Although one of the smallest projects that I have worked on in terms of dollars, the North Bank Pedestrian Bridge has been one of the most geometrically challenging. This 700-foot long structure snakes its way through a maze of existing infrastructure and in the process, exhibits some bizarre and interesting geometry. Horizontally, the basic shape is a simple reverse curve while vertically, approach tangents are connected by a single parabolic curve but this is where the “ordinary” ends. While the “deck” chords of the supporting pipe trusses follow the basic geometry, the “outer” chords undulate above and below the deck in a sinusoidal fashion resulting in trusses that appear to most nearly resemble warped strands of DNA.

Working for both the general contractor (Barletta Heavy Division) and the fabricator (Newport Industrial Fabrication), I have been involved in nearly every “geometric aspect” of the project from survey control on the ground to the intricate details of pipe bending and fish-mouthing.  Perhaps the biggest challenge of all was the control of the structure’s geometry in the shop.  Working with Newport Industrial personnel, I developed coordinate transformation procedures and shop survey methods that allowed millimeter-level control of the structure’s very complex geometry as it went through various stages of fabrication.

With erection of the superstructure now complete (Fall 2011), this has been a challenging but very satisfying project for all parties.

Civil Geometrics has been engaged by J.F. White Contracting to provide geometric and survey support services on the new Chelsea Creek Bridge between Chelsea and East Boston, Massachusetts.  This project involves the replacement of the old bascule bridge on Chelsea Street with a new longer (420′) lift span that will acommodate larger tankers and allow access to vital oil import facilities that serve much of New England.  Among the challenges that it offers are the high precision surveys that are required to position the scores of 2″ anchor bolts for the structure’s towers and the delicate alignment challenges that its machinery requires.  We look forward to moving forward with this interesting new project.

In the process of developing our software, we have been using Autodesk’s Civil 3D to check our results.  When some comparisons showed deviations, we were surprised to find that the errors lay not with our work, but with the venerable Civil 3D.  Lengthy correspondence with Autodesk’s developers and a recent (June 2, 2009) meeting at their office confirmed our conclusions.  Autodesk has been working hard to fix their problems and should be caught up soon.  Meanwhile, if you are doing high-speed rail design, use caution with compound spirals!

For years we have been developing software both to deal with project-specific tasks and to give us a competitive edge in the world of civil geometry. A new “integration engine” that allows our software to handle any type of transition curve, not just the familiar clothoid is now complete. This will allow us to more effectively resolve the geometry of structures that carry traditional “light rail” as well as high-speed rail.  Developed in the VBA language and embedded in Microsoft Excel, this software picks up where most other civil/survey software comes up short.  Many engineers and construction surveyors have developed their own library of spreadsheets to handle the tougher challenges that we face.  “Civil Geometry” provides those at the cutting edge of geometric development work to combine their Excel skills with a powerful set of COGO/alignment oriented functions embedded right in their spreadsheets.  This package is available free of charge to those needing the ultimate in civil number crunching capabilities.  Contact us for details.

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.