Main Roads
Technical Standard
MRTS 69A
Design of Fibre Reinforced
Polymer (FRP) Composite
Girders
August 2012
IMPORTANT INFORMATION
The requirements of this document represent Technical Policy of the department and contain Technical
Standards. Compliance with the department’s Technical Standards is mandatory for all applications for the
design, construction, maintenance and operation of road transport infrastructure in Queensland by or on
behalf of the State of Queensland.
This document will be reviewed from time to time as the need arises and in response to improvement
suggestions by users. Please send your comments and suggestions to the feedback email given below.
FEEDBACK
Your feedback is welcomed. Please send to mr.techdocs@tmr.qld.gov.au.
COPYRIGHT
© State of Queensland (Department of Transport and Main Roads) 2009
Copyright protects this publication. Except for the purposes permitted by and subject to the conditions
prescribed under the Copyright Act, reproduction by any means (including electronic, mechanical,
photocopying, microcopying or otherwise) is prohibited without the prior written permission of the
department. Enquiries regarding such permission should be directed to the Road & Delivery Performance
Division, Queensland Department of Transport and Main Roads.
DISCLAIMER
This publication has been created for use in the design, construction, maintenance and operation of road
transport infrastructure in Queensland by or on behalf of the State of Queensland.
Where the publication is used in other than the department’s infrastructure projects, the State of Queensland
and the department gives no warranties as to the completeness, accuracy or adequacy of the publication or
any parts of it and accepts no responsibility or liability upon any basis whatever for anything contained in or
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If the publication or any part of it forms part of a written contract between the State of Queensland and a
contractor, this disclaimer applies subject to the express terms of that contract.
August 2012
Department of Transport and Main Roads
Technical Standard
MRTS 69A
Fibre Composite Girders
Table of Contents
Page
1
SCOPE AND APPLICATION ......................................................................................................................1
1.1
Scope ...................................................................................................................................................1
1.2
Definition of Terms ...............................................................................................................................1
1.3
Referenced Documents .......................................................................................................................1
1.4
Notation ................................................................................................................................................1
1.5
Use of Alternative Materials or Methods ..............................................................................................2
2
DESIGN REQUIREMENTS AND PROCEDURES .....................................................................................2
2.1
Design Requirements...........................................................................................................................2
2.1.1
Aim ................................................................................................................................................2
2.1.2
Fundamental requirements and warning of failure .......................................................................2
2.1.3
Design for Ultimate Limit States (ULS) .........................................................................................3
Design for Serviceability Limit States (SLS) ........................................................................................3
2.1.4 ............................................................................................................................................................3
2.1.5
Design for Stability ........................................................................................................................3
2.2
Strength ................................................................................................................................................4
2.3
Durability ..............................................................................................................................................5
2.4
Design Life ...........................................................................................................................................5
2.5
Fire Resistance ....................................................................................................................................5
3
LOADS AND LOAD COMBINATIONS FOR STABILITY, STRENGTH AND SERVICEABILITY ...............6
3.1
Load Types ..........................................................................................................................................6
3.1.1
Vehicle Loads ...............................................................................................................................6
3.1.2
Other Loads ..................................................................................................................................6
3.2
Load Combinations ..............................................................................................................................6
4
MATERIAL PROPERTIES ..........................................................................................................................6
4.1
General ................................................................................................................................................6
Reinforcement .........................................................................................................................................7
4.2 ...................................................................................................................................................................7
4.2.1
Fibres ............................................................................................................................................7
4.2.2
Rovings .........................................................................................................................................7
4.2.3
Mats –Continuous Filament Mats .................................................................................................7
4.3
Matrices ................................................................................................................................................8
4.3.1
Polymer Matrices ..........................................................................................................................8
4.3.2
Acceptable Resins ........................................................................................................................8
4.4
Cores ....................................................................................................................................................9
4.5
Gel Coats .............................................................................................................................................9
4.6
Additives ...............................................................................................................................................9
4.7
FRP Pultruded Profile Sections ...........................................................................................................9
4.8
Lamina ...............................................................................................................................................10
5
METHODS OF ANALYSIS ........................................................................................................................10
6
BEAMS – STRENGTH AND SERVICEABILITY .......................................................................................10
6.1
General ..............................................................................................................................................10
6.2
Lateral Stability...................................................................................................................................11
6.3
Stiffness Criteria .................................................................................................................................11
6.3.1
Individual Girder Replacement ...................................................................................................11
6.3.2
Replacement of Three or More Girders ......................................................................................11
6.4
Ductility ...............................................................................................................................................11
6.5
Fatigue ...............................................................................................................................................11
Vibration .................................................................................................................................................12
6.6 .................................................................................................................................................................12
6.7
Temperature Effects...........................................................................................................................12
6.8
Thermal expansion.............................................................................................................................12
6.9
Creep and Shrinkage .........................................................................................................................13
7
END ZONES – SUPPORT DESIGN .........................................................................................................13
7.1
General ..............................................................................................................................................13
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8
CONNECTIONS ....................................................................................................................................... 13
8.1
General .............................................................................................................................................. 13
8.2
Cutting and Drilling ............................................................................................................................ 14
8.3
Holes ................................................................................................................................................. 14
8.4
Edge Distance ................................................................................................................................... 14
9
SUPPLEMENTARY REFERENCE .......................................................................................................... 14
Design of Fibre Reinforced Polymer (FRP) Composite
Girders
1
SCOPE AND APPLICATION
1.1
Scope
This Standard applies to the design of Fibre Reinforced Polymer (FRP) composite girders
for replacement of timber girders or entire bridge decks as part of the timber bridge
renewal scheme.
Design shall be in accordance with the Eurocomp Design Code and Handbook entitled,
‘Structural Design of Polymer Composites’ edited by John L. Clarke except where
specified herein.
This Technical Standard shall be read in conjunction with MRTS01 Introduction to
Technical Standards, MRTS50 Specific Quality System Requirements and other Technical
Standards as appropriate.
This Technical Standard forms part of the Main Roads Specifications and Technical
Standards Manual.
1.2
Definition of Terms
The terms used in this Standard shall be as defined in Clause 3 of MRTS01 Introduction to
Technical Standards.
1.3
Referenced Documents
Table 1 lists documents referenced in this Technical Standards.
Table 1 - Referenced Documents
Reference
Title
Eurocomp,1996 “Structural Design of Polymer Composites” – Eurocomp Design Code
and Handbook (J. Clarke, ed.), E & F Spon, London.
Structural
Engineering
Document 7 2003
Use of Fibre Reinforced Polymers in Bridge Construction, International
Association for Bridges and Other Structures, Zurich, Switzerland
Bank L (2006)
Heger et
al.(1984)
Composites for Construction – Structural Design with FRP Materials
Structural Plastic Design Manual, Manual of Engineering Prac. No.63,
ASCE, New York, N.Y.
1.4
Notation
The symbols used in this Standard are listed in Table 2.
Table 2 Notation
Symbol
Description
FRP
Fibre Reinforce Polymer or Fibre Reinforced Plastic
GFRP
Glass Fibre Reinforced Polymer

