TORSIONAL STRENGTHENING OF SPANDREL BEAMS WITH COMPOSITE LAMINATES

ABSTRACT

The present paper describes the experimental and analytical findings of a project focused on the structural strengthening of reinforced concrete (RC) spandrel beams using carbon fiber reinforced polymer (CFRP) composite laminates, and subjected to pure torsion. Current torsional strengthening and repair methods are time and resource intensive, and quite often very intrusive. The proposed method however, uses composite laminates to increase the torsional capacity of concrete beams. Six identical spandrel beams were built and tested. Two of the beams were considered as baseline specimens, the remaining four were strengthened using three different composite laminates. In order to eliminate the flexural and shear forces on the beam, a close to pure twisting force was applied at the end of the beam specimen. In traditional cast-in-place construction the slab adjacent to the spandrel beam does not allow a complete wrap around the beam. To simulate this, the CFRP laminate was provided only on three sides of the beam, and special anchors were used to allow a continuous torsional shear flow around the specimens. The experiments showed that this method increased the torsional strength of the spandrel beams up to 113%. Excessive concrete cracking followed by composite delamination caused the specimen failure. An equation was also developed which, for most of the specimens, accurately predicted the composite contribution. This analytical procedure was based on the existing information on the torsional resistance provided by closed stirrups, and on the equations developed to design the composite shear retrofit of RC beams.