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A numerical study on the structural performance of a ductile connection under fire conditions
Abstract
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.
... However, traditional connection types lack axial ductility to accommodate the net expansion of beams during early heating and the net contraction of beams during the high-temperature "catenary" stage. In order to prevent the brittle failure of connections and improve the robustness of steel framed structures in fire, a novel connection with high axial deformability has been proposed by the authors [1][2][3][4][5][6][7][8][9]. A component-based model of the bare-steel ductile connection has been developed by the authors and incorporated into the software Vulcan [3][4][5]. ...
... So far, the research on the fire performance of composite connections is still very limited. The performance of the ductile connection in bare-steel structures have already been well studied by the authors in previous papers [1][2][3][4][5][6][7][8]. It is necessary to study the high-temperature behaviour of the ductile connection in composite structures to verify whether the deformability of the ductile connection is still useful when used with composite floors. ...
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.
... Dynamic performance of retrofitted steel beam-column connections subjected to impact loadings is discussed in [265] and the effect of retrofitted methods on transformation of catenary action under impact load are revealed. A study on the structural performance of a ductile connection under fire conditions is reported in [266]. The behavior of slide hinge joints with a symmetric friction damper under drop weight impact tests is studied in [267]. ...
Abnormal events, that are unforeseeable low-probability and high-impact events, cause local failure(s) to structures that can lead to the collapse of other members and, eventually, to a disproportionate progressive collapse. Ordinary design procedures, which are usually limited to gravity and seismic/wind loads, are inadequate for preventing the progressive collapse. Therefore, a focus on strengthening and retrofitting techniques to mitigate progressive collapse is necessary. Parameters such as topology of the structure, nature of the triggering event, size of the initial failure, typology of the collapse and seismic design requirements affect the strengthening and retrofitting strategy. A discussion on the impact of these parameters on strengthening strategy is first presented. Then, a comprehensive review on strengthening and retrofitting techniques to mitigate progressive collapse is provided. The paper concludes with an ambitious comprehensive list of issues covering different aspects of future research agenda.
... Conventional commonly-used connection types lack axial and rotational deformability to accommodate the large deformation that a connected beam would experience in a fire accident. In order to improve the fire performance of connections, a novel connection with excellent axial and rotational ductility has been proposed by the authors (Liu et al., 2019a(Liu et al., , 2019b(Liu et al., , 2020a(Liu et al., , 2020b(Liu et al., , 2020c(Liu et al., , 2021a(Liu et al., , 2021b(Liu et al., , 2021c. ...
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.
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.
As a result of a world-wide intensive research activity, a new design concept for structural moment resistant joints has been suggested and implemented in design codes. In the present paper, its background is first briefly described and the main contributions to its development are presented. As a matter of fact, because of the high number of past and ongoing researches, reports and papers devoted to this topic, an exhaustive list of all these works could not be established in a limited number of pages.The possibilities of extension of the new design concepts, which have been first developed for steel beam-to-column joints under static loading, are particularly pointed out. This aspect appears quite important as in the near future it should provide designers with a unified design approach for structural joints whatever their loading, their configurations and the nature of their constitutive material(s).
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 presents a 3D mathematical model based on the finite-element method to simulate the structural response of steel and steel/concrete composite connections so that their moment-rotation-temperature characteristics can be predicted. The treatment of material nonlinearity at elevated temperatures is described. A special element has been developed to model the bolts, which may expand freely without creating unrealistic forces on the connected components. The composite concrete slab is modeled by 3D brick elements with a simple crack-crush capability. The numerical model was compared with the results from eight different series of connection fire tests, all incorporating tests with different loading levels. The type of connections included those that are normally assumed to be "pinned" and those that could be classified as "rigid." The range of parameters included the end-plate thickness and the number and size of bolts. This theoretical model is shown to be capable of providing accurate moment-rotation characteristics of connections that can be incorporated in the analysis of global frame behavior in the event of fire. It can also enrich the database of connection behavior at elevated temperatures.
A three-dimensional mathematical model has been developed to simulate the response of steel structures in the event of a fire. The model using isoparametric shell finite elements is based on a tangential stiffness approach which allows sophisticated simulations to be executed economically. The model includes the consideration of the material plasticity and deterioration with temperature, non-uniform thermal expansion across a section and large deformations at very high temperatures. Analyses are undertaken using time steps. This allows the complete account of stress history of the structure, especially when the rate of temperature rise differs in different parts of the structure. Comparisons are made with the test data obtained from real fire tests on both steel beams with different support and loading conditions, and with beam-to-column connections. Both the simulated deflection-time curve and fire resistance period are found to be in good agreement with the test evidence.
Although steel beams are often designed as simply supported, practical connection details generally afford significant rotational stiffness. When exposed to fire, this can have the effect of improving the survival of the beam. The analytical approach described provides a means of studying this. Indicative studies using this method are included to illustrate the influence of certain key parameters, including the connection type, its temperature relative to the rest of the beam, and the proportions of the beam itself. The results are compared with current simplified design approaches. The studies are based on currently available test data for a limited range of connection details, and a simple means of estimating high temperature connection characteristics for more general conditions is suggested.
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