Search

Sinusoidal corrugated web girders, which are in the focus of the current paper, have been increasingly used in the past years in civil engineering applications due to economical design. Recently, a number of experiments dealing with the particular behaviour of this girder type have been carried out at room temperature, while the structural behaviour at elevated temperature has not been widely analysed and requires further investigation and clarification. The current paper deals with the improved geometrically and materially nonlinear analysis with imperfections (GMNIA) of sinusoidal corrugated web girders under fire conditions. The developed finite element model, which is validated based on previous measurements during fire tests found in the international literature, is capable of modelling the specialties, e.g., the so‐called 'accordion effect', of corrugated web girders. The applicability of design formulae is also illustrated in the paper while an extensive numerical parametric study is also carried out to demonstrate the impact of different parameters on the stability behaviour and failure mode of corrugated web girders at elevated temperature. [ABSTRACT FROM AUTHOR]

Air-supported structures are widely used as public buildings. Air-supported structures are soft and most traditional fire-fighting installations cannot be used in them. Existing design specifications only specify the fire resistance of the materials to be used for air-supported structures and there is no fire resistance design method for air-supported structures. The destruction process of air-supported structures can be divided into three stages: pre-fracture, leakage, and collapse. Theorical and numerical models were used to research the time span of all those stages. A framework to estimate the collapse and evacuation time was proposed in this paper. Air-supported structures with different spans were researched in this paper, and we found that the height of a structure has a significant influence on its fire resistance. The evacuation time increased by more than 52 times when the structure's span increased from 20 m to 80 m. The pre-fracture stage contributed to more than 90% of the evacuation time when the span of structure was larger than 80 m. [ABSTRACT FROM AUTHOR]

In recent decades, reinforced-concrete bridges have experienced premature deterioration and other problems during service due to severe environmental effects such as fire and corrosion. Previous studies have shown that the use of ultra-high-performance concrete (UHPC) can improve the durability of bridge structures. In this study, four-point bending tests were conducted on twelve UHPC–NC laminated beams with different UHPC-layer heights and at different temperatures in order to evaluate their flexural performance under fire conditions. The test variables were the UHPC heights (20 mm, 50 mm, 80 mm) and temperatures (20 °C, 200 °C, 400 °C, 600 °C), and the effects on the flexural load capacity of UHPC–NC laminated beams under the influence of these factors were investigated. The test results show that the increase in temperature causes the concrete color to change from grayish blue to white and leads to a significant decrease in the flexural load capacity of the stacked beams. The height of the UHPC layer has an important effect on the stiffness of the stacked beams and delays the formation of local cracks, thus improving the durability of the stacked beams. [ABSTRACT FROM AUTHOR]

Air-supported structures are widely used as public buildings. Air-supported structures are soft and most traditional fire-fighting installations cannot be used in them. Existing design specifications only specify the fire resistance of the materials to be used for air-supported structures and there is no fire resistance design method for air-supported structures. The destruction process of air-supported structures can be divided into three stages: pre-fracture, leakage, and collapse. Theorical and numerical models were used to research the time span of all those stages. A framework to estimate the collapse and evacuation time was proposed in this paper. Air-supported structures with different spans were researched in this paper, and we found that the height of a structure has a significant influence on its fire resistance. The evacuation time increased by more than 52 times when the structure’s span increased from 20 m to 80 m. The pre-fracture stage contributed to more than 90% of the evacuation time when the span of structure was larger than 80 m.

