Reinforcement Arrangement Research Articles

Improving the crack resistance of inclined cross-sections of reinforced concrete containment shells in areas of emergency loads of pushing

The object of this research was the crack resistance of inclined sections of concrete and reinforced concrete fragments of protective structures under the action of emergency dynamic loads. The characteristics of dangerous emergency dynamic loads on protective structures (seismic, aircraft attack), the experience of increasing the crack resistance of inclined sections with various materials and design measures under static effects have been described. Areas of influence of dynamic loads on reinforced concrete structures reinforced with horizontal grids near the upper and lower faces need to increase crack resistance and eliminate the risk of splitting in the mesh plane. Comparison of the results of experimental studies of inclined sections of protective structures in the area of influence of local emergency load showed the feasibility of such structural measures. Additional horizontal reinforcement near the pushing face increases crack resistance by 55–65 %. When using the developed theoretical dependences, the error in determining the cracking forces and pushing strength does not exceed 20.7 %. Increased crack resistance is ensured by limiting the maximum diameters of the rods of horizontal grids and their pitch. Especially important is the arrangement of additional reinforcement in the middle zone, taking into account the actual tensile strength of concrete in the calculated dependences. Complete elimination of the danger of splitting in areas of probable action of emergency dynamic load in protective structures in the planes of the grids is recommended through the use of concrete of class not lower than C16/20, the use of reinforcement Ø12–14 mm. The optimal pitch of the rods is 50–125 mm. This makes it possible to increase the reliability of the design and operation of protective structures in case of emergency impacts, to reduce the cost of their repair after such impacts.

Effect of longitudinal reinforcement on the soundless chemical demolition degree of reinforced concrete columns

AbstractSoundless chemical demolition has great potential for application in the field of building demolition in densely built areas. However, the application of this method was limited due to less guidance can be applied to reinforced concrete. Thus, this study investigated the effect of longitudinal reinforcement on the crushing degree of concrete columns. Experimental results showed that the number of steel bars had a greater impact on the development of crack width than diameter. Moreover, the longitudinal reinforcement had a greater impact on the transverse cracks than other types of cracks. This study introduced fractal dimension and characteristic value of specimen to describe the overall crushing degree and reinforcement arrangement of the specimens, respectively. The fractal dimension increased with an increase in the characteristic value. This study explored the influence of longitudinal reinforcement on the crushing degree of concrete columns, which laid the foundation for soundless chemical demolition of buildings in densely built areas.

Modeling and influence of thrust force torque and delamination during drilling of natural fiber composite

AbstractNatural fiber composites are named sustainable, renewable environmentally friendly materials. Machining the fiber reinforced composite is difficult due to their anisotropic and heterogeneous nature. Computer numerical controlled drilling caused severe delaminating at the entry and exit of the drilled hole. These can be minimized in several ways such as process parameters, fabrication method, and reinforcement arrangements (Orientation/Treatment/Aspect ratio/Fiber volume fraction). Thrust force and torque are caused machining of composites, it can be controlled by spindle speed, feed rate, and cutting velocity. It has been observed that the output responses such as thrust, torque, delamination peel up and push out of composites depend on the diameters of the drill bit (6, 8, 10 mm), cutting speeds (1000, 2000, 3000 rpm), and feeds (10, 20, 30 mm/min). Total 27 numbers of holes were drilled based on Taguchi L‐27 factorial design orthogonal array. Response surface methodology has been employed to compare input drilling parameters and output responses. It is found that a smaller diameter drill bit of 6 mm with a higher speed of 3000 rpm and lesser feed of 10 mm/min produced high‐quality holes.

Tensile Experiments and Numerical Analysis of Textile-Reinforced Lightweight Engineered Cementitious Composites.

