Posts by retug (35)

Capacity Based Design of BRBs in ETABs

Unfortunately from my research, a capacity based design module for BRBs in ETABs does not exist. See snip below.

Given this glaring missing feature, I figured I would outline how I have "tricked" ETABs into doing capacity based design, the poor man's pushover approach to capacity based design for BRBs. The example images presented above are from the AISC Seismic Manual and will serve as the reference for this post. AISC and ETABs own all rights to their documentation.

The Approach

To tackle this problem initially, I went down the route of wanting to apply manually calculated expected strength loads to the BRBF frame. This approach falls short in that load redistributes and goes where it wants given the elastic nature of the model that is built. Trying to tell a specified BRB in the ETABS model to be at x kips is not doable with a traditional force based approach.

With this in mind, I went to a pushover, nonlinear analysis route. This would allow me to specify an exact force at which the braces should yield in both tension and compression(BRBs have slightly higher compressive strength than tensile strength) so I thought this might be the ticket.

Model Setup

Model setup is nothing special, I built the (4) story example model and modelled pinned based braces and columns, with continuous columns (more on this later).

I have uploaded this model to github if you want to play with the model and review.

The Fun Parts

The cool part of the analysis was faking ETABs into doing a capacity based design of the beams and columns, this was done through a pushover load case and non-linear hinge definitions for the axial deformation and load in the BRBs.

Defining a pushover load case is pretty in ETABs, see the screenshots below:

Above, I asked ETABs to move the upper most level 4 node over 36 inches so that I can make each BRB yield in the frame system.

I also defined a specific BRB material, a BRB frame section, and a BRB nonlinear hinge for each BRB.

Above is the material definition, I am not sure if ETABs ever uses this non-linear material definition, but for completeness, I put this in. 

To define the frame sections used in the AISC example, I made the (4) differing core sizes, sample shown below.

To define the frame hinge, I input the specified w and beta factors that were noted in the AISC worked example. See blow:

with all this in place, I crossed my fingers and hoped the results would match.

Pushover Results

The results pretty much exactly matched the AISC worked example which is great, the poorman's capacity based design approach seems to work and capture the design effects that AISC asks designers to consider.

Below you see each brace getting pretty close to the specified yield force, with the tension values being less than the compression values as expected.

It's fun to step through the pushover as well and see how the frame reacts as more and more displacement is induced. You can see when each BRB begins to yield and redistribute load down to the next frame. Below is the forces about 20 steps in the forced displacement. You can see the upper most braces have not yet yielded.

The capacity based design value compression and tension values for columns and beams matches the design example as well.

With these correctly determined capacity based design values, you can feed this load case into the design combos of ETABs and verify you beams and columns can adequately resist the capacity based demands.

Words of Caution

One should pay attention to continuity of columns from floor to floor. None of the examples in the AISC manual seem to consider this, but ETABs does. I am inclined to ignore these moments and just design for the capacity based axial demands, but it might be worth considering these moments if you are concerned about them. Below you can seem some really large moments in the columns due to the large displacements. Given that the columns are elastic, they will continue to develop bending moment as they do not know when to yield and give up.

You can resolve these moments and maybe conservative design values in ETABs by pinning your columns as shown below:

The new bending moments look like this, that's much better!

How do other Structural Softwares Handle Capacity Based Design of BRBs?

Given that I just outlined this process, I figured I would research how other structural design software handles capacity based design of BRBs. 

RISA has a cool, "semi" finite element approach where they essentially remove the brace, apply the specified compression and tension yielding values, apply artificial frame restraints and then do the "semi" finite element analysis on the reduced structure. I thought this was a really cool approach, but I could see a few areas where this could possibly break down. I would have to test it out more to see if this works in all cases.

From my reading, it sounds like RAM structural does this as well.

RAM does not provide a nice write up like RISA on how it is determining these values for beams and columns, but appears to be doing some form of capacity based design based on D1.4a which is good.

