Steel-reinforced Concrete Structures Research Articles

ОПЫТ ИСПОЛЬЗОВАНИЯ СТАЛЕЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ

The article considers the possibility of using steel-reinforced concrete structures in the design of buildings and structures

Behavior of FRP rods under uniaxial tensile strength with multiple materials as an alternative to steel rebar

Steel corrosion raises maintenance costs and reduces the durability of steel-reinforced concrete structures. Therefore, societies must create their own sustainable model based on finding new technologies that enable them to benefit from the available resources thus reducing their construction cost and maintenance burdens. Fiber Reinforced Polymer (FRP) introduces an innovative and alternative approach to replace traditional steel bars and strands. So, this paper investigates the behavior of synthetic and natural FRP of different fiber volume fractions (Vf) under uniaxial tensile load. To carry out this, four types of fiber are made by hand lay-up technique. Three of them are synthetic fibers which include glass fibers, nylon fibers, and polypropylene fibers, whereas jute is used as natural fibers. The results show hand lay-up technique of FRP gives resembles the results of the Pultrusion process. The tensile strength and the elasticity modulus increased by increasing the Vf, regardless of the type of fiber. The samples GFRP-3, PFRP-P2, NFRP-N2, and JFRP-J3 showed the highest tensile strength of 971.89 MPa, 130.74 MPa, 262.54 MPa, and 178.42 MPa respectively, that improve by 26.68 %, 19.57 %, 15.44 %, 26.55 %, while the modulus of elasticity showed improvement by 20.13 %, 42 %, 14 %, and 32.93 % compared with a reference sample of the same group respectively. Furthermore, Microscope images indicated good fiber distribution and resin-fiber impregnation across the FRP bars.

Numerical simulation method of SRC frame column based on FLPH model

In order to obtain the accurate numerical simulation of seismic performance for steel reinforced concrete (SRC) frame columns, a convenient and reliable numerical simulation method needs to be established. Based on the test results, a numerical simulation method of SRC frame column based on the finite length plastic hinge (FLPH) was proposed in this paper. The plastic hinge element model was obtained through analyzing the failure process of SRC column. The length of plastic hinge for SRC column was expressed by considering the contribution of bending effect and strain penetration effect in the plastic deformation of members furtherly. On the basis of the numerical integration method, the FLPH model suitable for SRC frame column was established by introducing the section stiffness correction coefficient at the integral point of the element. Finally, using the OpenSees finite element analysis platform, the test specimens were simulated by FLPH model established in this paper. The results shown that the hysteretic curves obtained by simulation are well with the experimental curves, indicated that the numerical simulation method for SRC frame column based on FLPH model can be well applied in SRC structures.

Structural Performance of Lightweight Aggregate Concrete Reinforced by Glass or Basalt Fiber Reinforced Polymer Bars.

Lightweight aggregate concrete (LWC) and fiber reinforced polymer (FRP) reinforcement are potentially more sustainable alternatives to traditional steel-reinforced concrete structures, offering several important benefits. To further the knowledge in this area, the physical–mechanical properties of LWC produced with 0%, 50%, and 100% expanded clay aggregate were assessed. Subsequently, the flexural behavior of LWC beams reinforced with steel reinforcement and glass and basalt FRP bars was tested. The results of the experimental program allowed quantifying of the effect of expanded clay aggregate incorporation on LWC properties. The use of FRP reinforcement was also compared to steel-reinforced concrete beam behavior. The results of this study can provide additional support for the use of innovative materials such as LWA and FRP reinforcement.

