Reinforcement Strain Research Articles

Experimental studies on tensile behavior of reinforced engineered cementitious composite members with double steel rebars

AbstractThis paper investigates the tensile behavior of reinforced engineering cementitious composite (ECC) members. Twelve reinforced ECC members were tested in uniaxial tension. The stress‐average strain curves, failure modes, and the strain of longitudinal reinforcement at selected sections were obtained during testing. The influence of reinforcement ratio on the load resistance and deformation capacity of members was determined. Test results showed that the tensile behavior of reinforced ECC members could be divided into three stages, namely, the elastic stage, the microcracking stage and the major cracking stage. ECC significantly contributed to the load resistance of reinforced ECC members before the formation of major cracks through tension stiffening effect. The load capacity and deformation capacity of reinforced ECC members increased with the increase of reinforcement ratios. For members with ungrooved steel bars, the ultimate load and ultimate strain increased by 130.0% and 115.2% with the reinforcement ratio increased from 1.01% to 2.26%. For members with grooved steel bars, the ultimate load and ultimate strain increased by 123.6% and 98.7% with the reinforcement ratio increased from 0.78% to 2.04%. Based on the test results, the failure mechanism of reinforced ECC members was analyzed and equations for predicting the load capacity of members were proposed. Comparisons between experimental and calculated load capacities suggested that the calculated results were in good agreement with the experimental values. The study on the tensile behavior of reinforced ECC members provides useful results for the design and application of reinforced ECC members.

Core versus Surface Sensors for Reinforced Concrete Structures: A Comparison of Fiber-Optic Strain Sensing to Conventional Instrumentation.

High-resolution distributed reinforcement strain measurements can provide invaluable information for developing and evaluating numerical and analytical models of reinforced concrete structures. A recent testing campaign conducted at UCLouvain in Belgium used fiber-optic sensors embedded along several longitudinal steel rebars of three reinforced concrete U-shaped walls. The resulting experimental dataset provides an opportunity to evaluate and compare, for different types of loading, the strain measurements obtained with the fiber-optic sensors in the confined core of the structural member against more conventional and state-of-the-practice sensors that monitor surface displacements and deformations. This work highlights the need to average strain measurements from digital image correlation techniques in order to obtain coherent results with the strains measured from fiber optics, and investigates proposals to achieve this relevant goal for research and engineering practices. The longitudinal strains measured by the fiber optics also provide additional detailed information on the behavior of these wall units compared to the more conventional instrumentation, such as strain penetration into the foundation and head of the wall units, which are studied in detail.

Punching shear behavior of RC slabs incorporating macro-synthetic fibers

The effect of macro synthetic fibers on punching shear behavior of reinforced concrete slabs was investigated. Twenty-four square reinforced concrete slabs (1500 mm × 1500 mm) were prepared, instrumented, and tested under monotonic, displacement controlled, center-point load in a simply-supported configuration. The main test parameters were the fiber volume fraction (0.5% and 1%), slab thickness (100 mm and 150 mm), and the flexural reinforcement ratio (0.9% and 1.5%). Test measurements included applied load, slab deflection, strains in the steel reinforcement and in the concrete. The development of the cracks for the duration of the test was also monitored and recorded. The test results showed that the punching shear strength, deflection capacity, and energy absorption of the FRC slabs were significantly improved by the presence of macro synthetic fibers. This improvement was associated by a more defined punching shear area, higher cracking density, higher strain in the concrete and a lower strain in the reinforcement steel. Furthermore, the level of improvement was found to be more pronounced in the FRC slabs with lower thickness, lower reinforcement ratio and higher fiber volume fraction.

