Retracted: Parameter Study of Highway Bridge Fires via Combined Fire Dynamics and Finite Element Modeling

With the rapid development of architectural technology, long-span structures have been widely used due to their vast interior space and beautiful architectural composition. Due to the characteristics and high costs of coating materials on large steel structures, fire resistance designs for these kinds of structures have become more and more important. This paper presents comprehensive case analyses of the fire performance of single-layer cylindrical reticulated shells. Nonuniform fire temperature fields of single-layer cylindrical reticulated shells in different fire scenarios were generated using a Fire Dynamics Simulator (FDS). The influences of different parameters on the air temperature field during a fire in a reticulated shell structure were analyzed. A Finite Element (FE) model was developed using the FE software ABAQUS to model the structural behavior of single-layer cylindrical reticulated shells in different fire scenarios. The effects of various parameters on the responses of single-layer cylindrical reticulated shells during a fire were investigated. Using the results from the performance-based analysis in this research, we propose some recommendations for fire resistance designs for single-layer cylindrical reticulated shells.

A study has been conducted at the National Research Council of Canada to evaluate the effectiveness of in-place emergency ventilation strategies to control smoke spread in the event of a fire in the Louis-Hippolyte-La Fontaine road tunnel. Some of these strategies date back to the design of the tunnel in 1964. Following a recent fire, the operating instructions have been revised. A scientific-based numerical and experimental evaluation of these operating instructions is the main objective of this paper. The numerical evaluation uses the fire dynamics simulator (FDS) model to investigate smoke ventilation in tunnels. The experimental evaluation is used to provide the necessary initial and boundary conditions for the numerical solutions. A parametric study is performed, using the FDS model, assuming a heat source of 20 MW in the tunnel. Two fire scenarios, deemed to cover the two main situations likely to occur in the tunnel, are simulated. The parameters examined are the capacity of ventilation fans and th...

The non-uniform conditions and potential progression of fires in larger spaces calls for modelling methods extending outside of the traditional compartment fire framework. Even though a handful of studies in the area exist there is still little guidance available on how progressing fires in large enclosures can be modelled. Three different methods to calculate far-field gas temperature in large enclosures are therefore reviewed in this paper with the help of a case study. The three methods used are: the analytical Alpert ceiling jet correlation, the Fire Dynamics Simulator (FDS) and a Multi-Layer Zone (MLZ) model.The enclosure used in the case study is intended to represent a large open space, i.e. an office, warehouse or supermarket. Two different user defined fire scenarios, which represent two progressing fires, are analysed.This is a comparative study and no experimental data is used to evaluate the models. However, it is considered reasonable to believe that FDS gives good predictions since it has shown to predict gas temperatures well in previous validation studies. The MLZ model has not been thoroughly evaluated, but it has been seen to overestimate experimental results slightly in a previous study.The results from FDS and the MLZ model show that there is a temperature distribution (vertical and horizontal) in both fire scenarios, which means that there are non-uniform conditions in the gas layer. The results also indicate that there is a correspondence between the MLZ model and FDS; however, as the heat release rate increase the difference between the models increases. The analytical correlation results in much lower temperature predictions than both FDS and the MLZ model. The main reason for that is that the correlation assumes the flow to be unconfined, which is not the case in this study.The main benefits of the MLZ model is the low computational time (about 1 minute on a laptop computer) compared to FDS (where the computational time was more than two days). Furthermore, the MLZ model provides temperature profiles both horizontally and vertically, which is not the case in conventional zone models.

