Laminated glass frameless glass railing system​ containing rigid PVB is increasingly used in structural applications

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       Laminated glass frameless glass railing system containing rigid PVB is increasingly used in structural applications. This combination improves the load resistance of the laminated glass panel, reduces deflection, helps reduce the thickness and weight of the glass, and in some cases, does not require heat treatment of the glass. The case of free-standing railings was studied in depth, and the commonly used thermally tempered laminated glass was replaced with annealed laminated glass.

       Experimental tests under static and dynamic shock loads discussed load, glass thickness, and linear fixation types. The results of the experimental research are also evaluated according to national legislation. Various aspects of post-breakage behavior are studied. Finally, the results show that the combination of hard PVB interlayer and annealed glass is acceptable and safe for railing applications.

       Hugues Lefèvre is the laminated glass frameless glass railing system product manager for AGC Glass Europe. He has more than 25 years of extensive field experience in the glass industry, including R&D, sales and marketing of glass products. He is a member of multiple glass technical committees and international associations. Hugues Lefevre holds a degree in mechanical engineering from the Catholic University of Leuven, an MBA degree from the EPM School and a legal certificate from the Catholic University of Leuven (Belgium).

       Anna Šikyňová joined the fascinating world of glass ten years ago. In 2015, she was appointed as the head of technical consulting services for AGC Glass Europe. Her work often involves combining the structural, thermal, safety, security, acoustics, and other design considerations of international projects. She holds a degree in civil engineering from the School of Civil Engineering, Slovak University of Technology, Bratislava (Slovakia).
       Due to the high demand for contemporary design-oriented frameless structures that can provide barrier-free views, the demand for frameless glass railing system that are only fixed on one side is increasing significantly (see Figure 1).
       The first generation of such railings appeared in the late 1990s, using metal fixing points to fix glass and metal profiles through holes in the glass.
       The second generation appeared around 2010 and consists of a uniformly supported system consisting of continuous aluminum profiles fixed to the ground and sandwiched between glass panels. Several companies have developed innovative linear aluminum profiles to replace point fixation. The new generation of structural glass railings reduces costs, makes installation easier and faster through standardized modules, and improves aesthetics (see Figure 2).

       Generally, heat-tempered or heat-strengthened laminated glass is used for structural railings, but since the stress concentration has been eliminated, is heat-treated glass really useful or necessary in the second-generation structural railings?

       Thermally tempered or thermally strengthened laminated glass has several disadvantages: complex and expensive production; long delivery time because it is not a stock product; imperfect aesthetics with optical distortion; may be affected by NiS fracture; aesthetics of edge finishing Poor and suspicious damage
       Recently, some interlayer manufacturers have introduced structured polyvinyl butyral (PVB) interlayers, which have significantly higher hardness than traditional interlayers [1].
       This article evaluates the use of annealed laminated glass frameless glass railing system containing these harder PVB interlayers as a solution to replace thermally tempered or thermally strengthened laminated glass in a uniform support system using continuous aluminum profiles.
       Structural glass railings are subject to the complex and constantly changing regulatory framework in Europe. The general principles and applicable loads can be derived from the structural Eurocode [6], but the specific glass Eurocode is not yet available and is still under development. In the special case of structural railings, in the absence of European glass size standards, the design of such structures is still subject to the constraints of national standards in various countries. These national standards are different and specify special requirements, such as static and/or dynamic Test the complete system (glass and fixed) as well as digital simulation.

       In the first part of this article, we introduced the requirements of these national standards for a group of European countries. In the second part, we use physical tests to investigate and check whether the annealed glass railings with hard PVB comply with Belgium .

