Shear Collapse or Vertical Failure

[joetheinspector]

A shingle Family dwelling unit has 3 feet cripple walls above the sill plate with the floor level of the house above. During a earth quake the cripple wall tips over (l / __ ).

Would that be called shear collapse or vertical failure?

I am sure where to post this so I am posting it here.

 

[Builder Bob]

Wouldn't this be considered an hinge????? same as platform framing if the sheathing isn't installed correctly? I would vote for shear - the movement of the weight above over came the shear at the hinge point and failed.

 

[Rio]

While it is the same as platform framing with the lower story walls not laterally supported that is how we've always called it, not laterally supported and have used the term hinge for when a multi story wall assembly isn't braced by a diaphragm.

For example, a two story house with a stairwell next to the exterior walls. Where the stairwell is it's normal to balloon frame that part of the exterior walls otherwise there's a hinge where the 2nd story walls stack on top of the rim and 1st story walls.

 

[Alias]

A shingle Family dwelling unit has 3 feet cripple walls above the sill plate with the floor level of the house above. During a earth quake the cripple wall tips over (l / __ ).Would that be called shear collapse or vertical failure?

I am sure where to post this so I am posting it here.

It would be a shear collapse IMO. My questions would be if inspecting post collapse -

1. What is the age of the structure? and 2) Are the cripple walls designed as shear or braced wall panels?

Having lived all over northern CA, including the Bay Area, I have seen numerous examples of what are referred to as "soft story" buildings. What you are describing would fit this category IMHO.

As Builder Bob and Rio stated, this type of framing acts like a hinge in an earthquake. Both the Northridge and Loma Prieta earthquakes have good examples of shear collapse.

Sue, who is not an engineer, nor do I play one on tv, but I have stayed at a Holiday Inn Express once.......

 

[Yankee]

I don't see the force of shear causing that type of failure. I would call it lack of lateral restraint at a hinge point.

 

[Phil]

Alias,

Question 3: How well is the cripple wall anchored or fastened at top and bottom.

There is a lot of literature on seismic retrofiting of wood cripple walls. For instance see: http://www.strongtie.com/ftp/examples/seismic/seismicretrofitdetails.pdf

 

[dhengr]

Joe:

If I understand your elaborate graphic correctly, that’s neither “a shear collapse or vertical failure,” although it might have lead to a vertical failure or bldg. movement. That 3' high cripple wall just rolled over, it had essentially hinge connections at the top and the bottom plates. For this to happen, there was no lateral resistance, shear resistance or shear walls in the direction perpendicular to the wall in question. These perpendicular walls are the most efficient way to resist the lateral loads which rolled your wall over. And, if those perpendicular walls were inadequately sheathed and nailed (or not sheathed at all) they would just tend to parallelogram over as the floor framing/diaphragm moved laterally and then downward. By my definition, at least, a vertical failure would mean the cripple studs failed as columns, or in crushing of the t&b plates, or some such.

 

[David Henderson]

To lessen the lateral movement HD's are common around here for seismic retrofits, in area's where drilling for the epoxy and all thread is difficult because of lack of room for the drill (short cripple walls) a UFP's can be used.(Simpson products), then the shear is added.

If holdowns are not part of the cripple walls, they will roll in a large enough event.

 

[peach]

it's a shear failure; I didn't stay at a holiday in express, but I watched my balsa bridge fail 2 weeks ago.. it was the shear.

 

[DRP]

No pics?

Self employed, motel 6 itty

I was looking for something on photobucket and remembered these. They are sort of related, there are some folks on another forum that are building on unbraced piers, I was trying to show the problem.

Then there were all kinds of cobbled together knee braces. Much better but the connection loads are high, a few 16's aren't going to do it.

I was pointing to at least sheathing things well. I got a message from one person saying "but you put a million nails in those panels". Sure could

The lateral force coming from the hand or foot in the pics could just as easily be the inertia above and ground motion below. In the bottom pic the lateral force on the side of the shoe wants to topple that wall out of plane. But, the force flows through the stiff floor diapragm to the perpendicular walls and is resisted by them. Something in that chain of shear restraint failed.