Impact of using higher strength concrete on the design of prestressed concrete bridges

Abstract

AASHTO highway live loads are sometimes increased to idealize more realistic traffic conditions. Certain regions in the Middle East require increasing the AASHTO HL93 live loads by a 1.5 factor based on comparisons with the British Standards HA + HB live loads. Even in the US, the AASHTO live loads may not always represent modern state-legislated truck configurations. This paper shows the impact of using higher strength concrete on the design of precast, prestressed girders subjected to stringent loading and environmental conditions. A parametric study that relates the girder size and spacing to the span length for HL93 and 1.5 × HL93 live loads as a function of the concrete 28-day strength and environmental classifications is conducted for this purpose. It is shown that increasing the 28-day concrete strength from 40 (5800) to 50 MPa (7200 psi) allow increasing the HL93 live load by 50% and reducing the service load tension stress limit from 0.5√f'c, MPa (6√f'c, psi) to zero without drastically changing the precast girder size and configuration.