Construction of strut and tie model (STM) at D-regions is based on elastic stress distributions by imagining the forces as resultants of stresses. Beside `smooth´ stress-trajectories there are `turbulent´ places having a decisive influence on the cracks. Therefore, it is useful to use alternative STMs, one constructed on the base of smooth trajectories, and another which fits the turbulent stresses. Examples are given for different types of structural elements.

IMS structures are skeletons assembled of precast concrete units, where floor units are connected to columns by post-tensioning. Ulterior tests show cables to exhibit significant corrosion in critical floor cross-sections. Variation of the failure risk of similar floor structures has been examined taking cable corrosion into consideration. Expected values of critical internal forces and load-bearing capacities of critical cross-sections have been determined by probabilistic methods. Internal forces computation applied 2D and 3D lattice programs run on IBM 386 computer. According to test results on a typical floor constructed 15 years ago assuming corrosion as probabilized from disclosures, failure probabilities of critical cross-sections compared to the original condition much increased, exceeding by about two orders the Hungarian Standard requirement. According to investigations, if in a cross-section, cables of a given direction undergo total corrosion or rupture, internal forces are rearranged, leading to progressive collapse of the floor.

The measurement and control of the reaction forces of a three-span 114.5 meter long reinforced concrete box girder bridge built by incremental launching is reviewed. Using the complex lifting and measuring system it was possible to determine the effective dead load of the bridge during the lifting at eight points. By means of the observed alteration of the reactions suitable to the different values and combinations of the vertical displacements it was possible to calculate the proper vertical position of the bearings answering the designed reaction forces. The 22% difference between the reaction forces of the designed and launched structure justified the necessity of checking. The decsease of the deviations under a 1% limit proved the suitbility of the measuring system and the method applied.

The paper deals with fundamental geometric assumptions of the static-kinematic analysis of triangulated surfaces. First, intrinsic and extrinsic properties of triangulated surfaces as analogues of those of smooth surfaces are introduced, then static-kinematic analogies between triangulated surfaces and pin-jointed single-layer space grids are dealt with. It is shown that Gaussian curvature of smooth surfaces cannot be interpreted for triangulated surfaces, and space grids, however, statements of Gauss´ Theorema Egregium can be replaced for statements concerning simple and useful connections between their intrinsic and extrinsic measures.

The bracing of buildings of the prefabricated and prestressed IMS skeleton system is provided by sway-to-shear and sway-to-bending structural members. An analysis of their contribution to the lateral stiffness is presented in this study. The adopted method is subjected to N.Rosman´s theory. An illustrating numerical analysis reveals that a casual deficiency of the framework rigidity of the nodes due to decrease of prestressing effect can cause a remarkable redistribution in the loading conditions of the bracing diaphragms.

In the structure of the 24 storey tall building at Pécs constructed by IMS prestressed concrete skeleton system in 1975-78 significant corrosion damages occurred at the prestressing tendons of the column floor-slab joints because of the high chloride content of the joining mortar. After only 10 years of service 70 per cent of the prestressing tendons were severely corroded and almost 30 per cent of them failed. Because of loss of the prestressing force the interaction between the floors and columns of the floor-slab system and the stiffening system of the building was weakened. Especially the cantilever type facade structures have got in a disadvantageous state while at the crossings of the prestressing wires and the columns and at the anchorages of the cantilever beams there are ungrouted sections. Because of the decrease of the safety of the structure the building containing 250 flats was evacuated for the period of the strengthening works. The detailed examinations of the experts proved the necessity of the given measures and simultaneously worked out the basic theoretical ideas of the strengthening of the structure. The column - floor junction (the local reinforcement) has to assure the support of the floor-slabs at the columns; the interaction and mutual work of the floor system; the safe fastening of the cantilevers. \noindent From the different variants the method which applies for the support of floor-slabs reinforced concrete drops at the edge columns and steel collars at the internal ones seems to be the most advantageous. For the repair of the stiffening system (the global strengthening) it is necessary to hold together the floor-slab system. Advantageous is the method which does not require the alteration of the foundation structure. The detailed inspection showed that by the strengthening of the top bracing of the existing shear walls the rigidity of the building might be guaranteed. According to the examination carried out it can be stated that the strengthening is technically possible. The supervision of the more than 300 000 square meter buildings constructed in Hungary by the IMS technology, the development of the methodology of corrosion exploration at damages and the improvement of the strengthening method were initiated with the inspection of the tall building at Pécs. The recognition of the corrosion at damages allowed to start the well organized strengthening works.

This paper gives review of the historical antecedents of Eurocode-2 in Hungary and East Europe. The method of permissible stresses, using uniform safety factor was first changed in 1950 in Hungary by the semi-probabilistic method using partial safety factors. This new method was accepted with some resistance on the part of the leading structural engineers. Nevertheless most of the East-European countries accepted the new method with some `political overtones´, to be follow the Soviet example. The authors assert in the papaer that due to the economic necessities, Hungary and the other East European countries gained experience with the regulations affording less safety than the EC2, and this offers an interesting set of experience to the West European countries which have intoduced or are introducing the semi-probabilistic procedure. The most significant point all the experience is the recognition that only one part of the parameters in the structural analysis determining safety can be handled statistically.During design the statistically not significant data such as the error of the structural model must also be taken into consideration. Based on the experience, the authors propose an alternative design method.

There are many problems of free cantilevered prestressed concrete to be solved by more convenient methods. One of these is the determination of the internal forces during the assembly and post-tensioning of the cantilevers. This question is also called the determination of the elastic shortening loss in already anchored tendons. A system of equations for the tendon forces as unknowns using the force method for the states of the construction of the cantilevers is written. The analytical solution of this equation is enabled by the recognition that the coefficient matrix of the system is a one-pair matrix modified by a diagonal matrix. Using the statement according to which the inverse matrix of a one-pair matrix is a symmetric tridiagonal matrix and vice versa the elements of the inverse of the one-pair matrix in the coefficient matrix can be produced. The task finally can be reduced to the inversion of the symmetric tridiagonal matrix modified by a diagonal matrix. This further problem can be solved by means of one-pair matrices formed by quantities gained by a recursive algorithm. The importance of the result consists in the fact that the internal forces of a free cantilevered structure in an arbitrary stage of construction can be written in case of any parameters (changing cross-section, length of segments, number of tendons, etc.)