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Optimization of Failure Modes of a Ductile Connection Under Fire Conditions
Abstract
Connections are the most vulnerable parts of a structure under fire conditions. A novel steel connection with high axial and rotational ductility has been proposed with the objective to improve the performance of steel-framed buildings in fire. Analytical model has been developed to determine the axial displacement of the top and bottom flanges of the beam end at high temperatures. A series of sub-frame models with this ductile connection have been built using Abaqus to study the influence of the characteristics of the connection part between the fin-plate part and face-plate part on the overall connection behaviour. The current critical failure mode of the ductile connection is bolt pull-out from the face-plate zone, and the tensile deformation capacity of the connection is not fully utilized. Therefore, measures to improve the bolt pull-out failure mode of the connection have been tested using the Abaqus sub-frame models, including adding a strengthening plate to the face-plate part of the connection and increasing the connection plate thickness. The simulation results show that the bearing failure of the beam web will become another critical failure mode of the connection, once the bolt pull-out failure is eliminated. To further optimize the high-temperature performance of the connection, the Abaqus steel frame models have also been used to test some measures to delay the occurrence of the beam web bearing failure, including adding strengthening plates to the part of the beam web in contact with the connection, and improving the material properties of the part of the beam web around the bolt holes at high temperatures.
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The resistance of beam-to-column connections to fire is an important consideration for the design of steel moment frames. The authors seek to study the effect of fire on such connections using finite element modeling in ABAQUS. The previously published first part of this paper detailed and validated the simulation technique by comparing model results to experimental results reported elsewhere in the literature. This, the second part of the paper, seeks to demonatrate the performance of four types of connections exposed to thermal loading: (1) bolted end plate, (2) bolted cover plate, (3) bolted tee, and (4) welded cover plate. A numerical study was performed to quantify the effects of thermal loading on beam buckling, displacement, rotation, connection stiffness, and moment-rotation behavior at temperatures between 20 and 900 °C. The bolted end plate connection exhibited the highest resistance to thermal loading with a significantly lower degree of degradation in connection performance compared to the other three connection types.
Steel connections are used to connect between beam and column in steel moment frame structures. As of present time, there is a huge lack of understanding of the performance of steel connections and their response to fire especially the uncontrolled fires. Therefore, in this paper, by using a finite element program ABAQUS and with the static analysis of coupled temperature- displacement and to fully understand the behavior of such connection under the fire scenario, developed a temperature-dependent models for different types of steel connections are implemented. Finite Element Analyses (FEA) of selected experimental models are performed to verify the implementation of these models. Fully detailed, field-variable-dependent conductivity element models of the connections are developed, and analyses are performed to determine the effects of heat on the behavior of the materials in the elastic and plastic areas are considered. Moreover, severe deformation in the nonlinear region was investigated. © 2018 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
Due to the high sensitivity of fire affected steel behavior, fire resistance of steel structures is of great importance. Moreover, since the connections act as the main means of integration of frame members, the behavior of steel connections in fire is significantly important. Considering the importance of this matter, this paper describes a spring-stiffness model developed to predict the behavior of welded angle connections made of bare-steel at elevated temperature. The joint components are considered as springs with predefined mechanical properties i.e. stiffness and strength. The elevated temperature joint’s response can be predicted by assembling the stiffness of the components which are assumed to degrade with increasing temperature based on the recommendations presented in the design code. Comparison of the results from the model with existing experimental data shows good agreement. The proposed model can be easily modified to describe the elevated temperature behavior of other types of joints as well as joints experiencing large rotations.
Based on temperatures measured in steel joints with different extents of fire protection, this paper proposes a simple method
to calculate temperatures in steel joints with partial intumescent coating fire protection. The method combines the simple
temperature calculation methods in EN 1993-1-2 (Committee of European Normalisation CEN, Eurocode 3: design of steel structures—part
1-2: general rules—structural fire design, 2005) for unprotected and protected steel structures through the introduction of
an exposure factor, which is the ratio of the unprotected surface area of the joint region to the total surface area of the
joint area. Using the measured temperatures for fully protected steel joints, this paper first extracts the effective thermal
conductivity of the intumescent coating used in the fire tests. Afterwards, this paper presents validation results based on
fire test results on joints with partial fire protection. Finally, this paper presents methods to calculate the exposure factor
for different types of partially fire protected steel joints.
