Incremental launch

With incremental launching method, we describe a method of production of bridges.

Here, the construction of the continuous bridge deck ( multi-span ) section by section behind an abutment in a manufacturing facility, which is also known as " clock cellar ". After the completion of a bridge portion that is displaced together with the portions of the previously prepared on the pillars ( " inserted " ) in order to produce the next stage ( clock ) can. The method is particularly applicable for longer bridges with straight or nearly circular outline and with uniform tops or tank radius in elevation.

History

This Production was initially used because of the limited plate lengths especially in steel bridges. In prestressed concrete was first in 1962 pushed the bridge over the Rio Caroni with the aid of slide bearings and launching nose in Venezuela. For the construction of the highway bridge Inn Valley at Kufstein optimized Fritz Leonhardt and Willi Baur this construction method and developed the still used technique of incremental launching method.

Description of the procedure

When incremental launching method in prestressed concrete takes the place of manufacture of bridges on teaching or feed mills, a factory-like production in repeating sections. Here, in a stationary casing behind the abutment of the superstructure in short sections ( bars ) is produced. The individual sections are concreted directly to each other and connected by tendons together to bending. Then the hardened new bridge section is raised a few millimeters and shifted by one clock length along with the other already finished bars in the direction of bridge axis forward. This is done by means of hydraulic presses and PTFE bearings. Then the next segment in the same location is made in the same mold. Usually a clock per week is made. At the front section of a steel launching nose is mounted to reduce occur when you move to reach the supports cantilever moments. In particular, hollow box sections are suitable for the incremental launching. The method is very economical because of its short transport distances, small appliances parks, good formwork and shoring utilization, and recurrent operations. The disadvantage is that due to the process of cross-section of the superstructure will remain unchanged and therefore must be required for the largest span construction height is decisive.

The sections insertion of steel bridges ( one speaks also of " launch " ) or steel beams of composite bridges works in the essential steps analogous to incremental launching in prestressed concrete. In contrast, however, refers to the production of the bars only in the assembly of support parts. The actual production of the steel construction will take place in workshops. Due to the often much lower dead weights of the parts of a launching nose is often not necessary. The sections can also have different lengths here. The size and weight of the items is limited mostly by the means of transport to the site.

Recent Developments

With the contact process ( concrete ) as it was applied in the Viaduct Schnaittach, it is now possible to also bridge decks with variable location in curved axis to produce (eg a clothoid ). In this case, an approximation polygon replaces the variable location in curved axis of the superstructure follow the individual bars as a joint chain with different bend angles. The clock manufacturing facility is thereby rotatable and may also be produced in plan tilted. When concreting a new clock to the About Bauzug already created the kink angle can be adjusted, resulting from the calculation of the approximate polygon. The balance of the advance occurring during lateral and elevational variations of the superstructure relative to the end position in the simplest case by transversely displaceable Verschublager on the pillars, in the case of a variable gradient through hydraulically height-adjustable stock with a corresponding control.