Analysis of the mechanism of transition to the limit state of Series 111 residential buildings during the 1988 Spitak earthquake

Abstract

The study aimed at investigating the reaction of a residential building (Series 111 nine -story block section ) to seismic impacts that can lead to destruction of the building . The article presents the results of the retrospective analysis of the seismic resistance of nine -story block sections in the city of Gyumri (Leninakan) under the influence of the 07.12.1988 Spitak earthquake . The seismic resistance of the block section wa s calculated using the ‘ pushover analysis ’ method . D irect dynamic calculation s were performed using a model of complex elastoplastic deformation of a mechanical system with two degrees of freedom. A n external impact was represented by the earthquake records taken at the Ghukasyan station . M acroseismic survey data collected after the 1988 earthquake are presented. T he block sections of Series 111 multistory residential buildings were designed by the Armenian research and design institutions ArmNIISA and Armgosproekt in 1975 for construction in the Armenian Republic on sites with seismicity of 7–8 points. V ibration tests were conducted to test the strength of a nine -storey block section in Yerevan in 1976, and it was discovered that the actual seismic resistance of the building d id not comply with the current earthquake-resistant construction standards. However, the test results were ignored . O n December 7, 1988 , the earthquake took place, and the Series 111 buildings collapsed in the cities of Gyumri (Leninakan) and Vanadzor (Kirovokan). In the State Commission Report regarding the Series 111 design , it was concluded that considering the damage due to the violations of the design and construction standards and taking into account the inspection calculations , the accepted design solutions of the residential buildings d id not meet the requirements of the regulatory documents for buildings designed to sustain seismicity of 8 points. Such design should not be used for seismic areas and must be critically revised . The retrospective analysis performed by the authors of th is article on the basis of experimental data not only confirmed the conclusions of the State Commission, but also made it possible to establish a mechanism for the transition of Series 111 block-section s to the limit state. Unfortunately, the state management of the construction industry failed to use this information and did not take any urgent preventive actions. In fact, t he authorities of the USSR supported the position of the Gosstroy of Armenia and allow ed them to continue the construction of Series 111 residential buildings with minor changes. I t was impossible to prevent the Spitak earthquake, but proper preventive actions could have reduced the amount of social and economic damage incurred due to the earthquake . The consequences of obvious design and construction errors discovered 12 years before the Spitak earthquake were ‘ written off ’ and explained by the natural disaster, including underestimated standard seismicity, features of the engineering-geological s ettings , and the unfavorable spectr um of the actual impact. T housands of people lost their life, and huge material damage was caused due to the loss of Series 111 residential buildings ( 300 000 square meters) . Such was the price of professional incompetence and departmental ambitions.