The tying capacity of connections between beams and columns is very important in maintaining structural integrity when beam deflections are high due to accidental loads such as fire, but has not so far been thoroughly studied. The project which is the subject of this paper has investigated the robustness of common types of steel connection when subjected to fire. The results reported here concern the performance of web cleat connections in fire, and are drawn largely from experimental investigations. During the testing programme, short cantilever stub beams were subjected to different combinations of shear and tying force. The rotational capacities and resistance to tying forces of their connections at high temperatures were investigated in the presence of other concurrent actions.Test results show that web cleat connections have excellent rotational ductility, and that their resistance reduces rapidly with increase of temperature. Web cleat connections can fail in a number of modes, the selection of which is highly dependent on the connection temperature. Finite element simulations of the test results have been shown to be able to reproduce the behaviour accurately up to the stage at which material failure happens. However, as the ultimate behaviour of connections is often controlled by material fracture, finite element analysis is limited in predicting the ultimate resistance of connections. Investigation of the behaviour of the connection, with some proposed modifications to the general finite element model, showed that finite element analysis can help to interpret the test results and expand the test observations to other similar applications.
Connections are vital to the survival of steel and composite framed structures in fire. To prevent brittle failure of connections at elevated temperatures, a novel connection with high ductility has been proposed previously. In this paper, the fire performance of this ductile connection in composite frames is investigated. In order to consider the influence of the out-of-plane structural behaviour, the 3-D models of a fire compartment of a typical composite framed structure with different connection types, including the ductile connection, idealised rigid and pinned connections, as well as commonly used end-plate and web-cleat connections have been built using Vulcan to compare the performance of ductile connection with other connection types. Comparison results show that the proposed ductile connection can provide additional ductility within composite frame to accommodate the axial deformation of connected beam at high temperatures. To further save computational costs, the 3-D composite frame compartment model has been reduced to a quarter of its original size by using symmetric boundaries. The influence of unconnected length between the slab and beam on the connection performance has also been investigated. It is found that the relative beam end slip is affected by the unconnected length. However, due to the inherent mechanical properties of the ductile connection, the influence of unconnected length on the force of the ductile connection is negligible, which can also reflect the deformation capacity of ductile connection.
Purpose
In order to improve the robustness of bare-steel and composite structures in fire, a novel axially and rotationally ductile connection has been proposed in this paper.
Design/methodology/approach
The component-based models of the bare-steel ductile connection and composite ductile connection have been proposed and incorporated into the software Vulcan to facilitate global frame analysis for performance-based structural fire engineering design. These component-based models are validated against detailed Abaqus FE models and experiments. A series of 2-D bare-steel frame models and 3-D composite frame models with ductile connections, idealised rigid and pinned connections, have been created using Vulcan to compare the fire performance of ductile connection with other connection types in bare-steel and composite structures.
Findings
The comparison results show that the proposed ductile connection can provide excellent ductility to accommodate the axial deformation of connected beam under fire conditions, thus reducing the axial forces generated in the connection and potentially preventing the premature brittle failure of the connection.
Originality/value
Compared with conventional connection types, the proposed ductile connection exhibits considerable deformability, and can potentially enhance the robustness of structures in fire.
The component-based model of a novel ductile connection has been incorporated into the software Vulcan in order to facilitate global frame analysis within a performance-based structural fire engineering design process. This paper reports on the validation and verification of the model, as well as the applications of the model in order to investigate the effects of the ductile connections on the structural responses of long-span frames at high temperature. Firstly, three single-beam models with the novel connections at both ends, connected to rigid supports, are used to verify that the component-based connection model has been correctly incorporated into Vulcan, via comparisons against detailed finite element modelling with Abaqus. The structural performance in fire of long-span frames with the novel ductile connections has been compared with the performance of the same frames with idealized rigid, idealized pinned and conventional end-plate connections, initially using a limited sub-frame model. Results show that, compared with the above mentioned three connection types, the ductile connection provides much higher axial and rotational ductilities to accommodate the deformations generated by the connected beams as their temperatures rise. As part of this process, these connections are instrumental in greatly reducing the axial forces to which the surrounding structure is subjected. Finally, parametric studies varying several key parameters have been carried out, in order to optimize the design of the ductile connection to enhance its performance subject to catenary action at very high temperature to prevent potential connection fracture and progressive collapse.
