Glass structure under extreme boundary conditions

Buildings with glass as structural elements are becoming more and more common. Under special boundary conditions such as high mountain areas or near the coast, this may become a challenge for construction site design and execution. The focus is on the climatic conditions in the mountains and ocean areas, such as extreme wind loads, extreme pressure on the insulating glass unit due to altitude differences, salt water close to the sea, narrow installation conditions and narrow time periods. The basic knowledge and applications of glass structures under these extreme boundary conditions are introduced. Two hilltop stations using glass applications, Nebelhorn (2224m) and Zugspitze (2962m), and a pavilion located in the Baltic Sea are displayed.
Glass is used as a building material in a variety of new applications, such as modern glass curtain walls or transparent railings. The new method of fixing glass and the almost unlimited freedom of size and shape provide numerous solutions to these problems. From the architect’s point of view, the glass railings and facades in high mountain areas should be as transparent as possible (majestic views), but at the same time they must act as protective barriers and load-bearing elements (huge loads). The construction situation in offshore tourist areas is similar. Experienced structural engineers can meet both sides at the same time.
Glass is increasingly used as a structural element. Structural elements mean that in the case of insulated glass, the glass will be subjected to wind, snow, linear loads, impact and weather loads. This requires careful design and structural analysis of almost all glass structures (such as exterior walls, railings and canopies).
Glass is a brittle material. Therefore, it is very important to consider stress peaks, such as those caused by point fitting or internal angle constraints. The bonding connection must be analyzed in a structural model close to reality.
Through the tempering process, the strength of the glass can be increased. Three levels of prestress are usually distinguished:
-Annealed glass (float glass) with a tensile strength of 45 MPa,-Heat strengthened glass (HSG) with a tensile strength of 70 MPa and-Fully tempered glass (FTG) with a tensile strength of 120 MPa.
In addition to the above-mentioned flexural strength, different fracture behaviors and different residual bearing capacities must also be considered. Laminated safety glass (LSG) (two or more layers of glass with an elastic interlayer made of PVB) is usually used to increase the safety in case of breakage. However, PVB is not the only interlayer material for laminated safety glass, and other interlayer materials with different characteristics are also available. For example, ionoplast interlayer behaves very hard, and it is not as sensitive to temperature rise as ordinary PVB interlayer. The FTG is broken into very small pieces, resulting in poor residual load-bearing capacity. It can be increased by using the above-mentioned hard interlayer.
Since the use of glass in structural engineering is a fairly new discipline, there are currently only a few regulations and design rules. According to the German standard DIN 18008, based on fracture mechanics and in line with the current concept of partial safety factors [2], [3], [4], [5], [6], [7], more applications are standardized
-Extreme weather conditions with high wind and snow loads. -Difficulty in entering the construction site. -If there is a significant difference in air pressure and temperature between the manufacturing and installation locations of the insulating glass unit (IGU). -High UV radiation may cause aging of adhesives and sealants. -High salt water content may cause corrosion of metal parts. -Laminated glass is a potential problem of delamination due to moisture. -Potential problems with the penetration of moisture and snow into the substructure.
The summit station of the mountain cableway “Nebelhornbahn” is located near the town of Oberstdorf, Germany, at an altitude of 2224 meters. The station was rebuilt in the summer and autumn of 2016. The building itself is a wooden structure, the outer wall is partially curved, and the railings are curved. The Nebelhorn region is famous for skiing in winter and hiking in summer.
The architect plan of Hermann Kaufmann ZT GmbH showcases organic, very transparent shapes made of wood, glass and bronze cladding, see Figure 1.
The minimum radius of the railing curved glass is 870 mm and the maximum radius is 6970 mm. Laminated safety glass with two layers of fully tempered glass and 1.52 mm thick PVB interlayer film is used. Use safety laminated glass with 1.52 mm thick ionic plastic interlayer in the flat area. The clamped glass railing is located on a small base to protect the glass of its base, see Figure 3. The total height of the railing is about 1.5 m, which is higher than the requirements of building codes. But in addition to its function as a protective barrier, it can also be used as a windshield for terrace visitors. The outer wall is composed of full-frame insulated glass units, some of which are used as sliding doors.
The feature of this project is curved glass. This kind of glass has some advantages, but there are also disadvantages, as shown in Table 1.
