FINITE ELEMENT ANALYSIS OF MULTICELLULAR FRP BRIDGE DECK

Abstract

The quest for a light weight structures is an ongoing task for Engineering community. However, Fibre reinforced polymers (FRP) do meet some of these requirements. The development in FRP commenced only in 1940s. After the use of FRP in defence, aircrafts, automobiles etc, it was employed in structural applications. FRP have many excellent structural qualities and some examples are high strength, material toughness, fatigue endurance, and light weight. Other highly desirable qualities are high resistance to elevated temperature, abrasion, corrosion, and chemical attack. Literature review indicates that extensive research is being carried out both in laboratory as well as on ground to design the FRP decks and study the response to various external effects. Lot of onground applications in the form of pedestrian bridges, hybrid bridges( with RC), all composite bridges and bridge decks as replacement in old bridges are underway in US , Europe, Australia, Korea etc. Two major types of FRP composite bridge decks are currently in use: sandwich type construction and cellular or stiffened structure. Web stability requirements and the limited top face panel span between the webs due to local tire pressure necessitate the development of new multi-cellular cross-sections. Multicellular FRP bridge decks with an advantage of box structure have a promising role to play. Some of the additional benefits of these decks are reduction in dead load and subsequent increase in live load rating, rehabilitation of historic structures, widening of bridges without imposing additional dead load, faster installation reducing cost and traffic congestion, and enhanced service life even under harsh environment. However, since it is a new material no design codes, guidelines or specifications are available. There is a need to create a database for better understanding and analysis of multicellular FRP bridge decks. The present . numerical study in an attempt in this direction. Among the refined methods for analysis of complex composite structures, the finite-element method is probably the most involved and time consuming. However, it is still the most general and comprehensive technique for static and dynamic analysis, capturing all aspects affecting the structural response. ANSYS 10.0(non commercial version) has been used to model and analyse the multicellular FRP bridge decks. In the present study, graphite epoxy material is chosen and parametric studies have been carried out to analyse the multicellular FRP bridge deck model. An attempt has been iii made to study patterns of stresses and deformations and quantify them in the model deck. Parametric studies done are; (1) Increase in number of cells - 3,5,8 and 10 cells , (2) Change in angles of fibre orientation - 00, 90° and ±45°, (3) Change in boundary conditions - two edges and four edges simply supported, and (4) Change in types of loadings- Patch load of 6.25 T/m and track load of 9 T/m2. Besides, the above studies, some additional studies on reactions at supports, aspect ratio etc have also been carried out to ascertain the patterns of load distribution and effective width due to changes in parameters mentioned above In the present work two extreme cases (00 and 900) and one moderate case (±450) of fibre orientations are considered to get lower and upper bounds of load transfer mechanism. Proper combination of angles of fibre orientation for given situation can be obtained by utilizing optimization tools. The unique advantages of each angle of fibre orientation are 00 fibre orientation improves stiffness whereas, 90° fibre orientation improves transverse load distribution and ±450 fibre orientation gives equal contribution to both and also improve local buckling characteristics as reported in literature. Theoretically, the torsional rigidity of multicellular decks reduces slightly with increase in number of cells. However, due to increase in number of webs, which also share the load, the deformation reduces with increase in number of cells. In case of 00 fibre orientation, webs become most effective in sharing loads hence deformation reduces. Moreover, webs of 00 fibre orientation are more effective than other fibre orientations. The transverse stress (SX) in this case represents distortional stress which is complementary to longitudinal stress (SZ). Longitudinal stress (SZ) mainly represents distortional warping stress and in general there is no reduction in value of SZ with increase in number of cells. On the basis of FEM studies a large data base on the pattern of stress and deformations have been generated, which will be helpful in understanding the multicellular FRP bridge deck better.