Abstract
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  24 May 1995 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513847667 
Publication status  Published  1995 
MoE publication type  G4 Doctoral dissertation (monograph) 
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Keywords
 prestress
 hollow core slab
 concrete structures
 precast concrete
 design
 prefabrication
 slim floor
 shear
 composite structures
 flexible support
 loading test
 composite beam
Cite this
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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: Thesis › Dissertation › Monograph
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 fullscale 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 loadbearing 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 fullscale 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 loadbearing 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  9513847667
T3  VTT Publications
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 