Performance Evaluation of Silane in Concrete Bridge Decks Using Transmission X-ray Microscopy

The corrosion of steel reinforcement in concrete structures is a most widespread problem. Silane is commonly used as a surface treatment material to reduce the entry of moisture containing harmful chemicals into the concrete matrix, thereby restricting corrosion. There is not a standard test method to evaluate the long-term performance of such sealers when applied on concrete. Moreover, the literature does not have a definitive conclusion on the performance of silanes. In this work, transmission X-ray microscopy (TXM) and optical imaging were used to investigate the mass transport properties and silane thickness of field samples treated with silane to gain insight into the performance of silane coatings. Quantitative measurements using optical staining techniques showed that the average measured silane thickness for all 14 projects was 2.5 mm. The TXM results revealed that, on average, the samples with silane coatings exhibited 8.5 times less penetration of outside chemicals, at a depth of 2 mm, as compared to uncracked samples without silane coatings. This work shows that silanes are a useful and practical tool to significantly reduce the permeability of in-service concrete and resist corrosion.

Corrosion Processes of Steel Reinforcement in Concrete Structures Based on Secondary Resources of Metallurgical Production

The study of the influence of the physical and mechanical properties of concrete on various hydraulic binders on the corrosion resistance of steel reinforcement has been carried out. As a binder, the following were considered: CEM I 42.5 N and a slag-alkaline binder (SAB) based on ground granulated blast-furnace slag of Novolipetsk Metallurgical Plant (NMP). For comparative tests, concretes of class B 25 (M300) were used on granite aggregate with a fraction of 2,5-7,5 mm. Indicators of physical and mechanical properties such as: compressive strength, porosity, water absorption coefficient and weight loss coefficient of reinforcement at the age of 28, 90 and 180 days are criterial. 5 % aqueous solutions of NaCl, Na2S04 were used as working media in assessing the corrosion resistance of reinforcing steel; MgS04. It has been established that steel reinforcement in slag-base concrete (SBC) has high corrosion resistance, both in an aqueous solution of NaCl and in solutions of Na2S04 and MgSO4. Slag-alkali concretes are characterized by low porosity, lower water absorption coefficient in comparison with concretes based on Portland cement.

Experimental Investigation of the Flexural Performance of Hybrid (GFRP and STEEL) Reinforced Concrete Beams

The corrosion of steel reinforcement is a key contributor to the inability of concrete buildings to withstand long-term exposure to the elements. Fiber-reinforced polymer (FRP) has become an alternative to steel reinforcement in concrete structures to solve this problem. One drawback is GFRP's low modulus of elasticity is one drawback. The main objective of this study is to develop a practical hybrid FRP bar for concrete structures, especially for marine and harbor concrete structures, using the concept of material hybridization. The purpose of hybridization is to increase the elastic modulus of GFRP bars with acceptable tensile strength and improve their flexural ductility, as well as enhance the corrosion protection performance of both GFRP. GFRP crust with steel core bar is being considered in the development of hybrid FRP bars. The elastic modulus of the hybrid GFRP bar can be increased by up to 280 percent, according to the findings of this study. The bars are manufactured locally, utilizing a double-part die mold and locally sourced raw materials. Four-line static loading is used to examine the flexural limit states of nine beams with parameters of 200 mm width x 350 mm thickness x 2000 mm length, including pre-cracking behavior, cracking pattern, deflection, load capacity and strain, and failure mechanism.

A Review on the Mechanical Behaviour of Bamboo Reinforced Concrete Beams

In light of the increasing demand for sustainable building materials, the effectiveness of bamboo utilization in various fields has become the object of scientists’ close attention. The increased interest in bamboo is explained by its sustainable characteristics, which make it the most preferred material for environmentally friendly and costeffective construction compared to conventional ones. Applicability of bamboo is vast and diverse: from decoration and furniture to structural members and reinforcement. Due to the low price, rich resources, and high elasticity, bamboo culms have also been used as an alternative to steel reinforcement in concrete structures. Extensive research has been done to assess feasibility of bamboo reinforcement in structural elements made of concrete. This article discusses the mechanical properties of three types of structural bamboo reinforced concrete (BRC) beams. Existing original papers on the mechanical behaviour of structural BRC members were studied, and the fundamental properties including typical failure modes, reasons of failure, load-displacement relationships, and influencing factors were discussed and described. Observations and conclusions of the review will contribute to deep understanding of structural feasibility of BRC beams and serve as a base for future research.

