AbstractSteel self-centering moment-resisting frames (SC-MRFs) are a class of low-damage seismic-resistant structural systems, which use posttensioned high-strength steel bars to provide ...self-centering capability and yielding or friction-based devices that are activated due to rocking in the beam-column interfaces, to dissipate seismic energy. Until now, research has mainly focused on the assessment of the earthquake resilience of SC-MRFs, while their fire behavior is unknown. To fill this gap in knowledge, this paper studies the fire behavior of different versions of a five storey SC-MRF. The first research objective is to reveal the main factors that affect the behavior of the SC-MRF at elevated temperatures. For that purpose, three-dimensional (3D) finite-element models are developed, and transient thermal/structural analyses are conducted to simulate the behavior of the SC-MRF under fire conditions. The second objective is to study how specific structural details of the beam-column connections affect the fire resistance of the SC-MRF. For that purpose, the structural details of the connections are modified and/or are considered fire protected. Based on the results of parametric analyses, suggestions for the enhancement of the fire resistance of SC-MRFs are provided. In all the transient thermal/structural analyses, the thermal problem is solved by adopting the closed cavity option, which allows simulating the radiative transfer of heat between surfaces during fire. The effectiveness of such an approach was validated through direct comparison with the provisions of Eurocode as well as with existing experimental data from fire tests on steel beams.
Research on the seismic performance of steel structures has led to the development of improved structures, which minimize structural and non-structural damage and can be reused immediately after an ...earthquake. Moreover, significant advances have been made for predicting the response of steel members, connections, and structural systems exposed to fire. Nevertheless, the research on the reuse of steel structures after a fire event is limited. A steel structure designed according to the current seismic codes can survive a fire without significant structural damage and may be repaired and reused. Therefore, it is of great importance to study whether the reuse of steel structures after a fire is safe in high seismicity areas. This paper investigates the seismic performance of steel columns that are pre-damaged due to fire. For this purpose, sophisticated finite element models have been developed and validated against experimental data. It was concluded that the models accurately predict the behaviour of beams-columns at elevated temperatures. First, the behaviour of the columns was studied using simplified boundary conditions; the surrounding structure was not included in the numerical model. Thermal-structural analyses were performed to determine the structural damage induced by the fire. Subsequently, the cyclic performance of the columns was investigated, considering both the residual post-fire deformations and the proper material properties. Aiming to obtain more realistic results, the complicated interaction between the heated columns and the surrounding structure was considered in the modelling. For this reason, the fire behaviour of a seismic resistant frame was simulated. Then, the behaviour of fire-damaged columns under cyclic loading was assessed. The analysis of the results demonstrates the effect of the post-fire damage on the cyclic behaviour of columns.
Fracture of steel at ambient temperature has been extensively studied. Such studies developed efficient micromechanical fracture models, which can be used to predict the behaviour of steel structures ...and components up to failure under extreme monotonic or cyclic loading, e.g. extreme deformations due to loss of column scenarios or large earthquakes. Considerable research has been also carried out on the high-temperature fracture of steel under creep conditions but its findings have not yet been applied to structural fire engineering practice, though ductile fracture has been reported as a common mode of failure for steel structural elements under fire conditions. This paper reports results of an experimental program carried out to investigate fracture of the S275 structural steel grade at temperatures ranging from 20 °C to 450 °C. A series of tests, including tensile and shear tests, are executed to extract information on fracture of structural steel for a wide range of stress triaxiality values. Moreover, numerical simulations of the tests are carried out using MSC Marc to get further insight for the role of stress triaxiality, Lode angle parameter, and temperature. Based on both the experimental and numerical results, a fracture model proposed in the literature is calibrated to predict fracture of structural steel for the temperature range 20 °C - 450 °C.
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•The plastic response of steel is affected by the stress state.•The material constants of the plasticity model depend on temperature.•Stress triaxiality and Lode angle parameter affect the ductility of steel at high temperatures.•The overall level of fracture strains increases at T = 450 °C.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This paper addresses the thermal buckling behavior of tanks having a fixed roof, as employed to store fuel in the oil industry. The study is performed based on finite element analyses of the shell, ...including linear analysis, linear bifurcation analysis, and geometrically and constitutive nonlinear analysis, in order to elucidate the mechanics of stress redistribution at pre-buckling and buckling states. Based on previous works, the roof is modeled as a conical shell with an equivalent uniform thickness. The results show that the stress field due to a uniform temperature around the circumference is considerably different from that obtained for a non-uniform field as modeled in cases of temperatures due to an adjacent fire: Under uniform temperatures around the circumference the shell does not provide vertical restrain and buckling is dominated by hoop action; whereas displacement constraints are present under a non-uniform temperature, leading to buckling dominated by meridional stresses. Contrary to what has been suggested, the tank under uniform temperature cannot be taken as an upper bound to the buckling of a tank under an adjacent fire. In the evaluation of critical temperatures, the influence of geometric relations H/D (height to diameter) and R/t (radius to thickness) are independent of each other. It is shown that the problem is not imperfection-sensitive. Finally, thermal buckling mode and critical temperatures are strongly dependent on the H/D ratio of the cylindrical shell.
•Stress distributions in tanks with fixed roof are investigated under thermal fields.•Buckling mechanism under uniform temperature is not a bound of the non-uniform case.•Plasticity may develop at shell bottom but does not affect the buckling mechanism.•Buckling temperatures depend on H/D and R/t ratio, but each geometric relation is independent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The paper deals with the numerical modelling of hooked steel fibres embedded in high-strength cementitious matrix. The pull-out of the fibres is first studied by means of accurate three-dimensional ...models which take into account the non linearities that are present in the physical model. The bonding properties of the fibre–matrix interface considered in the numerical model are based on experimental results of pull-out tests on straight fibres. The results of the numerical model are compared with respect to the results of experimental tests on hooked fibres. Then, the paper studies the effect of different fibre geometries to the load–displacement pull-out curves. It is concluded that fibres having a doubly bended shape have a superior behaviour compared to fibres having a single bended part. Finally, a simplified two-dimensional model is proposed that yield fast results which are similar to the ones obtained by its three-dimensional counterpart.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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