Hollow-Core Slabs on Flexible Supports

FE-Investigations of Prestressed Hollow-Core Slabs on non-rigid supports

Prof. Dr.-Ing. Josef HeggerDipl.-Ing. Sebastian BülteRWTH Aachen

Dr.-Ing. Naceur KerkeniHegger+Partners Consulting Aachen

Hollow-Core Slabs on Flexible Supports

Additional stress caused by 2-axial bending, lateral tension and shear distortion

Hollow-Core Slabs on Concrete Beams

Additional stress of prestressed hollow-core slabs supported on a regular concrete beam is little.

I

I

Q

R1R1

Q

R2VV

section I-I:

Transverse bending Transverse bending+ shear distortion

VVR3

Hollow-Core Slab on Steel Beams (Slim-floor)

Additional stress of slabs has to be determined for each individual case.

I

ISection I-I:

Q

R2 R3

Transverse bending+ lateral tension

VV

Q

R1R1VV

Transverse bending+ shear distortion

Bond Mechanisms

bearing forcesReinforcing rods Anchorage stresses

end splitting forces

bond forces

radial splitting forces

Prestressed tendonsLateralexpansionSlip

adhesion andfrictionHoyer effect (wedge-action)

Possible Solutions

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

0 20 40 60 80 100 120 140Zugkraft [kN]

Litz

ensc

hlup

f [m

m]

vornehinten

Zugkraft durch Hydraulikzylinder am hinteren Bauteilende

vorne hinten

Z

1. Slits in the soffit of the slabs with a length of approximately 50 cm starting from the support

2. Tests on prestressed hollow-core slabs on flexible-supports to determine the number of longitudinal cracks per element

3. Finite element analysis on floor systems to appoint the hidden assets of slim-floor structures

4. Additional reinforcing rods to resist the acting tensile force in the anchorage zone (Laps of rods and tendons are required)

Schlitz 50 cm LängeSlit of 50 cm length

Schlitz 50 cm LängeFilled voids with reinforcing rods

Finite Element Analysis of a Prestressed Hollow-Core Slab I

Section of the FE-model PHC (d = 265 mm)

Finite Element Analysis of a Prestressed Hollow-Core Slab II

Longitudinal deformation [mm] due to prestressing force

Finite Element Analysis of a Prestressed Hollow-Core Slab III

Principle stress [N/mm²]due to prestressing force

FE-Model

Hollow

-Core

Slab

Interface ElementsSteel Beam

3,50 m

3,00 m

400

200

300

3040

360 20

Steel Beam Section

Axe

of S

ymm

etrie

Longitudinal Stresses due to Prestressing

Mean Tensile Stresses due to Prestressing

Loads

Distributed Load

Line Load

Mean Compressive Stresses (V=193 kN/Slab)

Deformation at Failure (scaled in transv. Direc.)

Crack Pattern at Failure

Slits in the soffit of the slabs

Deformation at Failure (scaled in trans. Direc.)

Mean Compressive Stress at Failure

Crack Pattern at Failure

Crack Pattern at Failure

Future Investigation

3,50 m

Joint Concrete

Cast

in sit

u Con

crete

Steel Beam

Transversal Stresses due to Prestressing

Longitudinal Stresses due to Prestressing

Transversal Stresses at V=17 kN/Slab

Mean Compressive Stresses at V=17kN/Slab

Experimental Test Set-Up

Test set up regarding EN 1168

- Span of Slabs approx. 6,0 m- Span of Beams approx. 8,0 m

Measurement II

Aufbau an EN 1168 angelegt.

- Spannweite Hohlplatten ca. 6,0 m- Spannweite Träger ca. 8,0 m

- loading - crack opening- deflection of slabs / beams (a) slab/beam (e)- longitudinal cracking (strain gauges;b) - slip of strands (f) - strain of slabs and beam (c) - rotation of beam- relative displacement of slabs/ beam (d)

breathure-opening

lattice girder / stiffener

in-situ concrete

c b d

f

e

FE-Investigations of Prestressed Hollow-Core Slabs on non-rigid supportsProf. Dr.-Ing. Josef HeggerDipl.-Ing. Sebastian BülHollow-Core Slabs on Flexible SupportsHollow-Core Slabs on Concrete BeamsHollow-Core Slab on Steel Beams (Slim-floor)Bond MechanismsPossible SolutionsFinite Element Analysis of a Prestressed Hollow-Core Slab IFinite Element Analysis of a Prestressed Hollow-Core Slab IIFinite Element Analysis of a Prestressed Hollow-Core Slab IIIFE-ModelLongitudinal Stresses due to PrestressingMean Tensile Stresses due to PrestressingLoadsMean Compressive Stresses (V=193 kN/Slab)Deformation at Failure (scaled in transv. Direc.)Crack Pattern at FailureSlits in the soffit of the slabsDeformation at Failure (scaled in trans. Direc.)Mean Compressive Stress at FailureCrack Pattern at FailureCrack Pattern at FailureFuture InvestigationTransversal Stresses due to PrestressingLongitudinal Stresses due to PrestressingTransversal Stresses at V=17 kN/SlabMean Compressive Stresses at V=17kN/Slab