Раціональне використання несучої здатності сталевих профільованих листів незнімної опалубки сталезалізобетонних перекриттів

Building structures effective design should ensure uniform strength of all building load-bearing elements. Steel-reinforced concrete structures are made both during new construction and during the reconstruction of buildings or structures by a successful combination of steel, mainly rod elements, and monolithic concrete. Quite often, in order to increase the manufacturability of such floors installing and reduce the construction time, a monolithic reinforced concrete slab is arranged on a fixed formwork made of profiled flooring. To include a profiled sheet in compatible work with a monolithic slab, anchoring means are provided: protrusions on the sheets surface, rod reinforcement, etc. However, due to the usually equal pitch of the profiled sheets (steel beams) supports, they are unevenly stressed. On the basis of the conducted theoretical analysis, 6 slabs 6 m long, 1.06 m wide and 0.53 m made of K35-0.5 steel profiled flooring were designed, manufactured and tested according to a continuous three-span scheme, as a fixed formwork for monolithic steel-reinforced concrete floors. The samples were loaded with bricks. To measure deflections during sample loading, watch-type indicators with a division value of 0.01 mm were used. To measure strain electro tensile resistors were used. An analysis of supports installation variable step influence, as one of the methods of these floors load-bearing capacity use level balancing was carried out. It has been experimentally confirmed that when equalizing the values of the span or support bending moments (at the same time, the support moments are twice as large as the span), as well as deflections, the lengths of the extreme spans should be 25% less than the central spans.

Evaluation of Corrosion Condition of Some Steel-Reinforced Concrete Infrastructures Available In Pokhara Valley of Nepal

Assessment of the corrosion condition of different types of eighty steel-reinforced concrete (SRC) structures of Pokhara Valley (Nepal) was carried out in the present study using a half-cell potential measurement (HCPM) method without destruction of specimens. It is concluded from the experimental results that the SRC structures found at dried places in Pokhara areas showed a low percentage(i.e., < 10%) of corrosion risk, while the fencing pillars used for decoration as well as boundary purposes, and the sewer pipes at damp places found under the high percentage (i.e., > 90%) of corrosion risk. The SRC infrastructures, which have rough and cracked surfaces with high humid surrounding environments, are at high risk of corrosion. The SRC columns of the buildings in Pokhara Valley are at a slightly higher corrosion risk than the SRC roof structures.

Durable Steel-Reinforced Concrete Structures for Marine Environments

Even in harsh marine environments, concrete structures reinforced with steel can show excellent long-term durability, with little or no reinforcement corrosion. Very few actual reinforced concrete (RC) structures have been closely scrutinized over many years and subject to interpretation using recent state-of-the-art understanding gained from detailed laboratory observations. Such a case is described for an 80-year-old RC structure observed annually over about 30 years in what is essentially an extraordinary long experiment. Despite very high chloride concentrations, field excavation evidence showed that reinforcement corrosion overall remains minimal, except where insufficient concrete compaction permitted air-voids to initiate quite severe, very localized corrosion even with still high concrete pH. It is possible that the use of blast furnace slag as aggregate may have assisted the observed durability. The case study supports other studies that show that it is possible to achieve long-term durable and therefore sustainable RC structures without additives and using only conventional reinforcement steels and conventional cements and aggregates. However, the potential dangers of deep narrow cracking extending to the reinforcement and the potentially deleterious effects of alkali–aggregate reactivity of some aggregates needs to be considered.

