Tension Zone Research Articles

A Study on non Destructive Tests and Flexural Strengths of Geopolymer Concrete Using Combination of Different Fine Aggregates

Geopolymer concrete is a new technology that deserves more attention in the rapidly evolving sustainable construction industry. Furthermore, to avoid the depletion of natural resources, by-product waste management technologies are essential. Today, river sand is in short supply. DMS (Dredged Marine Sand), on the other hand, which faces disposal and land acquisition issues, proves to be a viable alternative to river sand. In this paper, a mixture of M-Sand and DMS was used in place of river sand, and non-destructive, Flexural strength of beam by monotonic loading and cyclic loadings were investigated. The findings indicated that DMS has attained flexural characteristics and with regard to cracks, very minor and vertical cracks are observed in all beams as in the case of monotonic loading. Further, they originate from the tension zone

Stress-strain state of combined steel-FRP reinforced concrete beams

Steel reinforcements in reinforced concrete structures are susceptible to corrosion under different exposure conditions. This can lead to some disadvantages, including concrete deterioration, reduced long-term service life, increased cost of the structure due to re-strengthening measures, and reduced overall durability of the structure. In order to solve these problems, the issue of comprehensive use of Fiber reinforced polymer (FRP) reinforcements as an alternative to steel bars is urgent. FRP reinforcements have specific advantages including corrosion resistance, high tensile strength, density four times lighter than steel, and also linear expansion coefficient under the influence of temperature is small like concrete. In order to increase the load bearing capacity and ductility, it is recommended to effectively use steel rebar together with FRP rebar as a combination reinforcement, taking into account brittleness characteristic of FRP reinforcement and low modulus of elasticity. In this article, concrete beams with combined reinforcement are modelled by using ANSYS Workbench 2022 software. By testing virtual model, deflection corresponding to the value of the applied load on the beam, compressive and tensile stresses in the concrete, and stresses in FRP and steel reinforcement located in the tension zone were determined and analyzed.

КАЗАЧЕСТВО ВО ФРОНТИРНОЙ СРЕДЕ ЮГА РОССИИ

The aim of the study is to analyze the influence of the frontier identity of the Cossacks on the socio-cultural processes of the South of Russia. In the framework of the work carried out, the main factors of the frontier nature of the modern Cossacks, their socio-cultural features of development in the environ-ment of the Russian border area, which developed after the collapse of the USSR, were studied. The Cossacks of the South of Russia have a long history of formation, due to their presence in the frontier environment, at the junction of civilizations, peoples, and cultures. Being between Orthodoxy and Islam, the Slavic and Turanian worlds, in a zone of constant tension and military conflicts, the Cossacks received in their socio-cultural code distinctive features, opportunities for stabilizing the habitat, reducing conflict with neighbors. Constant contact with representatives of other peoples, other countries is also reflected at the pre-sent stage of Cossack development. As a result, the author comes to the conclusion that the view of modern Cossack scholars on the very factor of the Cossacks-frontiersmen has to be revised in order to form a state policy towards the Russian Cossacks.

Shear strengthening performance of GFRP reinforced lightweight SCC beams: Experimental and analytical study

Light weight construction using Glass Fibre-Reinforced Polymer (GFRP) bars and structural light weight concrete (LWC) have increased recently and offers a wide spectrum of advantages over traditional normal weight concrete (NWC) structures. However, the shear strengthening and rehabilitation performance of LWC beams reinforced with GFRP bars is very limited and currently there are no guidelines related to it. Therefore, this study presents the results of an experimental investigation on the shear strengthening behaviour of lightweight self-consolidating concrete (LWSCC) beams reinforced with GFRP bars. The test parameters studied in the experimental program were the longitudinal reinforcement ratio and strip configuration or orientation. A total of twelve shear deficient GFRP reinforced beams were prepared with a shear span to depth ratio of 3.12 and subjected to static four-point bending. Five beams in each series were externally strengthened with different configurations of Carbon Fibre-Reinforced Polymer (CFRP) strips and one beam served as a control specimen to compare the performance of the strengthened specimens. Crack patterns, load–displacement response curves, and strain in the external CFRP strips were recorded until the failure ultimate load. The results of the experimental study indicated that the external CFRP strips improved the nominal shear capacity of GFRP reinforced LWSCC beams, and the contribution of external CFRP strips was sensitive to the reinforcement ratio. The nominal shear capacity of the strengthened specimens increased from 33.3 to 168% compared to the control specimen. U-wraps with horizontal strips in the compression and tension zone were the most effective configuration, showing the highest increase in shear strength compared to other strengthened specimens. Moreover, the shear capacity was theoretically predicted using different Fiber-Reinforced Polymer (FRP) design standards and guidelines which were compared with the experimental results. All the FRP design standards have overestimated the shear capacity of LWSCC beams, and a modified equation with a set of recommendations was proposed based on the experimental study. In addition, a reduction factor of 0.75 is recommended for conservative design.

