Shear resistance of prestressed hollow core slabs on flexible supports

Dissertation

Matti Pajari

Research output: ThesisDissertationMonograph

Abstract

Six full-scale loading tests for slim floors comprising prestressed hollow core slabs and spine beams have been carried out. In these tests, the observed shear resistance of the slabs was only 40 to 70% of the shear resistance observed in the reference tests in which slab units were supported on rigid bearings. In one floor test, yielding of the beam preceded the shear failure of the slabs. In five tests, the slab units underwent a shear failure before the yielding of the beam. According to the conventional calculation models, the beams should have failed first in all tests. At failure, the deflection of the supporting beams was relatively small, typically 1/400 to 1/250 of the span of the beam. However, a three dimensional finite element simulation and the observed failure mode, web shear failure, confirm that the reduction in shear resistance is due to transverse deformation in the hollow core units caused by the deflection of the beams. A calculation model for the analysis of the web shear failure of the slabs is proposed. In the model, the maximum principal stress in the web is calculated from three non zero stress components and compared with the tensile strength of the concrete. Two of the stress components, namely the axial stress and vertical shear stress, are calculated as in the conventional model. The third one, the transverse horizontal shear stress, is calculated using a linear composite beam model. The load-bearing capacity of floors can be enhanced by reducing the deflection of the beams, for example, by making the beams stiffer or continuous. Another approach is to reduce the transverse shear deformation of the slab ends, for example, by filling the voids with concrete or by providing the floor with a reinforced concrete topping.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Helsinki University of Technology
Supervisors/Advisors
  • Paavola, Juha, Supervisor, External person
Award date24 May 1995
Place of PublicationEspoo
Publisher
Print ISBNs951-38-4766-7
Publication statusPublished - 1995
MoE publication typeG4 Doctoral dissertation (monograph)

Fingerprint

Shear stress
Bearings (structural)
Concretes
Bearing capacity
Shear deformation
Failure modes
Reinforced concrete
Loads (forces)
Tensile strength
Composite materials

Keywords

  • prestress
  • hollow core slab
  • concrete structures
  • precast concrete
  • design
  • prefabrication
  • slim floor
  • shear
  • composite structures
  • flexible support
  • loading test
  • composite beam

Cite this

Pajari, M. (1995). Shear resistance of prestressed hollow core slabs on flexible supports: Dissertation. Espoo: VTT Technical Research Centre of Finland.
Pajari, Matti. / Shear resistance of prestressed hollow core slabs on flexible supports : Dissertation. Espoo : VTT Technical Research Centre of Finland, 1995. 164 p.
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title = "Shear resistance of prestressed hollow core slabs on flexible supports: Dissertation",
abstract = "Six full-scale loading tests for slim floors comprising prestressed hollow core slabs and spine beams have been carried out. In these tests, the observed shear resistance of the slabs was only 40 to 70{\%} of the shear resistance observed in the reference tests in which slab units were supported on rigid bearings. In one floor test, yielding of the beam preceded the shear failure of the slabs. In five tests, the slab units underwent a shear failure before the yielding of the beam. According to the conventional calculation models, the beams should have failed first in all tests. At failure, the deflection of the supporting beams was relatively small, typically 1/400 to 1/250 of the span of the beam. However, a three dimensional finite element simulation and the observed failure mode, web shear failure, confirm that the reduction in shear resistance is due to transverse deformation in the hollow core units caused by the deflection of the beams. A calculation model for the analysis of the web shear failure of the slabs is proposed. In the model, the maximum principal stress in the web is calculated from three non zero stress components and compared with the tensile strength of the concrete. Two of the stress components, namely the axial stress and vertical shear stress, are calculated as in the conventional model. The third one, the transverse horizontal shear stress, is calculated using a linear composite beam model. The load-bearing capacity of floors can be enhanced by reducing the deflection of the beams, for example, by making the beams stiffer or continuous. Another approach is to reduce the transverse shear deformation of the slab ends, for example, by filling the voids with concrete or by providing the floor with a reinforced concrete topping.",
keywords = "prestress, hollow core slab, concrete structures, precast concrete, design, prefabrication, slim floor, shear, composite structures, flexible support, loading test, composite beam",
author = "Matti Pajari",
note = "Project code: R5SU00543",
year = "1995",
language = "English",
isbn = "951-38-4766-7",
series = "VTT Publications",
publisher = "VTT Technical Research Centre of Finland",
number = "228",
address = "Finland",
school = "Helsinki University of Technology",

}

Pajari, M 1995, 'Shear resistance of prestressed hollow core slabs on flexible supports: Dissertation', Doctor Degree, Helsinki University of Technology, Espoo.

