Temperature simulation by FEA as a tool in forensic investigation

Temperature is a potential factor within many civil engineering failures. Finite element analysis (FEA) can be used as a powerful tool to allow the effect of temperature upon a material to be simulated as part of the investigation process. This paper describes the use of FEA to recreate the temperature history in three different structures: a slipformed caisson, a tunnel and a car park.

Loss adjustors requested an investigation of a newly constructed reinforced concrete slipformed caisson. The multi-celled caisson, approximately 34m long, 20m wide and 16m high, was intended to form the gate to a large dry dock. Unfortunately, at completion of the slipforming, substantial defects were discovered to the internal faces of the caisson which were not visible during construction. FEA was undertaken to recreate the temperature conditions within the concrete as slipforming proceeded. This analysis, together with information on the concrete mix, demonstrated that the increased temperature built up inside the caissons could trigger premature setting of the concrete leading to the observed defects.

Two 0.72m OD GRP pipes in the invert to a 3.2m OD diameter sewage transfer tunnel failed after approximately two years in service. The failure was believed to be partially connected with uneven restraint to the pipes from the concrete benching in which they were encapsulated. The benching was found to have developed longitudinal cracking prior to failure of the pipes and FEA was used to recreate the temperature and moisture conditions in the benching to determine if the longitudinal cracking arose from the design or a failure to cure the concrete.

Following problems with movements due to solar gain in a precast concrete car park, FEA was used to simulate the temperature profile through the deck. The 16m span of the deck units in combination with the use of a relatively dark coloured, thin, deck waterproofing system resulted in pronounced upward rotation of the deck units in sunny conditions coinciding with spalling at the bearing shelf. FEA of the replacement deck showed rotation at the support could be reduced by approximately 75% by the use of shorter spans and mastic asphalt surfacing.

The ability to simulate different scenarios in the above structures using FEA provided a means to identify the relative importance of different factors in each failure and to mitigate the risk of reoccurrence.

• Abstract

• Introduction

• Case Studies

• Conclusions

• References