Single angle W beam to HSS column

[RL1818]

Hi all,

I am having an issue with an eccentrically loaded single angle connection between a W14x38 beam and a HSS 6x6x1/4 column. I have four questions.

1. Do AISC table 10-11 and CISC table 3-40a take into account the out of plane eccentricity when transferring the shear load from the beam to the weld? If not can the CISC Eccentrically loaded weld groups table 2 be used even though the load is not symmetric between the two welds?
2. The W14x38 beam does not have enough space for 5-3/4" bolts with the 3" or 80mm spacing that is provided in the above tables. How will the values be affected or will they no longer be valid? I know the reduced spacing will reduce the angle capacity but by how much?
3. I want to weld the connection on both sides of the angle, a fillet weld near the HSS centerline and a corner weld on the column corner, as well as transverse welds along the top and bottom. Will this additional weld (additional compared to the AISC and CISC tables) increase the weld capacity enough to ensure the failure will be in the bolts?
4. Because I want to weld on both sides of the angle, will there be an eccentricity between the two longitudinal welds that needs to be considered?

Any help would be much appreciated.

 

[ProgrammingPE]

1. Do AISC table 10-11 and CISC table 3-40a take into account the out of plane eccentricity when transferring the shear load from the beam to the weld?

AISC Table 10-11 is for All-Bolted Single-Angle Connections, and it determines the eccentrically loaded bolt group coefficient for bolts at the column.

You mentioned welds, though, so did you mean Table 10-12, which is for single angle connections with bolts at the beam and welds at the column? That table does not consider eccentricity for the bolts at the beam since it is not required where there is only a single vertical row of bolts that is not more than 3" from the face of the column. The welds at the column are checked for in-plane eccentricity from the center of the beam web to the centroid of the L-shaped weld.

2. The W14x38 beam does not have enough space for 5-3/4" bolts with the 3" or 80mm spacing that is provided in the above tables. How will the values be affected or will they no longer be valid? I know the reduced spacing will reduce the angle capacity but by how much?

The values will no longer be valid. If you're straying from the configurations in the table then the only way to figure out the capacity is to check all of the limit states manually. The decreased bolt spacing will decrease your bolt tearout, angle shear yielding, angle shear rupture, angle block shear, and weld capacities (due to decreased weld length) all by different amounts since they're based on different lengths.

3. I want to weld the connection on both sides of the angle, a fillet weld near the HSS centerline and a corner weld on the column corner, as well as transverse welds along the top and bottom. Will this additional weld (additional compared to the AISC and CISC tables) increase the weld capacity enough to ensure the failure will be in the bolts?

You'll have to run the calculations to see how much weld is required so that the bolts control.

Welding the entire way around the single-angle at the column, though, will result in reduced flexibility. The flexibility in the connection comes from the unwelded side of the angle pulling away from the support, which you'll no longer have. If you're OK with that, then why not just use a Single-Plate connection instead since that's the behavior you're going to get with a fully welded single-angle. The flexibility then comes from bolt plowing at either the plate or the beam web provided that you do not exceed the maximum permitted thickness.

4. Because I want to weld on both sides of the angle, will there be an eccentricity between the two longitudinal welds that needs to be considered?

Correct. The eccentricity will be from the center of the beam web to the centroid of the weld group, so the weld closest to the beam will support a higher portion of the load.


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[RL1818]

Thank you very much for the reply! to respond:

If you're OK with that, then why not just use a Single-Plate connection instead since that's the behavior you're going to get with a fully welded single-angle.

A shear tab or single plate was the original idea for this connection but there is an issue with the HSS being thin walled and having a punching shear failure from end rotation or shear tab being pulled out as is outlined in Hollow Structural Section: A Design Guide on page 312. The angle replacing the shear tab adds shear area and prevents that failure. Is there a better way to prevent that failure?

As well how do I calculate the proportion of load on each weld?

Thanks

 

[ProgrammingPE]

...there is an issue with the HSS being thin walled and having a punching shear failure from end rotation or shear tab being pulled out as is outlined in Hollow Structural Section: A Design Guide on page 312.

The book you referenced, "Hollow Structural Section - Connections and Trusses", is referring to an equation that has been updated.

tp ≤ Fu/Fyp*t is Equation K1-3 in AISC 360-10 (or Equation K1-10 in AISC 360-05).

This has been replaced by Equations 10-7a and 10-7b in the 15th Edition of the Steel Construction Manual which is referenced by AISC 360-16. The equations are now shown below:

Ru*e ≤ ΦFu*t*lp²/5 (LRFD)
Ru*e ≤ Fu*t*lp²/5Ω (ASD)

I'm not sure if that will help your calcs, but I thought I should point that out.

...how do I calculate the proportion of load on each weld?

I think because you're welding all around and losing the flexibility in the angle that you're going to end up with both in-plane eccentricity (center of beam web to weld group centroid at column) and out-of-plane eccentricity (face of column to centroid of bolts at beam). You can figure out the stresses in the welds by using the elastic weld group methods for both eccentricities and then add them together.

Is there a better way to prevent that failure?

If you are still having punching shear issues, you could consider still using a shear tab connection but increase the HSS's wall thickness or weld a plate to the face of the HSS wall. Alternatively, you could use a WT as the connector. Each of these options will be straight forward to design and understand their behavior, unlike using a single angle which has eccentricity in two directions and a combination of fillet and groove welds.