EFFECT OF STEEL FIBER PROPORTION ON SIFCON MECHANICAL PROPERTIES

Slurry Infiltrated Fiber Concrete (SIFCON) is a relatively new high-performance material that may be thought of as a high-fiber content version of fiber reinforced concrete. This matrix is comprised of flowing mortar that must penetrate the fiber network implanted in the molds sufficiently. SIFCON combines excellent mechanical properties with a high ductility and toughness grade. SIFCON is utilized in applications that demand a high degree of ductility and energy absorption, most notably seismic-resistant reinforced concrete structures and structures exposed to abnormal or explosive loads. Additionally, pavement overlays, prestressed beam repair, and structural reinforced concrete element restoration have all been effective. The main aim of this study is to determine the effect of hooked-end steel fiber and micro-steel fiber on the strength of SIFCON specimens exposed to flexural and splitting loading. Three volume fractions of steel fiber (8,10, and12) % were used in this investigation. By weight of cement in SIFCON slurry, the proportion of Silica Fume SF substitution was 10%. Flexural strength was determined by testing specimens of (100×100×500) mm, and splitting tensile strength was determined at 7 and 28 days using cylindrical specimens with dimensions (150mm × 300m).. The results obtained from these tests were compared with SIFCON containing micro steel fiber. The test results show superior characteristics of SIFCON containing hooked-end steel fiber, as compared with micro steel fiber. For example, the flexural strength and splitting strength are 24.89 MPa and 10.14 MPa, respectively for SIFCON with 8% hooked-end steel fiber and 17.51 MPa and 9.1 MPa for control specimens with micro steel fiber.

DETAILS OF NORMAL SECTIONS STRENGTH CALCULATION OF FLEXIBLE REINFORCED CONCRETE STRUCTURES BY THE WOOD’S METHOD IN PC "LIRA SAPR"

Problem statement. The problem of realization of the calculation method of normal cross-sections strength of reinforced concrete constructions under flat bending, which is established in the current building codes of Ukraine, is considered. The main attention is paid to atypical and practically not considered calculation cases, typical for automated algorithms in the environment of SP "LIRA SAPR". The purpose of the article. Analysis of the feasibility of using the calculation method of current building codes with further development of recommendations, based on the specifics of computerized calculations. Methodology. Within the framework of the performed research, rectangular cross-sections of reinforced concrete structures with single and double reinforcement (provided a significant increase in the area of reinforcement of the compressed cross-sectional area) with variation of concrete classes, reinforcement coefficient and ratio of reinforcement areas were considered. The stress-strain diagrams of concrete and reinforcement are bilinear with characteristic values set for the first group of limit states. The character of change of cross-sections’ status diagrams "M - εc(1) " is investigated. Research results. It is found that for single-reinforced sections with decreasing reinforcement area there is a decrease of the value of deformation of the compressed fiber of concrete, which is used to find solutions for systems of nonlinear equilibrium equations of the deformation method. This leads to an increase of the execution time of calculations of the flat elements’ reinforcement by the Wood method. It is established that for sections with double reinforcement at relatively large values of the ratios of the reinforcement areas, the equilibrium of the section is at the maximum deformations of the compressed concrete fiber. Conclusions. An approach aimed at accelerating the calculation of sections with single reinforcement, which is based on the use of the relationship between the percentage (area) of reinforcement and the deformation of the most compressed fiber of the reinforced concrete element. Features of analytical algorithms for calculating the selected sections are taken into account by implementing this technique in the PC "LIRA SAPR", optimization and acceleration of automated algorithms for calculating reinforced concrete structures.

STRENGTHENING THE FOUNDATIONS OF PHYSICALLY OBSOLETE BUILDINGS

The problems and prospects of existing methods of strengthening the foundations of physically obsolete buildings are outlined, which is relevant for the preservation of buildings of architectural and historical value, as well as for mass renovation in large cities in cramped conditions with a high density of existing buildings. Method of calculation of hollow rectangular and round sections filled with concrete during bending is considered. In this article the dependence of compacted zone radius on initial characteristic of soil density and diameter of pressed pipe concrete element is analyzed. The conclusion is formed that the method of arrangement of the pipe-concrete horizontal distributor for simultaneous reinforcement of soil of the base and foundations chosen for the study allows to regulate the process of leveling the building settlement as a whole, and is also the most environmentally safe and does not negatively affect the surrounding buildings and structures.

