Design criteria (earthquake)
Decisive assessment criteria are
- the earthquake hazard,
- the reaction of the structure ( response spectrum ),
- the nature of the subsoil
- the importance of the structure.
The requirements for buildings at risk of earthquakes are set out in DIN EN 1998-1 ( buildings in German earthquake areas ) and must be complied with in some federal states. Additional DIN standards apply to special high-rise structures, such as DIN 19700 for dams such as dams and flood retention basins .
On the basis of the design criteria, it is calculated how a building must be erected within the framework of the requirements that apply to it (dimensions of the load-bearing parts, observance of construction rules). For important structures such as B. Hospitals have stricter requirements than for example single-family houses. A detailed calculation can be dispensed with under certain conditions.
Intensity classes and earthquake zone maps
The probability of the occurrence and strength of earthquakes is different for each building area depending on the geological situation; it is determined by a statistical evaluation of the earthquakes that have occurred in the past. The main investigations are the damage ( intensity ) of earthquakes, which can also be derived from historical reports. The direct measurement of the strength ( magnitude ) of earthquakes and the resulting calculation of the forces acting on structures is only possible for earthquakes whose seismogram is available. This has only been the case across Germany since around 1900.
For Germany, earthquakes are divided into four intensity classes in DIN 4919 using the EMS earthquake scale. A dimensioning of structures according to DIN 4149 is only to be carried out for classes 1 to 3. However, it is recommended to carry out such a dimensioning for structures in Zone 0 as well.
|Earthquake zone||EMS scale||effect|
|0||6 - 6.5||Slight damage to the building (e.g. cracks in the plaster, especially in buildings in poor condition)|
|1||6.5 - 7|
|2||7 - 7.5||Building damage, e.g. B. Cracks and crevices in masonry, collapsing chimneys. Most people in buildings are frightened and flee outside. Furniture shifts and lots of items fall off shelves and open cupboards. Many normal buildings are damaged, for example by cracks in walls and sometimes collapsing chimneys.|
On the basis of this evaluation, the responsible geological offices or other qualified bodies create earthquake hazard maps ( earthquake zone maps ). The evaluation of the earthquakes in Germany shows that earthquakes can only be expected in some areas with sufficient probability. Affected areas are the Lower Rhine Bight , the Upper Rhine Rift and the Swabian Alb (especially the Hohenzollern Rift ) in the west and, to a lesser extent, the Gera area in the east .
Plant earthquakes and design earthquakes
With regard to the possible damage from an earthquake, a distinction is made between the earthquake load cases "operational (earth) quake" and the "design earthquake ".
The operational earthquake is decisive when dimensioning the structure if the structure has to fulfill special functions at all times, as is the case, for example, in a hospital. For a building structure, this is an earthquake that may cause minor damage to the non-load-bearing elements, but in which the important facilities, e.g. B. a heart-lung machine , must remain operational. The structure must therefore absorb the earthquake in such a way that the deformations decrease again. The maximum size of the deformations that may occur in the event of an earthquake is determined by the restrictions on damage to non-load-bearing elements.
In addition to the company earthquake (company earthquake), the stronger safety earthquake or design earthquake is also used for dimensioning. In this earthquake, the structure is allowed to suffer limited damage but not collapse. The focus here is on stability. The rated earthquake is defined as that earthquake of a considered strength that occurs with a probability of 10% within 50 years.
In English the following equivalent terms are in use:
- Operating basis earthquake (OBE) (corresponds to the company earthquake )
- Maximum design earthquake (MDE) (maximum design earthquake ; corresponds to the safety earthquake / design earthquake )
- Maximum probable earthquake (MPE) (largest probable earthquake)
- Maximum credible earthquake (MCE) (maximum conceivable earthquake)
Reaction of the structure
The reaction of a building (response spectrum) to the forces generated by an earthquake, usually acting horizontally in different directions, depends on the construction (e.g. half-timbered , prefabricated house ) and the material (e.g. reinforced concrete , masonry ). The power transmission within the structure has a major influence on the response spectrum, for example through a securely connected and simple supporting structure, the avoidance of differently reacting parts of the building and sufficient resistance to twisting. It is also essential that the foundation of the structure reacts in a uniform manner and that large masses are avoided in the upper parts of the structure.
With the help of the properties of the materials used and the force transmission due to the construction method, the response vibration of a building to the earthquake vibration can be calculated, and thus also the forces occurring within the building. These serve as dimensioning criteria for construction and material.
The reaction of a building depends both on the immediate subsoil (3 - 20 m below the surface) and on the deeper subsoil. In the standard, both indicators are summarized as an S indicator . Without an expert opinion, the most unfavorable subsoil class C is to be used.
The subsoil class is described by means of the loosening caused by weathering :
- A: unweathered
- B: moderately weathered
- C: badly weathered
The condition of the subsoil must be verified for each structure by means of a subsoil report.
The deeper subsurface is divided into three classes
- R (from English rock ): solid rock (areas with solid rock bedrock)
- T ( transitional ): Transitional areas (areas with shallow loose rock and transitions between R and S)
- S ( sediment ): sedimentary basin (areas with deep loose rock)
The application of these measures to the given location on the situation is the resulting parameter S .
Importance of the building
The importance of the building for the general public is included in the calculation according to DIN 4149. A distinction is made between the four importance categories I to IV, from which an importance factor for the respective building results. Agricultural buildings such as barns, which are of little general importance, are classified in Category I; they are given an importance factor of 0.8. Category IV includes facilities of general importance such as hospitals, fire stations or disaster control facilities (importance factor 1.4).
- DIN 4149: 2005-04: Buildings in German earthquake areas. Load assumptions, dimensioning and execution of common buildings. Replacement for DIN 4149-1: 1981-04 and DIN 4149-1 / A1: 1992-12. Standards Committee in the Building Industry (NABau) in the DIN German Institute for Standardization eV, Berlin 2005.
- Udo Meyer: Earthquake-proof building with brickwork (PDF; 629 kB) Working group for brickwork in the Federal Association of the German Brick Industry. Retrieved August 8, 2009.
- Gottfried Grünthal: Earthquake Hazard for the Dimensioning of Dams According to DIN 19700. Volume of the report 14th Annual Conference “Safety- Relevant Effects on Flood Retention Basins - Extreme Operating Conditions .” Stuttgart, November 20, 2007 ( PDF file ; 950 kB)
- Free online tool for determining the earthquake zone , the reference value of the maximum ground acceleration a gR and the geological subsoil class according to Eurocode (also snow load zones, wind zones)
- Peter Knödel: Loads from earthquakes. (PDF; 127 kB) Example for the calculation of an elevated water tank based on the design criteria for earthquakes