Strength Reduction Factor/Resistance Factor
Clause
Reference
2.2
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MRTS69A
Fibre Composite Girders
Ktest
Reduction factor used in the absence of sufficient test 2.2
samples
Ro
Reference Strength/Characteristic Strength
Rtest
1.5
Department of Transport and Main Roads
Technical Standard
2.2
Minimum Test Strength in the absence of sufficient test
samples
Ru
Ultimate Design Strength
2.2
S*
Design action effects (i.e., effects due to load)
2.2
Vf
Fibre Volume Fraction
4.8
EI
Stiffness of the Girder
8.8
Use of Alternative Materials or Methods
This specification is not intended to prevent the use of materials or methods other than
those mentioned herein, however, any deviation is to be approved by the Deputy Chief
Engineer (Structures).
2
2.1
DESIGN REQUIREMENTS AND PROCEDURES
Design Requirements
2.1.1 Aim
The objectives of the bridge designer are that the structure he/she designs shall be safe,
durable, serviceable, constructible, economical and aesthetic. Bridges made of FRP
composites must meet or exceed the expectations for bridges made of traditional materials
for all of these objectives. In order to achieve this for FRP Composites, a technically
sound, valid approach based on research, existing performance data, experience, and
sound engineering rationale are required.
2.1.2 Fundamental requirements and warning of failure
EUROCOMP Design Code section 2.1 covers this section:
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
Structures made with FRP composites shall be designed to give reasonable
and adequate warning of failure prior to reaching an ultimate limit state.

