Concrete Structural Elements Research Articles

Durability of reinforced concrete beams strengthened by galvanized steel mesh-epoxy systems under harsh environmental conditions

Strengthening and rehabilitation of reinforced concrete (RC) structural elements are being efficiently carried out by fiber-reinforced polymer (FRP) composite materials. However, their long-term durability is still causing concerns for the repairing industry. Recently, the use of steel wire mesh-epoxy systems for strengthening is gaining the attention of researchers and engineers and their long-term durability warrants investigation. This paper presents the results of an extensive experimental study carried out on 60 RC beams strengthened in flexure by medium and high cord density galvanized steel mesh (MSM, HSM). In order to evaluate the durability of these strengthening systems, the RC beams were exposed to direct sunlight and immersed under saline water for 6, 12, and 24 months. The beams were tested under four-point bending till failure after each exposure period. The MSM and HSM strengthened beams showed up to 51 and 62% higher load-carrying capacity than that of the control beams at 28 days, respectively, and up to 82% after two years of sun and saline water exposure. Furthermore, the exposed beams showed significant delay in crack initiation, no pronounced degradation in strength or stiffness, and no delamination of epoxy. On the contrary, there was significant improvement in the strength of the exposed beams, especially that of the MSM. Based on ACI 440.2R-17 Guidelines, environmental reduction factors were proposed for the exposed beams. This study showed that galvanized MSM and HSM laminates could be promising and durable alternative materials for rehabilitation, retrofitting, and strengthening of RC members under harsh climatic conditions of elevated temperature, high salinity, and high humidity.

Assessment of the Mechanical Properties of ESD Pseudoplastic Resins for Joints in Working Elements of Concrete Structures.

Concrete structure joints are filled in mainly in the course of sealing works ensuring protection against the influence of water. This paper presents the methodology of testing the mechanical properties of ESD pseudoplastic resins (E-elastic deformation, S-strengthening control, D-deflection control) recommended for concrete structure joint fillers. The existing standards and papers concerning quasi-brittle cement composites do not provide an adequate point of reference for the tested resins. The lack of a standardised testing method hampers the development of materials universally used in expansion joint fillers in reinforced concrete structures as well as the assessment of their properties and durability. An assessment of the obtained results by reference to the reference sample has been suggested in the article. A test stand and a method of assessing the mechanical properties results (including adhesion to concrete surface) of pseudoplastic resins in the axial tensile test have been presented.

Concrete confinement with TRM versus FRP jackets at elevated temperatures

Despite the clear cost, ease of installation, and construction schedule advantages of confinement of concrete structural elements with fibre-reinforced polymers (FRPs) for strength and deformability enhancement, concerns as to their performance at elevated temperature, or in fire, remain. The results of a series of elevated temperature experiments on FRP and textile reinforced mortar (TRM) strengthening systems for confinement of circular concrete columns are presented. The behaviour and effectiveness of the respective confining systems is studied up to temperatures of 400 °C. A total of 24 concrete cylinders were wrapped in the hoop direction with different amounts of FRP or TRM, heated to steady-state temperatures between 20 and 400 °C, and loaded to failure in concentric axial compression under a steady-state thermal regime. The results indicate that the effectiveness of the FRP confining system bonded with epoxy decreased considerably, but did not vanish, with increasing temperatures, in particular within the region of the glass transition temperature of the epoxy resin/adhesive. Conversely, the TRM confining system, bonded with inorganic mortar rather than epoxy, demonstrated superior performance than the FRP confining system at 400 °C as compared against tests performed at ambient temperature.