The component‐based model of a novel ductile connection has been incorporated into the software Vulcan in order to facilitate global frame analysis within a performance‐based structural fire engineering design process. This paper reports on the validation and verification of the model, as well as the applications of the model in order to investigate the effects of the ductile connections on the structural responses of long‐span frames at high temperature. Firstly, three single‐beam models with the novel connections at both ends, connected to rigid supports, are used to verify that the component‐based connection model has been correctly incorporated into Vulcan, via comparisons against detailed finite element modelling with Abaqus. The structural performance in fire of long‐span frames with the novel ductile connections has been compared with the performance of the same frames with idealized rigid, idealized pinned and conventional end‐plate connections, initially using a limited sub‐frame model. Results show that, compared with the above mentioned three connection types, the ductile connection provides much higher axial and rotational ductilities to accommodate the deformations generated by the connected beams as their temperatures rise. As part of this process, these connections are instrumental in greatly reducing the axial forces to which the surrounding structure is subjected. Finally, parametric studies varying several key parameters have been carried out, in order to optimize the design of the ductile connection to enhance its performance subject to catenary action at very high temperature to prevent potential connection fracture and progressive collapse.
A novel axially and rotationally ductile connection has previously been proposed by the authors to prevent brittle failures of connections in fire. The study is now extended to investigation of the fire performance of the ductile connection in composite structures, particularly using a 3-dimensional model to consider the contribution of out-of-plane structural elements to the behaviour of the connection and the behaviour of the frame as a whole. In this paper, the design and the component-based model of the ductile connection have been briefly introduced. A composite frame has been designed according to the typical frame used in the Cardington full-scale fire tests. Three 3-dimensional composite frame models with different types of connections have been built using the software Vulcan to compare the performance of the ductile connection in fire with ideally rigid and pinned connections. Finally, 2-D models have been built to simulate the central and edge secondary beams of the composite frame to make a comparison between 2-D modelling and 3-D modelling.
To enhance the robustness of steel-framed structures in fire, a novel, axially ductile connection has previously been proposed. In this paper its performance is investigated when it is used to connect composite beams to steel columns in composite steel-concrete construction. The ductile connection is designed to satisfy the ductility demands of the composite beam at elevated temperatures. A reinforcement component has been added to the bare-steel ductile connection model to establish a component-based model of the composite ductile connection. The connection model has been incorporated into the software Vulcan, and is validated against detailed Abaqus FE models using solid elements. Results show that the proposed component-based model can efficiently represent the behaviour of the connection given by the detailed Abaqus simulations. Parametric studies using Vulcan have been carried out, varying three parameters; the connection thickness, the semi-cylindrical section radius, and the density of longitudinal reinforcing bars. Finally, a 2-D Abaqus composite frame model has been created to investigate the influence of shear studs on the behaviour of the composite ductile connections under different stud spacings.
In order to improve the performance of connections and enhance the robustness of structures in fire, a novel, axially ductile connection has been proposed. The component-based models of bare-steel ductile connection and composite ductile connection have been proposed, and incorporated into the software Vulcan to facilitate global frame analysis. These component-based models are validated against detailed Abaqus FE models. A series of 2-D bare-steel frame models and composite frame models with ductile connections, rigid connections, and pinned connections, have been created using Vulcan to compare the fire performance of ductile connection with other connection types in bare-steel and composite structures.
In order to improve the performance of connections and enhance the robustness of structures in fire, a novel, axially ductile connection has been proposed. The component-based models of bare-steel ductile
connection and composite ductile connection have been proposed, and incorporated into the software Vulcan to facilitate global frame analysis. These component-based models are validated against detailed Abaqus FE models. A series of 2-D bare-steel frame models and composite frame models with ductile connections, rigid connections, and pinned connections, have been created using Vulcan to compare the fire performance of ductile connection with other connection types in bare-steel and composite structures.