Experimental tests and analytical model for reinforced polyvinyl alcohol‐engineered cementitious composite beams in bending

AbstractPolyvinyl alcohol‐engineered cementitious composite (PVA‐ECC) exhibits strain hardening and multiple cracking characteristics under tension. Its superior tensile behavior may also influence the flexural behavior of reinforced PVA‐ECC beams. This paper investigates the load capacity and failure mode of reinforced PVA‐ECC beams in bending. Seven beams with different tensile reinforcement ratios, including six PVA‐ECC beams and one conventional concrete beam, were tested in the experimental program. The influence of reinforcement ratio on load capacity and failure characteristics was discussed in detail. Test results showed that with increasing reinforcement ratio, the ultimate load of beams was increased, but the failure mode was changed from fracture of PVA‐ECC in the tension zone to crushing in the compression zone, thereby limiting the full development of beam ductility. An analytical model is proposed to calculate the load and the vertical deflection of beams. In the model, the tension‐stiffening effect of reinforcement after cracking of PVA‐ECC is considered by defining the bond–slip relationship of reinforcement embedded in PVA‐ECC. Comparisons are made between experimental results in the literature and those calculated by using the analytical model to show the accuracy of the model in predicting the load–deflection relationship, the moment–rotation relationship, and the moment–curvature relationship.

A Parametric Investigation of the Influence of Knots on the Flexural Behavior of Timber Beams

The presence of knots significantly influences the mechanical behavior of timber. This research presents a parametric finite element analysis of the effect of knot characteristics on the flexural capacity of timber beams. Parameters include knot radius, longitudinal and vertical positions, length, and diving angle. The generation of the FE model is based on a technique developed in a previous research stage. The validation of the model is done via bending tests on a set of beams as well as a number of independent research studies. The numerical model accurately recreates the three-dimensional geometry of the knot and related fiber deviations. The capacity of the beams under bending is evaluated via the Tsai–Wu failure criterion. Findings reveal that the presence of knots in the tension zone leads to an early tensile failure and insufficient utilization of compression capacity, the decrease of bending capacity may rise significantly (up to 39% in this investigation), the knot inclination may positively or negatively influence the behavior depending on the diving angle, and moderate knot length can be detrimental to flexural capacity.

Selected Mechanical Properties of Glue-Laminated Timber Produced from Locally Repaired Timber.

This study aimed to evaluate the mechanical properties determined in a 4-point bending test of beams made of lumber from which knots had been locally removed and the resulting loss replaced with sound wood. Three sets of beams were prepared, which differed in the number of layers/lamellas and the position of the lamellas from which edge knots were removed. All the lamellas used in the tests were subjected to a modulus of elasticity assessment. In addition to the distribution of defects, it determined the position of a given piece in the beam structure. The tests showed that high mechanical properties could characterise the beams produced in this way, i.e., a modulus of elasticity close to 12 kN/mm2 and a strength above 40 N/mm2, if the lamellas without knots were located below the outer tension lamella. Significantly better results were obtained when PUR glue was used in the inserts rather than MUF. In this case, beams with an improved outer lamella in the tension zone using semi-circular inserts glued with PUR glue had an average strength of 34.6 N/mm2.

