With constant development in science and technology, glass curtain walls are finding increasingly more applications and their structures are also experiencing great changes. Fully spider fitting frame-less glass curtain walls, connect glass together in an open space using various types of light/heavy steel structures via various types of spider fitting members to form flexible and unobstructed glass facade. In this way, fully spider fitted glass walls not only maintain the safety of aluminum alloy frame glass curtain wall but also eliminate the disadvantages of the later in singular structure and restrictions from construction structures. As a result they provide unobstructed view as a whole, neat, bright and integrated with such advantages as safety, practicality and artistic taste thus becoming a vogue for modern construction and decorations.

Thermally toughened or tempered glass panels are used as single or insulated glass units. In case of single panels laminated safety glass is preferred due to safety reasons. This system consists of a number of accessories with metal arms. At the end of each arm, a sheet of glass is fixed by the corners with a special screw. The vacuum between these sheets is filled up with isolators to overcome mechanical pressure and weather conditions.

The rectangular glass sheets have 4 or 6 countersunk drilled holes into which countersunk stainless steel bolts acting as point-fixings. The space between the glass panes are filled with weather seal. The support elements that hold the fitting can be space frame, glass fin, tension cables or steel circular columns to provide the aesthetic effect as desired by the customer.

Heat Soaked Glass, the tempering process increases the strength of the glass’s many folds, offering greater resistance to breakage. However, the raw materials used in the manufacturing of tempered glass are not free from certain defects like nickel-rich contaminants such as stainless steel might be present, and then combine with sulfur to form nickel sulfide inclusions, which put tempered glass at potential risk of spontaneous breakage.

Spontaneous breakage due to NiS inclusions:

When glass is heat-treated, the nickel sulfide inclusions are modified into a form that grows or transforms with time and temperature. Once the glass is installed and the nickel sulfide inclusions are solar heated, small cracks may develop from the inclusion. If these cracks penetrate the tension layer of fully tempered glass, the resulting release of energy will cause the glass to spontaneously break.

NiS inclusions change their structure and volume during the heating process of tempering. This changed state is ^trapped^ during the quenching process. So at room temperature, the NiS inclusions tend to change back to their original state, which having a bigger volume, causes spontaneous breakage. This changing back of state could happen in a few minutes to a few years, making it unpredictable when the tempered glass may break. To minimize the risk of NiS breakages, a heat soak test is performed.

Heat Soak Process:

An effective Heat soaked test has been proposed and applied for tempered glass to avoid spontaneous failure in buildings, and the probability of spontaneous breakage was decreased. However, it was considered that a sufficiently low breakage risk remained because of small NiS inclusion and small residual stress.

Heat soaking of tempering glass has been carried out with respect to the draft of European Standard EN 14179. Following the tempering process, glass is heated to a temperature of about 290C for a minimum of 2 hours of the heat soak period, and then cooled slowly. This process allows the inclusions to revert to their original form and thus regain their stability. The advantage of using this process is that the heat-soak test removes over 95% of the problem without affecting the properties of the glass. The idea behind heat soaking is to allow the glass to break in the factory before installation to minimize the risks of accidents and injury. The amount and size of these inclusions vary from glass to glass. In all probability, the glasses that have NiS inclusions will break during this heat-soaking process.

Applications of Heat-Soaked Glass:

The use of heat-soaked tempered glass is recommended where the risk of spontaneous breakage would cause difficulty, either from a replacement point of view or where falling glass fragments may be unsuitable, such as roof or high-level glazing, balustrades, screens, and high-level curtain walling.

Heat soak glass is appropriate where there is a risk of human impact. If breakage does occur, the breakage pattern is such that the resultant pieces of glass are relatively harmless and are unlikely to cause severe injury.

Glass Fins

Glass fins represent the earliest form of structural glass facade, dating back to the 1950s French Hahn system used at the Maison de la Radio in Paris. Here 2-story glass plates were suspended and laterally stiffened by the use of glass fins set perpendicular to the plates at the vertical joints between them. But it was the Willis Faber & Dumas Building in Ipswich, England that popularized this emerging technology in 1972. In this curving facade designed by Foster Associates, multiple plates of reflective glass are suspended, providing one of the first examples of an entire building facade in frameless glass. This project inspired a diffusion of glass-fin technology in numerous applications throughout Europe and America in the 1970s, and continues to do so today. Glass fin-supported facades still represent one of the most transparent forms of structural glass facades, and are an especially economical solution at lower spans.

Glass-fin systems are quite simple in concept, utilizing a glass fin set perpendicular to the glass pane at each vertical line of the glass grid. The most challenging aspect of a glass-fin wall occurs when the span is too great to be accommodated by a single piece fin, and a splice detail must be developed to create a fin comprised of multiple glass pieces. Early systems used patch plates to fix the glass and fins together. Spider fittings are frequently used in this application today.

Glass is a transparent material seen by the light reflected from its surface. Thus, transparency in glass-fin walls is often compromised by the banding effect caused by the reflected light from the glass fin

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