The component-based model of a novel connection, which is designed to accommodate the high ductility demand of long-span steel beams in fire conditions, has been incorporated into the finite element software Vulcan. A single beam with the novel connections connecting it to rigid supports at both ends is first used to verify that the component-based model has been correctly incorporated into Vulcan, by comparing its results with those from detailed finite element models using the general-purpose package Abaqus. The performance of the novel connection has been compared with that of conventional connection types, including ideally rigid and pinned connections, endplate and web-cleat connections, using a sub-frame model. Results show that, compared with other connection types, the novel connection provides much higher axial and rotational ductilities, to accommodate the deformations generated by the connected beam as its temperature rises. To optimize the performance of the novel connection under the tensile axial forces generated by the eventual catenary action of heated, unprotected beams at high temperatures, parametric studies have been carried out on the influence of four key parameters, including the temperature of the connection, the inner radius of its semi-cylindrical section, the plate thickness and the bolt spacing. It is found that it is possible to optimize connection thickness, protection level, and inner radius of the semicylindrical section in order to delay the occurrence of bolt pull-out failure, and thus enhance a beam’s ultimate failure temperature. Finally, the combined static-dynamic solver of Vulcan is used to simulate the progressive collapse of a three-storey, three-bay frame with these novel connections. This progressive collapse simulation emphasizes the importance of connections for the survival of the entire structure in a fire event.
To enhance the robustness of connections in fire, the improved design version of a novel ductile connection has been proposed. Performance of the improved design version of novel connection has been compared with that of the previous design version using a sub-frame model. The comparison results show that the improved version of novel connection further enhances its ductility. Five case studies have been carried out, in which the novel connections are applied to sub-frames with different beam spans. Results show that the axial forces generated in the beams with novel connections are significantly reduced compared with those of the beams with rigid connections. The analytical models for the web-cleat component of the novel connection and the WCSC component, which considers the semi-cylindrical section and the web-cleat as a whole to deform, have been developed based on simple plastic theory. Then two schemes of component-based model have been proposed for the novel ductile connection and loading and unloading behaviour have been incorporated into individual component. Result curves of the two schemes of component-based model have been compared and validated against Abaqus simulations and experiments. Finally, the proposed component-based model has been applied to two simple examples to illustrate how different spring rows work in the process of connection deformation.
The ductility of connections is a key property in preventing the brittle failure and subsequent progressive collapse of steel-framed structures in fire conditions. Conventional connection types have insufficient ductility to accommodate the deformations generated by the connected beams as their temperatures rise, or to withstand the forces to which they are subjected. This paper aims to investigate the mechanical performance of a new type of connection proposed to meet the ductility demand created by long-span steel beams in fire conditions. This novel connection consists of two identical parts, each of which includes a fin-plate, an endplate and a semi-cylindrical section. Analytical component models have been developed and validated, based on which a component-based model is proposed. A simple Abaqus frame model with these novel connections has been created to assess the structural performance of the novel connection under realistic conditions.
In fire conditions the provision of connection ductility is key to the prevention of brittle failure and progressive collapse of steel and steel-concrete composite framed structures. This paper describes the development and testing of a novel connection concept intended to provide appropriate ductility enhancement compared to that of conventional connection types. The connection consists of two connection pieces, each of which takes the form of a web cleat which includes a semi-cylindrical section. This section allows the beam-end to move towards or away from the column-face by deforming plastically. A simplified analytical model has been developed to simulate the mechanical behaviour of the proposed connection, and this model will eventually enable the incorporation of this new connection type into global frame analysis to be used in performance-based structural fire engineering design. The model has been tested against FEA simulations and against model-scale experiment results, indicating that it can predict the behaviour of the connection with satisfactory accuracy. Preliminary sub-frame analysis results indicate that the proposed connection behaves similarly to an idealized pinned connection under ambient-temperature conditions, but provide significantly larger ductility, and resistance to disproportionate collapse, compared to conventional connection types.
https://authors.elsevier.com/a/1YgRA,3HWf42Wc
This paper reports on the development of a new component-based connection element, and its application to two very different types of beam-tocolumn connections at elevated temperatures. Where possible the element's component characteristics are defined up to and including fracture, which facilitates modelling of the progressive failure of connections as individual components fail. In performance-based design for robustness this will be needed in order to assess the need for ductility, and to track the progressive collapse of the structure. The element is generally consistent with Eurocode procedures, and has been incorporated into the nonlinear global structural analysis program Vulcan, which was developed at the University of Sheffield.
Extreme events such as earthquake and fire can cause severe damage to building structures. The possible coupling of various extremes such as earthquake followed by fire is more destructive. It is necessary to capture the behavior of building structures subjected to the post-earthquake fire (PEF) for safety reasons. This study aims to investigate the behavior of unstiffened welded steel connections subjected to the PEF scenario. Experimental tests were carried out on two groups of steel I-beam to hollow column connections with different column wall thicknesses under ISO fire including 4 connections with the same specifications within each group in which 3 connections were tested under the coupling of cyclic loading and subsequent fire while 1 connection was only subjected to fire. All undamaged and pre-damaged connections were tested in a gas furnace under the given constant static load which was about 30% of the ultimate monotonic loading strength of the connections. The furnace temperature, temperature distribution and the deflection of the beam were measured during the fire tests. It was found that the load-carrying capacity of the welded connections decreases significantly with the increase of the pre-damage level. Preliminary finite element modeling was carried out for a heat transfer analysis on the basis of uniform fire exposure as well, which showed nonuniform temperature distribution of the connections.
A component-based model for fin-plate connections has been developed to study the robustness of simple beam-to-column connections at elevated temperatures. The key aspect of this component method is the characterisation of the force-displacement properties of each active component at any temperature, represented by a non-linear "spring". The prescribed temperature-dependent characteristics of any given bolt row are governed by the failure mechanism of the weakest component, based on experimental and analytical findings. A major additional complication involves force reversal in components, which may occur because of temperature change, without any physical reversal of displacement. The Masing Rule has been adapted to incorporate this effect for particular force directions. To account for the bolt slip phases, force transitions between tension and compression take place only when positive contact between a bolt and the edge of its bolt hole is re-established. The results of high-temperature tests on connections have been used to substantiate the developed component model. The component-based connection model has also been used to study joint behaviour in structural sub-frame analyses. This approach will enable more valid performance-based assessment of the overall responses of connections, including their robustness, in design fire scenarios.
In practice, high strength steels have been more and more popularly employed in significant structures and landmark constructions. However, in current literatures of civil engineering the very limited reports on behaviour of high strength steel structures cannot sufficiently guide the design of high strength steel structures, especially for their fire safety. The post-fire performance of steel structures is of significance in the fire-resistance design and post-fire evaluation, since the residual forces and deformations redevelop in steel structures after fire, which might be more dangerous than the fire condition. In order to reveal more information and better understanding on the behaviour and failure mechanisms of high strength steel endplate connections after fire, an experimental study has been conducted and presented in this paper. Tests on seven endplate connections were carried out after cooling down from fire temperature of 550 °C. The experimental behaviour of high strength steel endplate connections after fire was compared with that of mild steel endplate connections as well as with their original behaviour at ambient temperature without fire exposure. Moreover, the provisions of Eurocode 3 were validated with post-fire test results of high strength steel endplate connections. This experimental study indicates that a proper design of endplate connection employing a thinner high strength steel endplate can achieve the same failure mode, similar residual load-bearing capacity and comparable or even higher rotation capacity after fire, in comparison with a connection with thicker mild steel endplate.
This paper presents a simplified robust 2-noded connection element for modelling the behaviour of partial end-plate connections under fire conditions. In this new model the partial end-plate connection is modelled as a 2-noded nonlinear spring element. The characteristics of the spring – such as stiffness, tension, compression, shear strengths and bending moment resistance – are determined based on each component of the connection. It is well known that the rotational response of a partial end-plate connection comprises of two stages, due to the shift of the compression centre of the connection from the end of the endplate to the centre of the beam bottom flange at large rotation. This two stage behaviour is considered in the model proposed. Compared to normal component-based models the most significant of the current model is that this simplified model has very good numerical stability under static solver condition. The model also retains the advantages of both simple and component-based models. Fourteen tests of partial end-plate connection previously conducted by other researchers were used to validate the proposed model. It is evident that the model is capable to predict the behaviour of flexible end-plate connections under fire conditions. In order to investigate the influences of the connections on the behaviour of steel structures, a series of numerical studies has been conducted on a 2D steel frame, subjected to ISO834 Fire and Natural Fire. It is clear that the model can be used to represent the partial end-plate connections in performance-based fire resistance design of steel-framed composite buildings.
In order to reveal more information and understanding on behaviour and failure mechanisms of high strength steel endplate connections under fire conditions, an experimental study has been carried out and presented in this paper. Full-scale tests on beam-to-column high strength steel endplate connections were conducted at elevated temperature 550 °C under steady state fire condition and at ambient temperature as reference. Further, their behaviour was compared with that of mild steel endplate connections. Moreover, the provisions of Eurocode 3 were validated with test results of high strength steel endplate connections. It is found that a proper thinner high strength steel endplate can enhance the connection’s rotation capacity both at ambient temperature and in fire (which guarantees the safety of an entire structure), and simultaneously achieve almost the same moment resistance with a mild steel endplate connection.
