Civil Engineering Association

The emphasis of this report is on methods for assessing a concrete structure following a fire and hence for determining the extent of the required repairs. The design approaches used to assess the strength of repaired elements, illustrated by the design examples in Appendix B, are in accordance with the relevant Eurocodes(3, 4, 5). In addition to structural damage, there may be smoke damage to partitions, electrical and mechanical systems etc. Although the associated costs of cleaning or replacing such systems can be significant, they are not considered in this report. The focus of this report is on fires in reinforced concrete buildings, including multi-storey structures, warehouses and factories, but the principles are equally applicable to civil engineering structures, such as bridges. However, tunnels are specifically excluded as an assessment of their performance will require specialised geotechnical input, which is beyond the scope of this report. There is a major difference between designing a structure to withstand a fire, allowing for safe evacuation and fire fighting, and assessing the extent of damage caused by a fire so that repair methodologies can be proposed. While designing structures is predicting performance during a future event, assessing structures is determining its residual strength after such an event. Hence, the focus in the latter case and in this report is on methodologies to measure on site the residual strength and deformations and to obtain evidence of the temperatures reached during the fire. Calculation methodologies are presented that may assist during the evaluation process, but the working party felt that any assessment needs to be based mainly on an on-site evaluation of the fire damaged structure, which is supplemented as necessary by laboratory testing, examination or numerical assessment. In all cases, it is important that the assessment work is carried out by a competent person, who is aware of the limits of applicability for any methodology and whether special considerations for certain construction methods are required. The competent person needs to be aware that material properties and calculation methodologies presented in Eurocode 2 may not be applicable to the specific situation, since effects such as cooling of the structure or restraint and residual stresses need consideration after a fire event. This means that although the structure may have served its purpose according to Building Regulations and allowed for safe evacuation and fire fighting, considerable effort may be required to strengthen the structure for future occupation after a fire. A brief chapter on repair techniques is included, which makes reference to more detailed guidance. The working party considered that techniques are common to all repairs, irrespective of the cause of the damage, and not simply to the repair of fire-damaged concrete structures. Finally appendices to the report includes summaries of a number of case studies of the assessment and repair of structures damaged by fire, worked examples and historical information on design and material properties given in British Standards and other documents.