Why You Don’t Need to Wait for IFC5 for Bridge Modeling

I’ve been following Industry Foundation Classes (IFC) for a number of years. IFC is a neutral file format based that is free as in speech and as in beer. In particular, I have been evaluating IFC as a base schema for modeling civil works such as roads and bridges. The general consensus at present from users and software vendors is that IFC for Bridge Information Modeling (BrIM) won’t really be possible until the Bridge-specific data types and extensions planned for IFC version 5 have been finalized in the spec and implemented by software vendors. The truth of the matter is that IFC is ready for BrIM now.

General - Goals of IFC5 Bridge and Road

Presently there is a group hard at work on the next major version of IFC which will be focused primarily on linear civil works such as highways, tunnels, and bridges. This work is intended to address perceived shortfalls in the general suitability of IFC as a data interchange format for these types of projects.

While I am certainly in favor of this effort, I take exception at the notion that IFC can’t really be used for heavy civil work - particularly BrIM - in the meantime. One software vendor in particular seems to be using the draft status of IFC5 as an excuse for dragging their feet on incorporating IFC compatibility into their flagship BrIM program.

In fairness, if their users aren’t requesting this functionality then I can understand if they aren’t making it a priority for development. But if that’s the case, own up to it. Don’t hide behind the timeline of a spec that is developed by a non-profit primarily under volunteer effort. Be straightforward with the user base - they will understand that software development is typically prioritized according to their needs and specific requests for functionality.

Geometric Positioning

In general, integrated 3D modeling as a whole has been much slower to catch on in heavy civil when compared to sectors more focused on vertical construction such as buildings, schools, and general commercial development. The primary explanation typically revolves around a fundamental difference in geometry positioning. In a building, columns, walls, and the like are typically referenced from a grid with letters increasing along one of the XY axes and numbers increasing along the other.

Horizontal Alignment

For linear work such as roads and bridges, positioning is primarily based upon a linear distance along one or more alignment baselines. Each baseline is typically comprised of a series of lines, arcs, and spirals. Elements such as the centerline of a pier are located by distance along (station), distance left or right from (offset), and angle relative to (skew) a horizontal alignment baseline.

Vertical Alignment

Elevations along the baseline are described by vertical tangent grades and parabolic transition curves between the tangent grades. The resulting 3D alignment baseline does not neatly obey any basic mathematical primitives and is often approximated with chorded linestrings. BSpline curves are often sometimes used for this purpose, although that is typically rare.

Typical Section

Horizontal and Vertical alignment combine to describe the centerline or baseline of a roadway. However, a roadway needs to have one or more lanes for it to actually be useful as a means of transportation. The arrangement and geometry of lanes on a roadway is referred to as the typical section. Oftentimes, the typical section across a given stretch of road or bridge is constant. However, if we are at a roadway intersection or interchange and need to accommodate turn movements or ramp entrances and exits, the typical section is going to vary.

In other words, one end of the bridge may have two through lanes and an auxiliary lane. The auxiliary lane could very well be a different width or even dropped completely by the time we get to the other end of the bridge. This may be described directly by a list of dimensions at various distances along a single alignment baseline.

Or, it could be described indirectly by the addition of a second alignment baseline that does not parallel the other. All of these factors combine to complicate the process of describing and locating the geometry of bridge model elements.

Superelevation

Not only can the lane widths vary, but these variations often involve changes in superelevation. Superelevation is the roadway engineer’s term for the banking that is applied to the pavement in horizontal curves. This concept is seen most profoundly on a race track, where extreme banking is necessary to keep the cars on the track at high rates of speed. In the same way, the outside edge of a highway curve is superelevated (raised above) the inside edge. This is typically described in terms of percentage cross slope, or rise over run, across the width of a travel lane.

Putting it all together

So, if we are going to properly model a bridge deck, which is the portion that you actually travel upon, we need to be able to locate elements correctly using one or more horizontal and vertical alignments while also accommodating typical section and superelevation. This is indeed very complex, and most current BIM offerings such as Revit do not include tools out of the box that excel at generating and managing this geometry in a parametric manner.

Linear Geometry in IFC

Horizontal and vertical geometry were added to the IFC standard with version 4. Geometry plus sectioned spine covers the rest, as outlined in Volume III of BrIM protocols proposed by the FHWA.

But why would I give up all our Intellectual Property?

First off, the question of IP is going to vary from client to client and from contract to contract. My hunch is that there isn’t quite as much patentable, unique IP on a typical design project as some might suspect. But ignoring that issue, let’s focus on a specific part of the infrastructure circle of life - Design to Fabrication.

Design to Fabrication workflow

This step involves the handover of contract documents that include the technical drawings (plans) and specific requirements (specifications) for the materials and methods to be used in the work. The information is transacted from the designer to the construction contractor, who will typically then involve numerous subcontractors and other third parties to complete the work.

Often times, the contract documents go to a fabricator for specific parts of the work. For example, the structural beams will be sent to a supplier who will develop specific fabrication details (shop drawings), then fabricate and provide the beams that are needed for the bridge.

This process is labor-intensive, time-consuming, and prone to error as another party recreates and re-establishes data from the design information. This specific exchange of information is a great place to provide data from the BrIM in an open format that can easily be exchanged.

At this point, the design is complete. Any complexity in terms of parametric geometry or other supposed intellectual property is of lesser value when compared to the process quality improvements when working from a shared BrIM.

You can think of the BrIM as more of a PDF than a CAD file. Indeed, this specific exchange and Model View Definition (MVD) is addressed in the FHWA study previously discussed. In summary, that study found that IFC 4 is suitable for the Design to Fabrication workflow for the two sampled bridges.

Summary

In closing, there’s no need to wait for IFC5 before incorporating IFC into BrIM workflows. New standards take time to be incorporated into software and further refined by lessons learned on actual live project data. IFC is well established and has been in use for nearly two decades. It is robust, extensive, flexible, and best of all - free and open. Why lock in to a proprietary format when a superior open source alternative is available?