tensile fatigue behaviour of...
TRANSCRIPT
: runout specimenmax : maximum fatigue stress
fe,i : elastic limit strength of each specimen
750
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250
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The objective of the present research is to know the strength and behaviour of UHPFRC under uniaxial tensile fatigue stress. Interests in tensilefatigue strength and behaviour come from the fact that UHPFRC shows itself at its best when applied to the zones where tensile stress is dominant(e.g. cantilever of bridge deck slab).
Tensile Fatigue behaviour of UHPFRC Doctoral student: Tohru MakitaSupervisor: Professor Eugen Brühwiler
Since late 20th century traffic volume and vehicle size have beenincreasing, which requires the increase of load bearing capcity of bridge deckslabs.
Application of Ultra High Performance Fibre Reinforced Concrete(UHPFRC) layer to concrete bridge deck slab was conceived as an effectivemethod to improve the performance of bridge deck slabs.
FACULTE DE L�’ENVIRONNEMENT NATUREL, ARCHITECTURAL ET CONSTRUIT (ENAC)
Strain (�‰)
I. Elastic II. Strain hardening III. Softening
Experimental tests
Objective
Uniaxial tensile fatigue tests were conducted on UHPFRC monolithic plates.
LVDTs for measuringglobal deformation
Aluminium plates (t = 2mm)for strengthening to causefailure in gauged area
fefu
e
u
I II III
S1: 1
S3: 3
S2: 2
S4: 4
Motivation
Figure 2 Specimen geometry, measuring devices and testing machine
Figure 1 Application of UHPFRC layer to concrete bridge deck slab
UHPFRC layer
concrete
Four types of tensile fatigue stress were set up in relation tostress strain curve of UHPFRC in quasi static tension.
Figure 3 Four types of tensile fatigue stress (S1 ~ S4)and stress strain curve of UHPFRC in quasi static tension
Test results and discussion
Log N
max/f
e,i
fu, u: ultimate strength and strainfe, e: elastic limit strength and strain
Figure 4 Wöhler diagram oftensile fatigue tests with S3 stress
0.65
Regression line (r = 0.85)
Glob
alde
form
ation(m
m)
Number of cycles
Localdeformation(m
m)
Number of cycles
: Maximum global deformation: Global deformation range
: Maximum local deformation of G1: Maximum local deformation of G2: Maximum local deformation of G3: Maximum local deformation of G4: Maximum local deformation of G5
G1G2G3G4G5
Zoning of specimen
Figure 5 Deformation growth curve of a tensile fatigue test with S1 stress(a) global deformation, (b) local deformation
(a) (b)
(Regression line was drawn without runout specimens .)
Figure 6 Fatigue fracture surface of (a) UHPFRC, (b) steel rebar(a) (b)
(Johansson 2004) Fatigue endurance limit of "yielded" UHPFRC is 65 % of elastic limit strength(Figure 4).
Even after localization of a macrocrack, UHPFRC sustained tensile fatiguestress, which was achived by stress redistribution (Figure 5).
Local deformation varied from zone to zone despite uniform stress over aspecimen (Figure 5(b)). This is attributed to local difference of elastic modulusinfluenced by fibre distribution and orientation.
Fatigue fracture surface of UHPFRC is similar with that of steel rebar (Figure6). Smoother surface area due to wear away is observed in both UHPFRC andsteel rebar (enclosed area with red line in Figure 6).
: Localization of a macrocrack
: Localization of a macrocrack
Distributed macrocracks Localized macrocrackMicrocracks
Stress(M
Pa)
Gauges for measuringlocal deformation
[unit: mm]