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Camber
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thirumalaichettiar
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PostPosted: Thu Jun 14, 2012 10:14 pm    Post subject: Reply with quote

Er.Jeet_mbm,

As Dr. N.S. said that the camber in concrete structures is given to nullify the max. dl deflection. If it is given it shall not be more than 505 deflection due to D.L.
More information how to reduce the deflections through the Design and construction technique are given in the ACI-435R-95-CONTROL OF DEFLECTION IN CONCRETE STRUCTURES.

T.RangaRajan.
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thirumalaichettiar
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PostPosted: Thu Jun 14, 2012 10:36 pm    Post subject: Reply with quote

Er.Jeet_mbm,

In addition to the information in my previous posting I found some information about CAMBER for cast in situ girders under the Bride details-Section 9.20 -sheet #6 where in the camber profile for Girder beam is given.

This is for your information.

The web site is;

http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge-design-details/bdd.html

Attached one sheet from that also.

T.RangaRajan.



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Jeet_mbm
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PostPosted: Fri Jun 15, 2012 11:01 am    Post subject: Re Camber in Beam Reply with quote

Thank you T RangaRajan Sir

I will study these and discuss with you all if any doubt remains.

With Regards

Jitendra Sharma
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sspawar
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PostPosted: Sun Oct 29, 2023 5:04 am    Post subject: Re: Re Camber in Beam Reply with quote

Dear respected Sefi member Jitendra ji

your questionnaires and answers

I have a doubt related to camber, so kindly through somelight, on this.
1- Can we use camber to Bye pass the deflection limit of IS:456.<o></o>
As per IS code – no, thereis no word camber in 456 as well in 24

2- Deflection which we have to compare with the given limit in IS 456 should befrom where? Initial CIS position or CAMBERED position (Refer Attached figure).<o></o>
As per standardillustrations /codes. it should not be question of debate--- don’t imaginecamber

3- If we study language of SP -24 (handbook of IS 456) and IS 1343 it is somehowdiplomatic . As per my understanding, I conclude something in attached figurerelated to RCC and prestress structure. Kindly comment on this.
SP 24 published in 1983 – permits higherdeflections ahead of stiffness (stiffness- aesthetic point of view) but limitto the safety n serviceability  (serviceability - designpoint of view)<o></o>
4. From my side rule of RCC beam will also be applicable to Steel Girders.<o></o>
Refer steel relatedcodes.<o></o>
Apart from this – it isa traditional practice to keep camber, which IS code does not prescribe.<o></o>
5. In simple word my doubt is ::
Say structural deflection is = 100 mm
       Codal permissible limit = 60 mm (say)
       providedCamber         = 70 mm
Now one can say Deflection is = 100-70 = 30 < 60 (codal requirement)
  So Hence codal requirement of deflection is fulfilled....!!!!

From my side this solution is not acceptable. What your views???? <o></o>
Yes, in modern days,it is considered as psycho effect, not only design point of view but aftergetting older age structure gets deflection downward too from horizontal (y-y axis)-means aesthetic point of view too.<o></o>



Jeet_mbm wrote:
Respected Members

        I am totally agreed with you all. But I had a discussion with one of structural designer, who is advocating about codal language and when I looked into this matter in detail, I found following statements.

As per Code:

Expanatory handbookSP-24-(1978) :
22.2 a - The final deflection (including the effects of temperature,creep and shrinkage) measured from the as-cast level of floor and roof........... should not normally exceed span/250. This limitation is based on crack limitation with which the code is very much concerned and to avoid psychological upsetting ofthe occupants or affect the appearance of structure.

IS-456:2000 Cl 23.2 andIS-1343-1980 Cl-19.3.1:
a) --The final deflection due to all load including theeffects of temperature, creep and shrinkage and measured from the as-cast level of the supports of floor and roof........... should not normally exceed span/250.


My Submission:
(Assuming the case in which camber is within permissible maxlimit for camber, and value is not too much)

In case of camber in RCC member –Due to cambering there is no stresses get developed (as  initial casting of shutters is in cambered profile) and in service condition as load act the structural deflection would be same as of un-cambered beam. Shown in figure -1 attached. So widening of crack would same as case of un-cambered beam

In case of Prestress beam camber is provided somehow due to external axial compressive force.  So when load act ----for the part of deflection equal to camber there would be no crack(in this range initial stress compressive stress get nullify) .  The deflection in excess to camber (deflection-camber) would only be responsible for crack width. That’s why I am saying the permissible limit should be compared with net deflection (Deflection-Camber) in pre-stressing case.

            Our distinguished SEFI member Mr Mallick Ji also put a very important point on this about --- comparing the two limitations of code with proper consideration of duration of load which is responsible for deflection.  Which is very relevant but I failed to get this statement in anywhere. Thank Mallick Ji for sharing this.

At last I once again need a nod from all respected members on my and Mallick ji’s conclusion.


With Regards

Jitendra Sharma
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vikram.jeet
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PostPosted: Mon Oct 30, 2023 1:18 am    Post subject: Reply with quote

Camber :-

All structures under the action of external loadings / forces when bend,, are subject to deflections,,
Spanning beams, girders, trusses undergo vertical deflection whereas columns and vertical members under act of horizontal forces undergo horizontal deflections.

In verical members,,deflections needs to be within limits,, otherwise second order effects P*delta will also come into picture  though these are always there but negligible/insignificant if deflections  check within limit ,,

In horizontal members beams etc,, functionality and aesthetics are main concerns.

For beams, especially long spans, there is always codal guidelines to workout deflections during design stage and same needs to be within permissible limits,, without any regard for site  provision of camber. A design will be insufficient if deflection check is not ok  and there will be need to modify the beam depth .

Camber is site provision and sometimes, it is also mentioned in drg notes. This provision generally ensures  that no sagging of beam due to it's deflection visible to nacked eye.

But camber is not any substitute for deflection as pointed out by Er Pawar  saheb.

In bridges weather of steel truss type or RCC,, camber is provided as site provision .
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vikram.jeet
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PostPosted: Tue Oct 31, 2023 4:10 am    Post subject: Reply with quote

Camber in steel bridges :-


Reference may be made to IRC 24 , specific guidelines for providing camber are given at clause 504.6 .

As per spirit of code, Camber is to be provided to ensure clearance under all loading conditions  and also to maintain appearance.

Further Beams and Plate girders upto 35 m span need not be cambered.
For open web girders (truss type) guidelines for camber are discussed in detail at its a annexure B.
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