Análise e dimensionamento de vigas de seção “L” de concreto pré-moldado utilizando o Método das Bielas

Dentre os elementos presentes nas estruturas de concreto pré-moldado estão as vigas de seção “L”, largamente utilizadas no perímetro (bordas e fachadas) das edificações. A geometria tridimensional e as cargas externas aplicadas excentricamente na aba lateral fazem com que este tipo de viga esteja submetido simultaneamente a tensões normais e tensões de cisalhamento, gerando assim um complexo estado tensional. O fato das ligações com os apoios também estarem submetidas a torção torna o projeto estrutural das vigas de seção “L” um dos mais complexos entre os elementos da indústria de concreto pré-moldado por particularidades que não ocorrem nos modelos de vigas convencionais. Nesse contexto, o presente artigo tem como objetivo apresentar a análise e dimensionamento de vigas de seção “L” utilizando o Método das Bielas. Para tanto, foi desenvolvido um estudo de caso com auxílio do software CAST contemplando todas as etapas de dimensionamento e respeitando os parâmetros recomendados pela ABNT NBR 6118:2014. Por fim a metodologia apresentada foi validada através de diferentes métodos analíticos alternativos presentes na literatura internacional, demonstrando que o Método das Bielas é uma ferramenta bastante atrativa para o dimensionamento de vigas de seção “L” de concreto pré-moldado.

Problems and perspectives of fire resistance for wooden constructions in high-storey buildings

Introduction. A significant problem in construction area in theRussian Federation is the impossibility of high-rise wooden building. To solve this problem, it is necessary to study the state of the issue abroad and in theRussian Federation, and analyze the development prospects of this area. Main (analytical) part. The article provides examples of modern facilities (inBerlin,London,Melbourne and other cities), reflecting the state of high-rise wooden construction abroad. In the buildings considered, together with the predominant wooden structural and wood-containing finishing materials, reinforced concrete structural elements necessary for the implementation of complex technical systems are used, which can significantly reduce the time of their construction. In addition, the chosen approach allows to enhance environmental friendliness of buildings and structures, — due to the use of wood-containing materials, huge volumes of carbon dioxide are preserved and its emissions into the atmosphere during construction work are significantly reduced. The paper reflects the main provisions of technical regulation in the field of fire safety of building materials and structures in theRussian Federation. It is shown that the main reasons for the impossibility of using wooden structures in high-rise buildings are related to the peculiarities of technical regulation in theRussian Federation, in particular, the lack of the necessary methods for testing and certification of wooden building structures in high-rise construction. The necessity to optimize existing methods for testing wooden building structures is shown. Examples of various documents regulating the production and use of wooden and composite building structures are given. The work reflects in detail the international experience in the implementation of the main provisions of regulatory documents, as well as European tests for fire resistance, which shows the possibility of implementing such an experience in theRussian Federation. Conclusions. To develop a regulatory framework for the possibility of using wood structures in high-rise construction, it is necessary to conduct large-scale experiments on wooden structures in order to study their fire resistance. In this case, it is necessary to take into account the features of combustible building materials.

Case Studies of High-strength Lightweight Concrete Using Expanded Siliceous Aggregate

Structural lightweight concrete has various applications including the construction of multi-story buildings, bridges, offshore oil platforms and other reinforced concrete structural elements. Structural lightweight concrete also was used in offshore construction. The development of compositions of high-strength lightweight concrete with an average density of 1100-1500 kg/m3 may be in demand for the manufacture of most of the typical concrete products with an ordinary strength 20-35 MPa. This study have shown that granular expanded siliceous aggregates can be used as an alternative to hollow microspheres to obtain high mechanical characteristics of lightweight concrete. Based on the principles of producing high-strength lightweight concrete using the example of “Thermogran” granules the possibility of achieving strength of lightweight concrete of more than 45 MPa with an average density of less than 1600 kg/m3 is shown. In the same time, specific consumption of cement on 1 MPa of concrete strength is 8.1…8.8 kg/MPa.