• Mechanical response characteristics of beam-column substructures exposed to fire are analyzed. • Explicit calculation formulas for determining the collapse resistance are derived in detail. • Proposed theoretical calculated formulas agree well with these from numerical simulations. • Error analysis is conducted to reveal deviation reasons between theoretical model and numerical simulations. This paper provides a simplified analytical model for the restrained steel beam-column substructure under a fire-induced progressive collapse scenario, which is applied to predict the collapse resistance of substructures under fire. The simplified model is formulated for axially and rotationally restrained two-span steel beam-column substructures under column-loss scenarios and involves rigid and semi-rigid connections. The response characteristics of restrained substructures exposed to fire under column-loss scenarios in each response stage are elaborately analyzed. A "negative" catenary stage, in consideration of the unique negative axial force effects induced by the temperature thermal expansion, was first introduced in the five-stage simplified model for restrained substructures exposed to fire against progressive collapse. Subsequently, the explicit calculation formulas for determining the vertical loads and deflection of both rigid and semi-rigid joint substructures exposed to fire were derived in a quantified way, based on rigid-plastic mechanisms and restraint coefficient methods. In addition, the corresponding numerical simulation analysis on a restrained two-span steel beam-column substructure with different end constraints and fire conditions was carried out to verify the applicability and reliability of established theoretical formulas. Comparisons of vertical load-deflection relationships between the calculation formulas and corresponding numerical simulation shows good accuracy. For more accurate prediction results, the error analysis was further conducted, and several theoretical formulas were modified, which were verified to be accurate and reliable after correction. With derived resistance functions, the resistance of steel beam-column substructures in fire-induced progressive collapse scenarios can be predicted. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate the effect of adding discrete glass fibers on the behavior of reinforced concrete (RC) beams under different fire and cooling conditions. Eighteen beams with different concrete compressive strengths were tested to study the behavior of reinforced concrete (RC) beams containing discrete glass fibers when exposed to different fire and cooling conditions. Nine beams were prepared from normal strength concrete (NSC) with compressive strength equal to 35 MPa while the other beams were prepared from high strength concrete (HSC) with compressive strength equal to 60 MPa. The beams contained different contents of discrete glass fibers. The modes of failure of tested specimens show that the crack patterns change according to fire condition and fiber content. Analysis of test results show that adding discrete glass fibers to NSC increased the residual stiffness of the tested specimens after firing and decreased the rate of the deflection gain during firing. Also adding fibers to concrete has a limited positive effect on the ultimate strength of the specimens compared to the control specimens. Its effect on deflection due to fire is more pronounced. Finally, the recommended optimum ratio of discrete glass fibers is not more than 0.5% of the total concrete weight.

Abstract This paper aims to study the structural behavior of tubular KT-joints subjected to axial loading at fire induced elevated temperatures. At first, a finite element (FE) model was developed and validated against the data available from experimental tests. Then, a set of 810 FE analyses were performed to study the influence of temperature and dimensionless geometrical parameters ( β , γ , θ , and τ ) on the ultimate strength and initial stiffness. The joints were analyzed under two types of axial loading and five different temperatures (20 °C, 200 °C, 400 °C, 550 °C, and 700 °C). Up to now, there has not been any design formula available for determining the ultimate strength of KT-joints at elevated temperatures. Hence, after parametric study, a new equation was developed through nonlinear regression analyses, for calculating the ultimate strength of KT-joints subjected to axial loading at elevated temperatures. Highlights • The ultimate strength and failure modes of tubular KT-joints at fire-induced elevated temperatures were investigated. • Tubular KT-joints were subjected to two types of axial loading. • Results of 810 steady-state FE analyses were used for the parametric study. • A set of new design equations was derived to calculate the ultimate strength of KT-joints subjected to axial loading. [ABSTRACT FROM AUTHOR]

This study presents experimental and numerical investigations of simply supported steel reinforced concrete (RC) beams under fire. The temperature field of cross sections, the vertical deflection at mid-span, and specifically the axial expansion displacement at beam-ends were measured during the fire tests. A novel finite element (FE) model of a RC beam under fire was developed, in which the water loss in the heat transfer analysis and the concrete transient strain in the mechanical analysis were considered. Based on the validated FE model proposed in this study, parametric studies were conducted to investigate the effects of the beam type, the protective layer thickness, and the load ratio on the thermal and mechanical behavior of simply supported RC beams. It was found that greater fire resistance and fire performance of girder beams in comparison to secondary beams contributed to the non-structural reinforcements, which effectively compensated for the reduced tensile capacities of structural reinforcements because of the degradation of the material properties. In addition, the history of normal stress distributions of concrete under fire can be divided into three phases: expansion, stress redistribution and plateau phases. [ABSTRACT FROM AUTHOR]

Low visibility and hot smoke environment under fire conditions can largely hamper the related fire rescue processes. Ultrasound obstacle avoidance technology is then useful for guidance. However, the biggest challenge of adopting ultrasound technology comes from accurate distance measurements under the disturbances of high temperature and soot particle concentration. It is critical to measure the propagation speed under the complicated fire conditions. Therefore, in this study, a baffle calibration method was proposed to improve the accuracy of distance measurement of an obstacle. The method is based on two ultrasound measurement systems, while one is used to calibrate the propagation speed of ultrasound based on the fixed distanced baffle and the other is for the dynamic measurement of obstacle distance based on the calibrated speed. The viability of this method on the guided vehicle was confirmed based on the experiments. From its comparison to those existing methods, such as constant speed and temperature compensation methods, it was known from that the proposed baffle calibration method provides the best prediction. It was obtained that the maximum errors based on the baffle calibration method are 2.75% and 2.62% under the two representative fire scenarios, respectively, which are much lower than those of constant speed (7.81% and 8.4%) and temperature compensation methods (10.4% and 5.12%).

