Book Details : | |
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Language | English |

Pages | 465 |

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Size | 14.1 MB |

Leo Razdolsky is the editor of Structural Fire Loads Theory and Principles PDF Book.

1. Overview of Current Practice.

2. Structural Fire Load and Computer Modeling.

3. Differential Equations and Assumptions.

4. Simplifications of Differential Equations.

5. Fire Load and Severity of Fires.

6. Structural Analysis and Design.

Structural Fire Loads: Theory and Principles is a practical book on structural fire loads for fire prevention engineers, structural engineers, architects, and educators.

The goal of this Structural Fire Loads Theory and Principles book is to bridge the gap between prescriptive and performance-based methods and to simplify very complex and comprehensive computer analyses to the point that structural fire loads have a simple approximate analytical expression that can be used in structural analysis and design on a day-to-day basis.

The main audience is practicing structural and fire prevention engineers. The scope of the work is broad enough to be useful to practicing and research engineers and to serve as a teaching tool in colleges and universities.

This Structural Fire Loads Theory and Principles book contains a large amount of original research material (substantially modified and increased) from the author’s previously published articles (Structural Fire Loads Theory and Principles).

At the same time, the Structural Fire Loads Theory and Principles book contains many other results obtained by other research primarily reflecting the most important data in the area of defining and computing the structural fire load.

It is worthwhile to underline here that the structural fire load in general as part of the performance-based method has been evolving very rapidly in recent years, and the author has limited himself to only very few research papers connected with the structural fire load.

The main portion of the Structural Fire Loads Theory and Principles book is devoted to the additional assumptions and simplification that are specifically tailored to the structural fire load problem only.

The main results are compared with the current provisions from Eurocode. This Structural Fire Loads Theory and Principles book is constructed in such a way that the research fire protection engineer will find the simplified versions of energy, mass,

and momentum equations written in dimensionless form and their solutions in tabular form, and the fire protection and structural engineer will find the “best-to-fit” analytical formulas ready to be used just for practical computations.

For emergency cases (e.g., an ongoing fire scenario), many sections of this Structural Fire Loads Theory and Principles book have the scaled graphical solutions that might help to do “on the back of the envelope”–type calculations.

This Structural Fire Loads Theory and Principles book has a large number of practical examples (for fire protection and structural engineering design) that are presented in a simple step-by-step computational form. The standard structural systems (beams, trusses, frames, arches, etc.) are used in all these examples.

Chapter 1 introduces the philosophy of structural fire load design and the assumptions that are made in this Structural Fire Loads Theory and Principles book in order to achieve the main goal:

provide the temperature-time relationships that are based on conservation of energy, with mass and momentum equations on the one hand and practical and simple formulas for future structural engineering design on the other.

It is indicated here that the burning process during fire development and the nonsteady combustion process have many similarities; therefore, the mathematical modeling of structural fire load also should be similar.

Chapter 2 presents an overview of the main simplified methods of obtaining the structural fire load at the present time: the timeequivalence method and the parametric design method (Structural Fire Loads Theory and Principles).

The ‘‘traditional way’’ of structural fire design using the standard temperature-time curve in many cases results in a design on the safe side, causing unsatisfactory costs for fire protection measures.

In some cases, the structural fire design with a standard temperaturetime curve can result in underestimation of thermal exposure.

The parametric natural fire model considers the actual boundary conditions of the fire compartment concerning fire load, ventilation conditions, geometry, and thermal properties of the enclosure.

The parametric fire curves are derived by heat-balance simulations, assuming a great number of natural design fires by varying the above-mentioned parameters (Structural Fire Loads Theory and Principles).

These curves have been incorporated into a Swedish standard and also have served as the basis for the parametric temperature-time curves of Eurocode 1-1-2 and can be applied to the structural fire design of small to medium rooms where a fully developed fire is assumed.

The parametric temperature-time curves of Eurocode 1-1-2, annex A, in some cases provide an unrealistic temperature increase or decrease. Chapter 3 provides a review of computer simulations of a design fire: zone and field models.

