Point-fixed glass systems that meet this architectural requirement are especially popular in ground entrances or public areas. Recent technological advancements have allowed the use of ultra-high-strength adhesives to attach these large pumices to accessories without the need to drill holes in the glass.
The typical ground location increases the likelihood that the system must act as a protective layer for building occupants, and this requirement exceeds or exceeds typical wind load requirements. Some tests have been done on the point fixing system for drilling, but not on the bonding method.
The purpose of this article is to record a simulation test using a shock tube with explosive charges to simulate an explosion to simulate the impact of an explosive load on a bonded transparent component. These variables include the explosion load defined by ASTM F2912 [1], which is carried out on a thin plate with an SGP ionomer sandwich. This research is the first time that it can quantify the potential explosive performance for large-scale testing and architectural design. Attach four TSSA fittings with a diameter of 60 mm (2.36 inches) to a glass plate measuring 1524 x 1524 mm (60 inches x 60 inches).
The four components loaded to 48.3 kPa (7 psi) or lower did not damage or affect TSSA and glass. Five components were loaded under pressure above 62 kPa (9 psi), and four of the five components showed glass breakage, causing the glass to shift from the opening. In all cases, TSSA remained attached to the metal fittings, and no malfunction, adhesion or bonding was found. Testing has shown that, in accordance with the requirements of AAMA 510-14, the tested TSSA design can provide an effective safety system under a load of 48.3 kPa (7 psi) or lower. The data generated here can be used to engineer the TSSA system to meet the specified load.
Jon Kimberlain (Jon Kimberlain) is the advanced application expert of Dow Corning’s high-performance silicones. Lawrence D. Carbary (Lawrence D. Carbary) is a Dow Corning high-performance construction industry scientist who is a Dow Corning silicone and ASTM researcher.
The structural silicone attachment of glass panels has been used for nearly 50 years to enhance the aesthetics and performance of modern buildings [2] [3] [4] [5]. The fixing method can make the smooth continuous exterior wall with high transparency. The desire for increased transparency in architecture led to the development and use of cable mesh walls and bolt-supported exterior walls. Architecturally challenging landmark buildings will include today’s modern technology and must comply with local building and safety codes and standards.
The transparent structural silicone adhesive (TSSA) has been studied, and a method of supporting the glass with bolt fixing parts instead of drilling holes has been proposed [6] [7]. The transparent glue technology with strength, adhesion and durability has a series of physical properties that allow curtain wall designers to design the connection system in a unique and novel way.
Round, rectangular and triangular accessories that meet aesthetics and structural performance are easy to design. TSSA is cured together with the laminated glass being processed in an autoclave. After removing the material from the autoclave cycle, the 100% verification test can be completed. This quality assurance advantage is unique to TSSA because it can provide immediate feedback on the structural integrity of the assembly.
The impact resistance [8] and shock absorption effect of conventional structural silicone materials have been studied [9]. Wolf et al. provided data generated by the University of Stuttgart. These data show that, compared with the quasi-static strain rate specified in ASTM C1135, the tensile strength of the structural silicone material is at an ultimate strain rate of 5m/s (197in/s). Strength and elongation increase. Indicates the relationship between strain and physical properties.
Since TSSA is a highly elastic material with higher modulus and strength than structural silicone, it is expected to follow the same general performance. Although laboratory tests with high strain rates have not been performed, it can be expected that the high strain rate in the explosion will not affect the strength.
The bolted glass has been tested, meets explosion mitigation standards [11], and was exhibited at the 2013 Glass Performance Day. The visual results clearly show the advantages of mechanically fixing the glass after the glass is broken. For systems with pure adhesive attachment, this will be a challenge.
The frame is made of American standard steel channel with dimensions of 151mm depth x 48.8 mm width x 5.08mm web thickness (6” x 1.92” x 0.20”), usually called C 6” x 8.2# slot. The C channels are welded together at the corners, and a 9 mm (0.375 inch) thick triangular section is welded at the corners, set back from the surface of the frame. An 18mm (0.71″) hole was drilled in the plate so that a bolt with a diameter of 14mm (0.55″) can be easily inserted into it.
