Case 2
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
- Examining the glass panel reveals the position of the affected area. It is situated at the right angled corner of the building where no glass frame or metal guard is installed to protect this corner.
- The installation technique at this corner makes use of two plain sheets of glass abutting each other. At the abutment the two glass panels are placed beside each other and sealed with a sealant. This is usually not adequate to resist any sudden impact load at this corner.
- Pure silica is attacked by alkaline solutions and thus common glass (soda-lime-silica) glasses when exposed to water, the water dissolves sodium ions from the surface of the glass to form alkaline sodium hydroxide.
This in turn attacks the silica. Glass fatigues under tension: that is under static load will ultimately break at low stresses due to the corrosion process where the glass is.
The initial tension enlarges surface cracks, not enough to start a fracture, but enough to expose new surfaces to chemical attack.
As the corrosion proceeds, the cracks open further and ultimately a crack that was progressing at the rate of fractions of a millimeter per hour by chemical erosion becomes a mechanical crack spreading at a rate of several thousand meters per second
- Thermal stress cracking [1]
At this corner, it can be said that the joint between these two panels are the weakest. Under tropical conditions, whether changes from hot to cold climatic conditions can induce thermal stress cracking on the glass panels. This is particularly common at areas where a strong shadow across the glass only allows part of the glass sheet to heat up in sunlight.
Consequences
Further cracking might show and eventually the whole sheet might shattered.