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.

El vidrio laminado como filtro (Revista AFL, 2012)

Articulo publicado en la revista AFL en mayo 2012 en este  link.
Article already published in this blog last 31st of December 2011 in this link.

Tempered glass: interesting point of view

View of a tempered glass pane

Interesting response from Paul Bieber in his blog regarding the tempered glass manufacturers.

The point of view of a glass expert should make the reader think over the way that glass industry might improve quality.


In the following lines, you may read an extract of his views published last October 2011.

Question: Lately, I can't seem to get glass tempered correctly from my fabricators. Even tough fabricators seem to be slow, they can't get my orders right and delivered on time. What can I do?

Response: Thanks for your note. You are not alone in this feeling. I have talked with many shop owners and most feel the same way. It seems that with pricing so low, most fabricators have reduced their labor force to bare bones, often keeping the lowest paid workers.And you get what you pay for.

What can you do?

-Understand fully your fabricator's tolerance level. You may be expecting glass that is a higher quality than they can produce. All fabricators will meet the ASTM C1048 specs, but some do a better job. Compare their written spec sheets. Some fabricators will be better for high volume work, while others specialize in furniture quality.

-Tempered glass has distorsion based on the direction going into the oven. Specify if the roller wave should be parallel with the height or width. If the glass height is larger than the oven's width, the glass can only be tempered in one direction.

-Order heat strengthened glass even when you don't need to meet codes. HS glass cools slower than fully tempered and develops less warp.

-Try to avoid long, skinny pieces of tempered. They always come out looking poorly. The largest ratio for good glass should be 12:1, length to width.

-Thin glass warps more than thick.

-Ground or polished edge glass will always look better than seamed edges.

-Heat treating glass with soft-coat low-E is an art. Make sure your vendor is certified by the float manufacturer to treat its low-E products.

-Tempered laminated glass is a pain in-the neck to produce. Order heat strengthened laminated whenever you can (I may introduce the comment regarding this point, nowadays there are such a excellent results in terms of quality)

-Make sure your purchase order and drawings can easily be read. The most common mistakes are misinterpretacions from your order.

-Avoid calling in orders. Use email to prevent misunderstandings.

By Paul Bieber has 30 years in the glass industry, including 21 years as the executive vice president of Floral Glass in Hauppauge (NYC). He retired in 2005. Nowadays he publishes articles in his blog at www.usgnn.com

Laminated glass, endless possibilities

Last 20th of October of 2012, Tecnalia  invited me to give a lecture for the Technical Conference: Perforated Sheet Metal for Enclosures and Architectural Meshes.

The lecture was based upon the use of metallic meshes within the laminated glass. I showed the point of view of Cricursa, who have developed lamination technologies followed by the requirements for laminating innovative designs in curved glass.

The facade industry is steadily making progress by demands of Architects and Designers.

Glass is still the one and only transparent filling for curtain walls and interiors designs because it offers versatility, through compatibility with a range of materials and the added value of being bent. Therefore, glass is offering adaptability to meet complex geometries.

The main technologies available for laminating either curved or flat glass are described as follows:

• Screen printing: the colour is baked during the tempering process, bonding it permanently to the glass.

Screen-printed laminated annealed curved glass

• Colour interlayers: the combination of different colour layers of 0.38 mm PVB thick creates a wide range of more than 600 colors.

Color laminated glass

Color laminated glass

• Solar control interlayer: high-technology solar control film is placed  between two layers of PVB, obtaining a high visible light transmission, in the meantime being controlled infrared solar energy.

• Ink-jet printig on interlayers enables the production of designs and photografic images in a laminated safety glass.

Ink-jet printing on PVB

• Metallic meshes have been for the last decade in fashion in architecture, being considered by Dominique Perrault, who has enhanced the use of stainless steel in his most distingued projects.

Metallic mesh laminated glass

• Plastic meshes has been threatening the place of the metallics, because of easiness to get laminated versus metallics and it requires less energy cost to manufacture. It is also manufactured from metal diposits that use the latest technological advances and provides solar control control and privacy functions, as well as unrivalled asthetic value.

Plastic mesh laminated glass 1 way vision 

Plastic mesh laminated glass 1 way vision 

The purpose of the industry is to achieve the quality required in those products, this means to develop adequate lamination strategies to suit different materials all put together.

This post is under construction because future innovative designs will demand further investigation to create new products to meet architectural requirements.

Spherical double curved glass

  

The rhomboidal bubble double curved glass pane exhibited at the Fad Gallery in Barcelona

The latest achievement in curved glass fabrication was shown at the Fad Gallery in Barcelona.

