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  • Users: Stazz
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  1. Stazz

    Non Linear Analysis

    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...
  2. Stazz

    Concrete shear wall buckling/deep beam buckling

    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...
  3. Stazz

    Pre-engineered building - Tie Rods

    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...
  4. Stazz

    Risa Wind Load Case 3 and 4 ASCE7-05

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

    Designing Columns for Concrete Buildings

    I'm designing a 15 story post tensioned building and I'm trying to design the columns in Risa Floor. I'm just wondering what the standard practice is for considering moments from the slab in the design of the column. 1) I want to design the columns as axial compression members only but I know...
  6. Stazz

    Flat Plate Modeling

    I'm modeling a 15 story post tensioned slab building and I just want to get some ideas on how to model the slab. 1) Can you model the slab as a true "Flat Plate" with just columns or do you need beams to define the slab edge and to collect the loads into the column. 2) I'm choosing 2 way for...
  7. Stazz

    UFC 4-023-03 Progressive Collapse

    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...
  8. Stazz

    Sloped Roofs: Cantilevers

    Whenever I slope a roof, I can't cantilever off the the side to make an overhang. Orginally I assumed that sloped roofs could not model overhangs. Then recently I realized that it works if I modeled the entire roof flat with the overhangs AND THEN sloped the roof. Was I having this problem...
  9. Stazz

    Sloped Roofs: Joists Designs

    I'm modeling a sloped roof and I'm trying to account for the negative wind pressures that are applied to the roof. I applied a negative Live Load to the roof (to act like the wind). I checked out the steel joists designs on the roof and the UTL load became negative (meaning the negative wind...
  10. Stazz

    Sloped Roofs: Wind Load Cases

    Risa floor doesn't seem to include the wind load cases into the load combinations. I tried a few things to bypass this shortcoming when I wanted to apply a Wind Load to the sloped roof of a Risa Floor model. 1)I put the wind load in as an OL1 surface load in the "y" direction and then added the...
  11. Stazz

    Sloped Roofs: Unbraced Length Lb

    I have a sloped roof modeled and axial loads are entering the members, which is ok, but this triggers the L/r<300 check to enter, which is also ok, but only if I was able to adjust the unbraced length of these members. I see an Lbtop and Lbbottom parameters that I can define but no Lbyy and Lbxx...
  12. Stazz

    ZZ axis section modulus for single angles

    This is driving me crazy, the section modulus for Axis ZZ in the AISC tables 1-7 for single angles seems wrong. They appear to be using Iz/c to get Sz but the "c" that they are using is wrong. From what I understand, these Axis ZZ values are for the minor principal axis which is the weaker of...
  13. Stazz

    Principle Axis Bending of Single Angles

    Come on, does this ever happen? AISC Spec F8 has a method for calculating the capacity in these cases. Is there really a practical application where a single angle is bending about its principle axis? I'm coding a calc sheet and I'm wondering if I should save myself some time and ignore this...
  14. Stazz

    Duel Grid System Layouts

    Does anyone have any tricks on how to model 2 project grid layouts in the same model. Ram allows you to display many different layouts, and I wonder if there is a way to do this in Risa Floor that I don't know about. I usually use the Drawing Grid as my second grid, but I usually have trouble...
  15. Stazz

    Cold Form Design Lists

    I was modeling some cold form trusses and I want to use the Dietrich database for the redesign list. I tried checking the box (make default database) for Dietrich but Risa is still choosing the AISI database for the redesigns. I think that I have to go into the redesign files and change the...
  16. Stazz

    Wall Panel Boundary Conditions

    When these wall panels are created in Risa Floor and then transfered to Risa 3d, how do the bases of these walls act? It shows a pin on the bottom corners of the wall but the node at these pins is translating down. What I'm actually trying to do is support the bottom of the walls on rigid...
  17. Stazz

    Wall Panel Openings

    I modeled a CMU wall and was trying to add openings (in the wall panel module) but I couldn't snap to any intermediate area in the wall and even if I could snap the opening wouldn't be created. After struggling for a while I deleted what seemed to be a layer of wall panel. After deleting...
  18. Stazz

    Running Load Combo's and Cases

    Why does Risa run each load combination rather than running the load cases and then superimposing them. I know that you need to run each load combination for a P-Delta analysis, but if you're not using P-Delta then why can't you superimpose the load cases? Is there a reason for this because its...
  19. Stazz

    Modeling compression only springs

    Is there a way to model compression only springs in an FE analysis. I know how to model for both compression and tension but the only way I can think of how to do compression only would be either to do an iterative analysis or a step loading analysis. Iterative: 1) Assume springs tension and...
  20. Stazz

    Continuous Concrete Beams

    I noticed this in 3d: Recently I was modeling continuous grade beams by spanning 5 individual beams node to node on simple supports as individual physical members between each joint. The ends were modeled as fixed and the beams were in a straight line so I would suspect that the end moments...

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