Title: Shortening Estimation for Post-Tensioned Concrete Floors—Part I: Model Selection
Author(s): Guohui Guo and Leonard M. Joseph
Publication: Structural Journal
Appears on pages(s): 27-34
Keywords: creep; equivalent concrete age; floor shortening; post-tensioned concrete; pour strip; relative humidity; shrinkage; volume-to-surface ratio
For post-tensioned (PT) concrete floors, shortening occurs due to elastic compression, concrete creep, concrete shrinkage, and temperature change. The longer the continuous concrete slab, the greater the cumulative shortening effect. More commonly, some restraints to shortening exist, such as shear walls and stocky columns. At best, restraint to shortening (RTS) can induce cracks and spalls that affect aesthetics and durability. At worst, it can affect structural safety. Therefore, appropriate models and procedures that can predict shortening are quite necessary. In the first part of this study, five concrete creep and shrinkage models are compared for both ultimate values and relative shortening rates. The B3 model is considered to be the most appropriate model. Adjustments to the B3 model are introduced by using equivalent concrete age to account for high early concrete strength frequently used in PT construction. Part II of this study covers detailed procedures to estimate PT concrete floor shortening.