Application and Construction Variants

all non-structural facade elements are removed and the building is upgraded to meet current thermal insulation standards without necessitating any changes to the load-bearing structure. In addition, prefabrication of the timber panel elements requires an integrated and detailed approach to the design in which the architect, structural engineer, building services engineers and contractors are in contact with one another in the early design stages. Only in this way is it possible to accommodate the different dimensional tolerances in the reinforced concrete and timber components while optimising joint design and construction sequences.

The Brundtland Commission of the United Nations (UN) refers to “sustainability” in the following terms: “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” Since the UN Conference on Environment and Development (UNCED) in 1992 and the Enquete Commission of the German Parliament in 1998, 178 countries have endorsed the joint “three pillars model” for sustainable development [1]. In accordance with this model, ecology (conservation of resources), economy (economic performance) and society (equal rights, peaceful coexistence, health etc.) must be given equal consideration to ensure, amongst other targets, sustainable building design and construction. Buildings cannot only make a significant qualitative contribution to the economy, culture and society, they are also highly important in the field of ecology. The energy they use is responsible for approximately 19 % of global CO2 emissions [2]. Furthermore, about 35 % of final energy consumption in Germany can be attributed to the buildings sector [3]. Consequently, the buildings sector has the potential of significant leverage in terms of ecological sustainability – by making more efficient use of energy and raw materials. Life cycle assessment (LCA) offers an effective approach to analyse the environmental sustainability of buildings. LCA calculates the energy and resource demand, waste and environmental impacts throughout the life cycle of the building, covering everything from the extraction of raw materials, the production of building components, the building’s construction and use to its eventual demolition and recycling. Hybrid construction using timber panel construction elements improves the ecological sustainability of buildings in several respects. It increases resource efficiency through the use of renewable raw materials and, if designed to be disassembled, the possibility to reuse materials and components in material cycles. Highly insulated timber panel construction elements contribute to energy savings during the use phase of the building (see “Thermal Insulation”, p. 33ff. and “Energy Efficiency”, below). In addition, hybrid construction has economic potential through cost and time savings (see “Economy”, p. 16f.).

Production of exterior elements Production of interior load-bearing structure End of life of exterior elements End of life of interior load-bearing structure

Global warming potential [CO 2 eq] 200 180 160 140 120 100 80 60 40 20 0 Non-renewable primary energy [GJ] 3,500 3,000

2,500

2,000

1,500

1,000

500

0

-500 Ventilation for 50 a Heating for 50 a Hot water for 50 a

Since the introduction of the 1st German Thermal Insulation Ordinance in 1977, the requirements for the energy efficiency of buildings in Germany have steadily increased. The result is that “modern” buildings consume increasingly less heating and cooling energy. The German Energy Saving Ordinance (EnEV) 2002 included the provisions of the Heating Systems Ordinance (HeizAnlV) and con-

6 Various facade materials a Light-coloured masonry facing, student hall of residence Hanover (DE) 2017, ACMS Architekten b, c Fibre-cement sheets varnished in various colours, Neue Burse student hall of residence, Wuppertal (DE) 2013, ACMS Architekten 7 Comparison of hybrid and concrete /masonry construction based on the example of a multistorey residential building in Penzberg (see example project p. 82ff.) a Global warming potential b Non-renewable primary energy

Christof Volz Stefan Winter

In addition to the building physics and sound protection requirements, other important aspects in building design include the construction concept and structural adequacy of hybrid construction. The structural engineer prepares design calculations and detailed construction drawings for the reinforced concrete structure and the timber panel construction elements. The concrete elements require formwork and reinforcement drawings, which show the geometry of all the reinforced concrete components and their reinforcement with an implied construction sequence. Extensive working drawings show the geometry, the timber materials used and the connection components for the facade elements. Fabrication of the timber panel construction elements, their transport to site and installation must be planned to ensure a smooth, efficient fabrication process within budget and on schedule. The interface between the load-bearing reinforced concrete structure and the primarily room-enclosing timber panel construction elements is particularly important in the design, because innovative connection details are key to facilitating rapid installation and satisfying the structural engineering requirements.

This chapter discusses the special structural and constructional features of hybrid buildings and how they should be considered during design and construction.

The design of hybrid buildings is governed by the currently applicable versions of the European standards (Eurocodes). DIN EN 1990 to DIN EN 1999 are the basis for the structural design calculations. The principles of structural design are set out in Eurocode 0 and in DIN EN 1990. These define the basic terms, which are used universally throughout other material-specific design standards, and the principal requirements for structural stability, reliability, economic efficiency and durability. An important part of Eurocode 0 is the representation of the design concept with partial safety factors and the listing of each situation to be analysed (load combinations). These partial safety factors increase the normative actions or reduce the material strengths to ensure an appropriate degree of safety. Eurocode 0 also describes two basic limit states: the ultimate limit state (ULS) calculation verifies the structural stability, while the serviceability limit state (SLS) calculation ensures that the structure functions properly during the use phase. The serviceability limit state calculation includes a check on the estimated deflection of building components against stipulated maximum values. The format of verification in accordance with Eurocode 0 is as follows:

Ultimate limit state (ULS) Ed ≤ Rd Ed = Calculated value of the effect of the actions Rd = Calculated value of the resistance

Serviceability limit state (SLS) Ed ≤ Cd Ed = Calculated value of the effect of the actions Cd = Calculated value of the limit for the critical serviceability criterion

