PC Beams with Unbonded Tendons: Analysis in Cracked, Uncracked and Ultimate State

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Title: PC Beams with Unbonded Tendons: Analysis in Cracked, Uncracked and Ultimate State

Author(s): A.E. Naaman

Publication: Special Publication

Volume: 231

Issue:

Appears on pages(s): 105-128

Keywords: bending analysis; external prestressing; nominal bendingresistance; prestressed beams; prestressed slabs; serviceability limitstate; ultimate limit state; unbonded tendons

Date: 10/1/2005

Abstract:
Assuming the prestressing force remains constant with applied externalload, the analysis of beams prestressed with unbonded tendons under service loads,where the section is uncracked, is no different than the analysis of beams with bondedtendons. However, after cracking, significant differences emerge, the most importantof which is that the stress in the unbonded tendon is member dependent, that is, itdepends on the deformation of the member, while the stress in the bonded tendon issection dependent, that is, it depends on the curvature of the section. This causes thestress in unbonded tendons to be significantly smaller than that for bonded tendons,and that is particularly important at nominal bending resistance.This paper summarizes the analysis procedure for beams prestressed with unbondedtendons at service and ultimate limit states; it focuses in particular on three problems:1) how to analyze a beam in the elastic uncracked range of behavior; 2) how to analyzea beam in the elastic cracked range of behavior; and 3) how to analyze a beam atnominal bending resistance.