Single vs. Double Beams for Mass Timber Construction
The most common framing configuration for mass timber construction consists of single glulam beams on column grid, supporting mass timber floor/roof panels. These beams usually only extend between adjacent columns, and are attached to the columns with hangers or via a notch seat into the column face. However, An alternative to the single beam system is the double beam system. With the double beam system, 2 beams are on each column grid, usually each just set off a small distance from column centerline and each supporting the mass timber floor/roof panel.
Although the double beam system may not be the most efficient system for all mass timber projects, it is worth evaluating. Some noted benefits include the ability to cantilever the beams beyond the column without needing to run the beam over the top of the column; smaller beam cross sections which could result in more "stock" member sizes; and simplified connections, often just relying on notches into the column and fasteners for stability and eccentricity.
In this video, I share a conversation I had with Rens Hayes of H+O Structural Engineering, a Boston-based engineering firm. They are working on a project which broke ground in the summer of 2021, 11 E Lenox in Boston, a 7-story mass timber, passive house, multi-family building which uses the double beam framing system. In this conversation, we discuss the reasons that the double beam system was chosen for this project.
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Ricky McLain is a structural engineer and mass timber specialist at WoodWorks. This video and this channel are based purely on Ricky's own observations, experiences and opinions and do not necessarily reflect the opinion nor beliefs of WoodWorks.
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Thumbnail credit: Monte French Design Studio and H+O Structural Engineering
Project AEC/Development Team: Patrick Haydon (Haycon), Monte French (Monte French Design Studio), Rens F. Hayes IV, P.E. (H+O Structural Engineering), Eli Gould (QWEB)
Пікірлер: 8
I have studio review in 2 days using mass timber. Wish I would have seen this a month ago!
@MassTimberHowTos
2 жыл бұрын
Bummer, best of lick with the studio. Hopefully the video is still helpful!
1- A single GL beam can be cantilever at the side of the column as well. Therefore, that is not an advantage only to the double beams. 2-The double beams method can create some fire safety for the top side of the column. But, double beams methods make the beam weaker along span in a fire event and increase the char rating of the beam significantly. It means double beams has a faster charring rate than a single beam when they have a similar size section area. Therefore, that is a disadvantage to the double beams. 3-Always double beams will be thicker than the width of the wall underside, which is an architectural disadvantage to the double beams compare to the single beam. 4- Two single beams have a higher load-carrying capacity than this double beams system, which is the cost-efficiency disadvantage of the double beams compared to a single beam. Finally, I think double beams method will increase number of required fixings/screws.
Here is the project link for 11 East Lenox: www.mfds-bos.com/project/11-e-lenox/
@MassTimberHowTos
2 жыл бұрын
Thanks!
No sound as soon the interview (i.e. 2 people in view) starts?? There is sound at the start and end of the clip when there is just 1 person in view. I would to love to hear what is being said (switching on subtitles is not quite the same due to transcription errors). NB Very interesting subject, thank you!
Great videos, keep it up! It looks like these mass timber buildings hold up well to 1st instance of fire. How do they fare for subsequent fire events? 2nd or 3rd fire events?
@MassTimberHowTos
2 жыл бұрын
As with any structural material, evaluation and potential repair may be necessary following a fire event. Some mass timber members are over-sized to provide a wild charring layer, so that charred layer may be able to be removed and replaced with new wood, without needing to remove the entire wood cross sections.