Greetings from Bridging Solutions!

This installment of “A Bridge Moment” is the second in a series titled Everything You Always Wanted to Know About Concrete Box Culvert Bridges* (*But Were Afraid to Ask)

What about 3 sided box culverts?

Three (3) sided box culverts (no bottom slab) are used when longer spans are required and they are almost always constructed using precast concrete. The 3-sided box culverts are available with flat top slabs, arched top slabs or full arches and are supplied with spans up to 48 feet and as long as 60 feet for special orders. The 3-sided box culverts are typically supported on shallow cast-in-place concrete spread footings, but precast footings are sometimes used for shorter spans (less than 24 feet).

Three sided box culvert with integral faux arch on fascia element

The CONSPAN bridge system (a 3-sided box culvert with an arched top slab) is the most familiar name when it comes to 3-sided box culvert products in Florida as a result of its pleasing aesthetics and a strong marketing approach by the product vendor. This product was originally a patented product that required a precaster to be a licensee of CONSPAN to be able to sell the product. The patent expired in 2003 which has allowed other precasters to manufacture and sell the product. CONTECH purchased the CONSPAN company business assets in 2005 and is the only company that can sell the product using the CONSPAN name.  Some of the generic names the author is aware of include Forterra Arch, Arched Box Culvert, and ECO-SPAN. The arched top slab is a benefit related to the structural design, but is a detriment related to the roadway design when the construction depth of the bridge needs to minimized.  In the private sector on land development projects, some civil engineers rely on product sales and specialty structural engineers for bridge engineering services without the benefit of a Structural (Bridge) Engineer of Record which adds a higher level of professional responsibility that most civil engineers don’t recognize.

3-sided bridge with arched top slab (aka CONSPAN)