Existing Crane Runway Beams 3

[Andrewstructure]

Using AISC Design Guide 7 and CMAA 74 for the evaluation of an existing underhung crane runway has yielded results that I feel are too conservative, based on observations of the long-term on site performance.

The main limiting factor in my calculations is weak axis yielding. Local bending (CMAA 74) limits this value even more; deflection limits the allowable wheel load further!

Does anyone have a source that focuses on evaluating existing cranes?

Also, is there any local bending analysis method that accounts for distribution of the wheel load along the flange? (note: this underhung crane does not have a crane rail)

 

[CTW]

I've never come across a source that provides an all in one guideline for evaluting existing runways. This tends to be one of those "engineering judgement" situations.

Depending on the age of the runway, it's possible that weak axis bending/torsion were neglected in the original design.

If you can provide some more information about the project such as reason for evaluating runway, crane size, crane use, deflection limit used, etc, then others may respond with their advice.

Do you have the original crane wheel loads from the manufacturer?

Below is an example calculation I have in my references for checking lower flange bending. The wheel load is assumed to distribute along the flange for a distance of 12 x the flange thickness. I don't recall how this distribution was determined though. The example is for an S-shape.


Crane wheels 6' - 0" o.c.
Load per wheel (pair) = 11.60 K
Load per wheel = (11.60/2) x 1.10 = 6.38 K
Assume stress distribution on the flange
tf = 0.622 is taken at the middle of the flange
Effective flange bending length
12tf = 12 (0.622) = 7.46 in.
Flange thickness at web based on 1:6 slope of flange
0.622 + (2.545/2) (1/6) = 0.834 in.
For an S 15 x 42.9: k = 1.375
Radius of fillet = 1.275 - 0.834 = 0.541 in.
Moment arm = 2.545 - 0.541 = 2.00 in.
Moment = 2.00 x 6.38 = 12.76 in-K
S = (7.46/6) x (0.622)2 = 0.47 in3
fb = Moment / S = 12.76/0.48 = 26.58 KSI
Fb = 0.75 (Fy) - 27 KSI (AISC F2-1)
Unity Check = fb/Fb = 26.58/27 = 0.98 < 1.00 (OK)

 

[Andrewstructure]

Do you have the original crane wheel loads from the manufacturer?
- No. I am using Mentor Dynamics and assuming that is similar.

The crane beam is a plate girder with a WT section for the bottom 1/6.

The bottom flange is very thin and narrow, so there is not much lateral capacity (3/8"x3.75"). The client wants to extend the runway another 80' but I am not going to be able to use the same section as the existing crane. I am sure they don't want to replace the other 170' with a w-shape.

 

[CTW]

I'm having trouble visualizing the plate girder. Are you saying the existing runway girder has a WT for the bottom flange, then a plate welded to the stem to form the web and then a plate top flange?

How deep is the plate girder and what is the span?

 

[Andrewstructure]

Yes, your visualization is correct, but the flanges of the WT were shortened for some reason.

16" deep with a 9.75"x.625 top flange, 3/8" web, WT is 1.75" deep, but welded to a 3/8" plate to form the rest of the web.

20' span, hanging from hangers, laterally stabilized at supports at top flange only. Class D.

 

[CTW]

I've been going back through my references and came across one from the CISC. I've never looked through it much unitl now. I noticed that in the section on underhung cranes, the author mentions your type of runway. He further states that some of these hybrid girders are proprietary designs and can be fabricated from different steels.

If you don't have the original steel grade used in the design, then this may explain your analysis results.

 

[Andrewstructure]

I also found this presentation by a crane manufacturer posted online that contains an alternative method for bottom flange local bending.

Unlike the CMAA method, this method distributes the bending load along the beam longitudinally.

 

[RockEngineer]

The same method of computing lower flange stresses is in Modern Steel Construction Magazine Dec 1999 under the Steel Interchange in answer to a question about how to calculate lower flange concentrated stresses. That article was written by David T Ricker. Some engineers prefer this method because it is logical and they understand where the stresses come from where the CMAA 74 equations are purely empirical to match test data. They definitely give different answers.

For your patented track, T/C American has made a lot of these over the years. Many of the systems over 50 years old that I have seen were theirs. If you contact them they may be able to help you determie if it is their track and give you some better data of the material strengths for the upper and lower flanges. The lower flange is usually made out of high strength steel while the upper flange is A36.

http://www.tcamerican.com/

The current standard for patented track systems, which is what your are describing, is ANSI MH27.1

 

[Andrewstructure]

Link to above referenced article:

http://www.modernsteel.com/steelinterchange_details.php?id=201

 

[Andrewstructure]

You were correct that the crane is a proprietary system. (see example here:

http://tarcatrack.com/Components.html)

This type of crane is called a “Patented Track Crane” and they are not to be designed per CMAA. The governing design code is MH27.1. (available here:

http://www.gorbel.com/pdfs/ANSI_enclosedtrack.pdf

and

http://www.gorbel.com/pdfs/ANSI_patentedtrack.pdf)

There are several of these manufacturers out there including:

Cleveland Tramrail/Gorbel (

http://www.gorbel.com)

ACCO Louden Rail Tram Beam (

http://www.accolifting.com)

TC American (

http://www.tcamerican.com)

You can identify the manufacturer by several methods:
1. Width of the bottom proprietary flange (3.33” for Tram Beam, 3.25” for others)
2. Web punching (Cleveland Tramrail has a ½ moon with a T cut in the web. See here:

http://tarcatrack.com/Home.html)

3. Look for markings on crane itself
4. If there are any other methods to identify manufacturer, please post!

From the Cleveland Tramrail/Gorbel site:
All Gorbel® Jib and Work Station Cranes are structurally designed in accordance with the AISC Steel Construction Manual

All Gorbel® Jib and Work Station Cranes are in accordance with OSHA Specification 1910.179 and ANSI Specification B30.11, as they apply to Jib and Overhead Cranes. All Gorbel® Work Station Cranes meet or exceed the requirements of MMA MH27.2 specification for enclosed track systems. All Gorbel® Cleveland Tramrail® systems meet or exceed the requirements of MMA MH27.1.

All Work Station Cranes are in accordance with the following Canadian Standards as they apply to Overhead Cranes: CSA Standard B167-96 and CSA Standard C22.2 No.33-M1984 (re-affirmed 1992)

 

[Andrewstructure]

I found a link to CMAA 74 in PDF form:

http://www.industrialhoistandcrane....nd_regs/CMAA/CMAA SPEC 74 Entire Standard.pdf