MODELING OF STRESS-DEFORMED STATE OF BENDED REINFORCED CONCRETE ELEMENTS IN ZONES OF CLEAN AND TRANSVERSE BEND

The article deals with the analysis of the stress-strain state (SSS) of a bent reinforced concrete element in zones of pure and transverse bending. It is assumed that a bent element in the process of loading (after the formation of normal and oblique cracks) is divided into blocks, united by uncracked concrete and reinforcement that has adhesion to concrete. SSS was formed using the results of experimental studies of special prototypes in the PC “Lira-SAPR”. A fi nite element model of a prototype has been developed in the form of a reinforced concrete rectangular beam loaded with two identical concentrated forces in the span. By the method of successive approximations, the process of formation and formation of a system of cracks is realized, with which the beam is divided into blocks during loading. The results of calculating the fi nite element model and their comparison with experimental data are presented.

Comparison of the effect of GFRP and steel reinforcement in concrete members subjected to compressive stress

Composite materials became more popular and commercially available as reinforcement for concrete elements. Fibre Reinforced Polymer (FRP) bar is an excellent thermal and electrical insulator with high tensile strength and low weight. These assumptions make them a possible substitution for steel reinforcement. Moreover, GFRP is not responsible to corrosion for that are suitable for structures with high humidity and unfavorable environment. GFRP is easier to handle due to its low weight. Also, it has electromagnetic neutrality. But it has some disadvantages. It has a low modulus of elasticity and sensitivity to elevated temperatures. Another drawback and uncertainty with designing is the impact of an alkaline environment, which decreases the long-term strength of GFRP bars. This paper describes a pre-experiment study of concrete elements resistance. The analysis is performed for a cross-section of 200x150 mm for a short concrete column with steel and GFRP reinforcement. The study compares P-M diagrams for steel reinforcement and GFRP reinforcement with different reinforcement ratios. Other characteristics such as tensile strength and modulus of elasticity must be considered to design the GFRP reinforced concrete element. The study also considers the contribution of GFRP reinforcement in compression. The analysis has shown, the shape of interaction diagrams of steel and GFRP reinforcement are significantly different.

Parametric Study of Concrete Members with GFRP Reinforcement Subjected to Bending and Axial Force

The paper deals with the possible replacement of steel reinforcement by GFRP reinforcement for concrete elements subjected to bending moment and compressive axial force. For the last 15 years, Fibre Reinforced Polymer (FRP) bars became more popular and commercially available as reinforcement for concrete elements. Composite FRP materials are still new in construction and many engineers are not familiar with their properties and behaviour. FRP has certain advantages over steel reinforcement. It is a durable material that is not subject to corrosion, does not conduct heat, is an electrical insulator and conducts electrical current, and is non-magnetic. In contrast, FRP also has certain deficiencies such as sensitivity to higher temperatures, alkaline environments, and reduction of mechanical properties at high levels of long-term stress. In the case of FRP reinforcements, the plastic branch is missing in the σ-ε diagrams, what leads to a sudden failure of the reinforced concrete element, either by tensile rupture of the reinforcement or by crushing the concrete. The most used FRP reinforcement is made of glass fibres - GFRP reinforcement. The paper deals with the possible replacement of steel reinforcement by GFRP reinforcement for slab and beam elements. The text describes a parametric study for different reinforcement ratio with GFRP reinforcement and steel reinforcement. The study is performed for a cross-section of 500x500 mm for a column element and a cross-section of 1000x250 mm for a slab element. The effect of longitudinal GFRP reinforcement in elements under compression was investigated. The study contains a comparison of interaction P-M diagrams of concrete elements with steel and GFRP reinforcement. For design of GFRP reinforced concrete elements, it is necessary to consider different material characteristics such as tensile strength and modulus of elasticity. The contribution of the GFRP reinforcement in compression was neglected due to the anisotropic nature of the GFRP reinforcement and the low modulus of elasticity. The main reference basis for the elaboration of a parametric study is the fib Bulletin No. 40.

Comparison of Stress Fields near Longitudinal Construction Joints of Tied and Doweled Sections in Portland Cement Concrete Pavements

In Portland cement concrete (PCC) pavements, tie bars are commonly used at longitudinal construction joints (LCJs) to prevent the lanes from separating. Meanwhile, the increase in multiple lanes due to greater traffic volumes has raised concerns about potential longitudinal cracking; this has led to the use of dowel bars instead of tie bars at LCJs. However, there is a paucity of studies focused on the comparison between the behaviors of concrete pavement based on the restrained conditions provided by tie and dowel bars at LCJs. In this study, we investigated the effects of the placement of tie and dowel bars at LCJs on the potential for longitudinal cracking in response to the increase in concrete stress that may occur when the lanes are tied together in PCC pavements. Field testing verified that the variation in concrete strain was more restrained in the case of a tie bar than a dowel bar, whereas it resulted in higher stress in the concrete element in the tie bar section. However, the use of dowel bars caused more movement in the transverse direction at LCJs as compared with tie bars. Thus, our results indicate that using dowel bars reduces the potential for longitudinal cracking; however, it may increase the potential for lane separation.