Bridge Modeling
“You cannot create bridges according to German bridge standards and requirements with Revit!” That was the general opinion in January 2015. In this article I will show you some strategies/methods and families that I developed while modeling a feasibility study for a customer last year.
German Bridge Standards/Requirements
Let´s start with the standards and requirements for bridges that we have in Germany. There are a lot and I will write about the three most important, interesting, and challenging ones in terms of modeling.
Alignment
Everyone knows that Autodesk® Revit® has no clothoid functions; AutoCAD® Civil 3D® has this ability. This immediately leads to the first challenge because we need the exact alignment in our project and/or family. We also need the information about the gradient. Again this can be provided by the Civil engineer using Civil 3D. But how to bring in this information—manually or in an automated way—in the best case?
Figure 1: Feasibility study bridge
Profile Orientation
In our infrastructure industry, all of the profiles are oriented absolutely vertical. This would lead to a Sweep with a 3D curve with one or more profiles, which are parallel to the global z-coordinate. This is something that Revit won´t allow us to do.
By the way, the same profile must be orthogonal at each station point on the alignment (XY-Plane).
Bracings/Railings
Assume for one moment that we have created the superstructure as a volume object that perfectly follows the alignment and has the needed profile orientation. We would then need to construct the bracings if we have a steel-concrete bridge, or the railings and guardrails every bridge has. All these objects have to follow the superstructure. Again we talk about a 3D path—a path we have to create, but we do not have a tool for this in Revit. (You can create these objects without such a tool as I did at the bridge for the feasibility study, but it´s hard!) We will see later that Dynamo provides an answer to create things like these with ease.
Figure 2: Different aspects and parts of a bridge
Spline and Sweeping Method
A year ago I started the construction of the superstructure as a swept blend. For this you need a path and two profiles at least. It was clear from the beginning that I would need some of the cool tools you have within the mass and adaptive component families. So the first choice was the adaptive component family template.
At this time I imported the alignment as a DWG-file first, then I placed points on the alignment lines and curves. After this I was able to collect all of them and use the “Spline through Points” command. That gave me one single line (spline) for my swept blend. The more points you place, the more accurate the spline will follow the original path.
Nowadays I can use Dynamo to create this spline for me, in the best way (without a DWG file), importing station points with X-, Y- and Z-coordinates directly. This basic Dynamo script was made by Andrzej Samsonowicz in Summer 2015 when we sat together at Autodesk´s headquarter in Munich.
Figure 3: Creating alignment and stations with Dynamo
Profiles
In the next step you have to create the bridge profiles. You can use the mass or adaptive component family template for this. In my case I used an adaptive one with parameters for the gradient height and for the placement angle. The last one to control the orthogonal orientation if you place it on a spline, the first one because I do not place the profiles on a 3D spline going through the gradient points. My concept is to use the 2D alignment spline on the XY plane and give each profile its gradient height via this parameter.
Figure 4: Adaptive profile family
Lofting Method
This allows you to switch between a Sweeping Method and, as an alternative, a Lofting Method. Lofting means that we have as many profiles for the superstructure and caps as we have station points. The spline can be divided with the “Divide path” tool also using “Intersection list” to get the exact station points along the alignment. After this we can use Dynamo to give each profile the correct gradient height via an Excel spreadsheet.
This Excel spreadsheet can be generated automatically from Civil 3D. Because of the simple nature of our station points I can use every other software, which creates an alignment and exports the coordinates of a defined number of stations on it into Excel.
Figure 5: Superstructure family
Assembling the Bridge
Independent from the chosen method I can create solids for the superstructure, caps, and road deck in the first family. The second family can be the abutments and maybe the third one will contain the railing and guardrails. Every family will be placed in the project file. Here we assemble the complete bridge and add topography, columns etc.
It is crucial that the superstructure, caps, and abutments depend on the alignment and the gradient. This leads to very complex shapes for every part of the bridge.
Adaptive Components
A good example for this is the wing wall of an abutment. The top of the wall has to be slanted into two directions because of the longitudinal sloping and cross-fall of the caps. The shown wing wall is the result of some modeling steps. Here I want to point out the great flexibility our adaptive component families have. The four-point Void family can be exactly placed on the surface of a wing wall (system family) that has been edited before to get the sloping.
Figure 6: Shaped abutment
Dynamo Intersection Method
As I wrote before, our rails and bracings have to follow the superstructure and the caps. This is logical and could be so easily solved if Revit has a tool that creates a 3D path on a curved surface. It has not (now) and of course I can use adaptive component families in conjunction with the divide surface command to get the job done.
But it´s mind blowingly easy if you use Dynamo. Just draw a line on the XY plane with the required distance from the alignment axis curve or from the edges of the caps. With my script I can pick this line plus the surface of the cap and let Dynamo create a curve exactly on the cap surface. This curve then will be divided and I can place an adaptive railing family on it. Hit “Repeat” and it´s done.
Sections in the Project
Still a problem, but one that can be solved with Dynamo is a longitudinal section through the bridge. Of course we will not be angry if Autodesk would add this functionality into Revit. What is also very annoying and a problem for me is the fact that Revit can´t dimension edges of a geometry exactly at the location where I create the section view. Instead it tries to dimension the start or end references of this geometry. For this we do not even need to talk about a complex, twisted geometry such as a bridge superstructure. Just think of sloped walls or slabs you want to dimension.
One of my solutions for this last year was my EXIM strategy (Export the section view created in the project as a DWG and Import it into a Detail family.) Bring this Detail family back in the project and you will be able to dimension the lines in the Detail family. You can also place elevation spots where needed.
To be honest this is a very static view, not an associative one. If you use the Lofting Method you will be able to dimension the profiles themselves in the project. And this will lead to a good old associative section view in Revit.
Present and Future
The success of the feasibility study led a lot of companies in Germany to start the process of using Revit to model bridges, even if it was obvious that some tools/functions are not available at the moment. They do so for two reasons, in my opinion.
First they see the great potential of Revit in combination with Dynamo. This combination will lead to completely new workflows beginning with the first design draft (like Zach Kron) to the ultimate (automated) rebar modeling experience.
The second reason is everything we know from the building construction industry. A 3D Revit bridge can be used for simulation, static analysis, and so on. It can be exported as an IFC file also, which is important because IFC for Infrastructure will be coming in the near future.
Oliver Langwich is a BIM Consultant, Revit Family Planner, Blogger, and Co-Founder of the Revit User Group D-A-CH. He is working for Contelos in Hanover, Germany, using Revit since 2007. Oliver can be reached for comments and questions at oliver.langwich@gmail.com.
