Deflection

[MrPayne]

Hi.
I am working on a task which requires me finding the maximum allowed deflection on an HE240B beam. The beam is 10 meters long with a support at 5 meters. I have found the formula on how much it will deflect, but need to know how much it is allowed to deflect.

Thanks

 

[drawoh]

MrPayne,

I think the key word here is "allowed". This generally is not determined by calculation. Your boss tells you what is allowed, or there is a standard somewhere telling you what is allowed.

Is this mechanical engineering, or is it civil and structural? There may be some building codes you need to have explained you.

--
JHG

 

[MrPayne]

Its for mechanical engineering. The beam will be used as a support to hoist some equipment, but the boss hasn't given any instructions for how much deflection is allowed. I've been trying to find some standard or codes, but there are many different opinions on how much is allowed. I've seen it from: Length/180, up to, L/500

 

[Jboggs]

In my opinion the "maximum allowed deflection" would only be an issue if there is some physical requirement affecting the loaded position or configuration of the beam, such as its alignment with some external structure. If there are no physical requirements and all the boss is really wanting is that the beam not fail in use, then the applicable rule has to do with the safety factor you apply when comparing the maximum loaded stress to the material yield stress. The safety factor could range from maybe 2 on the very low side to 10 or even more on the high side. Selecting the safety factor could be a matter of local code, or company standard, or departmental common practice, or simply the result of a meeting of the affected minds. I would ask co-workers in similar positions with more experience what their recommended safety factor might be. Choose one, and run it by the boss for his approval.

 

[MrPayne]

Okey. Thank you for the quick response. I appreciate it .

 

[Tmoose]

Depending on the load arrangement, and the "support" at 5 meters then there may be ways things might fail before the beam gets close to yield in a simple beam calculation.

http://2.bp.blogspot.com/-ZAwRo06wKmw/U6rraKlgxSI/AAAAAAAAB0E/r5BkuvlJFTE/s1600/Beam_mode_2.gif

http://1.bp.blogspot.com/-AXGui88k7...xA/s1600/PCS_calcul_crit_shell_6_fourche4.jpg

http://www.steelconstruction.info/images/thumb/4/4c/R19_Fig6.PNG/728px-R19_Fig6.PNG

 

[MJCronin]

http://www.eng-tips.com/viewthread.cfm?qid=97352

MJCronin
Sr. Process Engineer