Time-dependent vertical shortening prediction for super-tall buildings by using a modified B3 model to consider moisture distribution

Abstract

The time-dependent vertical shortening behavior is crucial for super-tall buildings. However, the existing models to predict shrinkage and creep do not consider the moisture distribution. In this study, the vertical shortenings of mega column and shear wall for super-tall buildings are predicted by a modified B3 model to consider moisture distribution of mega steel reinforced concrete sections. Firstly, the moisture distribution of mega section is numerically predicted with the wisely identified moisture diffusion coefficient and surface exchange coefficient. The predicted moisture shows favorable agreement with the measured result and the identified moisture diffusion coefficient (2.5E-4 m2/h) and surface exchange coefficient (1.1E-3 m2/h) are preferred. The total strain including elastic strain, shrinkage and creep is then predicted by the B3-fiber model to consider the moisture distribution, which provides the strain database of mega sections. Large differences exist in the strain predictions between the B3-fiber model and the traditional B3 model. The traditional model largely overestimates the strains of mega section. Thirdly, a modified B3 model is proposed to predict the vertical shortenings by introducing three correction coefficients to consider moisture distribution and verified by the strain database. The total strains predicted by the modified B3 model show good agreement with those by the B3-fiber model. Finally, a super-tall building project Shanghai Tower is employed as an example to demonstrate and validate the proposed modified B3 model. The vertical shortenings predicted by the modified B3 model show better agreement with measurements than those by the traditional model.