The verification procedure considers various combinations of actions to calculate the frequency of occurrence of a load during the life of a building component. Permanent, unchanging loads such as self-weight are designated with “G”, while variable, changing loads such as loads due to building use, wind, snow or earthquakes are designated with “Q”, “S” or “A”. In addition to the accidental action “Earthquake”, there is also an accidental load case “Fire action”. This is used to calculate the effects of heat on building components to verify that the structure can remain structurally stable for a defined fire resistance period. The partial safety factors G and Q are chosen to suit the design situation. The various loads are weighted, depending on their probability of occurrence, with combination factors i, because e.g. the simultaneous occurrence of full snow and full live load is improbable. The “permanent and transient” design situation is used in the ultim ate load state (ULS) to verify the structural stability (component design). The “quasi-permanent” action combinations are used for deformation calculations in the serviceability limit state (SLS). The verification of the building components is performed in accordance with the following material-specific European standards: • Eurocode 1: Actions (DIN EN 1991-1-1) • Eurocode 2: Design of concrete structures (DIN EN 1992-1-1) • Eurocode 3: Design of steel structures (DIN EN 1993-1-1) • Eurocode 4: Design of composite steel and concrete structures (DIN EN 1994-1-1) • Eurocode 5: Design of timber structures (DIN EN 1995-1-1) • Eurocode 6 Design of masonry structures (DIN EN 1996-1-1) • Eurocode 8: Design of structures for earthquake resistance (DIN EN 1998-1-1) • Eurocode 9: Design of aluminium structures (DIN EN 1999-1-1)

element

belement

the main load cases in the design. The fabrication, loading and delivery of the timber panel construction elements should be synchronised with the sequence of installation on site to avoid the requirement for temporary storage space. In addition to the weights and method of supporting the elements, the installation plan should also give details about the slinging points and the fastening elements for lifting in the elements. A horizontal installation orientation of the timber facade elements is advantageous because they can be put in place independently of the planned connection variant. The butt joints between the timber panel construction elements are designed to transmit force and be airtight to ensure that the joint can fulfil all its structural and building physics functions. The dimensions of the timber panel construction elements should not exceed h element ≈ b element = 3.70 m ≈ 15.00 m in order to ensure smooth delivery and installation, without incurring additional costs. Exemptions for loads issued on an individual case basis can cover dimensions of up to h element ≈ b element = 4.00 m ≈ 16.00 m. Vertically oriented timber facade elements can be used only for the self-supporting variant. The above-mentioned limits to dimensions must also be observed for timber panel construction elements to be installed as vertically oriented. Vertically oriented panels can be used over three to four storeys, depending on the storey height.

The interface between the reinforced concrete structure and the facade elements forms a significant part of the building design. Manufacturing tolerances and load-dependent deformations must be reconciled with one another so that installation can proceed smoothly and efficiently.

In the construction of buildings, manufacturing tolerances are always to be planned for carefully, because, after manufacture the elements or building components can differ from their intended dimensions, the design dimensions. This difference is known as deviation. The designer must consider how to compensate for these inaccuracies. A permissible variation (tolerance) is specified for the dimension (limit deviation) of the item of the works to be manufactured. Dimensional tolerances can be classified as one of the following tolerance types: • Manufacturing dimensional tolerances • Installation dimensional tolerances • Insertion dimensional tolerances or oversize deviation of the on-site construction • Dimension tolerances due to building components changing shape

DIN 18 202 specifies the material-independent tolerances that must be complied with when building structures in order to allow the building elements of the basic structure and fitting out to be connected without the need for adjustment work after manufacture. The specified normative tolerances are based on the accuracy normally achieved in standard practice. Other accuracies can be specified as well. Compliance with higher accuracy requirements leads to higher manufacturing costs and must be technically justifiable. The values for time and load- dependent deformations and those for temperature effects are not covered in DIN 18 202 [14] but must also be considered. DIN 18 203-3 contains the manufacturing tolerances for prefabricated timber components. Dimensional tolerances for angular deviations in length, width and thickness of timber panels are covered by DIN 18 202 (Fig. 16). The manufacturing tolerances for the reinforced concrete structure are in accordance with DIN EN 13 670 and DIN EN 13 369 (Fig. 15).

The deformation of reinforced concrete components such as slabs and beams, which bend in response to loads, depends on the level of loading. The reason for this is that concrete is highly resistant to compression loads (high compressive strength) but has very low tensile strength and creeps when subjected to long-term compression. In addition to this, concrete shrinks as it cures, which must also be taken into account. The strength of concrete in compression is generally a factor of ten higher than its strength in tension. Therefore steel reinforcement is required to take the tensile stresses. In beams, for example, this is provided in the bottom of the section around mid-span. Under light loads, building components loaded in bending are in State I (Fig. 17) because the concrete can resist the tensile stress arising from the load by itself. As the load increases, the concrete can no longer carry the tensile stress by itself and fine cracks form, which have insignificant effects on the load-carrying be haviour. The structural element then enters the cracked State II. Cracks in reinforced concrete components are nothing unusual. It is only by cracking that the bending element activates the steel reinforcement. A corresponding minimum amount of re- inforcement is provided to control the cracks and ensure the appearance satisfies aesthetic expectations. However, the formation of cracks results in an increase in deformations. The deformations in the