Extreme fire events in tunnels can have catastrophic consequences, including loss of lives, structural damage, and major socioeconomic impacts. The fire scenario itself is one of the primary parameters that would influence the level of damage in a tunnel. Standard hydrocarbon fire temperature–time curves exist but they are idealized and do not consider the actual fire duration and potential for fire spread within the tunnel. Furthermore, risk-based decision-making frameworks and performance-based design of tunnel linings require realistic sets of fire scenarios to quantify damage. This paper focuses on quantifying uncertainties in the temperature–time evolution of railway tunnel fires considering fire spread between train cars. In this study, 540 numerical simulations are conducted in fire dynamics simulator by varying ventilation velocity, amount of fuel, tunnel slope, ignition point, and criteria for fire spread between railcars. Temporal and spatial distribution of fire temperature in the tunnel is studied. The resulting 540 temperature–time curves at sections with the highest temperature are analyzed and statistics of the maximum fire temperature and duration, heating rate, and decay rate are provided. Fires with heat release rates larger than 40 MW are categorized as high-intensity with mean maximum temperature of 1007°C. Fires with heat release rates smaller than 30 MW are categorized as low-intensity with a mean maximum temperature of 245°C. The proposed framework can be expanded in future to establish guidelines for temperature demands in the design of concrete tunnel linings within risk-based frameworks to achieve required performance levels in railway tunnel fire events.

Valencia bridge fire tests: Validation of simplified and advanced numerical approaches to model bridge fire scenarios

High strength reinforced concrete (HSRC) has been used more frequently in the construction of high rise buildings and other concrete structures in recent decades due to its advantages and excellent performance over normal strength and conventional reinforced concrete. Some of these advantages include: higher strength, better durability and allowance for provision of using less concrete and smaller section sizes. Although HSRC performs better than normal strength reinforced concrete (NSRC) at ambient temperatures, NSRC has been found to perform better than HSRC at elevated temperatures and fire conditions. Provision of adequate fire resistance for reinforced concrete (RC) structures is essential as fire represents an extreme loading and hazardous condition to which a structure might be exposed during its life span. The fire resistance of RC members is evaluated using a prescriptive approach which is irrational and conservative. Current codes of practice and construction in industry are moving towards performance based fire design method with computing software, which is a rationally based method with each structure designed to meets its own need. This method requires comprehensive knowledge and modelling of concrete and reinforcement material behaviour and their response at elevated temperatures. The fire resistance of HSRC members (columns and beams) in this study was evaluated using a three-dimensional Finite Element (FE) model created in ANSYS. The stress – strain behaviour of concrete proposed in this research was used in modelling the behaviour of concrete in ANSYS, while other concrete and steel material properties were accounted for by using models proposed by other researchers. The fire resistance of the HSRC members is evaluated using coupled field analysis (thermal – structural analysis) with performance based failure criteria provided in the code of practice. The accuracy of the FE model was verified by comparing the thermal response, structural response and predicted fire resistance with fire test results obtained. Using the validated FE model, parametric studies were conducted to investigate the influence of various parameters affecting the fire performance of HSRC members exposed to fire. From the parametric studies conducted, simplified calculation models were developed for evaluating the resistance of HSRC members (columns and beams) exposed to fire. These models were validated with results from ANSYS and a fire resistance test. The simple model accounts for major factors such as member size, load ratio and fire scenario, and therefore can be easily incorporated into structural design. The FE model and simple calculation model provide a rational approach for evaluating the fire resistance of HSRC (members) and predict a more accurate fire resistance than the prescriptive approach.

A method for continuous box-girder bridge structure finite element (FE) model updating based on static-load testing is proposed. The procedure includes field static-load testing, FE modeling, FE model (parameter) updating, etc. Based on this procedure, the structure FE model updating for an expressway 5-span pre-stressed concrete continuous box-girder bridge is conducted. And the bridge structure static FE model, which is consistent with the static-load testing actual measure response, is gained. The updated FE model (parameter) is foundation of structural performance evaluation for the bridge.

