Structures designed following the code limitations and factors of safety are expected to achieve a reasonable afety. Reliability can be defined as the probability that a structure will not fail while it performs its intended function. It can be used as a highly efficient tool for calibrating code equations in order to maintain a homogenous reliability index beforeand after strengthening. The main objective of this research work is todetermine reliability indices for reinforced concrete (RC) beamssubjected to flexural failure before and after strengthening using MonteCarlo simulation. Also, an experimental work on reinforced concrete beams strengthened with carbon fiber reinforced polymer (CFRP) plateswas made in order to compare between experimental results and analytical model (ECOP code of practice for FRP). The following parameters were considered: Shear span to effective depth ratio, live load to dead load ratio, working moment to moment apacity ratio and number of layers of CFRP plates (1, 2 and 3layers). Software was developed by the author to get a wide range of results considering the prescribed parameters. The results indicated that the reliability of reinforced concrete beams remarkably differs after strengthening. Also, the reliability indices are significantly affected by beam geometry, loading scheme, FRP thickness and live to dead load ratios. The reliability analysis was carried out based on the guidance provided by Egyptian code of practice for the use of fiber reinforced polymer (FRP) in the construction fields. . The proposed numerical model gives a good estimation for the transmitted waves especially for veliical and nearly vertical breakwaters as well as the relative breakwater height decreases for different wave characteristics and beach slopes.7. The proposed numerical model was adjusted for the effective breakwater side slopes (1.5: 1 and 2: 1) by using a suitable calibration coefficient. The adjusted model gives a good estimation for wave characteristics when (02h/g>O.25.The summaries of recommendations are:1. Studying the efficiency of rubble mound submerged breakwaters constructed on movable sloping beaches.2. Studying the effect of the impermeable trapezoidal submerged breakwaters on the sediment transport and accordingly on the shoreline stability.3. Studying the effect of the breakwater crest width on the wave field around the impermeable trapezoidal submerged breakwaters.4. Studying the efficiency of the impermeable trapezoidal submerged breakwaters subject to oblique waves.5. Studying the efficiency of the impermeable trapezoidal submerged breakwaters under current-wave system.6. Studying the effect of the impermeable trapezoidal submerged breakwaters on the wave field when the breakwaters construct on movable bed.