The façade was designed by  Rafael de La-Hoz and comprises of thousand rhomboidal bubble glass units for a hospital in Mostoles. Cricursa was selected to manufacture the glass panels, also giving technical support during the design process.

The geometry is a double bending, first in one of the axis of the rhomboid, and secondly a spherical shape  sited at the centre of the pane with around 400 mm of deflection.

The glass dimensions are 4900 mm in width, 3360 mm in height and 12 mm thickness. 

 

The composition includes a low iron glass, with screen-printed in white with a particular pattern, achieving privacy and solar protection.

This is another example how curved annealed glass technology offers versatility and opens up to endless structural possibilities.

 

 

The rhomboidal bubble glass pane exhibited at the Fad Gallery in Barcelona

Photos courtesy by Marketing Cricursa

Glass curved technology

The aim of this article is to explain the difference between two glass curving technologies: hot bending and cold bending.

Hot bending technology is based upon the following basic process [1]: a flat sheet of glass is placed upon a mould that has the desired bending radius and is heated evenly to temperature of 650ºC. At this temperature the glass changes to a visco-plastic state, loses its brittleness and stiffness, and can, therefore, be shaped by gravity or mechanical pressure, obtaining the aimed geometry by cooling.

Hot bending allows a broad variety of geometries and compositions -cylinders, s-curves, double curved shapes-  to be achieved. The sheets are bent and then can be laminated and/or assembled into insulating glass units.

Manufacturers are steadily investigating, testing and, if the market demands it, expanding the manufacturing limits of radius, angle, thickness, girth and coatings, in order to offer architects and designers the largest sizes and greatest possibilities.

It is feasible in many cases to use coatings and ceramic frits in concave and convex sides, though the selection can be limited depending on varying factors such as glass thickness, size, radius, location adjacent to interlayers.

In order to attain a spherical, double curved and free form geometry with large deflections, curves with small radius such as 100 mm, processing with high temperatures is required.

Curved annealed laminated glass with a solar control and frit used on 40 Bond Street project, New York, 2006; Architect: Herzog & de Meuron (Produced by Cricursa, who have been bending glass since 1928)

 

Cold bending is a recent fabrication process. Flat glass panes are brought to the desired geometry by means of external contact pressure, which demands holding the curved glass unit in desired form.

Two basic techniques are used here: the glass can be curved at the construction site (and held in place by clamping strips) or  curved in factory before laminating (and held in place by the interlayer).

The company seele sedak has been instrumental in the development of a new lamination bending technology [2], which consists on using shear stiff laminates, to produce extreme large bent glass panels.

The Lamination process of cold bent glass can be divided into four basic steps [2]:

1.- Put together interlayers and flat glass, usually tempered. The glass can also be heat strengthened, annealed, with ceramic frits or coatings though these may affect the limits of what is possible.

2.- The glass is formed into the desired shape by physically pressing it onto the laminating framework and clamped into place.

3.- Lamination process, the aim is to achieve a high shear bond between the glass and the interlayer.

4.- Release from the scaffold form. During and after the lamination process, high quality control and observance of the stresses in the single panes due to the spring back effect is necessary. It is required to increase the curvature in the panel during the lamination process to get the exact shape after releasing the laminated panel from the framework.

Laminated cold bent glass manufacturing process

 

Both technologies provide fully bespoke, custom design solutions and the research and testing ensures the success of the most innovative designs. 

 

Bridge made of cold-shaped glass and spanning seven metres (by seele sedak, Glasstec 2008)

 

[1] Cricursa General catalogue

[2] Bruno Kassnel-Henneberg, seele sedak. Purely structural glass building envelopes (Glass Performance Days 2011)

With editing by charles.bostick@seele.com

Curved glass contributes with the facades of the future

Structural glass symbolizes modern architecture and it is considered an added value to achieve all glass facade and non-metal supported transparent structures.

The prospect of shapping glass has contributed to attain a broad variety of aesthetical and structural options through oversized pieces of glass with complex geometries. Its versatility has allowed to achieve a better integration between the aesthetic and functional objectives.

The Casa da Musica in Porto (Rem Koolhas, 2004) is an example how to make the best of curved glass, because glass develops both functions: structure and enclosure. The glass shape increases the set stiffness and any metallic frame is required. The curved glass pane is mechanically supported at the bottom and at the top, without any other support along the 6 meters in height of the vision area.

Casa da Musica in Porto (Rem Koolhas, 2004)

 

Casa da Musica in Porto (Rem Koolhas, 2004)

 

In glass bending technology, one distinguishes between hot-bending and cold-bending. Hot-bending consists on bending glass at high temperatures, being the most common manufacture method. On the other hand, cold bending can be done in two modes: bending during the assembly at the construction site or laminated bends are done in factory. In both cases, the glass are brought to the desired shape by means of external contact pressure.

