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.

Wednesday 25 December 2013

Traces of Peter Rice (Arup, 2012)

As Peter Rice took on his professional career in Arup, the outstanding engineering firm produced the documentary ¨Traces of Peter Rice¨ on occasion of the 20th anniversary of his death in 2012.

The documentary goes through his professional career including interviews with his colleagues, partners and people who had the opportunity to meet him.

Through this interesting documentary, the great Irish engineer is brought closer to those who only had the chance to read his books and visit his projects.

Monday 5 August 2013

Hotel Me in Barcelona (Dominique Perrault, 2008)

Summary--The specifications of the Hotel Me project required a particularly innovative facade design. This article describes and explains the unusual solution developed by the façade designers, in answering the specification’s requirements.

1. Introduction

One of the Engineer’s tasks is to execute the Architect’s design. Such a statement depicts the work done for the façade of the Hotel Me designed by Dominique Perrault and his design team. It is located at the junction of the Avinguda Diagonal and Pere IV Street in Barcelona. The building is a skyscraper of 117 metres in height (Photograph 1). The geometry is reminiscent of a number four, inspired by the stone heads of Easter Islands, with and adjacent 25 metres tall cube shaped building.

2. The Façade

2.1. Architecture

The façade is a unitized curtain wall system formed by several differing modules, combining heights of 2.6 and 4.6m, forming a saw tooth shape. Once installed, each unit incorporates the waterproofing, the fire, thermal and acoustic insulation, and moreover the internal architectural design for the room.

Each of the rooms is formed by four panel types (Photograph 2 and 3). Two of them are ‘opaque’ type being a triple skin 4.6 m high formed by an external laminated glass, a stainless steel metal shaped sheet sited in the air gap and a inner insulation sandwich panel with stainless steel bright polished as per design for the room.

Photograph 1. View from Avinguda Diagonal

Another type of panel is named the ‘filter’ being 2.6m high and allowing solar radiation to pass through a triple skin formed by two panes of glass with a stainless steel perforated shaped sheet fitted between the glass. The inner skin is accessible for maintenance.

The last panel is named ‘transparent’; being a window 2.6m high.

There is a fourth type of panel placed at the emergency stairs providing ventilation. This module is clad with vertical louvers of bright polished stainless steel.

Photograph 2.
The fitting of the unitized curtain wall modules in saw tooth orientation. Note the three types of panels, being the opaque 4.6m high, filter and transparent 2.6m high panels. This is the mountain-facing elevation and it can be seen how each module bridges two floors.
Photograph 3.
View from a standard room of inner side of unitized modules. The opaque modules can be seen with stainless steel bright polished finish, the filter with the perforated metal sheet and the transparent window. 

2.2. Engineering

The frame of the unitized curtain wall panel is formed by two layers of aluminium joined through a low conductivity material that breaks the thermal bridge.

The waterproofing of the union between the transom and mullion is resolved through a waterproofing sealant.

Each curtain wall module is formed by two panels including hooks to be hung on the brackets fixed to the concrete slab (Photograph 4).

Photograph 4.
Typical module clad with unitized curtain wall 7.2m high and 1.2m wide, covering two rooms. The panel above is transparent and the panel below is opaque.

One of the specification’s requirements was to provide the fire insulation at the gap between the curtain wall and the slab, including the fire insulation in the curtain wall module. In order to achieve this a rock wool panel was added in the module in front of the slab, and the joints were sealed with fire rated materials. Once the solution was designed, it was tested in a European notified laboratory, achieving 92 minutes of fire resistance.

The acoustic performance of the whole room with the curtain wall panels attached was also tested. The acoustic insulation achieved was 39 dB, being higher than the 30 dB required by the standard.

The waterproofing is achieved through the contact between the bubble gaskets fixed continuously through the aluminium frame (Photograph 5).

The filter and opaque panels include an air gap, where the stainless steel bright polished bent sheet is inserted. The particular design of the bent sheet required them to be bent through a manual process.

The opaque modules are cladded with the bright polished stainless steel as the finish for the room in the inner skin. This is fixed through an aluminium cover cap.

