Bottom Longitudinal Reinforcement Research Articles

Influence of concrete and unbonded ratio on RC beams

Hybrid aggregates, comprising normal-weight and lightweight aggregates, offer an effective means to enhance the physical and mechanical properties of concrete. However, the comprehensive effect of hybrid aggregate concrete on the flexural performance of reinforced concrete (RC) beams remains largely unexplored. In this study, utilizing LC30 lightweight concrete, LC40 gravel lightweight concrete, hybrid aggregate lightweight concrete, and hybrid aggregate concrete with reduced ceramsite content as matrix materials, RC ordinary beams and RC bond-slip beams with dimensions of 150 mm × 300 mm × 2400 mm were meticulously designed and fabricated. Employing a four-point bending test, the effects of the concrete matrix, the unbonded ratio, and the reinforcement ratio of the bottom longitudinal rebar on the flexural behavior of the two types of beams were scrutinized. Furthermore, the load–deflection and load–slip responses were subjected to numerical simulation using the finite element method. The findings demonstrate that hybrid aggregates exert a substantial influence on adjusting the dry apparent density, strength, and elastic modulus of concrete to align with design specifications. While the physical and mechanical characteristics of both beam types are primarily governed by the reinforcement ratio and unbonded ratio, the concrete matrix, despite its distinct properties, exhibits minimal effect on these attributes. Nevertheless, it significantly affects beam stiffness and the relative slip between the rebar and the concrete matrix. Both beam categories adhere to the plane section assumption and reveal that optimal collaborative performance between the rebar and concrete matrix occurs at a bottom longitudinal reinforcement ratio of 1%, albeit diminishing with escalating unbonded ratios. The failure progression of both beam types can be categorized into three stages: elastic phase, crack propagation phase, and compressive failure phase. The process of crack advancement, the load–deflection profile, and the load–slip behavior of the beams manifest similarities, albeit subject to variations attributable to the concrete matrix, bottom longitudinal reinforcement ratio, and unbonded ratio. The Menetrey–Willam constitutive model effectively replicates the load–deflection and load–slip characteristics of both beam types. However, its simulation precision is influenced by the friction coefficient existing between the rebar and the concrete matrix. Notably, this friction coefficient undergoes alteration in consonance with the concrete failure process, thereby reflecting the gradual degradation of bonding performance between the rebar and the concrete matrix.

Improvement of structural performance of RC Beams with external reinforcement method: an experimental investigation

The old existing RC structures around the world need to be examined and reinforced to increase their capacity for different reasons. Fiber-Reinforced-Polymer (FRP) is believed to be the most efficient system to retrofit and improve the strength of the RC members. However, in certain cases, engineers need to utilize the combination of flexural and shear FRP systems, which was not mandated in the standard code. Therefore, this research was focused on the structural behavior of RC beams strengthened with a flexural and shear FRP combination. The beam specimens were tested for failure under a two-point load configuration and the confining effect of the FRP was also investigated. The finding of the experimental test revealed the enhancement of the load capacity and ductility performed in RC beams. The specimen failure was indicated by the concrete crushing at the top part of the beam and the yield condition at the bottom longitudinal reinforcement. It was also discovered that the externally bonded FRP system could confine the concrete and result in the enhancement of ductility and compressive strength. The evidence presents the understanding of the structural behavior of the RC beam strengthened with the combination of flexural and shear FRP systems.

Shear Capacity Prediction Model of Deep Beam Based on New Hybrid Intelligent Algorithm

