Dr. Shamsher Bahadur Singh, P.E. (USA), F. ASCE

Professor, Birla Institute of Technology and Science Pilani, India


Failure and Strengthening of FRP Beams using CFRP Laminates


July 20, 2022 10:00 AM – 11:00 AM EST

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This presentation describes the experimental investigation and finite element based numerical modelling for predicting the response and failure of FRP beams and/ or girders.  Different types of cracked pultruded beams strengthened with carbon fiber reinforced polymer (CFRP) laminates with various forms and sizes of structural element such as T-shaped as well as angle shaped stiffeners of short and full sized depth, carbon fibers layers, cover plate, and bearing plates, were considered for the study. Flexural responses were determined for CFRP strengthened beams having length-to-depth (L/d) ratios 3 and 7. Beams had the crack length of 75 mm on the compression web-flange junction at the mid-span of the beam. The length of carbon fiber layers provided was 175 mm, 225 mm and 275 mm. Flexural responses of beams was determined under three-point bending test. It is observed that the beam having L/d ratio 7 and carbon fiber layers of length 175 mm, failed by debonding of the carbon fiber layers, while other beams of L/d ratio 7 and bonded lengths 225 mm and 275 mm failed by local failure of compression flange. Moreover, beam having L/d ratio 3 and strengthened with carbon fiber layer throughout the length of beam has strength and stiffness equivalent to the un-cracked beam. Based on this experimental study, suitable strengthening mechanism for strengthening the pultruded FRP beams using FRP laminates in different forms of structural element has been recommended. Furthermore, a detailed numerical modelling has been presented to predict the response and failures of FRP beams with and without stiffeners with validation of results with those of experimental study. Based on the finite element based numerical modelling, a detailed parametric study has been conducted.  Parametric study is performed on beams having different flange width-to-thickness ratios (5−15), depth-to-thickness ratios (21−40), and length-to-depth ratios (3−11) with different sizes and types of stiffening elements. It is observed that failure load of beams increases up to certain length of bearing plate, later it becomes constant. Under flexural loading, bearing stiffeners of a beam is found to fail, if the length of bearing plate is less than the flange width of T-shaped bearing stiffener. Similarly, if the length of cover angle or carbon fiber layer provided is less than the length of bearing plate, then the failure load is equivalent to the beam with having bearing plate only. Finally, it is demonstrated that the carbon fiber angles as strengthening elements are less effective than the cover angle for beams having effective depth-to-thickness ratio more than 21.