Romtec incorporates glulam beams into many of our building designs. These materials not only look great, but they are also a very reliable and durable structural component. What exactly is a glulam? A glulam is glued laminated timbers bonded into a single structural beam or column.
What are glulams made of? Well, it depends on where the beams are made. On the west coast, most glulam beams are made of Western Douglas Fir. Sizes include 3-1/8”, 3-1/2”, 5-1/8”, 5-1/2” & 6-3/4” widths, and there is a standard 1-1/2” increment depth. In the East, Southern Pine is used. Sizes include 3”, 3-1/2”, 5”, 5-1/2” & 6-3/4” widths, and there is a standard 1-3/8” increment depth.
There are 4 different types of glulam beams: simple span beams supported on both ends; continuous or cantilevered beams that extend beyond the support wall or post; tension beams that keep something from expanding or moving away; and compression beams (better known as columns). Romtec uses all four types of beams in our structures.
Typically, all our glulam beams are specified as 24F-V4 unless otherwise noted. Curious what those numbers and letters mean? In the 24F-V4 specification, the first part –24F– stands for 2400 psi allowable bending stress. Likewise, a 26F glulam would mean 2600 psi allowable bending stress. You can order several different stress levels such as 16F, 20F, 24F, 26F, 30F, but 24F is the industry standard and is what our engineers typically specify.
In the second part –V4– the “V” stands for visually inspected or graded. An “E” would mean mechanically graded. The “4” in the V4 stands for an “unbalanced” beam, which are mostly used as simple span beams, but they can also be used to cantilever as long as the cantilever isn’t very big. There are other glulam alphanumerical specifications as well. Sometimes we will specify a “V8,” which stands for a “Balanced” beam.
To compare balanced and unbalanced beams, view the differences in the two figures above and to the right. An unbalanced beam is designed for loading in the middle of the beam, which is supported on both ends and will bend or deflect as a result of the load. Look at Figure 24F-V4. Notice that the bottom cord, or “A” part, is made from a higher grade wood than what is on the top “C.” When the middle of the beam is bending down, the majority of the resistance is on the bottom where the beam is the strongest. “Balanced” beams are held at a fixed point like a wall with a load on the cantilevered end of the beam. The tension this time is on the top, so the higher grade lumber, “A” is on both the top and the bottom cords, as shown in Figure 24F-V8. The beam is “balanced” in this configuration. Additional numbers can be used to describe other layups for the beams.
Columns, on the other hand, do not experience tension or compression in the same way as a beam. A column’s load is distributed over the full length of the glulam, so it can be made from “C” grade lumber throughout. See Figure Comb. 3 below.
The appearance of glulam beams uses 4 different grades: framing, architectural, industrial, and premium. Romtec typically supplies architectural grade beams on our buildings. These high-quality beams are used where appearance is important. They offer a rustic wood grain look, but all large knots are puttied over to provide a pleasing and consistent wood tone.
Framing beams are typically supplied as full-width beams in applications where additional furring or framing is not required. The finish of framing grade glulam beams can vary in quality. Industrial grade beams are used where appearance is not a priority. There can be voids on edges of laminations that don’t have to be filled. Premium grade beams are made of the highest quality lumber and are used where the best specifically where visual appearance is required.
The location of a beam must also be considered. The wood species and adhesives for laminating the beam depend on whether the beam will be in a “wet” or “dry” location. A “wet” location is one where a beam is directly exposed to the elements. For such applications, Romtec might specify a beam made of Port Orford Cedar, which is considered one of the best types of wood for decay resistance. It is also regarded as the strongest of all the cedar varieties. Romtec also uses Alaskan yellow cedar, which is valued for its appearance and decay resistance.
All glulam beams (but not columns) have camber. Camber describes a “crown” shape that is purposely manufactured into a glulam beam. It is most often desired in long span applications to counteract deflection. Camber is manufactured into a beam to maintain the visual appearance of the beam by preventing any amount of sagging. Glulam beams typically have a 3500′ radius. This is sometimes called “zero camber.” See figure below for standard camber sizes. Beams with camber have “top” and “bottom” surfaces. Most beams are stamped to designate which surface is “Top” and “Bottom.” Getting the orientation of the beam correct is important since the strength of the beam is reduced by 25 percent if it is installed upside down.
The last thing I will cover is what does that stamp on the glulam mean? See the figure above. The first line reads “APA EWS” and means the “American Plywood Association Engineered Wood Systems.” Line two is “B” for simple span but it can also read “C” for a compressive member, “T” for a tension member, or “CB” for a cantilevered span member. The next three letters indicate the appearance. On the example IND stands for industrial finish, but there is also PREM for a premium finish, ARCH for architectural, and FRAM for framing.
The EWS Y117 is a lamination specification dealing with the process and types of glue used to manufacture the beam. Line three, EWS 24F-1.8E is the beam specification as we have been discussing. In this case its 2400 psi unbalanced beam mechanical graded. DF means this beam is made from Douglas Fir, AC or AYC would mean Alaskan Yellow Cedar and so forth depending on the type of wood used. In line four, MILL 0000 designates the specific mill where the beam was manufactured. ANSI A190.1-1992 is the American National Standard for Glulam Beams identification of ANSI standards.
Glulam beams and columns are a great building material. They are engineered to be used in many applications and offer a wide range of benefits when used correctly. Glulam beams and columns also provide buildings with an attractive design feature to give a restroom, pavilion, or other Romtec product a special appearance in parks and other popular applications.