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Fire Technology

, Volume 53, Issue 3, pp 1333–1351 | Cite as

Anisotropic Curvature and Damage of Unbonded Post-tensioned Concrete Slabs During Fire Testing

  • Johan Sjöström
  • David Lange
  • Robert Jansson McNamee
  • Lars Boström
Article

Abstract

Two furnace tests, using two different fire exposures, on unbonded post-tensioned concrete slabs (1700 × 1200 mm) are reported. Local curvature is measured along two lines approximately in the middle of the slabs both parallel (longitudinal) and orthogonal (transverse) to the prestressing direction. More pronounced curvature in the transverse direction is accompanied by the formation of cracks running predominantly in the longitudinal direction. While the transverse curvature relaxes back to the original state after the cooling phase the curvature in the longitudinal direction ultimately exhibits upward deflection due to the hogging moment caused by the prestress in the tendons acting on a cross section with temperature reduced mechanical properties at the fire exposed side. The effect on crack formation due to the prestressing can additionally be detected by ultrasonic pulse velocity measurements in the different directions through the depth of the slab, where a reduction of 5–25% is observed in the transverse direction compared to the longitudinal direction. The phenomenological mechanical behaviour of the slabs is captured in a finite element model which describes the evolution of stress in the prestressing tendons. This model additionally suggests that the curvature in the transverse direction is independent of the prestressing in the longitudinal direction.

Keywords

Concrete slab Fire Deflection Post-tension Standard fire curve Hydrocarbon fire curve Ultrasonic pulse velocity Crack formation 

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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • Johan Sjöström
    • 1
  • David Lange
    • 1
  • Robert Jansson McNamee
    • 1
  • Lars Boström
    • 1
  1. 1.SP Technical Research Institute of SwedenBoråsSweden

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