Behaviour of High Strength Concrete Columns Reinforced with GFRP

Bars and Helices under Different Loading Conditions

By

Hayder Alaa Hasan

A/P Muhammad Hadi

Dr. Neaz Sheikh

21/1/2016

Contents

Introduction

Objectives

Literature Review

Research significant

Experimental Program

Expected Outcomes

Summary

Objectives

• Evaluating the behaviour of high strength concrete columns reinforced with

longitudinal GFRP bars and transversally with GFRP helices through testing twenty

specimens under several monotonic loading techniques (concentric and eccentric as

well as flexural)

• Examining the effects of using steel fibre on ductility and total carrying capacity of

GFRP reinforced high strength concrete columns.

• Developing sets of interaction moment diagrams for circular cross section GFRP-HSC

column which will help in determining the axial load and bending moment capacities

of such types of columns

• Proposing an analytical model to predict the axial carrying capacity of concrete

compression members reinforced with GFRP bars.

Basic material components of FRP composite

Fibres Polymers

Matrix

Literature Review

Anti Corrosion Light Weight and

Non-Magnetic

High longitudinal Tensile Strength

Low Thermal and Electric

Conductivity

GFRP Advantages

Literature Review

Low Modulus of Elasticity

No clear Yield Point Before

Brittle Rupture

Low Transverse Strength

Susceptible to Fire

GFRP Disadvantages

Literature Review

varies with

type of

reinforcing

fibre

depending on

matrix type and

concrete cover

thickness

varies with sign and direction of

loading relative to fibres

Stress

Strain

GFRP

Steel

Concrete

Idealized stress strain curves for steel and GFRP

𝑓𝑓𝑢

𝑓𝑦

𝜀𝑦 𝜀𝑓𝑢 𝜀𝑠𝑢

Literature Review

Tensile strengths of GFRP ranging between (1000-1800MPa) and vary

with diameter with a 40% reduction for diameter increases of 9.5 to

22 mm

Compressive strengths are 30 – 50% of the tensile strengths

Literature Review

Design Guidelines

ACI 440.1R-06 CSA-S806(2012)

𝑃𝑜 = 0.85𝑓𝑐′ 𝐴𝑔 − 𝐴𝑓𝑟𝑝

Does not recommend using

FRP bars as longitudinal

reinforcement in

compression members

Literature Review

Existing Studies

𝑃𝑜 = 0.85𝑓𝑐′ 𝐴𝑔 − 𝐴𝑓𝑟𝑝 + 0.35𝐴𝑓𝑟𝑝𝑓𝑓𝑢

GFRP reinforced concrete

columns have approximately

10-13% lesser nominal axial

load carrying capacity than

steel reinforced concrete

columns

Typical concrete stress-strain curves in concrete (Wight and MacGregor (2009)

Axial stress vs. axial strain and lateral strain for concrete (Ahmad and Shah

(1982)

0

500

1000

1500

2000

2500

3000

3500

4000

0 5000 10000 15000 20000 25000 30000

Axial Strain 𝜇𝜀

Lo

ad (

kN

)

GFRP Reinforced Concrete Column

∆𝑆 1 The effect of GFRP reinforcement on the column compressive

strength

∆𝑆 1

Steel Bars Reinforced Concrete Column

40

difference 𝑖𝑛 𝑑𝑢𝑐𝑡𝑖𝑙𝑖𝑡𝑦

Afifi et al. (2013)

Due to the linear elastic behaviour of FRP bars, FRP reinforced members shows

no ductility as defined in the steel reinforced structures. Accordingly, To

improve the ductility of concrete members reinforced with FRP rebars, two

approaches are adopted:

1. Using the hybrid FRP rebar formed by combining two or more different FRP

reinforcing materials to simulate the behaviour of the steel rods.

2. Improve the property of the concrete. Where, ACI 440-2006 recommends the

FRP reinforced structures to be designed to fail by the concrete crushing rather

than by FRP rupture. Thus, the ductility of the system is dependent on the

concrete properties.

Literature Review

Tensile

strength

(MPa)

Length (𝒍)

(mm)

Diameter

(𝒅) (mm)

Aspect

ratio

𝒍 𝒅

Form Surface Melting point

(0C)

2500 13 0.2 65 Straight Brass

coated 1500

Steel Fibres

control

1%

2%

3%

Smooth steel fibres l/d = 83

Typical Compressive Stress-Strain Response of Steel fibre

Reinforced Concrete ACI-544-2008.

Literature Review

0 5000 10000 15000 20000

69

55

41

27

14

Axial Strain

Com

pre

ssiv

e st

ress

MPA

Research Significance

• This study aims to expand the understanding of the compression behaviour of

concrete columns internally reinforced with FRP bars.

• The GFRP reinforced high strength concrete columns has not been studied yet.

• The advantages of using steel fibre has not been addressed.

Therefore, high strength concrete columns reinforced with GFRP bars and helices

are investigated in this study. In addition, the effect of using steel fibres as a

solution to enhance the load carrying and ductility capacity of GFRP reinforced

HSC columns are established.

Experimental Plan

Design of

Specimens

Specimens

Preparation

Specimens

Testing

Expected

Outcomes

Experimental Plan - Design of Specimens

Main

Parameters

Type of

Internal

Renf. Steel Bars

and

Helices

GFRP Bars

and

Helices

GFRP

Renf. with

Steel fibre

Loading

Conditions

Concentric

Loading

Eccentric

Loading

Pure

Bending

Loading

Experimental Plan - Specimens Preparation

Experimental Plan – Specimens Testing

Denison 5000 kN testing machine

Apparatuses used for concentric and eccentric loading

Experimental Plan – Specimens Testing

Apparatuses used for flexural loading

Expected Outcomes

• The contribution of GFRP bars in the total carrying capacities of the

columns will be figured out. In addition, the effect of eccentric loads on the

performance of the GFRP high strength concrete columns will be clarified.

• The behaviour of GFRP high strength concrete columns under pure flexural

loads will also be assessed through testing a column specimen from each

group under four bending increasing loads.

• The efficiency of using GFRP helices in confining high strength concrete

columns will be examined. Accordingly, an analytical model will be

proposed to predict the stress-strain relationships of GFRP confined HSC

columns. Furthermore, interaction diagrams for GFRP-HSC columns with

circular sections will be prepared and drawn.

• Steel fibres will be added to eight GFRP-HSC columns and that will

contribute in studying the efficiency of using steel fibre in enhancing the

ductility of the system and its contribution in solving the brittleness issue

within the FRP bars in general and GFRP bars in particular

GFRP-HSC

Some researchers

investigated the

behaviour of

GFRP-NSC

Design codes and guidelines

don’t recommend reinforcing

concrete compression

members with GFRP bars

Summary

GFRP-HSC

Brittleness issue

in HSC and GFRP

Adding steel fibres in order

to increase the ductility and

enhance the performance of

the system

Hayder Alaa Hasan

2016