Sustainable office buildings in steel and composite construction

Abstract

Due to the dramatic consequences of climate change, the development of the world's population, and the increasing scarcity of natural resources, such as fossil fuels, ore, but also water and fertile soil, humanity is forced to move from a predominantly consuming to a resource-efficient, sustainable economy. The EU has set itself ambitious climate protec-tion targets: By 2050, the annual greenhouse gas emissions are to be reduced by 80 to 95 percent compared to 1990 levels. We must drastically reduce the consumption of non-renewable energy sources, and conserve natural resources. With the introduction of as-sessment systems, the construction industry is focussing on sustainability in the planning process. On the basis of parameter studies, the dissertation "Sustainable office buildings in steel and composite construction" provides recommendations on how the load bearing system of office buildings can be designed sustainably.

Taking into account the long-term adaptability of an office building to the changing needs of its users, this dissertation presents various forms of use and development of the struc-tural organisation of office buildings. This results in typical grids of the load bearing com-ponents, which serve as a basis for the design of the load bearing system. In order to cre-ate a sustainable construction, it is important to calculate the maximum span that allow the forgoing of the inner columns, but still meets all structural and static requirements.

After a compilation of the predominantly used slab systems, support and beam profiles for office buildings in steel and composite construction, as well as the technical requirements for the load bearing system, the rules for the design and construction of the individual structural components are explained according to the valid Eurocodes. Based on the German assessment systems DGNB and BNB, the basic principles and methods for as-sessing the ecological and economic sustainability of load bearing systems are examined in detail. In order to be able to depict a holistic analysis of the life cycle of the load bearing system that takes into account all working processes, this dissertation adds suitable as-sumptions for missing or incomplete environmental product declarations.

Taking into account the different construction methods, grid dimensions, material grades and construction forms, the parameter studies conducted within the scope of this disserta-tion provide optimisation possibilities of the load bearing system. Starting with an analysis of the individual structural elements, such as slab types, beam and column constructions, the structural systems consisting of those various components are being evaluated. As a result, recommendations regarding the sustainable construction of load bearing systems are being derived.

The examination of floor systems with downstand beams and slim-floor systems with steel or composite columns showed that the dominant influence on the ecology and the costs is caused by the slab systems. The expenses for the columns are substantially lower, so that their arrangement is based primarily on the requirements of the slab systems.

The parameter studies showed that, from an ecological and economical point of view, floor systems with downstand beams, providing a beam distance of 4.80 m excluding edge and holding beams, are particularly suitable for a free floor layout with span widths of 6 m to 15 m. If edge and holding beams are arranged, beam distances of 2.40 m to 3.60 m are preferable. Considering ecological and economical effects, it is better to forgo the construction of inner columns up to about 12 m. For larger spans, the construction height and the required amount of profile steel increase significantly compared to systems that include inner columns. The floor slabs can be made of reinforced concrete or com-posite slabs. Composite slabs are ecologically unfavourable due to the expenses of pro-filed sheets. However, due to their relatively easy instalment compared to reinforced con-crete slabs, they offer economic advantages. Considering ecological and economical ef-fects, both the reinforced concrete and the composite slabs with their different advantages and disadvantages show equal results. The use of higher steel strengths can often reduce profile steel masses. This is always the case when the load bearing capacity is decisive for the component dimensions. The savings have a positive impact on the environment and, despite higher steel prices, are also reducing the costs. By using higher concrete strengths, the thickness of the slabs can only be reduced slightly, and the higher costs of the concrete are compensated only in a few cases by the mass savings. It was not possi-ble to determine any compensation for the higher ecological impact of the mass savings in slabs examined.

For small to medium span widths, it is possible to implement slim-floor-systems with inte-grated floor beams. With regard to the construction height, ecological and economical aspects, the usage of the slim-floor-systems with inner columns is recommended. Due to the low construction height, the storey height and thus the volume that needs to be heated, as well as the facade area, can be reduced. As well, the number of storeys can be increased with the same building height. The flat underside of the ceiling allows a flexible arrangement of non-load-bearing walls and a simple cable routing. However, it should be noted that the technical equipment is to be arranged below the load bearing system; therefore, the load bearing system and the additional construction must be considered together when determining the floor height. The slim-floor-systems should be combined with prestressed hollow core slabs or other slab systems, which have a comparatively low weight, but at the same time allow larger distances between beams. From an ecological point of view, beam distances of 6.0 m to 7.2 m have proven to be favourable for systems with prestressed hollow core slabs. In addition, the length of the prestressed hollow core slab should be 1.0 to 1.5 times the span of the slab beams.

The selection of the building columns depends on the required load bearing capacity, fire protection regulations, the structural design and the required space. Within the scope of this dissertation, steel and composite columns have been examined. From a static and economic point of view, the use of composite columns is only required when the cross-sectional dimensions exceed 200 mm. The use of higher steel strengths makes it possible to increase the load bearing capacity, or to design smaller cross-sections for both steel and composite columns in the usual slenderness range of storey columns. Similarly, in-creasing the concrete strength of composite columns also enhances the load bearing ca-pacity.

Considering fire protection regulations, the parameter studies examine steel columns with fire protection plates and composite columns with geometric and structural requirements according to the table method corresponding to DIN EN 1994-1-2. A comparison of the variants showed that the increasing requirements of the fire protection regulations (R-Class) have a negative impact on the ecology, and furthermore increase the costs of contstruction and this influence hardly plays a role for fire protection plates. Within the investigated parameter range more economical results could be achieved for columns with concrete cores up to the class R60 compared to the clad steel columns.

Further results of the parameter studies are discussed in the dissertation and documented with charts. Based on these extensive evaluations and considering weighted economical and ecological interests, an informed choice between different sustainable building sys-tems and span widths, as well as material grades and constructional forms, can be taken.