Bridges

With the rapid growth in demand for transportation capacity in urban areas as well as on main connecting routes, the need to minimize disruption of existing services during bridge construction is ever increasing. The incremental launching of bridges is a key construction method to achieve minimal disruption to existing services. Incrementally launched bridges, however, have a unique set of challenges that must be addressed as part of the design, one of which is the geometry of the launch path. In order to launch a bridge the launch path generally has to be either a straight line or an exact circular path through space. In very rare cases have incremental launching been done even though the launch path was not limited to one of the above shapes. This paper is mainly concerned with presenting a practical method for the determination of circular curves in space for use in the design of incrementally launched bridges. The setting out coordinates of the piers, the casting yard, launching bearings and fixed bearings are all functions of the launch path. Another aspect directly affected by the launch path is the superelevation of the travelling surface due to the natural variation occurring on the inclined plane. Among others, the method as described in the paper was successfully applied in the design and construction of a 240.385m long incrementally launched bridge in Gauteng, South Africa.