In general, FRP composites exhibit little or no ductile behaviour beyond a
point of linear stress-strain behaviour of the material. The design should take
account of this behaviour by ensuring that a serviceability limit state is reached
prior to its ultimate limit state for the mode of failure being considered.

The design shall avoid the below occurring at serviceability load:
-
excessive deflection/deformation
-
buckling or wrinkling
-
local damage under normal service conditions
-
environmental damage
2.1.3 Design for Ultimate Limit States (ULS)
The strength ULS shall relate to the Ultimate Strength of the girder and shall satisfy
the following:
The GFRP sections shall not exceed of their ULS capacities at a strain of 0.009
(ultimate tensile strain*60% = 0.015*0.6), see Figure 1.
Figure 1: ULS and SLS strain limitations
Resin dominated failure modes shall not be permitted.
In addition to the above, FRP composite structures should be designed for ultimate
limit states in accordance with the requirements of Clause 4.1 of Eurocomp Design
Code.
2.1.4
Design for Serviceability Limit States (SLS)
At the SLS the girders shall satisfy the following conditions.
Strain in GFRP shall not exceed 0.001. This will apply to pultrusions as well as
sections made out of different manufacturing processes, see Figure 1.
Fibre composite structures should be designed for serviceability limit states in
accordance with the requirements of Clause 4.2 of Eurocomp Design Code.
2.1.5 Design for Stability
Fibre composite structures should be designed for stability in accordance with
Eurocomp Clause 4.7.
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Fibre Composite Girders
Department of Transport and Main Roads
Technical Standard
2.2 Strength
The FRP composite girders shall be designed for strength as follows:
(a) The most adverse design load combinations shall be determined in accordance
with the following load factors and the modifications provided in Section 3 of this
specification.
The following load factors shall be used in determining the design action effects
Action
Ultimate Limit State Serviceability Limit State
Load Factor
Load Factor
Dead Load
1.2
1.0
Super Imposed Dead 2.0
Load
1.3
Traffic Load
2.0
1.0
Crane Load
2.0
1.0
Number of Standard Lane Modification Factor
Design
Lanes
Loaded
1
1.0
2
0.9
Dynamic Load allowance shall be 0.4
Dynamic Load allowance for crane load shall be 0.25
(b) The design action effects S* of these loads shall be determined by an appropriate
analysis to consider real traffic load conditions.
(c) Ro shall be the characteristic strength determined from laboratory tests (a testing
program is mandatory, the number of test to be carried out to be agreed before).
(d) Ro, the characteristic strength is determined by the following equation:
Characteristic strength = mean strength – 1.64 (standard deviation). (Eurocomp
Design Code 4.11)
The ultimate design strength =  Ru =  Ro
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August 2012
In the absence of sufficient statistical samples:

Ktest = 0.75 when less than 5 samples are used

Ktest = 0.85 when more than 5 samples are used
Characteristic Strength = Ro = Ktest * Rtest
Where, Rtest = Minimum test strength in the absence of sufficient test samples
The ultimate design strength =  Ru =  Ro = Ktest * Rtest,
(e) The member shall be proportioned so that the design strength is greater than or
equal to design action effect, i.e.,
Ru > S * .
 Ktest Rtest  S *
The strength reduction factor specified for FRP Girders is as follows:
 = 0.25 – 0.65, where the lower bounds corresponds to brittle failure.
2.3 Durability
FRP Composites are prone to deterioration in acidic environments. Creep rupture
and stress corrosion are two consequences of exposure to acidic environments. UV
resistance of some resins is low and it is recommended that appropriate measures
be taken by the manufacturer to shield the FRP composite girders from deterioration.
The only true test for durability is the in-service highway bridge. FRP composites
deteriorate with environmental exposure and repeated application of load. This
degradation of Young’s modulus of Elasticity, E, has been measured experimentally
in accelerated durability tests for various FRPs. FRP composites components shall
be designed using a degraded E value estimated for the end of the design life.
2.4 Design Life
The required design life of fibre composite girders is dependant upon their
application. The following table outlines the requirements.
Table 3 Required Design Life
Application
Replacement Elements
Required Design Life
30 Years
Deck Replacement
50 Years
New Structures
100 Years
2.5 Fire Resistance
FRP composites are not inherently fire-resistant. Issues such as combustibility, spread of
flame, changes in mechanical properties and toxic fumes need to be considered.
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Fibre Composite Girders
Department of Transport and Main Roads
Technical Standard
Performance in a fire is generally improved by increased glass fibre content. The use of
fire retardant resins or addition of additives to the resin improves fire retardation.
Therefore a suitable fire retardant coating or a fire retardant resin or a fire retardant
additives to the resin shall be proposed for the FRP composite girders and the fabricator
shall achieve the Fire Resistance Level of 90/-/- for the FRP girders.
Fire testing on FRP composite beams shall be carried out in accordance with section 6 of
AS 1530.4 - methods for fire tests on building materials, components and structures. For
the structural adequacy, the load for the fire test shall be service load and deem to satisfy
the deflection criteria stipulated in section 2.12.1 of AS1530.4.
3
LOADS AND LOAD COMBINATIONS FOR STABILITY, STRENGTH AND
SERVICEABILITY
3.1 Load Types
3.1.1 Vehicle Loads
The Timber Bridge renewal program is targeted for Class A timber bridges.
The required loading for the FRP Composites are:
1) Class A loading
2) General Mass Limit (GML) 123 Tri-Axle 42.5 ton Semi Trailer
3) GML Road Train.
3.1.2 Other Loads

T44 loading

17T per line of Heavy Load Platform (HLP)

48T moving crane
3.2 Load Combinations
Load combinations shall be in accordance with section 2.2.
4
MATERIAL PROPERTIES
4.1 General
To produce FRP composite materials, two primary raw material constituents are required,
reinforcing fibres and a polymer resin matrix. As the components of composite materials
are fundamental to the behaviour of the composite in a structure and as the specification
of the material may change, the designer should always seek specialist advice from
polymer, reinforcement and manufacturing supplier or technical specialist.
FRP composite girders are manufactured in different ways: a) assemblage of only FRP
pultruded profile sections by means of gluing, b) assemblage of FRP pultruded profile
sections, FRP panels and steel in a hybrid section, c) assemblage of FRP pultruded
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profile section, steel, concrete, lightweight foaming in to a hybrid, and d) by means of
vacuum assisted resin infusion process.
The manufacturer shall provide test results of fibre, laminates, coupon test of FRP
pultruded profile section (web/flange) in the longitudinal and transverse direction. The
number of samples shall not be less than five (5) for any given property. The test shall be
carried out a NATA approved laboratory. The testing method shall comply with all relevant
standards, including ASTM standards.
Reinforcement
4.2
4.2.1 Fibres
In FRP materials, fibres provide both load carrying capacity and stiffness to the
composites. The most widely used fibres in civil engineering today are glass fibres.
With glass fibres, only the following types are permitted for use (compliance with
Eurocomp code):

E-glass (* refer note)

ECR-glass
The following table is an extract from Eurocomp Design Code and shall be used in design
of fibre composite girders.
* E-glass shall not be used in the following situations:

