Structural Fire Engineering Services: Case study on existing residential buildings, UK
A long-standing SOCOTEC UK & Ireland client and major residential developer identified breaches in protective layers during site assessments of existing residential buildings. The key question that needed answering for the client was whether extensive and costly remediation works would be required to retrospectively protect the structure, or whether a targeted approach could be adopted, all while maintaining safety and compliance.
Key information
- Client: Major UK Residential Developer
- Location: United Kingdom
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Project details and background
The client required an assessment of several existing steel-framed residential structures with precast concrete unit floors, in which compromised fire protection had been identified. Buildings are typically designed to achieve a specified structural fire resistance; however, throughout the life of a building, structural protection may be compromised by ageing, poor maintenance, or building works.
The project involved two residential buildings one five-storey and one six-storey structure both requiring evaluation to determine whether their inherent structural fire resistance could meet safety requirements despite the identified gaps in protection. Without a detailed understanding of structural behaviour under fire conditions, the client faced the prospect of blanket remediation across all affected buildings, with high cost, disruption, and environmental implications.
Solution
SOCOTEC's Structural Fire Engineering (SFE) team conducted performance-based structural fire analysis using advanced finite element modelling through a software called OpenSees. Thermo-mechanical models were developed to assess the steel-framed structures under fire conditions using the standard time-temperature curve.
The assessment considered exposed steel beams and fire-protected columns, using a conservative fire scenario assuming fire spread between flats to evaluate the behaviour of structural elements against established acceptance criteria.
Key findings from the analysis included:
- Assessment of the most critical structural locations, including the longest spanning beams, to evaluate the buildings' inherent structural fire resistance.
- Within the five-storey residential building, the central beam exceeded acceptance criteria during assessment. Significant bowing of the steel-composite floor resulted in high deflections and displacement rates during the early stages of fire exposure, indicating potential failure.
- SOCOTEC’s SFE team recommended passive fire protection for this isolated beam to prevent failure during a real fire event. All remaining modelled beams demonstrated adequate fire resistance and required no retrospective protection. Similarly, all columns met the required performance criteria, eliminating the need for additional fire protection measures.
- Within the six-storey residential building, all heated beams remained in compression throughout the analysis and none exceeded acceptance criteria. Column load redistribution did not result in overloading of heated columns, and no columns experienced reversal in vertical displacement.
- As a result, no retrospective fire protection was recommended for the beams. However, one column was identified as carrying the most significant loading and was highlighted as the most vulnerable element, with specific emphasis placed on inspecting its fire protection during future surveys.
This approach enabled targeted fire protection measures to be implemented only where required, avoiding unnecessary retrospective protection while maintaining compliance with structural fire performance requirements.
Conclusion
Structural performance assessment
SOCOTEC’s detailed analysis of the fire performance of existing structures was to determine whether the required level of resistance was achieved. The findings demonstrated that structural stability was maintained, despite insufficient protection in specific locations, with only a few isolated structural elements requiring retrospective passive protection.
Targeted remediation measures
These measures were recommended in conjunction with comprehensive fire strategy enhancements, including means of escape provisions and active fire protection systems. This proportionate, performance-based approach prevented unnecessary extensive remediation works by avoiding blanket remediation, whilst upholding safety standards and compliance.
Sustainability & cost benefits
By preventing unnecessary application of passive fire protection materials, the analysis significantly reduced the carbon footprint associated with manufacturing, transportation, and installation. In turn, this led to a substantial reduction in cost to the client, optimising expenditure whilst maintaining compliance and safety.
Operational & resident impact
SOCOTEC’s findings ensured there was minimal disruption to residents in the occupied building by targeting critical structural elements. This approach delivered significant benefits across multiple areas while maintaining safety and compliance requirements.
