When considering bridge deck forming systems designed to hold poured concrete, two options dominate the landscape: wood and steel. Wood, typically plywood forms, have been the traditional choice for years. Steel stay-in-place bridge forms, although less popular, are the superior choice.
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In new bridge construction and rehabilitation, steel stay-in-place bridge forms offer benefits that temporary wood forms cannot.
Steel stay-in-place bridge forms eliminate or alleviate the inherent dangers of bridge repairs or construction. This work often takes place at heights over waterways or over vehicular traffic, both risky environments for construction crews. Using steel forms is safer than wood forms for several reasons.
Unlike wood forms that must be assembled, installed and removed, steel stay-in-place bridge forms can be placed on supporting steel or concrete girders from above. Sev Mullen, district sales manager at New Millennium Building Systems, says this is a huge advantage of steel forms.
“When the bridge is going over roadways and especially over water, they don’t have to get on a barge or a boat underneath to work under the bridge,” he says.
Gerald Arvay, district sales manager at New Millennium, agrees.
“If you’re removing wood forms particularly over traffic, it becomes a very dangerous operation,” he explains.
New Millennium provides two steel stay-in-place bridge deck forms: Bridge-Dek® and Rhino-Dek®. Both provide a safe working platform immediately after installation. Wood forms made of plywood can fail when workers step on them.
“With Bridge-Dek® you’re working strictly on top of the bridge for the installation, and once it’s installed you have a safe working platform for the whole working length of the bridge,” Arvay says.
“It’s a safety factor,” Mullen adds. “That’s one of our big advantages.”
The safety of steel stay-in-place bridge forms also benefits areas under and around bridges—sometimes long after work is done. Bridges have a typical service life up to about 50 years, says Mullen, who estimates many of the rehabilitation projects he sees involve bridges built in the s and s. A recent American Road & Transportation Builders Association report found 45,023 of America’s 618,422 bridges are “structurally deficient” and need urgent repairs.
As bridges age or decay, weakened concrete can break away and fall, posing a risk to people, traffic and structures below. Steel forms that remain integral to the bridge structure prevent this.
“If the underside of the deck does eventually start to fail and deteriorate, and you don’t have the stay-in-place steel form underneath, you’re going to have falling concrete,” Arvay says. “If you do have the steel form, spalling deck concrete is contained and can’t fall and injure anyone.”
The same benefit is realized during construction.
“Steel deck also separates whatever’s under the bridge from, say, a dropped hammer or box of bolts,” Arvay says. “It keeps things from falling through.”
Speed of construction and project timelines are particularly important in bridge projects that may disrupt traffic flow and commerce in communities. Steel stay-in-place bridge forms streamline and facilitate construction in multiple ways.
By virtue of their design, steel bridge deck forms keep repair or new construction projects on schedule. Steel bridge deck seamlessly integrates with concrete or steel girders. The deck panels are easily staged on the job site and can be retrieved when needed.
Once on the frame, the strength of the steel deck can support workers instantly. This limits work interruptions and keeps workers on schedule. The deck panels’ factory-closed ends also mean the concrete pour can take place as soon as the forms are connected to the girders.
In harsh environments, polymer-laminated bridge deck, including Rhino-Dek from New Millennium, eliminates welding. That connection process could mar the protective surface. Instead, it is bolted or screwed to the girders, which is quicker and cheaper than welding in the field.
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Arvay and Mullen estimate installation time of stay-in-place bridge deck is 50 percent quicker than that of wood forms requiring assembling, installation and removal.
Taken together, the benefits of steel forms add up to overall cost savings. Compared to wood forms, steel reduces costs 20 percent to 25 percent.
Since steel bridge deck becomes part of the structure, it removes the need to buy materials for temporary wood forms. Most importantly, however, steel deck requires less labor.
“When you think about the labor involved to build the plywood forms and then strip them back out when the concrete has cured, the installed cost of the metal deck is less,” Arvay says.
