•The spatial and temporal distributions of fire temperature within the tunnel is presented from a series of FDS simulations.•A simplified method to incorporate concrete spalling in finite-element ...modeling is proposed.•Fire damage to a tunnel liner is characterized using temperature criteria and structural response.•Damaged volume of concrete, including spalling, is quantified for a range of fire scenarios.•Stability of the tunnel structure is checked for extreme fire scenarios.
There are no available guidelines or methodologies to design the concrete lining in a tunnel for loss of functionality following a fire event. Historical tunnel fires confirm that tunnel downtime following an extreme event can lead to major economic losses, while fire protection design of the concrete lining can be adjusted to minimize losses. This paper provides a framework to characterize fire damage in a tunnel structure, where spatial and temporal distributions of fire temperature within a tunnel structure are modeled, and statistics of the potential damaged volume of the concrete lining that would require repair are quantified. A simplified spalling model, considering an initiation time, rate of spalling, and finishing time, is incorporated within the analysis to provide a more realistic measure of the damage. The results show that incorporation of spalling makes a significant difference in the damage assessment. Structural stability of the tunnel is checked under an extreme fire scenario to verify that, while experiencing extensive damage, the structure does not collapse. This paper focuses on a passenger railway tunnel, and is a first step in establishing a risk-based framework to guide fire protection design of a tunnel lining. The proposed approach can be applied to other tunnel types.
•The fire behavior of reinforced concrete tunnel slabs during both the heating and cooling phases are simulated.•Three modeling strategies are investigated using beam, shell, and solid elements.•Five ...recent fire tests on loaded and restrained large-scale tunnel slabs, with varying concrete strengths, restraint levels, and fire scenarios, are selected to verify the models.•Temperature and displacement evolutions during heating and cooling obtained from the numerical models are compared with the experimental test data.•Shell elements perform the best by achieving a balance between model accuracy and efficiency.
This paper examines different modeling approaches to simulate the behavior of reinforced concrete (RC) tunnel slabs under fire during both the heating and cooling phases. Three modeling strategies are investigated by using beam, shell, and solid elements in addition to different methods to capture the effect of axial restraint on the slabs. The models consider temperature-induced plastic deformations and irrecoverable degradation of materials. The models also utilize distinct concrete properties for heating and cooling as well as account for the transient creep strain explicitly in the calculations. The results obtained from different modeling strategies are compared to five recent fire tests on loaded and restrained large-scale RC tunnel slabs, with varying concrete strengths, restraint levels, and fire scenarios. Temperature and displacement evolutions during heating and cooling obtained from the numerical models are compared with the experimental test data. When considering model accuracy and efficiency as the primary performance metrics, using shell elements to analyze the fire performance of reinforced concrete tunnel segments resulted in the best balance between the two. The numerical models and techniques developed in this paper will enable practicing engineers to reliably and rapidly assess fire damage to reinforced concrete tunnel linings, and to explore cost-effective designs of tunnels for fire.
•We propose a methodology for developing fire fragility functions for buildings.•The methodology is applied to a prototype multi-story steel building.•Uncertainties in fire, thermal, and structural ...models are considered in the analysis.•Event tree is used to combine fire scenarios in different building locations.•The functions allow for damage loss assessment due to fire in a community context.
This paper proposes a novel methodology for developing fire fragility functions for an entire steel building – meaning that the function is not specific to a location within the building. The aim is to characterize the probabilistic vulnerability of steel buildings to fire in the context of community resilience assessment. In developing the fragility functions, uncertainties in the fire model, the heat transfer model and the thermo-mechanical response are considered. In addition several fire scenarios at different locations in the building are studied. Monte Carlo Simulations and Latin Hypercube Sampling are used to generate the probability distributions of demand placed on the members and structural capacity relative to selected damage thresholds. By assessing demand and capacity in the temperature domain, the thermal and the structural problems can be treated separately to improve the efficiency of the probabilistic analysis. After the probability distributions are obtained for demand and capacity, the fragility functions can be obtained by convolution of the distributions. Finally, event tree analysis is used to combine the functions associated with fire scenarios in different building locations. The developed fire fragility functions yield the probability of exceedance of predefined damage states as a function of the fire load in the building. The methodology is illustrated on an example consisting in a prototype nine-story steel building based on the SAC project.