Accurate shear load capacity predictions are crucial to achieving the load-bearing requirements of concrete deep beams in a variety of construction structures. Conventional BP neural networks have the drawbacks of being prone to local optimums and having a sluggish rate of convergence for predicting the shear load capacity of reinforced concrete deep beams. To overcome this problem, this study incorporated the black widow optimization algorithm (BWO) and principal component analysis (PCA) into a BP neural network to create a unique Hybrid Intelligent Optimization Algorithm (PCA-BWO-BP). Firstly, PCA was used to reduce the dimensionality of the input variables of the shear load capacity prediction model of reinforced concrete deep beams. Secondly, BWO was introduced to optimize the weights and thresholds of the BP neural network. Finally, the four algorithms were compared and validated through the use of five model evaluators. The results showed that the PCA-BWO-BP model can explore the intrinsic relationship between member size, bottom longitudinal reinforcement, hoop reinforcement, concrete strength and the shear load capacity of reinforced concrete deep beams and generate reasonable prediction values, and the complexity of the prediction model can be effectively reduced by introducing the PCA algorithm, whereas the BWO algorithm can optimize the weights and thresholds of the BP neural network to improve the convergence and global search ability of the model. The mean absolute percentage error (MAPE) of the PCA-BWO-BP algorithm is 5.126, and the Nash efficiency coefficient (NS) is 0.989. The generalization ability and prediction accuracy are significantly better than those of the BP neural network, which can solve the problem relating to the fact that BP neural networks are prone to falling into the local optimum. The PCA-BWO-BP model has strong prediction ability, stability, generalization ability and robustness, which can predict the shear load capacity of reinforced concrete deep beams more accurately. It provides a new method and case support for further research on the shear bearing capacity of reinforced concrete deep beams.

Full-Scale Experimental Study on Flexural Performance of the New Precast UHPC Diaphragm Slab in Utility Tunnels

In this paper, a bending test of a precast ultra-high-performance concrete (UHPC) diaphragm slab was carried out. The test revealed that the flexural failure process of specimens under the action of a positive bending moment can be divided into three stages: the elastic, crack-propagation, and yield stages. The first stiffness reduction of the structure was caused by cracks at the bottom of the diaphragm slab, while the second stiffness drop resulted from the yielding of the bottom longitudinal rebars. During the loading process, the ultimate bearing capacity was 3.75 times higher than the design load value (150 kN vs. 40 kN). Additionally, a nonlinear finite element model was established using Abaqus software validated by the test and exploiting parameter analysis. Based on this model, the initial crack stress of the actual slab was determined to be 5.12 MPa. Parameter analysis indicated that the shear strength of the diaphragm slab was stronger than the flexural strength, and the diaphragm slab’s bearing capacity could be improved by increasing the ratio of bottom longitudinal reinforcement. This research confirmed that the new UHPC diaphragm slab used in Guangzhou Smart City is safe, and it also helped the design of similar UHPC slabs for utility tunnels.

Experimental and analytical investigation of the behaviour of reinforced concrete beam under pure torsion

An experimental investigation and FE analysis are conducted on utilising basalt fibre-reinforced polymer (BFRP) fabric to increase the resistance of RC beams against torsion. A total of 4 no. of beams were cast with the same concrete batch mix M20. One beam was used as a control specimen, i.e. unstrengthened beam, and the other three beams were strengthened using BFRP laminates for different configurations, which includes one beam of Full U-Wrapping, one beam of strip wrapping of 150 mm width and 150 mm spacing between two strips and one beam of strip wrapping of 300 mm width and 150 mm spacing between two strips. Under purely torsion conditions, all of the beams were tested. All these beams have 150 mm × 250 mm c/s dimensions and 2100 mm in length. The beam contains bottom longitudinal reinforcement of 12 mm dia. and top longitudinal reinforcement of 10 mm dia. Stirrups used are of 8 mm diameter with 100 mm spacing; at support, it is 40 mm spacing for the length of 150 mm.The torsion test setup, loading frame and special end supports were fabricated for applying torsional load on beam specimens. The beams were subjected to pure torsional loading and twisting moment, and strains and twist angles were recorded. The experimental investigation results were validated using FEM-based ANSYS software. The model of the beams was created in SOLIDWORKS software and then imported into ANSYS for FE analysis. The simulations of beams were carried out in ANSYS Workbench. The effectiveness of U-wrapped beams was found to be better than the other strip-wrapping techniques.

