Non-residential Buildings and Embodied Energy - Steel Structures.

The embodied energy burdens of commercial buildings vary considerably depending upon their specification, as illustrated in Fig. 8.1. For example, prestige office buildings can have twice the embodied energy content of lower specification offices.

This is due to the way they are clad and fitted out rather than  the effects of the structural frame.

Embodied energy is typically small in comparison to operational energy over the life of a commercial building (generally an order of magnitude less).The balance is however changing as improved designs reduce operational energy and the rate of change of use increases so requiring more refurbishment.

Comparison of embedded energy and operating energy for a basic  grade and prestige office over a 60-year life
Fig. 8.1 Comparison of embedded energy and operating energy for a basic  grade and
prestige office over a 60-year life

The embodied energy of the structural components of a typical office building is only about 25–30% of the total embodied energy and tends to vary relatively little irrespective of the type of structure.A life cycle assessment (LCA) study of a typical four storey office building compared five alternative steel and concrete structures.

No significant difference was identified between the embodied energy burdens of the different options.Although steel has a high embodied energy content per kilo- gram, its high strength to weight ratio means that a much lower volume of steel is required to construct a steel frame than the volume of concrete needed to construct an equivalent frame. The cross-sectional area and mass of steel structural members is very much smaller than that of equivalent concrete members.

The comparative lightness of modern steel frame structures has been important in reducing their embodied energy burdens. In addition to savings associated with the frame materials, designers can often adopt lighter foundation systems than would be required for other forms of construction. Alternatively the number of foundations may be reduced, since the spanning capabilities of steel can allow larger structural bays, and consequently fewer column bases requiring support.The larger bays also allow for more flexible use of space; steel frames are  easily adaptable, thereby prolonging the building life and reducing yet further the impact of embodied energy over the life cycle.

In composite construction, where beams act in tandem with the floor slab, the additional strength and stiffness that are achieved allow the use of relatively shallow beams. These have lower embodied energy and the volume of concrete in the floor is barely altered.

Modern portal frame design has played a significant role in reducing the em- bodied energy burden of single storey industrial and commercial buildings. Portal frames are capable of spanning considerable distances using relatively light sections.

Roof beam depths are generally of the order of span divided by 60, as opposed to span divided by 25 for a conventional beam and column roof. The combination of steel frames with light gauge purlins and rails supporting insulated cladding systems provides a very efficient form of construction resulting in the very high (95%) major share. Systems are available to meet the requirements of the new Part L to the UK Building Regulationsin terms of both insulation and air tightness.

A key element in achieving low embodied energy is the pursuit of structural  efficiency. By reducing the amount of structural steel required per unit area  of commercial building, designers can not only achieve elegant and economic  structural solutions, but also reduce embodied energy burdens.

0 comentarios:

Post a Comment