Fib models for modeling of chloride ion ingress and concrete carbonation: Levels of assessment of input parameters

AbstractDegradation processes affecting structural materials, such as chloride ion ingress, concrete carbonation, and the subsequent corrosion of reinforcement, are limiting factors for the service life of reinforced concrete structures and/or structural elements. The objective of a structural condition assessment is to determine the current state and estimate the future performance of a structure with a maximum degree of accuracy and a minimum of effort. There is therefore a need for advanced methodologies and predictive deterioration models for the assessment of structures/structural elements over time. In the paper, the focus is on the widely accepted models for modeling of chloride ion ingress into concrete and concrete carbonation process incorporated in the fib Model Code 2010. Three levels of assessment of input parameters are presented, starting with simple quantification based on codes/literature recommendations and progressing to higher levels of assessment using design documentation and visual inspection data, additional on‐site measurements, and/or laboratory tests.

Durability and Long-Term Performance of FRP-to-Concrete Joints under Environmental Conditioning: Experimental and Analytical Study

Abstract The external bonding of fiber-reinforced polymer (FRP) composite plates and sheets to the tensile surface of reinforced concrete structural elements is a viable retrofitting technique. The...

Prediction Models for the Mechanical Properties of Self-Compacting Concrete with Recycled Rubber and Silica Fume.

The paper aims to investigate the influence of waste tire rubber and silica fume on the fresh and hardened properties of self-compacting concrete (SCC) and to design multivariate regression models for the prediction of the mechanical properties of self-compacting rubberized concrete (SCRC). For this purpose, 21 concrete mixtures were designed. Crumb rubber derived from end-of-life tires (grain size 0.5–3.5 mm) was replaced fine aggregate by 0%, 5%, 10%, 15%, 20%, 25%, and 30% of total aggregate volume. Silica fume was replaced cement by 0%, 5%, and 10% of the total cement mass. The optimal replacement level of both materials was investigated in relation to the values of the fresh properties and mechanical properties of self-compacting concrete. Tests on fresh and hardened self-compacting concrete were performed according to the relevant European standards. Furthermore, models for predicting the values of the compressive strength, modulus of elasticity, and flexural strength of SCRC were designed and verified with the experimental results of 12 other studies. According to the obtained results, mixtures with up to 15% of recycled rubber and 5% of silica fume, with 28 days compressive strength above 30 MPa, were found to be optimal mixtures for the potential future investigation of reinforced self-compacting rubberized concrete structural elements.

Flexural performance of high volume fly ash reinforced concrete beams and slabs

In this study, the flexural performance of high volume fly ash (HVFA) concrete structural elements is investigated with the help of load-deflection tests on reinforced concrete (RC) beams and slabs. A total of 32 beams and slabs, 8 from each mix group were cast with different percentages of fly ash replacement varying from 0 to 60% for two plain concrete grades. The RC beams were tested up to the failure under a four-point bending test and for slab specimens, the load was applied at the centre. The tests on structural elements were carried out after 28 days of curing. The deflections at mid-span, cracking pattern, yielding and ultimate state conditions of RC beams and slabs are determined. Further, the finite element modeling using ABAQUS has also been carried out on RC beams and slabs for static load and the results are compared with the experimental values. The yielding and ultimate state of RC concrete with HVFA exhibit identical trend as compared to that of RC concrete without HVFA. It is observed that the load-deflection behaviour and cracking pattern of plain and fly ash concrete RC beams and slabs are in good agreement with the finite element model.

Numerical Solutions and Experimental Research in Justification of the Design Model of the Force Interaction of the Reinforcing Beam with the Anchoring Medium

The paper presents the research and engineering experience in the calculation and design of concrete structural elements, reinforced by fiberglass rods. The construction of a concrete beam reinforced by fiberglass rods is presented. Research in preserving prestressing forces in a beam subjected to weathering for about 30 years is considered. The creation and analysis of concrete-steel connection model is presented using LIRA-SAPR software. This is a work of scholarly interest.