TSSA metal fittings with a diameter of 60 mm (2.36 inches) are 50 mm (2 inches) from each corner. Apply four fittings to each piece of glass to make everything symmetrical. The unique feature of TSSA is that it can be placed close to the edge of the glass. Drilling accessories for mechanical fixing in glass have specific dimensions starting from the edge, which must be incorporated into the design and must be drilled before tempering.
The size close to the edge improves the transparency of the finished system, and at the same time reduces the adhesion of the star joint due to the lower torque on the typical star joint. The glass selected for this project is two 6mm (1/4″) tempered transparent 1524mm x 1524mm (5′x 5′) layers laminated with Sentry Glass Plus (SGP) ionomer intermediate film 1.52mm (0.060) “).
A 1 mm (0.040 inch) thick TSSA disc is applied to a 60 mm (2.36 inch) diameter primed stainless steel fitting. The primer is designed to improve the durability of adhesion to stainless steel and is a mixture of silane and titanate in a solvent. The metal disc is pressed against the glass with a measured force of 0.7 MPa (100 psi) for one minute to provide wetting and contact. Place the components in an autoclave that reaches 11.9 Bar (175 psi) and 133 C° (272°F) so that the TSSA can reach the 30-minute soak time required for curing and bonding in the autoclave.
After the autoclave is completed and cooled, inspect each TSSA fitting and then tighten it to 55Nm (40.6 foot pounds) to show a standard load of 1.3 MPa (190 psi). Accessories for TSSA are provided by Sadev and are identified as R1006 TSSA accessories.
Assemble the main body of the accessory to the curing disc on the glass and lower it into the steel frame. Adjust and fix the nuts on the bolts so that the external glass is flush with the outside of the steel frame. The 13mm x 13mm (1/2″ x½”) joint surrounding the glass perimeter is sealed with a two-part structure of silicone so that the pressure load test can begin the next day.
The test was carried out using a shock tube at the Explosives Research Laboratory at the University of Kentucky. The shock absorbing tube is composed of a reinforced steel body, which can install units up to 3.7mx 3.7m on the face.
The impact tube is driven by placing explosives along the length of the explosion tube to simulate the positive and negative phases of the explosion event [12] [13]. Put the entire glass and steel frame assembly into the shock-absorbing tube for testing, as shown in Figure 4.
Four pressure sensors are installed inside the shock tube, so the pressure and pulse can be accurately measured. Two digital video cameras and a digital SLR camera were used to record the test.
The MREL Ranger HR high-speed camera located near the window outside the shock tube captured the test at 500 frames per second. Set a 20 kHz deflection laser record near the window to measure the deflection at the center of the window.
The four framework components were tested nine times in total. If the glass does not leave the opening, retest the component under higher pressure and impact. In each case, target pressure and impulse and glass deformation data are recorded. Then, each test is also rated according to AAMA 510-14 [Festestration System Voluntary Guidelines for Explosion Hazard Mitigation].
As described above, four frame assemblies were tested until the glass was removed from the opening of the blast port. The goal of the first test is to reach 69 kPa at a pulse of 614 kPa-ms (10 psi A 89 psi-msec). Under the applied load, the glass window shattered and released from the frame. Sadev point fittings make TSSA adhere to broken tempered glass. When the toughened glass shattered, the glass left the opening after a deflection of approximately 100 mm (4 inches).
Under the condition of increasing continuous load, the frame 2 was tested 3 times. The results showed that the failure did not occur until the pressure reached 69 kPa (10 psi). The measured pressures of 44.3 kPa (6.42 psi) and 45.4 kPa (6.59 psi) will not affect the integrity of the component. Under the measured pressure of 62 kPa (9 psi), the deflection of the glass caused breakage, leaving the glass window in the opening. All TSSA accessories are attached with broken tempered glass, the same as in Figure 7.
