design fire scenarios for simulating fire resistance of ... wksp pres/session 1/albano.pdf ·...

Design Fire Scenarios for Simulating Fire Resistance of Structures

National Workshop on Structures in Fire: State-of-the Art Research Needs

Len Albano11 June 2007

Worcester Polytechnic Institute

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Design Fire Concept• Design fires define the thermal environment,

or time-temperature curve, for assessing structural performance.

• Design fires have been used in the design of smoke management systems.

• Contributes to fire safety by engineering design, based on assessing structural behavior under fire conditions.

• Fire safety is handled by regulation: compliance with fire resistance ratings expressed in terms of duration in standard furnace testing (ASTM E-119).


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Natural vs Standard Fires

Time

Tem

pera

ture

Standard Fire

L1

L2

L3

Natural Fires

L1, L2, and L3 refer to different fuel load densities.L1 > L2 > L3


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Presentation DesignObjective 1: Demonstrate that the

community of fire protection engineers has developed several, accessible calculation methods and computer-based tools for describing fire characteristics within a room.

Means: Provide brief background that identifies sample references, characterizes the available strategies, and summarizes related studies at WPI.


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Presentation Design

Objective 2: Identify research needs for advancing the concept of design fires in codes and standards for structural design practice.

Means: Parallel the philosophy and procedures for defining wind loads for structural design.


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Background


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Sample References

• Bwayla, A.C., Benichou, N., and Sultan, M.A. (2003). “Literature Review on Design Fires,” NRC Report IRC-RR-137.

• Society of Fire Protection Engineers (2002). The SFPE Handbook of Fire Protection Engineering, 3rd edition, Section Three Hazard Calculations.

• Franssen, J-M and Zaharia, R. (2006). Design of Steel Structures Subjected to Fire, 2nd edition, Chapter 3 Thermal Action.

• Bukowski, R.W. (2006). “Determining Design Fires for Design-level and Extreme Events,” SFPE 6th International Conference on Performance-Based Codes and Fire Safety Design Methods, Tokyo.


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Strategies for Describing Fires1. Standard Furnace Test conditions (ASTM E-119 or ISO

834 fire curves). 2. Parametric time-temperature relationships.

• Pre-flashover and post-flashover formulations.• Examples include Eurocode time-temperature relationships, BFD

curves, and Law’s Method.3. Computer-based Modeling Technologies.

• Zone models, e.g. CFAST and COMPF2.• Field or Computational Fluid Dynamics (CFD) models, such as

SOFIE and FDS.4. Design databases.

• Data from mathematical investigations, such as the Swedish fire curves.

• Fire test data for various objects and scenarios; sources include NIST Reports and BRE Design Fires Database.


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Sample Swedish Fire Curves

[taken from SFPE Handook, 2002]


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Related Studies at WPI1. Blauvelt, K. (2003). “A Comparative Study of the CFAST

3.1.7 Software Model and the Swedish Time-Temperature Curves,” Graduate study project.

2. Moore, A.E. (2003). “Development of a Process to Define Design Fires for Structural Design of Buildings for Fire,” Graduate study project.

reference publication: Moore et al. (2005). “Defining Design Fires for Structural Performance,” Proceedings, 2005 Structures Congress and the 2005 Forensic Engineering Symposium; New York, NY.

3. Collette, K.A. (2007). Comparisons of Structural Designs in Fire. MS Thesis, Fire Protection Engineering.


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Study by Moore (2003)• Combinatorial investigation of variables through use of

CFAST computer program. Scope included:– Three office layouts: simple workstation; executive suite; and bank

workstation (reference GSA, 1984).– Four ventilation conditions: none; door; door and window; two

doors and two windows. – Two types of interior wall construction: ordinary masonry block;

gypsum board.– Three heat release rates (HRR) for fire growth: one workstation;

two workstations; and four workstations.– Two ceiling heights.

• Published HRR data was used for furnishings and equipment (references included Madrzykowski, 1996; Madrzykowski and Vettori, 1992; Walton and Budnick, 1988).

• Flashover occurred in twelve of the sixty-eight scenarios investigated. The flashover scenarios were developed from fires involving multiple workstations.


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Moore (2003) …Sample time-temperature relationships

ASTM E-119 exposure


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Moore (2003) …Transient capacity of protected steel beam

Simple Quad with 50% Design LL

Bank 1996 Quad with 50% Design LL

ASTM E-119 exposure

ASTM E-119 exposure


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Moore (2003) …

Simple Quad with 50% Design LL

Bank 1996 Quad with 50% Design LL

ASTM E-119 exposure

ASTM E-119 exposure

Transient capacity of unprotected steel beam


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Study by Collette (2007)• Comprehensive comparison of temperatures within unprotected steel

members due to different fire exposures. Scope of exposures included:– ASTM E-119 and ISO 834 Standard Furnace Temperatures.– Nominal and parametric fire curves given in the Eurocode.– BFD fire curves.– Swedish fire curves.– CFAST results from Moore (2003).– Cardington test data.

