tensile fatigue behaviour of...

: runout specimenmax : maximum fatigue stress

fe,i : elastic limit strength of each specimen

750

250

250

250

150

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]