U-BOOT CONSTRUCTION TECHOLOGY

U-boot betons is a formwork made of recycled polypropylene, designed to create lightened intermediate slabs and raft foundations in reinforced concrete. The use of U-boot formworks permits to build specific mushroom slabs: the mushroom is part of the slab thickness. U-boot remains dip into the concrete casting. Thus, a grid of orthogonal beams, superiorly and inferiorly closed by plane slabs of different heights, is obtained without executing two distinct concrete castings, all that implies a remarkable saving of concrete and reinforcement. A simply supported reinforced concrete beam has two zones, one above neutral axis and other below neutral axis. The region below neutral axis is in tension and above neutral axis is in compression. As concrete is weak in tension, steel reinforcements are provided in tension zone. The concrete below the neutral axis acts as a stress transfer medium between the compression zone and tension zone. Polythene u boots of varying sizes of 50*50 mm, 60*60 mm & height of 40 cm, thickness of 10 cm at 5 cm, 10 cm, 15 cm spacing u boots are placed in compression zone. Hence the usage of concrete in beams and self-weight of the beams gets reduced considerably. The Load carrying capacity, Deflection of beams and crack patterns were studied and compared with conventional reinforced concrete beams. Key words: Orthogonal Slab, U- Boot, Mushroom slab

Erosion behavior of ions in lining concrete incorporating fly ash and silica fume under the combined action of load and flowing groundwater containing composite salt

In this study, the erosion behavior of ions in lining concrete incorporating fly ash and silica fume under the combined action of load and flowing groundwater containing composite salt. The results show that the transmission speed of Cl− and SO42− in lining concrete under different erosion conditions is: flowing groundwater–load action in the tension zone > flowing groundwater > static corrosion solution > flowing groundwater–load action in the compression zone. The addition of silica fume (SF) and fly ash (FA) can reduce the concentration of Cl− and SO42− in lining concrete, increase the ratio of combined Cl− to total Cl−, and reduce the ratio of combined SO42− to total SO42−. The addition of FA and SF can increase the lining concrete's resistance to Cl− corrosion by about 10–28%, and SO42− radical resistance by about 5–12%, and the more FA is added, the greater the increase.

The Smart Nervous System for Cracked Concrete Structures: Theory, Design, Research, and Field Proof of Monolithic DFOS-Based Sensors.

The article presents research on the performance of composite and monolithic sensors for distributed fibre optic sensing (DFOS). The introduction summarises the design of the sensors and the theoretical justification for such an approach. Lessons learned during monitoring cracked concrete are summarised to highlight what features of the DFOS tools are the most favourable from the crack analysis point of view. Later, the results from full-size laboratory concrete specimens working in a cracked state were presented and discussed in reference to conventional layered sensing cables. The research aimed to compare monolithic sensors and layered cables embedded in the same reinforced concrete elements, which is the main novelty. The performance of each DFOS nondestructive tool was investigated in the close vicinity of the cracks-both the new ones, opening within the tension zone, and the existing ones, closing within the compression zone. The qualitative (detection) and quantitative (widths estimation) crack analyses were performed and discussed. Finally, the examples of actual applications within concrete structures, including bridges, are presented with some examples of in situ results.

Influence of the proportion of FRP to steel reinforcement on the strength and ductility of hybrid reinforced concrete beams

The present study pertains to the influence of variation of FRP (Fiber Reinforced Polymer) proportion in tension reinforcement on the flexural behavior of RC beams with FRP and steel reinforcing bars. A total of 25 beams, including FRP-, steel- and hybrid FRP-steel reinforced ones, were tested to failure under four-point bending. Two types of FRP bars, GFRP (Glass Fiber Reinforced Polymer) and BFRP (Basalt Fiber Reinforced Polymer), were used and both over- and under-reinforced beams were tested. The beams in each group were designed to have close flexural capacities to fully reveal the effect of FRP proportion in the tension zone on beam ductility for a fixed bending capacity. A new analytical model was developed for estimating the bending capacities of beams. Different deformation and curvature ductility definitions were adopted and an energy-based definition, revealing the expected tendency in beam ductility, was determined. The test results revealed that the presence of even a single FRP bar in the tension zone results in reductions up to 40% in beam ductility as compared to the beam with full steel reinforcement. Each additional replacement of a steel bar with FRP was found to cause a further decrease up to 20% in beam ductility.