Failure mechanism and static bearing capacity on circular RC members under asymmetrical lateral impact train collision

This paper aims to validate circular reinforcement concrete (RC) members' responses to the effect of an asymmetrical lateral impact span train collision. It was determined that the RC members' failure mechanism and dynamic response characteristics were important. Numerical analyses were conducted on four specimens. The specimen's crack development pattern, failure mode, impact force, and deflection time history curves are verified. Due to the difference in impact velocity, longitudinal reinforcement, and stirrups ratios, shear cracks indicate two types. A finite element (FE) modeling method has been proposed and successfully demonstrated. Using the control variables to study the failure process and mode, which were affected by reinforcement ratio, impact velocity, and slenderness ratio, by analyzing impact response characteristics. It is found that parameters greatly influence shear cracks' type and development range. Simultaneously, the changes in impact velocity and slenderness ratio affect the failure mode of the members. RC members' mechanical properties and failure mechanisms are studied using test and FE analysis. Members' failure modes, bending moment distribution and development, shear forces, reinforcement strain, and energy consumption are also investigated. The development of type I and type II shear cracks is discussed. A method to determine the shear cracks was proposed through regression analysis by supplementing other scholars' test data and combining it with the study test data.

Design procedure and seismic response of low-damage self-centering precast concrete frames

The seismic design procedure of the low-damage self-centering precast concrete (LDSCPC) frame is proposed. Its effectiveness was verified by nonlinear dynamic analysis based on the OpenSees model, and the seismic response of the LDSCPC frame was studied. The results show that the difference between the designed base shear and the average base shear obtained by nonlinear dynamic analysis is approximately 2.5%. The peak strain of the longitudinal reinforcement in each story of the beam is significantly lower than the yield strain, and the precast beam of the LDSCPC frame can meet the design requirements according to the structural reinforcement. The displacement response of the LDSCPC frame under frequent earthquakes is similar to the displacement response of the reinforcement concrete (RC) frame. Under rare earthquakes, the average of the maximum drift of the LDSCPC frame meets the code limit of 0.02 rad, and there is almost no residual displacement. The limit state of post-tensioned (PT) tendons will appear much later than the limit state of drift. The seismic vulnerability analysis results show that the metallic yield dampers of the LDSCPC frame can reduce the failure probability of IO and BR performance levels by 4.58% and 7.54%, respectively, which can effectively reduce the displacement response of the structure.

Blind competition on the numerical simulation of continuous shallow steel‐fiber reinforced concrete beams failing in bending

AbstractThis article describes the second blind simulation competition (BSC) organized by the fib WG 2.4.1, which aims to assess the predictive performance of models based on the finite element method (FEM) for the analysis and design of fiber reinforced concrete (FRC) structures. Slabs supported on columns or piles have becoming competitive applications for FRC due to the technical and economic benefits may be obtained by combining properly the fiber reinforcement mechanisms to those provided by conventional reinforcement placed, as a strip, in the alignment of columns/piles. Therefore, a representative zone of this structural system, namely a hybrid fiber reinforced concrete (R/FRC) shallow beam, is chosen in this BSC to show the potentialities of FRC in these types of applications, as well as to assess the predictive performance of FEM‐based computational models on the design verification at serviceability and at ultimate limit state conditions (SLS and ULS, respectively). Two statically indeterminate shallow beams of two equal spans were tested up to their failure, by recording the applied loads, the strains in the conventional reinforcements and in the FRC of the critical zones of the structure. By using digital image correlation, the average crack width at the level of the flexural reinforcements was recorded. The participants had to predict these results by receiving information about the mechanical properties of the materials, the geometry of the prototypes and their loading and support conditions. In this article, the rules and the results of this 2nd BSC competition are presented, and the data obtained experimentally is thoroughly analyzed.

FE analysis of pulled-out eccentrically spliced longitudinal headed bars for precast beam-footing connections

ABSTRACT Load transfer in structural elements of RC constructions and the behavior of such constructions are basically dependent on the detailing of both the structural elements and their connections. Assessing analytically the characteristics and behavior of such structural elements and their connections under likely occurring loads is an important issue. For common detailing of footings in steel and precast structures, longitudinal reinforcement of foundation beams is bent horizontally and spliced with reinforcement of cast-in-place footings to insure an adequate juncture for load transfer. In this study, as concerned with reducing construction time and cost, instead of bending longitudinal reinforcement bars of both, beams and footings, headed reinforcement bars are adopted. By doing so, a discontinuity region is created where longitudinal bars of footings become eccentric to those of beams that are embedded in the footings. To allow the flow of tensile forces from longitudinal bars of beams to longitudinal bars of footings, a set of reinforcing ties is provided between them. As such setting of headed reinforcement bars is not common, thorough investigations have been carried out to confirm the relevance of the proposed tie reinforcement. In this paper, results of a finite element numerical investigation of pulled-out eccentrically spliced longitudinal headed bars with different detailing of transverse reinforcement, proposed for precast beam-cast-in-place footing connection, are presented and compared to test results. The elaborated modeling could fairly reproduce the global behavior of the six specimens, where the numerical results acceptably approached the experimental results in terms of initial stiffness, ultimate strength, crack pattern and strain of reinforcement.

