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STRUCTURAL RETROFITTING OF CONCRETE BEAMS USING FRP - Debonding Issues

Obaidat, Yasmeen LU (2011) In Report TVSM
Abstract (Swedish)
Popular Abstract in English

Concrete is one of our most common building materials and is used both for buildings,

bridges and other heavy structures. Typically, concrete structures are very durable, but

sometimes they need to be strengthened. The reason may be cracking due to environmental

effects, that a bridge is to be used for heavier traffic, new building codes, or damage resulting

from earthquakes.

Concrete is a material that can withstand compressive loads very well but is sensitive to

tensile forces. Therefore, concrete structures are typically reinforced by casting in steel bars in

areas where tension can arise. This cannot be done afterwards, and one... (More)
Popular Abstract in English

Concrete is one of our most common building materials and is used both for buildings,

bridges and other heavy structures. Typically, concrete structures are very durable, but

sometimes they need to be strengthened. The reason may be cracking due to environmental

effects, that a bridge is to be used for heavier traffic, new building codes, or damage resulting

from earthquakes.

Concrete is a material that can withstand compressive loads very well but is sensitive to

tensile forces. Therefore, concrete structures are typically reinforced by casting in steel bars in

areas where tension can arise. This cannot be done afterwards, and one strengthening method,

is therefore to glue reinforcement on the exterior of the structure in the areas exposed to

tension.

Fibre composite can be used in reinforcing concrete structures externally. Fibre composite

materials have low density, can be easily installed and are easy to cut to length on site.

Therefore, fibre composite as external reinforcement for concrete structures has become very

attractive and popular around the world.

It is important to understand the behaviour of a strengthened structure well and realize

what parameters affect the failure mode and load-bearing capacity. The aim of this thesis is

therefore to investigate and improve the understanding of the behaviour of reinforced concrete

beams strengthened with fibre composite.

These structures have a critical problem implying that they may fail in a sudden manner.

This failure involves separation between composite and concrete. Special attention is paid to

this phenomenon, which is called debonding.

One scope of this study was to develop computer modelling framework. Therefore, three

dimensional computations were conducted considering the nonlinear behaviour of the

materials. A new model for the concrete-fibre composite interface was included.

The computations were verified against experiments. The results confirmed the ability of

the computations to recreate the load-deflection behaviour, the crack distribution, and the

failure modes. Simulations and experiments showed that application of fibre composite can

increase the load capacity and the stiffness of the beams.

The influence of several parameters such as length and width of fibre composite and

properties of adhesive were investigated. Large width and length of fibre composite and soft

adhesive would yield to reduce tendency of debonding and increase thus of the utilization of

fibre composite and increase load capacity.

The findings from this study yield a proposal for a modification of design code rules. (Less)
Abstract
A 3D nonlinear finite element analysis modelling framework was developed for simulating

the behaviour of beams retrofitted with fibre reinforced polymer (FRP). The ABAQUS

program was used for this purpose. Concrete was modelled using a plastic damage model.

Steel bars were modelled as an elastic perfectly plastic material, with perfect bond between

concrete and steel. A cohesive model was used for modelling the FRP-concrete interface.

Bond properties needed as input to the cohesive model, such as initial stiffness, shear strength

and fracture energy were proposed based on fitting FEM results to experimental results from

literature. Initial stiffness was related to the adhesive... (More)
A 3D nonlinear finite element analysis modelling framework was developed for simulating

the behaviour of beams retrofitted with fibre reinforced polymer (FRP). The ABAQUS

program was used for this purpose. Concrete was modelled using a plastic damage model.

Steel bars were modelled as an elastic perfectly plastic material, with perfect bond between

concrete and steel. A cohesive model was used for modelling the FRP-concrete interface.

Bond properties needed as input to the cohesive model, such as initial stiffness, shear strength

and fracture energy were proposed based on fitting FEM results to experimental results from

literature. Initial stiffness was related to the adhesive properties. Shear strength and fracture

energy were expressed as functions of tensile strength of concrete and of adhesive properties.