Despite many cases of textile-reinforced engineered cementitious composites (TR-ECCs) for repairing and strengthening concrete structures in the literature, research on lightweight engineered cementitious composites (LECC) combined with large rupture strain (LRS) textile and the effect of textile arrangement on tensile properties is still lacking. Therefore, this paper develops textile-reinforced lightweight engineered cementitious composites (TR-LECCs) with high strain characteristics through reinforcement ratio, arrangement form, and textile type. The study revealed that, by combining an LRS polypropylene (PP) textile and LECC, TR-LECCs with an ultimate strain of more than 8.0% (3–4 times that of traditional TR-ECCs) could be developed, and the PP textile’s utilization rate seemed insensitive to the enhancement rate. The basalt fiber-reinforced polymer (BFRP) textile without epoxy resin coating had no noticeable reinforcement effect because of bond slip; in contrast, the BFRP grid with epoxy resin coating had an apparent improvement in bond performance with the matrix and a better reinforcement effect. The finite element method (FEM) verified that a concentrated arrangement increased the stress concentration in the TR-LECC, as well as the stress value. In contrast, a multilayer arrangement enabled uniform distribution of the stress value and revealed that the weft yarn could help the warp yarn to bear additional tensile loads.

Effects of reinforcement arrangements on load transfer in spring-based trapdoor tests

Five spring-based trapdoor tests allowing continuous displacement during both fill placement and localised static loading were conducted. Quartz sand was used as the test fill. Biaxial geogrids with and without ribs, having two different reinforcement stiffnesses, were used as reinforcement materials. Test results show that when two low-stiffness geogrid reinforcement layers were used, higher reinforcement spacing ratios (defined as the ratio of the reinforcement spacing between two reinforcement layers to the trapdoor width) induced more stable and efficient load transfer generally. Consequently, an optimum value of 0.3 and a worst-case value of 0.1 for the reinforcement spacing ratio were obtained and considered as representatives of two low-stiffness reinforcement layers for comparison with a single high-stiffness reinforcement layer, where their total reinforcement stiffnesses were approximately same. Generally, the inclusion of two low-stiffness reinforcement layers induced more stable load transfer. More importantly, compared with a single high-stiffness reinforcement layer, two low-stiffness reinforcement layers with the optimum reinforcement spacing ratio enhanced load transfer and induced less overall tensile forces, whereas the reinforcement arrangement with the worst reinforcement spacing ratio induced similar load transfer efficiency and overall tensile forces.

Parameters Influence on the Dynamic Properties of Polymer-Matrix Composites Reinforced by Fibres, Particles, and Hybrids.

In this paper, we present an extensive experimental study on the dynamic mechanical properties of composites with polymer matrices, as well as a quantification of the parameters that influence these properties. Polymer-composite matrices make it possible to form any reinforcement arrangement of fibres, particles, and layers, which makes it possible to form composite materials with certain dominant mechanical properties according to the internal arrangement for the application. In this study, we focused on the dynamic properties (i.e., damping parameters, such as the loss factor (tan d), logarithmic decrement (λ), storage modulus (E′), and loss modulus (E″)) of composites with polymer matrices, including parameters such as the fibre material, fabric weaving, fibre orientation, temperature, frequency, particle size, volume of short fibres, and epoxy resin type. If other articles focus on one type of composite and 1–2 parameters, then the benefit of this article lies in our analysis of 8 mentioned parameters in the experimental analysis of 27 different types of composites with polymer matrices. The tested fibre materials were glass, aramid, and carbon; the tested woven fabrics were twill, plain, unidirectional, and satin; the temperature range was from −50 to +230 °C; the frequency was 1 Hz and 10 Hz; the particle size was 0.1–16 mm; the volume percentages of the short fibres were 3, 6, and 12 vol.% of the hybrid polymer composites and the type of polymer matrix. We used the free-damped-vibration method with vibration dynamic signal analysis and the forced-damped vibration of dynamic mechanical thermal analysis for testing. We ranked the parameters that influence the dynamic vibration properties according to the effects. Among sets of results provided in the paper, considering the storage modulus, loss modulus, and loss factor, the best results of the fibre composites were for aramid-fibre-reinforced polymers, regardless of the weave type, with an advantage for unidirectional fabric. The best results of the particle composites were for those with fine filler sizes that incorporated the short fibres.

