New Ashton Arch – functional assessment of direct and indirect construction costs and evaluation of service life with respect to flooding risk.

AECOM SA (Pty) Ltd, Bridge Engineering, Cape Town, South Africa

^* Corresponding author: philip.ronne@aecom.com

Abstract

The bridge crossing the Cogmanskloof River in the town of Ashton, South Africa, had a history of over-topping due to severe flood events. The poor flood resilience of the bridge was aggravated by the generally hydraulically inefficient openings, the number of substructure supports in the river course, and a high debris load during flooding. The strategically important tourist route had to be closed, while localized flood damage repairs were undertaken, with resultant adverse effects on the local economy. As part of a road safety improvement project between the towns of Ashton and Montagu, improvement of the flooding resistance at the Ashton river bridge was required. This paper documents the functional evaluation of economicand technical-assessments of the flooding risks for the existing retro-fitted bridge. A new tied-arch bridge was the selected structural form of the replacement structure – based on the assessment of the key service life and constructability criteria. The structural form of the Ashton Arch paid careful regard to the scenic location and historic character of the previous multiple arch bridge form.