Would you stamp this? 6

[dreber]

So in ASCE 7-16, there is a new requirement in § 13.5.10 “If sliding or ductile connections are not provided to accommodate seismic relative displacements [for stairs], the stiffness and strength of the stair or ramp structure shall be included in the building structural model of Section 12.7.3, and the stair shall be designed with Ωo corresponding to the seismic force resisting system but not less than 2.5”

This has put the requirement to ensure bi-directional drift connections on the shoulders of building designers, who are now writing these requirements into their contract documents.

As the stair designer, I'm happy to stamp a connection like the one above, since I will only be relying on it to resist vertical (dead and live) loads.

However, I'm afraid that since this connection isn't a firm fixed connection that the movements in the stairway, and any potential squeaking or banging noises that could arise now, will come back to haunt me when building occupants are unhappy with their stairway that appears to be moving every time the wind blows.

I think I prefer a connection like this, since it's a bit more "positively attached" but I'm not sure that it won't make any noise either.

Keep in mind that one of these is obviously cheaper and my clients (AKA, my bosses) will strongly prefer the end stop connection to the bi-directional slotted connection.

=========================
David Reber

http://www.kadent-structures.com

 

[GC_Hopi]

Here's my contribution.

 

[GC_Hopi]

What's the purpose of the nut on the all-thread in the stop plate detail

Now the nut has a use. haha

 

[r13]

Back to simple me. A steal from bridge movable bearing design - let the stringer directly bear on embed SS pad with rigid bearing pad sandwiched in between, so the leg is free to move in any direction during seismic event, but stable for normal gravity load, or slight thrust.

I can see the upper connection is tough. What is a "bumper" support?

 

[dreber]

kissymoose - the design interstory drift can be over 2% of the story height, so if you have a 18ft story you can have 4.3" of movement in both directions, requiring a 9.5" long slot assuming you use a 3/4" diameter bolt

Some things aren't sized because these drawings are just for my musings, they won't be built.

The nut is there.... for.... nothing, really.

vertical seismic loads are not addressed, but these connections are permitted, at least so far as ASCE 7-16 § 13.5.10 goes.

GC Hopi, your first connection would potentially have a bunch of squaking and bumping noises, much like some of the ones I had detailed. The washer PL on your 2nd detail would fall into the hole during major movement.

In other news, I (or we) may have solved it. No bumping, squeaking, and not wildly complicated/expensive.

=========================
David Reber

http://www.kadent-structures.com

 

[JoshPlumSE]

I like that last connection. With one modification. Make the bolt longer and double nut it with the angle leg between the nuts. I just don't want the angle to plate to have any friction. Or, get painted together or spot welded by an overzealous construction worker.

 

[moments]

My typical role in these cases is that of base building engineer reviewing design-build stair submittals that are required to comply with the seismic drift provisions. We’ve been happy to coordinate with the stair designers by reviewing applied loading imposed by seismic force and displacement cases. Often the transverse forces can be easily resisted at the levels, and the transverse displacements impose forces in the stair framing that are within available capacities if the DB engineer models it. Thus, slotted connections along the stair stringers may adequate.

 

[dik]

I like GC Hopi and dreber's solutions, finger tight, with a little loctite red... any reasonable 'shake' will break the paint bond...

Dik

 

[GC_Hopi]

I saw these pre-engineered clips in a magazine yesterday. DriftReady™ Stairs And bonus is that they have some cool videos of the clip in action under a seismic event. Experimental test events, not a real events.

 

[r13]

Very good information. Seems the focus point is the ability to allow free motion of the connections at landings.

 

[JoshPlumSE]

GC_Hopi -

Great post. Thank you! I love the simplicity of the system. Very cool!