Double glazing is increasingly employed in glass curtain walls, but very little is known about its thermal response under fire conditions. In this work, a total of twenty seven 600 × 600 mm 2 double glazing units, with 6 mm, 9 mm and 12 mm air spacings, were tested. Three different installation types were adopted: 1) exposed frames, 2) horizontal-hidden frames and 3) vertical-hidden glass in order to study their potential effects on the glazing breakage behavior. A 500 × 500 mm 2 n -heptane pool fire was used to heat the glass panes. The breaking time, surface temperature, total heat flux, heat release rate, and crack and fallout morphology were measured and analyzed. The test result suggests that different installation types have a significant effect on the fracture behavior of double glazing, especially for glass panes located at the fire side. Glass in exposed framing is more prone to cracks than those in semi-exposed frame, but fallout may more easily occur in semi framing façades. When no, or very limited fallout occurs at the fire side pane, thicker air space leads to a longer breakage time of ambient glass panes, thus improving the unit's integrity during fire. The experimental results obtained in this study is valuable for the development of practical guidelines for fire safety design. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate the effect of adding discrete glass fibers on the behavior of reinforced concrete (RC) beams under different fire and cooling conditions. Eighteen beams with different concrete compressive strengths were tested to study the behavior of reinforced concrete (RC) beams containing discrete glass fibers when exposed to different fire and cooling conditions. Nine beams were prepared from normal strength concrete (NSC) with compressive strength equal to 35 MPa while the other beams were prepared from high strength concrete (HSC) with compressive strength equal to 60 MPa. The beams contained different contents of discrete glass fibers. The modes of failure of tested specimens show that the crack patterns change according to fire condition and fiber content. Analysis of test results show that adding discrete glass fibers to NSC increased the residual stiffness of the tested specimens after firing and decreased the rate of the deflection gain during firing. Also adding fibers to concrete has a limited positive effect on the ultimate strength of the specimens compared to the control specimens. Its effect on deflection due to fire is more pronounced. Finally, the recommended optimum ratio of discrete glass fibers is not more than 0.5% of the total concrete weight. [ABSTRACT FROM AUTHOR]

Façades made of glass are viewed as one of the weakest parts of a building which can easily break in case of fire and change the compartment fire dynamic by creating a new opening for air to enter. A total of six clear glass panes were placed 750 and 500 mm away from a 500 × 500 mm n-heptane pool fire to investigate the breakage behavior of fully exposed framing glass façades. Both float and toughened glass panes with a dimension of 600 × 600 × 6 mm were tested. The results presented include the time to breakage occurrence, heat release rates, incident heat flux, central gas temperatures and glass surface temperatures. The crack initiation and propagation as well as the loss of integrity of the glazing assembly were also recorded. The experimental results established that the critical temperature difference and heat flux for float glass were approximately 90 °C and 14 kW/m. All their cracks were initiated from the edge of glass pane and intersected rapidly, forming some islands, but the fraction of fallout was considerably small because of the protection of frame. However, the toughened glass did not break even though the center temperature reached a high value of 413 °C. Using finite element method, breakage mechanism of float glass pane is demonstrated, and the numerical predictions are further compared with the experimental measurements. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Breaking glass and its subsequent fallout may markedly affect enclosure fire dynamics. However, little is known about the thermal fracture behavior of framing glass façades in different installation forms. Sixteen 600×600×6 mm 3 solar control coated glass panes, installed in exposed, semi-exposed and hidden frames, were heated by a 500×500 mm 2 n-heptane pool fire to investigate the influence of frame constraints on glass breakage and fallout. Measurements were taken of the time to breakage occurrence, heat release rates, incident heat flux, central gas temperatures and glass surface temperatures. Measurements in relation to crack initiation and propagation as well as loss of integrity of the glazing assembly were also recorded. The experimental results show that all cracks initiated at the edge of covered sections and intersected rapidly, forming islands. The maximum temperature difference and heat flux that the glass can withstand are primarily in the range of 50–90 °C and 9–15 kW/m 2 . Using the finite element method (FEM), the breakage mechanism is demonstrated, the predictions of which are in reasonably good agreement with the experimental results. Among four different installation forms, semi-exposed framing façades showed better fire resistance than exposed framing façades. Meanwhile, the fire resistance of hidden framing façades may depend on the fire location. It is intended that these results will provide practical guidelines for fire safety design. [ABSTRACT FROM AUTHOR]

