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Splice of simply supported steel girders to make continuous

Splice of simply supported steel girders to make continuous

Splice of simply supported steel girders to make continuous

(OP)
Hi all,

Working on a major rehab for a structure constructed in 1952 (simply supported steel girders, non-composite CIP deck). The girders were made continuous for live load in 1984 with the use of this detail... Plates were welded onto top of top flange, webs, and top of bottom flange, reinforcement was inserted transversely from girder to girder through the webs, and a concrete diaphragm was cast.



Upon completing a detailed condition assessment and load rating for the structure, we identified this 1984 splice detail as a fatigue-prone detail (especially the transverse welds at the ends of the plates). Theoretical calcs suggest the fatigue-life of the detail has already been exceeded. Tasked with identifying appropriate action and designing detail for major rehab.

Options as I see them:
-Do nothing as visually the detail does not appear to have any problems (can confirm there are no microcracks using mag-particle). However, since fatigue life has been exceeded, who is to know if and when a crack does develop??
-Replace the detail with a similar detail but use all bolted connections. The bottom flange splice will likely need to be extended to allow for a portion without any bolts to accommodate the bearing.
-Revert the girders to simply-supported and provide a "link-slab" to eliminate the need for a joint. There are structural concerns with this given that the continuity was originally instigated to increase the load carrying capacity and to keep up with truck GVW increases of that era. Load rating will need to be rerun assuming the girders are not reverted to simple spans.

What do you guys think? Ever seen something like this? Concerns, suggestions?

RE: Splice of simply supported steel girders to make continuous

What is the design loading? Is the loading equal to the design loading? and what is giving rise to the fatigue loading? You have to assess the loading conditions.

Dik

RE: Splice of simply supported steel girders to make continuous

Neat. What's the situation such that it requires fatigue evaluation? Any chance you could get by without the welds on the ends of the plates? Can you elaborate upon the link slab business?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Splice of simply supported steel girders to make continuous

(OP)
Dik - design loading was in accordance with CSA S6 CHBDC code. Based on the detail category and number of stress cycles, the fatigue life calcs from S6 indicate that the life of the detail was surpassed 2 years ago.

KootK - we typically investigate fatigue prone details when completing structural load ratings for bridges. Especially given the age/type of superstructure.

Link slabs are a pretty neat concept in which you provide a continuous bridge deck over simply supported girders to eliminate the joints. See pic below. Lots of good papers published in PCI, ASCE, etc. regarding the use and design of such details. Haven't ever come across one personally in our City but first time for everything I suppose!


RE: Splice of simply supported steel girders to make continuous

I'm not seeing that web shear splice
but then maybe that's the problem ? I'd've nested angles in the corners of the existing I-beams, and used packers to fill mis-match.

personally I'd vote for option 2, and put in a "proper" beam splice; why bolted reinforcements (be they straps or angles), not welded ?. Probably less invasive then option 3.

another day in paradise, or is paradise one day closer ?

RE: Splice of simply supported steel girders to make continuous

Can the plate strength be developed without the transverse welds? Also, in NY, ultrasonic impact treatment of transverse welds is being used on a regular. I don't know much about it - I imagine shortly I will because I have a rehab project starting and there are 100's of cover plate welds that have to be evaluated - anyway, I attached the DOT spec for your information.

I agree that there's no point removing the connection and installing a link slab if you need the capacity.

RE: Splice of simply supported steel girders to make continuous

OP thanks... Dik

RE: Splice of simply supported steel girders to make continuous

Here's a link to the FHWA Fatigue Retrofit Manual. It discusses various treatments, including UIT, which is supposed to be able to improve the fatigue category by up to 2 levels. In the late 80's I was working in CT and we did a lot of weld peening. UIT is a more refined version of peening.


Link

RE: Splice of simply supported steel girders to make continuous

(OP)
Thanks for the link bridgebuster! I will look into it.

RE: Splice of simply supported steel girders to make continuous

You're welcome

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