New Developments in Structural Fire CodesMay 03 2017 · 0 comments · Building Code, NISHKIAN DEAN ·0
By Aerik Carlton
Structural fire consideration has been taking some large steps recently, with several codes and standards having added or altered structural fire sections. At Nishkian Dean, we have examined these structural fire design codes and methods from a structural engineering prospective for our clients and readers below.
A summary of these structural fire design codes includes:
ASCE 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures has added a new appendix to address structural fire considerations.
AISC 360-16 Specification for Structural Steel Buildings has refined and made additions to Appendix 4: Structural Design for Fire Conditions.
The National Institute of Science and Technology (NIST) has drastically expanded the Gaithersburg, Maryland, Fire Testing Lab to include a live-fire hood capable of testing a multi-story building portion with the aim of obtaining empirical large-scale structural system data to further refine and validate their free computational fluid dynamics fire modeling software. Europe, the United Kingdom, New Zealand, and Japan have all adopted performance-based methods for structural fire, and the US industry has been slow to recognize and allow this building design approach. These developments considering structural fire represent a paradigm shift for structures in a fire situation.
Prescriptive methods are the standard for structures in the US, but structural engineering codes and standards are trending toward performance-based methods. Fire Protection Engineers (FPE) have been using performance-based methods for fire for a couple of decades in the US, and Structural Engineers (SE) are beginning to develop similar methods (to be on par with our international colleagues). However, there are some marked differences in focus between FPE and SE. FPE considers smoke ventilation, egress, fire prevention systems, notification systems, and compartmentalization to restrict fire spread, while SE considers the effect fire has on the structures’ ability to remain stable and support service loadings.
Meuller et al. (2014) illustrated this difference in dramatic fashion by testing a reinforced concrete bearing wall under a single-sided heating condition. Prescriptive fire resistance methods consider the tested bearing wall as having a 2-hour rating, due to its thickness. However, the project found upon testing the wall, a complete failure occurred at approximately 42 minutes.
Building fires are rare events—the annual likelihood that a business-occupied building will experience a fire in any given year is on the order of 0.05% (Xin and Huang 2013). But just because the chances are rare does not mean we should not keep improving and refining our fire designs. We have been using prescriptive methods for building fire resistance for nearly 100 years, and yet we still don’t have a good representation of the effectiveness of these provisions.
We could potentially eliminate a lot of conservatism in our fire-resisting elements and still maintain a similar, or possibly improved, building performance at a lesser cost to building owners and developers. Through performance-based design approaches, we could eliminate prescriptively required fire resisting elements (pending jurisdictional fire official approval) such as a reduction of compartment walls thickness through polypropylene fiber addition to the concrete mix to reduce fire response spalling or by refining structural member fire resistance with intumescent paint. There is also a possibility that we could shift our designs toward structures that are more easily reparable after a fire, thus increasing the resilience and life cycle of our buildings.
If your project has structural fire requirements, or you have any questions about the updated codes, please feel free to contact Nishkian Dean.
Aerik Carlton, is an Engineering Designer with Nishkian Dean a structural engineering consulting firm in Portland, Oregon.
Mueller, K. A., Kurama, Y. C., and Mcginnis, M. J. (2014). “Out-of-Plane Behavior of Two Reinforced Concrete Bearing Walls under Fire: Full-Scale Experimental Investigation.” ACI Structural Journal, 111(5).
Xin, J., and Huang, C. (2013). “Fire risk analysis of residential buildings based on scenario clusters and its application in fire risk management.” Fire Safety Journal, 62, 72–78.