Members in salt-rich arid areas

In sea water – in tidal or splash zone

In soft or running water
Table 4 Typical Properties of fibres before processing
E-glass ECR-glass
Specific Gravity
2.54
2.71
Tensile Strength MPa
(22˚C)
3400
3300
Tensile Modulus GPa
(22˚C)
72
72
Elongation %
4.8
4.8
Coefficient of Thermal
Expansion
5.0
5.9
10^-6/ ˚C
.
4.2.2 Rovings
Any use of rovings shall be in accordance with ISO 2797 or equivalent: Glass Fibre
rovings for the reinforcement of polyester and epoxy resin systems.
4.2.3 Mats –Continuous Filament Mats
Any use of Continuous Filament Mats shall be in accordance with ISO 2559 or
equivalent:
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4.3
Department of Transport and Main Roads
Technical Standard
Matrices
4.3.1 Polymer Matrices
The fibre provides the actual load bearing function and stiffness to the composite. The
polymer matrix has the following functions:
-
fixing the fibres in the desired geometrical arrangement,
-
transferring the force to the fibres,
-
preventing the buckling of the fibres under compressive actions,
-
protecting the fibres from humidity, rain, fluids etc.
-
help resist fatigue
-
protecting the composite from UV degradation and weathering
Two types of polymer materials are identified, which are used as the matrices for
composite materials: thermoplastics and thermosetting polymers. For FRP structures
today mainly thermosetting polymers are used as the matrix. Thermosetting polymers
are a class of polymers that are worked in a liquid state and then chemically reacted
to form a cured, solid state.
The most common thermosets in use are unsaturated polyester resins, epoxy resins
and more seldom vinyl ester resins.
A knowledge of the service temperature is vital in selecting an appropriate stable resin
system. If the service temperature is closer to the heat distortion temperature, as with
all polymers loss of stiffness and significant creep will occur.
Control of the curing process and attainment of full cure of the polymer is essential for
attaining optimum mechanical properties, preventing heat softening, limiting creep,
reducing moisture diffusion and minimising plasticisation effects.
The selection and design of polymer resins is a critical aspect of the design of fibre
composite girders. Selection shall be in accordance with the provisions of Eurcomp
Design Code.
4.3.2 Acceptable Resins
The following types of resins are acceptable to be designed in accordance with the
properties and limits set out in Eurocomp Design Code.
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
Polyester Resins

Vinyl Ester Resins

Phenolic Resins

Epoxy Resins
The material properties of resins are shown below in Table 5.
Table 5 Minimum Required Properties of Resin
Property
Units
Polyester
Epoxy
Vinyl Ester
Phenolic
Resin
Resin
Resin
Resin
Tensile Strength
MPa
70
70
70
4070
Young’s Modulus
GPa
2-3
2-4
3.2-3.9
1.5-2.5
%
4
4
4
4
g/cm3
1.2-1.3
1.2-1.3
1.12
1.24
oC
90
120 90
110 90
120 90
%
5
2.5
5
5
Flexural Elongation
at Failure
Density
Heat Distortion
Temperature
Shrinkage (max)
4.4
Cores
Core materials may be load bearing or used as formers for shaping fibre composite
girders. Structural cores should be used for efficient sandwich construction. These
may be foam, honeycomb or solid materials.
4.5
Gel Coats
Gel coats are added to the surface of a composite structure for a variety of reasons: to
filter out ultraviolet radiation and improve weathering, to add flame retardency to
provide an increased thermal barrier, to improve chemical resistance, to improve
erosion, to provide an increase barrier to moisture, or to provide colour scheme and
improve general finish. Gel coats are to be considered non structural. The fabricator
to specify the appropriate gel coats for the structure.
4.6 Additives
Additives including, but not limited to, fillers, pigments and flame retardants are acceptable
for use. Their use should fully consider effects on the composite’s structural properties.
Fillers are added to the resin to reduce shrinkage, to reduce peak exotherm during cure, to
increase viscosity, to increase local harness, to reduce flammability. They can increase
modulus and compressive strength and may be included in surface coating for improving
