STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

thirumalaichettiar · Silver Sponsor Joined: 26 Jan 2003 Posts: 3554

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.

thirumalaichettiar · Silver Sponsor Joined: 26 Jan 2003 Posts: 3554

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.

Jeet_mbm · Posted: Fri Jun 15, 2012 11:01 am Post subject: Re Camber in Beam

Thank you T RangaRajan Sir

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

With Regards

Jitendra Sharma

sspawar · ... Joined: 05 Jun 2009 Posts: 1204

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>

vikram.jeet · General Sponsor Joined: 26 Jan 2003 Posts: 3738

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 .

vikram.jeet · General Sponsor Joined: 26 Jan 2003 Posts: 3738

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.