NUMERICAL EVALUATION OF PIERS SPACING EFFECT ON HYDRAULIC AND SEDIMENTARY PARAMETERS OF RIVER FLOWS USING BRI-STARS (CASE STUDY)

The scour of bridge piers is one of the most important factors aecting the stability of bridges constructed over rivers. Many studies have been conducted to evaluate the depth and intensity of scouring around bridge piers. Due to the complexity of this phenomenon, most existing formula cannot estimate the scour depth with reasonable precision. In this paper, regarding the importance of scouring in bridge design, a comparison was made between the formulas used for estimation of scour depth, and then the resulted data from analyzing dierent models with dierent ratios of pier spacing to pier width were investigated using BRI-STARS. Comparing Froehlich and CSU relations reveal that the Froehlich equation estimates the scour depth 11 percent more than the CSU formula. Also, the Froehlich is more conservative due to the design criteria. The increasing of scour depth in models with x/b<7 is negligible when the CSU formula was applied, and in models with x/b < 8.5 when the Froehlich formula was used. In order to select the optimum location of a bridge with regard to the scour condition, hydraulic parameters, such as free surface elevation, Froude number, depth the averaged velocity and bed erosion under the eect of pier location, were examined. Finally, by processing the resulted data, the best diagram and equation for estimating increases in scour depth, according to dierent pier spacing to width ratios, were presented. Also, it was shown that when y/b<3.2, the ow relative depth has an eect on scouring, but, when the y/b became less than 2.75, the scouring was not in uenced by ow relative depth.