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Condition for Birdcaging in a Strand (birdcaged wire rope on left) (Costello, 2003) Judge et. al (2012) captured the birdcaging effect in a full 3D FEM study of multilayer SSSCs. Experimental results showed that birdcaging occurred at the fixed end of samples after the loading end had ruptured entirely, (Figure 10). These results were then replicated by the model, which incorporated complex geometry and contact conditions,
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Following growth in the popularity of tensile structures and re-evaluation of safety standards, the ability of structural steel cables to withstand fire scenarios has recently been brought into question. Designers have recognised that the fire performance of spiral strand steel cables in particular is relatively unexplored, identifying a lack of bo...
Context in source publication
Context 1
... it is difficult to compress a strand into this shape in laboratory experiments, dynamic loading can cause a critical condition in axial and rotational strain as a function of time to be reached, resulting in zero contact force between the outer wires and the core ( Figure 9). It is possible to calculate the velocity of oscillations required in these properties to produce this condition (Costello, 2003). ...
Citations
... The 'importance factor' is most dependent on the geometric feature of the structural component, among other factors such as potential threats and economic impact 2 . Milne determines the arrangement of wires and wire geometry to influence the heat transfer and get reliable thermal predictions 14 . The importance of geometric features in fire design has led to the experimental methodologies conducted by Nicoletta et al. 15 providing reliable and realistic inscale data concerning the relation between cable geometry and its thermal response. ...
Structural cables are used to design critical bridge structures. These are not typically redundant; a loss or compromise of a few cables can lead to the progressive collapse. Previous experimental research has shown that the degradation of material properties and thermal expansion of structural cables is more onerous than the standard carbon prestressing steel. Despite its importance for design no well-validated methodology exists to aid in the thermal performance of structural cables in the event of a fire, particularly for spiral and locked-coil cables which inherently are complex due to their cross-sectional geometry. A state-of-the-art methodology for modelling structural cables' thermal response is presented. The methodology will enable the development of an understanding of the temperature distribution and thermal deformation in a cable cross-section and allow estimation of post-fire resilience. Validation is performed against experiments of locked-coil and spiral cables, subjected to realistic pool fires. The cables range from 22 to 100 mm in diameter and are constructed of galvanized or stainless steel. The cables are modelled undergoing non-linear thermal analysis in LS-DYNA. 2D models are found to provide conservative estimates for critical values such as peak temperature with 90% accuracy, while 3D models provide slightly more conservative estimates.
... 19 A later study examined the heat transfer in commercial spiral strand cables of diameters 32, 52, and 72 mm exposed to a radiant heater. 20 Although nonuniform heating was applied in this study, the development of thermal gradients may have been underestimated when compared to realistic fires due to the applied thermal exposure. 2 Successive work using the same thermal exposure examined the heat transfer in 50 and 70 mm diameter parallel strand cables constructed using individual bars of mild steel, then exposed to a radiant heater. ...
There are no contemporary code requirements for the fire resistance of bridge infrastructure, nor is there guidance available for practitioners who wish to design cable-supported structures for the fire. This research seeks to develop an understanding of the thermal response of steel stay-cables under exposure to a pool fire. Multiple varieties of locked coil and spiral strand stay-cables are instrumented with thermocouples and heated by a methanol pool fire. Novel imaging techniques observe the cables’ surface during heating and cooling and enable the calculation of thermal strains and deformations. Results herein illustrate a normalisation of cross-sectional temperatures outside of the localised heating region for cable diameters up to 140 mm, provide comparisons of heat transfer behaviours for different cable sizes and configurations, present novel thermal rotational effects, and calculation of cable thermal expansion values. Predictive thermal expansion values provided by the Eurocode are shown to underpredict cable thermal expansion in most cases.
... Fire performance of spiral strand steel cables Milne (2016) The material response of individual Grade 1860 wires based on samples from the cable manufacturer Bridon was assessed experimentally under tension and elevated temperatures in a furnace chamber in the studies by Milne (2016). The reduction of ultimate tensile strength, Young's modulus, and yield strength were monitored. ...
... Fire performance of spiral strand steel cables Milne (2016) The material response of individual Grade 1860 wires based on samples from the cable manufacturer Bridon was assessed experimentally under tension and elevated temperatures in a furnace chamber in the studies by Milne (2016). The reduction of ultimate tensile strength, Young's modulus, and yield strength were monitored. ...
