Monolithic Slab Research Articles

НЕСУЩАЯ СПОСОБНОСТЬ МОНОЛИТНЫХ ЖЕЛЕЗОБЕТОННЫХ ПЛИТ НА ПРОДАВЛИВАНИЕ ПРИ СТАТИЧЕСКОМ И ДИНАМИЧЕСКОМ НАГРУЖЕНИИ

Modern design standards of developed countries have significant differences in the design provisions for determining the bearing capacity of monolithic reinforced concrete slabs for punching and do not fully take into account the features of design solutions and operating conditions. The available design positions are designed for the static loading mode of structures. The stress-strain state of plates for punching under dynamic load is currently little studied, and as a result, there are no methods for determining the bearing capacity of plates for punching under dynamic loading. The article presents the results of experimental and theoretical studies of the bearing capacity of plates under static and dynamic loads. The methodology of experimental studies and the design of prototypes, equipment for conducting power tests are described, the results of studies on the penetration of fragments of the interface of flat reinforced concrete monolithic slabs with a column under dynamic and static loading are presented. A comparison of the destructive load for samples tested under dynamic loading with the destructive load for samples tested under static load is presented. The factors affecting the strength of the plates during punching under dynamic loading are determined. Proposals have been developed to improve the methodology for calculating the strength of flat reinforced concrete slabs when pushing through static and dynamic loads.

ESTIMATION OF VARIABILITY OF STEPS OF ARMATURE IN A MONOLITHIC REINFORCED CONCRETE COVER OF A TOWER INDUSTRIAL CONSTRUCTION

The work considers one of the possible reasons for reducing the operational reliability of monolithic thin-walled load-bearing reinforced concrete structures of existing industrial structures in relation to their design solution. As this reason is considered the variability of distances between axes of cores of working inspectedarmature of such designs is quite common.Comparison of design solutions with the qualityof construction and installation work makes it possible to identify the influence of unaccounted factors in the design of monolithic thin-walled reinforced concrete structures, which reduce their serviceability due to variability of concrete strength characteristics and actual longitudinal and transverse reinforcement due to variability of workingsteps. While processing the results of the survey ofmonolithic reinforced concrete thin-walled structures, which perceive the efforts of different levels,the question arises: which step of the working reinforcement, from a large number of actually measured steps, to choose in verified calculations –average or maximum, with extras.In the current norms, an indicator as the averagevalue of concrete strength for the calculation ofreinforced concrete monolithic slab structures doesnot appear, but is used as a statistically reasonablevalue of concrete strength, which takes into account its normalized variability with 95% security.Regulatory documents statistically estimates thevariability of reinforcement strength. At the sametime, they do not take into account the variabilityof the actual reinforcement of monolithic reinforced concrete structures, which is the subject forreconstruction of additional loads, but they aremade without observing the design distances between the reinforcement in these structures.When performing verified calculations of suchstructures for different design situations, to develop working designs for overhaul, reinforcement,reconstruction or dismantling, it is necessary todetermine which actual step of the working reinforcement should be taken with other defined design parameters of the structure.The authors instrumentally investigated and statistically analyzed the data of reinforcement of themonolithic reinforced concrete shell of the towerstructure, which made it possible to reasonablyaccept the values of the reinforcement steps in thetest calculations.

Stiffness of Post-Tensioned Girderless Floor With Different Column Grids

The paper considers models of monolithic flat floor slabs with five spans in both directions. The cell sizes are 6×6m, 6×9m, and 6×12m. The calculation method is based on the application of temperature load and rope modeling of rod elements. It is shown that post-stressing should be used for slab side lengths over 7 m, as the installation of pre-stressed reinforcement for shorter lengths is less feasible and causes high economic costs.

Investigation of force redistribution in the foundation slab of complex configuration in low-rise buildings

