Shear strengthening of fire damaged RC beams with stirrup reinforced engineered cementitious composites

Abstract This paper presents the results of an experimental research on the response of fire damaged reinforced concrete (RC) beams shear strengthened with stirrup reinforced engineered cementitious composites (ECC). A total of six beams including one normal temperature control beam were instrumented, five of which were heated according to ISO 834 heating curve for two hours. Four of the fire damaged beams were repaired, and then all the beams were subjected to four-point loading conditions to research the effect of strengthening with stirrup reinforced ECC on enhancing the shear strength and deformation ability of fire damaged RC beams. It was found that stirrup reinforced ECC is an ideal strengthening method for fire damaged RC beams. The strength and deformation ability of the strengthened beams were improved significantly compared with that of the control beams. The beams strengthened with ECC layer were able to develop uniformly distributed tiny cracks, which resulted in more ductile failure mode than the control beams. Also, the combination of ECC layer and strengthening stirrups significantly increased not only the shear load capacity but also the deformation ability of the fire damaged RC beams, which was quantified by shear ductility index. The use of closely spaced strengthening stirrups with a steel ratio of 0.24% even changed the failure mode of the beam from brittle shear failure to ductile bending failure. Moreover, digital image correlation (DIC) technique was adopted to measure the strain of the tested beams.