Rectification of “restrained vs unrestrained”

Abstract

Summary For furnace testing of fire‐resistant floor and roof assemblies in the United States, the ASTM E 119 standard (and similarly the UL 263 standard) permits two classifications for boundary conditions: “restrained” and “unrestrained.” When incorporating tested assemblies into an actual structural system, the designer, oftentimes a fire protection or structural engineer, must judge whether a “restrained” or “unrestrained” classification is appropriate for the application. It is critical that this assumption be carefully considered and understood, as many qualified listings permit a lesser thickness of applied fire protection for steel structures (or less concrete cover for concrete structures) to achieve a certain fire resistance rating if a “restrained” classification is confirmed, as compared with an “unrestrained” classification. The emerging standardization of structural fire engineering practice in the United States will disrupt century‐long norms in the manner to which structural behavior in fire is addressed. For instance, the current edition of the ASCE/SEI 7 standard will greatly impact how designers consider restraint. Accordingly, this paper serves as an exposé of the “restrained vs unrestrained” paradigm in terms of its paradoxical nature and its controversial impact on the industry. More importantly, potential solutions toward industry rectification are provided for the first time in a contemporary study of this paradigm.

Response to Vytenis Babrauskas “Comments on “The Historical Narrative of the Standard Temperature–Time Heating Curve for Structures” by Gales, et al.”

“…In 2018, ASTM E05 (which maintains E119) held a workshop on Advancements in Evaluating the Fire Resistance of Structures in Washington, D.C., that the lead author here co-chaired and that the authorship team helped to organize. This workshop featured several studies in which potential needs for changes to the ASTM E119 standard were discussed, especially in light of the rise of engineered timber structures [16][17][18] but even steel and concrete structures with the concept of restraint [19]. Each of these topics highlighted relatable aspects to the transition to performance-based fire design for structures.…”

Fire resistance and associated failure modes of axially restrained hollow core slabs

“…Furnace tests have evidenced the possible formation of CAA and a corresponding enhanced performance, but always in members with relatively short spans. This is mainly due to the size limitations of commonly used test furnaces, which typically measure 4.27 m (14 ft) to 5.18 m (17 ft) in length [11]. As the beneficial effects of CAA strongly decrease with increasing spanto-depth ratio, it is not guaranteed that this effect will enhance the fire resistance of HC slabs with more realistic span lengths.…”

Advancements in evaluating the fire resistance of structures

“…After stringent peer review, 12 of the 17 oral presentations are presented here as full papers. The papers accepted for this issue were on the following topics[5][6][7][8][9][10][11][12][13][14][15][16] :Due to modern developments in the construction materials industry, to ensure design safety, we are being challenged with requiring significant understanding of new materials and their performance in fire. Since 1918, the standard fire time-temperature curve has been utilized to assess the fire resistance of building materials.…”

“…After stringent peer review, 12 of the 17 oral presentations are presented here as full papers. The papers accepted for this issue were on the following topics: Comparative Energy Analysis from Fire Resistance Tests on Combustible vs Non‐combustible Slabs The Discrepancies in Energy Balance in Furnace Testing, a Bug or a Feature? A New Test Methodology for Studying the Response of Walls to Real Fire Environments Simulating Real Compartment Fire Conditions in a Furnace Rectification of “Restrained vs. Unrestrained” Fire Resistance of Cold‐formed Steel Framed Shear Walls under various Fire Scenarios Development and Application of a Simulation Approach for Fire and Structure Interaction of Concrete Members subject to Spalling Test Methods for Characterizing Concrete Properties at Elevated Temperatures Evaluation of Standard and Real Fire Exposures on Thermal Response of Rail Car Floor Assembly Best Practices for Modeling Structural Boundary Conditions Due To a Localized Fire Flame Extension and the Near Field under the Ceiling for Travelling Fires Inside Very Large Compartments An Extended Travelling Fire Method (ETFM) Framework for Performance‐based Structural Design …”