As an engineer, it makes things easy when the buildings being designed are rectangular. This tends to make the connections occur between nice perpendicular members, and standard connectors and joist hangers can be used.
But buildings are not always rectangular and connections are not always between perpendicular members. Non-perpendicular members can have a skewed connection, where the supported member is moved side to side from perpendicular; or a sloped connection, where the supported member slopes up or down from a standard horizontal orientation; or a combination of the two.
To help with these situations, Simpson Strong-Tie offers a couple of options. The option chosen may depend on the timeframe in which the hanger is needed, the load demands on the hanger or the cost of the hanger.
If the demand load is low and an immediate solution is desired, Simpson Strong-Tie offers several adjustable hangers that can be skewed, sloped or both in the field.
A common adjustable joist hanger is the LSU/LSSU series, which can be sloped up or down and skewed right or left up to 45 degrees.
Remember that these hangers must be installed to the carried member prior to installation of the supported joist.
Other series of hangers are only adjustable for skew or slope. For example, the THASR/L series is designed to accommodate connections skewed from 22½ to 75 degrees. Conversely, the new LRU ridge hanger is designed to support rafters at ridge beams with roof slopes of 0:12 to 14:12. Finally, the SUR/SUL/HSUR/HSUL series is not adjustable, but is manufactured with a skew of 45 degrees either right or left in several sizes.
If none of these pre-manufactured solutions fits your specific need, there are still options. This entails a custom-manufactured hanger. Many, but not all, joist hangers can be custom-made for specific slopes, skews, combinations of slopes and skews, and even alternate widths and alternate top flange configurations.
If this type of hanger is needed, a good place to start is the Hanger Options Matrix at the back of the Simpson Strong-Tie® Wood Construction Connectors Catalog. It is also available at strongtie.com. An excerpt is shown below. This chart identifies which hangers can be modified, how they can be modified and to what extent they can be modified. There are two tables – one for top flange hangers and one for face mount hangers.
Once the user has found a hanger that can be modified to fit the actual situation, the next step is to calculate any load reductions, if applicable. The column at the far right gives the Wood Construction Connectors Catalog page number that lists any load reductions for the various options. If multiple options with reductions are specified, only the most restrictive load reduction needs to be applied, not all the reductions.
As an example, let’s say we need to hang a heavily loaded double LVL hip member from the end of an LVL ridge beam. We would look at a GLTV top flange hanger, skewed 45 degrees to the right, sloped down 45 degrees, with its top flange offset to the left. We see from the table above that all these options are permitted. If we go to page 220 (or strongtie.com), we can see what the load reductions would be for these options. The reductions are as follows:
- Sloped and skewed configuration for the GLTV has a maximum down load of 5,500 pounds.
- Offset top flange for the GLTV requires a reduction factor of 0.50 of the table roof load.
- BUT, skewed and offset top flange hangers have a maximum allowable load of 3,500 pounds.
- Offset top flange results in zero uplift load.
So the allowable load of our skewed, sloped, offset top flange GLTV would be 3,500 pounds downward and 0 pounds uplift. In this case, it was clear what the reduction was for our combination of modifications. If it is not listed specifically and you have multiple modifications with multiple reduction factors, use only the factor that results in the biggest reduction, not all of the listed reduction factors.
The next thing to do is to call out the desired hanger properly so that Simpson Strong-Tie can manufacture it to your needs. This is typically done by taking the regular product name, adding an X, and then calling out the modifications individually at the end.
For our hanger, assuming the hip is 3-1/2″ by 11-7/8″, the standard hanger would be a GLTV3.511, and the modified hanger would be called out as a GLTV3.511X, Skew R 45, Slope D 45, TF offset L.
There is one final consideration when hangers are both sloped and skewed. In this case, the top of the supported member (joist) will not be horizontal when it is cut, one side will be higher than the other. The user must decide and specify where he or she wants the upper side of the joist to fall. There are three options: high-side flush, center flush or low-side flush. We see that often users will want to specify high-side flush so that the joist ends up flush with the top of the supporting member, but that would be up to the user. This specification is added to the end of the callout name listed above. These cases are illustrated below.
A related matter occurs when the top flange of a hanger is sloped up or down. In this case the user also has to specify whether the joist is to be low-side flush, center flush, or high-side flush. But, in this case, the side is in reference to the top flange, not the joist. Specifying low-side flush will result in the top of the joist being flush with the lower side of the sloped top flange, not the low side of the joist.
If all of this seems confusing and somewhat difficult, it can be. Fortunately, Simpson Strong-Tie has developed a new web application – the Joist Hanger Selector – which automates this entire process. This app is located on strongtie.com/software.
Once you agree to the terms and conditions, choose the type of hanger you want to specify, then select the types of members being connected. This is what it would look like for our example.
This is where the user specifies any modifications required. Required loads can also be entered at this point. This is what it would look like for our example.
Then, just click “CALCULATE” and the possible options will be shown. And here we see our GLTV3.511X, SK R 45, SL DN 45, TF Offset L, with a load of 3,500 pounds, just as we thought! I love it when a plan comes together.
Hopefully, this web app will help you specify custom hangers with ease. Are there any other applications we could develop that would make specifying connectors easier? Let us know.
The 22nd International Specialty Conference on Cold-Formed Steel Structures is coming up Nov. 5-6 at the Hilton Ballpark Hotel in St. Louis, MO. It is sponsored by the Wei-Wen Yu Center for Cold-Formed Steel Structures at the Missouri University of Science and Technology.
A biannual event, this conference brings together leading scientists, researchers, educators and engineers in the field of research and design of cold-formed steel structures to discuss recent research findings and design considerations. This year’s conference features 12 technical sessions covering a wide variety of topics. For more details, visit the conference website.