SHEAR LAG BEHAVIOR AND ITS INFLUENCE ON BUCKLING OF FRP BOX BEAMS

Abstract

Laminated composite box beam is the basic building block. It can be used both as a compression member and flexural member. Over the past decade FRP laminated composites are gaining popularity in marine, aerospace and civil industry for numerous structural applications. Being lightweight it is easy to handle and transport leading to short installation times and speedy construction which is a major criteria during disasters. Also the quality of work is improved in terms of corrosion resistance, endurance limit, damage tolerance, aesthetic appearance, longer life, low maintenance, fire retardancy etc. For an instance laminated composite FRP deck weighs approximately 80 percent less than a concrete deck. Reducing the dead load increases the allowable live load capacity of bridge without significant damage to the existing superstructure, thus lengthening its service life. Versatility of the material is such that it can be used even in earthquake prone areas for seismic retrofit or for remote installations in difficult terrains. Further the flexibility to tailor different properties of the structural elements by varying fibre orientation, number of layers etc. to achieve the strength and stiffness requirements in the required direction has enhanced their usage. Need of appropriate structural form with FRP is required to utilize its advantages. Thin-wailed box beam is chosen for study as it offers excellent flexural and torsional stiffness with minimum weight. Use of FRP in box beam form combines the advantages of both the material and form and results in an efficient generic structural element. FRP box girders comprising of FRP stiffened panels are predominantly under membrane compression (top flange), in plane shear (web), and membrane tension (bottom flange). Hence the use of laminated composite materials for these structural elements is aptly suited as they provide flexibility to designer to specify different material properties for different elements of the beam cross-section. This enables the shape of the cross-section to be exploited to the fullest by judicious arrangement of plies within the laminated composite panels, which form the beam.