Kris Bunda Design

Curved Balcony Design: FEA Simulation Weight Safety Check

SolidWorks Simulation - Factor Of Safety on balcony

SolidWorks Simulation - Factor Of Safety on balcony

I felt like this whole balcony extravaganza was getting a little too hysterically long, so I split it into a Design post and an FEA post. If you’re seeing this post first, but want to see The Origin Story of the world famous balcony series, click below:

♦ Curved (Rolled Sheet Steel) Decorative Balcony Designs that Mimic Wrought Iron Fabrication (Go to the balcony design post)


FEA Simulation

Here’s the meat & potatoes section. I don’t know why I said that. Actually, this is some screenshots and explanations of how I set up a simulation scenario, complete with fasteners, external fixtures, and mass loading. I wanted to safety test this thing to make sure you could park a subcompact car on it before someone’s grandchildren stand on it.

Simulation Problem Setup

Models:

To set this up, at first I kept trying to use the assembly file. This means I tried to mesh all the solid parts of the assembly. Then I tried to create shells and beams and solids and super-fine mesh controls and any and every combination of mixed mesh ever conceived of. There were always problems! I couldn’t get a believable result, if I could complete a solve at all!

Sometimes the road to simplicity is a complicated maze.

And it was all because I really wanted to get that grate deck top to mesh with all the slots in it, because I’m thinking with all that material missing, it will affect the strength, stiffness, and make it act more like a spring than a slab. But it just didn’t want to work, whatever I tried.

Curved Balcony SolidWorks Simulation Mixed Mesh & Mesh Controls Issues

So finally, after wasting way too much time on this, I just created single-body part versions of the 4 bolt-together subassembly weldments (Deck, Front Rail, Side Rail LH, Side Rail RH – and I really didn’t need one of the sides since I cut the railing in half for symmetrical solving). This means each subassembly has a configuration where everything is suppressed except the single-body part file version of itself. And I extruded a boss through the grate on the deck to make it solid.

Curved Balcony SolidWorks Simulation Parts Models Setup

This means there are essentially only 3 bodies in this simulation (after symmetrical cut out completely removes a side rail). I did this by saving the assembly files (*.SLDASM) out to part files (*.SLDPRT) and making sure to choose the little checkbox in the Save As dialog that saves all surfaces and bodies (“All components”). Otherwise, I was getting broken surfaces.

Save SolidWorks .SLDASM file as .SLDPRT part file with All components radio button checked

Then I had to do some massaging, adding in bosses, using the “Surface” tab to thicken and merge faces, using the “Direct Editing” tab’s “Combine Bodies” to get bodies to go together into one. This can also be a good diagnostic tool – if you can’t get bodies to combine, they must not be properly merged somewhere. So you’ll need to find a way to make a feature that connects the body to another. Of course, this is all for simplicity’s sake, so hopefully what you’re doing isn’t too complicated or time-consuming. Unfortunately, sometimes the road to simplicity is a complicated maze.


Global Contacts and Contact Sets

First, Let’s Show What Not To Do (Apparently Contact Sets don’t always override Global Contacts…)

I previously made the mistake of leaving on “Global Contact: Bonded” in this study. I didn’t think it would matter, as there are No Penetration contact sets in the study for all the faces that should have it, and contact sets are supposed to outrank global contacts. But it was obvious when looking at the displacement plot results that this rule was not being observed.

I must admit, I have had trouble getting the solver to exhibit the bonded behavior again to verify it. But it comes out with the following choices: Selected for non-touching faces, within 6mm of each other, to be bonded as incompatible mesh. Not sure why the contact sets didn’t supersede this errant global bonded contact, but you can see what the differences are below.

DON’T DO THIS: SolidWorks Simulation GLOBAL BONDED contact dialog problem – Non Touching Faces, Incompatible Mesh, 6mm

Here’s with the Global contact on, it makes some parts that should be just bolted together (No Penetration) act as if welded together.

SolidWorks Simulation: Parts acting welded together when they should be no penetration, because global bonded contact not submitting to contact set hierarchy.