specific properties.
4.7 FRP Pultruded Profile Sections
FRP pultruded profile sections come in many forms, square hollow section, rectangular
hollow section, circular hollow sections, and I sections.
Table 6 shows the typical mechanical properties of pultruded shapes.
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Fibre Composite Girders
Department of Transport and Main Roads
Technical Standard
Table 6 Typical Mechanical Properties of FRP Pultruded Profiles Sections
Property
Units
Parallel to fibre
Transverse to fibre
Tensile Strength
MPa
400-700
50-60
Tensile Modulus
GPa
20-40
5-9
Compressive Strength
MPa
200-550
Compressive Modulus
GPa
20-40
Shear Strength
MPa
30-85
Shear Modulus
GPa
3-7.5
Density
g/cm3
1.8-2
% Volume
30-60
Fibre Content
4.8 Lamina
Table 7 illustrates the lamina material constants for different fibre volume fractions which
can be used.
Table 7 Lamina Material Constants for Different Fibre Volume Fractions
Vf = 0.3
Vf = 0.4
Vf = 0.5
Vf = 0.6
E11 (MPa)
23500
30500
37500
44500
E22 (MPa)
6000
7000
8400
10500
G12 (MPa)
2230
2600
3120
3900
v12 (MPa)
0.35
0.33
0.31
0.29
5
METHODS OF ANALYSIS
Analysis shall be in accordance with Eurocomp Design Code Section 2.5.
6
BEAMS – STRENGTH AND SERVICEABILITY
6.1 General
FRP composite materials generally remain linear elastic up to the point of brittle failure
mode. FRP structural components are anisotropic rather than isotropic. The constitutive
properties of these materials can vary in each direction, and are a function of the specific
composition of the material. In the case of glass Fibre reinforced composites, the strength
and stiffness properties are typical function of the fibre volume ratios and the specific
orientation of the fibre.
The strength of the FRP composite Beam shall be determined from strain compatibility and
the constitutive material properties. However, the theoretical strength computed, based on
various strength theories, needs to be verified by testing to confirm the actual strength.
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Fibre composite girders are required to be designed in accordance with Eurocomp Design
Code as well as with the provisions of Section 6.
6.2
Lateral Stability
Girders shall be designed to be independent and not require lateral stiffeners. FRP
composite girders shall be designed such that it is torsionally stable in the lateral direction.
6.3
Stiffness Criteria
The required stiffness of FRP composite girders is dependant upon the application. For
cases where only a single timber girder is to be replaced, refer to section 6.3.1. For cases
where three (3) or more girders are being replaced refer to section 6.3.2.
6.3.1 Individual Girder Replacement
FRP composite girders to be used to replace an individual timber girder shall be designed
to meet the requirements of Table 8 below.
Table 8 Stiffness Criteria - Individual Replacement
Replacement Timber Girder Size
Target FRP Composite Stiffness
19 inch
3.5*1013 Nmm2 ± 10%
17 inch
2.9*1013 Nmm2 ± 10%
6.3.2 Replacement of Three or More Girders
FRP composite girders to be used to replace three (3) or more timber girders shall be
designed to meet the requirements of Table 9 below. The deflection limit is to be applied
for the average deflection of all girders on a bridge.
Table 9 Deflection Criteria - Three or More Girders
Serviceability
Live Load (1+a)LL ,
(1.0DL+1.3SIDL+(1+a)LL),
a =0.4
a = 0.4
Incremental Deflection shall be less than
Total Deflection shall
be less than
L/300
6.4
L/600
Ductility
The nature of FRP Composite material is such that they behave linear elastically until
failure and often result in brittle failure mode. It is recommended to engineer FRP
composite girders into a hybrid assembly such that the hybrid girders exhibit ductile failure
mode in the Ultimate Limit State case.
6.5
Fatigue
The FRP composite girders shall be designed and constructed such that, with an
acceptable level of probability, it is unlikely to fail as a result of fatigue loading or to require
repair of damage caused by fatigue.
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Technical Standard
Eurocomp Design Code section 4.13 sets out a methodology for fatigue assessment of
composites.
The following limit states shall be considered:

Serviceability: fibre debonding or resin cracking

Ultimate Limit State: failure of excessive local deformation of the component.
FRP composite girders are connected via bolt holes located at regular intervals along the
length of the member. Hence the fatigue behaviour of perforated FRP composite girders
shall be determined through adequate testing.
The Eurocomp Design Code limits the frequency of loading to 10Hz and the environmental
temperature is limited to 50oC. The frequency of loading is limited as the material heats up
at higher frequencies thus changing the failure mechanism.
Fatigue stress cycle of 1x106 at the serviceability limit state, at a normal strain of 0.1%
The SLS state limit of 0.1% normal strain at 1x106 shall be nominated to ensure that
fatigue meets the requirements of the Eurcocomp Design Code, Table 4.20.
6.6
Vibration
Road Bridge: All FRP Composite super structure:
The fundamental frequency of the road bridge (in the vertical direction) without live load
shall be greater than 5 Hz to avoid any issues associated with the first and second
harmonics. If the second harmonics is a concern, a dynamic computer analysis should be
performed
6.7
Temperature Effects
An important temperature related property of fibre composites is the glass transition
temperature (Tg). At temperatures above Tg composites soften from a glass-like state to a
rubbery state.
Fabricators to specify Tg for putlruded section and or sections made of different
manufacturing process as well as the adhesives used
It is essential to post cure the FRP product in order to ensure that optimum cure has been
achieved. The FRP products shall be post cured minimum two hours at a temperature
above the heat deflection temperature of the resin. Fabricators to specify the post cured
Tg for composite section.
Asphalt overlaying directly on FRP composite surfaces need adequate attention due to the
asphalt reaching the post cured Tg. Hence Tg shall not be less than 170oC corresponding
to Asphalt overlaying temperature.Lucy cranitch says that Tg of 170 will not be met by
most of the commonly used resins.
6.8
Thermal expansion
Most bridges experience daily and seasonal temperature variations causing material to
shorten with decreased temperatures and lengthen with increased temperature. The
temperature gradient is created when the top portion of the bridge gains more heat due to
direct radiation than the bottom. Because the strains are proportional to the temperature
change, a nonuniform temperature strain is introduced.
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Thermal coefficients of FRP composites vary greatly. The thermal transmissibility of
composites is not well documented and the differential temperature profile when exposed
to changing thermal sources (such as solar radiation) is not known.
The effects of difference in coefficient of thermal expansion between different materials
need to be considered. This included adhesives, steel, concrete, cores and FRP
composites.
The timber bridge super structure generally consists of a timber deck over laid with or
without asphalt placed on top of the timber girder. In a timber bridge renewal program, the
timber girders will be replaced with FRP composite. The decks are either timber or fibre
composites (subject to approval from TMR).
In a pilot study on a in-service FRP bridge located in a temperate Queensland region, the
maximum temperature gradient of 30oC was recoded between the top of the deck and the
soffit of the girder.
The designer shall incorporate in his design a linear thermal gradient of 20 oC or -10oC
over the depth of the deck and a constant temperature over the depth of the girder.
6.9
Creep and Shrinkage
Creep is mainly a property of the resin and creep is usually small in FRP composites.
Creep shall be incorporated into the design as per Eurocomp design code, Figure 4.13.
Shrinkage is not addressed in the Eurocomp design code and it is assumed that shrinkage
is not significant issue with fibre composites.
7
7.1
END ZONES – SUPPORT DESIGN
General
Eurocomp Design Code deals with stability of composite members in section 4.7. It covers
critical shear stress in the web, crushing of the web and buckling resistance. From the
characteristic strength properties of FRP composite elements it is possible to determine
the performance of girders at the support. Where this is not possible it is proposed that
reference be made to the Eurocomp Design Code. However end zone bearing can be
determined by testing.
8
8.1
CONNECTIONS
General
Connections shall be designed according to chapter 5 of the Eurocomp Design Code.
Bolted joints for shear and tension shall be designed according to section 5.2 and bonded
connections shall be designed according to section 5.3. For design methodology
Eurocomp Code shall be applied.
The FRP composite girders designed and fabricated for timber bridges shall accompany
the relevant connection details indicating how the FRP composite girders fit into the timber
bridge. The connection details are to be approved by TMR. It is the responsibility of the
FRP composite girder supplier/designer to submit the relevant calculations for verification.
Bolted connections shall be used for all main and secondary members. Connection shall
be adequately designed for forces and load transfer mechanisms to mitigate possible
failure modes. Galvanized or stainless steel bolts approved by TMR shall be used. In
addition, the adequacy of the connection can be determined by testing.
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8.2
Department of Transport and Main Roads
Technical Standard
Cutting and Drilling
The FRP composite girders are to be identified where drilling and sawing is permitted. The
limitation on cutting: cutting with a chain saw and cutting the girder in an angle shall be
