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Camber

 
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neelima
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Joined: 13 Nov 2010
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PostPosted: Sun Mar 04, 2012 6:47 am    Post subject: Camber Reply with quote

Hi all.

  Can anyone helps about camber and  types of camber,
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JVCSNL
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Joined: 26 Jan 2003
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PostPosted: Sun Mar 04, 2012 7:48 am    Post subject: Reply with quote

Large span beams and trusses deflection is also very large.  

Camber is provided in large span trusses and beams.  

In case of trusses, the central node of bottom chord is raised by some mm (called camber).  It is in reverse direction to natural deflection direction.  

The purpose is to allow initial deflection due to dead and live loads.  The truss will deflect by some amount of camber and hence, once the structure is in service, the bottom chord would be more or less flat or straight line.  Though, this looks theoretical, in actual, it is difficult to predict actual deflections.  Hence, camber value is many times kept different than deflection calculated in calculations.  

Regards,

Jignesh V Chokshi
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neelima
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PostPosted: Sun Mar 04, 2012 8:21 am    Post subject: Reply with quote

is there only one type of camber.. means only center point will be up for some mm.. or else is there any more classifications in camber
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spsvasan
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PostPosted: Mon May 07, 2012 7:30 am    Post subject: Reply with quote

Dear Er.Neelima

In the case of cantilevers, the camber will be highest at the tip.

Provision of camber does not alter structural behaviour. If camber is not provided the deflection of the structure will create an impression that the structure is sagging. Camber is provided to avoid this impression.

With best wishes
S.P.Srinivasan
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Dr. N. Subramanian
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PostPosted: Mon May 07, 2012 12:33 pm    Post subject: Reply with quote

Dear Er Neelima,

Check these sites to know more about camber:
http://www.modernsteel.com/Uploads/Issues/September_2004/30733_ej.pdf
http://www.modernsteel.com/Uploads/Issues/July_2006/30755_steelwise_camber.pdf

Best wishes
NS
neelima wrote:
is there only one type of camber.. means only center point will be up for some mm.. or else is there any more classifications in camber

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Jeet_mbm
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PostPosted: Fri Jun 01, 2012 12:18 pm    Post subject: CAMBER In RCC and Prestressed Beam Reply with quote

Respected Members

I have a doubt related to camber, so kindly through some light on this.

1- Can we use camber to Bye pass the deflection limit of IS:456.

2- Deflection which we have to compare with the given limit in IS 456 should be from where? Initial CIS position or CAMBERED position ( Refer Attached figure).

3- If we study language of SP -24 (handbook of IS 456) and IS 1343 it is some how diplomatic . As per my understanding, I conclude something in attached figure related to RCC and prestress structure. Kindly comment on this.

4. From my side rule of RCC beam will also be applicable to Steel Girders.



With Regards

Jitendra Sharma
08130970291



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Jeet_mbm
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PostPosted: Wed Jun 06, 2012 2:42 pm    Post subject: Camber Reply with quote

Respected Seniors;

I am still waiting for reply on my above question. Please give some thought to my doubt from your busy schedule.
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anshugoel
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PostPosted: Wed Jun 06, 2012 5:56 pm    Post subject: Re: CAMBER In RCC and Prestressed Beam Reply with quote

Here are some thoughts.

1- Can we use camber to Bye pass the deflection limit of IS:456.

Code requirements serve two broad purposes - safety and serviceability. Deflection limit is required for both. Any method used to serve the two requirements is acceptable.

2- Deflection which we have to compare with the given limit in IS 456 should be from where? Initial CIS position or CAMBERED position ( Refer Attached figure).

See opinion to 1 above and make a judgement for your particular case.

3- If we study language of SP -24 (handbook of IS 456) and IS 1343 it is some how diplomatic . As per my understanding, I conclude something in attached figure related to RCC and prestress structure. Kindly comment on this.

Code language is required to be logical, consistent and scientific - which should meet strict criteria applicable for these. If you find it diplomatic (i.e. does not meet the three requirements above) - you should write to Bureau of Standards and also the lead code developer to explain or edit. Your interpretation is correct. But please note that camber in construction for RCC beam without horizontal thrust is only an aesthetic approach.


4. From my side rule of RCC beam will also be applicable to Steel Girders.

Camber/Deflection are analytical - therefore material properties should not make any difference. However you would need to roll steel with particular specs to get the camber - generally there are strict requirements for each material grade. for instance ASTM A6 - restricts camber and sweep (i.e. camber on the other axis) to 1/8 of an inch times total length in feet by 10.
So if stock is 30 feet long, you will get maximum camber of only 3/8". Anything more needs to be specially ordered. Please look at Table 1-22 of AISC manual - if you have one. Otherwise I could put it up here.
Hope this helps.
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