A study of the redistribution of forces in the foundation slab of a complex configuration in the plan for the installation and non-installation of deformation seams between blocks of low-rise building using numerical simulation by the finite element method (FEM). Two variants of the foundation slab are considered - with the installation and non-installation of deformation seams.
 Due to the large difference in loads in different rooms and areas of the building to prevent uneven deformation of the bases as a foundation was adopted monolithic reinforced concrete foundation slab type with a thickness of 400 mm. The frame of the building is monolithic reinforced concrete with vertical load-bearing elements in the form of columns, pylons and walls, which are united by monolithic floor slabs, which create stiffness disks.
 The basis for the slab foundation are sandy soils dusty and small, medium density with lenses of plastic sands.
 After the calculations, the stress-strain state (SSS) of the foundation structures of the building was analyzed, namely: subsidence of the foundation slab, redistribution of bending moments in the foundation slab in the X and Y directions and selected the appropriate area of working reinforcement of the foundation slab. As a result of calculations, it was found that the presence of deformation seams significantly affects the redistribution of forces in the foundation slab of complex configuration in low-rise buildings. When installing them, there is an increase in bending moments in areas away from the junction of building blocks from 5% to 20%. A significant increase in bending moments occurs in the joint zone of the building blocks when installing deformation seams. In these areas, an increase in bending moments from 10% to 3 times, which significantly affects the cost of reinforcement of the foundation slab. It is also shown that the device of deformation seams practically does not affect the maximum values of subsidence of the foundation slab.
 Therefore, for low-rise buildings it is recommended to arrange a version of the foundation slab without deformation seams.

Experimental study and methodology for calculating the punching shear strength of reinforced concrete slabs

The results of studies on experimental samples of the strength and deformability of reinforced concrete slabs during punching are presented. The experimental samples were fragments of the nodes of the coupling of columns and monolithic slabs of the girderless frame. The variable parameter was the shape of the column cross-section. It is established that with an increase in the ratio of the sides of the column section , an excess of the calculated strength values over the experimental values is observed. The noted trend shows that the normative calculation method does not take into account the actual nature of the distribution of forces in the plate punching area. A technique is proposed to take into account the influence of the ratio of the sides of rectangular column section and the ratio of the side of column section to the working height of plate section on the plates punching shear strength. The comparison of experimental and calculated values of the punching shear strength of reinforced concrete slabs, obtained according to various normative methods and according to the proposed methodology, is carried out.

MONITORING OF MONOLITHIC OVERLAP WITH PRESTRESSED BEAMS

A method for monitoring the stress-strain state of building structures has been developed. A technical inspection of monolithic slab structures using electronic beacons for crack control was carried out. The basis of the monitoring system of monolithic reinforced concrete structures is a fiber-optic technology based on the control of changes in the parameters of the light wave. For the experimental part, a scheme for testing fiber-optic sensors has been developed.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ПЛИТ НА ПРОДАВЛИВАНИЕ ПРИ ДИНАМИЧЕСКОМ НАГРУЖЕНИИ

the issues of strength and deformability of reinforced concrete floors during punching remain insufficiently studied at present, despite the available publications in the technical literature. This article presents the results of experimental studies on punching of fragments of conjugation of flat reinforced concrete monolithic slabs with a column under dynamic loading. The purpose of these studies was to obtain experimental data on the stress-strain state of a fragment of a monolithic floor during dynamic punching with varying thickness and class of concrete, to reveal the failure patterns of experimental samples, and to obtain new experimental data. A setup for dynamic testing is described. Comparison of breaking load for specimens tested under dynamic loading with breaking load for specimens tested for static load is presented. The angles of inclination of the punching shear pyramid under static and dynamic loading are indicated.

Study on Flexural Behavior of Bubble Deck Slab Strengthened with FRP

Bubble deck sheets are a technique to remove all the concrete from the center of the floor sheet, thus reducing structural dead weight. Inefficient concrete in the center of the slab replaces the high-density hollow spheres (HDPE). The weight decreases and increases efficiency in the plane. Because the bubble deck slab consumes less material, it reduces greenhouse gas emissions into the atmosphere, enabling us to achieve green construction. The benefits include reduced energy consumption - both in production and transportation - and emissions - from production and transportation, mainly CO2 - as well as material, load, and value reduction. It is also a green technology. Reduce the volume of concrete in the bubble deck technology by substituting locally available spherical bubbles. This implies that the monolithic slab element is used to determine load carrying, deformation (deformation), crack, and failure properties in the plant and is subjected to static gravity loads. The resulting conclusions will be used to define the failure mechanisms, and the benefits of the bubble deck slab will be highlighted.

