Pretensioning of a railway bridge prototype with CFRP rods

Author: Gabriel Obrecht
Language: English

Abstract

Switzerland’s bridge infrastructure is ageing, and durability problems have become more prevalent over the last decades. As a result, the Swiss Federal Railways (SBB) have launched a project to investigate an alternative standard bridge system, which is more durable than the current one.

The thesis examined the prestressing process of a proposed bridge standard system prestressed with carbon-fibre-reinforced polymers (CFRP). CFRP is promising as it does not show any signs of corrosion or fatigue. However, prestressing with CFRP is challenging (especially due to its anisotropy) and not yet an established applica-tion.

Incorporating literature and prevalent design codes on this topic, as well as analytical calcula-tions and strain measurements during and after prestressing of two longitudinal beams belong-ing to a prototype, the bridge system was de-signed. Furthermore, analytical calculations on the long-term behaviour of the final proposed bridge system - which will be a further devel-oped version of the prototype - give an idea of what to expect over the lifetime of this bridge - especially in terms of prestressing losses.

The results show that prestressing losses of about 15% have to be expected over a lifetime of 100 years. This exceeds the initially expected losses, mainly due to increased shrinkage of the concrete mixture used. Adequate measures to minimise shrinkage, such as wet curing, should be taken. Moreover, and based on the results, additional CFRP prestressing is suggested for the actual bridge to still fulfil the design criteria. What is more, strain measurements showed a favourable bond behaviour in the region of the development length, suggesting the used sand coating ensures an adequate bond. From the measurements, bond stresses were determined.