Influence of Hybrid Fibres on Bond Strength of Concrete

Bond strength between embedded bar and concrete plays vital role in the design of various reinforced concrete structural elements. Use of metallic and synthetic fibres has been shown to be an effective method to enhance tensile strength, reduce shrinkage and improve durability properties of concrete. However, making of synthetic fibres will not only deplete the natural hydrocarbon resources, but also add greenhouse pollutants to the environment. Hence, sisal fibre was considered as a potential alternative to polypropylene fibre. An experimental study was conducted to evaluate the influence of sisal fibres as mono-fibre and in combination with steel as hybrid fibre on bond strength of concrete. The performance of steel polypropylene fibre reinforced concrete (SPFRC) is compared with that of steel sisal fibre reinforced concrete (SSiFRC). Bond strength was conducted onM30 grade concrete for curing periods of 7, 28 and 90 days. Fibre dosages of 0.50%, 1.00%, 1.25% and 1.50% by volume of concrete were used. Results indicated that increase in steel fibre dosage improved the bond strength slightly. However, increase in fibre dosage of either PP fibres or sisal fibres resulted decrease in bond strength. Furthermore, sisal fibre reinforced concrete (SiFRC) showed inferior performance in bond strength as compared to polypropylene fibre reinforced concrete (PFRC). A detailed statistical analysis revealed that although no strong correlation between the compressive strength and the bond strength was evident from the experimental study, means of bond strength of both the hybrid groups did not differ significantly. In addition, empirical equations were proposed to predict the bond strength of fibre reinforced concrete (FRC) based on compressive strength.

Regression Analysis for the Axial Strengths of Muti-Blended Steel Fiber Self Compacting Concrete from the Experimentation.

The present paper deals with triple blended Self-Compacting Concrete (SCC) where 53 grade of cement is blended with flyash and Condensed Silica Fume (CSF) at different percentages as replacements to the cement. The steel fiber of diameter 1mm; with an aspect ratios varying from 20,30 and 40 were mixed to get the higher mechanical properties such as compressive and tensile strengths at four different percentages. The required number of cube and the cylindrical specimens of triple blended steel fibrous SCC were prepared and evaluated for compressive and the tensile strengths. The magnitude of the test results have indicated that there is enhancement in the axial strength properties of this type of the concrete as the percentage of steel increases up to certain value to fulfil the needs of the SCC as per the America Concrete Institute (ACI) norm. The regression equation is derived for the experimental values for the compressive and the spilt tensile strength of steel fibere self-compacting concrete (SFSCC) and verified acceptance the equation. The results of present investigation would help in the preparation of optimum tri- blended steel fibrous SCC ,which are suitable for practical usages like floor slabs bridge decks, important highways, airport runways and thin shaped concrete structural elements.

Experimental and Analytical Investigation of Hybrid Layer Thickness Effect on Replacing the Rebar for Reinforced Concrete Beams

Many researchers emphasize the effectiveness of steel fiber to replace the reinforcing bar in the reinforced concrete structural elements. The fiber of different types, sizes and geometries have been added to the concrete mix with a pozzolanic material to produce Ultra-High Strength Concrete (UHSC), which has excellent properties, high strength, and durability. This paper is a lab work and theoretical study consisting of casting and testing. Twenty-one simply supported RC beams to examine the beam's behavior and the shear capacity with the full or partial depth of UHSC with or without steel fibers (UHSSFRC) for replacing the reinforcing bars. The beams were divided into five groups. Preliminary experiments tests were conducted and carried out to study hardened properties of concrete such as (compressive strength, splitting tensile strength, modulus of rupture and modulus of elasticity). The selected finite element program (ANSYS) was applied to model all tested beams. It was observed that the performance of the finite element representation gives and shows good agreement with the lab work results. The test consists of failure load, deflection, cracks and failure mode. The experimental laboratory work results showed that for (1% steel fiber with reinforcement ratio ρ=0.0105 full UHSC layer) was able to give the same shear capacity for beam with (reinforcement ratio ρ=0.0157 regular concrete), while for (2% steel fiber half UHSC layer and reinforcement ratio ρ=0.0105) was able to give the same ultimate shear loads of beam with (reinforcement ratio ρ=0.0157 normal concrete). This research reveals that the hybrid layer and steel fiber effects were able to substitute for a higher reinforcement ratio with the same shear capacity.

