AN ANALYSIS OF STEEL HEAT USING ANSYS: A REVIEW
1JAGGU MAHAR
2SHOAIB AHMAD ANSARI
1Research Scholar Heat & Power Engg, VITS Jabalpur
2Asstt . Prof. ,Department of Mechanical Engg. VITS Jabalpur
ABSTRACT:- In the present scenario the steel Heat design had many complicated parameters. Design of steel Heats fails for the buildings and the mainly failure occurs due to heat and temperature. Many researchers have formulated many problem on this issue, but due to high costing of model and prototype the problem remains same. By introducing the many solvers like FEA(FINITE ELEMENT ANALYSIS) technique we can reduce the cost of model and prototype.
1. BACKGROUND
Even though the steady progress and systematic knowledge in understanding the disaster resistant property of a building, we are still lacking behind to develop a curing characteristic for disaster resistant building. A lot of studies and research work is being carried out presently, to ensure the safety of buildings. In our modern times where there is a possibility of threats in form of terror attacks and natural disaster, it is our duty to ensure the safety of our building, Out of all the natural calamities fire has the most devastating and prolonged effect on any building
and also on human lives. But, there is no accurate method to estimate the fire endurance/resistance for a building due to the variability of fire characteristics, material properties of construction material, and other characteristics of a building.
Keeping in view the damage condition and risk involved to human lives, it is our duty to understand and harness the knowledge gained from past mistake and develops a technology which withstand amiable heat.
Fig.1.
The description of the effect of fire exposureon steel and concrete structural members is intended to improve understanding of how these structural members respond when heated and also what measures are commonly used to limit temperature rise in structural members.
1.1 Fire Behavior
Important aspects of fire Behavior in the affected buildings involve the following issues:
Burning behavior of materials, including mass loss and energy release rates.
Stages of fire development.
Behavior of fully developed fires, including the role of ventilation, temperature development, and duration.
1.2. Burning Behavior of Materials Once a material is ignited, a fire spreads across the fuel object until it becomes fully involved. The spread at which flame travels over the surface of the material is dependent on the fuel composition, orientation, surface to mass ratio, incident heat, and air supply. Given sufficient air, the energy released from a fire is dictated by the incident heat on the fuel and the fuel characteristics, most notably the heat of combustion and latent heat of vaporization.
1.3. Stages of Fire Development Generally, fires are initiated within a single fuel object. The smoke produced from the burning object is transported by a smoke plume and collects in the upper portion of the space as a layer. The smoke plume also transports the heat produced by the fire into the smoke layer, causing the smoke layer to increase in depth and also temperature. This smoke layer radiates energy back to unburned fuels in the space, causing them to increase in temperature.
Fire spreads to other objects either by radiation from the flames attached to the originally burning item or from the smoke layer. As
other objects ignite, the temperature of the smoke layer increases further, radiating more heat to other objects.
In small compartments, the unburned objects may ignite nearly simultaneously. This situation is referred to as ―flashover.‖ In large compartments, it is more likely that objects will ignite sequentially. The sequence of the ignitions depends on the fuel arrangement, and composition and ventilation available to support combustion of available fuels.
1.4. Behavior Of Fully Developed Fires
A fully-developed fire is one that reaches a steady state burning stage, where the mass loss rate is relatively constant during that period. The equilibrium situation may occur as a result of a limited ventilation supply (in ventilation controlled fires) or due to characteristics of the fuel (fuel- controlled fires).
1.5 Structural response to Fire 1.5.1 Effect of Fire on Concrete Concrete is one of the principal materials widely used in construction and, in fire protection engineering terminology, is generally classified as Group L (load bearing) building material: materials capable
of carrying high stresses. The word concrete covers a large number of different materials, with the single common feature that they are formed by the hydration of cement.
Because the hydrated cement paste amounts to only 24 to 43 volume percent of the materials present, the properties of concrete may vary widely with the aggregates used.
Traditionally, the compressive strength of concrete used to be around 20-50 MPa, which is referred to as normal-strength concrete.
Depending on the density, concretes are usually subdivided into two major groups:
(1) Normal-weight concrete, made with normal-weight aggregate, with densities in the 2,200 to 2,400 kg/m3 range, and
(2) Lightweight concrete, made with lightweight aggregate, with densities between 1,300 and 1,900 kg/m3.
