Bolt Design for Double Angle Stiffener Connection at Girder Web 1

[rsbmusicguy]

Hey all,

I am jacking a girder using a hydraulic jack to fix the respective bearing and due to the jacking load, I have to provide a double angle section at the web of the girder so the web does not buckle.

This is pretty typical for most of my jacking designs, my question is in regards to the bolts connecting the double angle to the girder web.

Do these connection bolts have to be designed for the full vertical jacking load (for shear and bearing, non slip critical connection)? If this is the case, I would have to provide a ton of bolts which will significantly reduce the area of my girder web. When I think of the double angles going into compression between the top and bottom flange of the girder, I am having trouble picturing the force transfer into the connection bolts at the web. I am looking for a way to justify not designing these connection bolts to take the full shear / bearing of the jacking force.

Let me know your thoughts, thanks!

RSB

 

[DrZoidberWoop]

You're probably going to have to attach a sketch of your scenario if you want any meaningful input. If the double angles are acting as stiffeners, then my workflow would be similar to the picture I attached. The vertical load will be taken into the web and distributed accordingly. It's the forces in excess of what the web can handle that necessitate the reinforcement.

I could be wrong based on my interpretation of your problem tho. Best of luck!

 

[BridgeSmith]

If the angles are tight against both flanges, then the bolts won't be carrying much, if any, shear.

If you use fully tensioned high strength bolts, and leave them in place, I would be very surprised if it wasn't still adequate with the holes required. The total bolt shear capacity need not exceed the axial capacity of the angle.

 

[KootK]

If the angles are there to prevent web buckling and nothing else, then the bolts do not need to transfer the reaction shear and, moreover, I'd probably stop the angles at the web fillet so that:

a) it would be easier to fabricate and;

b) reaction force wouldn't be inadvertently transferred to the angle.

My answer would change, however, if the angles were doing other jobs as well such as:

c) addressing beam web yielding

c) addressing flange bending

d) providing rotational stability to the beam at the jacking point.

 

[BridgeSmith]

Excellent summary, KootK.

 

[rsbmusicguy]

KootK - that was a great summary and I really appreciate it! The angles will also be provided to address beam web yielding at the beam.

That's a good point, web yielding will transfer an eccentric force on to the angles and therefore the connection bolts will act in a different manner.

What would you guys have to say about the connection bolts with respect to web yielding?

Thanks again,

RSB

 

[KootK]

Thanks for the kind words HR & OP.

For web yielding, I'd much prefer a welded stiffener if possible. I'm not sure you can deliver the reaction to a bolted stiffener without introducing slip into the connection that would neuter the strategy.

 

[rsbmusicguy]

Definitely - it would be possible to weld the stiffener but only in the compression zone of the beam. At that point, I guess you would check the allowable shear in the weld?

I get confused because if the bottom of the web yields (or stiffener deforms under compression), an eccentric force will be applied to the connection and therefore I have always imagined that the connection would go into mostly tension in order to withstand the deformation. Additionally, probably combined tension and shear will also apply since some shear will also come into play if the stiffener slips.

I have always designed for shear since I find it to be conservative...

 

[BridgeSmith]

IF you have the option to weld stiffeners, that would be the more straightforward design approach. If you have it available, check out the bearing stiffener provisions in the AASHTO Bridge design spec. You should be able to find everything you need to know for design in there.

Then you just have to decide whether to weld or finish to bear at the stiffener to flange interface. Depending on what the fatigue stresses are at that location, the welds to the flanges may have to be full penetration groove welds. We've always specified our bearing stiffeners finish to bear, but some of the fabricators have asked to do full pen welds instead.