Shear resistance of prestressed hollow core slabs on flexible supports : Dissertation. / Pajari, Matti.

Espoo : VTT Technical Research Centre of Finland, 1995. 164 p.

Research output: ThesisDissertationMonograph

TY - THES

T1 - Shear resistance of prestressed hollow core slabs on flexible supports

T2 - Dissertation

AU - Pajari, Matti

N1 - Project code: R5SU00543

PY - 1995

Y1 - 1995

N2 - Six full-scale loading tests for slim floors comprising prestressed hollow core slabs and spine beams have been carried out. In these tests, the observed shear resistance of the slabs was only 40 to 70% of the shear resistance observed in the reference tests in which slab units were supported on rigid bearings. In one floor test, yielding of the beam preceded the shear failure of the slabs. In five tests, the slab units underwent a shear failure before the yielding of the beam. According to the conventional calculation models, the beams should have failed first in all tests. At failure, the deflection of the supporting beams was relatively small, typically 1/400 to 1/250 of the span of the beam. However, a three dimensional finite element simulation and the observed failure mode, web shear failure, confirm that the reduction in shear resistance is due to transverse deformation in the hollow core units caused by the deflection of the beams. A calculation model for the analysis of the web shear failure of the slabs is proposed. In the model, the maximum principal stress in the web is calculated from three non zero stress components and compared with the tensile strength of the concrete. Two of the stress components, namely the axial stress and vertical shear stress, are calculated as in the conventional model. The third one, the transverse horizontal shear stress, is calculated using a linear composite beam model. The load-bearing capacity of floors can be enhanced by reducing the deflection of the beams, for example, by making the beams stiffer or continuous. Another approach is to reduce the transverse shear deformation of the slab ends, for example, by filling the voids with concrete or by providing the floor with a reinforced concrete topping.

AB - Six full-scale loading tests for slim floors comprising prestressed hollow core slabs and spine beams have been carried out. In these tests, the observed shear resistance of the slabs was only 40 to 70% of the shear resistance observed in the reference tests in which slab units were supported on rigid bearings. In one floor test, yielding of the beam preceded the shear failure of the slabs. In five tests, the slab units underwent a shear failure before the yielding of the beam. According to the conventional calculation models, the beams should have failed first in all tests. At failure, the deflection of the supporting beams was relatively small, typically 1/400 to 1/250 of the span of the beam. However, a three dimensional finite element simulation and the observed failure mode, web shear failure, confirm that the reduction in shear resistance is due to transverse deformation in the hollow core units caused by the deflection of the beams. A calculation model for the analysis of the web shear failure of the slabs is proposed. In the model, the maximum principal stress in the web is calculated from three non zero stress components and compared with the tensile strength of the concrete. Two of the stress components, namely the axial stress and vertical shear stress, are calculated as in the conventional model. The third one, the transverse horizontal shear stress, is calculated using a linear composite beam model. The load-bearing capacity of floors can be enhanced by reducing the deflection of the beams, for example, by making the beams stiffer or continuous. Another approach is to reduce the transverse shear deformation of the slab ends, for example, by filling the voids with concrete or by providing the floor with a reinforced concrete topping.

KW - prestress

KW - hollow core slab

KW - concrete structures

KW - precast concrete

KW - design

KW - prefabrication

KW - slim floor

KW - shear

KW - composite structures

KW - flexible support

KW - loading test

KW - composite beam

M3 - Dissertation

SN - 951-38-4766-7

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Pajari M. Shear resistance of prestressed hollow core slabs on flexible supports: Dissertation. Espoo: VTT Technical Research Centre of Finland, 1995. 164 p.