An iterative hybrid technique of Boundary element method, (BEM), anddistributed dislocation method, (DDM), is presented to solve two dimensionalcrack problems. The technique is to decompose the problem into (n+ 1) problemswhere n is the number of crack branches.The required solution will be the sum of these (n+ 1) solutions. The firstproblem is to find the stress distribution induced in the plate in the absence ofthe crack using BEM.All of the other problems are stress disturbance problems. Each of them ismodeled by an infinite plate containing a certain branch of the crack subjected totractions equal in magnitude and opposite in sign to that obtained from solutionremoved.In this research the load was partially taken into consideration. Thestudied beams were strengthened under applying loads. Two different values ofapplied loads were considered in this research, 60% and 80% of ultimate failureload.Twelve full scale beams with dimensions 15 x 25 x 300 ems wereexperimentally tested. The strengthening of tested beams, at the tension zone,were made by gluing carbon fiber reinforced plastic sheets (CFRP), gluing glassfiber reinforced plastic sheets (GFRP) or fixing steel plates.The sheets or plates used had either a rectangle shape or I-shape to allowbetter bonding. The beams were kept loaded, (for three days in case of thepresence of an adhesive) before testing them till failure. The deformations ofthe tested beams were measured, as well as the strains till failure. Crack patternwas also observed and the mode of failure was recorded.A numerical finite element analysis model was carried out on identicalspecimens to those experimentally pre-tested. Some extra models were alsotested numerically to examine the effect of some other different strengtheningparameters.Results were satisfactory and showed that beams strengthened under loadwere found to give a smaller ultimate failure load than the beams strengthenedwithout applied load.