Corrosion Crack Morphology and Creep Analysis of Members Based on Meso-Scale Corrosion Penetration.

In this paper, to study the development of load-carrying capacity and long-term creep performance of reinforced concrete beams under different corrosion patterns, the rate-dependent model of concrete is used as the basis to consider the creep development process from the meso-scale level. The porosity mechanics method is used to simulate the generation and penetration process of corrosion products. Three corrosion conditions are set: bottom longitudinal reinforcement corrosion, top longitudinal reinforcement corrosion and all reinforcement corrosion. The corrosion rate is used as the variable in each corrosion condition. The results show that: (1) the greater the corrosion rate in all conditions, the lower the bearing capacity. In addition, the corrosion of top longitudinal reinforcement causes the damage form of the beam to change to brittle damage; (2) the creep coefficient decreases with the increase in corrosion rate in all working conditions, but the main factor for this phenomenon is the obvious increase in initial deformation. Consequently, it is not suitable to follow the conventional creep concept (deformation development/initial deformation) for the development of plastic deformation of damaged members. It is more reasonable to use the global deflection to describe the long-term deformation of corrosion-damaged members.

Performance of precast concrete beam-column joint with a hidden corbel under progressive collapse scenarios

Collapse incidents of structures caused by extreme loads have attracted the attention of academia and building regulatory bodies worldwide. Due to inherent structural discontinuity, precast concrete (PC) structures are more vulnerable to progressive collapse than cast-in-situ reinforced concrete (RC) buildings. Therefore, studies on resisting collapse performance of PC beam-column joints for PC buildings are needed. In this paper, four 1/2-scaled PC beam-column joints with an in-built L-shaped corbel at each beam end were tested for progressive collapse under column removal scenario. These four joint specimens with identical non-seismic PC details were extracted from adjacent bays of the removed column, and the main parameters were the variations in the boundary and loading conditions. The deformation capacity, load-carrying capacity, catenary action (CA) and failure mode were evaluated and discussed. Parametric studies were also conducted by a proposed component-based mechanical joint model, to investigate the effects of PC interface location, mid-height reinforcement ratio and span-to-height ratio on the collapse resistance of the 2-span substructures. The experimental results show that this type of PC joint could achieve excellent hogging moment resistance but relatively lower sagging resistance. However, both PC joints under downward and upward applied loads could achieve a subsequent increase in resistance due to catenary action at large deformation stage. Numerical parametric studies indicated that shifting the precast interface inwards towards 1/3 point of single beam span and increasing mid-height reinforcement ratio could remarkably improve load-carrying capacity at the compressive arch action (CAA) stage. These detailing features could offset the negative effect caused by the discontinuous bottom longitudinal reinforcement, which is typical for gravity-dominant design in non-seismic countries, such as Singapore.

Experimental investigation on progressive collapse resistance of precast concrete frame structures with different beam-column connections

In this paper, twelve 1/4-scale precast concrete (PC) substructural specimens with different beam-column connections under progressive collapse scenario were tested and the results were compared with that of the corresponding conventional reinforced concrete (RC) subassemblies. For assembled monolithic concrete (AMC) specimens, the top longitudinal reinforcement bars of beam passed though the beam-column joint continuously. However, the bottom longitudinal reinforcement bars of beam were either anchored as a 90° bend or lap spliced in the cast-in-place joints. Moreover, the flange effects as well as the effects of transverse beam and slab were also investigated according to spatial subassemblies with or without precast composite slabs. For fully assembled concrete (FAC) specimens, dowel bars and corbel connections, as well as steel plates and hidden corbel connections were used in the beam-column joints. Test results showed that the AMC specimens with or without precast composite flanges (slabs) exhibited almost the same progressive collapse resistance as RC specimens in the literatures, except for the peak value of the vertical load at the compressive arch action (CAA) stage for the AMC specimen with lap-splice of bottom rebars in the joints. Significant CAA at small deformation stage and subsequent tensile catenary action (TCA) at large deformation stage developed in the laminated beams under column removal scenarios. Furthermore, the transverse beam and composite slab effects could obviously increase the capacity of an AMC two-span beam. However, unlike RC specimens, CAA and TCA were not completely developed in the FAC specimens due to pull-out failure of the rebars in the beam-column joints or premature failure of the welding points between steel plates and rebars.

