Automated Geometry Control of Precast Segmental Bridges

The short-line match-cast joint method of pre-casting concrete segments has proved to be the most versatile and reliable way to building pre-cast segmental bridges. The essential feature of match casting is that successive segments are cast against adjoining segment in the correct relative orientation with each other starting from the first segment away from the pier. The segments are subsequently erected on the same order and hence no adjustments are required between segments during assembly. The success of short-line match-cast joint method relies heavily on accurate geometry control during match casting as the scale of adjustments during erection is very small and difficult to implement. The required levels of accuracy in positioning the segments match-cast against each other are stringent in order to assure acceptable tolerances in the geometry of the structure. It was found that even a fraction of millimeter of error in segment casting gets amplified to several meters at the end of the bridge span and can result in significant rework. Stringent control of geometry and successive correction of errors are required to ensure that the geometry of the bridge is maintained. The paper will describe the match-casting process and the sources of errors in the process. Next the detailed steps to determine and correct the error are discussed. Finally a conceptual system comprising of a laser based measurement, processor controlled and a servo based form adjustment is proposed to automate the entire process.