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Does Risa have the capability to do a nonlinear analysis using time steps? I'm curious because I'm analyzing a building for progressive collapse and there are some nonlinear analysis options in the UFC that I wanted to experiment with. If not then is there a way to do this procedure manually...

I forgot to give some input... The formulation above is for lateral torsional buckling but I would think a shear wall is braced at each level. What we really need is a local buckling formula for an unbraced equal to the story to story height.

Ok, I finally got my hands on the ACI publication that ash060 mentioned and it does give a simple reduction factor for slenderness effects. It's essentially the same thing that AISC does for flexure. Its the same curve 1) Plastic Zone -> Linear Transition -> Elastic Buckling The lateral...

Wouldn't it be better to add bracing along the compression brace and/or make the original members bigger. Adding a column adds a footing and a lot of extra juice.

I've done a progressive collapse analysis of a concrete building in Risa. Concrete is good because its so redundant. Depending on the level of progressive collapse protection you need, you might not even need to run the computer analysis. We only did it in Risa just to make a pretty picture for...

What equation is used for the buckling of a very thing shear wall/beam. In ACI they have the general buckling formula but that's considering a uniform stress over the whole section. In this case it should be a linear varying stress. I might use AISC's equation for the local buckling of a W...

DaveAtkins, The tie rods are specified as A36 which makes sense with your 24 ksi requirement. Do you know why they have this requirement?

I just wanted to get some input in how you guys tweek the Baseplate - Tie Rod interaction on these buildings: I have 135' clear span pre-engineered frame with a 30' foot trib and the outward kick on this needs some tie rods. I designed the tie rods for strength first and then I went...

How come Risa 3D doesn't generate wind load cases for case 3 and case 4 in ASCE-7-05 Figure 6-9.

40 psf was minimum requirement per this RFP. In my model I accounted for a varying wind profile as f(height) but not for the simple calc. For both sections, there are 3 shear walls each, 2 at the ends and 1 in the middle which has the largest trib. I'll post a plan when I get to work, I need...

I did a calc similiar to this, I had the double angle top chord of a truss cantilevered to pick up a roof overhang. The double angle (2L) and WT sections are the same calc provision in AISC. If your T section is oriented such that the flange is in tension then I don't beleive Lateral Torsional...

I'm getting just about 0 tension at the ends of the walls for the wind load cases. If I use the stairwells, then I would suspect huge overturning and tensile forces at the boundary elements. Here's a quick calc... Height=154' Tributary wind length =140' Wind Load=40psf Wind Resultant =...

oops... where 0.93 = 0.84

FYI (and because I just figured this out a minute ago): 0.7W reduction = 0.84^2 * W where 0.93 = wind speed conversion from 50 year to 10 year. ^2 = to proportionate wind speed to a force e.g. deflections are proportional to the applied forces which are proportional to the square of the...

Well the building is 700 ft long x 54' deep. We have an expansion joint in the middle so each side of the building has 3 of these 54' deep shear walls. The middle shear wall is taking 140' x 154' area of wind.

Post tensioned shear walls seam ludicris, your making the concrete work much harder all the time in order to relieve the tension from something thats only going to happen 5% of the time (number made up). I'd imagine that these PT walls are for extremely light buildings with huge wind loads. How...

Rapt, What secondary reactions are on the columns? I'm just assuming moment reactions (M) from eccentrity of the tendons. Don't most of the Fx (horizontal) reactions get absorbed by the slab? and Fy (vertical) reactions are not existant as they disobey the laws of physics (If they push the...

rapt, I'm on the same page, to design the columns I used the axial load from load case DL+LL and I used the moments from load case DL+LL+PTsecondary.

Ok, that might be where I'm mixed up. ACI states that Ig = Moment of Inertia of gross cross-section WITHOUT considering reinforcement while Ieff = Effective Moment of Inertia the beam considering cracking. This is how it's defined in ACI. To rephrase: I'm trying to say that Ig should...

Also, requarding the shrinking of the PT floor and the effect this has on the columns...I read that the floor only shrinks 3/4" per 100' of floor. My one pull in the short direction is only 54' so the slab will shrink 3/8" total which will pull the exterior columns inward 3/16" each which is a...