Neural network prediction of joint shear strength of exterior beam-column joint

Beam-Column joints are the critical locations in the reinforced concrete structures as they experience a massive amount of deformations under earthquake. The shear failure of the beam column joint should be avoided for the safety of the structure. In the present study, prediction of joint shear capacity of exterior Beam-column joint is proposed using artificial neural network (ANN). Experimental investigations performed by different authors have been examined and used to prepare the data sets for training, testing and validating the neural network. Parameters responsible for the shear strength of the exterior Beam-Column Joints are identified and the artificial neural network model is proposed to predict the joint shear strength. Input parameters for the ANN model are width and depth of the joint, concrete compressive strength, length of beam, top and bottom longitudinal reinforcement in the beam, yield strength of longitudinal reinforcement in beam, ratio of beam to column depth, joint Shear reinforcement index, beam bar index and column load index. The performance of the neural network model is evaluated by the statistical relations like Coefficient of correlation, Root mean square error and Scatter index. The proposed model is compared with an empirical formula and different equations suggested by the design codes. The results show that the proposed neural network model can effectively predict the joint shear strength of the Exterior Beam-Column joint.

Failure Analysis of Steel Fiber-Reinforced Concrete T-Beams without Shear Stirrups

The shear failure of a reinforced concrete member is a sudden diagonal tension failure; flexible failure is gradual, associated with significant cracks, and leads to extensive sagging. Therefore, reinforced shear rebars are commonly used to ensure that flexible failure occurs before shear failure under extreme conditions. Extensive efforts are underway to replace conventional shear reinforcements with steel fibers. Here, a nonlinear analysis of a steel fiber-reinforced concrete T-beam was performed in order to estimate the maximum shear capacity with the aid of experimental test data. A continuum-damaged plasticity model and modified compression field theory were used for nonlinear analysis. Three 360 × 360-mm web elements were selected between the shear span; changes in the principal axis caused by crack development and propagation were traced. Changes in the crack angle according to the average strain of the bottom longitudinal reinforcement and the vertical strain of the web element were also determined. For verification, a strut-tie model was used to predict shear capacity. The experimental results and the finite element analyses were in good agreement.

Flexural behavior of GFRP bar-reinforced concrete beams with U-shaped UHPC stay-in-place formworks

Poor durability of reinforced concrete structures in harsh marine environments is an intractable issue. Replacing steel bars with fiber-reinforced polymer (FRP) bars and utilizing ultrahigh-performance fiber concrete (UHPC) for the concrete cover can greatly increase the durability of such structures. A new hybrid GFRP bar reinforced concrete beam with a prefabricated U-shaped UHPC stay-in-place formwork was tested. Herein, nine beams—one reference beam and eight hybrid beams with prefabricated U-shaped UHPC stay-in-place formworks—were subjected to four-point bending tests. The test parameters included the existence of a U-shaped UHPC stay-in-place formwork, the GRFP bar reinforcement ratio, the core concrete strength, and the bottom longitudinal reinforcement type. Experimental results showed that the hybrid beams had approximately 93.8–228.2% higher cracking loads and the hybrid beams (except beams U2 and U5) had approximately 5.9–19.0% higher ultimate loads than the reference beam. Increasing the GFRP reinforcement ratio improved the cracking load and bearing capacity of the hybrid beams, and the ultimate load increased with increasing core concrete strength. Premature failures in some hybrid beams due to partial debonding occurred between the U-shaped UHPC stay-in-place formwork and core concrete. Thence, the partial debonding should be avoided in further studies by proposing a more effective interfacial bonding method for the hybrid beam.