Zone models are relatively simple from a computational point of view and based on the assumption that the temperature in a fire compartment is uniformly distributed in each zone and the hydrodynamic portion of a burning process is practically omitted (Structural Fire Loads Theory and Principles).

There are many zone modeling packages available now on a market, and the summary of available current zone models is presented in this chapter.

The field computer models (FDS) are very comprehensive on the one hand, but on the other hand they are very complex from a computational point of view and very sensitive to even small changes in input data or any boundary conditions.

At the same time, it is a well-known fact that the physical properties of real burning materials are often unknown (or very difficult to obtain), and this is a very serious limitation in practical application of field models for design purposes.

The FDS model is very reliable when the heat release rate (HRR) of the fire is specified (given), and it is much less reliable for fire scenarios where the HRR is predicted (unknown).

This is why the field models are used primarily for investigation purposes of large projects but not for the design stages on a day-to-day basis.

A summary of available current field models is also presented in this chapter. The principal aim of Chap. 4 is to overcome the two major obstacles of simplifying (as much as possible) the conservation of energy, mass, and momentum equations in case of structural fire load only.

What this means is that all other life safety issues of fire protection, such as modeling the transport of smoke, a detailed mixture fractionbased combustion model, the activation of sprinklers, heat and smoke detector modeling, and so on, are not part of this simplification process. In order to achieve this goal, the following assumptions are made:

(1) All differential equations (thermal and mass transfer coupled with Navier-Stokes hydrodynamic flow equations) are written in dimensionless form. This drastically reduces the total number of parameters in the input data.

(2) The equations are simplified to such a degree that solutions will be acceptable and easy to use by the structural engineer (Structural Fire Loads Theory and Principles).

(3) For all practical purposes, it will be assumed in this study that the structural system is robust enough and doesn’t induce any measurable interior forces (moments, shears, etc.) when the maximum gas temperature in the compartment is below T = 300°C, and, therefore, the earliest stage of fire (initial burning) is not important (from a structural fire load point of view).

(4) The chemical reaction of the burning process can be drastically simplified and presented as a first-order chemical reaction.

(5) The dimensionless solution of differential equations should be verified against the standard fire test results as well as the natural fire test data results. Further simplifications are contained in Chap. 5.

First, the conservation of energy, mass, and momentum equations are broken up in two parts (similar to zone and FDS models):

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conservation of energy and mass on the one hand and the momentum equation (NavierStokes equations) on the other.

Almost universally the Navier-Stokes equations are written for a simple class of fluids (which most liquids and all known gases belong to) known as Newtonian fluids.

Second, the additional simplification has been made because the heat transfer due to radiation plays much more significant role than the heat transfer due to conduction and convection (in case of “small” fire compartments).

For larger sizes of fire compartments the convection forces have been added in hydrodynamic equations (Navier-Stokes equations), and the velocity field (or flow field) has been obtained.

These velocities then were included in the first approximation of the conservation of energy and mass equations, and corrected temperature-time functions have been obtained.

This type of computational procedure was repeated for each case of fire severity (very fast, fast, medium, and slow fire) and different geometric parameters characterizing the size of a fire compartment.

Since all differential equations have had dimensionless variables, the solutions are presented in a tabular form that is later substituted by the nonlinear analytical approximation.

Chapter 6 is dedicated to the application of computational procedures developed in the previous chapter to the functional relationships between SFL and opening factor, fuel load, fire duration, decay period, geometry of the fire compartment, etc.

The comparison of Eurocode parametric curves and SFL curves is also presented here. Finally, the computational procedure for passive fire protection design is established in this chapter.

The output of such computations is the temperature-time function that will be used for structural analyses and design in the next chapter.

Chapter 7 is devoted to the structural response factor (similar to the gust response factor for wind analyses) and structural analyses and design of various structural systems subjected to SFL.

The application of general mechanical creep theory to the analysis of stiffness reduction owing to high-temperature load is also presented here.

Traditional (standard) structural systems (such as beams, simple frames, trusses, and arches) subjected to SFL are analyzed and designed.

The website associated with this Structural Fire Loads Theory and Principles book, www.mhprofessional .com/sfltp, contains additional material the reader will find interesting.

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