Effect of Restraint on Fire Resistance of Prestressed Concrete

Selvaggio, S; Carlson, Clinton

doi:10.1520/stp44508s

Cited by 16 publications

(7 citation statements)

References 5 publications

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“…In fact, from the 1960s, the effects of restraint on concrete slabs in fire have been investigated by many researchers through fire tests [8][9][10][11], numerical analysis [12][13][14] and theoretical methods [15][16][17]. However, a review of literature shows that there are some obvious controversies on the effect of the restraint on the fire behavior of concrete slabs, as discussed in [18].…”

Section: Introductionmentioning

confidence: 99%

Fire behaviour of reinforced concrete slabs under combined biaxial in-plane and out-of-plane loads

Yong

Bisby

Tengyan

et al. 2018

Fire Safety Journal

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To better understand the fire behaviour of in-plane restrained reinforced concrete slabs, this paper presents six fire tests on two-way spanning concrete slabs under compressive bi-axial in-plane and flexural outof-plane loads. The data presented include furnace temperatures, temperature distributions, vertical and horizontal deflections, restraint forces, crack patterns, and characterisation of spalling of the six slabs during both heating and cooling phases. Comparison of the results indicates that bi-axial in-plane loads may have a negative effect on the vertical and horizontal deflection trends of the restrained slabs in fire. In addition, snap though behaviour and subsequent severe reversals of deflection trends were observed for the first time in concrete slabs with sustained bi-axial in-plane restraint during heating and cooling stages. Fire behaviour of the restrained slabs were considerably different from those of the simply supported slabs, and thus the effect of uniaxial or bi-axial in-plane restraints on the failure mode should be considered to establish reasonable failure criteria for these slabs. In addition, it is suggested that the corners of the in-plane restrained slabs should be reinforced by arranging the whole span top steels along two directions since the corners easily fracture with large diagonal cracks during fire tests.

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Section: Introductionmentioning

confidence: 99%

Fire behaviour of reinforced concrete slabs under combined biaxial in-plane and out-of-plane loads

Yong

Bisby

Tengyan

et al. 2018

Fire Safety Journal

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“…A first step to quantify the effects of restraint was made by Selvaggio [2] which led to the establishment of restrained and unrestrained fire resistance ratings of proprietary concrete and composite steel-concrete floor systems such as those listed in the Fire Resistance Directory [3] in the USA. The definition of restraint in these ratings is not well defined and there is no established basis for quantifying the restraint other than qualitative descriptions such as those in the ASTM E 119 testing standard [4].…”

Section: Introductionmentioning

confidence: 99%

Restraint of fire‐exposed concrete floor systems

2004

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SUMMARYThis paper describes the numerical analyses of restrained concrete floor slabs exposed to fire. The analyses of the slabs were carried out with the SAFIR finite element program considering a 200 mm thick slab, spanning 5 m between two end supports. The slabs were exposed to the ISO standard fire for up to 4 h and were analysed with pinned and rotationally restrained supports. Different heights of the line of thrust at the supports and different levels of axial restraint were also investigated. The analyses show that fully restrained pin-supported slabs can survive the 4 h ISO fire without collapse if the position of the line of thrust is located near the soffit of the slab. If the position of the line of thrust is located much above the soffit of the slab, the slabs will rapidly undergo large deformations and sag into a catenary, imposing axial tensile forces at the supports. The analyses have shown that even if the line of thrust is located close to the soffit, the slab can still deform into a catenary if there is insufficient horizontal axial restraint. In this study, rotationally restrained slabs experience much smaller vertical deflections than pin-supported slabs when exposed to fires. Rotationally restrained slabs with low levels of horizontal restraint do not collapse, due to the beneficial effects of moment redistribution. However, high levels of horizontal restraint can be detrimental, causing slabs to collapse at advanced stages of the fire.

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“…These proposals stemmed from the observation that the results from fire tests on structural assemblies tested under identical configurations, protection schemes, and temperature conditions varied considerably from test to test . Development of a varying degree of applied restraint against thermal expansion in standard fire tests was assumed to be the main reason for such variations . Additionally, during this time, there were debates about the feasibility of simulating realistic restraint within a test furnace .…”

Section: Origin Of Restraint Classificationsmentioning

confidence: 99%

Rectification of “restrained vs unrestrained”

LaMalva¹,

Bisby

Gales

et al. 2020

Fire and Materials

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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.

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Effect of Restraint on Fire Resistance of Prestressed Concrete

Cited by 16 publications

References 5 publications

Fire behaviour of reinforced concrete slabs under combined biaxial in-plane and out-of-plane loads

Fire behaviour of reinforced concrete slabs under combined biaxial in-plane and out-of-plane loads

Restraint of fire‐exposed concrete floor systems

Rectification of “restrained vs unrestrained”

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