This paper reports on an experimental investigation of the behaviour of reverse-channel connections between steel beams and concrete-filled tubular (CFT) columns in fire conditions. The objectives of the tests were to assess the behaviour of beam-to-column connections subject to the combinations of significant tying and shear forces and large rotations, which can arise during a building fire, and to provide test data to characterise and validate simplified temperature-dependent component-based connection models. It has been found that the reverse-channel connections not only provide a practical solution for connecting steel beams to composite columns but they also possess high ductility and strength. Such high ductility allows greater beam deformations in fire while reducing the magnitudes of the induced axial forces, thereby enhancing the fire resistance of the connections without requiring them to be stronger.
This paper describes the experimental results of ten fire tests on medium-scale restrained steel sub-frames to investigate the relative behaviour and robustness of different types of steel joint in steel framed structures in fire. The ten fire tests were designed to investigate the effects of two column sizes (simulating two different levels of axial restraint to the connected beam) and five different types of joint, including fin plate, web cleat, flush endplate, flexible endplate and extended endplate connections. Each test frame, in the form of "rugby goalpost" consisting of one beam and two columns, was connected through two identical beam to column joints. All the steelwork was unprotected except for the top flange of the beam which was protected to simulate the effect of a concrete slab in reducing the beam top flange temperature. The column ends were restrained to examine the effects of axial restraint on the beam and the joints. This paper presents the observations of structural fire behaviour, including joint failure modes and beam limiting temperatures, the development of deflections at beam middle span and axial forces in the joints at elevated temperatures. The main conclusions are: (1) failure (fracture) was observed only in joints when the beam was in catenary action and a variety of joint failure modes were observed which provides valuable data in understanding joint behaviour; (2) the medium-scale steel beams were able to undergo very large deflections (span8∼span6) without failure; (3) the specimens with stronger connections such as extended endplate reached higher than their limiting temperatures, defined as the beam bottom flange temperature at middle span at which the axial load in the beam returned to zero. But the difference in beam limiting temperatures using different types of joint is small, less than 50 °C; also the column size had little effect (less than 30 °C) on the beam limiting temperature; (4) the beams connected to the larger column experienced less deflections, but higher axial force due to the higher axial restraint to the beam, which led to fracture of the joint components in these tests; in contrast, the lighter columns visibly deformed and formed plastic hinges at the joints, but there was little evidence of connection fracture in the test frames using the light columns; (5) the web cleat connection appears to have the best performance. © 2011 Elsevier Ltd. All rights reserved.
This paper reports on a set of test results on flush end plate connections at ambient and elevated temperatures. The experiments aimed to investigate the behavior of connections at the ends of unprotected beams in fire situations, when they may be subjected to significant tying forces and large rotations at elevated temperatures, as a consequence of high beam deflection. A change in first fracture mode was observed with increasing temperature as the failing component became the bolts rather than the end plate as the strength of bolts reduces faster than that of steel in fire. At elevated temperatures, the use of thicker end plates can enhance the peak resistance, but reduces the rotational capacity of the connection. Finite-element analyses were performed to simulate the tested connections, and gave predictions very close to the observed behavior of the connections in both the loading and the postpeak resistance phases for all the tests at high temperatures. Via these simulations, minor cracks in the end plate, which were widely observed during the tests, were found to have little effect on the overall resistance. Development of the forces in each bolt row showed that, at the peak resistance of the connection force, their distribution can be far from uniform, which emphasizes the need for the full load-displacement-temperature relationships of bolt rows in simplified (component-based) analysis methods.
The degradation of steel and composite connection characteristics at elevated temperatures is investigated. Five series of tests are carried out in a portable connection furnace at the Building Research Establishment. The test series includes two full end-plate and one flexible end-plate bare steel connections, and two flexible end-plate composite connections. Moment-ratio-temperature curves for different connection types are interpolated from the results obtained from tests at constant level with increasing temperature. It is found that the elevated temperature tests of all types produced failure modes similar to those which happened to the same connection at ambient temperature. In nearly all cases the degradation is small up to 400 °C.