Performance investigation of high-proportion Saudi-fly-ash-based concrete

Approximately 544 million tonnes of fly ash (FA) are generated annually worldwide, 80% of which is disposed of in landfills. Thus, using FA as a replacement for cement has turned out to be popular in construction industries around the world because of its strong properties and crucial role in decreasing the volume of pollutants and CO2 produced by cement production. Meanwhile, the use of Saudi FA (SFA) as a suitable supplemental cementing material to partly substitute cement in the design of SFA-based concrete is highly imperative. An extensive experimental study was conducted to utilize increased levels of SFA in the production of concrete. Six concrete mixes were utilized: five out of the six mixes were made with different levels of SFA and one mix was used as a reference. This study presents the findings of using different volumes of SFA with variable proportions (i.e., 0%, 10%, 20%, 30%, 40%, and 50%). Experimental tests were performed to study the properties of SFA-based concrete, including slump test, air content, setting times, thermal profile, specific gravity, sieve gradation, flexural strength, compressive strength, tensile strength, wear depth, resistance to abrasion, and elasticity modulus, at different time intervals for one year. However, the hardened strength properties and resistance to abrasion exhibited incessant and substantial enhancement at 56 days and up to one year, which is generally attributable to the pozzolanic reaction of SFA. Subsequently, all strengths increased when thermal heat decreased, and test results indicate that SFA can potentially substitute cement in concrete by up to 50% for the fabrication of structural concrete elements in the construction industry.

A PROBABLISTIC APPROACH TO EVALUATION OF THE ULTIMATE LOAD ON FLEXURAL RC ELEMENT ON CRACK LENGTH

The fracture mechanics of concrete and reinforced concrete is a promising direction in the development of methods for reinforced concrete structural elements design and inspection. At the same time, probabilistic methods of design and behavior analysis of structural elements are of particular interest. The article describes a probabilistic approach to load-bearing capacity and reliability analysis of flexural reinforced concrete elements based on the crack length criterion. The functional relationship between the critical stress intensity coefficient of concrete and the design compressive strength of concrete is given. The article presents a method for the reliability analysis of flexural reinforced concrete elements at the operational stage with limited statistical data about the critical stress intensity coefficient of concrete. The ultimate value of the failure probability (or reliability index) should be set for each object individually based on the value of the acceptable risk.

Structural Materials: Identification of the Constitutive Models and Assessment of the Material Response in Structural Elements Strengthened with Externally-Bonded Composite Material.

This article investigates the material behavior within multiple-component systems. Specifically, a structural concrete element strengthened to flexure with externally-bonded fiber-reinforced polymer (FRP) material is considered. Enhancements of mechanical performances of the composite structural element resulting from synergies in the framework of the multiple-component system are studied. The research work comprises the determination of the constitutive relations for the materials considered separately as well as the investigation of materials’ response within a complex system such as the composite structural element. The definition of the material models involves a calibration of the model constants based on characterization tests. The constitutive relations are integrated into the finite element model to study the material behavior within the multiple-component system. Results obtained by finite element analysis are compared with experimental results from the literature. The finite element analysis provides valuable information about the evolution of some internal variables, such as mechanical damage accumulation. The material synergies find expression in the load-carrying capacity enhancement and the delay in the damage accumulation in concrete.

Mechanical interaction of a reinforced concrete slab and a steel beam in bridge spans

The paper aims to clarify the rules of calculation of steel-reinforced concrete bridge superstructures on the basis of generalization of modern scientific achievements in conjunction with the possibilities of computational software and computer technology in the field of calculations of multi-component sections without the need to use simplifying hypotheses that affect the accuracy of the calculation. An algorithm for calculating continuous multi-span beams of bridge structures with the possibility of taking into account the flexibility of the shear joint between concrete and steel structural elements is proposed, which increases the accuracy of determining the stress-strain state (SSS) of the structure. The results of the work can be used in the design of steel-concrete bridge superstructures. The significance of the work lies in the fact that the proposed analytical dependences in the joint use of modern computing power will clarify the calculation of steel-concrete bridges, thereby increasing the level of reliability of bridge structures, laid at the design stage.

