Shoring an Unreinforced Masonry Wall 2

[DaveVikingPE]

...and it's 40 ft high, three storys.

Challenging, difficult project this is, involves shoring an exterior stair tower. The only problem is, the entire wall is URM. I've contacted DUR-O-WALL and discussed their Brace-Rite system. I like it, but I'd like to contact a tilt-up contractor and pick their brains about using tilt-up shores for my purposes.

Wind speed is 110 mph!

Ideas?

 

[njineer]

Diagonal shores apply a horizontal component of load to the wall, which is what I think you need. However, diagonal shores simultaneously apply a vertical component of load to the wall. The vertical component is upward when the horizontal force is toward the shore. The shoring system needs to be able to develop that upward vertical component in a way that does not lift the top off the URM wall as it tilts toward the shore. If you are bracing a reinforced tilt-up wall, the vertical component is resisted by the weight of the panel by developing the vertical component into the vertical reinforcing. The URM wall does not offer that possibility. Your shoring system will need to have a vertical member that connects to the brace point and to a point below at which you can use make a connection that will resist the uplift using the weight of the wall above to resist the vertical component.

I have used a 3-member raked shore: a vertical 8x8 against the wall, a horizontal 8x8 member on the ground, and a diagonal 8x8 member that connects to the vertical and the horizontal. The horizontal member projects into a hole that is purposely cut into the wall at thd base of the wall -- there it can develop the uplift force, using shims to make a tight fit. The diagonal member must be designed as a wood column. The connections at each end of the diagonal can be made by cutting a horizontal surface at the top that bears against a vertical 2x8 lag-screwed to the vertical 8x8, and a vertical surface at the bottom that bears against a horizontal 2x8 laged to the horizontal 8x8 [in this way, each end of the diagonal bears into a corner formed by an 8x8 and a lagged 2x8. The bottom connection of the vertical 8x8 to the horizontal 8x8 must be designed to transfer the vertical component of the bracing force as an uplift force into the horizontal 8x8 --I used a strap that wraps tightly [with square corners] around the bottom of the horizontal 8x8 and lags to each side of the vertical 8x8. The horizontal 8x8 needs to be restrained against sliding. This system works one-way only: toward the raked shore.

 

[DaveVikingPE]

Nice!

Excellent advice + plus I now understand what's at stake by not taking uplift extremely seriously.

 

[Duchas]

One of the problems I worry about with (Temporary?) shores or props is will they actually do anything, and if they do, how do you know it's safe to remove them later. They cant really be intended to be permanent.
Is the tower free standing, or is it attached to a larger building?
Have you considered installing reinforcement in the tower such as some of the products from the the system marketed by Cintec (check out

http://www.cintec.com

)They have a variety of masonry reinforcement products, which can be custom designed/manufactured for particular structures.
Following on from my initial comment, I would be inclined to try to finally solve the problem initially rather than installing shores if possible or feasible. In my experience temporary shores often have a habit of being left for the long term, and this isn't always desirable.
All the best!

 

[DaveVikingPE]

cintec has some very interesting products and a good website. Thanks!