Punching and post-punching shear failure behaviors of laterally-restrained and eccentrically loaded flat plate slab-column joints with drop panels

In concrete flat plate slab-column joints with drop panels, successive punching shear failures often occur at the slab-drop panel interface and along the column perimeter. When such joints are subjected to combined bending-shear actions under an eccentric load, their punching and post-punching shear failure behaviours are further complicated which can significantly impact the progressive collapse behaviour of the structural system. An experimental study was conducted on six laterally-restrained slab-column joint specimens with drop panels. Different levels of load eccentricities and different drop panel thicknesses were considered. Two punching shear failure sections were also identified. For a thick drop panel, the first punching failure took place at the slab-drop panel interface, followed by the second punching shear failure occurring along the column perimeter. For a thin drop panel, on the other hand, punching shear failure only occurred at the column perimeter. The damage patterns, the reinforcement strains and the joint strengths before and after punching failure at two different sections were analysed. Numerical simulation was conducted to investigate the effects of load eccentricity on the inclination of the punching cone. Numerical results showed that the punching cone angles at the slab-drop panel interface and at the column perimeter are, on average, 11.6° and 27.1°, respectively. In addition, larger eccentricity contributed to higher cross-sectional shear stresses on the eccentric loading side, leading to reduced punching shear strength and earlier damage. Furthermore, the experimental and numerical punching shear strengths were compared against the predictions of the Chinese, American and European design codes. Finally, a post-punching strength prediction method was proposed, and the predicted strengths deviated from the experimental results by −16% and 23%, for the thick and thin drop panels, respectively. In addition, the integrity reinforcement was also found to contribute at least 80% to the post-punching shear strength.

Shaking table test study on dynamic performance of a base-isolated frame structure under an isolation bearing removal scenario

Studies on the progressive collapse of structures have been at the forefront in structural engineering domain recently. The progressive collapse of isolated structures is quite different from that of conventional fixed-base structures. Once an initial failure occurs in the isolation layer which is the most vulnerable to accidental events due to the low horizontal stiffness, progressive failures at other locations may lead to a large-scale collapse of isolated structures. This paper presents a 1:4 scale model shaking table test of a three-story irregular plane reinforced concrete (RC) frame isolated structure to investigate the progressive collapse resistance of isolated structures. An edge bearing was removed quickly by an electromagnetic failure excitation device during the first seismic input case. The dynamic responses such as the macroscopic crack distribution, acceleration responses, displacement responses, internal forces of the isolation bearings, and concrete and reinforcement strains of the failure span beams were evaluated. The results show that the significant vertical deformation with dynamic impact response was produced at the failure point under multi-directional dynamic coupling excitation, i.e., the combined effect of the vertical unbalanced load caused by sudden failure of a bearing and horizontal earthquakes. This sudden failure of the isolation bearing not only had an impact on the internal forces of bearings adjacent to the failure bearing, but also on other non-adjacent bearings. As the tensile and compressive stress of adjacent bearings were more likely to exceed design limits under earthquakes, the risk of overturning collapse for isolated structures markedly increased following the failure of a few bearings. In addition, vertical and low-frequency components of earthquakes could have a significant influence on dynamic responses and damages of isolated structures, especially in the area of bearing failure. The experimental results obtained in this study act as important references for the progressive collapse design of isolated structures.