Abstract: 911 World Trade Centre Tragedy put fire safety of constructional steel structures into question. Since then, more and more research attention has been paid to the elevated-temperature mechanical properties of structural steels, which is a critical basis of evaluating the fire performance of steel structures. In the literature the available mechanical properties of structural steels under fire conditions were mainly obtained from steady state test method, as steady state test method is easier to perform than transient state test method and offers stress–strain curves directly. However, the transient state fire condition is considered to be more realistic to represent the real condition when constructions are exposed to fire. In order to reveal the deterioration of mechanical properties of the commonly used high strength structural steel S460N under transient state fire condition, tensile tests were conducted under various constant stress levels up to 800MPa. The reduction factors of elastic modulus, yield and ultimate strengths of S460N under transient state fire condition were obtained and compared with current leading design standards and available literature. The application of such accurate elevated-temperature mechanical properties reduction factors of S460N can ensure a safe fire-resistance design and evaluation of steel structures with high strength steel S460N under transient state fire condition. This experimental study also supports other relative research on fire performance of steel structures with S460N under transient state fire condition. [Copyright &y& Elsevier]

• A STM approach is proposed for unsymmetrically-loaded RC deep beams at elevated temperatures. • The model considers load inequality , load asymmetry and web steel contribution on strut capacity. • Six deep beams are tested under combined effect of unsymmetrical loads and fire condition. • Load inequality and asymmetry significantly affected the overall behaviour of heated deep beams. • STM yielded conservative predictions for unsymmetrically-loaded deep beams at elevated temperatures. This paper focuses on the condition where a reinforced concrete (RC) deep beam is subjected to two concentrated loads (P 1 and P 2), which are positioned at respective distances a and c from bottom supports. In general, equal shear spans (a = c) and equal point loads (P 1 = P 2) are commonly assumed in most experimental programmes. Nevertheless, such cases are rare in practice. In contrast, due to the fact that deep beam floor normally subjects to irregular layout of column grid, deep beams are usually subjected to unequal load magnitude (load inequality or P 1 ≠ P 2) and unsymmetrical load positions (load asymmetry or a ≠ c). Although previous research has demonstrated the significant influences of load asymmetry and inequality on the structural performance of deep beams at room temperature, no research programme has been performed to study their influences on the fire performance of deep beams. As a result, this study is proposed to investigate the shear behaviour of unsymmetrically-loaded deep beams at fire condition, analytically and experimentally. The current research first derives a strut-and-tie-model (STM) to predict the shear capacity of RC deep beams under unequal/unsymmetrical loading conditions and at elevated temperatures. The STM takes into account the effects of unsymmetrical loading configurations, contribution of steel reinforcement on strut capacity, and thermal-induced gradient. Additionally, a test programme on six RC deep beams under fire condition is conducted for verification of the proposed model. Observations from this experimental programme show that load asymmetry and inequality have different effects on the fire performance of deep beams. To be more specific, an increase in load inequality leads to an alteration in failure mode of the deep beams, whist load asymmetry does not affect the failure mode as much. On the other hand, increasing load inequality can result in a significantly increased mid-span deflection at failure and a slightly increased failure time. Besides, effect of load inequality on deflection and failure duration depends on the loading positions. Furthermore, the proposed STM yields good agreement between test data and model predictions for unequally- and/or unsymmetrically-loaded deep beams, at both room and high temperatures. [ABSTRACT FROM AUTHOR]