STUDY OF THE BRIDGES BUILT IN UKRAINE IN 1998 AND 2001, THAT WERE DESTROYED BY LONG-TERM OPERATION AND FLOODS

Purpose. The aim of the work is to summarize design errors, construction defects and shortcomings and bridge defects after long-term operation on the basis of real field studies and analysis of scientific and technical sources. Methodology. To achieve this goal, an inspection of scientific and technical sources and regulations on the technical condition of transport facilities in Ukraine was conducted. In particular, it is a bridge in the city of Khust, built in 2000 on the site destroyed by floods in 1998 and a monolithic frame-cantilever bridge on the highway Mukachevo-Rogatin km 92 +700, built in 2001 on the site of partially destroyed in March 2001. The authors also took part in the construction, testing for static and dynamic loads of six steel-reinforced concrete bridges in Kobiletska and Kosivska Polyana, which were erected in 2000 on the site of those destroyed by the 1998 flood, as well as overpasses and bridges of long-term operation, – this is the Beregovsky bridge in the city of Mukachevo and the overpass in the village of Vistova. The results of the analysis and synthesis of the above studies became the basis for establishing the corresponding design errors, defects and shortcomings in construction and shortcomings in the operation of bridges and overpasses. Results. The analysis of domestic and foreign scientific and technical sources regarding the technical condition of the constructed reinforced concrete, steel-reinforced concrete bridges and bridges and overpasses of long-term operation is carried out. The analysis and synthesis of the problems of ensuring the reliability and durability of transport structures in the conditions of their operation in the air, soil and water environment. It is established on real examples of design errors, defects and shortcomings in construction, shortcomings in operation. The possibility of restoring the bearing capacity using modern materials and technologies is shown. Scientific novelty. As a result of the analysis of transport structures, scientific and technical sources and a number of studies of reinforced concrete and steel-reinforced concrete structures of bridges built after the floods in 1998 and 2001 and bridges (overpasses) of long-term operation, it was possible to summarize the main reasons that significantly affect the degradation of the structures of these bridges and overpasses. The possibility of restoring their bearing capacity and durability using modern materials and technologies is shown. In particular, it was found that in addition to power factors, factors of the air, soil and water environment also significantly affect. Practical significance. On the basis of these data, and observing the indicated objects for 20 years, it was possible to generalize and establish design errors, defects and shortcomings in construction and shortcomings of long-term operation. This makes it possible to propose areas of theoretical and experimental research and calculation methods, to take them into account in the design and operation of such structures. In particular, on the basis of these data, a technique was created and tested on real objects, which makes it possible to significantly increase the durability and reliability of such structures, using modern materials and technologies for repair and restoration work.

Seismic Performances of SRC Special-Shaped Columns and RC Beam Joints Under Double-Direction Low-Cyclic Reversed Loading

Steel-reinforced concrete (SRC) special-shaped column and beam frame structure is a special structural form that can meet the requirements of high bearing capacity and satisfy the esthetic requirement of buildings. In this study, a new joint design approach is adopted to focus on the seismic behavior of SRC special-shaped column and reinforced concrete (RC) beam joints under low-cyclic double-directional reactions through pseudo-static tests with a controlled stirrup distance. The joints of SRC specimens were compared with those of RC specimens by controlling the area of steel and reinforcement, and hysteresis cycle skeleton curves and load and strain hysteresis cycles were analyzed. The specimen with profiled steel was found to have better energy dissipation capacity. The energy dissipation capacity and stiffness degradation of the nodes were analyzed. The test results showed that the energy dissipation capacity of the SRC joints was better than that of the conventional concrete column joints, and the stiffness degradation of RC joints was more significant than that of SRC joints.

Bond strength of GFRP bars to high strength and ultra-high strength fiber reinforced seawater sea-sand concrete (SSC)

Fiber reinforced polymer (FRP)-reinforced seawater sea-sand concrete (SSC) structures are prospective substitutions for traditional steel-reinforced concrete structures, especially in maritime environment. To demonstrate the feasibility of the FRP-reinforced SSC structures, an in-depth understanding on the bond strength of glass FRP (GFRP) bars to SSC under pull-out loading is essential. In this regard, pullout tests on 45 specimens with a 10 mm diameter GFRP bar embedded in ultra-high strength concrete (including normal concrete with river-sand and fresh water and SSC) are conducted in this study. Particularly, the experimental tests focus on some key factors that governing the GFRP bars in concrete, such as the bar embedment length, the polyethylene (PE) fiber volume fraction, and the concrete strength (i.e., 80 MPa and 120 MPa). Three major failure mechanisms and two types of average bond stress-slip curves are obtained from the tests. The results show that substitution of seawater and sea sand for normal concrete has no distinct effect on short-term change in bond strength (less than 9%). In addition, it indicates that the increase in concrete strength and PE fiber content could improve the bond strength, whereas increasing the embedment length (from 2.5 times to 10 times of bar diameter) could result in a decrease in bond strength (by 20–30%). Furthermore, it demonstrates that the CMR model has better performance than the mBPE model in capturing the experimentally observed ascending part of the bond-slip curve.

