Engineered Wood Product (EWP): The Wood I-Beam/Joist

Engineered Wood Product (EWP): The Wood I-Beam

Let’s begin by looking at developing some discussions and shared operational experiences dealing with a specific engineered wood product (EWP) that being the Wood I-Beam. The wood I-beam has been around for over twenty-five (25) years, with structural components of wood composite I beams with laminated veneer lumber (LVL) flanges, hardboard, wafer board or plywood webs.

Everyone is probably aware and has insights into engineered wood truss systems and assemblies and the many inherent operational and safety issues affecting incident operations. But other engineered wood products, such as wood I-joists/beams and laminated veneer lumber (LVL), surfaced in the mid-1970s.

Even so, it was not until the early 1980s that engineered wood became widely accepted, and continues to gain popularity as the material and system of choice in present day design and construction systems. Building upon the knowledge of creating veneer wood and the ability of the rotary lathe to create thin sheets of wood, John K. Mayo was issued a patent for plywood on August 18, 1868. Engineered lumber took another step forward with the development of oriented strand board (OSB) in the late 1970s and its expanding popularity as a building component in the majority of today’s construction.

Since the 1980’s, a number of additional engineered wood products have been developed and are being implemented in many types of construction, occupancies and applications. According to published industry reports, the sales of engineered wood products have doubled every five years over the past two decades.

Components – Wood I-joists are composed of two horizontal components called flanges and a vertical component called a web. Wood I-joists are used as a framing material primarily in floors, but may also be used as roof rafters where long length and high load capacity are required. Wood I-joists offer the advantages of exceptional stiffness, light weight, and long span capability.
Holes may be cut in the web according to manufacturer’s recommendations, allowing ducts and utilities to be run. I-joists are dimensionally stable, and thus are unlikely to warp, twist or shrink; they are uniform in size; and are consistent in their manufacturing. The “I” shape allows the most efficient use of wood necessary to carry design loads. This is achieved by placing the material with high strength and stiffness in the flanges. Similarly, the web material is high quality, but with different structural properties. I-joists utilize the geometry of the cross-section and high strength components to maximize strength and stiffness of the available wood fiber. Flanges are manufactured from end-joined, solid sawn lumber or structural composite lumber (SCL), while webs typically consist of high strength plywood or oriented strand board (OSB).

Manufacture of I-joists - All web and flange materials are carefully graded to ensure they will perform properly in I-joists. The flanges range from 1-5/16” to 1-1/2” thick and from 1-1/2” to 3-1/2” wide.

Today, the web material used almost exclusively is OSB. I-joists manufactured prior to the early 1990s also had webs made of plywood. Web material in typical residential I-joists is either 3/8” or 7/16” thick.

Performance Requirements for Code Acceptance - Although I-joists differ among manufacturers, they are all manufactured to an industry consensus standard. I-joist performance is closely monitored by the manufacturer and an independent third-party quality control agency. The quality control program assures the product continually meets code-recognized test standards. The two most important performance characteristics are strength and serviceability.

Fire Incidents with I-Joists - Specific fire incident reports indicate that when directly exposed to fire (unprotected), the loss of strength of I-joists often occurs in conjunction with burn-through of floor sheathing. Within the I-joist itself, the web is consumed first (because of reduced mass). Once the web is consumed, the bottom flange is no longer attached to the joist and falls from the system. Numerous fire incidents have been reported where the only remaining structural components in the floor system were the top flange and floor sheathing. The resulting floor systems, while remaining intact, had over 12" of deflection. Similarly, many reports indicate that firefighters either felt a floor become “soft” or “spongy” or visually observed deflection and exited the structure. ( Source: AF&PA; http://www.woodaware.info/guideijoists.html)

Let’s begin our discussion by having you share some experiences and insights at incidents and operations that you may have responded to that had wooden I beam structural assemblies;

What were your experiences with the wooden I beam product in the identified occupancy or structure?
How did the material perform and what impact did the presence of the engineered systems have on structural performance of the occupancy under fire conditions?
How was firefighter safety affected?
What are your lessons learned that can be shared?
Have you made any efforts to modify your response procedures and protocols for structures involving EWP systems?

We’ll attempt to identify other incident operational and technical issues to increase your knowledge and understanding of these systems under structural fire conditions, as the discussion thread and interests expand.