• Lumped parameter analyses used for heat transfer.– Steel sections obtained from Cardington test data.– Steel sections obtained from U.S. office building.

• Comparisons included:– Transient steel temperatures during an entire fire event as well as during

the fire growth and fire decay periods.– Maximum steel temperatures achieved.– Elapsed times to maximum steel temperatures.


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Observations from Collette (2007)

• BFD and Swedish Fire Curves provided strongest correlations to the data compiled in natural fires, as described by Cardington test data.

• Parametric design curves generally did not provide strong correlation with natural fires for both the heating and cooling phase of steel beams.

• Standard Fire Resistance Tests must be “modified” to better represent natural fires.


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Collette (2007) …Steel temperatures from Cardington test data and BFD fire curves


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Collette (2007) …Correlation between predicted and actual steel temperatures


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Collette (2007) …

Time delay

Steel temperatures from Cardington test data and “delayed” Swedish fire curves


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Collette (2007) …Correlation between predicted and actual steel temperatures


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Objective 2: Identify research needs for advancing the concept of design fires in codes and standards for structural design practice.

Means: Parallel the philosophy and procedures for defining wind loads for structural design.


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Assumptions1. An overarching framework for structural fire

safety will be established. It will define performance objectives that can be translated into limit states for evaluating structural performance.

2. A steady and unambiguous approvals process for structural fire safety by engineering design will be established.

3. Structural engineers will continue to be responsible for the design and performance of building structures, including design for fire conditions.


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Wind Loads for Structural Design


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Wind Loads for Structural Design 1. Wind effects on building structures are complex

phenomena, involving– Climatological and topographical characteristics. – Building geometry and dynamic characteristics.

2. Scope of wind design criteria addresses life safety and property damage concerns:

– Evaluation of Main Wind-Force Resisting System.– Evaluation of building components and cladding.


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Wind Loads (continued) 3. Procedures for determining design wind loads

are derived from accumulated knowledge, incorporating

– Theoretical and experimental research – Empirical observations– Engineering judgment and practical experience.

4. Procedures are defined to span a broad spectrum of problems, and they are consistent with established structural analysis and design methods.

– Simplified Procedure– Analytical Procedure– Wind Tunnel Procedure

Increasing information detail and

engineering/computationaleffort


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Design Fires for Structural Design


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Design Fires for Structural Design 1. Fire growth and scenarios for assessing

structural behavior are a complex phenomena, involving

– Occupancy (human factors and contents).– Interior design (room geometry, finishes, and

furnishings and their arrangement).– Ventilation.– Performance of structural systems, materials, and

their protection.


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Design Fires for Structural Design 1. Fire growth and scenarios for assessing

structural behavior are a complex phenomena, involving

– Occupancy (human factors and contents).– Interior design (room geometry, finishes, and

furnishings and their arrangement).– Ventilation.– Performance of structural systems, materials, and

their protection.To understand the technical basis and to practice structural

fire safety by engineering design, structural engineers need education on basic principles of fire growth and the behavior of structures in fire conditions.


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Design Fires for Structural Design 2. Fire is not a load; it is a dynamic environment,

influenced by many variables. Fire growth in even a simple building depends on the initial construction, characteristics of the occupants, changes in finishes and furnishings, and future alterations.


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Design Fires for Structural Design 2. Fire is not a load; it is a dynamic environment,

influenced by many variables. Fire growth in even a simple building depends on the initial construction, occupant characteristics, changes in finishes and furnishings, and future alterations.

Safety factors are needed to account for uncertainties, providing conservatism without causing excessive overdesign. Guidance is needed to identify an acceptable scope of alterations over time. Guidance is also needed to recognize atypical conditions that may require alternative fire descriptions and analyses.


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Design Fires (continued)3. The integrity of walls and floor and ceiling

assemblies (barriers) controls/delays fire movement from the room of origin. The integrity of the structural systems and their elements contributes to barrier performance.


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Design Fires (continued)3. The integrity of walls and floor and ceiling

assemblies (barriers) controls/delays fire movement from the room of origin. The integrity of the structural systems and their elements contributes to barrier performance.

Research and design guidance are needed on design fires for assessing the relationship between barrier and structural performance.


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Design Fires (continued)4. A menu of calculation methods and computer-

based modeling technologies provides the capability to tailor fire descriptions to building structures of various types and complexities.


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Design Fires (continued)4. A menu of calculation methods and computer-

based modeling technologies provides the capability to tailor fire descriptions to building structures of various types and complexities.

Accepted procedures for defining design fires should be technically credible and consistent; they should produce similar results and design decisions for a given situation.


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Philosophy of Design Loads

“It is not a question of how much load of any kind it is possible to pile on a square foot of floor area. The question is to make the buildings absolutely safe without wasting large quantities of materials in places where it is not needed. … The working load should be the probably maximum load which may be reasonably expected to occur”

Schneider, 1905, ASCE Transactions.


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Thank you.

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