Flexural capacity prediction of steel fiber reinforced concrete beam with recycled fine and coarse aggregate

In this study, the flexural performance of the steel fiber reinforced concrete beams with recycled fine and coarse aggregates was investigated through the experiments. The effects of steel fiber volume fraction, recycled fine and coarse aggregate replacement ratio, and concrete compressive strength grade on the flexural performance of steel fiber reinforced recycled aggregate concrete (SFRAC) beams were systematically studied in terms of failure mode, flexural capacity, cracking patterns, load-deflection response, and load-tensile reinforcement strain response. The results showed that the flexural capacity and deflection of beams increased and decreased with the increase of steel fiber volume fraction, respectively. The beam with 100% replacement ratio of recycled fine aggregate and 0.5% volume fraction of steel fiber presented the similar or even better flexural performance than that of the ordinary concrete beam. By adding 1.0% volume fraction of steel fiber, the flexural capacity of beam with both 100% replacement ratio of recycled fine and coarse aggregates was higher than that of the ordinary concrete beam. Based on the experimental results of SFRAC beams in this study and other literature, the effects of steel fiber volume fraction and recycled aggregate replacement ratio on the flexural capacity of beams were quantitatively analyzed. Lastly, a model for the prediction of SFRAC beam flexural capacity was proposed and verified.

Shear strengthening of concrete deep beams using pre-fabricated strain-hardening cementitious composite plates

This study investigates the efficiency of near surface embedded (NSE) pre-fabricated strain-hardening cementitious composite (P-SHCC) plates for shear strengthening of reinforced concrete deep beams (RC-DBs) through testing 12 identical specimens. For this purpose, P-SHCC plates of 20 mm thickness have been prepared according to the test variables, cured for about 30 days, and then dipped into the concrete cover of the strengthened DBs at the critical shear span. The use of pre-fabricated plates is intended to alleviate any volumetric change issues associated with SHCC material. The studied parameters were the net spacing between the P-SHCC plates (0, 75, 112, and 150 mm), the width of the strengthening plates (60, 75, and 90 mm), and the ratio of steel reinforcement embedded inside the P-SHCC plates (0 %, 0.67 %, 1.50 %, and 3.00 %). Furthermore, the prestressing level relative to the yielding strain of the steel reinforcement embedded inside the P-SHCC plates was of interest. Experimental results exhibited a successful employment of the P-SHCC plates in enhancing the ultimate load capacity of RC deep beams, especially when prestressing was introduced. The gain in the ultimate capacity reached up to 68.5 %, relative to the un-strengthened control beam (BC), depending on the test parameters. Besides, incorporating steel reinforcement inside the P-SHCC plates had a pronounced effect on both the serviceability and ductility characteristics of the strengthened DBs. Specimens strengthened by reinforced P-SHCC plates demonstrated around 1.57-times improvement in energy absorption capacity when compared to their counterparts strengthened by plain P-SHCC plates. Finally, a strut-and-tie model (STM) in addition to a simpler equation based on regression analysis were used to assess the shear capacity of the strengthened DBs, considering the contribution of P-SHCC plates. The proposed two equations were in good accord with the experimental results.

ОСОБЕННОСТИ ДЕФОРМИРОВАНИЯ СЕЧЕНИЙ ИЗГИБАЕМЫХ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ ПРИ ДЕЙСТВИИ НАГРУЗОК БОЛЬШОЙ ИНТЕНСИВНОСТИ

Many buildings are exposed to special effects of high intensity. When calculating reinforced concrete constructions both for special emergency loads and for seismic loads, the development of plastic strains in reinforcement is supposed just at the design stage. The experimental investigation of plastic deformations influence of the stress-strain state of normal sections of bending reinforced concrete elements has been made. According to the results of experiments, it has been found, that the hypothesis of plane sections is not observed in all cases. The approximation of deformations graph along the cross-section height by the bilinear function, variable during the load process, i.e hypothesis of bilinear sections, is more accurate. The dependence of coefficient A of the hypothesis of bilinear sections on the coefficient of plasticity for reinforcement deformations has been determined based on the results of numerical calculations of beams with symmetric reinforcement and beams without compressed reinforcement in a finite element software package Abaqus. The comparison of obtained numerical results with experimental data has been made, which has shown their satisfactory convergence. The maximum deviation does not exceed 13 %. The assessment of influence of coefficient of hypothesis of bilinear sections on the limit value of coefficient of plasticity for curvature, corresponding to the beginning of the destruction of compressed area of concrete is given.