Setting time and standard consistency of Portland cement binders blended with rice husk ash, calcium carbide and metakaolin admixtures

The use of pozzolanic materials to reduce carbon dioxide (CO2) emissions and enhanced properties of mortar and concrete has received increased interests in the last decades. In this study, admixtures such as metakaolin (MK), rice husk ash (RHA) and calcium carbide waste (CCW) partially replaced Portland cement (PC) at 5, 10, 20 % in multiple combinations of aforementioned admixtures as binders and the effect of setting times (initial and final) and standard consistency on the binders were evaluated. The Department of Environment (DOE) approach for mix proportions was employed. The mixes are in six groups consisting of control PC, each admixture replaced PC at 5, 10 and 20 % replacement level in binary mixes, then two of the admixtures replaced PC at same replacement level in ternary and the three admixtures replaced PC in quaternary mixes respectively. Results indicated that RHA significantly influenced the standard consistency of the binders incorporating the three admixtures as compared with CCW and MK. The requirement of water in the binder increased with increase in percentage replacement level of RHA within the binder due to its porous nature. At 5 % replacement level, it was 9 % above control value, 21 % and 39 % at 10 and 20 % replacement level subsequently. Similarly, setting times at the aforementioned replacement levels are 27 % and 6 % above the control value for initial and final setting time. For 20 % replacement level, it was 24 % and 38 % above the control value for the initial and final setting time respectively. This is due to reduction in PC content leading to less content of Tricalcium silicate aluminate (C3A) and amount of carbon content within the pozzolanic materials which retard the rate of reactions. By and large, the admixtures retard the setting times of quaternary binder, and increased its water of consistency which can be overcome by activation. However, they are useful in the construction of concrete structural elements or structures that requires longer time for placement. Furthermore, it will be worthwhile to investigate same properties at the nanoscale since these have been established at the micro level.

Influence of critical parameters on UHPFRC structural elements subjected to blast loading

Response of structures subjected to blast loading is a highly complex phenomena involving time-dependent deformation, geometric and material nonlinearities and loading rate based material properties. During an explosion, blast loads act as an impulsive load of very short duration developing enormous heat and pressure. With increasing terrorist threats, attention is needed to study dynamic response of structures under blast loading. Ultra high strength concrete (UHPC) has been found to considerably enhance strength, member size, weight reduction and workability and is now a day used due to improved energy absorption capacity, workability and anti-abrasion ability. Investigations conducted by several researchers to study blast-resistant capacities of UHPC have demonstrated possibilities of using the material in structures susceptible to terrorist attack. The present paper provides comprehensive review of published research to study blast loading effect on Ultra high performance fibre reinforced concrete (UHPFRC) structural elements in terms of variables like standoff distance, charge weight, types of blast loadings, grades of UHPFRCs, etc., both analytically and experimentally. UHPFRC slab panels, beams, columns, and other fibre composite structures have been studied at structural level to draw fruitful inferences and conclusions. It has been found that UHPFRC possesses increased capacity to disseminate large amount of energy during blast loading and demonstrates better performance after blast damage contrasted with normal strength concrete and High strength concrete. Detailing in UHPFRC structural elements under seismic condition offers improved blast performance, and UHPFRC can more effectively resist compression and shock waves. Low Strength and low ductility fibres added to UHPFRC further illustrates minimal influence on the blast performance and fracture energy. Shear failure is also found to be one of the dominant modes in UHPFRC under blast loading at close standoff. Based on extensive review, further research is proposed to solve complex problems to achieve appropriate design of structural UHPFRC members.