Experimental Evaluation of Post-Cracking Deflection Behavior in Prestressed Concrete Beams

Abstract

Precast prestressed concrete beams are more efficient and effective than the traditional reinforced concrete beam, but their performance is more difficult to predict. This experimental thesis was run to quantitatively compare deflections between laboratory precast prestressed concrete beams to ACI 318-19 and PCI Design Handbook (8th edition) design methods. A full design and testing procedure is detailed for 12 rectangular beams with varying levels of partial prestressing to compare the effects of mild steel in prestressed beams. The rectangular beams are designed with uncracked, transition, and cracked sections at a constant service load. Testing procedures are detailed for full sized, typical double tee sections designed by Metromont. This research analyzed and commented on the performance of the different rectangular beams and double tees in relation to calculated deflection prediction curves. Additional comments are made on the cracking of the rectangular beams in relation to previous studies. Results from the rectangular beams deflections show a consistent low prediction in initial stiffness, varying results at service, and higher inaccuracy in post cracking predictions with increasing mild steel when using the effective moment of inertia and bilinear methods for predicting deflections. Cracking patterns show similar results from previous studies and vary when mild steel is introduced. Findings from this research conclude that the current methods for predicting deflections are not reliable in all situations.