Bond stress distribution analysis between non-prestressed steel strand and concrete in novel beam-to-column connection

The Precast Prestressed Assembled Structural (PPAS) system frame is a novel prefabricated concrete structure, which mainly use 15.2-mm high-strength steel strands as the bottom longitudinal reinforcement. In addition, a certain length of non-prestressed steel strands with 90-degree hooked anchorage type are reserved at the beam end and anchored into concrete column to form a novel beam-to-column connection. The good bond and anchorage performance of steel strand in concrete column is the prerequisite for this connection. However, the bond behaviors such as the bond stress distribution, the bond stress transfer mechanism of the steel strand-to-concrete interface etc. has not been fully understood. For this reason, pull-out tests on six specimens, including thirty-six steel strands with various anchorage type, embedment length and anchorage position, were performed in this research. The results indicated that, compared with straight-line anchorage type, the steel strand with 90-degree hooked anchorage type could increase the ultimate average bond stress and bond stiffness. In addition, the embedment length and anchorage position of the steel strands also had different degrees of influence on the average bond stress. The evolution of strain-pullout load behavior of steel strand was strongly related to the bond position. The anchorage type of steel strand greatly affected the distribution pattern of bond stress between steel strand and concrete. However, the bond stress distribution was always non-uniform along the embedment length, regardless of the anchorage type or embedment length.

Pull-out behavior of non-prestressed steel strands in novel beam-to-column connection

Abstract The Precast Prestressed Assembled Structural (PPAS) system frame structure has been gradually applied in building and storage structures. In this building system, the 15.2-mm high-strength steel strands are used as the bottom longitudinal reinforcement of the precast beam, and a certain length of non-prestressed steel strands reserved at the beam ends are anchored into the concrete column to form a novel beam-to-column connection. For a reliable design of the connection joint, the mechanical behavior of this connection should be taken into account. This paper summarized the results obtained in the pull-out tests of the steel strands with different research variables, including anchorage form, anchorage position, and embedment length, and it was found that the use of the steel strand with 90-degree hooked anchorage form in the concrete column significantly affected the pull-out behavior of steel strand, such as failure mode, pull-out load versus slip curve, and ultimate load, etc. In particular, compared to the specimens of steel strands with straight-line form, the specimens having steel strands with 90-degree hooked form shows a 62% increase in ultimate load in average.

Prediction model for compressive arch action capacity of RC frame structures under column removal scenario using gene expression programming

Compressive arch action (CAA) is one of the important resistance mechanisms against progressive collapse in reinforced concrete (RC) frame buildings at small deformations. In this study, the distinguishing features of Gene Expression Programming (GEP) are utilized in order to establish a prediction model for the CAA capacity of RC beam-column substructures. The proposed equation correlates CAA capacity with six input parameters, i.e., compressive strength of concrete (fꞌc), double-beam span-to-depth ratio (Ld), width of beam (b), top and bottom longitudinal reinforcement ratio at the joints (ρt &ρb, respectively), and the ratio of axial restraints stiffness to the axial stiffness of beam (α). The data for the above-mentioned variables is collected from different studies to develop the proposed model and subsequently implemented for the verification purpose. Different statistical and external validations criteria recommended in literature are carried out to assess the performance of the developed model. Furthermore, sensitivity and parametric analyses are also performed using criteria available in literature. The performance of the genetically developed GEP model was checked and compared with models developed by using regression techniques. The GEP model demonstrated superior performance to linear and non-linear regression methods. The results show that the developed model is successfully capable of evaluating the CAA capacity of RC beam-column substructures and is incredibly imperative for prediction rationales.

Bond performance of reinforced concrete beams with electric arc furnace slag aggregates

The present study was conducted to evaluate the bonding performance of reinforced concrete beams with electric arc furnace oxidizing slag aggregates. The specimens were tested by varying the aggregates, and the top and bottom longitudinal reinforcement position, depending on concrete placement. The specimens containing electric arc furnace oxidizing slag aggregates showed bond performance that was on average of about 8% to 20% higher than that of the specimens using natural aggregates. The bond strength was higher at the corner longitudinal reinforcement than at the inner longitudinal reinforcement and higher at the bottom reinforcement than at the top reinforcement, regardless of the aggregate type. The experimental results were consistent with results from previous studies with concrete containing natural aggregates. Comparison with previous studies confirmed the excellent bond performance of the concrete with electric arc furnace oxidizing slag aggregates, and demonstrated the use of concrete containing electric arc furnace oxidizing slag aggregates for structural members.

