Design of Glass Structures

¶ … Glass Structures

There has been a dramatic increase in the use of structural glass in building, as a result of interest from architects and improvements in glass technology. Glass plays an important role as it keeps out rains, transparent yet durable and provides security barriers. Glass is a brittle material and it fails unknowingly without giving out results or permanent deformation. Glass although it is strong is sensitive to surface imperfections. Failure is realized from a tensile component of stress (Wilson, 2008).

Important element in the design is that of redundancy in event of sudden failure of leaf of glass as a result of effect loading or fracture by impurities inherent in glass safety and use of lamination should be taken into consideration.

DYNAMICS OF GLASS MATERIAL

Dynamic of glass materials exist for instance soda-lime glass. Soda-lime glass is mostly used in the construction of industry it is a green tint as a result of the presence of iron in the mix that enable it to lower the melting temperature and reduce floating glass production costs. The properties of soda-lime glass include:

Density 2500kg/m3

Young's modules 70kn/mm2

Poisons ratio o.23

Refractice index 1.52

The velocity of glass increases with increase in temperature. Shand, (2010) points out that glass transition temperature has been given to the approximation when glass changes from an infinitely mobile fluid to an elastic solid.

The design thickness of glass is supposed to be the minimum tolerance allowed for monolithic glass. From research, standards of production in the UK set the design thickness of 12mm thick glass as 11.7mm and that for 15mm and 19mm to be 14.5mm and 18mm.

Design of glass panes, the stated data from 700 samples of 6mm thick Annealed glass from 20 batches from 9 different float plants this was realized from test done for bending strength. The range of failure stresses which was between 32N/mm2 and 121N/mm2 portrayed that it was very wide, had a mean of 70N/mm2. (Bruce, 2011, p.21)

Characteristics strengths revealed:

Annealed 46N/mm2

Heat-strengthened 70N/mm2

Toughened 120N/mm2

Annealed glass is subject to stress corrosion which is fond to cracking under long duration loads. Annealed glass is also vulnerable to thermal shock that causes cracking due to internal stresses resulting from temperature differences. The modeling of the annealed glass can be done by re-heating the glass the cooling the outer surface. The cooling prestresses the outside skin enhancing the capacity of extreme fibres to be able to resist tensile stress. Residual which is the extend of stress is determined by the rate of cooling. The toughened glass has a minimum residual surface of 100N/mm2 while heat-strengthened have a minimum residual surface stress of between 41-49N/mm2 (Mahesh, 2010, p.9)

The critical area in the design of the glass structure is connection .Connection links the series of elements .The choice of connection type is based on various factors such as: