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.
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
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 Testing
Denison 5000 kN testing machine
Apparatuses used for concentric and eccentric 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
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