Resources

NIST test data

Full-scale composite floor system fire tests

The NIST conducted three fire experiments on full-scale steel-concrete composite structures. The test specimens were loaded and subjected to the ASTM E119 fire. The baseline floor specimen (Test 1) was designed for a 2-hour fire rating. The two other experiments aimed at testing alternative designs of the floor system, with variation in fire protection of the steelwork and on amount of steel reinforcement in the composite slab.

Test #1 served to evaluate the performance of a floor assembly designed according to the currently applicable prescriptive provisions for a 2-hour fire resistance rating in the US. All primary and secondary beams were protected with a thickness of SFRM based on the UL ratings. These fire protection thicknesses were derived from standardized testing according to ASTM E119. The steel reinforcement area in the slab was 60 mm²/m. The connections were over-sprayed with an SFRM thickness of at least 25 mm.

Integrity failure happened about 90 mins, and the test stopped at 106 mins. This design thus fails to meet the 2 hr requirement.

Test #2 is the same as Test #1 except the slab reinforcement, which was increased from 60 mm²/m (welded wire in S755) to 230 mm²/m (no. 3 bars in S480) to investigate the influence of slab reinforcement on structural integrity.

The structure survived the fire with no integrity failure until the end of the cooling phase.

Test #3 investigated the response of the assembly with unprotected secondary beam. Compared with Test #2, no SFRM was applied on the central beam in the compartment and its end connections. This allowed investigating the effect of tensile membrane action of the floor as a resisting mechanism.

The structure survived the target 2-hour ASTM E119 fire exposure. The first major crack was observed after 132 mins.

Numerical modeling of the NIST tests

The NIST fire tests provided crucial data on the performance of different design methods for composite floor systems in the U.S. We used numerical modeling with the nonlinear finite element (FE) software SAFIR to build on these experimental findings, understand the limit states, and simulate the response of the structures under a range of natural fires. The numerical models were validated against the NIST structural fire tests. The models captured the fire response of the composite floor systems designed according to prescriptive and performance-based methods and allowed quantifying the effect of design modifications on the fire-induced losses.

The models were also used to determine the minimum required area of steel reinforcement in the composite floor to avoid the extensive cracking observed in the NIST Test 1 and maintain integrity for 2 hours under full-scale ASTM E119 fire resistance testing. For the prescriptive design with protected central beam, this minimum amount of S755 welded wire reinforcement is 100 mm²/m with a strain limit of 5 %, to be compared with the 60 mm²/m of relatively brittle wire steel mesh currently prescribed. For the performance-based design taking advantage of tensile membrane action, the minimum amount of S480 steel bar reinforcement is 170 mm²/m.

Ma, Chenzhi, and Thomas Gernay. “Numerical analysis of full-scale structural fire tests on composite floor systems.” Fire Safety Journal 146 (2024): 104182.

Construction costs database

To facilitate the construction cost estimation, we developed a cost database is for 130 prototypes of steel framed composite buildings with different occupancies, dimensions, and fire ratings. The data was obtained from a commercial cost estimator. The cost of passive fire protection on steelwork is found to range from 0 to 1.20% of the total construction cost for composite buildings with sprayed fire resistive material in the United States. The total cost of fire safety measures (including active measures such as sprinklers) ranges between 4% and 12% of the total construction cost in composite buildings.

Ma, Chenzhi, Ruben Van Coile, and Thomas Gernay. “Fire protection costs in composite buildings for cost-benefit analysis of fire designs.” Journal of Constructional Steel Research 215 (2024): 108517.

Fragility curves database

Fragility curves are useful tools in the PRA for assessing the probability of different damage levels under varying hazard intensities. They are commonly used in seismic engineering, notably when implementing a performance-based seismic design according to the Pacific Earthquake Engineering Research Center (PEER) method. A suite of seismic fragility curves for different structural typologies was developed and can help in community seismic damage assessment. The development of fire fragility curves has received comparatively limited attention until recently.

To advance understanding of the comparative performance of different fire designs, we conducted probabilistic damage analysis of various composite floor designs under natural fire conditions. The analyses were completed with the FE software SAFIR.

Results show that the performance-based design using tensile membrane action has a higher probability of moderate damage but a lower probability of integrity failure than the prescriptive design. Parametric analyses show that increasing the amount of slab reinforcement or the amount of axial restraint at the boundaries further reduces the probability of failure.

Ma, Chenzhi, and Thomas Gernay. “Fragility curves for structural fire performance of various composite floor designs under natural fire.” Reliability Engineering & System Safety (2025): 110820.

Integrated web-tool for cost-benefit analysis

We implemented this economic impact analysis framework in a web-based user interface, and its validation/application based on the NIST test data, to allow assessment of the economic impact of adopting a PBD in lieu of a prescriptive design for steel-concrete composite floors. The step-wised website allow user to estiamte the initial construction cost, the lifetime maintenance cost, the direct and indirect losses due to fire event, the environmental impact, and the co-benefits. Then all the cost components are integrited to calculated the lifetime cost and inform the stakeholder to make decisions.

References

Journal Articles

J1. Ma, C. & Gernay, T. Numerical analysis of full-scale structural fire tests on composite floor systems. Fire Safety Journal 146, 104182 (2024).

J2. Ma, C., Van Coile, R. & Gernay, T. Fire protection costs in composite buildings for cost benefit analysis of fire designs. Journal of Constructional Steel Research 215, 108517 (2024).

J3. Ma, C. & Gernay, T., Fragility curves for structural fire performance of various composite floor designs under natural fire, Reliability Engineering & System Safety, 2025, 110820.

Peer-reviewed Conference Proceedings

C1. Ma, C., Van Coile, R. & Gernay, T. A user interface to compare the lifetime costs of prescriptive and performance-based fire designs of composite buildings. in 13th International Conference on Structures in Fire (2024).

C2. Ma, C. & Gernay, T. Parametric numerical study of fire experiments on steel-concrete composite floors. in 13th International Conference on Structures in Fire (2024).

C3. Ma, C. & Gernay, T. Structural fire analysis of steel-concrete composite floors designed with prescriptive and performance-based methods. in Proceedings of the Annual Stability Conference Structural Stability Research Council, San Antonio, Texas (2024).