InTrans / Aug 10, 2015

A new look at wood, one of the original bridge-building materials

More than 25 percent of U.S. bridges are structurally deficient or functionally obsolete. The problem is especially critical on rural roads.

Timber bridges offer useful solutions because of their affordability, ease of construction, and efficient use of “green” naturally sustainable forest resources. In fact, wood bridges may be considered the original accelerated bridge construction (ABC) option.

Yet too often the advantages of timber bridges are under-appreciated by road agencies that base their opinions on out of date, anecdotal information about timber bridges.

The National Center for Wood Transportation Structures (NCWTS) at the Institute for Transportation provides information, technical expertise, and assistance to engineers and bridge owners to promote the use of wood transportation structures such as bridges.

The NCWTS is a university-­agency partnership between Iowa State University, the Federal Highway Administration, U.S. Department of Agriculture Forest Products Laboratory, and the National Park Service. The NCWTS works directly with industry and agency partners to integrate university and government research and provide the bridge community with current, relevant, and applicable timber bridge information and support. It also supports a national demonstration and technology transfer program.

For one demonstration project that will culminate in summer 2015, the NCWTS is leading the design, development, construction, and monitoring of the first glulam timber bridge on GRS-IBS abutments to be constructed in Iowa.

“Glulam” is glue laminated timber, an engineered wood product consisting of individual structurally graded laminations of wood, usually two inches thick or less, bonded together. This engineered timber not only is stronger than its solid sawn predecessor but also, if properly maintained and inspected, has a service life that spans 70-plus years. In addition, glulam can be fabricated in many shapes and sizes. Another advantage is that glulam structures are lighter than traditional bridge construction materials such as concrete and steel, resulting in less dead load on the substructure and thereby requiring smaller (both in size and quantity) construction equipment. Glulam bridges are easily constructed by both experienced bridge contractors or a county bridge crew to save additional costs.

For more information contact

Travis Hosteng, NCWTS director,

This aritcle is part of the CTRE EnRoute 2014 Year-at-a-Glance series. Download the full document (.pdf).