What is deck launching?
Deck launching is a construction technique used to move the deck of a viaduct from the plant to its final position.
It consists of launching the segments horizontally (each horizontal section between pillars) until reaching its final position, when they are lowered vertically. The technique also uses other techniques such as tensioning and heavy lifting.
When it comes to large viaducts, we are specialized in producing a deck in sections (segments) in a manufacturing park, moving it to its final infrastructure and passing it over the piles via a concatenation of special support and jacks. The segments can measure up to 100 meters (as is the case with the Uztarreta viaduct) and are placed at high altitudes.
Manufacturing and transportation
Everything starts at the manufacturing park, close to the civil construction site, where the concrete and steel segments that will form part of the horizontal decks are manufactured. When the decks are large, they are built on the construction site (some can be hundreds of meters long).
In this highly industrialized manufacturing area we can construct them quickly, safely and with high quality. In this area we also carry out other activities such as structure tensioning before moving it. Once the segment is built, it has to be moved. If it is small, the segment is moved on the road.
Here is when heavy lifting specialists come into play, because each section has to be lifted and placed on special transportation and the opposite has to be done on-site. Although it is most common for construction to be carried out on-site due to the size of the sections.
If built on site, the procedure starts by launching the deck horizontally until coinciding with the vertical piles. In order to do this, a launching nose is inserted at the front part of the section, making it possible for it to always be in contact with the following pile, and a group of hydraulic jacks move the load just a few centimeters at a time.
Deck launching phases
The launching process consists of four phases:
- A vertical jack lifts the deck.
- A horizontal jack pushes the platform approximately 20 centimeters.
- A vertical jack lowers the deck. The cycle is repeated to move the decks forward.
This technique usually takes a number of days and is the safest way to move the decks. In each phase the stability of the piles are checked and during the launching procedures, post-tensioning often needs to be performed. This is done to “brace” segments together to provide the continuity needed by the deck and to help it withstand loads during launching operations.
When the whole deck has been launched and placed in their final location, it is time to take the launching nozzle apart and perform exterior post-tensioning. Exterior post-tensioning operations facilitate inspection, re-tensioning operations and the durability of the construction.