1.6.2 Effect of Fire on Steel
Fire resistance is defined as the property of a building assembly to withstand fire, or give protection from it (ASTM 2001a). Included in the definition of fire resistance are
two issues. The first issue is the ability of a building assembly to maintain its structural integrity and stability despite exposure to fire. Secondly, for some assemblies such as walls and floor-ceiling assemblies, fire resistance also involves serving as a barrier to fire spread. Fire resistance is commonly assessed by subjecting a prototype assembly to a standard test.
Results from the test are reported in terms of a fire resistance rating, in units of hours, based on the time duration of the test that the building assembly continues to satisfy the acceptance criteria in the test. Fire resistance rating requirements for different building components are specified in building codes. These ratings depend on the type of occupancy, number of stories, and floor area. Because the standard test is intended to be a comparative test and is not intended to predict actual performance, the hourly fire resistance ratings acquired in the tests should not be misconstrued to indicate a specific duration that a building assembly will withstand collapse in an actual fire.
Generally, the fire resistance rating of a structural member is a function of:
Applied structural load intensity.
Member type (e.g., column, beam, wall).
Member dimensions and boundary end conditions.
Incident heat flux from the fire on the member or
assembly.
Type of construction material (e.g., concrete, steel,
wood).
Effect of temperature rise within the structural member on the relevant
properties of the member.
The fire performance of a structural member depends on the Heat and mechanical properties of the materials of which the building component is composed. As a result of the increase in temperature caused by the fire exposure, the strength of steel decreases along with its ability to resist deformation, represented by the modulus of elasticity. In addition, deformations and other property changes occur in the materials under prolonged
exposures. Likewise, concrete is affected by exposure to fire and loses strength and stiffness with increasing temperature. In addition, concrete may spall, resulting in a loss of concrete material in the assembly. Beams and trusses may react differently to severe fire exposures, depending on the end conditions and fabrication.
Unconnected members may collapse when the stresses from applied loads exceed the available strength for beams and trusses. In the case of connected members, significant deflections may occur as a result of reduced elastic modulus, but structural integrity is
preserved as a result of catenary action. In the case of slender columns, the susceptibility for buckling increases with a decrease in the modulus of elasticity. Where connections of floor framing to columns fail, either at the ends or intermediate locations, column slenderness is increased, thereby increasing the susceptibility of a column to buckling. Steels most often used in building design and construction are either hot-rolled or cold-drawn. Their strength depends mainly on their carbon content,
though some structural steels derive a portion of their strength from a process of heat treatment known as quenching and tempering.
2. RESEARCH STUDIES S. Sreenath et al. (2011)
Plastic zone method of advanced analysis, which uses shell elements to model the entire structure, is the most accurate method available to predict the ultimate strength and behaviour of steel frames. The disadvantage of such full shell plastic zone models is that it is computationally expensive and hence its use is limited to small structures. Beam elements in commercial finite element packages can model residual stress and capture spread of plasticity, but cannot model local buckling of plates that the member is made up of, which leads to unloading and failure in steel frames. A hybrid model using shell elements only in the regions vulnerable to elastic or inelastic local buckling and beam elements in other locations could overcome this limitation of full beam element model. The issues in using this hybrid model are, knowing a priori the location and
length of the shell element region and connecting the beam and shell regions without any artificial stress concentrations or incompatible displacements. In this study, in addition to addressing these issues, the hybrid model is systematically evaluated by studying its performance in structural elements. It is seen that the hybrid model strength predictions has an average error of only 0.91% but requires on an average 83% less computational time when compared to the full shell plastic zone models.
Dale P. Bentz (2010)
Fire resistive materials (FRMs) serve a critical function in insulating (steel) structures to limit steel temperature rise during a fire exposure. This paper provides an overview of FRMs, focusing on the
measurement of their
thermophysical properties. After a brief review of the standard fire test conventionally used to evaluate the performance of FRM-protected components and systems, the measurement of thermophysical properties at room and elevated temperatures is considered.
Standard test methods available for each property measurement are
noted and example results for FRM materials are presented. These property values can provide critical inputs for simulations of the Heat performance of components and systems during standard and real world fires.
