Strengthening of Ferrocement Beams in Torsion by CFRP Strips

Abstract

Torsion is resisted well by closed form reinforcement, due to the circulatory nature of the torsion inducing shear flow stresses in a beam. Therefore, it will be more efficient to have strengthening schemes, which are wrapped in closed form around the cross section. An experimental work was carried out and used superplasticizer with mix 1:1.5 to improve the mechanical properties of mortar. 12 rectangular beams (50x120)mm and 1m length are cast, strengthened and tested under pure torsion. The Variables considered in the test program include: effect number of wire mesh layers ( unit ), this unit consists of two layers of wire mesh with skeletal steel, (2, 3, 4) units and effect spacing of CFRP strips, (100,160,200) mm c/c. Test results are discussed based on torque – rotation behavior and influence of parameters on ultimate torque and failure modes. Generally, using optimum dosage of super plasticizer (1.4 % of weight of cement) gave compressive strength 65.65 MPa. Increasing the number of units from 2 to 4(reinforcement near the surface of beam section) led to increased ultimate torque by (13.44 %) and from 2 to 3(uniformly distributed reinforcement) led to increases the ultimate torque by only (3.24 %). When the beams are strengthened with CFRP strips, the lowest and highest increase in torque is at 112 % (4-units,@200 spacing) and 312 % (4-units,@100 spacing), respectively. The ultimate torque of beams with CFRP strips @ 100 mm and 160 mm spacing is greater than beams with CFRP strips @ 200 mm spacing by ( 94.34,45.28) %, respectively for the group having 4-units.