DETERMINATION OF RELIABILITY OF OPERATION OF MULTI-STOREY FRAME BUILDING AT DIFFERENT VARIANTS OF COLUMN REINFORCEMENT

Abstract

The article considers the issues of variant design of bearing elements of monolithic reinforced concrete crossbarless frame. In particular, the columns, in order to ensure increased reliability of operation of the frame in cases of exposure to various adverse conditions. Such conditions include factors of disproportionate destruction (progressive collapse), which can significantly damage the building. With variant reinforcement of columns, it is possible to achieve a state when the reliability of safe operation of the building will be most pronounced, which may be a recommended measure in the design of multi-storey buildings. It is noted that a rational increase in the reinforcement of columns on the lower floors leads to an increase in the parameter of trouble-free operation of the entire building in emergencies, and this is a sign of increasing the reliability of the entire designed frame of the building. The technology of estimating the reliability parameters is that along the height of the column there are four to five sections with a certain percentage of reinforcement, the maximum percentage (up to 2% -3.5%) is located in the lower zone of the columns, and the smallest % -1.0%) at the top of the columns. This armature is appointed proceeding from statistical calculation of a skeleton and the received internal efforts of M, N, V. In the resulted article as the device of calculation of a 14-storeyed with a cellar of a inhabited frame building the software and computer complex "SCAD" version 21.1.9.5 is used. The emergency situation is predicted in the form of an explosion in the basement of a residential building, which led to the destruction of three columns of the corner of the building and one stiffness diaphragm. Five possible options for column reinforcement were compared (there are 585 columns in the frame of the building). In the first and second embodiments, the reinforcement of the lower two zones was ϻ = 1.57%, the upper two zones ϻ = 0.5%, in the third variant, the reinforcement of the lower two zones was ϻ = 2.57%. In the fourth and fifth variants, the lower two zones had reinforcement ϻ = 1.0%, the upper two zones ϻ = 1.57%. In each of the variants the strength of the concrete changed: for the I and IV variants it corresponded to class C20 / 25; for II, III and V variants the concrete class corresponded to C32 / 40. The parameter of failure-free operation P (t) for the frame in each case was determined by the method of Kudzis AP The calculations showed that the values of P (t) for each option were: I - 0,978; II - 0.986; III - 0.998; IV - 0.969; V - 0.983. Thus, the most effective was the third option (maximum reinforcement of the lower tiers of the columns), which is recommended for implementation in the actual design. Keywords: disproportionate destruction, reliability and safety of operation, reliability indicators, reinforced concrete monolithic framework, variant reinforcement, efficiency of the accepted decisions.