Ebook: Challenging Glass 3

Dear reader,

Once again, glass engineering, research and design specialists gather in the historical town of Delft, for the third edition of the Challenging Glass Conference (CGC3) at the TU. The proceedings of this event lie before you. Relative to the two previous occasions, the conference has made a considerable growth spurt and now features some 90 papers, distributed over seven topics, as well as five key note addresses.

Fascinating contributions can be found under each topic. ‘Curved & Bended Glass’ has grown significantly, ‘Laminates & Composite Designs’ as well as ‘Projects & Case Studies’ are traditionally well represented. Under the topic ‘Joints, Fixings & Adhesives’, it is clear that structural adhesive bonds in glass construction are on the rise and here to stay.

But a quarter of all papers is still related to the topic ‘Strength, Stability & Safety’. Clearly, there is, even now, much to learn about the basics of glass design. We urge the authors to grab every opportunity for discussion and debate: there is still a considerable way to go before we will have reached a common understanding of the nature of glass failure and how we should translate that into design guidelines.

Preparing these proceedings has been a privilege, and we trust any participant in Challenging Glass 3 will move on with new ideas and inspiration to apply in his/her own work. We would like to express our gratitude to the key note speakers as well as to the other presenters and authors. Furthermore, we thank the Scientific Committee members, the supporting organizations, our main sponsor Glas Trösch, as well as our other sponsors, and, of course, all participants.

Welcome to Challenging Glass! Wishing you a stimulating and enjoyable conference,

Freek Bos, Christian Louter

Joint Chairmen of the Organizing Committee

Rob Nijsse, Fred Veer

Chairman and Secretary of the Scientific Committee

The introduction of new structural configurations within the field of glass engineering is the topic of this address. The generation of these design ideas and the process by which they are realized is particular to the production of architecture and although there is considerable cross fertilization with the world of product design there are some fundamental differences in the two processes that highlight in what circumstances architectural invention can best thrive.

On the new 1 World Trade Center Tower an exterior permeable façade treatment was to be designed for the lower 20 floors cladding a concrete shear wall and mechanical louvers. Engineering and design had to be balanced with the client's desire to streamline maintenance issues for the tallest office building in the western hemisphere. The scope of the podium façade treatment includes over 12.000 m2 in total area with more than 4.000 glass fins each free spanning 4m in height between attachments. Various glass fin-metal connection details were evaluated for aesthetic and performance criteria.

The Japan Post Tower is a 200 m tall building, rising on the site of the former Tokyo Central Post Office in the Marunouchi business district, Tokyo. The complex, designed by Helmut Jahn, integrates in the base area the restored historic façade of the old Post Office. On the north side, the façade of the highrise is characterized by three asymmetrical folds and by four glass screens framing the unitized glass façade. Such screens have to reach a high degree of transparency, while still being able to withstand tornados (up to 8.5 kN/m²) and high earthquake loads (up to 1.2 g).

The refurbishment of the Meuse river boulevard in Venlo instigated Scheuten Glass to donate a giant-sized, 6 metre high version of the stacked glass statue the Sphinx, which had originally been made as a 80 cm sculpture to commemorate the city's 650th anniversary back in 1993. Many hurdles had to be taken to, starting with the preliminary feasibility study, on to adhesive selection, joint design, glass selection, cutting methods, glass sheet layout, and final construction procedure.

This paper describes engineering and fabrication innovation behind the rebuilding of the Apple 5th Avenue Glass Cube in New York City. The original of which was completed in 2006 and as a result of a number of years of glass fabrication and connection innovation, with which the authors have been instrumental, a proposal for a replacement structure embracing all the technology and techniques mastered was enacted.

The structural use of glass has been explored extensively over the last decade, especially with Apple stores where the boundaries for their application have been advanced significantly. This paper reviews the history and also the state of the art in the structural use of glass. The aim of this paper is to discuss a way forward in relation to glass as a structural material, so that future innovations are not driven solely by the ability to produce and laminate large pieces of glass. Future challenges lie in having a unified understanding of glass as a structural material, high-lighting current limitations when designing with structural glass in relation to current codes in different parts of the world. A continued dialogue on the wider applications of structural glass will advance the state-of the art beyond its current range of use.

