Accelerated Bridge Construction could solve a growing issue as many bridges across Australia come to the end of their structural lives.
Many bridges throughout the country are reaching the end of their usable life span. In New South Wales alone, 650 have been deemed “unserviceable” or “likely to be currently unsafe.” More than $340 million is needed in the state just to bring its timber and concrete bridges up to a ''satisfactory'' condition. An innovative technique, however, could provide the answer to this crumbling infrastructure.
Work that occurs from on-site construction activities can have significant social impact on mobility and safety. In many cases, the direct and indirect costs of traffic detours that result from the loss of a bridge during construction can exceed the actual cost of the structure itself. Partial lane closures and other bridge activities that occur alongside adjacent traffic can also lead to safety issues.
Accelerated Bridge Construction uses innovative planning, design, materials, and construction methods in a safe and cost-effective manner to reduce the on-site construction time that occurs when building new bridges or replacing and rehabilitating existing bridges.
There are both innovative geotechnical and structural solutions that are now helping achieve this goal.
The Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS), for example, lowers costs, slashes construction time, improves durability, and increases safety all at the same time.
GRS-IBS technology uses alternating layers of compacted granular fill material and fabric sheets of geotextile reinforcement to provide support for the bridge. GRS-IBS also provides a smooth transition from the bridge onto the roadway, and alleviates the "bump at the bridge" caused by uneven settlement between the bridge and approaching roadway.
Costs are reduced by 25 to 60 per cent from conventional construction methods. It is easy to build with common equipment and materials and easy to maintain because it requires fewer parts. The flexible design also means that it can be easily modified in the field for unforeseen site conditions, including utilities, obstructions, existing structures, variable soil conditions, and weather.
From a structural perspective, pre-fabricated bridge elements and systems are at the heart of the ABC approach. These pieces are used in combination with unique structural placing methods such as Self-Propelled Modular Transporters (SPMT), which are a combination of multi-axle platforms operated through a state-of-the-art computer-controlled system that is capable of pivoting 360 degrees as needed to lift, carry, and set very large and heavy loads of many types.
SPMT transporters move at walking speed and are capable of carrying large bridge structures from off-site locations, positioning them precisely into final position. The SPMT then exits the site, opening the area to traffic possibly within minutes or certainly within a few hours.
America has been using Accelerated Bridge Construction (ABC) on hundreds of small projects across the country but now New York’s Department of Transport is using the ingenious technique on a major interstate highway.
Replacing the 135-metre bridge on the I-84 connecting New York with Connecticut using traditional construction would have taken more than two years, involved multiple closures, and required a temporary bridge, adding $2 million to the overall cost.
Using ABC, support structures were built around the existing bridge, a new roadway was built on top, the bridge underneath demolished and the new bridge simultaneously slipped in onto new supports.
Construction of the associated elements has taken less than a year while the new bridge was moved into place in a matter of hours.
With time running out for many bridges in Australia and budgets remaining tight across local governments, ABC seems a logical engineering approach for this creaking area of the country's infrastructure.