REPAIR OF MASONRY AFTER DYNAMIC IMPACTS. CALCULATION AND DESIGN METHODS

Civil engineers are encouraged to apply novel techniques, to improve and to adapt well-known methods amid the reality of modern life. An impressive number of restoration and strengthening techniques are developed for unreinforced masonry (URM) material well-known for centuries. Masonry may need restoration and strengthening due to errors made in the course of design, construction or long-term operation of buildings and structures. Besides, masonry needs strengthening in seismic areas. Strengthening of masonry structures, subjected to dynamic impacts during military operations, was initiated after the Second World War. Construction technologies advanced considerably over the last seventy years, and today shotcrete, a widely known strengthening technique, can be applied for a good reason. This article addresses shotcrete as a method for restoring masonry damaged by explosion impacts. Results of the laboratory testing of materials and parts of structures are provided together with improved methods of analysis. The methodology for computer-aided analysis of buildings is also presented, taking into account the staged nature of work and the ability of external shotcrete to support loads. Practical restoration of buildings is addressed in the conclusions section, and conclusions are drawn there

Plasticity of anchors in damaged by earthquake concrete base

Most frequently used types of anchors were subjected to experimental studies to obtain valid data on post-installed anchors, such as mechanical anchors (wedge expansion anchors, undercut anchors); bonded anchors (with epoxy resin) and bent cast-in-place anchors. The authors studied the effect of an earthquake-induced damage (plastic deformation) of a concrete base and multi-cyclic dynamic loads, similar to seismic ones, on plasticity of anchors. Plastic phase deformation in case of reinforced concrete base was simulated as a system of cracks of different opening width. The results of the research show that increase in the width of the crack opening from 1.5 to 3.0 mm leads to a decrease in the values of the plasticity factors. Dynamic loading does not lead to a significant change in the plasticity factor related to static loading for all failure mechanisms, except for the bond failure. On the base of obtained results reduction factors of seismic loads may be determined for further calculation of anchor joints subjected to seismic impact

BOUT THE PROBLEM OF ANALYSIS RESISTANCE BEARING SYSTEMS IN FAILURE OF A STRUCTURAL ELEMENT

This paper focuses on the methods of calculating load-bearing systems in the case of a failure of a structural element. This kind of failure makes it necessary to assess further behavior of the structure with a possibility of the progressive collapse development. The stress-strain state analysis of a load-bearing system in the case of a failure of a structure is carried out by two main methods – static and dynamic calculation. It is shown that the static calculation (quasi-static analysis using the dynamic amplification factor) is not a universal method. This paper justifies the application of the direct dynamic calculation in the mode of direct integration of motion for the design analysis of load-bearing systems with high rigidity stories (protection structures for a load-bearing system). It also gives recommendations for selecting parameters of the direct dynamic calculation in the case of a failure analysis of a bearing structure

Geometric characterization of solid ceramic bricks for construction in Ecuador

In Ecuador, about 95.9% of dwellings are built with masonry, however the local production of bricks does not meet technical standards and there is no scientific research on its geometric characterization and the technical state of their production. The geometric characterization of bricks is essential for the standardization of materials and constructions and allows the design of structures with a higher degree of accuracy. This research, conducted in 12 provinces of the 3 continental regions of the country, where 79% of the buildings are concentrated, studies for the first time the geometric characteristics of solid clay bricks in Ecuador. The results show that 67% of the brick production in Ecuador is artisanal and 98% of the factories do not comply with the technical standards for brick production. The authors present the characteristic dimensions of solid bricks produced in different regions of Ecuador. The results show a high variation in brick dimensions depending on the region, and even in a same province the dimensions depend on the factory, since its production does not comply with any standard. Ecuadorian standards regulating brick geometry need to be updated taking into account the real characteristics of the national brick production

Failure Mechanisms and Parameters of Elastoplastic Deformations of Anchorage in a Damaged Concrete Base under Seismic Loading

The article addresses mechanisms of anchorage failure in a concrete base studied within the framework of physical experiments. The authors investigated the most frequently used types of anchors, such as the cast-in-place and post-installed ones. The anchorages were studied under static and dynamic loading, similar to the seismic type. During the experiments, the post-earthquake condition of a concrete base was simulated. Within the framework of the study, the authors modified the values of such parameters, such as the anchor embedment depth, anchor steel strength, base concrete class, and base crack width. As a result of the experimental studies, the authors identified all possible failure mechanisms for versatile types of anchorages, including steel and concrete cone failures, anchor slippage at the interface with the base concrete (two types of failure mechanisms were identified), as well as the failure involving the slippage of the adhesive composition at the interface with the concrete of the anchor embedment area. The data obtained by the authors encompasses total displacements in the elastic and plastic phases of deformation, values of the bearing capacity for each type of anchorage, values of the bearing capacity reduction, and displacements following multi-cyclic loading compared to static loading. As a result of the research, the authors identified two types of patterns that anchorages follow approaching the limit state: elastic-brittle and elastoplastic mechanisms. The findings of the experimental research allowed the authors to determine the plasticity coefficients for the studied types of anchors and different failure mechanisms. The research findings can be used to justify seismic load reduction factors to be further used in the seismic design of anchorages

