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Regarding shear links in beams and Flat slabs

 
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Fenil_Shukla
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Joined: 21 Nov 2019
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PostPosted: Fri Feb 07, 2020 11:44 am    Post subject: Regarding shear links in beams and Flat slabs Reply with quote

In elements such as beams or flat slabs (for punching shear),when the shear force acts shear stirrups or links are used to resist that forcethat means the links provided will be in tension. Now if we provide just enoughcapacity of the links, they will fully stressed. As I understand, for fullystressed steel at any section, we need it to be anchored by development lengthbeyond that particular section on both side. However it is not generally a casein beams/flat slabs(punching shear). They are just attached to main longitudinalsteel by 180 degree hook which is much less then required development length tobe effective. Why it is so & why are we not taking the anchorage length ofthe link for development length on both ends?<o></o>
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kawshik9
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PostPosted: Sat Feb 08, 2020 6:38 am    Post subject: Reply with quote

Er.Fenil_Shukla,


Please refer Clause No.4.3.5(b) of SP 34-1987 , according to which


  " Stirrups and ties-Not withstanding, any of the provisions of this Handbook, in case of secondary reinforcement, such as stirrups and transverse ties, complete development length and anchorage shall be deemed to have been provided when the bar is bent through an angle of at least 90°round a bar of at least its own diameter and is continued beyond the end of the curve for a length of at least eight diameters, or when the bar is bent through an angle of 135° and is continued beyond the end of the-curve for a length of at least six bar diameters or when the bar is bent through an angle of 180° and is continued beyond the end of the curve for a length of at least four bar diameters."



Reason behind the clause may be stirrup bar is subjected to max. tensile force only at one section (i.e where anticipated shear crack intersects with  shear reinforcement) and by providing standard bends will take care of development length.

I request senior members to enlight us on the reason behind above clause.


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thirumalaichettiar
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PostPosted: Sat Feb 08, 2020 2:00 pm    Post subject: Reply with quote

Er.kawshik9,
u r correct. The stirrups r added for forming hinges during seismic forces. for that it is necessary to heave hook bent to 135 degree with a min lenth of 3' or 12dia (please check this with the code) for good anchorage. The stirrups vertical legs r accounted for the resisiting the vertical loads but stirrups are used as closed form for the torsion also.
The anchorage for this is provided by the hook length.
T.Rangarajan.
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