Baasansuren TOGTOKHBAYAR （M2)

Shear Behavior of RC Beams with UFC Permanent Formworks using PBO and

Steel Fibers

Introduction: Ultra-high Strength Fiber Reinforced Concrete (UFC)No.1

UFC is advanced cementitious material which consists of fibers and silica fume

Compressive strength >150 MPa Cracking strength >4 MPa

Rebar is unnecessary Available for a complex structure

High flowability

• Advantages High tensile strength High elastic modulus Light self-weight

PBO (Polyparaphenylene Benzobis Oxazole)

• Disadvantages Poor resistance to axial

compressive force

Fiber bridging

effect

High strength

PBO fiber

• Recommendation for Design andConstruction of Ultra-high StrengthFiber Reinforced ConcreteStructure (Drafts),JSCE

Shear carried by UFC can becalculated as followings:

Background: UFC-RC hybrid beamNo.2

Vrpc

Vf

VUFC

• Previous Study Chang et al.(2017):

1. UFC has good agreement with asimple evaluation method.

VTotal = VUFC+ VC

2. PBO fiber length improved theshear capacity.

• To investigate mechanical properties (𝑓c’, 𝑓cr , Ec, GF, Tension SofteningCurve) of the UFC using PBO and steel fibers.

• To investigate the shear behavior of RC beams with UFC permanentformworks.

Research Objective

P8, P15, P22

300

SF P22-S

Vf : Shear carried by fiber Vrpc : Shear carried by UFC matrix

VUFC=Vf +Vrpc

Material test: Fresh propertiesNo.3

Mixing and fresh properties(kg/m³)

Name Length(mm)

Diameter(mm) W B S SP D

Flowvalue (mm)

PBO 1 Vol.%15 0.23

195 1287 90530.61 6.44

300x300PBO 1.5 Vol.% 260x250PBO 2 Vol.% 180x190Steel 1.5 Vol.% 15,22 0.20 32.18 6.44 310x305

*here: W: Water, B: Premix binder, S: Silica sand SP-Superplasticizer, D- Defoaming agent

PBO 2Vol.% PBO 1Vol.%

180x190 300x300

PBO1.5Vol.%

260x250

Flow value increased withthe decrease in PBO fibervolume content

Steel 1.5Vol.%

310x350

Material test: Compression and splitting cylinder testNo.4

• Compressive strength testmethod

Ø50x100mm

• Splitting cylinder test methodØ100x150mm

179

164155

150

130140150160170180190

Compressive Strength (N/mm²)

Steel 1.5% PBO 1% PBO 1.5% PBO 2%

8% 6.7 7.17.8 8.2

0

3

6

9Cracking Strength (N/mm²)

PBO 1% PBO 1.5% PBO 2% Steel 1.5%

Steel PBO

• Test method:400x100x100mm

Material test: Three-Point bending notched beam testNo.5

5

30

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7

Tens

ile s

tres

s (N

/mm

²)

Crack width (mm)

Steel 1.5%PBO 2%PBO 1.5%PBO 1%

0

5

10

15

20

25

30

0 2 4 6 8 10 12 14

Load

P (k

N)

LPD (mm)

Steel 1.5%PBO 2%PBO 1.5%PBO 1%

20.1

5.9 5.4 5.0

0369

12151821

Fracture energy (N/mm)

Steel 1.5% PBO 2.0% PBO 1.5% PBO 1.0%

The peak load and transferred tensile stress were improved with the increase in PBOfiber volume content.

Beam tests: Specimen’s outlineNo.6

t=3033

0260

Specimen name Fibervolume

Parameter 1Type of fiber

Parameter 2Thickness, t (mm)

Parameter 3Interface

20_SM_PBO

1.5%

PBO20

Smooth20_R_FM Steel Configured

20_R_PBOPBO

Configured30_SM_PBO

30Smooth

30_R_PBO Configured

d=26

5

a=800 a=800

D6 stirrups

Bolts D10

a/d=3.0

320

240t=20

30_R20_R32

0

t=20240

t=30

330

260

20_SM 30_SM

3D25SBPD930Longitudinal reinforcement

CL

Test result: Fiber type, UFC formwork thickness and interfaceNo.7

0306090

120150180210

0 2 4 6 8 10 12

Shea

r for

ce (k

N)

Deflection (mm)

R_FM R_PBO SM_PBOt =20 mm

0306090

120150180210

0 2 4 6 8 10 12

Shea

r for

ce (k

N)

Deflection (mm)

R_PBO SM_PBOt =30 mm

Step1. Flexural crackinitiation

Step3. Diagonal crack

Step2. Flexural crackpropagation

Step4. Fiber bridging

1

23

4

Test result: A simple evaluation methodNo.8

Vcal

Vexp

VcalVexp

VcalVexp

0

50

100

150

200

250

Shea

rfor

ce(k

N) SM_PBO R_PBO

R_FM

VcalVexp

Vcal Vexp

0

50

100

150

200

250

Shea

r for

ce (k

N)

SM_PBOR_PBOt =30 mm

35%44%

20%

28%3%

Calculated shear capacityV Total =VUFC +VC

Vrpc = 0.18(𝑓 'c)1/2ꞏbpd

VUFC = Vrpc +Vf

Vf = (𝑓v/ tan𝛽 )ꞏbpz

VC=0.20𝑓′c13 100pw

13(

1000d

)14 (0.75+

1.4a d⁄ )bwd

Niwa et al.

bp

2bp

2

• Shear carried by UFC

• Shear carried by concrete (Vc)

t =20 mm

Vrpc

Vf

VUFC

βu

VC

VC

New assumption for the shear calculationNo.9

Smooth : Since RC and UFC arenot bonded to each other and theshear contribution of RC was notimproved by UFC. VC=0.

VTotal = VUFC

Configured : Since RC and UFCwere bonded, the shear carried byRC was supported by UFC.However, VC could not work asmuch as its original capacity.

VTotal = VUFC +20%VC

Specimen name VC (kN) VUFC (kN) VTotal (kN) Vexp (kN) Vexp/VTotal

20_SM_PBO 75.8 93.6 93.6 113.6 1.2120_R_FM 77.2 135.8 178.8 135.0 0.75

20_R_PBO 71.8 173.7 188.1 197.2 1.0430_SM_PBO 74.5 128.9 128.9 198.8 1.5430_R_PBO 77.5 140.9 156.4 159.4 1.02

RC

UFC

RC

UFC

ConclusionsNo.10

1. With the increase in PBO fiber volume content,compressive strength tended to be decreased and thecracking strength was slightly increased.

2. The shear capacity of UFC-RC hybrid beam with steelfiber showed the higher capacity than that of specimenwith PBO fiber.

3. The thickness of UFC permanent formwork highly affectedthe shear capacity.

4. The shear capacity of RC beams with UFC permanentformworks could not be evaluated by a simple evaluationmethod. The calculated values were up to 44% higher thanthe experimental values.