Designed to be long-lasting, steel bridge deck forms lower long-term maintenance costs. The deck can be galvanized to resist corrosion from road salt used in winter or can be covered in a polymer-laminate coating to endure saltwater environments. Rhino-Dek, for example, has a 124-year service life, the Florida Department of Transportation has determined.
Not only are a significant number of new bridge structures being built of all types and sizes, but critically many existing bridge assets require maintenance and repair to meet the demands of society.
We can offer integrated products and systems, which produce efficient and clever solutions when combined together. PERI UP scaffolding can provide access and working platforms, and combined with our civil engineering range VARIOKIT, can be suspended or configured for any geometry required.
Either for new structures or the refurbishment and reinforcement of existing ones, we have an extensive range of formwork systems including lightweight handset to bespoke heavy-duty steel forms. Finally, our shoring systems, based on a modular lightweight concept of minimum pieces with maximum capacity, provide the reassurrance required during the construction phase to support the structure until it is capable of supporting its own mass.
The components of a bridge are divided into substructure, superstructure and equipment. Which of the structures and superstructure cross-sections are used, depends on factors such as length, span, materials, type of use, loads and the topographical and geological conditions.
They are classified according to different aspects; potentially by their positioning in a geographical feature like river, valley or slope and according to their construction material in concrete, steel, wood or composite.
When considering the structural design, the focus is on the structural/superstructure cross-sections and the component groups.
In general, bridges are divided according to their construction principle into in-situ concrete bridges, prefabricated and segmental bridges. There are four different construction methods for in-situ concrete bridges:
This method is suitable for bridge structures with a low overall height and free access to the underside of the bridge. Depending on the level of the terrain, the shoring can be set up as stationary or movable. The loads from the structural formwork are transferred to the subsoil via the shoring/falsework.
This process is suitable for bridge structures with large pier heights and the underside of the bridge that is difficult to access. The feed gantry is one of the self-supporting formwork and scaffolding systems. After concreting in sections, the system is moved in the longitudinal axis with movable support beams - without any additional support between the bridge piers. The loads from the structural formwork are absorbed by the feed gantry and passed on to the piers of the bridge.
With this process a high level of cost-effectiveness is possible thanks to uniform work processes. The superstructure will be constructed whilst stationary in sections in a field factory behind the bridge. After a new bridge section has been manufactured, it is lifted hydraulically and moved in the direction of the longitudinal axis until the stem rests securely on the support saddle of the next support.
The cantilever construction method is suitable for bridge structures with large spans and difficult topography - for example when crossing bodies of water, valley cuts, etc. With cantilever construction, the superstructure is constructed symmetrically from the pillars according to the balance beam. There is therefore a front carriage on both sides of the pillar, which moves the formwork to the next concreting section via a cantilever arm structure. There the next construction phase is added to both freely cantilevered component ends.
Our bridge solutions are generally based on a single system, the VARIOKIT engineering construction kit, which can purchased or rented on a project-specific basis. VARIOKIT can create a wide variety of supporting structures, for example trusses or shoring towers. At the same time, the engineering construction kit is also the basis for all types of formwork processes - from the cornice cap console, cantilever construction, steel composite carriages to climbing formwork. With electric and hydraulic components, the VARIOKIT engineering kit can be expanded to include mechanical functions that enable the formwork elements to be raised, lowered, moved, climbed, shuttered and stripped.
With only three core components - the steel bar SRU, the climbing rail RCS, the heavy-duty spindle SLS, approximately 80% of all heavy-duty structures can be constructed with these three core component parts. Another 15% are also system components from the VARIOKIT engineering kit; the remaining 5% are project-specific special components. This consistently simplified construction principle of the VARIOKIT engineering construction kit enables a high level of safety and speed - both during assembly and dismantling, but also in use on the construction site.
Another key system advantage of VARIOKIT is its ability to be combined with the PERI UP scaffolding, protection and shoring system. Both systems are based on the metric scale with a grid of 12.5, 25 and 50 cm and are therefore completely compatible with each other.
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