I am confuse about holdown calculat 1

Define your terms and provide legible sketches.

BA

Mountainrunner said:

There is not gravity or anything like that

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I would contact the folks over at NASA, they deal with this kind of thing often.

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”

It's really hard to tell what's going on from your drawing, but I assume you are dealing with a structure subjected to lateral loads, with some sort of mechanical fasteners at its base.

If that's the case there are two aspects of the analysis you could be struggling with.

Step 1) Structural Analysis

To get the loads in the fasteners/tie-downs you need to use simple statics principles. To get tension in the base fasteners from a lateral load you need to sum the moments about one of the fasteners and ensure static equilibrium is met. Again, hard to tell what is going on with your calculation, but it looks like you may understand this part.

Step 2) Fastener strength

This ones much harder to help with without knowing what kind of fastener you are using. Do you have bolts into concrete, soil anchors, bolts to steel? The failure modes will be vastly different depending on your particular situation.

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”

While it is technically correct that the uplift at a holddown is equal to the unit shear in the shearwall times the height of the shearwall (as you show in your calcs), it makes more sense if you look at the overall free body diagram of the shearwall.

For example, looking at the upper left shear wall, the force on that wall = [3 kips/(4' + 9' + 4')] times 4 feet = 0.706 kips. The overturning on the wall = 0.706 kips times 8 feet = 5.65 kip-feet.

This must be resisted by a force couple at the bottom of the wall. Holddown force at left side of wall = compression force at right side of wall = 5.65 kip-feet/4 feet = 1.41 kips.

Repeat for each shear wall. Each of your shear walls will require a holddown at each end of the wall. For your case, you will need 10 holddowns for the five walls.

DaveAtkins