Main Roads Technical Standard

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Main Roads

Technical Standard



MRTS
69A


Design of
Fibre
Reinforced
Polymer (FRP)

Composite

Girders







August

201
2






IMPORTANT INFORMATION

The requirements of this document represent Technical Policy of the department and contain Technical
Stand
ards. 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 wi
ll 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@t
mr
.qld.go
v.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 (inc
luding 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 De
partment 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 publicat
ion 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
omitted from the publication or for the consequences of the use or misuse of the publication or any parts of it.

If the publication or any part of it forms part of a written contract between the State o
f Queensland and a
contractor, this disclaimer applies subject to the express terms of that contract.


August

201
2



Department of Transport and Main Roads

MRTS 69A

Technical Standard

Fibre Composite Girders


Page
i

of
ii

MRTS 69A

August 2012


Table of Contents

Page

1

SCOPE AND APPLICATIO
N

................................
................................
................................
......................

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 PROCEDU
RES

................................
................................
.....................

2

2.1

Design Requirements
................................
................................
................................
...........................

2

2.1.1

Aim

................................
................................
................................
................................
................

2

2.1.2

Fundamental re
quirements 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 COMBI
NATIONS FOR STABILIT
Y, STRENGTH AND SERV
ICEABILITY

...............

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

A
cceptable 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 SERVICE
ABILITY

................................
................................
.......................

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



8

CONNECTIONS

................................
................................
................................
................................
.......

13

8.1

General

................................
................................
................................
................................
..............

13

8.2

Cutting and Drilling

................................
................................
................................
............................

14

8.3

Holes

................................
................................
................................
................................
.................

14

8.4

Edge Distance

................................
................................
................................
................................
...

14

9

SUPPLEMENTARY REFERE
NCE

................................
................................
................................
..........

14




Page
1

of
1

MRTS69A

August 2012


Design of
Fibre
Reinforced Polymer (FRP)
Composite
Girders

1

SCOPE AND APPLICATIO
N

1.1

Scope

This
Standard

applies

to the
design

of
F
ibre
Reinforced Polymer (FRP)
compos
ite 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 refe
r
enced 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
Engin
eering
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 Mate
rials

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

Clause
Reference

FRP

Fibre Rein
force Polymer or Fibre Reinforced Plastic


GFRP

Glass Fibre Reinforced Polymer




Strength
Reduction Factor/Resistance Factor

2.2

MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
2

of
1

MRTS69A

August 2012


K
test

Reduction factor used in the absence of sufficient test
samples

2.2

R
o

Reference
Strength
/Characteristic Strength

2.
2

R
tes
t

Minimum Test Strength in the absence of sufficient test
samples


R
u

Ultimate Design Strength


2.2

S*

Design action effects

(
i.e., effects due to load)

2.2

V
f

Fibre Volume Fraction

4.8

EI

Stiffness of the Girder

8.8

1.5

Use of Alternative Materia
ls 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

DESIGN REQUIREMENTS
AND PROCEDURES

2.1

Design Req
uirements

2.1.1

Aim

The objectives of the bridge designer are that the structure he/she designs shall be safe,
durable
,
serviceable,
constructible
, economi
cal

and aesthetic.

Bridges made of FRP
composites must meet or exceed the expectations for bridges made of
traditional materials
for all of these objectives.
I
n 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

requir
ements and warning of failure


EUROCOMP Design Code section 2.1 covers this section:



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 composi
tes 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



Page
3

of
1

MRTS69A

August 2012


2.1.3

Design for Ultimate Limit State
s

(ULS)


The strength ULS shall relate to the Ultimate Strength of the girder and shall satisfy
the following:

The GFRP sections shall not exceed
o
f their
ULS
capacities at a strain of 0.0
09

(ultimate te
n
sile strain
*
60%
= 0.0
15*0.6
),

see Figure 1
.

Figure 1
: ULS and SLS strain limitations




Resin dominated failure mode
s

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 F
igure 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.

MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
4

of
1

MRTS69A

August 2012


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
S
ection

3

of this
specification.



