CHAPTER 5 FINITE ELEMENT ANALYSIS OF GFRP COMPOSITE BRIDGE DECK PANELS

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1 80 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

2 81 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 ), 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.

3 82 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 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 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

4 83 Figure 5.3 All dimensions are in mm 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.

5 84 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 Model Model Model

6 85 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 Model Model

7 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 Width Depth Flange and outer web thickness Inner web thickness Additional stiffeners 45 15

8 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 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

9 88 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 noded solid 45 elements The load was uniformly distributed over two rectangular patch areas of mm mm up-to ultimate load on bridge deck panel in

10 89 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.

11 90 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)

12 91 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 Flexure Shear Models Ultimate Load, (in kn) Maximum Deflection, (in mm) Maximum bending Stress (in MPa) CSIS1A WRIS1A WRER1A CSIS2A WRIS2A WRER2A 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.