Bending experiment on a novel configuration of cold-formed U-shaped steel-concrete composite beams

This paper discusses a novel configuration of rebar truss stiffened cold-formed U-shaped steel-concrete composite beams (RCUCB). The open steel U-section is stiffened by a rebar truss. The interface between concrete slab and lower part (including steel U-section, encased concrete, and reinforcement) is enhanced with uniformly distributed inverted U-shaped rebars. The reinforcement is installed at the bottom of the lower part to control the concrete longitudinal deformation. A flexural experiment on ten specimens was conducted considering reinforcement ratio, steel ratio, beam depth, and shear stud spacing (at the bottom of steel U-section). Typical flexural failure mode was observed and the rebar truss and inverted U-shaped rebar were found to provide significant integrity for the RCUCB. Thus, the RCUCB can achieve plastic bending capacity and excellent deformability. The mid-span deflection, plastification factor, and ductility factor of the RCUCB are up to L0/20, 2.08, and 24, respectively. An effective slab width of b + L0/3 may be chosen according to the strain distribution. The bending capacity calculated according to EC4 and JGJ 138-2016 agrees generally well with the test result. Finally, design details pertaining to the width to thickness ratio of bottom steel soffit, the height to thickness ratio of steel web, the transverse reinforcement ratio of concrete slab, and bottom longitudinal reinforcement are suggested accordingly.

Experimental investigation and analytical calculations on shear strength of full-scale RC slabs with shear reinforcement for nuclear power plants

In this study, a series of 27 tests on 27 full-scale reinforced concrete (RC) slabs measuring 4m×2.6m×0.3m is presented. RC slabs are frequently used in the construction of civil engineering structures such as buildings, car parks and bridges. They may be subjected to several types of forces acting, most often bending and shearing forces. Shearing forces have generally been more thoroughly investigated due to their brittle failure mode. This is especially the case for reinforced concrete slabs subjected to concentrated loads near to supports. Situations such as localized heavy loads from equipment and slabs loaded by walls or columns are commonly found and for constructability and cost-effectiveness reasons, shear reinforcement (stirrup) of concrete is an important issue in a power plant project. This new experimental study is a continuity of the previous studies conducted by Bui et al. (2017a,b) and Nana et al. (2017) in which all the slabs were tested without shear reinforcement. The originality in this study is that the slabs are this time studied with shear reinforcement except for references slabs. These full-scale slabs designed as usually in nuclear buildings, are submitted to a concentrated load near a linear support, the investigation of their shear behavior is presented. The main aim was to evaluate the influence of the shear reinforcement on the shear behaviour of slabs. The shear strength and the associated failure modes were quantified. Then we also addressed the influence of several variables such as bottom longitudinal reinforcement, tension and compression axial loads. Until now, rarely have experiments in the literature addressed the effect of the uniaxial load on the shear resistance of reinforced concrete slab. The experiments are used to evaluate the pertinence of Eurocode 2 for the shear design of reinforced concrete slabs in comparison with the French approach, the ACI 318-14 code and Model Code 2010 formulation using the level of approximation LoA II.

