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Base isolation of buildings is the most efficient way of designing seismically resistant structures. Application of seismic isolators allows mutually independent movements of the ground and the structure during earthquakes. The application of seismic isolators increases the natural period of vibrations, which reduces the seismic forces in the structure. The paper analyzes the influence of the application of lead rubber bearings on the response of the structure to the action of an earthquake. A reinforced concrete frame structure was analyzed both for the case of base isolation and rigid foundation. Based on the comparative analysis of the natural period of vibrations, base shear seismic forces, displacement of the top level of the structure and relative inter-storey drift, conclusions were drawn about the efficiency of application of this type of seismic isolator. The required amount of ductility of a structure, as well as damage to structural and non-structural elements, is greatly reduced by base isolation.

The structures with semi-rigid connections comprise systems with the connections in joints which are not absolutely rigid, but allow, in general, some relative movements in directions of generalized displacements. Such type of connections is considered very little, or not at all, in designing of structures in today's engineering practice. If the influence of rigidity of semi-rigid connections is underestimated, and they are treated in the design as pinned, it has a negative impact on cost of a structure. But if it is overstated, the calculation results are not on the side of safety, what is reflected on bearing capacity, durability and stability, especially in the case of precast structures. Therefore Eurocodes take due account to the structures with semi-rigid connections. Matrix formulation of the analysis of systems with semi-rigid connections opens wide possibilities for relatively easy calculation by use of computers that is shown by example of seismic design. The interpolation functions, stiffness matrix, equivalent load vectors, and the consistent mass matrix are presented in this paper, particularly with an emphasis on systems with semi-rigid connection.

Criteria that are adopted in earthquake resistant design of pipelines and gas lines have to take into account seismic movements and seismic generated forces that are of significantly high probability level of appearance along the length of pipeline. A choice of criteria has to include an acceptable level of seismic hazard, while design criteria should be calculated. Seismic hazard is defined as a part of natural hazard and means probability of appearance of earthquake of corresponding characteristics in certain time and place. For design needs and calculation of influences caused by seismic forces the most important is seismic hazard of maximal horizontal acceleration due to ground vibration during earthquake. The methodology of seismic hazard calculation as base for micro seismic zoning is presented in the paper. It is shown calculation of seismic hazard of maximal horizontal acceleration due to ground vibration that is applied for 985 points at the territory of Republic of Serbia, based on which maps for return periods of 50 and 200 years are drawn.

Most often, in the case of typefied prefabricated systems, foundations are designed and constructed as prefabricated elements as well. When the structure is exposed to high intensity loading and founded on a weak soil, beam foundations are often used instead of pad foundations. Beam foundations, stiffening girders, as well as beams which support the façade elements or partition walls, are treated as beams on elastic foundations, while joint of these girders to pad foundations or vertical support elements of a precast structure can be treated as semi-rigid. Modeling of systems with semi-rigid joints on elastic foundations, for different levels of rigidity of connections, is illustrated by an example of a frame under static loading. On the basis of the results of the calculation carried out in this paper, it is evident that taking into account the elastic foundations of the member and the corresponding degree of fixation of the member on this foundations significantly affects the magnitude of the forces in the cross-sections of the member, and on the redistribution of influences in the entire structure. Yet, the foundations-and-soil interaction exerted the highest influence on the magnitude of the stress in the foundation structure itself.

The paper deals with a brief presentation of a part of the performed experimental tests of the prefabricated reinforced concrete structural system 'AMONT' for construction of various types of modern industrial halls. The test results are analyzed for two industrial halls both constructed according to this structural system but in the different phases of construction, tested in the full scale by application of AMBIENT vibration method. From the obtained Fourier spectra for measured ambient vibrations in two orthogonal direction for the structure without walls and the other with façade and filling walls, a significant discrepancy in their natural frequencies has been observed, and some conclusions about the influence of panel walls on dynamic characteristic the frame structure have been drawn out. The paper used some data of the research after the earthquake in Montenegro which took place on 15th of April 1979.

The paper points out to the differences of the First order theory and Second order theory and of the significance in practical calculations. The paper presents theoretical foundations and expressions of calculations of impacts on the stability of structure, that is, review of the Second order theory in a bridge with members semi-rigid connections in joints. In the real structures in general and the especially in the prefabricated structures the connection of members in the nodes can be partially rigid which can be very significant for the changes in tension and deformation. If the influence of the normal forces is significant and the structure is slender then it is necessary to carry out a calculation according to the Second order theory because the balance between internal and external forces really established on the deformed configuration and displacements in strict formation are also unreal. The importance and significance of the calculations and distribution of impact according to the Second order theory were presented in numerical examples as well as the calculation of critical load as well as the buckling length of members with semi-rigid connections in joint.