Structural Engineers are the Future of Structural Fire Protection!

Kevin J. LaMalva- Structural/Fire Engineer at Simpson Gumpertz & Heger, USA

For the past century, project stakeholders have tolerated a strikingly inefficient and amorphous system for protecting structures from uncontrolled fire. Also, structural engineers are often absent from the structural fire protection design process. However, due to recent advancements put forth by ASCE/SEI, now is a great time for structural engineers to get involved with structural fire protection and lead its implementation in practice. Encouragingly, this area represents one of the most promising opportunities for structural engineers to add value to building design.

Why do we thermally insulate structural systems?

Structural fire protection addresses the low-probability and potentially high-consequence event of uncontrolled fire exposure within the built environment. The onset of fire in engineered buildings is most often controlled by fire sprinkler systems, which are widely implemented in the United States. Fires may also be controlled by direct intervention from building occupants and/or fire department personnel. If these active measures were invariably effective, applied structural insulation would serve no purpose. In reality, fire sprinkler systems have performance limitations, and direct intervention may be hindered by logistical obstacles (e.g., fire department aerial hose spray limitations during high-rise building fires).

Traditionally, structural fire protection is prescribed for structures after they have been optimized for ambient design loads (i.e., gravity, wind, seismic, and others). Furthermore, structural fire protection is most commonly specified using the long-standing prescriptive design method, in which the fire-resistance of structural components is qualified through standard fire testing with a specific heating exposure (e.g., ASTM E119 time-temperature curve) and acceptance criteria. In essence, the prescriptive design method is an empirical indexing system (i.e., generalized classifications) that promotes construction that is generally robust to fire exposure; however, the actual anticipated structural system performance under fire exposure is not confirmed or quantified. Overall, this century-old prescriptive framework endeavors to reduce the heating of individual structural components with the intent of mitigating the risk of structural failure under fire exposure. Accordingly, the vulnerability of buildings to structural failure from uncontrolled fire varies across different jurisdictions; which have differing structural design requirements for ambient loads and as a function of building system and component configuration.

Historically, structural engineers have remained outside the fray of structural fire protection practice. However, a fast-growing segment of the structural engineering community in the U.S. has become more assertive that their involvement and assimilation into structural fire protection practice is very much needed. The emerging field of structural fire engineering involves the explicit design of structural systems to adequately endure thermal load effects from uncontrolled fire exposure. Within this framework, thermally-induced forces and degraded material properties from fire exposure can be limited by means of rationally-allocated structural insulation, and the ability of a structural system to endure fire effects can be enhanced by means of specific member sizing, connection/reinforcement detailing, and/or other measures to provide added structural robustness. Structural fire engineering essentially approaches structural fire protection from both the demand (heating) and capacity (structural response) sides of the equation, instead of solely focusing on the demand side, as is traditionally done. Unlike the prescriptive design method, structural fire engineering cannot be executed by any type of design professional (e.g., an architect). Rather, structural fire engineering explicitly requires the participation (or more ideally the responsible charge) of a Structural Engineer in all cases.

In cases where an alternative to the prescriptive design method is sought, the U.S. has lacked an industry consensus on the matter until recently. Notably, ASCE/SEI 7 now permits designers to utilize structural fire engineering as an alternative to the code-default prescriptive method. Specifically, Section 1.3.7 states that structural fire protection shall be provided per prescriptive requirements of the applicable building code, or by employing a performance-based approach in accordance with the new Appendix E section per building authority approval. Also, the new ASCE/SEI Manual of Practice No. 138 provides specific guidance for conducting a structural fire engineering design. Effectively, Appendix E and MOP No. 183 elevate the value and necessity of structural engineers when alternatives to the prescriptive method are sought by project stakeholders.

New ASCE/SEI guidance should validate structural engineers who wish to engage and lead in the field of structural fire protection. Also, building officials now have tools to comprehensively evaluate structural fire protection variances. The future is bright in this space for structural engineers to impact the industry, which will soon be explicitly demonstrated.

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References:

1. LaMalva, K.J., “Developments in Structural Fire Protection Design – A U.S. Perspective,” The Structural Engineer, Vol. 96, Issue 1.

2. ASTM E119 (2016). E119-16a Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM International, West Conshohocken, PA.

3. LaMalva, K.J., “The Time is Right for Structural Engineers to Embrace Structural Fire Protection,” ASCE/SEI Update, 26 April 2018

4. [1] Ellis, A. “Unleashing the Profession: How Performance-Based Design Will Shape Our Future,” STRUCTURE Magazine, March 2019

5. LaMalva, K.J., “Structural Fire Protection’s Shifting Paradigm,” Fire Protection Engineering, Q2 2017, Issue #74, Society of Fire Protection Engineers

6. Recommended Minimum Technical Core Competencies for the Practice of Fire Protection Engineering, Society of Fire Protection Engineers, Bethesda, Maryland, 2018.

7. LaMalva, K.J. “Introduction to Structural Fire Engineering,” Life Safety Digest, Fall 2019

8. ASCE/SEI 7: Minimum Design Loads and Associated Criteria for Buildings and Other Structures, American Society of Civil Engineers: Structural Engineering Institute, Reston, VA, 2016

9. ASCE/SEI Manual of Practice No. 138: Structural Fire Engineering, American Society of Civil Engineers: Structural Engineering Institute, Reston, VA, 2018

10. Cocke, D. ‘SEI Annual Report: Performance-Based Design,’ American Society of Civil Engineering: Structural Engineering Institute (ASCE/SEI), April 2019

11. Post, N. “More Guidance Coming on Structural Fire Engineering,” Engineering News Record (ENR)

12. Civil + Structural Engineer. “ASCE/SEI Announces Research Grant on Advancing Performance-Based Structural Fire Engineering Design,” 13 September 2018, Civil + Structural Engineer Magazine.