Precast concrete voussoir geometry in a skewed arch bridge

Abstract

The replacement of Midmill Bridge, a reinforced concrete arch bridge crossing Cruden Water in north-east Scotland, was accomplished by the construction of an arch comprising discrete interlocking precast concrete voussoirs. By eliminating reinforcement entirely from the arch structure, durability was improved. The re-aligned road crosses the river obliquely and to maintain the spandrels parallel to the road the arch has an end skew of 35˚. Skewed arches pose a design challenge as the geometry of the coursing of the voussoirs is surprisingly complex. Three-dimensional computer-aided design modelling was deployed to obtain a single precast voussoir block that could be set out and placed on the barrel falsework requiring no more than conventional site skills and resources. In total 479 copies of this single voussoir were cast to construct the majority of the arch barrel. The voussoirs are placed in the English or helicoidal arrangement with special precast blocks to form the arch springings.

Editorial: Arch bridges – modern developments

“…Redpath (2013) explains how the chosen solution not only provided the most economic initial capital outlay but also offered the most durable solution because of the absence of steel reinforcement. The innovative use of 3D modelling allowed the discrete voussoir blocks to be precast and then erected on site by conventional site resources to produce an economic structure with a pleasing traditional appearance.…”