Experimental and theoretical study of the strength of plates for pressure

Introduction. The issues of strength and deformability of reinforced concrete floors during punching remain insufficiently studied at present, despite the numerous publications in the technical literature. This article presents the results of experimental studies of the punching shear strength of fragments of conjugation of flat reinforced concrete monolithic slabs with a column under static loading. The purpose of these studies was to obtain experimental data on the stress-strain state of a fragment of a monolithic floor during static punching and to develop a spatial model based on the finite element method with subsequent numerical studies. Materials and methods. Experimental studies were carried out on a test bench. The characteristics of prototypes are given: dimensions, reinforcement, class of concrete and reinforcement. A test setup is described. For the numerical simulation of the slab-column interface, the ATENA software package was used, which allows for physically and geometrically nonlinear calculations of reinforced concrete structures, taking into account the real work of the materials used to create experimental models. Results. Comparison of the results for the breaking load, obtained during the experiment, with the results of numerical modeling by the finite element method and with the results of calculations using the methods of SP 63.13330.2018 and Eurocode 2. The diagrams of the distribution of deformations in reinforcement and concrete, breaking loads and patterns of distribution of cracks in the samples are obtained. Conclusions. The analysis of experimental and numerical studies made it possible to formulate the conditions for the pun­ching shear strength of flat slabs with longitudinal reinforcement and to give recommendations on the strength calculation under central loading.

Self-stressed steel-reinforced concrete floor slab stress-strain state numerical analysis taking into account the concreting stages

In steel-reinforced concrete floor slabs, structurally ensuring the joint operation of monolithic reinforced concrete slab and steel crossbars, a successful combination of its components positive qualities is realized at a high level: compression forces are perceived by monolithic slab, and tensile forces by steel beams. Reinforced concrete slabs in such structures have a relatively equal weight with a payload on interfloor slabs for public buildings. Having effectively developed the sequence of concreting the slab through the span in two stages, it is possible to create pre-stressing in the floor steel crossbars, located in the spans of the second concreting stage, and in monolithic reinforced concrete slab of the first concreting stage. In this sense, the term “self-stressed” is used in this work. By creating pre-stresses in the steel crossbars of the floor, it is possible to reduce their cross-section or to increase their span and to achieve savings in metal costs on the building frame. Pre-stressing of the monolithic reinforced concrete slab of the first concreting stage in the opposite to operational bending form, will increase crack resistance of the specified sites of a monolithic overlapping and will give the chance to reduce its reinforcement.

Influence of monolithic plate manufacturing technology on physical and mechanical characteristics of the coating

During operation in an open atmosphere, bridge structures are exposed to extreme natural and climatic conditions, chemicals and constantly changing temporary and dynamic loads. Bridge structures built in the 60s and 80s of the last century have approached a critical situation and require major repairs. Goal. The most vulnerable elements of the bridge structure are the upper part of the concrete span structures (slab) and waterproofing, so there was a question of strengthening the slabs and replacing the waterproofing layer. Metodology. When forecasting the durability of bridge structures, it is necessary to take into account the influence of temperature and humidity and climatic factors together with force factors. Result. The real necessity of mounting a monolithic reinforced concrete slab for strengthening a top slab of girder structures and putting a new waterproofing layer on it is shown. Originality. The technology of spraying a waterproofing layer that allows to waterproof a surface of any complexity evenly and reliably is offered. Practical value. Overhead monolithic slab enhances the bearing capacity of the power elements of the bridges and can be increased by 1.5–2 times.

Method of manufacturing reinforced concrete floor slabs using non-removable void formers

The article provides a critical analysis of the work on the manufacture of monolithic reinforced concrete, relying on the contour, hollow floor slabs using box-shaped, spherical and tubular hollow-formers. The paper proposes a method of manufacturing monolithic reinforced concrete hollow floor slabs based on the contour using circular tubular polyethylene cardboard holders of rectangular or square shape in plan. The subject of the research is a method of continuous production of reinforced concrete floor slabs with round voids based on the contour using non-removable void formers, their technical and economic efficiency of solutions to reduce the weight of monolithic floor slabs by reducing the resources for their production. The technical and economic feasibility of manufacturing monolithic reinforced concrete floor slabs based on the contour with the use of non-retrievable void formers from round pipes of square and rectangular shape in plan has been substantiated. Materials for the manufacture of void former are proposed. The technical result has been determined - the maximum weight reduction of the proposed hollow core slabs compared to solid slabs.

Winter concrete: problems and solutions

Monolithic construction in winter faces problems of concrete strength set at negative ambient temperature. In order to ensure the necessary temperature conditions for hardening concrete use different methods of heating structures. One of the most effective ways is to warm up using a heating wire. The tasks of stood concrete in winter conditions are multifactorial, and computer modeling can significantly improve the efficiency of work. The ELCUT software complex is a tool in solving such problems, based on the method of the final elements. On the example of a monolithic foundation slab, the process of hardening of concrete at the temperature of the coldest five-day and medium-winter in Bratsk was simulated. The calculation of the concrete strength set and the analysis of temperature fields, taking into account the requirements for crack resistance, has been made. Computer simulations allowed to pick up the parameters of laying the heating wire in the concrete.