ЖЕСТКОСТЬ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ ПРИ ИЗГИБЕ С УЧЁТОМ ПОПЕРЕЧНОЙ И ПРОДОЛЬНОЙ СИЛ (ЧАСТЬ 1)

The paper provides a physical and computational model for determining the parameters of limit states of reinforced concrete structures under complex stress state such as bending with effect of axial and shear forces. The forward and backward transitions for determining the stiffness matrix coefficients of reinforced concrete bar structures with inclined and normal cracks have been constructed on the basis of the adopted cross-section discretization scheme and the duality theorem between force and deformation parameters by A.R. Rzhanitsyn. Determination of the stiffness of structures in the zone of inclined cracks was performed on the basis of the model of composite strips into which the zone with inclined cracks is divided. It is assumed a hypothesis about the character of deformation distribution in a complexly stressed reinforced concrete element with inclined cracks. For this model the effective shear modulus has been obtained. It allows to determine the average relative linear and angular strains of concrete and reinforcement at the point adjacent to the shear joint between inclined cracks. Using this model and the experimentally obtained value of the relative shear in the inclined crack, the dowel forces in the reinforcing bar crossed by the inclined crack were determined. The use of the obtained analytical dependences in the practice of designing reinforced concrete structures allows to clarify significantly the definition of displacements and width of opening of inclined and normal cracks, as well as to bring the calculation and physical model based on experimental data as close as possible.

Assessment of the reliability of bent reinforced concrete elements under corrosive effects

The main problem of reducing the reliability and durability of reinforced concrete structures is the corrosion of concrete and reinforcement of operated buildings and structures. Calculation of structures made of reinforced concrete, taking into account environmental influences, is complicated by the stochastic nature of the parameters of corrosion processes. The conducted studies are aimed at solving the problem of improving the methodology of the probabilistic approach to the calculation of corrosion-damaged reinforced concrete elements. The article considers a probabilistic assessment of reliability for the most common bent reinforced concrete elements, taking into account corrosive wear and the time factor. The modeling of the effect of corrosion processes on the stress-strain state of a reinforced concrete element was carried out using the concrete deformation diagram, which takes into account the decrease in strength characteristics with an increase in the concentration of an aggressive medium in concrete. The scheme of propagation of an aggressive environment in concrete is adopted according to the diffuse front method. Corrosion processes in reinforcement were taken into account by reducing the effective cross-sectional area of reinforcing bars. The change in the properties of steel (its embrittlement) with an increase in the concentration of an aggressive medium was not taken into account. Reinforcement corrosion was simulated after the incubation period, after the concentration of the aggressive medium on the surface of the reinforcing bars reached a critical value. The determination of the moment of the onset of the limit state in the element was carried out on the basis of a nonlinear deformation model at each point of the section of the element to achieve the maximum possible tensile or compression strains in concrete and reinforcement. To solve the problem of reliability assessment, the method of statistical modeling implemented in a specialized software package was used. To apply this method, according to previous studies, the probabilistic parameters of all random variables were taken: mathematical expectation and standard deviation. Based on the results of the reliability assessment, graphs of the decrease in the reliability of a bent reinforced concrete element from the time of exposure to an aggressive environment were obtained.