Fire accidents can cause severe damage to aircraft and jeopardize passenger safety. Current research on civil aviation safety generally focuses on guaranteeing continued operational safety and airworthiness, typically treating fire as a potential hazard or risk factor. In addition, fire prevention design in civil aviation is generally based on pessimistic assumptions that components have lost their intended functions in fire scenarios, leading to redundant or inadequate fire prevention design. Therefore, this paper proposes a probabilistic assessment methodology for structural failure severity of aero‐engine components in fire scenarios based on cumulative failure frequency (CFF). The proposed methodology first considers all possible combinations of fire scenarios that may occur in an aero‐engine by discretizing the probability distributions of the random variables associated with these scenarios. Subsequently, fire simulation using the fire dynamics simulator in conjunction with heat transfer analysis is carried out to determine the temperature distribution of structural elements. To enhance the computational efficiency of consequence analysis, a temperature approximation model based on the extreme learning machine is then introduced to reduce computational burden. Finally, structural failure severity is quantified by identifying the state of each structural element with the inclusion of the transition state and calculating the corresponding CFF. A case study is presented to demonstrate the applicability of the proposed methodology in identifying critical structural elements in fire scenarios, thereby validating its practicality and effectiveness.

The study of column dynamics in high-rise buildings is a subject of interest for building engineers because of their safety implications. In this study, a numerical analysis is performed using Fire Dynamics Simulator considering the temperature, velocity, and pressure of vertically rising smoke in buildings of various sizes as a function of fire size. The numerical analysis results were analyzed and verified for confined and open systems. The results of this study show that as the building area decreased and the fire size increased, the buoyancy flow accelerated, and the total building temperature rose. The lower pressure of the building floor due to the smoke's buoyancy increased the vertical pressure gradient throughout the building. These findings can be used by design engineers to develop design safety guidelines. Keywords: Fire Dynamics Simulator, Buoyant Smoke Dynamics, High-rise Buildings, Wall Effects

A bridge comprising of two girders, such as a twin steel box-girder bridge, is classified as fracture critical (i.e., nonredundant). In this study, the various bridge components of the twin steel box-girder bridge are investigated to determine if these could be utilized to improve bridge redundancy. Detailed finite-element (FE) models, capable of simulating prominent failure modes observed in a full-scale bridge fracture test, are utilized to evaluate the contributions of the bridge components on the ultimate behavior and redundancy of the bridge sustaining a fracture on one of its girders. The FE models incorporate material nonlinearities of the steel and concrete members, and are capable of capturing the effects of the stud connection failure and railing contact. Analysis results show that the increased tensile strength of the stud connection and (or) concrete strength are effective in improving bridge redundancy. By modulating these factors, redundancy could be significantly enhanced to the extent that the bridge may be excluded from its fracture critical designation.

Purpose Aiming at the problems of high cost, high risk and traffic impact of in situ load testing of Bridges after fire, this paper proposes a fire bridge structural damage identification method based on a fire dynamics simulator (FDS)-Kriging model modification and a unit modal strain energy damage index, so as to effectively assess the damage of bridge structures after fire. Determine whether it can continue to be used and whether it affects driving safety. Design/methodology/approach Propose a fire bridge structural damage identification method to establish the FDS-Kriging model correction. Findings The finite element model of the fire bridge modified using FDS-Kriging approach can reflect the actual situation of the bridge structure more accurately, and the damage location and degree identified by the modal strain energy method are consistent with the actual bridge. Therefore, the effectiveness of the proposed method has been verified, and a new strategy for fire bridge damage identification has been provided. Research demonstrates that the finite element model of the fire-damaged bridge, modified using the FDS-Kriging method, can more accurately reflect the actual structural state. Moreover, the damage location and severity identified via the modal strain energy method align well with the actual bridge conditions. Thus, the effectiveness and engineering applicability of the proposed method are validated, offering a comprehensive new strategy and technical support for the integrated performance evaluation, damage identification and reliability analysis of fire-damaged bridges. Originality/value By determining the finite element correction interval and combining it with the Kriging model, the method realizes the fine correction of the finite element model of the fire bridge. Structural damage identification is carried out by using the unit modal strain energy damage index. This verifies the effectiveness and engineering applicability of the proposed method, which offers a novel approach and technical support for the comprehensive performance evaluation, damage identification and reliability analysis of fire-damaged bridges.