       All physical tests are carried out by certified laboratories in each country/region, using different aluminum rail systems for fixing, AGC Stratobel Strong [18] as annealed laminated glass frameless glass railing system combined with rigid structure PVB.
       The glass railings are designed according to different national standards. They use finite element analysis for simulation or testing in the laboratory.
       Some countries have specific loading and design rules for glass railings. In countries where there is no specific regulation, Table 6.12 in Eurocode 1 is used to determine the design load. Tables 1, 2 and 3 show the railing loads for different countries and different usage categories (category A residential, category B office, category C area where people may gather, category D shopping area).
       All buildings are exposed to the wind, but sometimes the wind load is forgotten during the verification process of the railings. In addition, the railing, as an independent wall, is more likely to be exposed to strong winds than the exterior wall. In tall buildings, the wind load may exceed the load imposed by the user.
       Some railing systems and their fixation to the main structure are designed to resist loads in only one direction. People often forget the fact that wind can work in both directions. Belgium and France have a clear procedure to include wind loads in the testing process.
       Railings as protective barriers should protect individuals from various dangers or should restrict their activities. Different shock tests are designed to prevent certain accidents. The soft impact test is represented by a cylinder or a bag equipped with two pneumatic tires, with an average weight of 50 kg, which simulates the impact of a human.
       The impact of the steel ball simulates the accidental throw of the tool (hard impact). Test the dynamic impact on the original settings (glass configuration, dimensions, support system and anchoring of the main structure). German and Czech standards allow the use of finite element analysis to simulate soft shocks. Tables 4 and 5 describe the impact tests in selected countries.
       The allowable deviation depends on the national standard. Some countries allow high deflection (Italy), while others maintain very strict applicability standards (Belgium).
       National regulations do not always mention the temperature during the test. If mentioned, the temperature is in the range of 15°C to 25°C.
       In France, when high surface temperatures are expected (for example, railings are exposed to solar radiation), the test results cannot be used.
       In the European Union, there is only one standard that requires glass railings to be tested at a specific temperature: Slovak Standard STN 74 3305:2016. Railings made of brittle materials must be able to withstand the impact of the cylinder and two tires at -15°C. Depending on the category of use, the tire will fall from a height of 1000 or 1400 mm.
       Frameless glass railing system is a brittle material. Its behavior during and after accidental damage is difficult to predict and may vary depending on the application, size, support system, composition, glass type, interlayer type, environmental conditions, etc. When designing protective barriers, the behavior analysis after damage must be considered. Only Belgium, Italy and Germany mentioned the testing procedures for post-damage conditions.
       In Germany, unprotected upper edges of freestanding railings are not allowed. In the UK, all railings must be equipped with handrails except for railings that use tempered laminated glass (which can remain stable after failure). In Sweden and the Czech Republic, railings of stairs and ramps must be fitted with handrails. Belgium, Italy, Spain, and France allow the use of unprotected edges.
       It can be seen that the requirements for verifying railings vary from country to country. In fact, for certain characteristics, national standards may even contradict each other.
       According to the French standard DTU 39 P5, the use of a frameless glass railing system clamped at the bottom requires official technical approval. Tests conducted in France are always performed without handrails and the minimum width of the glass. As we all know, wider free-standing railings are more resistant to soft shocks than narrow railings.
       The results presented in this article are test results that comply with the protocols detailed in the national standards of each of the above-mentioned countries. Details of each result can be found in the officially certified laboratory report. This means that if the report is affirmative, then the complete system—track fixing system and annealed laminated glass with hard PVB—can be used for actual projects in the country.
       We tested 15 types of aluminum fixed rails provided by the largest suppliers: Onlevel 60 (side and top); Aluminco Crystal line, A20 and L line; Massimo Logley Defender 450; Faraone Ninfa 4 and Ninfa 5; Comeza SV top and sides; Q railing Easy Eco top.
       The guide rail and glass are installed and fixed in the laboratory according to the standard supplier's installation manual.
       In all cases, laminate annealing Stratobel Strong is used, cutting from large panels and edge grinding/polishing. We tested a variety of glass thicknesses: 88.2, 1010.2, and 1212.2. In all cases, we will test a 100 cm wide railing with a local adjustment function between 100 and 120 cm in height.
       These tests are performed in the following laboratory: WTC-CSTC Center Scientifique et Technique de la Construction, 1342 Limelette, Belgium.

       Some findings of annealed laminated glass and hard PVB are positive, which means that these complete systems can be used in a test configuration in Belgium. These findings are consistent with known results [1]. Obviously, due to the different torsion, stiffness, and rail dimensions, the same test with different types of rails will not produce the same results. This means that every fixed system must be tested and approved in accordance with national legislation.

       Regarding the Belgian legislation, we can see that the maximum deflection standard is the strictest. For this, the use of rigid PVB is essential to reduce the deformation under line load [1].
       These tests are carried out in laboratories operated by railway suppliers. We confirmed the results of the survey through final tests conducted in an official accredited laboratory: Politecnico di Milano, Laboratorio Prove Materiali, 20133 Milan, Italy.
       Some findings of annealed laminated glass and hard PVB are positive, which means that these complete systems can be used in tested configurations in Italy. Obviously, using different types of guide rails for the same test will not produce the same results, especially for deformation, due to its own fixed rigidity.
       In addition, we tested the same guide rails, but fixed with 4 and 6 polymers per meter. The 6-block configuration results in better and more positive results. Since the stress distribution along the glass fixture is more uniform, the number of fixtures on the fixed block will also have an impact on performance and results. This result suggests that a true fully linear blocking system should be tested, but this is not yet complete.
       A supplier also modified its rail system and designed a special rail for annealed laminated glass frameless glass railing system. This method produced excellent results (see Table 8, Fixed 12).
       These tests are carried out in laboratories operated by railway suppliers. We confirmed the results of the survey through the final test conducted in the official accredited laboratory: Applus+ Laboratories, 08193 Barcelona, Spain.
       In this particular case, according to the Spanish standard, in addition to soft shocks, hard shocks must also be considered.
       Some of the findings of annealed laminated glass and hard PVB are positive, which means that these complete systems can be used in a test configuration in Spain. These findings fully confirm the results obtained with Belgian and Italian standards.
       The fixture 13 is not strong enough to support the ULS static load. It must be re-adjusted after each test because it is unstable. This confirms that every fixed system must be tested and approved in accordance with relevant national legislation.

       It is interesting to note the damage behavior of annealed laminated glass with hard PVB (see Figures 3 and 4). A large number of aligned medium-sized fragments appeared near the railroad tracks. This is completely different from the breaking of heat-treated glass, and it is also different from the breaking of overall annealed glass. This type of breakage is safe because the glass remains in a vertical position and continues to prevent people from falling. Similar fracture behavior is observed for dynamic and static loads.

       All previous results were obtained at a standard temperature within the range of 20°C ±5°C defined by the national standard.
       We tested it in accordance with the Slovak standard STN 74 3305:2016 because it is the only country that requires testing at a different temperature, namely -15°C.
       The test is carried out in an officially accredited laboratory: Technicy a Skusobny Ustav Stavebny, Skusobne Laboratory, Bratislava 82104, Slovakia.
       The test system includes annealed glass 1010.2 and hard PVB, which passed the soft impact test (the most critical) at low temperatures.
       Due to the lack of European standards on glass size, structural glass railings are subject to complex regulations in national standards of various countries, which vary from one country to another, and stipulate special requirements for static and/or dynamic testing of the complete frameless glass railing system.