huangyhg

trolley beam
i'm designing a continous (140') beam to be hung from existing roof trusses (spaced 14' o.c.) that is to have personnel suspension trolleys on it. the dilemma i'm running into is this... how to splice this beam. field welding would be the simple solution, although it is not feasible for this application.
the splices can only use web plates because flange plates will interfere with the trolley operation. can i design a web plate only splice to handle the moment? there is no defined contraflexure point since it is a moving point load, although i can place the joint at a location where the envelope is best. if i do design a web plate splice to handle the moment should i take the reduced stiffness of the joint into account in the structural analysis? i'm apprehensive about using a shear splice as any rotation between the two connected beams will hinder trolley movement across the joint.
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would it be feasible to locate a zero moment splice at a support?
another option may be to offset the splice from a support. allow the "i" beam to cantilever. count the splice as a pin support for the other "i" beam tied into it.
you may still want to provide a weld on the top of the bottom flange ground smooth to provide a smooth surface for the wheels of the trolley.
regards, jpj
jike,
so basically have a series of simply supported beams? good idea. possibly... if i were to hang the two beams from a common plate (that would then bolt to the supporting truss), how would you go about calculating edge distance, spacing and # of bolts for a flange in a hung configuration like that? would you still use a shear splice?
i would use a shear splice plate to force alignment of the two separate beams (sometimes they don't quite align perfectly). i would also weld the bottom flange and grind smooth where the wheels run as virtualengineer suggested.

use aisc standard edge distances and spacing. bolts may receive additional load due to prying force. see aisc manual or good steel textbooks on how to calculate this.
here is what i do (i realize you may not be able to do exactly the same given constraints):
1) shear splice about a foot away from supporting beam or truss. you can use steel plate both sides, field welded to trolley beam web. you can use erection bolts, and then remove after weld is made so that bolts don't interfere with trolley wheels).
2) hang trolley beam from supporting beam or truss with 4 bolts.
3) in addition to bottom flange weld recommended by virtualengineer, i like to weld top flange, as i am afraid that the combination of the bottom flange weld and the shear splice will create enough continuity in the "simply supported" beam that you may end up with distress in the shear splice if you don't weld the top flange.
follow-up to my previous post:
on the last project where i used detail exactly as described, the contractor called me and asked if he could remove the bolts and weld all around the plate since the bolts were in the way of the trolley wheels! obviously he had ignored my notes requiring the field weld and requiring that the erection bolts be removed. you never know what is going to happen out there!
the ideas that my colleagues introduced are good and practical. the most practical solution is:
they make hanger to support trolley for situations like yours. do a search on the internet and you will find them. if you cannot, contact me and i can point you in the right direction.
i designed miles of trolleys, straight and curved.
you will need to somehow introduce a brace that will take the longitudinal load due to traction moment from the trolley to the beam. they also make these gizmos.
regards,
lutfi
folks,
i am confused by the splice detail you are proposing. the post said field weld is not feasible in the first place, but it seems you still need the weld. in that case, why not just do field weld to form a long continuous beam. i did a monorail extension in a recent project using groove weld to top, bottom flanges and web, with grinding smooth at web and bottom flange.
i'm going to revisit this issue with the contractor. this trolley beam is being installed 120' up in an atrium with no side access. i was told that welder access wouldn't be possible. welding it on the floor and hoisting it into position may be possible, but i'm scared to do that with a 140' long 6" deep w-section. i was hoping to hire superman to fly the sections up and weld them, but he's tied up on another project for the next few months.
it seems that the question about welding the bottom flange depends upon whether it is ok for the trolley to bump across this joint. i would hope that a trolley manufacturer could help answer this question. when a monorail has a switch, doesn't the trolley wheels have to bump across this joint. is this any different?
if the joint width is kept to some acceptable tolerance, then perhaps the manufacturer would allow it. is this any different that a railroad train rolling over a bolted rail splice versus a welded rail splice? granted it is different but it is similar.
please contact the trolley manufacturer and let us know what he says.

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