All of this is to say, ETABs and CSI, let's step it up to make engineers lives easier. The process I outlined above can work to accurately design beams and columns for capacity based BRBs, but it's a bit convoluted, albeit cool.

NOTE: I am no expert in this and I hope the process I have outlined captures the intent of the code. If you see any flaws in my approach, please comment/message me. I want to make sure my beams and columns don't fail.

E2R - ETABS Revit Connection Tool

After the development of R2R, RAM Structural to Revit connection tool, I wanted to make an E2R, ETABS to Revit connection tool. Below are some screenshots of the newly developed tool.

I made a youtube video on how to use the tool here. This video goes in depth on each button and things to look out for while using the tool.

The tool will be available on the Autodesk App Store soon hopefully and freely available to download and test out. Please let me know if you encounter any bugs as you use the tool.

The tool works to check ETABS beams vs Revit beams and is ideal for large steel framed structures in ETABS to quickly backcheck framing sizing and discrepancies between ETABS and Revit.

The Coding - More To Come

MVVM Magic and Modeless Mayhem in Revit

After making the RAM to Revit tool, I wanted to make a similiar tool, but with ETABs this time.

I learned a lot making the RAM to Revit tool, but also learned a few things that I would like to do differently given the chance. 

MVVM Magic

MVVM standards for Model-View-ViewModel and it serves as a way to effectively decouple the user interface (in my case my xaml code) from my data (Model). You do this through creating a ViewModel that allows the model and the view to be completely separate. 

I will admit, I am speaking like I know what this means, but it is still somewhat of mystery to me, but I think this will prove beneficial in making the ETABs to Revit tool. The amount of coding I spent keeping the UI and the data on the backend "sync"ed up for the R2R tool started to become overwhelming, and it is my understanding that MVVM will be a much cleaner way to keep the data and the view separate.

Below is a gif of the view being dynamically updated with updates that occur in the revit model, really cool stuff. Big thanks to scgq425 on the revit api forums for helping me out with this.

Sample code on github.

Learning Points with MVVM and Revit

I struggled with getting my MVVM code to work because I was using a IEnumerable (does not inherit a lot of the MVVM goodness) when I should have been using an ObservableCollection to store my revit beam data.

public ObservableCollection<RevitFramingModel> StructuralFramingElements
        {
            get { return _structuralFramingElements; }
            set
            {
                _structuralFramingElements = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(StructuralFramingElements)));
            }
        }

I also struggled with trying to trigger the data to update when a change is performed in the revit document. After searching the revit api documentation, it seemed like the IUpdater interface would do the trick. From the revit documentation:

IUpdater Interface - The interface used to create an updater capable of reacting to changes in the Revit model.

I wanted to react to changes to my beams, so I thought this would do the trick. Throwing the IUpdater interface in the my View Model, my code seemed to be working.

public class StructuralFramingUpdater : IUpdater
    {
        static AddInId m_appId;
        static UpdaterId m_updaterId;
        private readonly MainViewModel _mainViewModel;

        public StructuralFramingUpdater(AddInId id, MainViewModel mainViewModel)
        {
            m_appId = id;
            m_updaterId = new UpdaterId(m_appId, new Guid("FBFBF6B2-4C06-42d4-97C1-D1B4EB593EFF"));
            _mainViewModel = mainViewModel;
        }
        public void Execute(UpdaterData data)
        {
            ObservableCollection<RevitFramingModel> structuralFramingElements = _mainViewModel.StructuralFramingElements;
            // Check if the modified element is a structural framing element
            foreach (ElementId elementId in data.GetModifiedElementIds())
            {
                Element element = data.GetDocument().GetElement(elementId);
                if (element != null && element.Category.Name == "Structural Framing")
                {
                    // Update the corresponding RevitFramingModel
                    RevitFramingModel framingModel = structuralFramingElements.FirstOrDefault(m => m.Id == element.UniqueId);
                    if (framingModel != null)
                    {
                        framingModel.Name = element.Name;
                    }
                }
            }
            _mainViewModel.StructuralFramingElements = structuralFramingElements;
        }
        public string GetAdditionalInformation()
        {
            return "Structural Framing Updater: updates structural framing models when changes occur";
        }
        public ChangePriority GetChangePriority()
        {
            return ChangePriority.Annotations;
        }
        public UpdaterId GetUpdaterId()
        {
            return m_updaterId;
        }
        public string GetUpdaterName()
        {
            return "Structural Framing Updater";
        }
    }

