STRUCTURAL USE OF TEMPERED GLASS. 3

[muran]

HELLO FRIENDS,

Have you ever noticed how a suspended glazing system ( ie, Glazing system without any metallic frame) commonly used for front glazing of Automobile showrooms resists the windload acting on it with the hel of glass fins ? If you have got any ideas/ informations in this area please let me know.

Thanking you muran

 

[RiBeneke]

Try Viracon mlass manufacturers.

http://www.viracon.com

They seem to have design information.

Regards
Richard Beneke

 

[JAE]

There is another company, British I think, called Pilkington, that uses a frame-free glass system. They have a building facade up in San Antonio, Texas for the USAA company. About four stories high...pretty impressive.

 

[engineD]

The Institution of Structural Engineers have a relatively new publication on the structural use of Glass which may be of help

http://www.istructe.org

 

[timh]

As a facade engineer in Australia, my firm gets involved in quite alot of what we call "frameless point fixed glass". This type of a system is one up on the frameless glass systems using glass fins where by the glass is supported at its corners by patch fittings (commonly called spiders). To allow rotation at the fixing point we normally insert a very small ball joint within the thickness of the glass that allows rotation of the glass pane under wind or dead loads.

The spider is then fixed to some structural element (vertical mulliuon truss etc) and in alot of cases here in Sydney those elements turn out to be stressed trusses consisting of very thin high tensile stainless steel rods stressed to a point where by under the most extreme wind and thermal load condition neither of the chords goes into compression. Highly nonlinear analysis required due to large displacement theory which we normally do in an FE pacakage.

The whole system looks very lean and architects love it for the podium areas of high profile CBD buildings where structure is frowned upon and lots of glass are liked! Providied the client can foot the bill ($1200 AUD per sq. metre).

By the way the glass in these situations is normally toughened and heat soaked glass (provided it is not overhead which requires laminated glass) to get rid of any impurities and to get a higher yeild strength from th glass in the limit state. Due to the complex loading conditions and point fixings we also analysis the glass panels in a FE package

 

[Rowland33]

To Timh, Could you provide a reference that indicates overhead glass should be laminated? I have a similar situation. Many thanks.

 

[timh]

Rowland33

The Australaian Standard AS 1288-1994 "Glass in Buildings" states in Clause 6.3 "Sloped overhead glazing(including rooflights)"........glass used in overhead glazing at slope less than 30 degrees to the horizontal shall be Grade A safety glass"

Grade A safety glass is defined as either laminated galss or toughened glass.

However Clause 6.3 goes onto to say that "... Where the highest part of an overhead glazed panel is greater than 5 metres above the ground then toughened glass shall not be used" This is obviously due to the safety provisions of shattering toughened galss falling onto people below.

As a general rule our company does not use the 5 metre rule and rather adopts any overhead glazing as being laminated. Whilst this has disadvantages in terms of not being able to use the increased yeid strength of toughened glass it does does give a lower risk design particularly in places of public traffic.

A word of warning about using sloped overhead laminated glass. Some laminated glasses when inclined have in the past had slippage occurr between the front and rear pane due to self weight either side of the interlaminar interface. It only takes a very small displacement between the panes to shear the laminate and distort the vision through the glass. This can be overcome by approprite detiling of blocking at the base of the panel and can also be checked by checking the interlaminar shear.

Hope this is of assitance. If required Ican scan the section from the code and email.