STATE OF THE ART ON BOND BETWEEN FRCM SYSTEMS AND MASONRY/CONCRETE SUBSTRATE: DATABASE ANALYSIS AND IMPROVED MODELS

The use of the Fabric Reinforced Cementitious Mortars (FRCMs) is nowadays a promising solution for the strengthening of both reinforced concrete and masonry structural elements. The application consists of a bond-dependent face-to-face plastering of an open grid or mesh by means of an inorganic-based matrix, i.e. a cement-based mortar. The main advantage of such a strengthening technique is the good compatibility with different types of substrates since the most suitable matrix can be selected focusing on the most similar breathability and stiffness. On the other side, the strengthening efficiency could be over-estimated if the potential bond failure is neglected. The FRCM-bond behaviour depends on many parameters, e.g., mechanical properties of substrate and reinforcement, environmental conditions, etc. Due to the wide range of variability of these parameters, nowadays, formulations for a reliable prediction of the maximum strain which the FRCM is able to develop for avoiding bond failure are not available. At this scope, the present paper collects a large database of experimental results of bond tests available in literature in order to investigate the main parameters influencing the performance of this strengthening technique, to identify the aspects that have to be further studied, and to calibrate an empirically-based analytical model proposed by the authors to predict the maximum design strain in the FRCM reinforcement. The parameters assumed in the model are the following: type of substrate (i.e. masonry or concrete), type of fabric (i.e. carbon, glass, steel, basalt), type of matrix (i.e. cement, lime, alkali-activated based) and failure mode (detachment, slippage, rupture, etc.). The database was clustered depending on the failure mode in order to calibrate targeted and more accurate equations.

Numerical evaluation of impact resistance of concrete columns reinforced with GFRP bars under various axial force ratios and impact velocities

Fiber-reinforced polymer (FRP) bars have the characteristics of high strength, lightweight, and corrosion resistance, which can be used as a substitute for conventional steel bars in a corrosive environment. A three-dimensional (3D) model of the concrete column considering the dynamic increase factor of the concrete, steel bars, and FRP bars was developed using finite element (FE) method to investigate the difference of the concrete columns with steel bars and FRP bars in the impact behavior. The failure pattern, impact force, displacement, reinforcement strain, internal force, and energy of GFRP-RC and RC columns were compared. Then, the effects of the axial force ratio of 0–0.6 and the impact velocity of 1.2–5.6 m/s on the impact behavior were further discussed and an optimal axial force ratio was recommended in this study. The results showed that the impact force, internal force, and local deformation of the GFRP-RC column were slightly smaller than those of the RC column, but the duration and displacement increased. The increase in axial force ratio caused the concrete at the top and bottom of GFRP-RC columns to be crushed, whereas the impact resistance of GFRP-RC columns was best when the axial force ratio was 0.2. The more serious damage to the concrete occurred at the local impact position and both ends of the column as a response to the increase in the impact velocity. The concrete exhibited larger energy dissipation for GFRP-RC columns when subjected to different axial force ratios and impact velocities.

Flexural behaviour and ultimate bending capacity of high-volume fly ash reinforced concrete beams

Large number of studies analyzed physical and mechanical properties of high-volume fly ash concrete, but only a few discussed its structural behavior. Material properties are an important input parameter for structural analysis, but they are insufficient for reliable conclusions to be made. This study analyses flexural behavior of reinforced concrete beams made with 63% of low-calcium class F fly ash in total cementitious materials mass, using experimental method and analyzing current code predictions (EN 1992-1-1). The analysis was done by comparing beams made with two longitudinal reinforcement ratios, made with traditional cement concrete (OPC) and high-volume fly ash concrete (HVFAC), both corresponding to concrete class C30/37. Beams were tested in a four-point bending test measuring vertical displacement, crack development, concrete strains and longitudinal reinforcement strains. According to this research, the flexural performance of HVFAC beams is similar to flexural performance of corresponding OPC beams in terms of ultimate bending capacity. The significant difference was noticed regarding cracking extent that was higher in HVFAC beams. Available ultimate bending moments code predictions can be applied on HVFAC beams with similar precision and variation of results, like for OPC beams. However, this cannot be concluded for parameters depending on the cracking behaviour, like cracking moments or deflections. Results and analysis presented in this study indicate that HVFAC can be used in structural elements subjected dominantly to bending, like beams and slabs. More research regarding structural behavior of HVFAC using full-scale long-term tests is needed to develop larger database for reliability analysis.