... Five key experimental studies under elevated temperatures are provided in the literature of cables with a shape and diameter different from the typical seven-wire strands used for concrete construction, namely those of Fontanari et al. (2015), Milne (2016), Lugaresi (2017), Nicoletta et al. (2019a), and Robinson et al. (2019). Fontanari et al. (2015) have carried out the most complete experimental investigation into the thermomechanical performance of structural cables. ...
Structural cables are widely used on large-scale structures such as bridges and stadia around the world. This paper presents a review of current research and development associated with the thermal and mechanical performance of structural cables when subjected to fire loading. The findings of this study highlight key knowledge gaps, which are subsequently used to propose the future research agenda. The particular focus of the review is on large-diameter cables, composed of both multiple strands and multiple wires, which are commonly used on structures of concern to civil and structural engineers. It is determined that the fire performance of structural cables is influenced by several factors such as the cable shape, diameter, metallurgical characteristics, uniformity of thermal exposure conditions, time-dependent effects of fires, and their terminal characteristics. The thermal expansion coefficients and reduction of material properties provided in EN 1992-1-2 and other research studies may not be appropriate for exposed prestressed cables because they were developed for tendons encased in concrete construction and creep is not accounted for. In particular, the material characterization at elevated temperatures may not necessarily be the same as that of normal high-strength steel owing to the different cold-working process of cable wires. Very limited studies have investigated experimentally or numerically the fire performance of structural cables with a shape and diameter different to the typically studied seven-wire strands used for concrete construction, leading to a number of knowledge gaps. The experiments conducted so far have shown that for unprotected cables a significant thermal gradient develops and early failure occurs with an increase in the cable diameter leading to an increase in its failure time. A range of simplified and advanced methods have been proposed in the literature; however, these generally lack extensive validation against experimental evidence. Numerical studies have shown that the presence of air cavities between strands can lead to larger thermal gradients in particular for unprotected cables because the cavity acts as insulation, unlike protected cables, where the temperature is more uniform within the section. The testing procedure of PTI DC45.1-12, which is the only available standard for stay cables, lacks extensive verification and validation to ensure that the aims of the standard are achieved. Further research is required to confirm that the two-phase procedure adequately captures all underlying physics under realistic fire exposures and its applicability for cables with characteristics different from the sample tested.
... Only very few experiments have ever been performed with the aim of understanding the thermal behaviour of steel cables. Those that have been performed considered only either uniform axisymmetric heating by placing a cable sample in an oven [26,27] or asymmetric heating from one side [27,28]. Degasperi [26] tested two cable assemblies: a Locked Coil rope and a Warrington Seale rope (6 spiral strands twisted around a polymeric core). ...
... A series of small-scale experiments have also been carried out at the University of Edinburgh [27,28]. The temperatures in the samples were recorded via K-type thermocouples at different locations within the cable cross-section. ...
... The temperatures in the samples were recorded via K-type thermocouples at different locations within the cable cross-section. Milne [28] tested existing cable specimens that were once part of a construction project and were provided by a manufacturer. Due to the difficulty in inserting thermocouples inside the samples, in the next set of experiments by Lugaresi [27] the specimens were assembled in the lab from straight steel rods which facilitated the insertion of thermocouples. ...
Cable-supported structures such as bridges and stadia are critical for the surrounding community and the consequences arising from a major fire event can be substantial. Previous computational studies into the thermal response of cables often employed simplistic heat transfer models that assumed lump capacitance or cross-sectional homogeneity without proof of validity. This paper proposes a methodology for calculating the thermal response of a cable cross-section allowing for heat transfer by conduction through each strand contact surface and radiation across inter-strand cavities. The methodology has been validated against two experiments of cables subjected to radiant heating and an input sensitivity analysis has been undertaken for the heat transfer and material parameters. The approach is compared against simple heat transfer lumped methods for a parallel-strand cable where it is shown that these-lumped models are not always conservative. The model is then coupled with a two-dimensional generalised plain strain model to study the likely effect of the cross-sectional temperature gradients on the mechanical response. The study considers three qualitatively different hydrocarbon jet fire scenarios, both with and without external insulation for fire protection. It is shown that the proposed methodology can reproduce realistic cross-sectional temperature distributions with up to 50% temperature difference at the cable external surface and can capture the phenomenon of load shedding in a gradually heated cable. It is also shown that assuming a lumped thermal mass neglects the possibility of moment-inducing temperature gradients which are not considered in the ambient design of cables that is driven by tensile capacities. The proposed model and its predictions contribute towards an improved understanding and a more informed structural design of cable-supported structures in fire.