Experimental investigation on the mechanical and interfacial properties of fiber-reinforced geopolymer layer on the tension zone of normal concrete

This study aimed to understand the mechanical and interfacial properties of fiber-reinforced geopolymer (FRG) layer on the tension zone of normal concrete. A trial mix of FRG using local materials obtained in Hokkaido was investigated. Compression and splitting tensile tests on the FRG test pieces were conducted under different mixing procedures, constituents, volume fractions of the polyvinyl alcohol fiber, curing conditions, and ages. Flexural tests using FRG-normal strength concrete (NSC) composite specimens with different FRG layer thicknesses were carried out. By placing the FRG layer on the tension side of the composite specimen, the flexural strength and energy absorption were significantly increased. The flexural strength for the NSC alone was 3.5 MPa, while the FRG-NSC composite specimens showed higher flexural strengths of 6.1–6.6 MPa. Also, XRD, FTIR, and SEM analyses were carried out for the FRG samples.

Application of sawdust concrete in construction

Sawdust concrete is a type of lightweight concrete in which some of the mineral aggregate is replaced by sawdust - a by-product of wood processing. It is not a new material, but its potential is not utilised to its full degree. Taking into account the most important advantages of sawdust concrete - lower density and greater thermal and acoustic insulation than ordinary concrete - it is worth to consider the possibilities of its usage in construction wider than currently . In order to present the properties of sawdust concrete, the review of contemporary technical literature has been performed.
 For the production of sawdust concretes mineralized sawdust from various types of trees, ordinary cements, mineral aggregates and water, are used. The usage of additives and admixtures is also allowed. The properties of the finished sawdust concrete are mainly influenced by the proportion of its components, especially the amount of fine aggregates replaced by sawdust. The construction products made of sawdust concrete are characterized by a low coefficient of thermal conductivity λ and soundproofing properties. In bending tests, a simply supported sawdust concrete beam behaves similar to a regular concrete beam, cracks first appear in the tension zone. Tensile strength, compressive strength and Young's modulus of sawdust concrete products depend on the proportion of components and the method of sawdust preparation before applying in the sawdust concrete-mix. Compared to ordinary concrete, the obtained values for sawdust concrete are lower, but partially fall within the ranges for the lower classes of ordinary concrete.
 There are several possible applications of sawdust concrete in construction. One of the perspectives is to use it to build walls in buildings that require soundproofing between rooms, or to replace wood with it when renovating old buildings. However, further tests of sawdust concrete are needed in terms of the most favourable composition for its mechanical properties, and to define the standards according to which sawdust concrete elements should be produced.

Influence of adding short carbon fibers on the flexural behavior of textile-reinforced concrete one-way slab

The application of textile reinforcement to the tension zone of the reinforced concrete slabs as a means to enhance flexural capacity has been investigated by researchers in the past. However, the effectiveness of adding short carbon fibers as internal reinforcement in the textile-reinforced concrete one-way slab needs to be studied. The paper presents the experimental research conducted on four full-scale (1500×500×50) mm one-way slabs. An innovative Polyacrylonitrile (PAN) textile grid was used as internal reinforcement in combination with short carbon fibers. The first one consists of fine-grained concrete and short carbon fibers. Two textile-reinforced RC slabs have eight layers of fabric (textile-reinforced concrete (TRC) 8 L) with two percentages of short carbon fiber (0.264% and 0.528%), and one reference textile-reinforced concrete slab without short carbon fiber was fabricated to investigate the flexural behavior under a four-point loading system. The findings indicate that TRC + short carbon fiber showed significantly improved flexural capacity, load-deflection, and load-concrete strain behaviors compared with TRC. The new TRC+ 0.264% short carbon fibers (SCF) and TRC+ 0.528%SCF improved the load-bearing capacity by about 24.19% and 31.56%, respectively, as compared with TRC. Also, the intensity of the crack pattern was measured to compare the ductility of TRC+ short carbon fiber to that of traditional TRC.

