Modelling temperature and stress development in large concrete elements under sequential construction conditions: Experience with the Msikaba Bridge foundations

This paper describes the development and use of a finite-difference model for predicting the time-temperature profiles in the large concrete foundations for the Msikaba cable stayed bridge on the N2 motorway in South Africa. The important features of the temperature prediction model were the need to account for sequential construction in incremental layers as well as for the effects of solar radiation on the top surface of the concrete layers. The predicted temperature profiles were then used to estimate the likely thermal strains in the concrete and the related risk of cracking. The primary objective of the temperature and stress predictions was to determine a suitable combination of construction layer thickness and time interval between placement of concrete layers to minimize the risk of cracking. The modelling indicated that a concrete layer thickness of 2 m placed at 5 to 7 day intervals would be acceptable for this project.