محمد واقفی

One of the causes of destruction or damage of many bridges worldwide is local scour around the bridge piers. Research on factors affecting scour pattern around bridge piers is hence highly important. The present work is an experimental study of local scour around rectangular piers, with different ratios of length to width, located in different positions of a 180 degree sharp bend. The experiments were conducted in a rectangular channel including a 180 degree bend, with a ratio of central curvature radius to channel width of 2, width of 1 m, height of 0.7 m, and flow depth of 0.18 m, under incipient motion conditions (with a ratio of flow velocity to critical velocity of 0.98) and bed sediments with an average diameter of 1.5 mm and standard deviation of 1.14. The results indicated that the length of the rectangular pier must be a minimum of 3 and a maximum of 5 times its width in a 180 degree sharp bend. The pier with a ratio of length to width of 3 had a better performance regarding scour reduction along the bend than other rectangular piers. The maximum depth of scour hole around the piers occurs when the piers are installed in the 90 degree position of the bend. Increasing the inclination angle of the pier skewed towards inner and outer banks in the 90 degree position resulted in an increase in depth and volume of scour hole in comparison with a case where the pier was installed perpendicular to the flow direction. Inclination of the pier towards the outer bank with 15 and 30 degree angles has decreased the maximum depth of the scour hole in front of the pier nose by about 20 and 8 percent respectively. Employment of collars is proposed as one of the most effective and efficient methods of control and reduction of scour around bridge piers. Therefore, research on flow and scour pattern around a combination of pier and collar is also of high importance. Thus, the research entailed an experimental investigation of the effect of increasing different ratios of collar