The paper describes the main directions of non-metallic composite application in concrete reinforcement. The development routes of the structural analysis with composite reinforcement are formulated. The reinforced concrete structure combines the elastic reinforcement element with an adhesive composition having inelastic properties. It is shown that the structural reliability is ensured by adhesion of composite core reinforcement to the concrete. When performing external reinforcement of composite materials, it is necessary to ensure the joint operation of reinforcing elements and the main structure. Today, design methods of concrete structure reinforcement with composite materials do not take into account shear strains in the contact seam. Adhesion of composite material to concrete is indirectly assessed by introducing the service factor of composite material when its design resistance is assigned. Experimental studies concern concrete structures reinforced by bent elements with external reinforcement made of various composite materials. Reinforced concrete beams with A500 and A600 class reinforcement are considered. Test beams are reinforced with fiberglass, coal and carbonates canvases. Some of test beams have U-shaped anchors at the ends and are made of composite materials. Reinforced beams fracture by different schemes: composite peeling due to the adhesive destruction in the area of formation of normal and inclined cracks, compositepeeling with the destruction of protective layer, composite rupture. A part of reinforced concrete beams before the reinforcement are cracked in the stretched zone. Cracks do not affect the load-bearing capacity of reinforced beams.
-The paper outlines different solutions to address the problem of progressive collapse when designing buildings and structures and proposes possible modes of progressive collapse of structural systems. It presents the requirements stipulated by regulatory documents for assessing progressive collapse of buildings. It overviews some studies aimed at the evaluation of progressive collapse of structural systems. Based on the analysis and generalized provisions of normative documents and scientific research, some measures to prevent progressive collapse in design of buildings and other operated facilities are proposed.Keywords -building structural systems, structural safety, brittle failure, progressive collapse, disproportionate collapse, corrosion damage At present, an increased number of devastating natural and human-made disasters have caused the urgent need for applied and theoretical studies of the resistance of structural systems to progressive destruction.The term progressive collapse was first used in the 1970s and today its definition has been offered. Basically, progressive collapse is referred to as a failure that in its final stage (resulting damage) significantly exceeds the initiating local damage that develops in a chain-like manner. The cause of progressive collapse is generally attributed to a sudden destruction of one element, which entails instant stressredistribution on other elements and eventually their collapse. This process develops as long as the structure is completely destroyed or until stress equilibrium in an undestroyed part of a building is reached. It is very important to determine the causes and paths of progressive collapse of a structure when developing methods for protecting buildings and structures. In [12], a descriptive classification of progressive collapse is given. As shown in [8], the design of structural systems with allowance for progressive collapse is possible through the limit state method that requires determination of the mode and nature of failure. The authors propose the following modes of the progressive collapse of structural systems: -Mode 1. Sudden failure of all elements of one of the upper floors, which initiates a subsequent collapse of elements of the upper floors, resulting in a dynamic load on the floors below. Possible causes are attributed to the fall of an aircraft, snow load, gas-air explosion, fires.-Mode 2. Failure of one of the elements of the structural system followed by stress-redistribution on adjoining elements and resulting in the collapse of these elements in a domino effect. The causes are attributed to the impact from a vehicle bumping, a local explosion, a significantly increased operational load, a repeated seismic load on a damaged building.-Mode 3. Loss of resistance by one of the components of a structure or a structure being a segment of the structural system. The causes are attributed to a significantly increased operational load, a change in the load path as compared with the design one.-Mode 4. Transformation of staticall...
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