ADJUSTABLE HEAD RESTRAINTS FOR MASONRY

[AlexImmanuel2014]

i have some queries with regards to usage of head restraints in masonry wall application.

head restraint connecting masonry and beam over it is popular used to resist out of plane loads acting on wall.
attachment shows one typical head restraints. if you see the attachment , you will find that the manufacture provides design resistance in N/m for various spacing of head restraints.

i couldn't understand why the design resistance is in N/m . this value is w.r.t to unit height of wall or something else.

2. is their any accurate hand calculation approach for finding ultimate strength to prevent material failure .

i made an attempt to do it. however i need an expert to comment on the approach to find its strength.as it has two sleeves , one inside and the ooutaide formin ashape of C.

or is it better to perform a FEA anaalysis on it.

 

[CELinOttawa]

No. This type of proprietary device has a capacity determined by testing, and FEA is only good to give a ballpark before testing. You could try CFS code provisions, but I think you need to ask the manufacturer for more information.

 

[KootK]

N/m makes sense to me as the wind/eq loads imparted by the wall at the head will be force per unit length. You can easily convert that to force per anchor by multiplying by the anchor spacing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CELinOttawa]

Without a design example I wouldn't make any assumptions. Don't take responsibility for something you don't have to - Ask! Manufacturers are more than happy to help you spec their product.

And if you need more info than they can offer, use someone else's product rather than engaging in product design you aren't paid for!

 

[AlexImmanuel2014]

dear koot k

i exactly did the same , i calculated the force per anchor ,

i took the rectangular leaf segment only and considered load acting on the centre , by statics i got the straining actions and accordingly i calculted allowable loads considering appropriate safety factor .

see the snapshot for the approach .

link:

http://files.engineering.com/getfil...d47-608c9624fefb&file=FBD_head_restraints.png

however the appraoch the approch will only help me to check for material failure of the metal components of the tie.

for embedment failure, failure of the fastener, or buckling failure of the tie ,it is probably difficult to use the above approach and yes like others have said it may require some test results from manufacturer.also serviceability and deformations, and member strength, stability, and
integrity all these may have to be kept in mind.


pls note the head restriants are made of stainless steel and usually thickness of metal ranges from 1.5 mm to 2.0 mm ( verified from one local fabricator)

thereby i request expert to please share their view. is this approach good enough for preliminary considerations. these days many local fabricators are making these head restriants but they dont have test values .price being a key factor ,products like that of aancon are high. i hope my concern is clear among us.

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there is one more query i would like to furnish ,

could you please tell me where are the design provisions for stainless steel design mentioned in codes.



the british practice - SCI P 291 provides guidelines but there is no code title like BS-5950
thats the same for american - AISC DG 27 ,not separate code title is given ,only a guide is published

the euro code ofcourse has - BS EN 1993-1-4 : general rules supplementary rules for stainless steel .
AISC DG 27 has similar provisions as that of eurocode.


i couldnot see any code title mentioned , though i am following AISC and BS guide equations for study but i just wanted to know why there is no title for the code provided for stainless steel design by the writers. are these provisions not yet certified from organisations. it become difficult from consultants to make the customer understand .

moreover , i have seen some supplier provide calculation for marble fixings of stainless steel they mention design as per DIN 18800 . DIN 18800 applicable for genral purpose structural steel . i dont think it should be used for stainless steel .

i would like seniors and experience professionals to please highlight yours views on it .i am a young structural engineer and your views would really help me on order to grow my understanding and to be clear