R. R. Krishnamoorthy et al (2009)
A series of ten small-scale experimental works was conducted in a gas furnace. Temperatures were measured in a number of protected and unprotected steel members at various locations. This paper compares the test data against the predicted values computed by finite element analysis package.The paper considers the geometry of the members, the exposure conditions and the Heat property of the fire protection material. The Heat predictions using ABAQUS agreed well for unprotected members, however, in protected members the results were reasonable good although it did not exhibit a good match in the initial time-temperature stage. This mainly attributes to the Heat behavior of the intumescent coat.
C. Crosti (2009)
This paper focuses on the structural analysis of a steel structure under fire loading. The use of an analysis with thermo- plastic materials, geometric nonlinearities and modeling of the fire action using parametric curves, allows a faithful evaluation of the effective behavior of steel structures subject to fire. In this context, once these two basic factors are clarified in isolated beam elements, they are applied to a steel structure under fire loading. This is done to highlight the importance of the right choice of analyses to develop, and of the finite element codes that are able to model the resistance and stiffness reduction due to the temperature increase. In addition, considering that for such a structure the evaluation of the structural collapse is very tricky and depends from many factors, a factor worth highlighting in a performance based approach is the global configuration of the structure itself.
In this paper, the material used is a thermo-plastic type. The mechanical evolutive parameters
taken into account in structures subjected to fire are:
Young‘s Modulus, (EO);
Effective Yield Stress, (sy) , which represents the maximum
capacity of the material;
Coefficient of Heat expansion, David N. Bilow et al (2008)
After the 9-11 attack on the World Trade Center, interest in the design of structures for fire greatly increased. Some engineers have promoted the use of advanced analytical models to determine fire growth within a compartment and have used finite element models of structural components to determine temperatures within a component by heat transfer analysis. Following the calculation of temperatures, the mechanical properties at various times during the period of the fire must be determined. This paper provides structural engineers with a summary of the complex behavior of structures in fire and the simplified techniques which have been used successfully for many years to design concrete structures to resist the effects of severe fires.
J. Ding et al (2007)
This paper employs the commercial finite element analysis package ANSYS to model the Heat and structural behaviour of isolated CFT columns in fire. Although CFT columns have been numerically analysed by many researchers, this paper presents details of a number of features which have often been neglected by many researchers, including the influence of an air gap and slip at the steel/concrete interface on CFT column temperatures and structural behaviour, the sensitivity of CFT fire resistance to concrete tensile behaviour and CFT column initial imperfections. The finite element model is validated by comparing the simulation results against experimental results of standard fire resistance tests on 34 CFT columns with different structural boundary and loading conditions. A numerical parametric study is then performed to investigate the sensitivity of simulation results to different assumptions introduced in the finite element model. The results of these numerical studies show that whether or not including slip between the steel tube and concrete core in the numerical
model has minor influence on the calculated column fire resistance time. The fire resistance of CFT columns with an air gap is generally slightly higher than that without an air gap. However, including slip gives a better prediction of column deflection behaviour. Using different tensile strength or tangent stiffness of concrete has a minor effect on the calculated column fire resistance.
F.D. Queiroz et al (2006)
The present investigate on focuses on the evaluation of full and partial shear connection in composite beams using the commercial finite element (FE) software ANSYS. The proposed three-dimensional FE model is able to simulate the overall flexural behaviour of simply supported composite beams subjected to either concentrated or uniformly distributed loads. This covers: load deflection behaviour, longitudinal slip at the steel–
concrete interface, distribution of stud shear force and failure modes.
The reliability of the model is demonstrated by comparisons with experiments and with alternative numerical analyses. This is followed by an extensive parametric
study using the calibrated FE model. The paper also discusses in detail several numerical modelling issues related to potential convergence problems, loading strategies and computer efficiency.
The accuracy and simplicity of the proposed model make it suitable to predict and/or complement experimental investigations.
Ju Chen et al (2006)
This paper presents the mechanical properties of high strength structural steel and mild structural steel at elevated temperatures.
Mechanical properties of structural steel at elevated temperatures are important for fire resistant design of steel structures. However, Current design standards for fire resistance of steel structures are mainly based on the investigation of hot-rolled carbon steel with normal strength, such as mild steel. The performance of high strength steel at elevated temperatures is unknown. Hence, an experimental program has been carried out to investigate the mechanical properties of both high strength steel and mild steel at elevated temperatures.