I used chatgpt to write a lot of this code, it was funny to see that chatgpt was essentially "copying" this portion of the web:

https://help.autodesk.com/view/RVT/2022/ENU/?guid=Revit_API_Revit_API_Developers_Guide_Advanced_Topics_Dynamic_Model_Update_Implementing_IUpdater_html

I noticed the the Guid between both programs was identical, pretty funny.

Modeless Mayhem

The next item I wanted to solve with the R2R tool was the lack interactiveness, when the popup window for R2R begins, you are not able to interact with your revit model. This is a huge downside that I want to come back to, but for now, I wanted to make sure the E2R would not be limited in the same way.

The fix to make the window "modeless", switching the popup window from 

mainWindow.ShowDialog(); to mainWindow.Show();

This simple little change did the trick. I think making the full fledged E2R tool modeless will be more complicated than this moving forward with multiple windows and popups, but for now, I hopefully optimistic that I can keep this application modeless with little coding brainpower spent.

ETABs to Revit tool coming soon... 

???

Autodesk Platform Services - A First Step

I'm not really sure what Autodesk Platform Services is or why I should use it, but Autodesk is pushing this hard it seems. The tech looks cool so I figured I would follow their first tutorial.

The first example they provide on APS is how to upload your local revit model to their cloud service and view the revit model in your web browser. Really cool! The example model shown in the gif above was the same model I built to show off the RAM to Revit tool.

A Return to Javascript

The documentation, found here on autodesk's github and the web example, is really well put together, I just made one stupid error that cost me about 4 hours of debugging and one stupid post to stackoverflow to try to solve. I have been meaning to come back to the concrete design tool for awhile which is written in javascript, so when I saw the tutorial recommended node.js and javascript as the first option, I hopped on the oppurtunity to refresh the javascript skills.

A few blog posts ago, I think I mentioned that one day I hope to experience less "firsts" in programming, this was a great example of less "firsts". I had played with all the tech stacks they utilized in the example, node.js, npm, javascript were all at least somewhat familiar to me. Finally! No watching 10 hrs of videos just to have a basic understanding of where we need to begin. 

Also, APS is built using three.js which I have experience with in building the about page on the website as well as the concrete design tool, how cool! It's crazy how all these tech stacks build on top of each other, finally starting to feel like a semi-experienced programmer.

APS Tutorial

As I had mentioned, the APS turorial was really well put together, but I will highlight a few things I found a bit unclear for my beginner programmer mindset.

First, make sure you are using powershell if you are on windows to input the commands in the documentation. Originally I was in git, which was not the right spot. The image below you can see git was working, but eventually I realized I needed to be in powershell.

The code is pretty advanced, so a lot of times where I had absolutely no I idea what I was copying and pasting. Throwing the code into chatgpt and asking it to explain it to me was helpful.

At the authentication step of the process, the docuemtation mentions that you should be greeted with a window that I was not getting. I should have realized that I had made a mistake and went back to fix it, but instead I forged (pun intended, APS used to be known as Forge) on to make my previous mistake much worse.

My mistake, in the .env file, you are supposed to store your APS_CLIENT_ID and APS_CLIENT_SECRET in a string. 
The code that is put up on the website looks like this:

APS_CLIENT_ID="<client-id>"
APS_CLIENT_SECRET="<client-secret>"

I replaced this as

APS_CLIENT_ID="<MYTESTCLIENT>"
APS_CLIENT_SECRET="<DKLJSADKNVDSLK15154541215F>"

Be sure to remove the "<" and ">", this stupid error led me down quite the rabbit hole trying to debug. See my stupid stackoverflow post here: 

https://stackoverflow.com/questions/78138283/autodesk-platform-services-access-token

My code is up on github, but it's just a copy of the autodesk code. Feel free to take a peek.
 