The wind speed was checked at a speed of 50 m/s in the expert report. The resulting wind load is 4.7 kN/m².
According to European norms EN 1990 and DIN 18008-1, the following load groups are considered for railings:
In addition, it is necessary to treat a partially broken glass plate as an accidental design situation.
The curvature of the glass is taken into account in the finite element analysis, and the same is true for the bonding constraints. The latter is usually used in the case of curved railings, because otherwise the inevitable tolerances of the clamping structure will result in binding forces in the glass.
Another theme is the anchoring on the wooden base. In addition to analyzing the problem, it is also very important to prevent snow or rain from penetrating into the base point of the railing.
In addition to the load-bearing capacity of the complete glass, the remaining load-bearing capacity must also be determined. It must be ensured that the glass structure does not (immediately) collapse when damaged, so as to ensure the safety of pedestrians, such as pushing the glass curtain wall. Depending on the type of application, the verification of the remaining resistance is done through different tests or numerical methods.
If it can be safely assumed that at least one glass layer of LSG remains intact, because it is protected from all accessible sides, then the numbers prove possible. The load reduced by LC 3 must be carried by the remaining layers alone. However, the edges of the glass—especially in the case of railings—are usually not adequately protected against strong impacts. These complete crushing elements must also provide sufficient residual load-bearing capacity. Since reliable numerical simulations of damaged LSGs are impossible (currently), full-scale testing and/or expert reports cannot be avoided.
The behavior of a glass plate after it breaks depends on many factors. The type of glass (heat-tempered or heat-strengthened glass), the type of lamination between the glass plates (PVB, ionomer or cast-in-place resin) and the type of fixing device are the main influencing factors.
The dynamic effects in the form of impact loads must also be considered. The German standard allows three types of verification:
The first two methods do not include curved glass. Therefore, pendulum tests or at least expert investigations must be charged.
The pressure generated in the space between the glass and the mechanical stress of the edge seal are very high.
Under uniform load, the performance of curved glass is much harder than that of flat glass. For the so-called “climatic load”, an almost constant volume condition (volume = constant) is applied.
According to DIN 18008-1 [8], it is not allowed to consider beneficial shear connections in edge sealing. Therefore, there are often two situations that need to be considered in the calculation:
Research such as the influence of the elastic restraint of the spacer, the consideration of adhesion (complete or delamination), the consideration of the type of sealing material, and many other aspects are very important. Especially the sealing material plays an important role in the calculation. For example, polymers have non-linear behavior. The stiffness depends on geometry, temperature, strain rate and aging. The question is whether it is necessary to implement all these phenomena into calculations.
Due to the huge difference in air pressure and temperature between the production plant and the installation location, valves need to be installed in the space between the glass plates during transportation to the top of the mountain. The manufacturer allows the valve to open for 10 minutes without severely affecting the inflation.
In order to minimize the time spent in the cold area on the top of the mountain, the set-up time was transferred to the workshop. The glass panel elements glued in the substructure are prefabricated (Figure 7). Due to the performance of the helicopter, the width of the elements has been optimized.
-The winter starts early, and the temperature is below zero degrees Celsius-Minimizes the operational failure of the ropeway between the peak summer season and the peak winter season-Many project members conduct transactions on very narrow construction sites
The glass elements are transported by truck to the intermediate station “Seealpe”, and the last step of the transport is completed by helicopter (Figure 8). Due to the high cost of helicopters, it is very important to optimize the size and weight of prefabricated components.
The top station of the “Zugspitze” is located near the town of GarmischPartenkirchen at an altitude of 2962 meters. A new ropeway is currently under construction, including a renovated and partially rebuilt hilltop building. It is the highest construction site in Germany. The project will be completed in 2017.
The wind pressure in the expert report is as high as 5.4 kN/m², and the snow load on the platform is 15 kN/m².
For the structural design of the IGU, the climatic load has a major influence. According to DIN standards, the following formulas apply accordingly:
The next step is to approximately calculate the volume factor. The volume and load change in a linear relationship:
-Winter starts early, the temperature is below zero degrees Celsius, and there may be snow in summer. -Many project members and trading on very narrow construction sites
The glass elements are transported from the Austrian side of the mountain to the top of the mountain by a second existing cable car.