Evaluation on the progressive collapse resistance of infilled reinforced concrete frames based on numerical and semi-analytical methods

The effect of infill walls on the progressive collapse behaviour of reinforced concrete (RC) frames should be fully considered due to the formation of alternative load paths. To explore the configuration that could affect the progressive collapse resistance of infilled RC frames, parametric analyses are performed based on the validated simulation method. In the study, the impact introduced by the extra tie and integrity rebars in walls is emphasised. It is indicated that the variation in the reinforcement ratio of tie rebars leads to a limited change in structural progressive collapse resistance. In contrast, with the arrangement of the integrity reinforcement, the progressive collapse resistance of the infilled frames is enhanced and the propagation of the diagonal cracks in partial infill walls is suppressed. The notable re-ascending trend in the resistance curve for models with integrity rebars reveals the significant development of the catenary action in the integrity reinforcement. Then, with the help of linear regression and gene expression programming (GEP) techniques, a semi-analytical model is proposed for the prediction of the load-bearing capacity of infilled frames after column loss. In the prediction model, the linear effect of geometrical parameters and the non-linear effect of openings on the progressive collapse resistance are included by introducing three modification coefficients. Based on the statistical assessment, the capability of this explainable model is verified, and the appropriate amount of integrity reinforcement to mitigate the progressive collapse is discussed.

Effect of stirrup, longitudinal reinforcement and steel fibers ratios on the torsional behavior of high strength concrete beams

Many factors affect the torsional behavior of reinforced concrete beams, such as concrete strength, section dimensions, aspect ratio and concrete cover. Improvements in the torsional behavior of RC members had led researchers to investigate the effect of additional factors such as steel fibers, torsional reinforcement ratio and reinforcement arrangement. Based on the above, there is a gap in previous studies in taking effect of the distribution of stirrups with longitudinal reinforcement steel with steel fibers. Twenty-six reinforced concrete beams 250 mm wide, 250 mm high and 1150 mm long are investigated under pure torsion. Consider the effect of the steel fiber ratio, stirrup ratio and the longitudinal reinforcement ratio of high strength concrete. The results show the behavior of the concrete changing from brittle to ductile when increasing the ratio of the steel fiber registering the maximum torsional ductility index (3.98). The increase in the percentage of steel fiber to 6% caused a 105% increase in torque, but it was a slight increase in torque with respect to the percentage of steel fibers 2%. The optimum ratio of the steel fiber is 2% in terms of increased torque and workability, as it gave an increase in torque which reached 98.8%. Increasing the percentage of the stirrups to 2.5%, while the percentage of longitudinal reinforcement and the percentage of steel fiber was fixed, which led to an increase in torque which reached 130.4%. Increasing the percentage of the longitudinal reinforcement to 50%, while the percentage of stirrups and the percentage of steel fiber was fixed, which led to an increase in torque which reached 66.9%.

Finite element analysis of steel-concrete composite connection with prefabricated permanent steel form

Composite structural members are widely used due to superior performance to traditional structural members consisting of either concrete or steel material. This study proposes steel-concrete composite beam-column connections utilizing prefabricated permanent steel form and presents a finite element analysis to ver-ify the structural performance of the system, which is based on the experimental data conducted under cyclic loading protocol simulating seismic action. Five different design specimens are covered where the key varia-bles include the asymmetric section of the steel beam, the type of the column, and the detail of longitudinal reinforcement placement. The specimens were modeled in ABAQUS with solid and truss elements for concrete and steel parts, respectively. In addition, the nonlinear material behavior of the concrete was considered in the model where the concrete damaged plasticity model was assigned. The interaction between concrete and steel was also investigated to capture the structural behavior of the specimens measured from the test. The analysis showed that the concrete section improves the structural performance of the composite beam while preventing the steel beam from bucking. The finite element analysis was not capable of catching the strength degradation at the ultimate state but provided reliable results with overall moment-story drift behavior.

