Thursday 25 December 2014

Spontaneous breakage in toughened glass

When you find a butterfly shaped pattern at the origin of a broken glass pane, it might be the clue that you are in front of a spontaneous breakage.
The butterfly shape is noted at the point of origin of the break.
The inclusions are impurities introduced in the mass glass prior to the production of float glass. The tempering process is based upon to heat up the glass firstly and afterwards is cooled down to compress the surface of the glass pane, obtaining improved mechanical properties.

If one of those inclusions within the mass glass is Nickel Sulphide (NiS), this remains in a high temperature form because it did not get enough time to cool down as the rest of the mass glass. Subsequently, the NiS will return to its low-temperature after a period of time. During the process, the NiS volume will increase its volume, causing the sudden breakage of the glass pane. This is known as spontaneous breakage.
NiS will only cause the breakage of the tempered glass providing they are situated in its tensile zone. As the inclusion increases the volume, it releases all the energy embedded in the compressed zone.

Stresses in toughened glass 
Nowadays, the production of float glass totally free of nickel sulphide does not appear to be possible.
The spontaneous breakage follows a Gaussian function; such graph is a characteristic symmetric bell curve shape. This shows that the number of breakages is initially reduced, and then it goes up to a maximum value and finally decreases following a similar curve. This function is formulated collecting data of the number of breakages over a period of time.

The spontaneous breakage follows a Gaussian function, at the vertical axis includes the number of breakages and at the horizontal includes the time
One of most effective way to prevent this phenomenon is to carry out the Heat Soak Test (HST) after the tempered fabrication process. This is a destructive method that consists of introducing the tempered glass panes into an oven during a reduced period of time to accelerate the expansion of the NiS inclusions. In such way, the contaminated glass panes will fail inside the factory prior to be delivered to the Client.

Tempered glass panes within a Heat Soak Test oven
Façade engineers should always undertake such failure investigations to determine the most likely root of the glass failure and if the NiS inclusions are the cause of the failure.

Thursday 31 July 2014

Kempinski Hotel (Munich, 1993)

Façade of the Hotel Kempinski in Munich
The façade of the Kempinski Hotel in Munich is a landmark for those who are interested in structural glass. Along with La Villette in Paris (Peter Rice, 1987) represent the step forward achieved in architecture through the innovation design in façades.

The façade is transparent without an apparent structure that holds the glass wall in place. Only an unnoticed fitting sited at each corner of every glass pane is visible from the access of Terminal 2 in Munich´s airport. The attention of the observer is drawn and only for curiosity's sake is worth exploring to understand how this particular structural system operates.

Interesting observations can take place when the observer is placed within the lobby. The glass panes are mechanically held in the small fittings fixed in the vertical cables hanging on the roof and connected on the floor. At the same time, a horizontal pre-stressed cable is fixed between the columns of the primary structure and connected through each of the fittings at every horizontal glass joint.

Façade view from the interior where the particular structural system can be explored
Detail of the fitting where the vertical and horizontal cables are connected with the glass pane
The wind load appears to be transferred to the columns through the horizontal pre-stressed cables and the dead weight appears to be supported through the vertical cables suspended on the roof. Both cables are integrated behind the joints of the glass panes.

Image of the vertical cable connected on the floor
Image of the horizontal cable connected on the primary structure
The glass seems to be toughened laminated and some ripples of air bubbles are visible at the edge areas within the glass pane.

This ambitious design leaded by the architect Helmut Jahn and the engineering firm Schlaich Bergermann und Partner provided continuity to Peter´s Rice legacy in façade engineering.

Interior view from the lobby

Sunday 27 July 2014

“10 Ideas without answer. The evolution of the façade as an excuse” Xavier Ferrés i Padró




Last 20th of June 2013, the Grup Idea organised the IdeaPikaPika event, held at the Trespa Design Centre located in Barcelona. Xavier Ferrés i Padró, the outstanding Architect and Facade consultant, gave a conference about facades, but from a different approach.

Friday 28 February 2014

The BIQ House (Hamburg, 2013)




An experimental building located in Hamburg named BIQ (Bio Intelligent Quotient) uses algae within the façade to generate heat, create biomass and provide shade to the building under the sun radiation. The documentary produced by the engineering firm Arup explains the details of this innovative project.

Friday 31 January 2014

Façade reflective issues at The WalkieTalkie in London

View of the skyscraper under construction
An interesting physical phenomenon occurred a few months ago. The façade of a skyscraper under construction on 20 Fenchurch Street in Central London appeared to have cause some damages to a car parked on a nearby street.

The façade of the “Walkie Talkie”, as the building is dubbed due to its particular shape, appears able to reflect enough solar radiation able to melt the wing mirror and the badge of a car. As a temporary measure, a screen has been erected to prevent further damages until this is resolved.
This issue will probably be raised in future façade projects with reflective glass panes or any other sort of reflective cladding material.

View of the badge melted car (Photo of BBC News)
The image above shows  a possible explanation of this phenomenon 

You may find further information about the project in this link.

The following video of The Telegraph shows an interesting point of view of the effects observed.