The external glass is laminated transparent float, structurally bonded to the aluminium frame. Due to the requirements of the Quality Control team, additionally a cover cap was used for fixing the glass mechanically onto the frame.

The internal glass, an insulated low emissivity unit, is present in the transparent and filter modules.

The façade is resolved and interfaced with the perimeter elements such as vertical dividers, ceilings and finished floors. The acoustic insulation (Photograph 7) and fire insulation elements (Photograph 6) are executed in situ. Subsequently, the finishing trims are installed.

Photograph 5. View of the union of two modules. Note the broken thermal bridge, the bubble gaskets, the waterproofing sealant at the union between transom and mullion, and the cover cap as a mechanical fixing component.

Photograph 6. The technical design for the composition at the dividing line between rooms that achieves 45 dB of acoustic insulation.

Photograph 7. The technical design for the horizontal fire insulation composition covering the gap between module and slab.

2.3. Execution

The main activities for the assembly, brackets and modules, were carried out from the outside the building due to the particularities of the project, as described below:

The limited thickness of the floor, did not allow the bracket installation on the slab surface. It was consequently installed on the slab edge from the outside of the building.

The design of the main structure of the building, with concrete walls as divisions at the façade facing the sea and the metallic structure at the façade facing the mountains, did not enable the use of any kind of equipment for horizontally shifting the modules along the floor plan after unloading the prefabricated units. The panels had to be individually lifted up to each storey in order to be installed. Hence, a free surface on the slab was needed, in order to move, erect and install these panels.

Therefore, a customized auxiliary system was designed to resolve the conflict with the elements in the interior of the building to allow installation from the outside, optimising safety, convenience and performance.

This kind of track running continuously through the full perimeter of the building, as it was not feasible to work from inside due to the interference with the structure of the building. This rail supported two cradles and a mini-crane (Photograph 8).

The cradles were allowed to move horizontally and vertically throughout the entire façade. The cradle included all the elements to carry out the works efficiently. The mini-crane could hoist and install the curtain wall modules (Photograph 9). It was designed to allow a maximum load of 1100kg. It was possible to hoist a curtain wall panel from the ground floor to the 32nd storey, and then it could be horizontally moved to the final position, aligned and installed (Photograph 10).

The vertical displacement of the module was guided by a tensile cable system the same height as the building.

The method statement for the assembly was based on the shifting of the modules to the package, the dismantling of the package to the individual modules, the hoisting by the mini-crane and the guidance of the tensile cable system. Once the module reached the respective storey, it was horizontally moved to its position, where it was aligned by the jacking bolts at the hook bracket, ensuring the contact between the bracket and module.

The daily average performance was 70 square metres, with the wind being the main issue. The daily performance, considering only the net days worked, was 90 square metres.

The quality control plan was rigorous, inspecting the welding and torque settings of the brackets, module tolerances to meet the requirements of the project and to achieve the environmental performance designed.

With regard to the dimensional control, a survey of main structure was periodically carried before analyzing and making the decisions on the position of the façade, whilst absorbing the misalignments of the structure.
Photograph 8. The customized auxiliary system to install the modules. The system was installed on the 32nd storey through a cantilever beam. Note the vertical displacement of the module.
Photograph 9. Mini crane, lane system and cantilever beams as a structural system.

Photograph 10. Unitized curtain wall module during horizontal displacement at 31st storey.

3. Conclusions

Without any doubt, the unitized curtain wall system, minimized the installation works on site, improving the delivery times and the quality of the final product, in comparison to an in situ façade system (Photograph 11).

The success of such a particular façade was based on the façade being defined four months prior to being erected onto the building, rigorous planning and successful cooperation among the staff of the façade company and main contractor, obtaining the approvals of the consultants and architects to carry out the façade works properly coordinated with the rest of subcontractors.

Photograph 11. View of the building from Pere IV Street.

Note 1: This article has been already published in journals of architecture (Revista Hueco Arquitectura; AFL Arquitectura de Fachadas Ligeras; Infodomus; L´Informatiu del CAATB). The original version is posted in this blog in the following  link .

Note 2: The building was named as Hotel Sky during the project execution.