Monorail Has Significant Construction Advantage in Austin
‘High-quality, low-cost local concrete is the key’
Patrick Bachman, P.E.
Member, Austin Monorail
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:
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,
(San Marcos), Texas Concrete Products (Victoria and Waco), and Bexar Concrete
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.
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.
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).
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.
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
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