DETERMINING THE FIRE RATING OF CONCRETE STRUCTURES, Case study of using a probabilistic approach and travelling fires

Abstract

As part of a refurbishment the height of a building in London is to be increased resulting in a change of the fire rating of the existing level from R60 to R90 as per prescriptive guidance. To investigate whether the inherent fire resistance of the structure would be sufficient a state-of-the-art probabilistic approach was adopted, with the approach extended to consider 2D heat-transfer to concrete elements. After determining the required reliability of the structure based on an acceptable risk level, a Monte-Carlo assessment was conducted. This considered for the proposed internal layouts and determined the range of input parameters to be randomly varied in order to define the required range of design fires analysed. The assessment demonstrated that the inherent structural fire resistance would provide sufficient structural reliability for the new use of the building and that no additional fire protection was required to the concrete frame.

Member and structural fragility of reinforced concrete structure under fire

“…Moreover, results from empirical models are in complete disagreement with comparatively modern risk-based approaches, indicating the existence of significant uncertainties in the system, which resulted in obtaining the response to be highly sensitive to these uncertain parameters (Van Coile et al, 2013;Huang and Delichatsios, 2010). Considering these aspects, probabilistic approaches are observed to have the potential to provide appropriate understanding for assessing the variabilities and uncertainties to achieve safe and economic design of structures susceptible to catastrophic fire (Khorasani et al, 2015) as is enormously proved in the field of earthquake engineering (Roy and Matsagar, 2017;Saha et al, 2016a). The quantification of structural vulnerability is a critical objective in structural fire engineering as the risk assessment strategies enable designers and key stakeholders to study tradeoffs in utility and cost for determining best engineered solution for a given target performance level .…”

“…The quantification of structural vulnerability is a critical objective in structural fire engineering as the risk assessment strategies enable designers and key stakeholders to study tradeoffs in utility and cost for determining best engineered solution for a given target performance level . Therefore, to measure the uncertainties associated with the random variables, the development of fragility functions becomes an attractive procedure for assessing the vulnerability of structures under fire (Khorasani et al, 2015;Gernay et al, 2018). The use of probabilistic frameworks by developing fragility functions has been in use over a significant period to evaluate vulnerability at structural and community level under seismic hazard (Ellingwood and Kinali, 2009;Saha et al, 2016b).…”

“…Moreover, the fire models in the design guidelines are unable to provide the required confidence level for achieving desired structural performance exposed to fire (ElMohandes and Vecchio, 2016), which necessitated adopting the probabilistic approaches to investigate the fire performance for structural fire safety. Hence, the probabilistic approach provides relatively worthwhile knowledge about the reliability of structural systems, which is a crucial component of more resilient built environment (Khorasani et al, 2015).…”

“…Initially, probabilistic methodology in fire safety engineering was used to investigate load and resistance factors for designing structures exposed to fire (Ellingwood, 2005). Thereafter, Monte Carlo (MC) simulation and reliability techniques were used to investigate member level performance of RC structures considering uncertainties in structural capacity and fire loading (Sidibé et al, 2000;Shi et al, 2013;Guo et al, 2013;Balogh and Vigh, 2016;Kho et al, 2017). It was concluded that the proposed methodologies provided insight into more practical approach to assess the reliability for more complex JSFE 11,4 structural systems.…”