Transparency of building envelopes is an increasingly important requirement for clients and architects and can only be achieved through use of significant quantities of glass. Equally, the push for small, slender structural elements creates pressures in terms of code compliance, particularly where structural safety is a significant design factor. Greater practical understanding of the contribution of glass panels to total structural performance is needed in order to meet both objectives.
Combining glass panels with another structural material (to form a hybrid glass structure) can contribute significantly to the overall structural performance of a building, result in material savings and reduce construction time. Materials commonly used alongside glass in hybrid structures include steel, stainless steel and fibre-reinforced polymers.
Current guidelines for the analysis, basis of design, methodology and constructability of hybrid glass structures are scattered, scarce and sometimes inconsistent. This project set out to review the diverse range of projects and applications where hybrid glass structures have already been used successfully.
Glass may be combined with other suitable materials that complement or augment those physical properties of glass that, without mitigation, are relatively deficient.
Particular consideration of the differential thermal expansion and thermal capacity of the materials is important, as well as the magnitude and distribution of connection forces between components and predicted failure modes.
Glass in structural systems can differ significantly in form, including planar, single or double curved geometries.
With increasing energy costs, improving thermal performance of building envelopes is an increasing focus of attention. Another increasingly important parameter is the shading coefficient as reductions in cooling demands is a high priority for buildings with envelopes with a high ratio of transparent to opaque areas.
As well as developing envelope detailing to mitigate energy loss, attention also is turning to harvesting some of the energy to create energy-passive buildings. Examples include the latest generation of photovoltaic cells and thermochromic glass.
Innovative structures built to date using hybrid glass structural systems include the distinctive form created at the Bombay Sapphire distillery (pictured) in Hampshire, UK.
Structural efficiency can be expressed as the total material used per unit volume of structure created. In practice, cost rather than structural efficiency tends to be the main basis for comparing different structural schemes. Cost estimators incorporate scheme complexity factors such as procurement, constructability, access and maintenance, alongside material costs. The wider application of innovative, complex design concepts such as hybrid glass systems can therefore benefit significantly from upstream investment and development to enable them to become ‘mainstream’ products and compete more readily against longer-established materials and more familiar technologies.
The use of advanced hybrid glass structures offers diverse advantages to building projects, including the following attributes:
- structural performance
- optical behaviour
- aesthetic and architectural aspects
- thermal properties
- relatively low embodied energy
- acoustic insulation.