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CHAPTER 5

FINITE ELEMENT ANALYSIS OF GFRP

COMPOSITE BRIDGE DECK PANELS

5.1 GENERAL

Bridge decks made of FRP have been widely studied and

increasingly used in highway bridges, both in new construction and

replacement of existing bridge decks. It is known that FRP composite

materials have a number of advantages including, high specific stiffness and

specific strength ratios, good fatigue behaviour, and corrosion resistance.

However, compared to traditional construction materials, such as steel,

timber, and concrete, GFRP materials have more complex material properties

and structures exhibit distinctive behaviours. Investigations of the behaviour

of FRP bridge decks were conducted through laboratory tests on FRP deck

components, and field tests on FRP bridges. Field tests were performed under

service loads which are significantly lower than failure loads.

Experimental investigations on the other hand are more suitable for

strength/capacity assessment studies through destructive testing. However,

such tests seldom consider the entire structure due to equipment limitations

and associated costs. Furthermore, parametric studies in experimental

procedures are time consuming and prohibitively expensive. Computer

simulations based on advanced methods, such as the FEM, are reliable and

cost effective alternatives in structural analysis for the study of structural

response and performance. FEM procedures have been successfully employed

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in research studying the performance of FRP bridge decks or their

components. The general purpose finite element software ANSYS or

ABAQUS can be used for the modeling and analysis of multicellular FRP

composite bridge deck panels with different cross sectional profiles and that

has many analytical capabilities, ranging from a simple, linear, static analysis

to a complex, nonlinear and transient dynamic analysis. In this study the finite

element software ANSYS is used for the modeling and analysis of

multicellular FRP bridge deck panels. A preliminary analysis was carried out

on models created using ANSYS by taking IRC class A loading, to optimize

the cross sectional profile that can be used for the fabrication of the

experimental models.

5.2 PERFORMANCE CRITERIA

From the literature review, it has been observed that the design of

GFRP bridge deck panels is driven by stiffness and hence maximum

deflection is the governing criteria in design. The loads imposed on the bridge

decks include dead load, which includes the self-weight and weight of future

surface wearing course, and the live load imposed in the form of wheel load.

These loads should be factored up suitably to account for impact and variation

in material properties. The deflection produced by this factored load must be

less than the limiting value of deflection. AASHTO has set up a deflection

limit of Span / 800 for FRP bridge deck panels.

5.3 IRC CLASS A LOADING

According the specifications given by the Indian Roads Congress

(IRC 6 - 2000), IRC class A loading is to be normally adopted on all roads on

which permanent bridges and culverts are constructed. The IRC class A train

of vehicles is shown in Figure 5.1.

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Figure 5.1 IRC class A train of vehicles (axle loads in tones, linear dimensions in m)

To obtain the maximum bending moment and shear force, the

maximum wheel load should be considered as shown in Figure 5.2. The

ground contact area for the maximum axle load of 114 kN as specified in IRC

6 - 2000 is 500 mm perpendicular to the direction of motion and 250 mm

parallel to the direction of motion. The minimum clearance to be ensured

between the outer edge of the wheel and the inner face of the kerb is 150 mm

for all carriage way widths. The width of a single lane carriage way is 3.75 m

and that of two lane carriage way is 7.5 m as per IRC 5 - 1998. The ground

contact area for the maximum axle load and the distances between the wheels

in both directions has been indicated in Figure 5.3.

Figure 5.2 IRC Class A loading

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All dimensions are in mm

Figure 5.3 Ground contact area for maximum Axle load of IRC Class A loading

5.4 SELECTION OF CROSS SECTIONAL PROFILES

Multi-cell box sections are commonly used in deck construction

because of their light weight, efficient geometry, and inherent stiffness in

flexure and torsion. Also, this type of deck has the advantage of being

relatively easy to build. It can either be assembled from individual box-beams

or manufactured as a complete section. Various cross sectional profiles of

multicellular bridge deck panels available in the literature were selected and

analyzed for IRC Class A wheel load using ANSYS, the standard FEA

software. The cross sections considered for analysis are shown in Figure 5.4.

The overall dimensions are arrived at based on the Indian Roads

Congress codes. The overall length of multicellular bridge deck panels were

kept equal to the carriage way width of single lane, 3750 mm. and the width

considered was 1000 mm.

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Model 1 Model 2

Model 3 Model 4

Figure 5.4 Cross sectional profiles considered for optimization

The depth and skin thickness of the cross section of bridge deck

panels were varied by trial and error basis. IRC class A loading was imposed

in the form of rectangular patch loads and the maximum deflection at the

center of each panel under the factored load was obtained using ANSYS.

Comparison of the deflection values for all the models is shown in Table 5.1.

A cross sectional profile of the fourth model is satisfied the deflection criteria

with minimum weight and is considered for further study. The analysis is on

the cross sectional profile of the fourth model with varying thicknesses of

flanges, webs and stiffeners as shown in Figure 5.5.

Table 5.1 Deflection values for various models

Model Deflection (in mm) Model – 1 6.50Model – 2 5.64Model – 3 2.49Model – 4 2.34

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Model -5

Model -6

Model -7

Figure 5.5 Cross sectional profiles with flange, web and stiffener thicknesses

Table 5.2 Deflection values for Optimized models

Model Deflection (in mm) Model – 5 3.34Model – 6 2.84Model – 7 2.34

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5.5 SIZE OF THE EXPERIMENTAL MODEL

The optimized cross section consists of a 3-cell section with

additional stiffeners connecting the web to the top flange it. The thickness of

the top flange, bottom flange and the exterior webs are kept as 60 mm. The

thickness of additional stiffeners is kept as 45 mm. The experimental models

used in this investigation are a 1:3 scale model of a 3.75m bridge

superstructure. The dimensions of the prototype and one-third scaled model of

the bridge deck panel are given in Table 5.3 and depicted in Figure 5.6.

Figure 5.6 Cross sectional profile of one - third scaled model

Table 5.3 GFRP Bridge Deck Panel Dimensions

Parameter Prototype (in mm) Model (in mm) Length 3750 1250Width 1000 333.33Depth 450 150Flange and outer web thickness 60 20Inner web thickness 45 15Additional stiffeners 45 15

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5.6 ANALYSIS OF GFRP COMPOSITE BRIDGE DECK PANEL

The GFRP bridge deck panel having the dimensions as specified

above was analyzed by assigning the orthotropic material properties

corresponding to the composites composed of the following materials.

E-Glass fibres in the form of CSM and ISO

E-Glass fibres in the form of WR and ISO

E-Glass fibres in the form of WR and ER

The followings are notations for the six multi-cellular GFRP

composite bridge are considered for analytical purpose and they are tested

analytical using ANSYS as stated below

1. CSIS1A - CSM and ISO under flexural loading condition

2. CSIS2A - CSM and ISO under shear loading condition

3. WRIS1A - WR and ISO under flexural loading condition

4. WRIS2A - WR and ISO under shear loading condition

5. WRER1A - WR and ER under flexural loading condition

6. WRER2A - WR and ER under Shear loading condition

The static analysis of multicellular GFRP composite bridge deck

panel of size 1250 mm × 333.33 mm × 150 mm was carried out using

ANSYS, the standard finite element software. SOLID45 brick elements were

used to model the bridge deck panel. SOLID45 element is defined by eight

nodes having three degrees of freedom (translations in x, y and z-directions)

at each node with orthotropic material properties. Orthotropic material

directions correspond to the element coordinate directions. This element has

plasticity, creep, swelling, stress stiffening, large deflection and large strain

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capabilities. The geometry, node locations and the coordinate system for

SOLID45 element are shown in Figure 5.7.

The bridge deck panel was assumed to be simply supported over

two opposite edges. Analysis is carried out for long edges simply supported

and short edges are supported simply as shown in Figure 5.8. The boundary

conditions were simulated by arresting the three translational degrees of

freedom in x, y and z directions at one end (hinge support) and two

translational degrees of freedom in y and z directions at the other end (roller

support).

Figure 5.7 8 noded solid 45 elements

The load was uniformly distributed over two rectangular patch

areas of 166.67 mm × 83.33 mm up-to ultimate load on bridge deck panel in

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the form of equivalent nodal forces. Figure 5.8 shows the geometry model of

GFRP bridge deck panel. Figure 5.9 shows the corresponding FE model.

Figure 5.8 Geometry model of bridge deck panel

Figure 5.9 Finite element model with patch loads

The deflected shape of the deck panel under the load is shown in

Figure 5.10 and the deflection contour of the bridge deck panel is shown in

Figure 5.11 for WRIS2A and WRIS1A. Figure 5.12 shows the deflection

contour of GFRP bridge deck panel made out of WRER2A and WRER1A in

the case of two long edges and two short edges simply supported condition.

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Figure 5.10 Deflected shape of the GFRP bridge deck panel (WRIS2A and WRIS1A)

Figure 5.11 Deflection contour of the GFRP bridge deck panel (WRIS2A and WRIS1A)

Figure 5.12 Deflection contour of the GFRP bridge deck panel (WRER2A and WRER1A)

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The maximum deflection and ultimate load carrying capacity of

three different models under flexure (short span hinged) and shear (long span

hinged) conditions are tabulated in Table 5.4. From the calculated values the

maximum bending stress is low when compared to that of the maximum

deflection.

Table 5.4 Ultimate Load and Maximum deflection from ANSYS

Models UltimateLoad, (in

kN)

MaximumDeflection,

(in mm)

Maximum bendingStress

(in MPa)

Flexure CSIS1A 199.5 2.23 48.5WRIS1A 248.8 2.56 31.4WRER1A 264.2 2.34 27.5

ShearCSIS2A 138.9 0.33 51.7WRIS2A 184.5 0.44 34.2WRER2A 246.8 0.38 28.9

5.7 CONCLUDING REMARKS

The best cross section is arrived at based on the mathematical

model of GFRP bridge deck developed by using ANSYS. Since bending

stress is low, the deflection is considered as a parameter for further studies.

The experimental observations are mainly included the measurement of

deflections which will indirectly indicates the strength / stiffness of the

member.