AbstractStructural risk assessment against fire requires robust material models that take into account the uncertainty in material behavior over a range of elevated temperatures. Such probabilistic ...material models can directly inform performance-based design procedures for building fire safety. The objective of this research is to quantify uncertainties in retained strengths of steel and concrete when exposed to fire. First, hundreds of experimental data points covering a temperature range of 20°C–1,000°C are collected from literature. Then, different distribution candidates and modeling approaches are used with the collected data to identify probabilistic models for temperature dependents strength of steel and concrete. The proposed models are continuous probability distribution functions, with simple mathematical representations that are easy enough to arrange into systematic code for implementation in analytical and computational frameworks. Additionally, the proposed stochastic functions consider continuity in reliability appraisals during transition from room temperature to elevated temperatures. These models are applied to probabilistic evaluations of structural performance of three steel and two concrete columns, and the influence of the model choice is compared using fragility curves. Finally, the proposed probabilistic models, developed using different approaches, led to close results when characterizing the performance of structural members.
Historic events and prior research confirm that fire following earthquake (FFE) can cause major social and economic losses in a community. FFE is influenced by a number of interacting factors. This ...paper identifies 27 cause factors (CFs) for FFE through data mining method and literature review. The CFs are grouped into four clusters: management, source of ignition, environmental factors, and earthquake hazard. Interpretive Structural Modeling (ISM) is used to construct the hierarchy structure of the CFs and analyze their internal relationships. As a result, a five-level ISM is built, in which, the direct, indirect, and source of CFs are identified. Subsequently, MICMAC (cross-impact matrix multiplication applied to classification) analysis is completed to partition the CFs into four quadrants (independent, linkage, autonomous, and dependent) based on their effect index and dependence index, and evaluate the degree of relationship between the CFs. The findings show that the causal influence network with 27 CFs has a strong hierarchy, with the CFs propagating unidirectionally from the bottom layer to the top layer. The CFs in the ignition category are more dependent and influenced by other categories as expected. Investing in a resilient electric network, enhancing design standard of buildings and appropriate retrofitting, and optimizing fire prevention strategies considering seasonal hazards could reduce the risk of FFE in a community. The results of this study provide insight into the interrelationships between the CFs for FFE and can be used to identify effective risk reduction strategies and improve fire safety.
AbstractDesign requirements for passive fire protection of steel structures in the United States are primarily based on prescriptive approaches. Yet performance-based design has gained attention in ...recent years for its potential to unlock design solutions that are robust, cost effective, and applicable to complex architectural configurations. For example, prior research has shown that fire protection on selected secondary beam elements in composite floor systems is not necessary due to the development of membrane action in the concrete slab during fire. In addition, the evaluation of a structure’s performance under realistic fire scenarios, required in a performance-based approach, is enabled by recent developments in advanced computational modeling. However, currently there are no systematic guidelines to determine the reliability of a performance-based fire engineering design. This study provides a comparative analysis of the fire performance of a floor system designed following prescriptive and performance-based approaches. The floor system is adopted from a prototype steel–concrete composite office building. Further, a parametric study is conducted to investigate the effects of several parameters on the thermal-mechanical response including the modeling approach, fire curves, applied gravity loads, and hazard scenarios. Performance is measured using survival time at the structural system level, but also with predefined thresholds in deflection and reinforcement bar temperature. The results demonstrate that the performance-based design is robust, and verification of safety is not dependent on a particular demand value or performance measure. Most importantly, the performance-based design shows resistance when subjected to natural fires with large percentage fractile of fire load as well as in multihazard post-blast fire situations.
•The fire performance of reinforced concrete tunnel lining sections is studied.•Four ground conditions ranging from shallow soft soil to deep rock are included.•The fire performance of lining ...sections is simulated during heating and cooling.•Fire-induced deformations and internal forces in the tunnel sections are compared.•Effect of temperature-dependent soil properties on tunnel fire behavior is studied.
