A combined finite difference and finite element model for temperature and stress predictions of cast-in-place cap beam on precast columns

Abstract

In this study, a combined finite difference and finite element model was developed to predict the temperature development, thermally induced stresses and associated cracking risk in the concrete of a cast-in-place cap beam cast on precast columns of a bridge. The numerical model considers degree of hydration dependent heat rate, Young’s modulus development, strength development and early age tensile and compressive creep behavior. The temperature and stress analyses were performed on two sections of a cast-in-place cap beam (with a cross section of 1.6 m × 2.1 m): one at mid-span of the cap beam and the other on top of the precast column. The results show that the section of the cap beam at the column had high tensile stresses at the mid-sides which exceeded the early age concrete tensile strength when not covered with insulation blankets during construction. Additionally, the use of insulation materials, reduction of initial concrete temperature and proper choice of casting time can significantly mitigate the thermal stress and cracking risk of the cap beam. The model can be conveniently programmed and be a useful tool to help engineers control concrete temperature and take measures to minimize the risk of early-age thermal cracking for cast-in-place pier caps and its connection to a precast column, or other similar concrete members/connections, thus accelerating construction schedules for bridge projects.