This paper deals with one of the most effective repair methods for badly damaged masonry structures - their "clasp" with steel post-tensioning tendons. The use of steel post-tensioning tendons is fast, economically profitable and a powerful solution. Suitable locations for tension ropes is important for building active wiring (post-tensioning) where tension is immedciately brought into the structure. After tightening the prestressing, the steel supports the construction without delay, builds up sufficient compressive reserve and moreover ensures serviceability.

Generally the input data for precise design and assessement of prestressed masonry structures is not suficient and detailed. In simple cases the necessary intensities of the prestressing forces can be calculated from an equilibrium of forces. In most situations the engineer has to manage with own experience and the prestressing proceeds piecewise and under the supervision of the designer.

While designing the post-tensioning, first exact rules for prestressed masonry in standards are not provided, second the real characteristics of the repaired masonry are not known. For the layout the prestressing it is necessary to make some testing to determine the masonry properties. Considering the suitability and accuracy it could be advisable to conduct an experiment which is usually very financially and time consuming. The simplest way for verification is numerical modelling by means of some computer program.

Currently the structural analyses are made by means of numerical methods mainly finite element method. All simulations implicit in this contribution were calculated using ANSYS. Two basic three-dimensional models of the masonry quoin were created. In the first model real properties of masonry are replaced by parameters of homogenous material. The second version (the "micromodel") consists of a detailed painted bricks and mortar joints with appropriate material values.

General principles and procedures for design and assessement of prestressed masonry structures are mentioned in Eurocode 6, eventually Eurocode 2, but detailed application rules for calculations of prestressing force or the state of stress analysis are not provided in the present standards. Reconstructions of damaged masonry structures hardly depend on the individual situation, on the quality and the status of present materials, on the failure size or the degree of damage.

Considering all these reasons it is very difficult to set clear rules suitable for the general application during reconstructions. The best solution then is designers' choice of appropriate prestressing force, location of tendons, dimensions of anchorage plates or amount of additional support.

The results of numerical solutions will be subsequently used for experimental testing that are preparing at the Faculty of Civil Engineering in the Technical University of Ostrava.

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