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Re: rotation at bearings

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The idea is great.  Actually, this is exactly how I modeled it in 3D.
In reality, however, it will result in the longitudinal seismic being transmitted to only one bearing out of 4. 
Well, wait... Obviously, it won't be symmetrical, but it may just work... I'll try.  
Good one. Thanks.
As far as "surrendering" goes - on a principle, I am against that, as long as I feel being right or proven otherwise.  However, I would readily agree with the opposing side, if any good argument would be given, not like "my 3D model is better than yours"...
Besides, surrendering (man, what a terrible word!) would result in me redesigning, like, 30% of the project (obviously, gratis).
Thanks again.
----- Original Message -----
Sent: Wednesday, October 06, 2004 10:36 AM
Subject: Re: rotation at bearings


        There should be a way to get out of this battle.  I agree with you; but sometimes you just have to surrender.

        What happens if, in order to retain your desired longitudinal stability, you slot the end of only one of the beams?  What about adding an end beam between your two pinned end beams with a vertical "pinned" connection at mid point?  Either idea should eliminate the theoretical problem envisioned by the reviewer.

        Just a couple of possible solutions to solve what I also consider a non existing problem.

Good luck.


H. Daryl Richardson

"S. Gordin" wrote:

Fellow engineers.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

I hate long posts.However, please hear me out.

For more than a month now I am going back and forth with an independent reviewer on the design of two pedestrian bridges.  I managed to prove my points on all issues, but...  On the remaining one issue I seem to have exhausted all means of persuasion within reason and logic.  So, I would appreciate a good advice.

Here it is...

An 80'x8' steel half-truss pedestrian bridge with four bearings: two with two dia.1-3/8" holes each on one end of the bridge, and two with 1-3/8"x3" slotted holes on the other.  A total of 8 anchors 1" diameter, CIP. 

According to the reviewer, the 3D analysis of the bridge shows that the application of the transverse (wind or seismic) lateral force on the bridge produces the longitudinal reactions in the pinned bearings on one end of the bridge.

I responded that such forces will never develop, mainly, because there is no such thing as an ideal hinge (unless it is so purposely designed). 

Indeed, the ø1? anchor bolts of the subject bridges are located in ø1-3/8? baseplate holes (3/8? gap).According to my own 3D analysis , the maximum movement of the bridge at the supports due to the horizontal-plane rotation under the transverse force of a 100 MPH wind is 0.18? << 3/8?. This means that actual ?pins? and lengthwise reactions (due to transverse forces) in those bearings will never materialize.

The reviewer still insists on putting slotted holes in all four bearings and to account for longitudinal seismic through actual dynamic impact on the abutment backwall and anchors.Alternatively, the reviewer suggested designing the bridge abutments and anchor bolts for the couple of longitudinal forces resulting from the application of the transverse (wind or seismic) force?

To compare: the actual (transverse) wind reactions are about 9.3 kips per bearing.The aforementioned longitudinal forces resulting from the same force are about 33 kips (acting concurrently).

The question is ? am I correct here? If so, how can I convey the message to the reviewer?Any suggested sources?

Thank you. 

V. Steve Gordin, PhD
Registered Structural Engineer
<?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />IrvineCA