As we move into 2009, we are finishing up with our data preparation for the DART expansion project in Dallas. Of the 26 miles of new rail corridor, about 12 miles are on elevated structures consisting mostly of composite deck on AASHTO beams. Our last major task is the development of cambered digital terrain models for the deck that reflect the superposition of nominal geometry and anticipated dead-load deflection. This allows survey crews to easily set grades for the stay-in-place deck forms without struggling with grade sheets in the field. A similar set of DTMs with partial camber can be used to grade the plinths that carry rails on the deck. Definitely another interesting and enjoyable project.

With the recent completion of the I35W Bridge in Minneapolis, we have resumed a more civilized lifestyle. The demanding pace of this fast track project put enormous strain on all who participated. The payoff was completion of a $237M project in about 10 months resulting in a substantial early completion bonus for the contractor. For our part, the usual challenges of segmental bridge construction were compounded by a design-build environment in which the design seemed to be only minutes ahead of construction.

Data preparation for the project included pre-cast segment geometry, erection geometry, and cambered digital terrain models for the various phases of the cast-in-place spans. For the as-cast surveys, we developed a unique trilateration approach and used statistical methods to achieve a high degree of precision in horizontal tracking. This method had the added advantage of not requiring a clear line of sight down the length of the casting beds, something that would have been difficult in the harsh Minnesota winter.

In spite of the long hours and a renewed addiction to caffeine, it was a pleasure working with the Flatiron/Manson construction team and Figg Engineering on this high-profile project.