STRESS-DEFORMED STATE OF REINFORCED CONCRETE U-SHAPED FRAMES CALCULATED BY THE FLEXIBLE STAGE OF WORK AND BY THE MOMENT REDISTRIBUTION STAGE

Abstract

Reinforced concrete U-shaped frames are widely used in the construction of various buildings and structures. During new construction, they are planned to be used for protective structures of civil protection. Frames belong to statically indeterminate systems, the static calculation of which is currently performed as elastic systems. In real operating conditions, due to the manifestation of plastic properties of concrete and reinforcement, the determined forces can be redistributed between the normal sections of the frame elements and deviate from the values ​​calculated for the frames as elastic systems. Normative documents recommend that statically uncertain reinforced concrete structures be calculated taking into account such a process.

The moment redistribution in statically indeterminate reinforced concrete structures has been studied for several decades, but there is no perfect method for calculating frames today. Regarding this, it is relevant to research the stress-strain state of cross-sections of frame elements calculated by two methods and determining their advantages and disadvantages.

The article has the results of theoretical studies of the stress-strain state of a reinforced concrete U-frame with a span of 12 m and a height of 4 m, loaded by concentrated vertical forces in the span and at the crossbar nodes. The goal of the research was that the stress-strain state of the cross-sections of the crossbar in the middle of the span and at the connection nodes with the risers was determined using the deformation method. Bending moments in these cross-sections were previously determined according to the elastic stage of the frames with the redistribution of forces.

On the basis of the conducted research, the following conclusions were made: taking into account the possible redistribution of forces in the design of U-shaped reinforced concrete frames makes it possible to create a more uniform stress-strain state in the cross sections, which contributes to the simplification of the reinforcement of the frames, the reduction of the nomenclature of the carcass, the simplification of the manufacturing technology and the achievement of the costs of the working carcass by 12% or more; it was confirmed that the artificial redistribution of forces between sections in U-shaped reinforced concrete frames does not negatively affect the crack resistance and stiffness of their elements. In such frames, cracks are evenly distributed on the upper and lower surfaces of the crossbar, which also improves their aesthetic perception; for a final positive assessment of the calculation of reinforced concrete U-shaped frames, it is necessary to perform their experimental studies in parallel with identical frames calculated as elastic systems.