Under the condition of increasing continuous load, the frame 3 was tested twice. The results showed that the failure did not occur until the pressure reached the target 69 kPa (10 psi). The measured pressure of 48.4 kPa (7.03) psi will not affect the integrity of the component. Data collection failed to allow deflection, but visual observation from the video showed that the deflection of frame 2 test 3 and frame 4 test 7 were similar. Under the measuring pressure of 64 kPa (9.28 psi), the deflection of the glass measured at 190.5 mm (7.5″) resulted in breakage, leaving the glass window in the opening. All TSSA accessories are attached with broken tempered glass, the same as Figure 7 .
With increasing continuous load, the frame 4 was tested 3 times. The results showed that the failure did not occur until the pressure reached the target 10 psi for the second time. The measured pressures of 46.8 kPa (6.79) and 64.9 kPa (9.42 psi) will not affect the integrity of the component. In test #8, the glass was measured to bend 100 mm (4 inches). It is expected that this load will cause the glass to break, but other data points can be obtained.
In test #9, the measured pressure of 65.9 kPa (9.56 psi) deflected the glass by 190.5 mm (7.5″) and caused breakage, leaving the glass window in the opening. All TSSA accessories are attached with the same broken tempered glass as in Figure 7 In all cases, the accessories can be easily removed from the steel frame without any obvious damage.
The TSSA for each test remains unchanged. After the test, when the glass remains intact, there is no visual change in TSSA. The high-speed video shows the glass breaking at the midpoint of the span and then leaving the opening.
From the comparison of glass failure and no failure in Figure 8 and Figure 9, it is interesting to note that the glass fracture mode occurs far away from the attachment point, which indicates that the unbonded part of the glass has reached the bending point, which is rapidly approaching The brittle yield point of glass is relative to the part that remains bonded.
This indicates that during the test, the broken plates in these parts are likely to move under shear forces. Combining this principle and the observation that the failure mode seems to be the embrittlement of the glass thickness at the adhesive interface, as the prescribed load increases, the performance should be improved by increasing the glass thickness or controlling the deflection by other means.
Test 8 of Frame 4 is a pleasant surprise in the test facility. Although the glass is not damaged so that the frame can be tested again, the TSSA and surrounding sealing strips can still maintain this large load. The TSSA system uses four 60mm attachments to support the glass. The design wind loads are live and permanent loads, both at 2.5 kPa (50 psf). This is a moderate design, with ideal architectural transparency, exhibits extremely high loads, and TSSA remains intact.
This study was conducted to determine whether the adhesive adhesion of the glass system has some inherent hazards or defects in terms of low-level requirements for sandblasting performance. Obviously, a simple 60mm TSSA accessory system is installed near the edge of the glass and has the performance until the glass breaks. When the glass is designed to resist breakage, TSSA is a viable connection method that can provide a certain degree of protection while maintaining the building’s requirements for transparency and openness.
According to the ASTM F2912-17 standard, the tested window components reach the H1 hazard level on the C1 standard level. The Sadev R1006 accessory used in the study is not affected.
The tempered glass used in this study is the “weak link” in the system. Once the glass is broken, TSSA and the surrounding sealing strip cannot retain a large amount of glass, because a small amount of glass fragments remain on the silicone material.
From a design and performance point of view, the TSSA adhesive system has been proven to provide a high level of protection in explosive-grade facade components at the initial level of explosive performance indicators, which has been widely accepted by the industry. The tested facade shows that when the explosion hazard is between 41.4 kPa (6 psi) and 69 kPa (10 psi), the performance on the hazard level is significantly different.
However, it is important that the difference in hazard classification is not attributable to adhesive failure as indicated by the cohesive failure mode of adhesive and glass fragments between the hazard thresholds. According to observations, the size of the glass is appropriately adjusted to minimize deflection to prevent brittleness due to increased shear response at the interface of bending and attachment, which seems to be a key factor in performance.
Future designs may be able to reduce the hazard level under higher loads by increasing the thickness of the glass, fixing the position of the point relative to the edge, and increasing the contact diameter of the adhesive.
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