In order to achieve a double-curved, spherical, curves with small radius or complex geometries, high temperatures are required during the fabrication process.

This post is under construction. In fact, it will be under construction during a long time. Creativity  is the limit, because curved glass contributes with the facades of the future.

Apple Store in Shanghai and how to make the most of membrane stresses (Bohlin Cywinski Jackson Architects, 2010)

The author of the Blog in front of the Apple Store in Shanghai

Apple Store in Shanghai contributes to the design of buildings considered icons of structural glass achievement today. The store, inagurated last July 2010, is located in the Pudong financial district, situated between the Oriental Pearl Tower and the Shanghai World Financial Center, one of the tallest skycrapers worldwide.

The authors of the design are Bohlin Cywinski Jackson Architects, a prominent american architecture studio, who already designed another Apple stores, such as those in New York and in London.

The glass cilindrical envelope is formed by tempered curved glass panes of 12 meters in height. The design achieves the best integration between aesthetic and functionality through its structural system, because structure and envelope are formed by glass.

The facade resists wind loads through acting all the glass panes together as a shell. This is achieved through the stainless steel conectors that link all the glass panes together. This structural system develops less stress in each glass pane, decreasing the glass thickness accordingly and making the design happen.

The glass panes are supported by a glass laminated fins, forming a frame with the glass roof beams that support the top of the cylinder.

In order to obtain a 12 meters curved tempered glass, an customised oven was built for this project to manufacture the largest pieces of curved tempered glass.

Through this design and materials, Apple communicate perfection, innovation and passion for being the best.

Internal view of the glass roof of the Apple Store in Shanghai

Apple Store in Shanghai



Criterios para la elección de un vidrio adecuado

1. DIMENSIONES: que sea posible fabricar. Según la composición del vidrio requerido sea realizable según las tecnologías de transformación que se disponen.

2. ASPECTO: Reflexión exterior (Re).

3. ILUMINACIÓN: Transmisión Luminosa (TL), que sea la adecuada para el uso del espacio que se proyecta.

4. SEGURIDAD: cumplir la normativa que corresponda. España dispone del CTE, en el Documento Básico SU, Seguridad de Utilización.

5. COMFORT: condensaciones, radiación ultravioleta, aislamiento acústico y temperatura cara interior son los parámetros a tener controlados para obtener un diseño adecuado.

6. AHORRO ENERGÉTICO: Factor Solar (FS) y transmitancia (U) son las dos variables a considerar. España está regulado por el CTE, en el Documento Básico DE-HE Ahorro de Energía, que indica los valores de FS y U según la situación geogràfrica.

Vidrio: Conceptos generales

El vidrio, como elemento con más presencia en la fachada, forma parte del filtro que permite obtener la luz y utilizarla como se desee.

Una de las principales cuestiones a resolver de las fachadas, es obtener un eficiente control solar, con alta transparencia luminosa, al tiempo que un balance térmico positivo.

El balance térmico dependerá de la orientación de la fachada y la época del año. El cerramiento deberá ser capaz de ganar calor cuando las temperaturas externas son bajas y rechazarlo, en caso contrario, favoreciendo o evitando el efecto invernadero.

El efecto invernadero, consiste en la energía solar que entra en un edificio a través de un acristalamiento, es absorbida por los objetos, que al calentarse, reemiten una radiación térmica en forma de onda infrarroja, a la cual los vidrios son opacos. La energía solar que entra, queda apresada en el edificio que tiende a calentarse. Un ejemplo, es el interior del coche a pleno sol, con las ventanillas cerradas, que los objetos como el salpicadero emiten calor que no puede ser evacuada a través de los vidrios. Para evitarlo, una solución es garantizar la circulación de aire.

Es importante conocer como obtener beneficio de cada orientación, según la trayectoria del Sol (Figura 7):

- Orientación norte: no se beneficia del sol, pero la calidad de luz natural es muy constante, no produce reflejos, no calienta. Las naves industriales de diseño tradicional con cubiertas en forma de diente de sierra, orientaban las zonas de visión a norte y las zonas opacas a sur. Las bibliotecas, salas con ordenadores o zonas de oficinas buscan esta orientación.

- Orientación sur: aprovecha al máximo los beneficios del sol en invierno y permite obtener ganancias térmicas durante los meses fríos, donde la trayectoria del sol es baja. En verano, donde la trayectoria del sol es alta, se deben prever elementos de protección solar.

- Orientación este y oeste: reciben la máxima energía en verano, por la mañana se aprovecha la luz del este y por la tarde del oeste. La posición del sol es baja, se deben prever elementos de protección solar, con el fin de reducir la entrada de calor y los efectos de deslumbramiento.