Effective thickness of laminated glass as per AAMA/ASTM/GANA standards 1

[Ben]

how to calculate the effective thickness of two 8 mm glass laminated with pvb of 1.52 mm[total thickness of glass is 8+1.52+8=17.52mm] using AAMA/ASTM/GANA standards?

i am grateful if u provide me the allowable stress and deflection of the same.

thanks in advance

 

[klaus.]

well if you omit the strength of the PVB foil the eff thickness is simple
eff_t = 3 root out of ( t1^3 + t2^3)
( Sorry , I do not know how to write formula here )
for 2 x 8 mm this is eff_t = 10 mm

PVB foil is anyway very soft for long term load ( e.g. DL ) and warm temperature so it is on the save side not to consider PVB Stiffness unless for wind load

Regarding allowable stress...depends on the type of glass... there is different types
Regarding deflection ...depends also on manufacturing warranty ...but should not be less than L/100









best regards
Klaus

 

[Ben]

Dear klaus,
thanks for your kind response.

Actual thing is
Based on the BS standards, the allowable deflection is span/65 or 25 mm, whichever is less
if i consider the total thickness of glass i.e 17.52 mm then only the it will be within the allowable limit.
hence i consider 17.52 mm for the FEA analysis.
but now the consultant refer it as wrong and to consider the effective thickness along with the pvb.
bt if i consider what u mentioned as effective thickness i.e 10mm it exceeds the limit.

Help me to solve this issue based on the standards.


Regards,

 

[klaus.]

what country are you working ?
glass design is tricky

Deflection L/65 is very high... is it edge displacement or center of glass pane displacement ?

Well the glass 2x8 mm with foil is somewhere between 10mm and 17.52 mm
depending on the stiffness of the foile
if you take 17.52 this means the foil is fully stiff ...no consultant will accept that
you can use other foil...like SPG Foil which is stiffen than PVB

or you can use spacial glass design program which allows to use different foil stiffness
then the eff_thickness might be maybe 12 mm




best regards
Klaus

 

[Ben]

Thank you dear klaus.

please go through this

i am a beginner.not familiar about those foil.

understood what you meant but dont know in detail.
will try to solve it

if i am wrong .please educate me regarding the same

regards,
midshel

 

[klaus.]

Ok
you are design a glass balustrade ...not just a glass Window
This is a different story...
For glass balustrade you need to consider special requirements regarding the post breakage behavior
You need to make sure, that even it glass break it has to be safe enough so people dont fall down
If you are not familiar with glass design I suggest, that you pass this on to a experienced glass designer

You can read german glass code DIN 18008 part 4 on details for glass balustrade
I am not sure if British or US codes give details on this




best regards
Klaus

 

[Ben]

Dear klaus,
thank you for the kind response,

i will study those things and get help from my seniors,



regards,
Midshel.