Skull stiffness of children is of great significance to protect brain tissues during traffic accidents. In this paper, the effects of skull stiffness on traumatic brain injury (TBI) are investigated by using a validated 6-year-old child head finite element (FE) model according to Chinese standard GB/T 24550-2009 Results showed that the HIC value, intracranial pressure, Von Mises stress and shear strain of brain tissue increased with the decrease of skull stiffness during the impact of FE model with engine hood. Therefore, the injury risk of the child head decreases with the increase of skull stiffness. And the skull with higher stiffness can provide a better protection for brain tissues during traffic accidents.

There has been a growing demand for nonlinear model updating procedures in the structural dynamics community as advanced vehicles have started to incorporate nonlinearity into their designs. Finite element (FE) model updating is difficult for a nonlinear structure for several reasons: there may be many unknown parameters in the FE model so that multiple solutions may exist, and it is very expensive to compute the structure’s nonlinear normal modes from a full FE model that are an excellent metric to use for nonlinear updating. A recent work showed that some of these challenges can be overcome by updating a nonlinear reduced order model (ROM) rather than the full FE model. The updated ROM can be used to compute response statistics, stresses and ultimately life of the structure. However, one drawback of this approach is that one does not gain physical insight into which parameters in the FE model were in error, and so it is difficult to transfer the lessons learned to future FE models. This work explores the feasibility of updating a FE model to correlate with a ROM with a set of known parameters. The target ROM parameters consist of the linear stiffness and the nonlinear stiffness coefficients which have been identified previously by updating the ROM to correlate with experimental measurements. In this process an optimization routine is setup in which the free parameters are those of the FE model, such as boundary stiffness springs, imperfections, pre-stress, etc. The optimization procedure is wrapped around a ROM creation algorithm that iteratively tunes the FE parameters, creates a ROM, and evaluates the ROM parameters with respect to the target ROM in order to minimize the objective function. This work will demonstrate the procedure on a numerical example of a curved beam in order to verify its effectiveness on the nonlinear model updating.

Adiabatic surface temperature is an efficient way of expressing thermal exposure. It can be used for bridging the gap between fire models and temperature models, as well as between fire testing and temperature models. In this study, a full-scale compartment fire experiment with wood crib fuel was carried out in a concrete building. Temperatures were measured with plate thermometers and ordinary thermocouples. Five plate thermometers and five thermocouples with a diameter of 0.25 mm were installed at different positions. These two different temperature devices recorded different temperatures, especially near the floor surface. The adiabatic surface temperature was derived by a heat balance analysis from the plate thermometer measurements. The thermal inertia of the plate thermometer was taken into account to correct the measured results. In addition, the fire experiment scenario was also simulated with fire dynamics simulator. The fire source was specified as a given heat release rate, which was calculated from the measured mass loss rate of the wood fuel. The adiabatic surface temperatures at these measuring positions were simulated by the fire dynamics simulator model and compared with the experimental adiabatic surface temperatures. The comparative results showed that fire dynamics simulator predicted the adiabatic surface temperature accurately during the steady-state period.

Smoke is the main cause of fire death. In order to minimize the potential danger of smoke hazard, a rational VR based fire training simulator should fully consider all aspects of smoke hazard. In the simulator, the visualization of data based on FDS (Fire Dynamics Simulator) and FED fire dynamic data and volume rendering is further optimized, which can be effectively and quickly applied to virtual fire protection. In addition, a comprehensive smoke hazard assessment model based on FED and FED is established to assess the IHD value of different paths, which represents the safety of different paths, and can be used for evacuation or rescue in virtual training. Taking the case of campus fire drill as an experiment, the research shows the accuracy and effectiveness of smoke assessment based on FDS and FED model. The road force with the highest safety can be selected through the comprehensive model. So the assessment model is proved to be valuable.