Bombardier Innovia Monorail 200 - Anatomy of the Bombardier Beam

The following question and answer session took place between Keith Walls, The Monorail Society Vice-President for Thet Monorail Society and Carlos A. Banchik, P.E., then-Structural Design Coordinator for Carter-Burgess in Las Vegas, Nevada during the construction of the Las Vegas Monorail. Carlos was the engineer of record on the original MGM-Bally's Monorail. Many of the questions reflect those that we get from our visitors and Carlos has first hand knowledge of the subject.

Q. What Codes are followed in the design of the Las Vegas Monorail Project?

A. The guiding document for structural guideway design used in the Las Vegas Monorail is the American Concrete Institute document: ACI358.1R-92. Analysis and Design of Reinforced and Prestressed-Concrete guideway Structures. Then we use the American Association of State Highway and Transportation Officials (AASHTO) publication Standard Bridge Design for Highway Bridges.

Q. What type of loads do you design for in a typical monorail structure?

A. There are many sets of loads and load combinations required to ensure the structural capacity of the monorail beam, as it is a very slender member. Most of the Live Loads are provided by the vehicle vendor (Bombardier), then "live" loads due to braking, centrifugal loads, impact, etc. are superimposed to the "basic live load". Don't forget that there are many other loads to consider, such as construction loads (post-tensioning loads) and environmental (temperature, concrete creep and shrinkage, wind, seismic). The combination of all these loads is provided in tables contained in the documents outlined above.

Q. What is the distinctive characteristic of a monorail beam when compared to a regular bridge structure?

A. I would say it is the casting of the beams and the lack of the ability to adjust the geometry once the beam has been cast and erected. The monorail beams are what we would consider a mechanical casting more than a structural casting due to the tolerances required for proper riding. In your typical bridge structure, there are slabs cast on top of beams, which we lack in a monorail system. The importance of the secondary pours or slabs is that the engineers and the contractors compensate for riding surface unevenness and the deflections that accompany the construction of any structure. In a monorail structure, the top and side surfaces are cast at once and there is no chance to implement much change after the piece is cast.

Q. Being that the casting tolerances for a beam like the one you described above are so tight, where are the castings done?

A. The typical cast is done in a set of expensive forms that mirror the guideway alignment is 120' long section, regardless of the beam length. When you add the fact that the beams are super-elevated to improve riding quality, (i.e rotated around the vertical plane) and that they also contain vertical curves, you have a very complicated three dimensional geometry that needs to be captured in concrete and steel. Each beam is approximately 70 Tons in weight, with 7' high ends, 5' in the middle.

Q. How do you erect each beam?

A. The erection is very critical and typically it uses two cranes to facilitate control over the cast piece. Careful setup on top of the columns is required to ensure the proper geometry is locked in placed prior to casting closure pours between the beams. I encourage your readers to submit any questions they might have about this technology, I will be glad to respond to them, or research for the answer. We will provide you with pictures of the actual construction so you can share them with your readers.

Thank you Carlos!

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