Monorail Has Significant Construction Advantage in Austin

‘High-quality, low-cost local concrete is the key’ 

Patrick Bachman, P.E.

Member, Austin Monorail Project

 When calculating capital construction cost, that is the cost to initially build a Monorail system, it is not widely known that Monorail has a significant construction advantage in Austin over almost any other area of the country or the world. This is due to the high-quality, low-cost concrete  available in Texas. Texas has a very well developed precast concrete industry. Some details:

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TxDOT alone purchases about $1,000,000 worth of precast concrete products *per day*. In central Texas, we are situated near three of the biggest producers, Heldenfelds (San Marcos), Texas Concrete Products (Victoria and Waco), and Bexar Concrete (San Antonio).

 

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Texas is blessed with abundant high-quality aggregate, a highly skilled concrete labor force, and a well developed transportation network to move these products around the state.

 

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Much of the monorail guideway structure is precast and post tensioned. In Las Vegas, all of the beams were precast. This is the preferred bridge type in Texas. We routinely produce this type of bridge for about $40/sf, whereas the national average is closer to $69/sf. Concrete strength for precast concrete beams in Texas is routinely 8500-psi. This is considered "high-strength" concrete elsewhere. Typical concrete strength is 5000-psi in many other areas of the country.

 

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The "crossheads" or "bent caps" (forms the horizontal tee at the top of the column) may be precast. This has been done in California on a transit project, and was proposed in Las Vegas. This concept is currently being developed on TxDOT bridges around the state with success. If this concept were used, the only portion of the guideway cast on site, would be the column and drilled shafts (foundation).

 

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Much of the difficulty associated with precast concrete structures has to do with the connection between precast elements, e.g. the column to crosshead, and crosshead to guideway beam connections. The problem with these connections is made more difficult with the introduction of large seismic forces. Texas has virtually *no* seismic force.

 

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Surface light rail has no such advantage based on geographic location. To summarize, the Austin monorail has a significant cost advantage compared to monorail in other areas of the country, due to the highly advanced precast concrete industry in Texas. Surface light rail has no such geographic advantage because it will not use a great deal of precast technology.

 

 

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Last updated: 04/30/03.