Flexural Performance of Prestressed Composite Recycled Aggregate Slabs with Steel Tube Trusses

A new type of prestressed composite recycled aggregate floor slab was developed and its flexural performance was studied. The composite floor comprises a top cast-in-place slab made of recycled coarse aggregate concrete and a bottom precast concrete slab with grouted steel tube trusses. The cracking load, ultimate load, deflection, steel tube strain, concrete strain and failure process are studied for different contents of recycled coarse aggregates. Results show that the mechanical performance of the prestressed composite recycled aggregate slab has two distinctive stages. And the load bearing capacity decreases with the increase in the amount of recycled coarse aggregates. When the composite slab fails, the prestressed steel wires in the tension zone yield and concrete in the compression zone is crushed. This failure characteristic reflects that the reinforcement ratio of the component is appropriate. The cracking moment and ultimate moment calculation formulas of the composite slab are established and could predict the cracking and failure points. In the formulas, the influence of the amount of recycled coarse aggregates on the flexural capacity is considered. By controlling the content of recycled aggregates, the composite slabs with steel tube trusses can be sued in practical applications.

Crustal deformation and dynamics of the south-eastern tibetan plateau from stress fields and geodesy

South-eastern Tibet rotates clockwise around the eastern Himalayan syntaxis due to the eastward extrusion of the eastern Tibetan lithosphere and it attracts much attention as a window for studying the dynamics of continental collision between India and Eurasia. Competing geodynamic models to describe the deformation of the eastern Tibet have been the debating subject and the dynamic processes responsible for plateau evolution remain poorly understood, partly because the mechanical state at depth and its relationship with surficial deformation are unclear. In this context, a continuous east-west oriented tensional zone was identified at the south-eastern edge of the Tibetan Plateau based on seismogenic stress field and global positioning system data. The profiles of surficial velocity field reveal a relatively speedy motion belt parallel to the Xianshuihe fault extending from north to south in the rotating region east of the tensional zone. Segmented features of the profiles around the extensional zone indicate its close relation with flow channels delineated from magnetotelluric images. Therefore, the deformation at the south-eastern edge of the Tibetan Plateau is mechanically coupled within the crustal depth. We propose a complex regional kinematics with a localised speedy belt and a continuously extensional zone, where material coupling and deformation compatibility were revealed within the crustal depth.

Mechanical Characterization of Glued Laminated Beams Containing Selected Wood Species in the Tension Zone.

The aim of this study was to determine the mechanical properties of laminated beams containing selected wood species in the tension zone using a four-point bending test. Three beam types were manufactured with respect to the timber used in the tension zone, i.e., beams containing oak or beech timber of I and II quality class and pine timber with no defects (as defects had been removed). The manufactured beams were assessed with respect to bending strength and the modulus of elasticity. The obtained results were compared with the performance of BSH (Industrial beams GL made in Germany—Brettschichtholz) industrial beams. We concluded that beams made from pine timber are an appropriate alternative to spruce beams. The static bending strength of the beams made with hardwood faces was 70% higher than that of beams made with pine wood. All types of beams manufactured in the laboratory met the requirements of at least the GL24c class.

Impact of Leptin on the Expression Profile of Macrophages during Mechanical Strain In Vitro.

Childhood obesity is a growing problem in industrial societies and associated with increased leptin levels in serum and salvia. Orthodontic treatment provokes pressure and tension zones within the periodontal ligament, where, in addition to fibroblasts, macrophages are exposed to these mechanical loadings. Given the increasing number of orthodontic patients with these conditions, insights into the effects of elevated leptin levels on the expression profile of macrophages during mechanical strain are of clinical interest. Therefore, the aim of this in vitro study was to assess the influence of leptin on the expression profile of macrophages during simulated orthodontic treatment. RAW264.7 macrophages were incubated with leptin and lipopolysaccharides (LPS) from Porphyromonas gingivalis (P. gingivalis) or with leptin and different types of mechanical strain (tensile, compressive strain). Expression of inflammatory mediators including tumor necrosis factor (TNF), Interleukin-1-B (IL1B), IL6, and prostaglandin endoperoxide synthase (PTGS2) was assessed by RT-qPCR, ELISAs, and immunoblot. Without additional mechanical loading, leptin increased Tnf, Il1b, Il6, and Ptgs2 mRNA in RAW264.7 macrophages by itself and after stimulation with LPS. However, in combination with tensile or compressive strain, leptin reduced the expression and secretion of these inflammatory factors. By itself and in combination with LPS from P. gingivalis, leptin has a pro-inflammatory effect. Both tensile and compressive strain lead to increased expression of inflammatory genes. In contrast to its effect under control conditions or after LPS treatment, leptin showed an anti-inflammatory phenotype after mechanical stress.