Experimental and Numerical Modelling of Shear Behaviour of Full-scale RC Slabs Under Concentrated Loads

In nuclear buildings, situations such as localized heavy loads from equipment, slabs loaded by walls or columns are commonly found. For constructability and cost-effectiveness reasons, shear reinforcement of concrete is an important issue in a new nuclear plant project. This study presents an experimental and numerical investigation of the shear behaviour of full-scale reinforced concrete (RC) slabs without shear reinforcement under a concentrated load near a linear support in nuclear buildings. The main aim was to evaluate experimentally and numerically the influence of several variables: bottom longitudinal reinforcement, bottom transverse reinforcement, compressive strength, concrete aggregate size, slab depth and loading plate length on the shear behaviour of RC slabs under a concentrated load. First, an experimental campaign was performed: a series of ten tests on nine full-scale slabs (one slab measuring 3.2m×2.9m×0.3m; six slabs measuring 4m×2.6m×0.3m; one slab 4m×2.6m×0.35m and one slab 4m×2.6m×0.4m) already presented in Bui et al. (2016). The originality of this study is that three new tests added three full-scale slabs measuring 4m×2.6m×0.3m to analyse the influence of the compressive strength and the loading plate length on the slabs' shear strength, which had not been tested in the 2016 study. Then concrete damaged plasticity (CDP) in Abaqus software was used for three-dimensional (3D) modelling and calibration. The proposed numerical model showed that the RC slabs' behaviour was in good agreement with the experimental results.

STRENGTH AND CRACK RESI STANCE OF REINFORCED CONCRETE BEAM STRUCTURES UNDER THE ACTION OF LOW-CYCLE LOADS OF CONSTANT SIGN AND CYCLIC ALTERNATING LOADINGS OF HIGH LEVELS

Purpose. To investigate and to analyze the behavior of the areas near supports of reinforced concrete beam elements under the action of low-cycle loads of constant sign and repeated alternating loadings taking into account the influence of constructive factors and factors of external action for the future using of obtained results for improvement of calculated engineering technique. Methodology. Three series of experiments were performed to research this problem. Test specimens are reinforced concrete beams of rectangular cross section with sizes 200´100 mm, with length 1975 mm, that were reinforced with two flat welded framework with symmetrically located top and bottom longitudinal reinforcement 2Ø14А500С and transverse reinforcement 2Ø3, 4, 5ВрI with relative shear span = 1, 2, 3, that were made from concrete С 16/20, С 30/35, С 40/50, and that were tested by monotonic load, low-cycle alternating loading (= ±0,50; ±0,65; ±0,80) and repeated load of constant sign (= 0…0,50; 0…0,65; 0…0,85). Findings. This material considers and analyses obtained and processed experimental data, that discover the influence of low-cycle loads of constant sign and repeated alternating loadings of high levels on the main proofs of crack resistance and strength of inclined and vertical sections of areas near supports of reinforced concrete structures tacking into account the change of selected by planning of an experiment constructive factors and factors of external action. Originality. In this paper the systematized experimental data are given, that reflect new features of reinforced concrete beam elements work under the action of mentioned loads. Practical value. The research results are being introduced to the practice of design and calculations of areas near supports of reinforced concrete elements that are subjected to the action of low-cycle loads, and also the results can be used in educational process of technical academies.

Experimental investigation of shear strength of full-scale concrete slabs subjected to concentrated loads in nuclear buildings

The following study analyzes the shear behavior of full-scale slabs without shear reinforcement (the design of slabs used in nuclear buildings) under a concentrated load near a linear support. Experimental tests were conducted to quantify the shear strength and the associated failure modes. We addressed the influence of several variables, such as bottom longitudinal reinforcement, bottom transverse reinforcement, compressive strength, concrete aggregate size, and influence of the slab depth. A series of ten tests on nine full-scale slabs (one slab of 3.2m×2.9m×0.3m; six slabs of 4m×2.6m×0.3m; one slab of 4m×2.6m×0.35m; one slab of 4m×2.6m×0.4m) are presented. Realistic boundary conditions with the slabs supported on all four sides were used. The experiments are firstly used to evaluate the pertinence of Eurocode 2 for the shear design of reinforced concrete slabs without shear reinforcement in comparison with the French approach, and then to make comparisons with the ACI 318-14 code. We also studied the verification of a new proposal for the extension of Eurocode 2 proposed by Lantsoght et al. (2015).