Recent structural collapses caused by fire have focused attention on research concerning fire safety in building design. Steel connections are an important component of any structural steel building, as they provide links between the principal structural members. The evaluation of the performance of steel connections at elevated temperatures has been a topic of several research programmes in the last few years. Determining the behaviour, available strength and stiffness of moment connections in fire conditions has been a dominant theme in these research works; however very little information on the behaviour of simple shear connections in fire conditions has been disseminated. Fin plate shear connections are easy to fabricate and install; as a result, they have gained popularity with fabricators because of their economy. In this research, the robustness of simple fin plate beam-to-column connections is being investigated under catenary tension from highly deflected beams in fire. A highly detailed three-dimensional (3-D) finite element (FE) model has been created using the ABAQUS software. This is a complex model accounting for material and geometric non-linearity, large deformation and contact behaviour. Contact is critical to model the shear behaviour of the joint, and contact elements have been used both at the bolt–hole interface and also at the surface between the web of the beam and the fin plate, taking into consideration friction between the surfaces. The connection model has been analysed through the elastic and plastic ranges up to failure. Bolt shear and bending, and plate and web bearing have been observed as failure modes. A comparison between available experimental data at ambient and elevated temperatures and other analytical results shows that the model has a high level of accuracy. When the connection model was extended to include an attached beam, it was found that it eventually experiences large tensile force when exposed to fire.
Behaviour of steel connections in fire is a multi-dimensional problem involving parameters such as temperature, tying forces and large deformations. Investigation of this behaviour will remain one of the main subjects for fire engineering research in the coming years. Finite element simulation plays an important role in the study of connections because fire tests are expensive to perform. Unlike normal structural analyses, finite element simulation of bolted steel connections is a challenging task, as large numbers of contacts exist in the model. This leads to convergence difficulties in static solvers. This paper explores the use of an explicit dynamic solver to analyse bolted steel connections. By comparing the results with those from static analysis and tests, it is shown that the explicit dynamic solver, with proper control, gives satisfactory predictions of the responses of steel connections up to post-failure deformations.
Current design codes for fire resistance of structures are based on isolated member tests subjected to standard fire conditions. Such tests do not reflect the behaviour of a complete building under either normal temperature or fire conditions. Many aspects of behaviour occur due to the interaction between members and cannot be predicted or observed in tests of isolated elements. Performance of real structures subject to real fires is often much better than that predicted from standard tests due to structural continuity and the provision of alternative load paths.This paper reports on the results of a collaborative research project (Tensile membrane action and robustness of structural steel joints under natural fire, European Community FP5 project HPRI—CV 5535) involving the following institutions: Czech Technical University (Czech Republic), University of Coimbra (Portugal), Slovak Technical University (Slovak Republic) and Building Research Establishment (United Kingdom). It consists of an experimental programme to investigate the global structural behaviour of a compartment on the 8-storey steel–concrete composite frame building at the Cardington laboratory during a BRE large-scale fire test, aimed at the examination of the temperature development within the various structural elements, the corresponding (dynamic) distribution of internal forces and the behaviour of the composite slab, beams, columns and connections.
Accidental fires and full-scale structural tests have indicated that steel connections can be subjected to large deformations and fracture in fire. This is not currently considered in fire engineering design approaches because the connections are assumed to heat up more slowly than the structural frame members and therefore retain a greater proportion of their strength. A project at the Universities of Sheffield and Manchester has investigated the robustness of common types of steel connections when subjected to fire. In the test programme the connections were subjected to combinations of shear force and tying force, and loaded to large deformation and fracture. This paper reports on the test results on fin plate connections. The test results indicate that bolts are vulnerable to shear fracture and that failure is usually controlled by bolt shear rather than by plate bearing. Fin plate connection resistance reduces rapidly with increase of temperature.The test results are compared to values suggested by the current United Kingdom design guidance and Eurocode 3 Part 1.8. A previously developed component-based model is also used to simulate the test results.
World trade center building performance study: data collection. Preliminary observations, and recommendation
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structural robusyness in fire. In: Proceedings of the 12th international conference on structures
in fire (SiF2022), The Hong Kong Polytechnic University, Hong Kong, China, 2022
The behaviour of steel fin plate connections in fire
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Sarraj M (2007) The behaviour of steel fin plate connections in fire. University of Sheffield, Sheffield
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