UFC 4-023-03 Progressive Collapse

[Stazz]

Is anyone familiar with the Unified Facilities Criteria for Progressive Collapse?

I have a question on the tie force method in section 3-1. It says that you must demonstrate that the elements are able to withstand the required tensile tie forces while undergoing a rotation of 0.2 RAD. How would you go about calculating the tensile capacity of a beam while it's rotating 0.2 radians at it's supports?

My guess is that you must have the connection already detailed and then calculate the forces in the bolts under a rotation of 0.2 radians in the connection. And then add to those stresses the stresses from the axial force from the beam. Actually this procedure makes sense after typing it. Does anyone know a proper method for achieving this?

 

[KBVT]

The required tie strength is defined for each material type in Chapters 4 through 8. UFC 4-023-03 gives a prescribed tensile force capacity that must be achieved based on a percentage of the gravity load seen by the tributary area between each tie. Check for capacity requirements for internal ties, peripheral ties, external column ties, etc.

 

[Stazz]

Thanks, it also says that you can use the floor system already in place to resist these tie forces. So for a composite slab on metal deck, it says that you can use the composite beams as long as they can undergo a rotation of 0.2 rad + the tensile tie force. I'm just wondering how to design a member for a rotational displacement plus a tensile force.

At the end of the day though I think it would seem easier to just add rebar in the slab as ties rather than get fancy with the steel connections. Also, I'm assuming that you can use the metal deck as the tie force as long as the panels are welded together properly in lieu of reinforcement.

 

[Gumpmaster]

I assume you're looking at the version that just came out a couple of weeks ago?

.2 radians is 11.5 degrees. A really big rotation. You're not going to get any bolted connection to work. They're trying to push you to using the reinforcing in the slab as the ties, as you stated. Look at figure D-4 on page 123.

The days of using your primary structural elements as ties are over.

 

[KBVT]

I wasn't aware that the newest version had already been released. I attended a seminar concerning the new version and the intent was that the structural steel framework was not eligible to be utilized as ties anymore. As Gumpmaster mentioned, the required rotation is not feasible with steel connections. Reinforcement in the slab is the best bet.

 

[Stazz]

Thanks Gumpmasterflex. That's what I needed to hear.

I've attached the new version that I've been working off of. It does state in section 3-1.3.1 that you can use the structural members (beams, girders, spandrals) to resist the tie forces if their connections can undergo the 0.2 rad rotation while taking the tie force.

In 3-1 though it states that this must be approved by a 3rd party engineer.

 

[vmirat]

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