Numerical Assessment on Bonded and Unbonded Prestressed Concrete Beams

The tendon stress in bonded prestressed concrete (BPC) beams is section-dependent while it is member-dependent in unbonded prestressed concrete (UPC) beams, leading to marked difference between these two structural systems. However, little work has addressed the bond effect of steel tendons. This research presents comparative investigations of BPC and UPC beams with various prestress levels. A numerical model is experimentally validated. Numerical assessments are conducted for simply supported and continuous scenarios, focusing on the effects of bond condition and prestress level. The results show that BPC beams exhibit better crack pattern (i.e., smaller crack width with larger crack zone) than UPC beams. The difference in ultimate loads or deflections between BPC and UPC beams depends heavily on the prestress level (the values of UPC beams are around 64% and 94% of those of BPC beams at prestress levels of 25% and 75%, respectively). Unbonded tendons produce greater moment redistribution in continuous scenarios than bonded tendons. It is also shown that the ACI code cannot well describe the bond impact of steel tendons on moment redistribution in continuous scenarios. A modified ACI equation is proposed, which can predict accurately the moment redistribution in both BPC and UPC beams.

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