> For the complete documentation index, see [llms.txt](https://docs.enercalc.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.enercalc.com/sel-faq/using-the-software/calculation-modules/beams2/wood-beam/how-is-wood-beam-calculating-f.md). # How is Wood Beam calculating Fb\* and Fb’ for glulam beams How the Wood Beam module calculates Fb\* and Fb' for glulam beams considering tension location, CV, CL, and Cfu. ## How is Wood Beam calculating Fb\* and Fb’ for glulam beams? The calculation of Fb\* and Fb’ depend upon CD or Lambda, so the discussion should always focus on a particular load combination. 2018 NDS defines Fb\* as follows: ![](https://1076748670-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FtBL2fEQRwrlKSM2irFL0%2Fuploads%2Fgit-blob-a4b4c9da7a9bc99db83201d9430fa137b1df8e86%2FFb_star.jpg?alt=media) Some glulam beams have two different values for Fb, depending upon whether the bottom or the top is in tension. This means it is theoretically possible to calculate two different values of Fb\* leading to two different values of CL, depending upon which surface is in tension. And this could change along the length of a beam. ENERCALC SEL uses a conservative simplification for the calculation of Fb\*. It uses the smaller of the Fb values to calculate just a single value of Fb\* for each load combination, resulting in just a single value of CL for each load combination. But when it comes to the calculation of Fb', the program does actually consider the location of the tension. So if the tension is on the bottom at a location of interest, ENERCALC SEL calculates Fb’ as follows: Fb'(bottom in tension) = (Fb\*) \* (lesser of CV and CL) \* Cfu And if the tension is on the top at a location of interest, ENERCALC SEL calculates Fb’ as follows: Fb'(top in tension) = (Fb\*) \* (lesser of CV and CL) \* Cfu --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.enercalc.com/sel-faq/using-the-software/calculation-modules/beams2/wood-beam/how-is-wood-beam-calculating-f.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.