What's Next?

I've had people ask, why are you doing this? What's the end goal? Sometimes you don't need an end goal to enjoy the journey. For now, I'm going to keep going with the examples that are up on the APS github. It looks like there is some really cool dashboards that can be created and other exciting stuff. Again, nothing immediately jumps out as me as I need this to improve X/Y workflow, but I have to admit it is cool. 

Another item to research, how much will this cost? APS runs a currency called tokens. How much are tokens? How many tokens are consumed? I've got a lot of questions that I need to dig into to understand a bit more. I have a feeling though, with a name like "tokens" its gonna cost a lot. Maybe it's one of those, if you have to ask, you can't afford it type deals? Let's hope not!

RAM to Revit - First Update V1.0.1

The beta release of the RAM to Revit tool has gone well. I have a few people using the tool in practice and have heard some good feedback so far. I am actively trying to maintain this and make it better, so if you have any requests, please reach out. I will try to get your feature added.

Big Update #1 - Calculate X Y and Rotation Function Upgrade

The calculate X Y and rotation function has been greatly improved and does a much better job at trying to guestimate the rotational and offset parameters between your RAM coordinate system and your Revit coordinate system. My error, I had not converted the intersection point of the RAM gridlines into the Revit coordinate system which led to some really bad estimates on X and Y offsets. This has been revised now and should work in a majority of cases.

Update #2 - Mouse Tracking of Coordinate in the Mapping Plane

Should the "Calculate X Y and Rotation" button not do a good job of estimating the X Y and rotation parameters, I have added mouse coordinates in the lower left of the mapping plane. This should allow for easy hand calculations of the X and Y offset parameters should you not be aligned.

Update #3 - Additional Beam Info - RAM Beam #, Camber, LRFD Start and End Reaction

I had a user ask for some additional information the datagrid, RAM beam #, Camber, and beam end shear reactions. Eventually they want to map the start and end reactions into the revit beam for quicker documentation. Side note, I feel sorry for you east coast engineers, sometimes it's just easier to design the simple shear tab connections. 

I am working with this user to see how they like to schedule their end reactions and hope to have a way to write the start and end reaction parameter into the Revit beam soon. More to come on this. The reactions that is recorded is an LFRD factored load reaction that only looks at RAM Steel Beam gravity results. It checks both 1.4DL and 1.2DL + 1.6LL and nothing else. Use with caution.

I also have one user with a weird bug that will not allow them to access the RAM structural API.

I am hoping that this new update will give me a little more insight into why it is not working on their computer. I finally learned how to generate a meaningful error message using the "try" "catch" keywords in C Sharp. Hopefully the exception that is thrown is more insightful than my previous error message.

private void getRAMResults_Click(object sender, RoutedEventArgs e)
{
    if (ramFilePath == null)
    {
        MessageBox.Show($"You must select a RAM Structural model first, .rss", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
        return;
    }
    //List<string> storyNames = RAMInfo.GET_STORY_NAMES(ramFilePath);
    try
    {
        List<string> storyNames = RAMInfo.GET_STORY_NAMES(ramFilePath);
        ramFloorComboBox.ItemsSource = storyNames;
    }
    catch (Exception ex)
    {
        MessageBox.Show($"An error occurred: {ex.Message}\n\nLikely errors include:\n\n1. RAM Structural is not installed on your computer\n\n2. Your RAM structural file is corrupt, check for .USR file \n\n3. Clear your working file directory, usually located here C:\\ProgramData\\Bentley\\Engineering\\RAM Structural System\\Working" , "Error", MessageBoxButton.OK, MessageBoxImage.Error);
        return;
    }
}