This paper compares the fire performance of bored reinforced concrete tunnel lining sections under four ground conditions, ranging from shallow soft soil to deep rock. The fire performance is analyzed using a verified finite element beam-spring model. The investigated lining sections are adopted from realistic high-profile tunnels. A series of analyses are conducted to evaluate the performance of tunnel sections under a wide range of fire scenarios and ground conditions. First, the fire behavior of the four tunnel sections under the RABT-train fire curve is simulated during heating and cooling, and the results are reported in terms of structural performance and sectional stress–strain response. Second, the time to reach a limit state for the four tunnel sections is quantified under an extended RWS fire curve. Finally, a simplified methodology is proposed to include temperature-dependent soil properties, including the heat induced excess pore pressure and change in subgrade reaction modulus under elevated temperatures. The influence of temperature-dependent soil properties on the structural fire performance of a shallow tunnel section in soft clay is studied. The results show that bored reinforced concrete linings could experience significant irrecoverable damage from exposure to major fires. The moderate-depth tunnel section in soft soil and the deep tunnel section in high lateral pressure rock are the two critical cases, due to the large deformations and high internal forces, respectively. The importance of including temperature-dependent soil properties in tunnel fire analyses is demonstrated.
Fire hazards are a major threat to tunnel structures; however, the existing understanding of the behavior of tunnel linings under fire is limited, which restricts cost-effective and safe design of ...tunnels for fire. The research work in this paper aims to experimentally evaluate and quantify fire damage to tunnel linings considering a combination of influencing factors. The effects of three parameters on fire damage to the ceiling (typically the most damaged area) of a tunnel lining are studied through five furnace tests on large-scale reinforced concrete slabs. The parameters include: (1) concrete composition - presence/absence of polypropylene fibers, (2) the level of structural restraint (induced using post-tensioned strands), and (3) the fire intensity and duration. These parameters are selected to reflect realistic scenarios and provide a rational basis for evaluating tunnel damage, in terms of crack pattern, spalling, discoloration, non-destructive testing, and deflections during fire and after cooling. This research provides vital experimental data for fire damage assessment of reinforced concrete tunnel linings, and assists in verifying numerical models for analyzing structural performance during both the heating and cooling phases of fire.
•A total of five fire tests on large-scale reinforced tunnel concrete slabs are conducted.•The considered test parameters are concrete composition, level of restraint, fire intensity, and fire duration.•Fire damage to the slabs is evaluated from multiple aspects.•The lack of active or passive fire protection may lead to irrecoverable damage under moderate railway tunnel fires.•Moderate railway tunnel fires result in an average reduction of 15–20% in concrete strength.
This paper improves the existing frameworks on simulating fire following earthquake (FFE) by explicitly modeling the suppression process and the fire department response. The paper focuses on the ...impacts of FFE on urban areas and quantifies induced economic losses based on resources and efficiency of the fire department during post-earthquake fires. Layers of infrastructure systems, including transportation, water, and electric networks, and the building inventory are modeled and the earthquake damage to the community is characterized. The behavior of fire spread inside and between buildings is simulated based on major fire spread mechanisms. In parallel, the suppression activities are explicitly modeled and a decision-making algorithm for fire engine assignments to locations of ignition is implemented. The proposed methodology is applied to a case study. The performance of fire department response is characterized using the probability of exceedance of unsuccessful suppression scenarios, presented in the form of fragility functions. The expected direct economic losses are also presented as a function of earthquake intensity. The proposed framework can be used for planning and response applications, and to identify the tipping point of a community, above which the rate of fire spread exceeds that of suppression and the fires burn out of control.
Fire hazards can cause severe and irrecoverable damage to reinforced concrete (RC) tunnel linings. Historically, major fire events have led to months of downtime and millions of dollars of losses ...owing to repair costs and affected operations. The potential threat to the serviceability of transportation networks emphasizes the need to establish a standardized and effective post-fire damage assessment method to guide repairs and restore functionality. This paper proposes a fire damage assessment framework for RC tunnel linings that integrates advanced modeling with visual inspections, non-destructive testing and material sampling. The framework quantifies fire damage to RC tunnel linings in terms of surface discoloration, crack width, concrete spalling, sectional temperatures, strength loss of materials and residual displacement. A damage classification system is proposed based on a collection of international guidelines and feedback from industry experts to map damage metrics and repair strategies. A case study, using data from recent experiments, is conducted to demonstrate the applicability of the proposed framework and the benefits of the information obtained from numerical modeling. This framework can also be integrated with risk-assessment methods to optimize the fire design of tunnels with associated active and/or passive fire protection.
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