Originally published: February 19th, 2016.
By David Metcalfe
Last updated: April 4th, 2024.
Accelerated precast construction of culverts and small bridges is made possible through innovative scheduling, delivery, design, manufacturing and construction methods to reduce on-site construction time and costs, while improving safety and reducing impacts on road users.
The standardization of accelerated precast construction in North America by transportation planners and designers focuses on identifying efficient ways to build transportation-related structures in a time of increased public demand for infrastructure rehabilitation, expansion, and replacement, along with the ongoing demand for skilled labour. The inclusion of engineered structural mesh in precast concrete structural design may provide immediate relief to limited municipal and provincial infrastructure budgets, while contributing to the resiliency of modern highway systems.
Precast reinforced concrete boxes, arches, and other three-sided spans are used not only for culverts and small bridges, but also for drainage and retention/detention components of stormwater management systems. Box and pipe culverts are in fact underground bridge structures. Simultaneous construction activity is possible using precast boxes and slabs for highway infrastructure applications. More than one structure on a project can be assembled at the same time, thereby speeding up project delivery.
Structural welded wire reinforcement (WWR) offers several other benefits over the use of traditional rebar:
WWR is made from higher yield strength steel, up to 550 MPa (80 Ksi) compared to regular 400 MPa (60 Ksi) rebar.
Steel content of a precast structure could be reduced by as much as 27%.
WWR is easier and faster to install, with reduced set-up time and smaller crews than for individual rebar placing and hand tying. Savings can be as much as 50% – 80%.
Smaller wire mats (more closely welded together and equally spaced) result in improved crack control in precast products.
WWR ensures proper positioning in mold forms with the added benefit of hassle-free inspections.
WWR can be bent and rolled to fit a wide range of precast and poured-in-place structures, including pipe and boxes.
Construction with mesh-reinforced products can be as much as 20% faster than projects that specify standard rebar reinforcement.
Using welded wire reinforcement makes the placing or assembly processes easier and thereby contributes to a safer workplace. There is a decrease in the risk of work-related accidents.
Deformed and welded bars create a solid anchor in concrete and there is no reinforcement shifting while concrete is being poured.
WWR mats are generally available in widths up to 10 feet and lengths up to 39 feet.
Much investment has been made into the technology of precast boxes for culverts in recent years. Not too long ago, the largest precast box was 3.75 m x 3.75 m. Some customers needed larger structures to accelerate construction schedules. Precasters responded with concrete boxes that are 6.25 m wide and 4.4 m high. Engineered structural wire mesh can accelerate installation time because less steel area is required for the same resistance. Full compliance with standards and codes is assured during installation.
The health and safety of the travelling public is of paramount interest to all involved in the construction of highway infrastructure. The speed of accelerated precast construction, facilitated by precast concrete elements produced with engineered structural wire mesh, not only ensures safe transportation systems, but ones that are resilient to natural and man-made disasters.
Changing weather patterns are affecting the hydraulics of critical infrastructure systems, such as storm sewers, culverts and small bridges in many urban areas.
David Metcalfe, C.E.T., is with Numesh Inc.