STRENGTH MODEL FOR CALCULATING CENTRALLY COMPRESSED CONCRETE ELEMENTS WITH COMPOSITE REINFORCEMENT, TAKING INTO ACCOUNT THE SPACING OF STIRRUPS

The article discusses the relevance of developing techniques for confined elements with FRP reinforcement. The method for calculating centrally confined concrete columns with non-metallic GFRP reinforcement (without regard to its compression work) is proposed for the first time in the Russian Federation. The strength model was developed based on the well-known theoretical model of confined concrete. The article considers the effect of strengthening the concrete core of the columns, which is obtained due to the more frequent placement of both transverse and longitudinal reinforcement. The dependence of the bearing capacity of concrete columns on the strength of the transverse reinforcement material is shown. It was proved that with a decrease in the spacing of the longitudinal reinforcement, the area of ​​the effectively confined concrete core inside the reinforcement cage increases. It was shown that, due to the low compressive modulus of elasticity of the FRP reinforcement, the stress in it will be comparable to the concrete stress. Therefore, the compressive strength of the FRP reinforcement can be neglected in the case of determining the bearing capacity of centrally confined concrete elements. As a result, a strength model for calculating confined concrete elements with FRP reinforcement was proposed, considering the spacing of transverse reinforcement, the longitudinal and transverse reinforcement ratio, and the strength of the material of transverse reinforcement. The developed strength model can be applied not only for square, but also for columns of round and rectangular sections.

Simulation of the crack width in reinforced concrete beams based on concrete fracture

The concrete cracking is simulated by the finite element method combined with the constitutive model based on the nonlinear fracture mechanics. The model uncertainties for mean and maximum crack widths are found by comparing the simulated crack widths with data obtained by laboratory testing of 18 reinforced concrete beams. The reinforcement arrangement, dimensional simplification, and numerical discretisation effects on the model uncertainty are investigated. Two reinforcement types, i.e. steel and glass fibre-reinforced polymer bars, are considered. The shrinkage effect on the cracking predictions is included. The fracture energy parameter according to fib Model Code 2010 is used in the simulations. The numerical model offers an adequate prediction of crack widths for the beams with a single layer reinforcement and exhibits less accuracy for the multilayer bar arrangement. The presented numerical model represents an advanced tool for the crack width assessment in the design of reinforced concrete structures in serviceability limit states.

Influence of different geometric arrangements of discontinuous reinforcement on tensile strength and fracture behavior of carbon/epoxy laminates

This study presents the influence of different geometric arrangements of butt joint formed by plain weave fabric prepreg layers on mechanical and fracture behavior of carbon/epoxy laminates tested under tensile loading. The experimental test results showed a reduction of up to 17% on the tensile failure load, due to the presence of the discontinuity in the reinforcement, when compared to the continuous fiber reinforced composites. However, statistical analyses demonstrated that the different staggering methods of the butt joints did not affect considerably the tensile mechanical behavior of the laminates. The stress concentration in the embedded joint regions was observed by finite element analysis results, which predicted the tensile failure load and also the failure region, according to Hashin criterion. SEM analyses revealed that all specimen configurations exhibited fracture in the butt joint regions, with the occurrence of cohesive failure of the matrix originated in the co-curing process, associated with a strong interfacial adhesion with the fibers. This behavior evidences a high interfacial strength of the co-cured plies joints, which is attributed to the good quality of the prepreg material associated with the efficiency of the laminate manufacturing process. The numerical studies showed a good fit with the available experimental results regarding tensile failure load. Therefore, the implemented finite element model proved to be adequate to accurately predict the tensile strength of plain weave fabric laminates containing layer joints.

Exploration to novel arrangements of longitudinal reinforcement of gravity railway bridge pier by shaking table test

Gravity pier is widely used in the high-speed railway in China. However, it is vulnerable to earthquakes due to the low longitudinal reinforcement ratio (generally less than 0.5%). This study investigated ratios and arrangement forms of the longitudinal reinforcement of gravity piers. Four scaled specimens were designed and constructed, including two novel longitudinal reinforcement forms, to explore more reasonable arrangements economically and effectively by shaking table test. The test adopted the El-Centro earthquake record to load. The crack patterns, acceleration, and displacement responses of specimens were recorded and analyzed after each loading. The results showed the two novel forms proposed in this study have exhibited excellent seismic behavior than traditional forms. We validated rationalities and economies of the two novel longitudinal reinforcement arrangement forms for gravity piers. These two proposed in the study may provide references for the seismic design of high-speed railway gravity piers.