Failure analysis and treatment of nasal septum deviation correction based on tension zone

目的： 以张力区为切入点，分析鼻中隔偏曲矫正术失败的原因并探讨处理方法。 方法： 收集2011年3月至2021年2月于解放军总医院第四医学中心耳鼻咽喉头颈外科行二次鼻中隔矫正术的14例患者，行鼻科和影像学相关检查，分析并定位患者鼻中隔偏曲所在的张力区。根据患者的鼻部体征分别采取经鼻内入路和鼻外入路减张法功能性鼻整形术。分别采用鼻阻塞症状评分量表和视觉模拟量表评估患者术后鼻塞改善情况和对鼻外形的满意程度。采用SPSS 25.0软件进行统计学分析。 结果： 术中确认张力区全部位于方形软骨后上缘、尾侧端或背侧缘。鼻中隔张力区部位为尾侧端及同时合并背侧缘者，鼻中隔偏曲部位在尾侧端的发生率明显高于其他部位（χ2=15.59，P<0.05），外鼻畸形的发生率也明显增高（χ2=6.88，P<0.05）。术后14例患者的鼻中隔偏曲均得到满意矫正，术后鼻塞程度明显减轻（t=7.71，P<0.05），10例伴鼻畸形者的鼻外观改善（t=-6.39，P<0.05）。随访6~12个月，无鼻中隔穿孔、鞍鼻、鼻腔粘连等并发症出现。 结论： 鼻中隔偏曲手术失败的主要原因是对造成偏曲的张力区判断不准确、减张不彻底。对于合并外鼻畸形的鼻中隔偏曲患者，应同时矫正鼻中隔偏曲和外鼻畸形。.

Variation in bending deformation behavior and improvement in bendability of extruded pure Mg through Gd addition

In this study, the twinning and slip behaviors of pure Mg and Mg–1Gd extrudates during bending deformation are investigated by subjecting the extrudates to three-point bending tests. The pure Mg extrudate has a coarse grain structure with a strong basal texture. The Mg–1Gd extrudate has a uniform and fine grain structure with a typical rare-earth (RE) texture because the added Gd causes the suppression of grain-boundary migration and the textural tilting during extrusion. When bending deformation is imposed, cracks are formed in the lower region (tension zone (TZ)) of the bending specimens of both extrudates. However, the bending yield strength and failure bending strain of the Mg–1Gd extrudate are 56% and 68% higher than those of the pure Mg extrudate, respectively. Both the extrudates exhibit similar deformation behaviors in the upper region of the bending specimens, in which {10–12} twinning is activated in most grains. However, because the activation stress for {10–12} twinning is lower in the pure Mg extrudate, its bending yield strength is lower than that of the Mg–1Gd extrudate. In the TZs of both the extrudates, a small amount of {10–12} twinning is caused by the minor tensile stress imposed along the width direction, and the dislocation slip is predominantly caused by the major tensile stress imposed along the longitudinal direction. In the TZ of the pure Mg extrudate, slip is activated to a limited extent during bending because of its strong basal texture, which is unfavorable for basal slip. In contrast, in the TZ of the Mg–1Gd extrudate, basal slip vigorously occurs owing to its RE texture. Furthermore, nonbasal slip also occurs because Gd addition reduces the difference between the critical resolved shear stresses of basal slip and nonbasal slip. Consequently, the bendability of the Mg–1Gd extrudate improves through the effective accommodation of the longitudinal tensile strain in the TZ during bending.