M.B. Wong et al (2003)
The aim of using fire protection in a building is to reduce the rate of temperature rise of its structural components in case of fire. For protected structural steel, the Heat properties of the insulation materials affect the rate of temperature rise and are crucial in determining the minimum requirements for fire safety for both the steel and the insulation materials. The determination of the required thickness of the insulation materials can be performed by means of test results, analytical solutions or numerical methods.
The current Euro code 3 provides simple analytical solutions for estimating the temperature rise of both protected and unprotected structural steel in a fire. This paper presents a sensitivity analysis to examine the appropriateness of using these analytical solutions for structural steel components protected with insulation materials of contrasting properties including Heat conductivity and density.
Results of the analysis show that, for certain types of insulation materials, the temperatures predicted by the Euro code may
differ substantially from those by exact analytical solution. An alternative formulation is presented when these types of insulation materials are used for fire protection of structural steel.
A.S. Usmani et al (2001)
This paper presents theoretical descriptions of the key phenomena that govern the behavior of composite framed structures in fire.
Behavior of composite structures in fire has long been understood to be dominated by the effects of strength loss caused by Heat degradation, and that large deflections and runaway resulting from the action of imposed loading on a ‗weakened‘
structure. Thus ‗strength‘ and
‗loads‘ are quite generally believed to be the key factors determining structural response (fundamentally no different from ambient behavior). This paper attempts to lay down some of the most important and fundamental principles that govern the behavior of composite frame structures in fire in a simple and comprehensible manner. This is based upon the analysis of the response of single structural elements under a combination of Heat actions and
end restraints representing the surrounding structure.
Wolfgang Kuhn et al (1999)
This report presents a fast data assimilation method to produce an interpolating time and space temperature distribution for steel members subject to fire testing. The method assimilates collected temperature data into the numerical integration of the heat equation. This physically based method also allows the computation of lateral and axial heat flux into and inside the member.
Lie T.T. (1978)
Lie T.T. suggested an analytical formulation for calculating steel temperature in a fire event.
Equations were proposed for determining fire load and temperature of steel section for different conditions. Two examples were also been presented to illustrate the use of the equations.
Further, these equations were justified by comparing the analytical results with data from other experimental studies. In the present paper the method is applied to structural steel protected by materials having various Heat
properties. The influence of fire severity on the fire performance of steel members, as well as the influence of other important factors that determine their fire resistance, are examined.
N.J.K. Cameron et al
The computer models developed of the full-scale fire tests at Cardington greatly increased the understanding of the behavior of composite framed structures in fire.
It became clear that their structural response under Heat effects was markedly different to that under ambient conditions. In order that the behaviour of composite framed structures in fire is fully understood it is essential that the fundamental principles governing the behaviour of the frame are understood. This paper describes an elastic analysis method for determining the large-deflection behaviour of a laterally restrained floor slab in fire conditions. Both the Heat expansion of the slab and a Heat gradient through the slab are considered. When the deflections and internal forces are compared against results from analyses using the finite element package ABAQUS they compare
well. The application of these results in design of structures to resist fire is highlighted.
3. FINITE ELEMENT ANALYSIS PROGRAMS
The use of finite element software be has become a reliable method to predict the behaviour of structures exposed to fires. Computer modelling serves as a cost effective and less time consuming alternative to the actual preparation and fire testing of structural assemblies. Development of programs for fire modelling began in the 1960‘s which lead to the finite element software be available today. There will be several programs, summarized in the following section, that were specifically written for modelling the behaviour of structures subjected to fires. Most of the early programs were developed by individual researchers in order to model one specific element, such as steel beams or concrete columns, which were subjected to fire. In general, these programs will be limited because analysis of any other element is not permitted and development has stopped on many
of the programs. Currently, many commercially available software be programs will be used to model structures exposed to fires. These programs have not been developed specifically for this task; however, they offer numerous possibilities and have the pre- and post- processing capabilities necessary to perform a Heat analysis combined with a mechanical event. Software packages such as ABAQUS, ALGOR, ANSYS, and Nastran will be used in numerous engineering fields for their powerful pre- processing and post processing capabilities. These programs allow the engineer to spend more time developing the model and interpreting the results since the formation of the element and global stiffness matrices will be automatically performed by the finite element software.
4. CONCLUSION
We studied number of article for my proposed work for heat analysis, so I decide to complete my proposed work for the analysis of heat in steel structure using ansys.
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