Finite element modelling of reinforced concrete one-way slabs strengthened using basalt textile reinforced mortars

PurposeThis paper employs a textile reinforcement strain comparison to study the response of Textile Reinforced Mortars (TRM) strengthened reinforced concrete one-way slab members in flexure using the finite element method. Basalt TRM (BTRM) is a relatively new composite in structural strengthening applications. Experimental data on BTRMs are limited in the literature and numerical analyses can help further the understanding of this composite. With this notion, Abaqus finite element software is utilised to create a numerical method to capture the mechanical response of strengthened slab members instead of time-consuming laboratory experiments.Design/methodology/approachA numerical method is developed and validated using existing experimental data set on one-way slabs strengthened using Basalt TRMs from the literature. An explicit solver is utilised to analyse the finite element model created using calibrated Concrete Damage Plasticity (CDP) parameters according to the experimental requirements. The generated model is applied to extract load, deflection and rebar strains sustained by strengthened reinforced concrete slabs as observed from the experimental reference chosen. The applicability of the developed model was studied beyond parametric studies by comparing the generated finite element tensile strain by the textile fibre with available formulae.FindingsCDP calibration done has shown its adaptability. The predicted results in the form of load versus deflection, tensile and compressive damage patterns from the numerical analysis showed good agreement with the experimental data. A parametric study on various concrete strength, textile spacing and TRM bond length obtained shows TRM’s advantages and its favourability for external strengthening applications. A set of five formulae considered to predict the experimental strain showed varied accuracy.Originality/valueThe developed numerical model considers strain sustained by the textile fibre to make results more robust and reliable. The obtained strain from the numerical study showed good agreement with the experiment results.

Study of the static and endurance strength of reinforced concrete specimens loaded with the account of the characteristics arising in the process of aircraft takeoff and landing operations on airfield pavements

The article shows that the impact of aircraft with multi-wheel bearings on airfield pavements is a cyclical pattern, as a result, constant sign and alternating stresses arise in the material. The results of cyclic loading parameters calculations of coatings under the influence of aircraft with multi-wheeled bearings (load cycle asymmetry coefficient, values of the maximum and minimum stresses of the loading cycle), performed using the SCAD software-computer complex, which implements the finite element method in the form of the displacement method, are presented. The necessity of carrying out tests to determine the endurance strength of reinforced concrete under various loading conditions for more complete consideration in determining the operating modes of airfield pavements is shown, and the loading parameters of reinforced concrete specimens during their endurance tests are determined. A general view and a layout diagram of an experimental setup for determining the static and endurance strength of large-sized cement concrete samples are presented. A technique for determining the static strength of reinforced concrete samples is presented, including the determination of the criterion for their destruction (appearance of fluidity in the reinforcement of the sample), the applied strain-measuring, ultrasonic and acoustic methods for determining the stresses magnitude and strains in cement concrete and structural reinforcement, the dynamics of changes in the measured parameters on one of the samples is shown. The results of the reinforced concrete samples fatigue tests with dimensions of 1500x400x200 mm under various loading conditions are presented, with reference to which regression equations were obtained to determine the number of loading cycles to failure, and endurance coefficients were obtained based on 106 loading cycles. Based on the carried out studies, conclusions are drawn, and the need to develop practical recommendations for taking into account the cyclic nature of the load impact from aircraft and the fatigue strength of cement concrete when assigning operating modes for airfield pavements is indicated.

Influence of facing conditions on the dynamic response of back-to-back MSE walls

This paper presents an experimental study of shaking table tests on two back-to-back mechanical stabilized earth (MSE) walls with full-height rigid facing and modular block facing, respectively, to investigate the influence of facing conditions on the dynamic response. The reduced-scale MSE wall models were designed according to the similitude relationships considering model geometry, reinforcement stiffness, and input motions. The back-to-back MSE wall models were constructed using poorly graded backfill soil and geogrid reinforcement, and then were excited using a series of sinusoidal input motions with increasing acceleration. The threshold acceleration where acceleration amplification factors suddenly increase significantly for the back-to-back MSE walls with modular block facing is smaller than that for the full-height rigid facing walls. The full-height rigid facing walls have smaller facing displacements than those for the modular block facing walls under the same motions and can resist stronger earthquakes in terms of facing displacements. For the back-to-back MSE walls with full-height rigid facing, incremental reinforcement tensile strains increase significantly with increasing input acceleration, while the reinforcement strains of the modular block walls are similar under different input motions for the conditions investigated.