-----Original Message-----
From: Bouma, Mark [mailto:mbouma@ntta.org] 
Sent: Wednesday, August 26, 2009 1:51 PM
To: Nancy Cline
Subject: RE: Any thoughts?

 

I reviewed the HNTB e-mail and their recommendation of an independent design review makes sense.  It is not an uncommon concept in the engineering market for owners to commission and
independent design review for complex structures such as long span bridges.  NTTA retained HNTB in 2006 to perform an independent design check of the Turner Collie & Braden (AECOM) design
for the Lewisville Lake Toll Bridge arch span.  This involved HNTB taking either the 60% or 90% plans (I forget which) and running and independent structural analysis of the bridge using
the geometry and member sizing proposed in the design.  They analyzed overall member sizing and connection details.  If I recall correctly, we paid about $75k for this work.

 

Addison is preparing to spend a large amount of money constructing a number of bridges that will be high profile structures in the Town.  It may be wise insurance to invest in a design
review to ascertain that the bridges do meet current AASHTO design standards, especially in light of staff concerns.  I would include questions to both the original design firm and the
design reviewer regarding:

·         Did the design include special event loading where the sidewalks may be at capacity but the roadway deck is either unloaded or fully loaded?

·         Interim construction loading?

·         Ability to replace cables or a hanger rods in case of damage or deterioration?

·         Wind analysis concerns and/or harmonic vibration analysis due to slenderness of structure?

·         Maintenance concerns and inspection requirements during bridge life cycle?

 

I would further recommend that a competent construction management team, whether Town staff or consultant, monitor the construction to ensure conformance to plans and specifications
since it sounds like the design may not have the redundancies common in more traditional bridge design.

 

I suggest you retain a firm that has relevant Texas experience in the design of arch bridge structures.  There are several firms in this region that could provide this expertise.  Several
arches have been designed and/or built in the Dallas are recently, including the Calatrava bridge, Arapaho Road and LLTB.  A number of arches have also been designed and built in the
Houston area of US 59 in the last decade (http://www.modernsteel.com/Uploads/Issues/November_2003/30723_Houston.pdf).

 

Hiring an independent engineer to perform the design review may provide you a more unbiased response rather than having the designer contract with another party.  This review would provide
you with better information on whether to continue with the bids you have received.

 

 

-----Original Message-----
From: Nancy Cline [mailto:ncline@addisontx.gov] 
Sent: Tuesday, August 25, 2009 6:16 PM
To: Bouma, Mark
Subject: Any thoughts?

 

Do I insist that design engineer  contract with an experienced vehicular engineer to review and revise plans?  Depending on review, is it worth it to reject bids?

 

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