Garage complexes as the infrastructural basis of a modern city

The problem of the effective organization of parking spaces, the need for the construction of a multi-storey garage complex located in the transport-service system of the city investigated. The requirements of the existing federal law and regulations governing the conditions for placing the garage complex and car maintenance areas in relation to residential, public and business buildings located in the immediate vicinity have been worked out and considered. The construction site of Autohall garage complex, having weak, water-saturated clay soils, has been investigated. A constructive solution is considered and the advantage of using reinforced concrete column piles as supports reinforcing the soil is revealed. MONOMACH software complex solves a wide range of problems and has a number of advantages over other automated systems. The program implements a wide range of possibilities for inter-program communication. The construction of a monolithic frame of the complex, its volumetric model in COMPONOVKA program was consistently performed. Program GRUNT determined spatial modeling of the soil body according to the given engineering and geological surveys, the physical and mechanical characteristics of the soil, the bed coefficient. A monolithic foundation slab on a pile foundation was imported into PLITA program and the calculation of the optimal thickness of the slab, reinforcement of the lower and upper zones, numerical modelling of the work of the stress-strain state, i.e. an optimal design solution was chosen that excluded uneven deformations of the base, i.e. the design solution excludes ultimate deformations of the base.

Application of the software package in the improvement of floors made of hollow core slabs

An overview of the rationale for the unweighted hollow-core floor slabs use is given. The technological and design features of hollow-core floor slabs are considered. The possibilities of rational use of unweighted hollow-core floor slabs are presented. The calculation of monolithic floor slabs was carried out in the Lira software package on the basis of existing technologies, current standards and the methods for calculating the unweighted hollow-core slabs. The performance of floor slabs with spans equal in two directions is considered. It was found that regardless of the span of the floor slab, the effect of reducing its own weight exceeds the effect of reducing the section rigidity. The total deflection due to the own weight of the floor slab and the payload on it for the hollow core slabs is lower than for solid slabs of the same span. The use of unweighted monolithic slabs provides a reduction in the dead weight of the floor slab up to 35%. Reducing the load on the slab also provides a reduction in the reinforcing steel materials application rate. The use of unweighted monolithic floors by reducing the weight of structures and reducing their deflections will significantly optimize the structural schemes of buildings. The performed numerical experiment makes it possible to establish the boundaries of the effectiveness of the unweighted hollow-core monolithic floor slabs‘ use, upon reaching which the use turns out to be significantly more profitable than the use of traditional beamless floors.

Quality improvement of monolithic steel fiber concrete floor slabs with void formers

The features of the technology for the monolithic floors construction using void formers have been studied, its disadvantages have been identified and the ways to eliminate them have been proposed. At the first stage of this work, the reasons for the low quality of monolithic floors with void formers were studied by the method of visual and measuring control, and by comparing with known scientific and industrial data. At the second stage, by the method of systematization the main defects and damages arising in the construction, repair and usage of these floor slabs were classified and ways to eliminate them were proposed. At the third stage, the features of the quality control system, carried out directly during the construction of monolithic floor slabs using void formers, were studied, the composition of operations and control tools were proposed. According to the research results, it was found that the use of steel-fiber concrete in floors with non-removable void formers allows to reduce the percentage of reinforcement by 9.82%, compared to other known options, and also to reduce the consumption of concrete in comparison with a solid monolithic slab almost by half. The proposed quality control system will improve the efficiency of monolithic floor slabs using void formers.

Evaluation of the deformability of balcony plates of monolithic residential buildings

The calculation and design solutions of balconies of modern monolithic residential buildings are considered. Such balconies are part of a monolithic floor slab, which relies on internal supporting vertical structures. They have a larger extension, and when using brick walls to fence balconies -and more loading. The experience of operating monolithic residential buildings with balconies with their removal of 1.2 … 2.5 m and a brick balcony railing with a two-chamber stained-glass window showed the possibility of increased deformations of the balcony cantilever sections of the floor slabs of such buildings. If for such balconies the maximum deflection provided by the project for the balcony cantilever sections of the slab will be close to the maximum permissible values, then deviations from the design that were allowed during the construction of the building (reducing the class of concrete versus design, changing the location of the working reinforcement of the slab during concreting) can lead to increased deflection of balconies. Computer modeling allows you to accurately reflect the real work of the structure, and performing calculations in a nonlinear setting -to obtain an adequate deflection of the console balcony slab. The main approaches to modeling the design scheme of a flat floor slab with a balcony part are considered for determining plate deformations taking into account non-linear deformation of materials, as well as taking into account plate reinforcement.

