Upload
abdul-raheem
View
245
Download
0
Embed Size (px)
Citation preview
8/10/2019 HCS Testing
1/16
Toward a standardized procedure for
hollow-core slab testingMarco di Prisco and Marco G. L. Lamperti
Department of Structural engineering
8/10/2019 HCS Testing
2/16
Marco di Prisco and Marco G.L. Lamperti
2
Aims of Research
To verify reliability of predictions
To optimize experimental lever arm
To investigate the residual shear capacity
EXPERIMENTAL
INVESTIGATION
EC2 MC '90
LITERATURE
Most criticalShear Value
Fibre reinforcement quantification to preventshear failure
8/10/2019 HCS Testing
3/16
Marco di Prisco and Marco G.L. Lamperti
3Experimental Program 1
Four hollow-core slab types from30 to 45 cm thickness
Shear and bending test
Real-scale performed tests: 18
8/10/2019 HCS Testing
4/16
Marco di Prisco and Marco G.L. Lamperti
4Experimental Program
Bending Test set-up
Bending test set-up:
distribuited load controlled vs.
Distributed Load-controlledset-up 4PB Stroke-controlledset-up
8/10/2019 HCS Testing
5/16
Marco di Prisco and Marco G.L. Lamperti
5Experimental Program
Shear Test set-up
with flexural cracking
1.5 < < 3.5
without flexural cracking
3.5 < < 5.0
Stroke-controlled4-Point Bending
8/10/2019 HCS Testing
6/16
Marco di Prisco and Marco G.L. Lamperti
6Material characterization
Tested according UNI specifications gave resultes 1936 < fptk < 2020 N/mm2
Concrete
Steel
Cubic specimens (150 mm side)casted at the same time of slabs
Cores directly extracted from testedslabs
8/10/2019 HCS Testing
7/16
Marco di Prisco and Marco G.L. Lamperti
7Experimental Results
No bond failure was observed
Two different test set-ups wereadopted for only the V35 to induce
shear failure with or without flexuralcracking
After shear crack formation manytest presented a progressive strandslip
Bending tests
Shear tests
The real collapse was not reached insome cases due to the large mid-span deflection obtained
8/10/2019 HCS Testing
8/16
Marco di Prisco and Marco G.L. Lamperti
8Experimental Results
Bending Test
Although a flexural collapse did never occurred, because of the high deformabilityof hollow-core slabs, closed-loop control allows a better test procedure that caneasily follow structural damage evolution.
0 40 80 120 160
freccia [mm]
0
40
80
120
160
200
P[
kN
]
fr Var30-F1
fr Var30-F2
simul. elastica
simulazione
Pcrcon fctf=1.05fctm
8/10/2019 HCS Testing
9/16
Marco di Prisco and Marco G.L. Lamperti
9Experimental Results
Shear Test 1Top-Chord collapse
Strand Slip failure
8/10/2019 HCS Testing
10/16
Marco di Prisco and Marco G.L. Lamperti
10Experimental Results
Shear Test 2
The small load lever arms corresponded to large residual bearing capacities after thepeak load, while larger lever arms caused small residual load capacities.
The higher force value in the chords reduces the shear resistant mechanisms as wellas to the higher elastic strain release in the crack propagation associated to the largerbending deformation.
8/10/2019 HCS Testing
11/16
Marco di Prisco and Marco G.L. Lamperti
11Adopted Design Models
The adopted material models, are suggested from Fib Model Code 90 and EuroCode2.
The moment-curvature relation is derived from a plane-section model.
Concrete - compression Concrete - tension Steel - tension
8/10/2019 HCS Testing
12/16
Marco di Prisco and Marco G.L. Lamperti
12Adopted Design Models
In order to predict the shear loads, both the empirical equations adopted forcracked and uncracked in flexure cases were computed. According to Walraven(1982) and FIB, the following equations are here taken into account:
with flexural cracking
without flexural cracking
8/10/2019 HCS Testing
13/16
Marco di Prisco and Marco G.L. Lamperti
13
Experimental vs.
Theoretical Results
The load displacement curves for bending collapse were very well reproduced byadopting the beam theory.
The cracking moment was calculated by neglecting the tension stiffening and consideringthe tensile strength of the concrete.
The shear tests are not equally well reproduced, especially for small shear span. Thisresult could be mainly related to the not perfectly planar extrados surface of the hollow-core that involves a stiffness reduction.
8/10/2019 HCS Testing
14/16
Marco di Prisco and Marco G.L. Lamperti
14
Discussion of Results - An analysis performed according to
Kanis valley approach highlights ajump between 3.66 and 4.17 of a/d,strictly related with the passagefrom VRt toVR1 shear resistance.
The 300 mm deep element showeda border condition for a/d = 4.23.
8/10/2019 HCS Testing
15/16
Marco di Prisco and Marco G.L. Lamperti
15
Discussion of Results -
By taking into account the residual values an evaluation of steel fibre addition could becarried out by computing the maximum between the increase of VR1 needed to reach theultimate bending moment adopting a load lever arm close to 4, and the increase of theresidual shear capacity when VRt takes place. In this case we could expect that steel fibreaddition stabilizes the crack associated to both VRt andVR1 failures, as recently shown byElliott (2002), even if the elastic energy associated to the bending of a real span hollow
core could significantly affect the values investigated.
8/10/2019 HCS Testing
16/16
Marco di Prisco and Marco G.L. Lamperti
16
Concluding Remarks
The experimental investigation confirmed the predictive relations introduced byprevious authors in the range of 300 450 mm deep hollow core elements.
A closed loop hydraulic jacket, with 1000 kN of maximum load capacity, madedisplacement controlled tests possible.
The residual shear capacity of the structures was exploited in order to preventbrittle failures in these elements.
When the structures were cracked in flexure, the residual values were smaller thanin the case of uncracked structures.
A border value of about a/d = 4 was detected to separate the cracked-in-flexure
cases from the uncracked ones. The use of steel fibre to prevent brittle failure has to be encouraged, even if it
should be validated on real-size beams, in order to take into account the real elasticrelease rate in the crack propagation at failure.