Investigation of the Stress-Strain State of a Steel Column Base Connection for Seismic Regions

Currently, the main type of connection between a steel column and a reinforced concrete foundation is a steel base, which is often economically unprofitable due to its size, number or diameter of anchor bolts. Not only in Armenia, but also in most countries, a steel base is the main type of connection between a steel column and a reinforced concrete foundation. The usage of other types of connections is associated with both new calculation methods and technological problems. The possibility of computation and design of the connection of a steel column with a reinforced concrete foundation in seismically active regions using shear studs is considered in this work, a reinforced concrete section with longitudinal reinforcement is used for this type of connection which ensures a smooth transfer of forces from the column to the foundation. Based on the example of the connection of a single-story industrial building column shows the change in the stress-strain state of the connection under axial force and bending moments for seismic regions. Not only the feature and construction technology of the connection considered in the work, but also proposes a calculation method with future possibility of its subsequent inclusion in the building codes of the Republic of Armenia.

Predicting the Strength of Rectangular Reinforced Concrete Columns Confined with FRP Sheets

A complete reorganization about the behavior of rectangular RC columns confined with FRP sheet is very important to predict the axial compressive strength values of the strengthened rectangular RC columns. That is because the process of strengthening RC rectangular column depending on several parameters that role this type of strengthening. These parameters include the characteristics of the used fiber, the grade of concrete and the geometry of the cross section including the rectangularity aspect ratio, corner radius, and size of specimens. Besides that, using a wide scope of experimental data may affect positively to generalize a model that considers the whole parameters affect the value of the axial strength. So, in this paper a review about parameters that affect the axial compressive strength values of rectangular RC columns was conducted. After that, based on the test results regarding FRP-confined rectangular RC columns available in the literature or conducted by the author, some existing confinement models for rectangular RC columns were assessed. Further, a new model is proposed through regression analysis of the database. A new model is proposed through regression analysis of the database. The proposed model was found to be in good agreement with the test results in the database. Finally, based on the results conclusions were drawn.

Physical-Chemical Studies of the Process of Condensation of a Clinker-Free Binder

The possibility of using a clinker-free binder as an alternative to expensive and energy-intensive Portland cement is being considered. The pozzolanizing effect of volcanic rocks is presented, where along with the binding of calcium hydroxide by silica to hydrosilicates, the binding of calcium hydroxide by “free” alumina to hydroaluminates also takes place. In the process of hardening of the clinker-free binder, the phase mineralogical composition of the formed new formations differs from the new formations that are synthesized during hardening of traditional Portland cement, which explains the difference in their properties. The new formations that are formed during the hardening process of clinker-free cements are mainly low-basic hydrosilicates, and alkaline aluminosilicates give the cast-in-place stone water resistance, frost resistance, waterproofing, etc., in a word, durability. Physical and chemical studies of the hardening process of clinker-free lime-igneous cements have been carried out, which indicates the possibility of replacing the energy-intensive Portland cement with cheaper clinker-free cement.

Strength of Normal and Inclined Sections of Bent Reinforced Concrete Elements with Zone Reinforcement Made of Steel Fiber

On the basis of theoretical and experimental studies, the prerequisites and the method of calculation of bent and compressed-curved reinforced concrete structures with zone reinforcement made of steel fiber, working under static and short-term dynamic loads, are formulated. In the developed method for calculating the strength of normal and inclined sections, a nonlinear deformation model is implemented, which is based on the actual deformation diagrams of materials. The developed calculation method is brought to the program of calculation of reinforced concrete structures with zone reinforcement of steel fiber under short-term dynamic loading, taking into account the inelastic properties of materials. The numerical studies made it possible to determine the influence of various parameters of steel-fiber reinforcement on the strength of reinforced concrete elements. To confirm the main results of the developed calculation method, experimental studies of reinforced concrete beam structures reinforced with conventional reinforcement and a zone steel-fiber layer are planned and carried out. Experimental studies were carried out under static and short-term dynamic loads. As a result of the conducted experiments, data were obtained that characterize the process of destruction, deformation and cracking of steel-reinforced concrete elements under such types of loading. The dependences of changes in the energy intensity of reinforced concrete structures with zone reinforcement made of steel fiber in the compressed and stretched cross-section zones under dynamic loading are obtained. The effectiveness of the use of fiber reinforcement of normal and inclined sections of bent and compressed-curved elements to improve the strength and deformative.

Experimental Study of Hysteresis in Clayey Soils under Compression

The energy dissipation for one cycle of clay soil deformation over the area of ​​a hysteresis loop under conditions of one-dimensional deformation has been experimentally studied. Several series of trials were carried out under different conditions of soil density and moisture and different loading modes. It was established by the experiments that after several cycles of loading and unloading of the samples, the transient process of the closed loop formation ends and certain dependences of stress on deformations are established in the sections of the ascending and descending branches of the hysteresis loop. To determine these dependencies, rheological relations obtained directly from the hysteresis loop by approximating the arcs of its contour have been used. By integrating the approximating rheological dependences along the branches of the loop, the dissipated energy per deformation cycle has been obtained as a function of cyclic deformation amplitude, measured by the area of the hysteresis loop. Experiments on obtaining a hysteresis loop were carried out on a compression device with a cyclic sample. Samples with different states of density and moisture content were produced by consolidating a paste having yield point moisture under different pressures. Several series of experiments have been carried out. In the first series, soil absorption coefficients were derived for different states of density-moisture at different loading rates. In the second series, three types of clayish soil (clay, loam, sandy loam) were studied. Dissipation coefficients have been found out for the indicated soils. In the third series, three types of clay soil were tested under different conditions of density and moisture. The dissipation coefficients have been obtained. In the fourth series, the dependences of the absorption coefficient on the amplitude value of the cyclic stress for three types of clay soil were disclosed. It was found that a change in the loading rate within the range from 0.05 MPa to 0.2 MPa does not lead to the significant change in the absorption coefficient, the increase in the number of clay fractions in the sample leads to an increase in the absorption coefficient, a change in the amplitude of cyclic loading (in the indicated range of change) does not affect the absorption coefficient.

