After destructive Spitak earthquake of December 7, 1988 important scientific and engineering problems and questions appeared in the sphere of construction, in the first place referring to overestimation of the seismicity of the territory of the republic and providing required level of seismic resistance of newly erected and also damaged buildings and constructions, including masonry bearing walls. It should be noted, that masonry buildings of various number of storeys and structural decisions are the basis of existing urban and rural building in the republic. According to predicted data during many years natural stone (mainly tuff) will be one of the main wall materials for the mass construction. Because of increasing of normative seismicity of the territory of the republic for 1-2 points, new conceptional approaches for seismic zoning, defectiveness of Building Codes functioned before /1-3/ for the buildings with bearing walls of local atone materials and others there was a need in the development of new Republic Codes on Earthquake Engineering and masonry structures taking into account the results of analyses of the consequences of the earthquake. SNFA II-2.02-94 "Earthquake Engineering. Standards of Design" and SNPA IY-13.01-96 "Masonry and armo-masonry structures" were developed and used at present, in which material changes and additions have been done in comparison with earlier current standards. The following vies and circumstances ware taken into account for the development of Codes: the main properties and features of all types of local stone materials and masonry systems were not reflected in Building Codes functioned before in the Republic having no analogues outside the Republic; in projects of buildings and constructions it is necessary to note special requirements and technology of the performance of some kind of works being shown in independent Codes after Spitak earthquake of December '7, 1988 in Armenia the restoration (strengthening) of damaged buildings at disaster zone and also increasing seismic resistance of the buildings outside that zone became the actual problem - because of general increasing of design seismicity of the territory of the republic. Meanwhile, the chapter on restoration and strengthening of masonry structures was lack in Union Codes functioned before; for the past few years after the earthquake, separate republic normative and instructive documents were developed. Let's in brief pay our attention to main principles of new Republic Building Codes on Earthquake Engineering. Specifically, in SNPA 11-2.02-94 the conception of the category of the masonry for the resistance to seismic effects is lack and depending on applied method of increasing their seismic resistance the classification of masonry is given by its structural decisions (types), namely: 1. The masonry of complex structure with vertical reinforced concrete cores by compulsory joint with anti-seismic belts in all storeys and foundation. In addition for the provision of joint work under the load of the masonry and reinforced concrete core, the last should be bined with-the wall masonry in 60 cm ( two rows of masonry) by height with reinforced nets passed through the body of cores and appeared on both sides at a distance of 60 cm. The walls of complex structure can be designed both with cores forming a distinct frame (I a) and also with strengthening walls and partitions, that is to say, forming indistinct frame (Ib). 2. Masonry of vertical and horizontal reinforcement applied by design. Vertical reinforcement should be anchored in antiseismic belts and foundation. Horizontal reinforcement (as a mesh) should be fixed at the pace not more than 60 cm by height; 3. The masonry being reinforced by horizontal steel meshes at the pace not more than 60 cm by height according to its design. 4. The masonry in which structural reinforcement of conjugations and intersections of walls is performed by steel grids. Besides the grids are fixed in the masonry of buildings at a distance of 90 cm arranged at the first, GO cm - at the second and 30 cm at the third seismic zones. In all cases for the masonry of all types minimum value of temporary masonry resistance to axial tension along unbinded sections (normal adhesion of the mortar and, stone) is fixed which is equal to 120 KPa(1,2 kgs/cm(2)); the requirement for the arrangement of concrete layer of the thickness 8 cm on the top of the wall masonry of each storey being reinforced by grids ( for the floors of precast reinforced concrete panels) is suggested; structural decisions for the floors poured in place by precast reinforced concrete slabs (panels) are given and depending on applied method of pouring the acceptable pace between reinforced concrete frames is shown, which substitute cross and longitudinal walls; appropriate structural and other requirements are given for the applied wall materials and their volume mass, arrangement and rigidity of walls and others. Specifically the following requirements are introduced: the type of the masonry and the material of walls within the building (section), as a rule, should be the same. The use of different structures or materials is accepted for the performance of the following conditions: horizontal rigidity of walls of each storey shouldn't differ from the same of adjacent storey for more than 20%; wall materials within one storey should be similar; So. during the period after Spitak earthquake the basis of republic normative documents where actually all normative data are reflected for the design, erection and acceptance of newly constructed and restored buildings with bearing walls of local masonry under seismic conditions of the republic. Observance of normative requirements of SNPA II-2.02-94 and SNPA IY-13.01-96 will provide the desired level of seismic resistance of erected and operated buildings with bearing masonry walls in Armenia.