The following load factors shall be used in determining the design action effects


Action

Ultimate
Limit State
Load Factor

Serviceability Limit State
Load Factor

Dead Load

1.2

1.0

Super Imposed Dead
Load

2.0

1.3

Traffic Load

2.
0

1.0




Crane Load

2.0

1.0



Number of Standard
Design Lanes
Loaded

Lane Modification Factor

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 d
etermined by an appropriate
analysis

to consider real traffic load conditions.


(c)

R
o

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)

R
o,
th
e ch
aracteristic strength is determined by the following equation:

Characteristic strength =
mean
strength


1
.
64

(standard

deviation). (Eurocomp
Design Code 4.11)

The ultimate design strength =


R
u

=


R
o




Page
5

of
1

MRTS69A

August 2012


In the absence of sufficient statistical samples
:



K
test

= 0.75 when less than 5 samples are used



K
test

= 0.85 when more than 5 samples are used


Characteristic Strength =
R
o

= K
test

* R
t
est


Where, R
test


=
Minimum test strength in the absenc
e of sufficient test samples



The ultimate design strength =


R
u

=


R
o

=


K
test
* R
test
,

(e)

The member shall be proportioned so that the design strength is greater than or
equal to design action effect, i.e.,





R
u


>

S
*
.




K
test
R
test



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 environment
s
. Creep

rupture
and stress corrosion are two consequences of
exposure to
acidic environment
s
. UV
resistance of some resins is low and it is recommended that appropriate measure
s

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 accelerat
ed durability tests for v
a
rious FRPs. FRP composite
s

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

Required Design Life

Replacement Elements

30 Years

Deck Replacement

50 Years

New Structures

100 Years


2.5

F
ire

Resistance

FRP composites are not in
herently fire
-
resistant. Issues such as
combustibility
, sprea
d

of
flame, changes in mechanical properties
and

toxic fumes need to be considered.

MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
6

of
1

MRTS69A

August 2012


Performance in a fire is generally improved by increased glass fibre content
. The u
se of
fire retardant resins

or addition of additives to the resin improve
s

fire retarda
tion
.

Therefore a
suitable
fire retardant coating

or a fire retardant resin or a fire retardant

additives
to the resin

shall be pr
opose
d for the FRP composite girders
and the fabricator
shall ach
ieve the F
ire
R
esistance
L
evel
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 sati
s
fy
the deflection criteria
stipulated in section 2.12.1 of AS1530.4
.


3

LOADS AND LOAD COMBI
NATIONS FOR STABILIT
Y, STRENGTH AND
SERVICEABILITY

3.1

Load Types

3.1.1

Vehicle Loads

The Timber Bri
dge renewal program is targeted for Class A timber bridges.

The required l
oading
for
the FRP Composite
s
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
H
eavy
L
oa
d
P
latform

(HLP)




48T
moving crane




3.2

Load Combinations

Load combinations shall be in accordance with
section 2.2.


4

MATERIAL PROPERTIES

4.1

G
eneral

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, reinforce
ment and manufacturing supplier

or technical specialist
.

FRP composite girders
are manufactured in different ways: a)
assemblage of only
FRP

pultruded
profile

section
s

by means of gluing,
b)
asse
m
blage of
FRP

pultruded
profile

sections, FRP panels and stee
l in a
hybrid


section
, c) assemblage of
FRP p
ultruded

Page
7

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1

MRTS69A

August 2012


profile
section, steel, concrete, lightweight foaming in to a hybrid
,
and
d) by means of
vacuum assi
s
ted resin
i
nfusion process
.

The manufacturer shall provide test results of fibre, laminates, coupon
test of
FRP

pultruded
profile

section (web/flange)
in the l
ongitudinal

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 sha
ll comply with all relevant
standards, including ASTM standards.


4.2

Reinforcement

4.2.1

Fibres

In FRP materials, fibres provide both load carrying capacity and stiffness to the
compo
s
it
e
s
. The most widely used fibres in civil engineering today are glass fibres.


W
ith glass fibres, o
nly 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
-
glas
s 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 Gr
avity

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

10^
-
6/
˚
C

5.0

5.9

.