Evaluation of the Thermal properties of Epoxy-Agro waste (Egg shell and Palm kernel shell) Nanoparticle coating for Mild Steel

Epoxy has been widely used as a coating material to protect the steel reinforcement in concrete structures, because of its outstanding processability, excellent chemical resistance, good electrical insulating properties, and strong adhesion/affinity. The major disadvantage raised from exothermic curing reaction of highly crosslinked epoxy matrix is brittleness and microcracks that change the epoxy coating performances. The barrier performance of epoxy coatings can be enhanced by the incorporation of inorganic filler particles at nanometer scale which can be dispersed within the epoxy resin matrix to form an epoxy nanocomposite. The parametric addition of eggshell ash nanoparticles (ESAnp) and palm kernel shell ash nanoparticle (PKSAnp) in epoxy for the coating of mild steel was studied. Thermal decomposition was observed in terms of global mass loss by using a TGA Q50 thermogravimetric analyzer. Improvement of 78.05% and 82.56% thermal properties were obtained for the epoxy-4wt%ESAnp and epoxy-5wt%PKSAnp at 1000°C. This work showed that epoxy-4wt%ESAnp and epoxy-5wt%PKSAnp have best properties for thermal applications.

Stochastic Damage Constitutive Relationship of Steel-Reinforced Concrete Bond-Slip

The bond-slip damage of the interface between profile steel and concrete is the key point of steel-reinforced concrete structure. This paper is based on the statistical analysis of a large amount of experimental data and the distribution characteristics of bonding stress on the bonding surface of the profile steel and concrete, and the conversion rules between the three parts (chemical bonding force, frictional resistance, and mechanical interaction) of the bond force are obtained. According to the mutual conversion rules of the three parts of the bonding force on the steel-reinforced concrete bonding surface, a mesomechanical model based on the spring-friction block element is established. Taking into account the discreteness of concrete performance on the bonding surface and the randomness of defects, using the stochastic damage theory, a constitutive model of stochastic bonding damage on the steel-reinforced concrete bonding surface is established. The comparative analysis with the results of a large number of steel-reinforced concrete pull-out tests shows that the model can reasonably reflect the damage characteristics of the steel-reinforced concrete bonding surface.

Minimizing embodied energy of reinforced concrete floor systems in developing countries through shape optimization

Less Economically Developed Countries (LEDCs) are struggling to meet the demand for affordable housing in their growing cities. There are several reasons for this, but a major constraint is the high cost of construction materials. In India, which needs over 20 million urban housing units by 2022, material costs can constitute 60 to 80% of the total cost of residential construction. Nonetheless, their construction mimics the materially inefficient practices of the More Economically Developed Countries (MEDCs), which were developed to reduce labor over material costs. As a result, prismatic beams and flat slabs are often used despite their structural inefficiency. The mounting use of steel-reinforced concrete structures in LEDC cities also raises concern for the environmental costs of construction; for example, construction accounts for 22% of India’s carbon emissions. At the building scale, at least 50% of the structural mass and embodied energy is just in the horizontal spanning elements.This research addresses these challenges with a flexible methodology for the design and engineering of materially efficient structural floor systems that can reduce the economic and environmental costs of urban construction. Construction costs and embodied energy are direct products of material choice and quantity. In response, this paper presents a strategy for the numerical shape optimization of ribbed one-way concrete floor slabs. Designed for the constraints of India, the elements are optimized to reduce the embodied energy associated with the slab’s concrete and reinforcing steel while resisting the same loads of an equivalent solid flat slab. The optimization method includes a novel approach to 3D shape parameterization, as well as a decoupled analytical engineering analysis method that accounts for the key failure modes and constraints of reinforced concrete design. The result of this work is a shaped slab design method that can reduce the embodied energy of one-way concrete floors by 48–64%.

