beams was used to study the effect of the cracking moment prediction on the deflection prediction, and another beam was used to study the deflection of an unbonded prestressed one-way slab-type member with no bonded steel for crack control. A unified procedure was formulated for predicting the location of the centroidal axis of cracked nonprestressed and prestressed concrete members. The four beams described above, plus one additional full-sized bonded prestressed beam under two-cycle short-time loading, were used to compare experimental and computed results. The agreement ranged from reasonably satisfactory to quite good. Both procedures empirically account for the effect of concrete tensile stresses, including in small moment regions, from the top of each rack to the neutrai axis and also between cracks, referred to as tension stiffening.