Warnemünde is a former fishing village on the Baltic coast, now part of the city of Rostock. A new flood protection wall is due to be built along a river in an architecturally sensitive inner-city area. Transparent or movable solutions are necessary, while the barrier must withstand water, flotsam, ice and the impact of boats of up to two tons weight. Here the optimum solution is a 4-layer laminated glass wall. The article describes the research required to establish realistic impact loads (via transient-dynamic finite element analysis), the safety concept and the applied design criteria for glass sections.

This paper concerns two cantilevering steel-glass structures recently built in New York, USA. Each structure consists of two outward tilting primary steel beams with a length of 27m, a central column, and a glass surface providing lateral stability and weather protection. Twelve panels of four-layer laminated safety glass with dimensions of 2,3×4,4m are connected to the underside of the beams. The glass panels act as the only bracing system of the structure; no additional bracing is required. The connection between glass and steel is made by custom-built point fittings with four fittings per glass panel connected by a two-part injection mortar. At the column kink a ‘glass knee’ of two frameless four-layer laminated safety glass panels is used for even load distribution.

The three pavilion facades for the renovation of the Eiffel Tower's first floor constitute a new challenge in the field of transparent skins with free forms: this smooth double curved surface adapts to the high-performance thermal constraints of a of a unique public interior space. In avoiding the standard facetted solution, the developed project retains the full integrity of the initial Architectural proposal while guaranteeing economic feasibility. Thanks to the optimization of a parametric model, the variable double-curved surface of the transparent skin can be approximated from a quadrangular cylindrical panel surface. This process implies zero torsion at structural nodes and permits the fabrication of structural elements from developable curved sheets by welding thus enabling a standard compact detail.

The recent works at Apple Stores in Hamburg, Germany and SoHo, New York, USA have incorporated the installation of new internal glass structures: 12m straight stairs; 10m balustrades forming the atrium perimeter of the upper storey; and 5m bridges. The design of each project elegantly balances structural glass elements with connecting metal fittings through the choice of super jumbo glass panels and inserted laminated connections. An overview of these projects is presented focusing on challenges which have arisen during design, fabrication and installation. These include the global stability and dynamic behavior of the stair and bridge; matching the limited tolerances of large glass panels with movements of existing structure; and dealing with restraints imposed by building authorities.

In this paper three special glass structures are treated. Two are buildings; one is a surprise: a work of Art. The material glass plays a dominating structural role in them. The structural ins and outs of each type of building are considered with a special interest in the safety that these glass structures have to provide in order to be accepted by the authorities as structures that comply with the official standards that have to be respected. The three realized structures are as well a proof that glass slowly is turned into a trustworthy building material.

King Abdulaziz Center for World Culture is a new development in Dhahran, Saudi Arabia designed by Snøhetta architects where five complex geometry buildings, called Pebbles, accommodate different civic and cultural functions. Penetrating the ground level podium are three open-air spaces called Oases, each with a glazed wall leading into the basement areas. Each Oasis façade is fully glazed, up to 15m tall and constituted by faceted double glazed panels tilting in and out of plane, all with different shape. The architectural intent called for a fully transparent design with flush glass. Buro Happold proposed a solution using glass fins as secondary support and a toggle system for retaining the glass. Buckling of the slender fins is resisted by horizontal glass beams. The team was able to build on previous experience in considering buckling and restraint issues for tall the slender fins, but the fins' 15° lateral inclination presented a significant stability challenge. The adopted design connects each fin to one side of the double glazed units, so each set of fins and glazing units acts a stable L-shaped structural unit. Unique connection details were developed to achieve the necessary structural behaviour. Detailing around access doors and movements of supporting structures posed further complications which have had to be resolved in an architecturally sensitive manner. The glass fins and the façade panels have been analysed both individually and in a global model to verify the stresses and deflections were within the limits in all the different conditions. This paper presents the design criteria, the findings and the solutions adopted to achieve the architects' vision.