BOND STRENGTH OF GFRP BARS IN FIBER CONCRETE IN COASTAL ENVIRONMENT CHARACTERISTIC OF THE MEKONG DELTA

Glass fiber-reinforced polymer (GFRP) is considered an alternative to steel reinforcement in concrete structures in highly corrosive environments. The bond characteristics of GFRP bars in concrete is an important parameter that determines the feasibility of using this material with non-corrosive concrete. Thus, the paper presents the experimental results of the bond strength of GFRP bars in fiber concrete in a coastal environment characteristic of the Mekong Delta in the south of Vietnam. Research results within 2 years showed that the bond strength of GFRP bars in fiber concrete increased over time and gave a maximum value corresponding to 5.0% silica fume content. In this study, the correlation between the bond strength of control specimens that were cured in the laboratory and specimens that were cured in actual conditions was established. In addition, the experimental results also showed that the impacts of salty water and alum (pH, salinity, temperature, wet-dry cycle) had almost no effect on the bond strength of GFRP bars in fiber concrete. These environmental influences need to be investigated further.

Azadirachta indica Leaf Extract as Green Corrosion Inhibitor for Reinforced Concrete Structures: Corrosion Effectiveness against Commercial Corrosion Inhibitors and Concrete Integrity.

The construction industry has extensively demanded novel green inhibition strategies for the conservation and protection of carbon steel-reinforced concrete structures. For the first time, the effect of Azadirachta indica leaf extract (Neem) as a potential corrosion inhibitor of carbon steel in reinforced concrete under corrosion in saline simulated media was evaluated. To assess the corrosion inhibition behavior of the Neem natural organic extract, three inorganic commercial inhibitors were tested to compare following the criteria established by Stratful for half-cell potential under a simulated chloride environment. Moreover, the effect of concrete integrity by the Neem treatment was recorded after different temperature conditions, slump, weight alteration, air content, compressive strength, and chloride-ions penetration. The results suggested that the Neem treatments did not alter the concrete integrity and the physicochemical parameters. We reached a promoted long-term corrosion protection of 95% after 182 days of evaluation. Thus far, our current results open up a new promising “green” road to the conservation of carbon steel in reinforced concrete for the construction industry.

Bond Behavior of Steel-Recycled Aggregate Concrete Interface After High Temperatures and Spraying Water Cooling

Using recycled aggregate concrete (RAC) in steel-reinforced concrete structure is an effective way to eliminate the adverse effects of recycled aggregate, which has an excellent application prospect. Fire has a great destructiveness to steel-reinforced recycled aggregate concrete (SRRAC) structure; hence, the bond performance of SRRAC after high temperature, as the prerequisite for the composite between steel and RAC, is the key problem for structural safety and the corresponding safety assessment after fire. In this article, the residual bond behaviors of steel-recycled aggregate concrete interface after different high temperatures and spraying water cooling were studied through the push-out test. The failure modes and load–slip curves were examined. The ultimate bond strength, residual bond strength, and elastic bond shear stiffness of specimens after high temperature and cooling for the regime of spraying water were evaluated and compared to that of natural air. A parametric analysis of temperature, replacement percentage, and studs was conducted. A calculation approach for the ultimate bond strength and residual bond strength of SRRAC after high temperature was developed based on the sensitive analysis of gray system theory and regression analysis. Results showed that the bond properties of SRRAC specimens after high temperature were decreased as exposure temperature increased. The cooling regime of spraying water has a more significant influence on the ultimate strength and residual strength than that of natural air. The specimens with studs on both flange and web have the highest bond properties after high temperature. In all the factors, the number of studs showed the largest gray relational degree to the bond strength of SRRAC. The developed approach provided a reliable prediction of bond strength for SRRAC after high temperature.