Applications of Structural Fire Engineering
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Published By Czech Technical University In Prague - Central Library


Feiyu Liao ◽  
Zhaohui Huang

This paper presents a robust hybrid finite element procedure for predicting the large individual cracks within reinforced concrete floor slabs at elevated temperatures. For modelling the cracks formations and propagations within the floor slabs, the smeared crack model is used for modelling early stages of crack evolution, and then the ‘delayed extended finite element method (D-XFEM) is proposed for capturing individual big cracks within the floor slabs. The new model has been validated against previous fire test results. A series of parametric studies has been conducted on a composite floor to understand the influences of different protection conditions of the support steel beams on both global responses and cracking patterns of the composite floor under fire conditions.

Du Yong ◽  
J.Y. Richard Liew ◽  
Mingxiang Xiong ◽  
Jie Zou ◽  
Zeng Bo

This paper investigates the behavior of large span grid structure exposed to a localized fire. The localized fire may generate hot smoke and thus induce non-uniform temperature distribution in the grid structure. The thermal expansion of the heated members tend to be axially restrained by the adjacent cold members thus inducing additional forces on the critical members of the grid structure. The buckling resistance of axially restrained member at elevated temperature may be obtained based on second order analysis of member with initial lateral imperfection by considering force equilibrium at deformed geometry and cross section resistance being reached. The critical temperature of the member is reached when the axial force reaches its buckling resistance. It is found that the critical temperature of members with initial lateral imperfection was higher than that without such imperfection for chord members with large slenderness ratio and high axial restraint.

Ioan Both ◽  
Ioan Mărginean ◽  
Calin Neagu ◽  
Florea Dinu ◽  
Dan Dubina ◽  

Bolted end plate connections are widely used in multi-storey steel frame structures. Their design is based on the component method, which evaluates the behaviour of the basic components through equivalent T-stubs, to model the tension zone that constitutes the most relevant source of deformability. The paper presents the results of an experimental research on bolted T-stubs, tested under elevated temperatures, in normal and high strain rate loading conditions. The influence of the loading rate on the resistance and ductility of the T-stubs subjected to elevated temperatures is emphasized.

Danie Roy ◽  
Umesh Sharma ◽  
Pradeep Bhargava

A series of 21 reinforced concrete T- beams of length 1400 mm were cast using normal strength concrete. After 90 days of ageing, the beams were heated to 600°C and 900°C temperatures in an electric furnace. While three control beams were treated at room temperature, eighteen beams were heat damaged. The heat damaged beams were strengthened with FRP laminates and then tested until complete failure. Two different strengthening patterns of glass fiber reinforced polymer (GFRP) strengthening materials were used. The strengthened beams were then tested in a loading frame under 4 point loading condition. The load-deflection curves for the beams were examined to evaluate the capability of various strengthening patterns. Structural performance of various strengthening patterns were gauged in terms of failure mode, flexural strength, secant stiffness and the energy absorption capacity i.e. area under the load-displacement curve. It was observed that the beams exposed to different temperatures experienced a reduction in ultimate load carrying capacity ranging from 14 % to 61%. The secant stiffness and energy dissipation were reduced in the range of 34% to 56% and 10% to 41% respectively. The study shows that GFRP wraps were quite capable of restoring the flexural strength of heat damaged beams.

Urška Bajc ◽  
Miran Saje ◽  
Tomaž Hozjan ◽  
Igor Planinc ◽  
Sebastjan Bratina

The influence of the cross-sectional dimensions on the buckling load capacity of reinforced concrete column exposed to ISO fire load is presented. The fire analysis is divided in two separate phases. In the first phase, the calculation of the temperatures over the cross-section of the concrete column is performed. Here more advanced hygro-thermal analysis is executed to take into account the influence of moisture on the distribution of the temperatures. In the second step of the fire analysis, the mechanical analysis is performed. The mechanical and thermal properties of concrete and reinforcement at elevated temperatures are used in accordance with EN 1992-1-2 (2004). For two different cross-sections, the parametric study has been performed. The critical buckling time and critical buckling capacity as a function of a load and slenderness of reinforced concrete column have been determined.

Robert Kowalski ◽  
Marian Abramowicz ◽  
Paweł Chudzik

<p>An important issue in advanced analysis of reinforced concrete structures exposed to fire is to determine the response of structural elements (cross-sections) to the effect of high temperature. The unsteady heat flow results in a nonlinear temperature distribution. In practical structural calculations performed by simplified computer programs the average temperature value and the appropriate temperature gradient are used. This paper presents substitute values of these parameters and detailed analysis of nonlinear temperature distribution in 20, 25, 30 cm thick reinforced concrete slabs exposed to one-sided standard fire.</p>

Dušan Ružić ◽  
Igor Planinc ◽  
Urban Rodman ◽  
Tomaž Hozjan

In the present study the fire analysis of a curved reinforced concrete beam exposed to concrete spalling is presented. Due to the complexity of physical and chemical processes in concrete at elevated temperatures, the proposed numerical model is divided into two consecutive mathematically uncoupled phases. In the second phase of the fire analysis a partially coupled numerical model is introduced in order to evaluate the effect of concrete spalling on the behaviour of curved RC beam in fire. In addition, the effect of depth, time development and the length of spalling area on the fire resistance of a curved RC beam is discussed.

Natasa Kalaba ◽  
Patrick Bamonte ◽  
Roberto Felicetti

The present work is aimed at investigating the residual behaviour of prestressed concrete members exposed to natural fires, since experience has shown that substantial losses of the load bearing capacity may take place during the cooling phase. This topic is of great practical significance, because the knowledge of the residual response can help the engineers to decide whether a structure can be refurbished after being exposed to fire, with minor costs, or whether demolition is inevitable.Sequentially coupled thermo-mechanical analysis was performed on typical inverted T and double T-beam sections, subjected to heating and subsequent cooling.The results show that the residual deflection is primarily governed by the load level and the section shape and that the magnitude of the residual deflection can be even several times higher than the initial value.

Mohammadali Javaheriafif ◽  
Buick Davison ◽  
Ian Burgess

This research is intended to predict the inevitable through-depth crack development in a composite slab, across its area and in particular around its edges at large deflection. Based on previous work, a theoretical model has been proposed to simulate the local behaviour of slab beyond initial cracking. The model has been successfully implemented in the software VULCAN as a new line element. Comparisons between the existing theoretical model and FE modelling have shown that the proposed element provides a sufficient level of accuracy beyond initial cracking. However, further improvement is needed to enable a precise investigation of the local and global behaviour of composite slab systems, and the influence of through-depth cracking on the slab’s performance.

Mislav Stepinac ◽  
Vlatka Rajčić

<p>Until recently, the fire resistance of buildings was based on the ISO standard curve. ISO standard curve used by the current norm is too simple, unrealistic and lead to uneconomic situations with no guarantee of security proportional to the invested money. Unlike the fire design of the steel, concrete or composite structures, methods for fire design of timber structures have been greatly simplified. Generally, it is not necessary to check the reduction of strength in the residual section because each increase of temperature is considered small and it is ignored. Global fire safety concept of timber structures is presented according to the recommendations from Eurocode norms. Special attention was given to natural fire design with two different methods of parametric exposure which are given in EN1995-1-2.</p>This paper presents reliability analysis of a glulam beam in a case of fire. The limit-state functions for maximum bending stress of glulam beam in fire conditions are formed. Reliability indexes are obtained from the limit state of the beam exposed to 30 min fire. Reliability index in the Eurocodes (reliability class RC2) compared to the calculated reliability indexes obtained by the methods of reduced strength and effective section were described.

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