Shear enhancement in RC beams with stirrups simultaneously loaded within 2d and at 3d from supports

Shear enhancement occurs in reinforced concrete (RC) beams when loads are applied within around 2d of supports where d is the beam effective depth. This paper examines shear enhancement in RC beams, with stirrups, which are loaded both within 2d of supports and at 3d from supports where shear enhancement is minimal. Simultaneously loading beams both inside and outside 2d of supports commonly occurs in practice but has not previously been systematically studied. A total of eight beams were tested in two groups of four having different reinforcement arrangements. The tests suggest that the shear resistance depends on the angle of the failure plane which is related to the loading arrangement. A strut and tie model (STM) is developed for analysing beams simultaneously loaded within and outside 2d of supports. The accuracy of the STM predictions is shown to be improved by relating strut strength to the strain in the flexural reinforcement. The proposed STM and nonlinear finite element analysis (NLFEA) with 3D solid elements are used to investigate parametrically the influence of loading arrangement on shear resistance. The strength predictions of the STM are shown to compare well with those of NLFEA. Comparisons are also made with shear strengths calculated using fib Model Code 2010 (MC2010) and the draft new generation of Eurocode 2 (prEN1992-1:21). The differing philosophies of these two methods are discussed.

Optimization of Continuous Fiber Path Planning for an Additively Manufactured Open-Hole Specimen

This study presents a numerical method for optimizing the quantity and the placement of reinforcements along the principal-stress trajectories. The model representing carbon fiber composite structures consists of solids and embedded one-dimensional beam elements. Based on the Runge-Kutta method, the reinforcing structure is optimized considering the manufacturability of additive manufacturing (AM). For a case study, the optimization method is performed on an open-hole specimen. The Young’s modulus and the tensile strength of the optimized structure show an increase of more than 30 % and ~50 % in the simulation, respectively, compared to the reference specimen from another study. Robotic additive manufacturing is used to fabricate the specimen for experimental validation. The prediction of absolute values of tensile strength are reliable comparing to the experimental test, however, there is a deviation of more than 30 % in the linear-elastic behavior possibly due to the presence of voids in the printed part.

Behavior of Reinforced Concrete Deep Beams with Openings under Vertical Loads Using Strut and Tie Model

This research aims to study the effects of the size and location of openings on deep beams. The analysis of deep beams with openings presents a rather complex problem for engineers, as there are currently no guidelines within the design codes for this problem. Using the strut and tie model is a feasible solution, but also gives some uncertainties due to the various models that can be used. This paper proposes using a strut and tie model for the deep beams with openings where reinforcement is laid out in the form of embedded struts and ties. The study is divided into an experimental and a numerical part. The experimental study was conducted on eight reinforced concrete deep beams under vertical loads. Seven of the beams had web openings of different sizes and locations, while the eighth specimen was a reference beam without any openings. The beams had the same concrete dimensions with the size of the openings in the web taken as 150 150 mm and 300 300 mm, and the location of the opening in the horizontal direction was varied between 0.11 to 0.4 the span. The experimental results were analyzed in terms of cracking pattern, mode of failure, and load-deflection behavior and then compared to numerical analysis conducted using a finite element program. A parametric study followed to investigate the influence of reinforcement arrangement and reinforcement around the openings on the behavior of deep beams. The results showed that large web openings that directly interrupted the compression strut had the most reduction in beam capacity and that the location of the opening did not significantly affect the strength of the beam in the case of small openings. Doi: 10.28991/CEJ-SP2021-07-011 Full Text: PDF

Post-punching failure mechanism and resistance of flat plate-column joints with in-plane constraints

Flat plate-column joints with in-plane constraints exhibit a suspension mechanism under large deformations after punching shear failure, which significantly affects the progressive collapse behavior of the entire flat plate structural systems. However, in-plane constraints were ignored in the existing tests by which the suspension mechanism could not be exhibited and consequently the post-punching resistance was significantly underestimated. To fill this gap, a static pushdown test was conducted on eight flat plate-column joints with in-plane constraints until their post-punching resistances being completely lost. The influences of the punching directions and the structural parameters including slab thickness, reinforcement amounts and arrangement of flexural reinforcement on the post-punching failure mechanism were analyzed. An analytical method for calculating the post-punching strength was proposed and validated by the test results. The contributions of each layer of reinforcement to the post-punching resistance were also quantified.