addressed by the fabricator. Cutting of girders will expose fibres and sealing of cutting
edge shall be carried out by the site crew with the instruction from the fabricator.
The FRP composite girders manufactured shall have provision to drill on site as well at the
factory.
8.3
Holes
Holes are to be plugged with an approved sealant to avoid ingress of water and also to
prevent tearing of fibre due to bolt movement in the case of fatigue or other issues leading
to durability problems.
Girders are to meet the requirements of ULS and SLS even with holes considered.
It is mandatory to test perforated girders for fatigue loading. Fatigue test shall be carried
our for 1 million cycles, The fatigue load shall be 70% and 20% of the serviceability load.
After every 200,000 cycles, a spiking load of 100% serviceability load shall be applied
8.4 Edge Distance
A minimum edge distance 3*bolt diameter from the nearer edge of the hole to the physical
edge of the member shall be provided to protect against tear-out, web crushing or tensile
failure.
9
SUPPLEMENTARY REFERENCE
Guide for the Design and Construction of Structures made of FRP Pultruded Elements,
National Research Council of Italy, Rome, CNR-DT-205/2007
NHCRP Report 503, Application of Fibre Reinforced Plymer Composites to the Highway
Infrastructure, Transport Research Board, Washington D.C. 2003.
Chambers, R, ASCE Design Standard for Pultruded Fiber-Reinforced-Plastic (FRP)
Structures, J. of Composites for Construction, February 1997, pp. 26-38.
Ellingwood, B, Toward Load and Resistance Factor Design for Fiber-Reinforced Polymer
Composite Structures, J. of Structural Engineering, ASCE, April 2003. pp 409-458.
Bank, L et al, A model specification for FRP composites for civil engineering structures,
Construction and Building Materials, 17(2003), pp 405-437.
Hillman, J, Investigation of a Hybrid-Composite Beam System, Final Report for HighSpeed Rail IDEA Project 23, Transport Research Board, Washington DC, 2001
Bank L, Composite for Construction: The design Basis for Pultruded FRP Members,
Composite World, October 2007, www.compositesworld.com/articles/composite-forconstruction/.....
ASCE Prestandard-2010: Pre-Standard for Load and Resistance Factor Design (LFRD) of
Pultruded Fibre Reinforced Polymer (FRP) Structures (Final).
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Commentary
C.1.1 Scope
FRP composite products intended for timber bridge replacement shall be looked into in a
holistic manner. There are pitfalls in approaching the FRP composite products in isolation.
The designer shall not only design the FRP composite girders but also have a well thought
out scheme as to how the girder fits into a timber bridge. Hence FRP composite girders
destined for timber bridges accompany the relevant connection details.
The FRP composite girders shall satisfy the dual requirements - the structural
requirements as well as the functional requirements. FRP composites material behaves
linear elastically to failure and the failure mode is brittle in nature.
It is preferable to engineer the FRP composite girders such that the product exhibits
ductile behaviour. This behaviour needs to be confirmed by adequate testing.
The most widely applied FRP composite material today (due to cost consideration) is
Glass Fibre Reinforced Polymer (GFRP). It exhibits relatively low modulus of elasticity,
and thus most applications are governed by deflection. Hence FRP composites girders are
governed by serviceability criteria.
C.2.1. Design Requirements
The design philosophy of structural design of civil engineering structures is summarised
as: “The purpose of design is the achievement of acceptable probabilities that the structure
being designed will not become unfit for the use for which it is required, i.e., that it will not
reach a limit state.” (Hager et al. The ASCE Plastic Design Manual.) This philosophy has
to be the guide for the use of FRP composites in mainstream structural products in civil
engineering structures.
Design of the FRP composite bridge super structures will be based on commonly used
liner-elastic methods and properties supplied by the FRP Composite fabricator. Since
there are no accepted design codes and the application of the technology is new, it is
mandatory that a testing program should be part of the fabrication process. Each girder
should be proof loaded to a predetermined test load prior to acceptance into the works.
One representative sample of each batch shall be tested for ultimate load capacity.
C6.9 Thermal expansion
Most bridges experience daily and seasonal temperature variations causing material to
shorten with decreased temperatures and lengthen with increased temperature. It has
been observed that these temperature fluctuations can be separated into two components:
a uniform change and a gradient. The uniform change is the effect due to the entire bridge
changing temperature by the same amount. The temperature gradient is created when the
top portion of the bridge gains more heat due to direct radiation than the bottom. Because
the strains are proportional to the temperature change, a non-uniform temperature strain is
introduced.
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Department of Transport and Main Roads
Technical Standard
The response of a structure to the AS5100, curvilinear temperature gradient is more
complex than it uniform counterpart and can be divided into two effects: (1) gradient
induced axial strain, and (2) gradient induced curvature.
It is entirely possible that in a bridge structure where the deck as well as the bridge girders
were made of FRP composites. And also the girders may be an hybrid type consisting of
assemblage of pultrusions, steel, resins and cores. The effect of difference in thermal
coefficient need to be considered.
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