Title: Shortening Estimation for Post-Tensioned Concrete Floors—Part II: Calculations

Author(s): Guohui Guo and Leonard M. Joseph

Publication: Structural Journal

Volume: 110

Issue: 1

Appears on pages(s): 35-42

Keywords: creep; equivalent concrete age; floor shortening; post-tensioned concrete; pour slip; relative humidity; shrinkage; volume-to-surface ratio

DOI: 10.14359/51684327

Date: 1/1/2013

Abstract:
Part I of the study compares five concrete shortening prediction models, and the B3 model is considered to be the most appropriate model. Part II of the study provides detailed procedures to estimate post-tensioned (PT) concrete floor shortening. Different relative humidity values during and after construction are used to simulate the actual conditions concrete floors experience. For typical PT construction, concrete floor shortening due to elastic compression, concrete creep, and shrinkage can be estimated as approximately 1 in. (25 mm) per 100 ft (30.5 m). If different relative humidity values during and after construction are considered, the construction period can affect total floor shortening by more than 15%. Total shortening is minimized by longer construction exposure in regions with high relative humidity and shorter construction exposure in regions with low relative humidity. The helpful effect of pour strips in reducing PT floor shortening is studied and appears rather limited for typical construction.