Behavior of Anchors Embedded in Concrete Damaged by the Maximum Considered Earthquake: An Experimental Study

The article presents experimental tests carried out to investigate the effect of crack width (0.4, 0.8, 1.5, and 3.0 mm) on the behavior of anchor bolts under static and dynamic loading. Ultimate loads for anchors reached 220 kN depending on the anchor type, the diameter, and the crack opening width. Mechanical and bonded anchors were studied as the most frequently used anchor types. Two states of concrete, resulting from the design earthquake and the maximum considered earthquake, were simulated in the course of the experiments. Within the framework of the study, dependencies between the bearing capacity and stiffness of anchorages, on the one hand, and the level of concrete damage, on the other hand, were identified for different types of anchors. The data, generated in the course of the study, were used to identify the types of anchorages recommended for embedment in seismic areas. Plasticity coefficients and seismic load reduction coefficients were determined for different types of anchors and levels of concrete damage as a result of experimental studies. Reduction coefficients can be contributed to the design of anchorages embedded in seismic areas

Deformation and power characteristics monolithic reinforced concrete bearing systems in the mode of progressive collapse

The paper considers the question of substantiating the choice of criteria for limiting states of monolithic reinforced concrete bearing systems for the regime of progressive collapse. Based on the results of computational and theoretical studies, structural elements and structural units of monolithic reinforced concrete buildings are determined, the destruction of which occurs first of all in the event of a failure of the vertical bearing structure. It is established that the destruction of such structural units and structural elements leads to the initialization of the process of progressive collapse. A computational and theoretical analysis has been performed to determine the ultimate deformation effects or load values according to the criteria for the bearing capacity of crutial units of monolithic reinforced concrete systems with different span sizes. It is established that as a basic criterion for estimating the stress-and-strain state of monolithic reinforced concrete structures for the mode of failure of a vertical bearing structure, the relative deformation amount corresponding to the formation of the “fracture” zone of the retaining section of the overlap under the action of transverse forces can be adopted

Plasticity of anchors in damaged by earthquake concrete base

Most frequently used types of anchors were subjected to experimental studies to obtain valid data on post-installed anchors, such as mechanical anchors (wedge expansion anchors, undercut anchors); bonded anchors (with epoxy resin) and bent cast-in-place anchors. The authors studied the effect of an earthquake-induced damage (plastic deformation) of a concrete base and multi-cyclic dynamic loads, similar to seismic ones, on plasticity of anchors. Plastic phase deformation in case of reinforced concrete base was simulated as a system of cracks of different opening width. The results of the research show that increase in the width of the crack opening from 1.5 to 3.0 mm leads to a decrease in the values of the plasticity factors. Dynamic loading does not lead to a significant change in the plasticity factor related to static loading for all failure mechanisms, except for the bond failure. On the base of obtained results reduction factors of seismic loads may be determined for further calculation of anchor joints subjected to seismic impact

Modelling post-critical deformation processes of flat reinforced concrete elements under biaxial stresses

This paper examines the issue of mathematical modelling of local destruction processes of flat reinforced concrete structures beyond design basis impacts. Analysis of the peculiarities of the local failure mechanisms, which are formed in wall concrete structures, was conducted. The paper shows that the processes of post-critical deformation of flat concrete structures occur through several mechanisms with the relevant strength criteria. The method of post-critical deformation modelling of reinforced concrete structures under biaxial stresses is proposed and justified. The modelling is conducted by the gradual change of the analysis model in the areas of failure using finite elements with stiffness parameters, which corresponds to the conditions of interaction between structure parts separated by a crack

Modelling post-critical deformation processes of flat reinforced concrete elements under biaxial stresses

This paper examines the issue of mathematical modelling of local destruction processes of flat reinforced concrete structures beyond design basis impacts. Analysis of the peculiarities of the local failure mechanisms, which are formed in wall concrete structures, was conducted. The paper shows that the processes of post-critical deformation of flat concrete structures occur through several mechanisms with the relevant strength criteria. The method of post-critical deformation modelling of reinforced concrete structures under biaxial stresses is proposed and justified. The modelling is conducted by the gradual change of the analysis model in the areas of failure using finite elements with stiffness parameters, which corresponds to the conditions of interaction between structure parts separated by a crack