Comparative Analysis of the Use of Thermal Insulation Materials Depending on Climatic Conditions and Comfort Microclimate Supply Systems

The use of thermal insulation materials to reduce the heating and cooling demand of the building in order to provide energy efficiency is the main solution. But there is a wide range of these products on the market and, therefore, the choice and application of these materials is a rather difficult task, since many factors must be taken into account, such as environmental safety, cost, durability, climatic conditions, application technology, etc. Basically, comfort microclimate systems are designed based on normative standards, where the thickness of the thermal insulation material is selected depending on the required heat transfer resistance. These values are calculated taking into account climate conditions, that is the duration of the heating period, as well as taking into account sanitary and hygienic requirements. This article discusses the thermal performance of building materials, and also provides a comparative analysis of the use of thermal insulation materials depending on climatic factors and on the system providing comfort microclimate. Based on the calculations by mathematical modeling and optimization, it is advisable to choose the thickness of the thermal insulation, taking into account the capital and operating costs of the comfort microclimate systems. Comparing the optimization data with the normative one, the energy efficiency of the building increases by 50-70% when applying the optimal thickness of the thermal insulation layer, and when the thermal insulation layer is increased, the thermal performance of the enclosing structures has improved by 30%, which contributes to energy saving.

Modeling a Weak Foundation in Interaction with Reinforced Sand Piles under a Low-Rise Building

One of the ways to increase the bearing capacity and stability of a water-saturated base by introducing a sand pile vertically reinforced along the contour with geosynthetic material (geogrid SSP 30 / 30-2.5) is experimentally substantiated. This constructive solution is used in low-rise construction. For the theoretical substantiation of the suggested method, it is proposed to model the interaction of a weak foundation and a reinforced sand pile on the basis of the linear theory of viscoelasticity. Calculation of vertical displacements of the pile and comparison with the results of in situ experiments is presented.

Development of Dry Sand-Lime New Multicomponent Mortars into the Historical Cultural Monuments Applied on Local Raw Basis

The visual and instrumental research of the technical condition of historical cultural constructions and their stone additions, documentation of their existing damages, as well as complex development and implementation of further collapse preventing measures and construction durability ensuring measures are presented. Application of processed sand-lime complex mortars based on local raw is offered for blockage of composition cracks during the rehabilitation work taking into consideration some averaged indices of Mape Antique I, Italian “Mapey” firm, similar injection mortar orientation basic characteristics (physical and mechanical characteristics, leakage, viability) and complete laboratory detailed examination results of the component mineralogical and physical and mechanical characteristics of the substances originally used in the construction. The data on local based raw processed sand-lime construction complex mortars (blockage mortar, injection mortar) physical and mechanical characteristics, thermographic dilatometric properties dependence on composition and fastening conditions of mortars are presented

The Influence of Cement Grain Structure on Physical and Mechanical Properties of Cement

The paper presents the study of morphological characteristics of cement particles and reveals the influence of the structure of the cement grain composition on the physical and mechanical properties of cement. The following portland cements produced by “Hrazdan Cement Corporation” LLC, which have 52,5 MPa and 42,5 MPa compressive strength limit and hydraulic additives up to 20% and over 20% have been used for the experiment: CEM II/ A-P 42,5N, CEM II/ B-P 42,5N, CEM II/A-Q 42,5N, CEM II/B-Q, CEM II/A-L 42,5N, CEM II/B-L 42,5N, CEM II/A-M 42,5N, CEM II/B-M, CEM III/A-S 42,5N and CEM III/B-S 42,5N. Grain distribution in all the samples has been studied using a CILAS laser analyzer. Microscopic analysis of all the fractions has been carried out with the help of James Swift optical microscope. The given grain compositions have undergone chemical analysis in compliance with the requirements of interstate ISO 5382-2019 and ASTM C114-18 standards. Experimental studies and analyses show that the cements with microsilica have the highest value of water-cement ratio-W/C = 0.7, the highest by volume compression are the cements with volcanic slag-4 mm, the beginning of the bonding period is the longest in case of limestone cements - t = 140 minutes, followed by microsilica cements, and in third place there are artificial slag cements, the results of which are as follows: 130; 124 minutes. The summarized data show that microsilica cements have the highest compressive strength limit among the cements having the same percentage of additives-48.87 MPa.

Modification of Irind Mine Pumice Surface

In the last decade, a continuous increasing research activity is focused on the surface modification of natural porous materials for the efficient removal of oil contaminants from water. A continuous in-situ oil/water separation technique for oil spill cleanup had been designed using surface modified Irind mine pumice as a sorbent. Irind mine pumice is an aluminosilicate rock, with well-developed porosity, mechanical strength, high buoyancy, chemically inert and eco-friendly, therefore it must exhibit certain water-and oil absorption capacities. The modified pumice absorbs a broad variety of oils and organic solvents with high oil absorption capacity and negligible water take-up at both static and dynamic conditions. Irind mine pumice have been used with grain sizes ranging from 2.5 ... 5.0 mm. Oligomethylhydride siloxane is used as a modifier.