Fire Resistance Of Composite Beams Research Articles

Fire Resistance of Composite Beams with Composite Slabs under Hinge Constraints

To study the fire resistance of monolithic composite beams and separated composite beams with composite slabs under hinge constraints, constant-load temperature rise tests were conducted on a full-scale two-span continuous beam. The test phenomena, temperature distribution, displacement changes, and failure modes of the composite beam were studied during the entire process of the fire. The results showed that the cracking of the seams between the precast slabs of the separated composite slabs led to an increase in the burned area of the composite slabs and an increase in the temperature of the composite beams. No obvious cracking was observed at the postpouring seams of the monolithic composite slabs, the integrity and fire resistance of which were better. After the temperature stopped increasing, the steel beam cooled faster than the concrete composite slabs. The deformation recovery of the steel beam was restricted by the composite slabs, which were subject to the joint action of the constraining force generated by the deformation recovery of the steel beam and the external load, resulting in longitudinal cracks along the medial axis of the top of the slabs. The deformation recovery ratios of the two types of composite beams with composite slabs under hinged conditions after the temperature stopped increasing were similar. The calculation method of the axial force and horizontal displacement of the composite beam with composite slabs under the hinge constraint at the beam end in the fire was established, and the calculation results were in good agreement with the test results, with good calculation accuracy.

Experimental and analytical investigation on fire resistance of glulam-concrete composite beams

The timber-concrete composite beam characterized by good mechanical behavior, low susceptibility to vibration and high sound insulation has a wide application in high-rise and long-span timber structures. However, the published study on the fire resistance of TCC beam is limited. In this research, one short-term failure test at ambient temperature and five full-scale fire tests were performed on the glulam-concrete composite beams. The influences of the load ratio, presence of timber board and fire-rated gypsum plasterboard on the temperature field and fire resistance were investigated in detail. The test results showed that the fire resistance of the composite beam was decreased with the increase of the load ratio. The composite beam with timber board interlayer outperformed the beam without the interlayer in terms of fire resistance. Moreover, the fire-rated gypsum plasterboard protection on the glulam beam could effectively improve the fire resistance of the composite beam. The finite element models of the composite beams were established to predict the temperature field of composite beams under fire. The average temperature values of concrete slabs under different fire times were obtained from numerical simulations. Considering the influence of high temperature on the glulam beam, concrete slab and shear connectors, the calculation methods of load carrying capacity and bending stiffness of the composite beam under fire were proposed.

Fire Resistance of Composite Beams with Restrained Superposed Slabs

To investigate the fire resistance of composite beams with restrained superposed slabs, three specimens were tested under uniformly distributed loads in a furnace. The effects of the thickness of the postcast top layer in superposed slabs and the spacing of shear studs on the structural behaviours of composite beams under fire were further examined. During the tests, the temperature distributions of the superposed slabs and steel beams as well as the displacements at their key positions were recorded and analysed. It was found that the temperature of the concrete superposed slabs decreased long their heights from the bottom. The most drastic change of the temperature along the slab cross section was found in the region with a distance of 40 mm to the slab bottom. The concrete superposed slabs could impose restraints to the steel beams due to their incompatible deformations. Cracks were developed on the top surfaces of the specimens and the superposing interfaces between the precast slabs and postcast top layers were not broken. Through the comparisons of different specimens, the spacing of shear studs could have a significant effect on the fire resistance of composite beams, especially for their deformation recovery capacities. In contrast, the effect of the thickness of the postcast top layers was negligible. ABAQUS was employed to simulate the temperature fields and deformation behaviours of composite beam specimens based on a sequenced thermomechanical coupling analysis. The numerical results agreed well with the experiment data, which validated the developed numerical model.

Analytical study on lateral torsional buckling of partially encased beams under ISO834 fire exposure

European standard EN1994-1-2:2005 provides tabulated values and simplified calculation models for assessing fire resistance of composite beams, but does not consider the design checks against lateral torsional buckling under fire. This research presents an analytical method to calculate the buckling resistance moment of laterally unrestrained partially encased beams in fire conditions. The proposal applies a reduction factor for lateral torsional buckling in fire design condition to the moment resistance of the homogenised section at time t, determined by EN1994-1-2:2005. Two finite element models capable to simulate the thermal and mechanical behaviour of partially encased beams are also presented, including the validation against fire tests conducted by Piloto et al. Based on these models, a numerical analysis of partially encased beams with the same geometry and material properties as used in experimental tests is presented, evaluating different load levels when exposed to standard fire ISO834:1999. The numerical results of fire resistance according to standard EN1363- 1:2012 and the numerical ultimate time, when beams suffer instability, are used to validate the proposal, using experimental and analytical heating result according to EN1994-1-2:2005.