Experimental tests were performed to investigate the behaviour of retrofitted beams. The

model was verified through comparison with the experimental data regarding failure mode

and load-displacement behaviour.

The influence of several parameters such as length and width of FRP and properties of the

adhesive were investigated. The result showed that when the length of FRP increases, the load

capacity of the beam increases for both shear and flexural strengthening. The result also

showed that the FRP to concrete width ratio and the stiffness of FRP affect the failure mode

of retrofitted beams. The maximum load increases with increased width ratio. Increased FRP

stiffness increases the maximum load only up to a certain value of the stiffness, and thereafter

the maximum load decreases. The maximum load also increases when the stiffness of

adhesive decreases.

An improvement of the calculation of interfacial shear stress at plate end in a design rule

for simply supported beams bonded with FRP was proposed. The proposed design rule was

applied to an existing defective beam and the result was verified using the FEM model. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Täljsten, Björn, Luleå tekniska universitet, Luleå
organization
publishing date
type
Thesis
publication status
published
subject
in
Report TVSM
pages
163 pages
publisher
Department of Construction Sciences, Lund University
defense location
Lecture hall V:C, V-building, John Ericssons väg 1, Lund University Faculty of Engineering
defense date
2011-12-06 10:15
ISSN
0281-6679
ISBN
978-91-7473-194-1
language
English
LU publication?
yes
id
e731ca6b-e517-4e8d-9a83-4fde23a310a0 (old id 2203666)
date added to LUP
2011-11-14 09:51:03
date last changed
2016-09-19 08:44:45
@phdthesis{e731ca6b-e517-4e8d-9a83-4fde23a310a0,
  abstract     = {A 3D nonlinear finite element analysis modelling framework was developed for simulating<br/><br>
the behaviour of beams retrofitted with fibre reinforced polymer (FRP). The ABAQUS<br/><br>
program was used for this purpose. Concrete was modelled using a plastic damage model.<br/><br>
Steel bars were modelled as an elastic perfectly plastic material, with perfect bond between<br/><br>
concrete and steel. A cohesive model was used for modelling the FRP-concrete interface.<br/><br>
Bond properties needed as input to the cohesive model, such as initial stiffness, shear strength<br/><br>
and fracture energy were proposed based on fitting FEM results to experimental results from<br/><br>
literature. Initial stiffness was related to the adhesive properties. Shear strength and fracture<br/><br>
energy were expressed as functions of tensile strength of concrete and of adhesive properties.<br/><br>
Experimental tests were performed to investigate the behaviour of retrofitted beams. The<br/><br>
model was verified through comparison with the experimental data regarding failure mode<br/><br>
and load-displacement behaviour.<br/><br>
The influence of several parameters such as length and width of FRP and properties of the<br/><br>
adhesive were investigated. The result showed that when the length of FRP increases, the load<br/><br>
capacity of the beam increases for both shear and flexural strengthening. The result also<br/><br>
showed that the FRP to concrete width ratio and the stiffness of FRP affect the failure mode<br/><br>
of retrofitted beams. The maximum load increases with increased width ratio. Increased FRP<br/><br>
stiffness increases the maximum load only up to a certain value of the stiffness, and thereafter<br/><br>
the maximum load decreases. The maximum load also increases when the stiffness of<br/><br>
adhesive decreases.<br/><br>
An improvement of the calculation of interfacial shear stress at plate end in a design rule<br/><br>
for simply supported beams bonded with FRP was proposed. The proposed design rule was<br/><br>
applied to an existing defective beam and the result was verified using the FEM model.},
  author       = {Obaidat, Yasmeen},
  isbn         = {978-91-7473-194-1},
  issn         = {0281-6679},
  language     = {eng},
  pages        = {163},
  publisher    = {Department of Construction Sciences, Lund University},
  school       = {Lund University},
  series       = {Report TVSM},
  title        = {STRUCTURAL RETROFITTING OF CONCRETE BEAMS USING FRP - Debonding Issues},
  year         = {2011},
}