Here’s with the Global Bonded Contact suppressed (and proper No Penetration contact sets in place):

SolidWorks Simulation: Subweldment parts now deform independently, correctly, because global bonded contact suppressed.

Here’s the Contact Visualization Plot, to show what is happening when the Global Bonded contact is on. The solver thinks, in some areas, the parts are both bonded and not bonded. No wonder it would take so long for the problem to start solving when this was happening. Also, notice all the little red spots on the scrolls  on the front rail. I think that’s the “6mm” non-touching faces option trying to weld together all these parts to themselves. This is why the Contact Visualization Plot tool can be very helpful in telling you what SW Simulation thinks the relationships are between parts.

Confusion: It’s clearer to understand why the assembly thinks some parts are welded when looking at contact visualization plot, notice that the red (bonded) areas atop the purple (no penetration) areas.

Hopefully this helps as a “What Not To Do with Simulation Contacts” lesson.


No Penetration Contact Sets & Contact Visualization Plot

The relationships between the 3 weldments are explained to the simulation software by clicking the interfaces (circled in red below) and marking them as “No Penetration” contact sets. No Penetration is appropriate because they are bolt-together pieces, and they should deform as such under stress, instead of acting as if they’re glued or welded.


External Loads


Fixtures

In addition to the fasteners used, there are some fixture features made to recreate environmental conditions.

All fixtures highlighted in the feature tree will make its arrows appear light blue in the screenshots below.

Curved Balcony SolidWorks Simulation Fixture 1
Curved Balcony SolidWorks Simulation Fixture 2
Curved Balcony SolidWorks Simulation Fixture 3
Curved Balcony SolidWorks Simulation Fixture 4 – Virtual Wall
Curved Balcony SolidWorks Simulation Fixture 5 – Foundation Bolts
SolidWorks Simulation Fixtures – BOLT CONNECTORS – Dialog Box, Size, Torque, Material

Simulation Results

Displacement Plot

Although SolidWorks Simulation may present these plots in very exaggerated scales of deformation, you can see I set the units to inches, the chart options to 3 decimal places, and the Max callout shows that the most deflection of the assembly under load is less than a sixteenth of an inch. Frankly, I find it hard to believe if you put 3,000 lbs on this thing, there’d be so little movement, but it’s also not as if there’s much leverage involved. This deck hugs the side of the building pretty closely.

Curved Balcony SolidWorks Simulation NO PENETRATION Displacement Plot 1
Curved Balcony SolidWorks Simulation NO PENETRATION Displacement Plot 2

Stress Plot – Von Mises

Curved Balcony SolidWorks Simulation NO PENETRATION Stress Plot – Von Mises 1
Curved Balcony SolidWorks Simulation NO PENETRATION Stress Plot – Von Mises 1B
Curved Balcony SolidWorks Simulation NO PENETRATION Stress Plot – Von Mises 2

Some Examples of Visual Cues in Simulation Stress Plots, and What They Say about Design & the Study

Stress Plot Visual Cues – Bolt hole stress concentrations tells you that the fasteners are actually doing something, and the simulation problem was probably set up correctly in this respect.
Stress Plot Visual Cues – Checking another part’s bolt hole stress concentrations. Sometimes one contact set between 2 parts’ interface is correct, but another pair of parts are interacting improperly. Check thoroughly for cues, and use the Contact Visualization Plot tool.
Stress Plot Visual Cues – Concentrating the loads across sets of footprints doesn’t seem to matter. Probably because the steel plate is .188″ thick, and it doesn’t have all the material for grating removed. It’s a coarse mesh, too.
Stress Plot Visual Cues – Seen here that the weight is pushing the deck down and the corner of these ribs would be forced into the wall of the building due to a hinge effect from other constraints.

Factor Of Safety Plot

FOS Wizard:


If you made it this far: You’re a glutton for punishment. And: Let me know if you have questions on anything I did, why I did it, or if you have suggestions on what I could’ve done better or faster, in the comment section.

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