Front scaffolding
The porch frame ( French poutre de LANCEMENT , English launching gantry ) is used for section-wise construction of the superstructure long prestressed - box girder bridges from prefabricated segments in cantilever used.
The front scaffolding is a mobile steel scaffolding that extends over two, usually two and a half bridge fields , which is supported on the pillars that have already been built . It picks up the box girder segments produced in the contact process and delivered via the existing sections of the bridge and transports them to their intended place in the superstructure.
In the traditional method, the 2 to 3 m long segments are placed in pairs on either side of the outer pillar to maintain balance. There they are bonded with epoxy resin to the ends of the cantilever arms that have already been installed and anchored with tendons . As soon as a bridge field is closed in this way and the cantilever arm on the other side of the pillar has been built in front of the middle of the next bridge opening, the front scaffolding is moved to the next bridge field.
The further developed processes take up box girder segments up to 40 m in length and place them between the two pillars.
The front scaffolding was developed by Jean Muller in 1963 and was first used in France between 1964 and 1966 for the construction of the Viaduc d'Oléron .
It is not to be confused with the advancing scaffolding developed in Germany between 1959 and 1964 , which is used to create the superstructure with in-situ concrete using a movable formwork frame.
