Keisuke MINOWA

Investigation of Environmental Action Model Applied to Prediction of Shrinkage of Concrete in Structures

Takumi SHIMOMURA

Temperature and humidity are major factors in determining shrinkage in concrete. Also, solar radiation and rainfall is taken into account when estimating shrinkage of real concrete structure in natural environments. In this investigation, Nadachi-Bridge was investigated as a case study, due to the nature of cracks present on the balustrade, drying shrinkage was assumed as the main cause for the cracks.
The?objectives?of?this?study?are to estimate the crack occurrence in concrete structures from its appearance and evaluate them quantitatively; verify the applicability of shrinkage prediction by drying shrinkage prediction formula in real concrete structures, and propose a model that accounts for environmental actions with respect to drying shrinkage predictions in real concrete structures.
The actual shrinkage was estimated from the crack width and compared with the results from drying shrinkage prediction formula. The estimated shrinkage was smaller than that of the prediction formula, it was deduced that the shrinkage prediction formula excessively predicts the drying shrinkage when the average relative humidity is applied. 
Therefore, solar radiation and rainfall are expressed in the analytical program to check the influence of these factors, which predicts the strain of concrete structures under natural environments. Analytical results confirm that temperature rises on the surface of concrete structures while temperature inside of concrete is increased due to solar radiation which promotes shrinkage. On the other hand, shrinkage is reduced due to the wetting process of rainfall.
Based on the prediction of shrinkage of actual concrete structures and from numerical simulations, it was considered a necessity for a new environmental action model for shrinkage prediction under natural environments. Therefore, using the results of numerical simulation, it was proposed to identify an apparent relative humidity, considering the influence of solar radiation and rainfall, and apply it to the shrinkage prediction formula as an environmental action. The apparent relative humidity is not greatly different in all parts of Japan, and it is around 85 to 90%. The results of shrinkage of Nadachi-Bridge which using the prediction formula applying the apparent relative humidity roughly agreed with the shrinkage estimated from cracks.