Improving the manufacturability of floor slabs by pre-installing elements that partially replace reinforced concrete and formwork

The article discusses well-known and perspective constructive and technological systems for the installation of monolithic and precast-monolithic floor slabs of civil and industrial buildings. It shows examples and expediency of using all kinds of inserts made of plastic and other light materials and products for replacing a part of heavy monolithic reinforced concrete. An original resource-saving method for the installation of precast-monolithic floor slabs with a simultaneous increase in the degree of their construction readiness is proposed. This effect is achieved by reducing their own weight and the use of permanent formwork. Reduction in own weight of the precast-monolithic floor slab is ensured by the use of volumetric lightweight trapezoidal or rectangular inserts, preferably made of expanded polystyrene, during its installation. The use of permanent formwork will eliminate the need for the subsequent performance of labor-intensive finishing and insulation works. To confirm the effectiveness of using the proposed method of precast-monolithic floor slab installation, the operation of two floor slabs was modeled in the LIRA SAPR computing complex - the proposed reinforced concrete innovative slab and a solid reinforced concrete slab. Having analyzed the calculated forces, deformations and the corresponding consumption of reinforcement and concrete, comparative indicators were obtained for the proposed innovative slab and for a typical solid floor slab. As a result, significant savings in material and cost have been proven.

СУЧАСНІ ТЕХНОЛОГІЇ ЗБІРНО-МОНОЛІТНИХ ПЕРЕКРИТТІВ ДЛЯ РЕКОНСТРУКЦІЇ ГРОМАДСЬКИХ БУДІВЕЛЬ

During the reconstruction of the school building in Khmilnyk, Vinnytsia region, in order to create an inclusive resource center, it is necessary to replace the existing wooden floor. The floor of a building is a horizontal load-bearing structure created between two vertical rooms to separate them in height. At the same time, it serves as a floor for the upper room and as a ceiling for the lower room. Therefore, it is important to select a more modern reliable version of the floor, the technology of which will meet the limitations and requirements that arise in the reconstruction of public buildings. The main selection criteria are: simplicity of technology and speed of installation of the floor without additional material, energy and labor costs and without the use of cranes or large mechanisms; the possibility of both complete replacement of the floor and replacement of only certain damaged areas; relief of the load from the floor on the existing structures of the building; ensuring the necessary strength, rigidity and reliability of the floor; excellent heat and sound insulation properties with high fire resistance and environmental friendliness; compressed conditions for construction and installation work. Floors used for the reconstruction of buildings should combine a number of advantages and allow the necessary communications and repairs to be carried out without interfering with the existing structural scheme of the building. Modern technologies of prefabricated monolithic floors combine the advantages of traditional prefabricated and monolithic floors, but at the same time without their disadvantages. A number of technological solutions to facilitate the construction of the floor and the simplicity of its installation and subsequent operation allow the use of such floors for the reconstruction of existing buildings. The article analyzes the existing system of covering the school building, provides pre-design solutions for the replacement of the floor and attic, identified their shortcomings. Modern prefabricated monolithic floor systems are considered. The main elements are light metal or reinforced concrete beams with a spatial steel frame, hollow or lightweight blocks, reinforced monolithic slab, which is poured on the site after the installation of beams and blocks.

Development of a fast-hardening retarding high-early-strength concrete with low-alkalinity sulphoaluminate cement and practical application

To widen bridges, a usual method is to cast joint connections between new and old bridge decks without traffic interruption. The traffic vibrations have negative influence on the quality of joint connections. Shortening the construction time can alleviate the impact on the traffics, a fast-hardening retarding high-early-strength concrete (FRHC) for the connections is in need. In this study, low-alkalinity sulphoaluminate cement (LASC) concrete was modified to gain these characteristics. Based on FRHC concrete, four slab specimens including a monolithic concrete slab and three joint FRHC slabs were cast to investigate their flexural behaviors. With proper splicing details in joint connections, the joint FRHC specimens behaved approximately similar to the monolithic specimen. Combing the laboratory tests and engineering practice, the newly developed FRHC mixture succeeded in fast-hardening, retarding and high-early strength and the joint connections filled with FRHC have a good flexural performance.