4.2.2

Rovings

Any use of rovings shall be in accordance with ISO 2797

or equivalent
: Glass Fibre
rovings for the reinforcement of polyest
er and epox
y

resin systems.

4.2.3

Mats


Continuous

Filame
n
t Mats

Any use of
Continuous Filament M
ats shall be in accordance with ISO 2559

or
equivalent
:

MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
8

of
1

MRTS69A

August 2012


4.3

Matrices

4.3.1

Polymer Matrices

The fibre provides the actual load bearing function

and stiffness to the composit
e. T
he
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, f
luids

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 polyes
ter 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 l
oss 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 type
s of resins are acceptable to be designed in accordance with the
properties and limits set out in Eurocomp Design Code.



Polyester Resins



Vinyl Ester Resins



Phenolic Resins



Epoxy Resins








Page
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MRTS69A

August 2012


The material properties of resins are shown below in Table 5.


Ta
ble
5

Minimum Required Properties of Resin

Property

Units

Polyester

Resin

Epoxy

Resin

Vinyl Ester

Resin

Phenolic

Resin

Tensile Strength

MPa

70

70

70

40
70

Young’s Modulus

GPa

2
-
3

2
-
4

3.2
-
3.9

1.5
-
2.5

Flexural
Elongation
at Failur
e

%

4

4

4

4

Density

g/cm
3

1.2
-
1.3

1.2
-
1.3

1.12

1.24

Heat Distortion

Temperature

o
C

90

120

90

110

90

120

90

Shrinkage (max)

%

5

2.
5

5

5


4.4

Cores

Core materials may be load bearing or used as formers for shaping fibre composite
girders. Structural cores s
hould 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 va
r
iety of reasons: to
filter out ultraviolet radiation and improve weatherin
g, to add flame retard
e
ncy 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.
T
heir 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
i
nclude
d in surface coating for improving
s
pecific properties.


4.7

FRP

Pultruded

Profile

Sections

FRP

p
ultruded
profile sections

come in many forms, square hollow section, rectangular
hollow section, circular hollow sections, and I sections.

Table 6 shows the typic
al mechanical properties of pultruded shapes.



MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
10

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MRTS69A

August 2012


Table
6

Typical Mechanical Properties of
FRP
Pultruded
Profiles
S
ections

Property

Units

Parallel to fibre

Transverse to fibre

Tensile Strength

MPa

400
-
700

50
-
60

Tensile Modulus

GPa

2
0
-
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/cm
3

1.8
-
2

Fibr
e

Content

%
Volume

30
-
60




4.8

Lamina

Table 7 illustrates the lamina material constants for different
fibre vol
ume fractions which
can be used
.

Table
7

Lamina Material Constants for Different Fibre Volume Fractions


V
f

= 0.3

V
f

= 0.4

V
f

= 0.5

V
f

= 0.6

E
11

(MPa)

23500

30500

37500

44500

E
22

(MPa)

6000

7000

8400

10500

G
12

(MPa)

2230

2600

3120

3900

v
12

(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 SERVICE
ABILITY

6.1

General

FRP composite materials generally remain linear elastic up to the p
o
int

of bri
t
t
le 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 spe
ci
fic
orientation of the
f
ibre.

The strength of the FRP composite Beam shall be determined from
strain compatibility and
the constitut
ive material properties. However, the theoretical strength com
p
uted
, based on
various strength theories,

need
s

to be verif
i
ed by test
ing to conf
i
rm the actual strength.


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MRTS69A

August 2012


Fibre composite girders are required to be designed in accordance with Euro
co
mp 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
torsio
n
ally
stable in the lateral
direction.

6.3

Stiffne
ss 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 se
ction 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

Re
placement Timber Girder Size

Target FRP
Composite

Stiffness

19 inch

3.5
*10
13
Nmm
2

±

10%

17 inch

2.9*10
13
Nmm
2

±

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

(1.0DL+1.3SIDL+(1+a)LL),

a = 0.
4

Total Deflection shall

be less than

Live Load (1+a)LL ,

a =0.4


Incremental Deflection shall be less than

L/300

L/600


6.4

Ductility

The nature of FRP Com
p
osite material
is such that they behave linear elastically
until

failure and often result in brittle

failure

mode
. It is reco
m
mended to e
ngineer

FRP
composite girders
into a hybrid ass
e
mbly 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 t
hat, 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.

MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
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MRTS69A

August 2012



Eurocomp Design Code section 4.13 sets out a methodology for fatigue assessment of
composites
.

The follo
wing 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 50
o
C. T
he frequency of loading is limited as the material heats up
at higher frequencies thus changing the failure mechanism.

Fatigue stress cycle of 1x10
6

at the serviceability limit state, at a normal strain of 0.1%
The SLS
state
limit of 0.1%

normal
strain a
t 1x10
6

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 l
ive 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 sh
o
uld be
performed

6.7

Temperature Effects

An important temperature related property of f
ibre composites is the glass transition
temperature

(T
g
)
. At temperatures above T
g

composites soften from a glass
-
like state to a
rubbery state
.

Fabricators to specify Tg for putlruded sectio
n

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. Fabrica
tors 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 170
o
C

corresponding
to Asphalt overlayin
g temperature
.
Lucy
cranitch says that Tg of 170 will not be met by
most of the commonly used resins.



6.8

Therma
l

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 i
ntroduced
.


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MRTS69A

August 2012



Thermal coefficient
s

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 lai
d 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 Qu
eensland region, t
he
maximum temperature gradient of 30
o
C
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
o
C

or
-
10
o
C
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.
Cree
p

shall be incorporated into the desi
gn

as per Euroc
omp 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

END ZONES



SUPPORT DESIGN

7.1

General

Eurocomp Design Code deals with stability of composit
e 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 perform
ance 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

CONNECTION
S

8.1

General

Connection
s

shall be designed according to
chapter 5 of the Eurocomp Design Code.
Bolte
d 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 girder
s 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 st
eel bolts approved by TMR shall be used.

In
addition, the adequacy of the connection can be determined by testing.



MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
14

of
1

MRTS69A

August 2012


8.2

Cutting and
Drilling

The FRP composite girders are to be identified where drillin
g

and sawing is
permitted. The
limitation on
cutting:

cut
ting 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 composi
te girders manufactured shall have provision to drill on site as well at the
factor
y.

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 20
0
,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 me
mber shall be provided
to protect against tear
-
out, web crushing

or tensile
failure.

9

SUPPLEMENTARY REFERE
NCE


Guide for the Design and Construction of Structures made of FRP Pultruded Elements,
National Res
e
arch Council of Italy, Rome, CNR
-
DT
-
205/2007

NHCR
P 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)
St
r
uctures, J. of Composites for C
onstruction, February 1997
, pp. 26
-
38
.

Ellingwood, B, Toward Load and Resi
s
tance 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 compo
sites 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 High
-
Speed Rail IDEA Project 23, Transport Research Board, Washington DC, 2001

Bank L, Composite for Construction: The design Basis for Pultruded FRP M
em
bers,
Composite World, October 2007,
www.compositesworld.com/articles/composite
-
for
-
construction/
.....


ASCE Prestandard
-
2010: Pre
-
Standard for Load and Resistance Factor Design (LFRD) of
Pultruded Fibre Reinforced Polymer (FRP) Structures (Final).





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August 2012



Commentary


C.1.1 Scope

FRP composite products intended for timber bridge replacement shall be looke
d 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. Hen
ce 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 beha
ves
linear elastically to failure and the failure mode is brittle in nature.


It is preferable to engineer the FRP composite girders such that th
e

product exhibit
s

ductile behaviour. This
behaviour
need
s

to be confirmed by adequate testing.

The most wide
ly 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 wi
ll 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 civ
il
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 teste
d for
u
ltimate
l
oad 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 temper
ature fluctuations can be separated into two components:
a uniform change and a gradient. The unif
orm 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.

MRTS69A

Department of Transport and Main Roads

Fibre Composite Girders

Technical Standard


Page
16

of
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MRTS69A

August 2012


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 ax
ial 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 t
he girders may be an
hybrid type consisting of
assemblage of pultrusion
s, steel
, resins and cores. The effect of difference in thermal
coefficient need to be considered
.