The tea house is located on the Baltic Sea, close to the tourist town of Timmendorfer Strand and can only be reached by a pedestrian bridge. Wind and sea water have a very large impact on the building; this must be taken into account in the design of the building and the transparent part: a large facade area, which also has the function of an anti-fall device, accessible glass-almost no higher than the water surface, The internal railings and external windbreaks are made of glass. The tea house was designed by Hamburg-based Schuberth architects and inspired by Japanese architecture.
The facade is located on the ground and first floor of the building. The IGU is used as an anti-fall device and measures 4630 mm x 2730 mm. Due to exposure conditions, wind zone 3 is mandatory.
-Laminated safety glass with two layers of 8 mm full tempered hot dip glass and a 0.76 mm thick PVB interlayer-14 mm cavity-10 mm full tempered hot dip glass layer
The load-bearing column is moved to the inside, and only the transparent cover can be seen from the outside.
The dimensions of the barrier-free floor in the two areas are 4760 mm x 3300 mm. Ten glass elements with dimensions of 850mm x 1545mm (area 1) and 800mm x 1545mm (area 2) are located directly above the water surface.
Analyze according to DIN 18008 [1]. The ground floor is used as a restaurant, so a load of 5.0 kN/m² and alternate single point loads are considered (Table 2, Table 3).
The additionally installed windshield has a high wind load of up to 2,2 kN/m² and its dimensions are 1400 mm (width) x 1500 mm (height). Laminated safety glass of 2x8mm fully tempered and hot-dipped glass is used. The main problem was the installation of highly corrosion-resistant anchor rods on the bridge leading to the teahouse (Figure 21, 22).
Building in special locations is often challenging, but it’s worth a try. Must consider extreme boundary conditions and complex customer requirements. Experience in the use of glass structures, extensive knowledge of current glass technology, state-of-the-art manufacturers and engineering expertise have led to the impressive solutions presented.
[1] ETAG 002: Structural Sealant Glass System (SSGS) European Technical Certification Guidelines [2] DIN 18008-1: 2010-12: Glas im Bauwesen – Bemessungs- und Konstruktionsregeln – Teil 1: Begriffe und allgemeine [3Grundla] DIN 18008 -2: 2010-12: Glas im Bauwesen – Bemessungs- und Konstruktionsregeln – Teil 2: Linienförmig gelagerte Verglasungen [4] DIN 18008-2: 2011-04: Glas im Bauungsungs- und Konstruktionsregeln-Teil 2 Verglasungen, Berichtig-ung zu DIN 18008 2: 2010-12 [5] DIN 18008-3: 2013-07:Glas im Bauwesen – Bemessungs- und Konstruktionsregeln – Teil 3: Punktförmig DINungerte [5] 18008-3: 2013-07:Glas im Bauwesen :Glas im Bauwesen – Bemessungs- und Konstruktionsregeln – Teil 4: Zusatzanforderungen an absturzsichernde Verglasungen [7] DIN 18008-5: 2013-07: Glas im Bauwesen – Bemessungs- und Konstruktionsregeln, Teil 4: Zusatzansunforderungen an absturiebert, Bauwesen [7]; Sanierung Hypo-Hochhaus – Gebogene 3-fach Isolierverglasung der neuen Doppelfassade. Stahlbau Sonderheft Glasbau April 2014, Ernst & Sohn Verlag, Berlin [9] Siebert, B., Herrmann, T.: Glass railings and exterior walls on pedestrian bridges, the 9th German-Japanese Bridge Symposium held in Kyoto. September 2012 in Kyoto [10] Feldmeier, F.: Bemessung von DreifachIsolierglas. In: Stahlbau Spezial 2011-Glasbau. Ernst & Sohn, Berlin, 2011. [11] Siebert, B., Pistora A. Teehaus am Timmendorfer Strand. Glasbau 2015. Ernst und Sohn Press
We would like to thank StahlGlasbau Dann GmbH (www.dann-gmbh.de) for the installation pictures.
Building 8, SIRIM Complex, No. 1, Persiaran Dato’ Menteri, Section 2, PO Box 7035, Darul Ehsan, 40700 Shah AlamSelangorMalaysia


Post time: Dec-07-2021