Prefabrication is the designing and manufacturing of assemblies under factory conditions, then transporting them to—and assembling them on—a construction site. The technique is most widely used for concrete and steel sections in structures where a particular part or form is repeated many times.
In civil engineering, prefabrication plays a key role in the construction of bridges, roads, tunnels, and more. Prefabrication can be used for:
- cantilevered decks of elevated bridges in highway projects
- parapets of expressways and road curbs
- precast girder units and beams for elevated roadways, tracks, viaducts, and pedestrian footbridges
- decks for long span bridges
- tunnel linings, especially for tunnels formed by tunnel boring machine
- sea walls
- railway platforms
- noise barrier panels
- overhanging ducts and service channels for underground facilities
- storm water discharge culverts
… and many other elements of a civil design project.
Contributing Factors to the Prefabrication Trend in Civil Engineering
The main reason for prefabrication construction is to reduce the overall construction time on a project. This time savings can yield significant budget savings.
Prefabrication allows for work to be conducted simultaneously onsite and offsite, as well as helping with better coordination among the project team.
Less onsite staging, such as scaffolding, is needed. Weather does not impact construction. Prefabrication can also reduce onsite resources, such as labor and equipment, and minimize waste. Factory conditions offer quality control checks on each piece produced.
Prefabricated concrete, for example, can avoid the imperfections frequently found in concrete poured onsite. The lack of exposure to the elements, and the ability to fabricate in factory conditions rather than on ladders or from scaffolding also improves quality.
Examples of Civil Design Projects Using Prefabrication
The new replacement Goethals Bridge, linking Elizabeth, New Jersey, to Staten Island in New York City, is currently under construction and has a cable-stayed design. The replacement bridge will be located directly south of the 88-year-old existing Goethals Bridge.
The design of the $1.5 billion project was led by Kiewit-Weeks-Massman. Prefabricated steel will compose two spans, one eastbound and one westbound, to measure 1,635 feet. The project team is constructing 36 precast concrete structural support columns for the foundation—18 each for the eastbound and westbound roadways—consisting of prefabricated steel rebar shafts.
Prefabricated anchor boxes will be installed at the top section of the bridge’s eight towers. The new bridge is scheduled to open in 2017 on time.
The Crossrail railway project in London is Europe’s biggest underground construction project.
Twenty-six miles of twin-bore tunnels have been built for the addition of 10 stations and linking to 30 existing stations. Eight tunneling machines bored the 6.2 diameter rail tunnels, 40 meters under London.
Over 200,000 prefabricated concrete segments line the tunnels. Seven segments and a keystone will be used to make up tunnel rings, locked together to build a concrete tube reinforced with steel fibers. Each segment weighs 3,000 kilograms and each keystone weighs 1,000 kilograms. Crossrail construction is being delivered on time and within budget.
Panama Canal Expansion
The Panama Canal expansion project adds a new lane to the existing two lanes to allow for passage of large vessels, such as container ships, bulk carriers, and tankers. Work began in 2014 and is expected to be complete in May 2016 at a cost of over $5 billion. The new lane will have two locks chambers, one on the Pacific side and one on the Atlantic side.
Installation of 16 prefabricated rolling steel lock gates was completed last year. They were manufactured in Italy, then shipped, tugged, and “rolled” to the site.
When complete, ships will enter through two-pair of buoyant gates, which are 7-feet-thick, weigh up to 3,200 tons, and are up to 82-feet high. In addition, 46 prefabricated steel lock walls were put into place to hold water in the lock chambers that range from 45- to 55-feet thick at the base to 8 feet at the top.
West Kowloon Terminus Station North
The West Kowloon Terminus Station North is the largest civil contract awarded for the Hong Kong section of the Guangzhou-Shenzhen-Hong Kong Express Rail Link.
Located in Kowloon, the terminus will serve as Hong Kong’s international gateway to China. Engineering firm BuroHappold designed a curved, steel, and glass roof to accommodate a large central space to provide natural light and views of Hong Kong Island. The free-form roof will be made up 7,000 tons of prefabricated steel trusses weighing up to 40 tons each.
Doubly-curved trusses, triangular in cross-section, will form three long curved lattice trusses. These will be supported by prefabricated curved steel columns up to 50 meters in height. A concrete roof beam for the steel roof will be comprised of six concrete cantilevering beams, with eight concrete sections spanning between each beam.
INDUSTRY SOLUTION EXPERIENCE: Civil Design for Fabrication