crane runway beams - differing adjacent spans, mid-span splices

[OUe]

I'm designing a top-running bridge crane's runway beam and gantry tower support system. The bridge crane spans 94', the gantry towers (triangular lattice tower) span 25', 16', and 24'. Because I haven't designed a crane system in nearly 4 years, I am a little rusty. I have a radio/cab operated bridge crane, so I understand the impact loads to the runways, and I'm using AISC DG #7 with AISC 360-05 for ASD and top flange lateral/torsional/sidesway buckling.

There were a couple questions from the mechanical engineer who is the project manager. He is asking if the runway beam spans are ok and if they can make a nice 2-beam (interior splice in the middle of the 16' span).

1. I told him that I recall some rule of thumb about runway spans not allowed to exceed 20% of the adjacent span, but that I wasn't confident on it and I'd get back to him. I honestly can't remember why this rule of thumb is bothering me.
2. Secondly, I told him that I'd prefer not to design a splice at the mid-span and it would be counterintuitive to save on the cost of buying additional beams of 40' length. The cost of the connection (I wouldn't do anything less than a CJP moment connection) would cost more than the beams. I didn't even want to mention the fatique issues, but it is certainly a worthy concern.

I'm mostly looking for a clarification of number 1 above, but any additional comments would be great. THANKS! OUe

 

[JedClampett]

Don't splice in midspan. If you need a splice, and for 64' you likely will, splice over the support. You can have a 40 ft and a 25 ft span. It's still two beams, without a nasty splice detail.

 

[hokie66]

I never use continuous runway beams. Simple spans have always been required in the industrial environments where I have worked. Although continuous beams may function well for light duty cranes, I still wouldn't do it.

Not sure where that rule of thumb comes from. It doesn't ring a bell with me.

 

[amec2004]

>>I never use continuous runway beams. Simple spans have always been required in the industrial environments where I have >>worked. Although continuous beams may function well for light duty cranes, I still wouldn't do it.

That's correct. that's because

1) negative moment may cause fatigue issue on the support connection
2) runway beam thermal expansion may be an issue if there is no gap at the support location

>>I have a radio/cab operated bridge crane, so I understand the impact loads to the runways,

For cab operated crane, the impact factor=25%
For pendant operated crane, the impact factor=10%

CAB-OPERATED CRANE --> A crane controlled by an operator in a cab located on the bridge or trolley.

There are two types of overhead cranes, cab operated and pendant/remote-controlled. While the operation of both types is different, many overhead crane operators can operate either type. In a cab-operated overhead crane, the operator sits in a cab on the crane. He moves as the crane moves. For a pendant/remote-controlled overhead crane, the operator stays on the ground and controls the crane from a remote control attached by a cable to the crane.

Cab Operated Crane --> A crane controlled by an operator sitting in a cab located on the crane’s bridge.
The operator moves as the crane moves.
Pendant Operated Crane --> A crane controlled by an operator staying on the ground and controls the
crane from a remote control attached by a cable to the crane.

From Table 2.1 of CISC Guide for the Design of Crane-Supporting Steel Structures 2nd Ed, Cab Operated Crane has larger vertical load impact factor, side thrust and tractive force than Pendant Operated Crane,

Most cranes are Pendant/Remote operated. If unknown, pick Cab operated to be conservative.

>>I'm using AISC DG #7 with AISC 360-05 for ASD and top flange lateral/torsional/sidesway buckling.

AISC Design Guide 7 uses the top flange to resist the lateral side thrust load and thus the torsional effect to the whole section is not considered. This is actually the AISC recommended simplified approach for crane runway beam design.


>>There were a couple questions from the mechanical engineer who is the project manager. He is asking if the runway >>beam spans are ok

You have to run a calc to check if it’s OK

>>and if they can make a nice 2-beam (interior splice in the middle of the 16' span).

Runway beam splice is always at runway beam support location. It’s a big NO NO if you splice at the mid span, which is the max positive moment location. You have all kind of issues, especially the fatigue issue to the splice connection

>>I told him that I recall some rule of thumb about runway spans not allowed to exceed 20% of the adjacent span,

No such rule of thumb.


>>I didn't even want to mention the fatique issues, but it is certainly a worthy concern.

That’s a big concern. CJP gets crack and bolting get loose -->raining bolt as Jim Fisher mentioned in his seminar

See attached PDF for typical splice detail at support location


anchor bolt design per ACI 318-11 crane beam design

http://www.civilbay.com

 

[rowingengineer]

">>I never use continuous runway beams. Simple spans have always been required in the industrial environments where I have >>worked. Although continuous beams may function well for light duty cranes, I still wouldn't do it.

That's correct. that's because

1) negative moment may cause fatigue issue on the support connection
2) runway beam thermal expansion may be an issue if there is no gap at the support location"

We have a few discussions in my office about the reason for the simple span designs. The thermal issue is often mused over, in general most crane tracks are fully welded for the full length of the building with joints only provided at expansion joints or 60m because of difficulty to install. Thus are these just floating over the joints with stress continued from these elements small enough to ignore.

As for fatigue we discuss if use should be considered in this equation and also stress levels.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[hokie66]

By "crane tracks", I assume you mean crane rails. Rails should not be welded to the beam, but rather should use rail clamps, or hook bolts in the case of light cranes.

 

[rowingengineer]

By crane tracks I mean the 50x50 flat bar they welded onto the top of the beams. Crane rails don't in my mind have the same thermal issues as they don't generally get welded as you noted.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."