A micromechanical and numerical model for effective thermal conductivity of areca fiber and coconut shell particulate-reinforced hybrid composites

The present investigation reports on the thermal conductivity of areca fiber and coconut shell particulate (CSP)-reinforced polymer composites. The fiber and particulate reinforcement percentages were 10–40wt.% with various weight ratios as 1:1, 1:3, and 3:1. The main focus has been given to the development of a micromechanical model to calculate the effective thermal conductivity of areca fiber and CSP-reinforced hybrid composites. In the numerical study, steady-state one-dimensional heat conduction analysis is performed with a periodic arrangement of cylinders and spherical reinforcement using ANSYS software. Unitherm [Formula: see text]Model 2022 equipment was used to measure the experimental thermal conductivity values of the hybrid composite materials and validated with the micromechanical and numerical values. The experimental results attained for thermal conductivity are supported by the proposed micromechanical model. The measured values of the composites were found to be in very close agreement with the micromechanical model and the numerical analysis. It is concluded from this study that the addition of areca fiber and CSP improves the thermal insulation capability of neat epoxy.

Investigation of punching shear behavior of flat slabs with different types and arrangements of shear reinforcement

Punching shear behavior is experimentally investigated through testing a total of thirteen reinforced concrete flat slabs. Four different types of punching shear reinforcement configurations are examined, namely, ordinary closed rectangular stirrups (ST group), rectangular spiral stirrups (RSP group), advanced rectangular spiral stirrups (ARSP group), and circular spiral stirrups (SP group). Each configuration included three different spacings of 100, 150 and 200 mm. In addition, a reference slab specimen is cast without any punching shear reinforcement. The test results indicated that the circular spiral reinforcement scheme has the highest enhancement with regard to the punching shear capacity compared to the other reinforcement schemes. The percentage of enhancement of the SP group compared to the reference specimen ranges between 23% and 30%. For the other three different rectangular schemes, the enhancement of the punching shear strength for the RSP group and the ARSP group is in the range of 15–23% and 16–25%, respectively. Finally, the punching shear capacity of the ST group increased by 9–13% compared to the reference specimen. The shear carrying capacity of the specimens is also calculated using the ACI 318-19 code and Eurocode 2 equations. The results showed that both codes are capable of predicting the shear carrying capacity for all the schemes. Also, although both codes are conservative, the Eurocode 2 gives a better estimate of the shear carrying capacity than the ACI 318-19 code.

Strengthening of Reinforced Concrete Beams Subjected to Concentrated Loads Using Externally Bonded Fiber Composite Materials

Renovation, restoration, remodeling, refurbishment, and the retrofitting of buildings often imply applying forces (i.e., concentrated loads) to beams that before were subjected to distributed loads only. In the case of reinforced concrete structures, the new condition causes a beam to bear a concentrated load with the crack pattern that resulted from the distributed loads which had acted before. If the concentrated load is applied at or near the beam’s midspan, the new shear demand reaches the maximum where cracks are vertical or quasi-vertical, and where inclined bars are not common according to any standards. So, the actual shear capacity can be substantially lower than new shear demand due to the concentrated load. This paper focuses on reinforced concrete beams whose load distribution has to be changed from distributed to concentrated and presents a design method to bring the beam’s shear capacity up to the new demand. The method consists of applying fiber composites (fiber-reinforced polymers or fiber-reinforced cementitious material) with fibers at an angle of 45° bonded to the beam’s web. This kind of external reinforcement arrangement has to comply with some practical measures, which are presented as well. The paper also provides the analytical model that predicts the concentrated load-carrying capacity of a beam in the strengthened state. The model accounts for the crack’s verticality, which nullifies the contributions of steel stirrups, aggregate interlock, and dowel action, and for the effective bond length of each fiber, which depends on the distance between the ends of the fiber and the crack it crosses.