Vacuum glass Structural performance
As new generation of energy-saving and environmentally friendly materials, vacuum insulating glass is the energy-saving glass with the most development potential in the future. In recent years, researchers have devoted to the R&D of vacuum glazing thermal performance,while the study on VIG strength ,structural performance, design and Engineering reliability evaluation is very rare.
The vacuum glass is composed of two pieces of glass with 0.1mm-0.3mm vacuum space, micro support pillars are used to support the special structure,and the surrounding is sealed with low melting point glass solders or metals. For this special structure, architects and designers are very concerned about the deformation, load-bearing characteristics and strength,and safety performance.
1.Safety performance of vacuum insulating glass
1.1 Most VIG are made with tempered glass.
After years R&D,vacuum glazing has developed from annealed VIG to now fully tempered VIG,VIG will break into many small particles and won’t cause serious injury, many manufacturers has got SGCC certificate based on ANSI-Z97.1 impact test, the 10 largest crack-free particles weigh no more than the equivalent weight of 10 square inches (640 square millimeters) of the original specimen.
1.2 Vacuum glass has low impact resistance.
Even though most VIG passed ANSI-Z97.1 test ,but different from normal tempered glass that won’t break at 1200mm height,VIG will break even at 450mm impact height.
The micro support pillars function is to balance the atmospheric pressure difference between the inside and outside of the glass,so pillars positioning design is the key point of producing VIG.When the contact area between pillars and glass panels too large, it will increase the thermal conductivity and affect the transparency. However, small contact area between pillars and glass panels will cause concentrated load will be concentrated load due to the effect of atmospheric pressure,and bring up glass breakage possibility.
The interaction between the glass substrate and the support pillars causes three stresses:
- The bending stress of the glass itself.
- The compressive stress of the support pillars;
- The contact stress between the support and the glass.
Dr Cenk Cocer’s article the performance of vacuum insulating glazing units subjected to a soft body impact, showed that annealed VIG is not strong enough to resist impact,the research are based on annealed VIG sealed with glass solders,while HaanGlas Pro is sealed with low temperature metal materials and can easily pass the soft body impact test,and proved our safety when applied in high rise buildings and facades.
In 2023,June,HaanGlas Pro got 1C3 grade in the EN12600 Dual tyre impact test,which enable HaanGlas PRO to be applied in most buildings.
VIG deflection under temperature difference
Because the vacuum chamber blocks the conduction of heat flow, there is a large temperature difference between the inner and outer VIG surface, resulting in a mismatch in the expansion length. Because the inner and outer glass are sealed together by the low-melting point materials, the edges of the two pieces of glass restrict each other when they expand and contract, resulting in spherical bending deformation and bending tensile stress of the vacuum glass as a whole.
Increasing the VIG thickness can significantly reduce the maximum surface bending tensile stress .The thicker glass, the bigger micro support pillar distance and is beneficial to further reduce the heat conduction.
Refrigerator manufacturers shall research the deflection under long time temperature difference and find solutions on door frame and materials to ensure long lifetime.
Vacuum Glazing wind resistance performance.
3.1Vacuum insulating glass equivalent thickness
Researchers from Beijing Synergy and China CTC conducted plenty of tests and calculation on VIG equivalent thickness and got conclusion that:
(1) The length and width of the vacuum glass have no obvious effect on the equivalent thickness.
(2) The thickness of the vacuum glass substrate has an influence on the equivalent thickness, and the greater the substrate thickness, the smaller the equivalent thickness coefficient. .
(3) The equivalent thickness coefficient of N3+V+N3,N4+V+N4,N5+V+N5 vacuum glass can be taken as 0.95, 0.9 and 0.85 separately.
(4)Since the elastic modulus of heat strengthened glass, tempered and annealed glass is basically the same, therefore, glass been heat treated or not won’t affect the equivalent thickness.
3.2 Factors to consider during designing buildings with VIG
China Building Materials Academy and Beijing Synergy VIG also got conclusion :
(1) The deformation of the inner and outer glass of the vacuum glass is coordinated,equivalent thickness glass can achieve the best resistance to external forces.
(2) When designing the strength of the vacuum glass windows&doors, the vacuum glass can be regarded as a whole and calculated according to the four-sided simply supported theory.
(3) The strength design of the vacuum glass shall consider the influence of the tensile stress on the glass surface under the action of atmospheric pressure, and the safety factor of the vacuum glass shall be based on the comprehensive safety of the glass under the action of the persistent stress.
3.3 Wind resistance of vacuum insulating glass
After installation, vacuum glass will be affected by atmospheric pressure difference, temperature difference and wind pressure,and the superimposed stresses of these three stresses at the center and edge of the plate may exceed the design value of glass strength.
In fact, the vacuum glass is assembled behind the curtain wall or doors and windows, because the edge is supported by the frame or sealant, the actual bending under the wind pressure is much smaller than the completely free state. According to Intertek test,Maximum wind resistance of windows installed with HaanGlas Pro VIG can reach ±9000Pa wind pressure and maintains structural and functional integrity.
For super-large or high-rise curtain walls, hybrid vacuum glass should be selected Glass, namely vacuum + insulating glass or vacuum + laminated glass structure to ensure safety performance.
In 2023,both China architectural department and American architectural department are drafting technical code for vacuum glass,architects and designers will be more encouraged to apply VIG in building facades&windows based on the safety instructions.
HaanGlas is your turnkey vacuum insulating glass manufacturer,contact us for your renovation project.