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Fwd: Article on "Bulb Tees" in March 1997 Civil Engineering Magazine

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The article is entitled"Bulb-Tees Make More Efficient Long-Span Bridges"
by Leo Spaans, P.E. or Janssen & Spaans Engineering, Inc., Indianapolis.

It has intrigued us here in our firm, because it seems to make claims 
for the bulb-tee girder that, on the face of it, are hard to understand. 
For example:

1) Janssen claims that "bulb-tees redistribute girder forces more 
efficiently" than other concrete I-beam configurations.  However, as far
as we can determine, the live-load distribution factors for bulb-tees 
are exactly the same as those for other concrete I-beams.  Is THIS the
redistribution of girder forces that Janssen refers to, or does he 
simply mean that the greater section properties allow it to carry more 
moment?

2) One of the case studies that Janssen mentions refers to a bridge 
design for Bartholomew Co., Indiana.  The bridge as originally designed 
required 18 spans of 89 ft., with five AASHTO Type IV girders each span. 
The redesign using bulb-tees yielded 16-106 ft. spans with three 
bulb-tee girders each.  However, in OUR experience, AASHTO Type IVs are 
regularly used up to about 120 ft. spans.  It looked to us as though 
Janssen were touting the efficacy of the bulb-tee over a very 
UNeconomical AASHTO girder design.

3) This impression was further exacerbated by the fact that the redesign
on the afforementioned project utilized 5,000 psi deck concrete with 60 
ksi reinforcement, as opposed to the 3,000 psi/40 ksi of the original 
design.  I have been in this business for only 15 years, and my 
colleague for 30.  In that time, NEITHER of us has EVER used 40 ksi 
steel.  Once again, it looks like Janssen was merely dragging an
outmoded design into the latter half of the twentieth century!

In summary, much of what Janssen touts regarding the bulb-tee girder is 
undoubtedly significant.  But I would appreciate answers to these 
questions before I would feel confident in the data, enough to further 
consider utilizing them in our design.

Although Janssen refers to the inherent conservatism of state DOTs, the 
fact is that considerable standardization of the bulb-tee configuration 
must occur before the economies of scale can work to make them viable as
a routinely-specified structural member.

N.B.: If anyone has an email address for Mr. Janssen, I'd love to send 
this to him, and get his response directly.


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From: poly(--nospam--at)flash.net (Bill Polhemus)
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Subject: Article on "Bulb Tees" in March 1997 Civil Engineering Magazine
Date: Wed, 26 Mar 1997 19:47:30 -0600
Organization: Chez Polhemus, Katy, Texas, USA
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Richard Lewis, P.E.
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