This paper briefly reports on the structural design of the large (26 m×24 m) sashless glass ceiling that covers the entrance stairs of the underground shopping mall in front of Kawasaki Station, located in Kawasaki City, one of the largest satellite cities in Tokyo. The glass ceiling is totally suspended from an L-shaped gate composed of spatial truss frames. Because these structures were constructed in a heavy seismic zone, they were carefully designed to withstand well during earthquakes whose maximum ground acceleration reaches 350 cm/sec², yet use a minimum number of effective elements to maintain transparency of the structure. On March 11. 2011, the Great East Japan Earthquake hit this structure; however, none of the components including the glass panels were damaged.

The ancient temple of Apollo Epicurius at Bassae in the Peleponnese in Greece is a unique world heritage monument. The limestone used however is very susceptible to the elements (ice, rain, acid rain). Currently the temple is protected by a canopy. A case study has been made to build a glass pavilion around the temple. This needs to meet some very strict criteria. First it needs to be as invisible as possible. Secondly as columns cannot be placed inside of the monument glass beams with a 24 m span are required. Lastly the climate inside has to be kept comfortable, preferably using passive systems only.

Glas Trösch, a well-known glass manufacturer and glass finisher, supplies high-quality glass solutions for all sectors of the construction industry as well as for the automobile industry. An all-glass staircase is used to show that, as an innovative glass producer, Glas Trösch has embraced the trend towards large façade components. The example clearly illustrates that large, complex structural all-glass components can feature astonishingly simple yet visually attractive details, if the solutions chosen are appropriate for working with glass as the main material.

For the 2011 London Design Festival, David Chipperfield Architects and Arup worked closely together to realise Two Lines, a free standing glass pavilion that showcases Sefar Architecture Vision, a metal coated fabric laminated between two glass panels. David Chipperfield Architects wanted the pavilion not only to be a landmark on London's South Bank next to the Royal Festival Hall, but also to invite the public to walk into it, interact and experience the unique appearance of the glass with the shimmering translucent mesh that constantly changes with orientation, view angle and light conditions. The design features two interlocking forms (“Lines”) that are similar in shape but with opposite orientation. One Line features copper and one aluminium coated mesh, each Line consists of fourteen free standing glass wall panels, orientated on a rectangular grid and supporting five glass roof panels. The different orientation of the glass walls not only creates an interesting space that guides the view of the visitor, the arrangement also stabilises the 3.6m tall structure. The glass panels are laminated with DuPont Sentry Glass that encloses a 50% open mesh that has a copper or aluminium coating on one side and is black from the other. The design of the connectors supports the Architectural concept: reduced linear stainless steel connectors where electrochemically coloured to match the colour of the mesh. The bonded connectors were factory bonded to the glass, this reduced the onsite installation time. The project was designed and realised within less than five months with the combined effort of the Architect, Engineer, the Material Suppliers and specialist contractor Bellapart.

After winning an international competition held in 1993 to design the Master Plan for the Abandoibarra area of Bilbao, Pelli Clarke Pelli Architects designed its main compositional element: Torre Iberdrola. The tower was conceived as a softly rounded triangle in plan that tapers upwards towards the sky. Access to the building is through a sculpturally shaped glass lobby which encloses a large landscaped area. The tower is clad with a double-skin façade that follows the geometry of tilted cylinders, in order to standardize the curtain wall panels and reduce costs. The lobby is enclosed by a warped glass wall that creatively solves the challenges posed by its complex 3D geometry by using cold-bent glass and hybrid glass-and-steel structural fins.

In this contribution the performance of an adhesively bonded glass to metal connection with a carefully selected epoxy adhesive is investigated experimentally. Deliberately pushing the limits of conventional safety concepts for the sake of the experiment, laminated glass canopies were suspended on stainless steel local point-fixings, adhesively bonded to the upper glass sheet only. Subsequently, the suspended system was subjected to a ball-drop test, a uniform load and a hammer impact. Different glass types and canopy arrangements have been tested in this way. Depending on the design parameters, several compositions demonstrated surprisingly good residual structural safety: even after 24 hours of full loading in broken conditions, the heat-strengthened canopy configurations did not collapse.