Security against tipping
The tilt resistance is the resistance of a structure or object against tipping over to the edge of its footprint. It is one of the criteria for verifying the stability of flat foundations , foundations , (angle) retaining walls , dams and is also used for vehicles, etc.
A special form of tilting girders is described under lateral torsional buckling .
calculation
The tipping safety factor is the quotient of resisting (holding) and attacking (driving) forces or torques :
With
- M 1 (static torque) the sum of the holding (resisting) torques; the holding forces are in particular dead weight , but also anchors , (passive) earth pressure and others.
- M 2 (overturning moment) the sum of the driving (attacking) torques; the driving forces can be water pressure , earth pressure, wind pressure , earthquake forces etc. When vehicles move, dynamic forces such as B. added centrifugal forces .
The tilt safety factor should always be greater than 1, so that the applied torques can be maintained.
The arithmetical proof of the tilt safety is called tilt safety proof. Evidence is provided if the calculated safety factor is greater than the value specified or required for the case in question.
The tilt safety verification is carried out around an assumed pivot point in a joint, e.g. B. the outer edge of the base joint of a building, or out around the outer edge of the stand area.
With binders
In reinforced concrete - / prestressed concrete - ties examines the tipping safety. The cross-section of the truss is sensible to choose. If the truss height increases, the risk of tipping also increases. An oversized truss can carry higher loads, but is more prone to tipping. A well-used truss cross-section with a low height is more stable.
The decisive criterion is the width of the upper belt ; if the upper belt becomes wider, the risk of tipping is reduced. Many manufacturers of precast elements use formwork forms with narrower upper flange widths than expected by DIN 1045-1 / DIN EN 1992 . In these cases, proof of tilting safety is required and there are usually noticeable top chord reinforcements on the sides, i.e. H. left and right, to insert into the top belt.
The state of installation usually does not pose a problem with tipping safety, but must be taken into account, especially in the case of laterally supported trusses.
literature
- Dirk Hölter: Proof of tipping safety for reinforced concrete and prestressed concrete girders, in: Beton- und Stahlbetonbau, 2009, pp. 695–697
- Achim Hettler , Karl-Eugen Kurrer : Earth pressure . Ernst & Sohn, Berlin 2019, ISBN 978-3-433-03274-9 .
- Karl-Eugen Kurrer: History of Structural Analysis. In search of balance , Ernst and Son, Berlin 2016, p. 56ff, ISBN 978-3-433-03134-6 .