Abstract: It is evident from a series of tests on simply supported reinforced concrete slabs that the failure of the slabs at large deflections is due to the formation of individual large cracks. This failure mode was also observed in the Cardington full-scale fire tests. Previous research indicates that the global behaviour of concrete slabs subject to large deflections can be well predicted by the smeared cracking model; however, the model cannot quantitatively predict the openings of individual cracks within the slabs at large deflections. For the discrete approach it is usually assumed that the cracks are formed along element edges, therefore continuous re-meshing is required during the analysis. Consequently, the results are mesh-dependent and the computing cost is high. In recent years, mesh independent finite element procedures, such as embedded (EFEM) and extended (XFEM) approaches, were widely used for modelling of the crack initiation and growth in structural members. However, most of the meshless models developed are either based on in-plane loading conditions or confined to thin shells with assumed full-depth cracks, which form apparent displacement jumps within an element. For a reinforced concrete slab, an out-of-plane load causes coupled stretching and bending of the slab, cracks are usually initiated at discrete positions and then propagated, until at last some individual full-depth cracks are formed. Pure stretching or assumed full-depth cracking is inadequate for modelling this kind of failure. Therefore, in this research, a non-linear layered procedure with embedded weak discontinuity is developed to quantitatively model the progressive tensile failure of reinforced concrete slabs subjected to large deflections. The current model inherits the advantage of the smeared approach, and at the same time, introduces the opening width of crack explicitly by taking the advantage of the better description of the kinematic characteristics of the EFEM approach. A series of validations have been conducted against test data at both ambient and elevated temperatures, and the research shows that the model developed in this paper is not sensitive to the FE mesh size and the aspect ratio of the slab. The results predicted by the model developed agreed well with the test data in terms of deflection and crack open width, also agreeing well with those modelled by the smeared model. Hence, this new approach provides a numerical method to predict the load capacity as well as identifying the occurrence and severity of crack failure in reinforced concrete slabs subjected to extreme loading conditions, such as fire. [Copyright &y& Elsevier]

Owing to the lack of an analytical research on the evaluation of mode change of web panels in addition to the need for shear design curves of unstiffened plate girder web panels exposed to shear buckling especially at elevated temperatures, the present article considers the mentioned topics. To this end, the web panel shear design relationships mentioned in AISC360-16 are modified to be used in fire conditions. This is achieved by direct utilization of steel stress-strain reduction factors in EN1993-1-2 at elevated temperatures. Analytical equations and design curves are developed to estimate the ultimate shear strength, failure mode and critical limiting temperature for the web panels under the action of a specific shear load. The results based on the curves are compared to the findings of current paper numerical analysis, existing experimental and numerical studies, indicating a good agreement between the results. • The shear behavior of unstiffened web panels (UWPs) subjected to shear buckling at elevated temperatures was investigated. • Design curves have been developed to predict the shear strength and failure mode of UWPs at a constant temperature. • Design curves have been proposed to determine the critical limiting temperature of UWPs subjected to constant shear load. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the structural behavior of two-planar tubular TT-joints subjected to axial loading at fire induced elevated temperatures. A total number of 270 FE analyses were performed to investigate the effect of temperatures and dimensionless geometrical parameters (β , γ , and τ) parameters on the ultimate strength and initial stiffness. The joints were analyzed under axially compressive and tensile loads at five different temperatures (20 °C, 200 °C, 400 °C, 550 °C, and 700 °C). Up to now, there has not been any design equation available for determining the ultimate strength of two-planar tubular TT-joints at elevated temperature. Results of the parametric study were used to develop a set of design formulas, through nonlinear regression analyses, to calculate the ultimate strength of two-planar tubular TT-joints subjected to axial loading at elevated temperatures. • Static behavior of two-planar tubular TT-joints at fire-induced elevated temperatures was studied. • Effects of temperature and joint geometry on ultimate strength, failure modes, and initial stiffness were investigated. • Results of 270 steady-state FE analyses were used for the parametric investigation. • Parametric equations were developed to determine the ultimate strength of axially-loaded TT-joints at high temperatures. [ABSTRACT FROM AUTHOR]

Low visibility and hot smoke environment under fire conditions can largely hamper the related fire rescue processes. Ultrasound obstacle avoidance technology is then useful for guidance. However, the biggest challenge of adopting ultrasound technology comes from accurate distance measurements under the disturbances of high temperature and soot particle concentration. It is critical to measure the propagation speed under the complicated fire conditions. Therefore, in this study, a baffle calibration method was proposed to improve the accuracy of distance measurement of an obstacle. The method is based on two ultrasound measurement systems, while one is used to calibrate the propagation speed of ultrasound based on the fixed distanced baffle and the other is for the dynamic measurement of obstacle distance based on the calibrated speed. The viability of this method on the guided vehicle was confirmed based on the experiments. From its comparison to those existing methods, such as constant speed and temperature compensation methods, it was known from that the proposed baffle calibration method provides the best prediction. It was obtained that the maximum errors based on the baffle calibration method are 2.75% and 2.62% under the two representative fire scenarios, respectively, which are much lower than those of constant speed (7.81% and 8.4%) and temperature compensation methods (10.4% and 5.12%). [ABSTRACT FROM AUTHOR]