Experimental and Numerical Study of Fire Resistance of Composite Beams

In this paper, the standard fire resistance test under load and associated numerical study were carried out to evaluate the fire resistance of unprotected partially encased beams and slimfloor beams. The temperature evolution and the deflection increase of the composite beam specimens were investigated and the effects of the key behavioral parameters including the load ratio, the reinforcement, and the fire exposure were analyzed. The test results showed that the temperature rise of the partially encased beams and slimfloor beams is considerably slow compared to the conventional H-shape composite beams. Up to at least 90 minutes, the reinforcements in the partially encased composite beams maintained below the temperature at which the cold steel strength is sustained. Unprotected partially encased beams and slimfloor beams in the experimental program achieved the fire resistance more than 2 hours according to the limiting deflection criteria. This implies that unprotected partially encased beams and slimfloor beams can be very promising alternatives to enhancing the fire resistance of steel beams. This study also conducted the fully coupled thermal-stress analysis by using the commercial code ABAQUS to the thermal and structural behaviour of composite beams in fire. The numerical predictions provide acceptable correlations with the experimental results. Keywords - Partially encased beam, Slimfloor beam, Fire resistance test under load, Coupled thermal-stress analysis, Fire resistance

Nonlinear behaviour of unprotected composite slim floor steel beams exposed to different fire conditions

An efficient nonlinear 3D finite element model has been developed to investigate the structural performance of composite slim floor steel beams with deep profiled steel decking under fire conditions. The composite steel beams were unprotected simply supported with different cross-sectional dimensions, structural steel sections, load ratios during fire and were subjected to different fire scenarios. The nonlinear material properties of steel, composite slim concrete floor and reinforcement bars were incorporated in the model at ambient and elevated temperatures. The interface between the structural steel section and composite slim concrete floor was also considered, allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the composite beam. Furthermore the thermal properties of the interface were included in the finite element analysis. The finite element model has been validated against published fire tests on unprotected composite slim floor steel beams. The time–temperature relationships, deformed shapes at failure, time–vertical displacement relationships, failure modes and fire resistances of the composite steel beams were evaluated by the finite element model. Comparisons between predicted behaviour and that recorded in fire tests have shown that the finite element model can accurately predict the behaviour of the composite steel beams under fire conditions. Furthermore, the variables that influence the fire resistance and behaviour of the unprotected composite slim floor steel beams, comprising different load ratios during fire, cross-section geometries, beam length and fire scenarios, were investigated in parametric studies. It is shown that the failure of the composite beams under fire conditions occurred for the standard fire curve, but did not occur for the natural fires. The use of high strength structural steel considerably limited the vertical displacements after fire exposure. It is also shown that presence of additional top reinforcement mesh is necessary for composite beams exposed to short hot natural fires. The fire resistances of the composite beams obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite beams at elevated temperatures. It is shown that the EC4 predictions are generally conservative for the design of composite slim floor steel beams heated using different fire scenarios.

EXPERIMENTAL STUDY ON SHEAR STRENGTH OF HEADED STUD SHEAR CONNECTORS AT HIGH TEMPERATURE

The paper is intended to summarize findings from high-temperature tests on headed stud shear connectors conducted as part of a study on the fire resistance of composite beams. Two headed stud shear connectors on a H-shaped steel beam are embedded in two types of slab models, representing a reinforced concrete slab and a composite slab with profiled steel decks, respectively. The test parameters other than model configurations include strength of concrete, level of shear loading, and heating conditions. A total of sixteen models were tested. It is found that the most crucial design parameter is the temperature at the bottom of a headed stud shear connector. Based on the test results, a new formulation is proposed to calculate with a good accuracy the shear capacity per stud only taking account of the heat-induced degradation of steel / concrete materials.

Fire Resistance of Composite Beams Composed of Rolled Steel Profile Concreted Between Flanges

Fire resistance tests were performed for composite beams composed of rolled steel profile concreted between flanges. In the present paper, the fire resistant test results and numerical analysis results are described. As a result of the fire resistant tests, the relation between the fire resistance time and applied bending moment of the composite beam is clarified. Analytical results agreed with tests results and consequently, the analytical model can be used to predict the behavior of this composite beam in a fire.

Fire resistance of composite beams to Eurocode 4 Part 1.2

Part 1.2 of Eurocode 4 deals with the fire resistance of composite structures. A simple calculation method is given for assessing the fire resistance of composite beams. This paper explains the state of progress of this calculation method (in 1993) and covers both the heat transfer and mechanical response.

Experimental and Numerical Studies of Composite Beams Exposed to Fire

The development of appropriate computer models to predict the response of buildings to fire is now making it possible to analyze specific structures under realistic fire‐exposure conditions. By means of experimental tests carried out at the University of Braunschweig on simply supported composite beams connected to reinforced concrete slabs, a theoretical study for estimating the effective slab width of composite concrete beams exposed to fire has been set up using a finite‐element analysis. The satisfactory agreement between the experimental and the calculation results confirms the efficiency of the finite‐element theory for determining the fire resistance of composite beams. The influence of the top transverse reinforcement in the concrete slab on the fire resistance and crack propagation are examined. The application of the results in designing fire safety of buildings is also discussed.