Transition from Circular to Rectangular Section

Two methods are widely used for the design of transitions from circular to rectangular box sections. One method is based on a straight line variation of area between the circular section and rectangular box section with the provision of circular corners. This method results in a surface profile that is difficult to form, varying from a parabolic curve to a straight line; if approximations are made in the surface profile, an uneven surface results. The second method is based on the provision of oblique circular quarter cones at the corners, with radius of the circular corners varying in a straight line from zero at the rectangular box section to radius R at the circular section. With this method, a straight line variation in area is not achieved; a very serious hydraulics defect is. The method described in this paper is a modification of previous methods to achieve an almost straight line variation in area through the transition, with a minimum cost in form work. This method is based on the travel of a point on a circular section through the length of transition to its corresponding point on a rectangular box section. The circular section gradually takes the shape of the rectangular box section within the transition, with no concentration of flow at any section of the transition, due to geometric change of shape. The proposed method is also applicable to any other type of transition, e.g., from circular to standard horseshoe shape.