Bending Zone Research Articles

Assessment of wastewater treatment potential of sand beds of River Ganga at Varanasi, India

Abstract Inadequate sewage treatment plant (STP) capacity, limited power supply, and discharge of partially treated and raw sewage create a significant sanitation problem in Varanasi city, India. This problem becomes severe during the lean period of the river. To reduce the burden on STPs, sewage can be treated and filtered in a naturally occurring sand bed at the convex bank side of the river. In the present study, a 7-km stretch of the sand bed of River Ganga at Varanasi has been selected. This stretch is divided into three zones: entrance, middle, and exit zones. The objective of this research is to assess the filtration potential of selected sections in respective zones and to find out the most suitable zone, out of the three, for wastewater filtration. Seven basic parameters such as dissolved oxygen, biological oxygen demand, electrical conductivity, total dissolved solids, salinity, pH, and temperature were measured before and after filtration, through the sand bed of the three zones of River Ganga. Of the three selected zones of the river bend, filtration length and the amount of available sand were found to be maximum in the middle zone. Experimental results and survey work show that the sand bed in the middle zone of the river bend is best suited for wastewater disposal and filtration.

Creep deformation and permeability evolution of the K1/J2 paleoweathered rocks in the bending zone under triaxial unloading–loading confining pressure

Creep deformation and permeability evolution of the K1/J2 paleoweathered rocks in the bending zone under triaxial unloading–loading confining pressure

Elastic–Plastic Stage of Transverse Deformations in the Compressed Zone of Real Reinforced Concrete Beams

The relationship between transverse and longitudinal deformations (Poisson ratio) in the compressed zone of bending reinforced concrete elements is still not properly considered in designs. This factor is important as it is related to the formation of transverse cracks in the compressed zone of the elements. The main aim of the present research was an experimental investigation of the Poisson ratio in the compressed zone of real single- and two-layer reinforced concrete beams as well as a comparison with the theoretical model proposed in this study. The elastic and elastic–plastic stages were analyzed using experimental data for real beams with a span of 8 m. It was shown that the term “Poisson coefficient” had a limited validity for elastic longitudinal deformations up to 0.5‰. After reaching this limit, the suitable term was “Poisson ratio”. The obtained results allowed a more accurate prediction of transverse deformations and the corresponding cracks, defining a new limit state for bending reinforced concrete elements. Therefore, the authors recommend that the obtained results are considered in order to increase the design accuracy of reinforced concrete bending elements. The outcomes of this study and the proposed theoretical concept should be included in modern design provisions.

Numerical Study on the Sagging Damage of the Simplified Hull Girder Subjected to Underwater Explosion Bubble

The pulsation of the bubbles resulting from underwater explosions can lead to severe damage to the structure of the ship’s hull, and even to its sinking. To study the damage mechanism of a simplified hull girder (SHG) subjected to near-field underwater explosion bubble, the Coupled Eulerian–Lagrangian (CEL) method based on verifications of the calculation accuracy was used to simulate 11 SHG structures. The sagging bend mechanism of SHGs was analyzed from the perspective of plastic hinge lines. Moreover, the length formula of the potential bend zone was studied through the assumed plastic hinge lines. The influence of transverse bulkheads on bending mode and total longitudinal strength was investigated. The results show that SHGs’ sagging damage is composed of regular plastic hinge lines, mainly depending on side plates’ folding—W-shaped in this paper. When facing the near-field underwater explosion bubble, the distant transverse bulkheads influence the total longitudinal strength and do not always play a positive role.

Mitigation of gravitropic bending of snapdragon cut flowers through SNP treatment via ROS asymmetry elimination and auxin sensitivity reduction

Snapdragons (Antirrhinum majus L.) are an important fresh-cut flower in the international flower market. During storage and transportation, snapdragons often undergo a gravitropic response that has a substantial adverse effect on their ornamental and market value. The gravitropic response is a complex physiological and biochemical process that is affected by signals such as auxins and reactive oxygen species (ROS). In this study, we found that the pretreatment of exogenous nitric oxide (NO) donor sodium nitroprusside (SNP, 0.2 mM) effectively inhibited the gravitropic bending of snapdragon cut flowers after horizontal placement. The gravitropic stimulus induced higher ROS (O2−∙ and H2O2) accumulation in the lower side compared to the upper side of the bending zone of the control flower stems. Compared to the control, a substantially higher accumulation of ROS was induced through the SNP treatment, correlating with the increased activity of catalase (CAT) and ascorbate peroxidase (APX), as well as the enhanced expression of AmAPX1 and AmCAT1. However, unlike the control, no ROS asymmetric distribution was found for the SNP-treated flowers. Four free auxins, IAA, IBA, ME-IAA and ICA, were detected in the flower stems, among which, only IBA showed asymmetric distribution after the gravitropic stimulus. An IBA content that was approximately 26% higher was detected in the lower side compared to the upper side of the control flower at 2 h, but no difference was found for the SNP-treated flowers. A higher expression of the AmPIN3 gene at the lower sides compared to the upper sides of the control may be correlated with the transient IBA asymmetric distribution. Interestingly, an expression of AmIAA2 and AmSUR50 that was around 2-fold was detected in the lower side compared to the upper side of the control, indicating that higher auxin sensitivity may be induced in the lower side. However, the expression of AmIAA2 and AmSUR50 was reduced by the SNP treatment, implying that high ROS levels may reduce auxin sensitivity. Furthermore, a higher AmExp1 and AmH+–ATPase1 expression in the lower side compared to the upper side was found for the control but not for the SNP-treated flowers, indicating the two genes may be involved in the bending of the flower stems. The above results reveal that SNP treatment eliminates the asymmetric distribution of ROS and reduced auxin sensitivity of snapdragon flower stems, thereby eliminating their asymmetric growth and further inhibiting their gravitropic response.

Insights into the palaeoenvironments, structure and stratigraphy of the lower Miocene of the Eastern Carpathians Bend Zone, Romania

The ages of several Oligocene to Miocene sedimentary formations from the Eastern Carpathians Bend Zone are poorly constrained due to palaeoenvironmental factors, reworking of fossils, structural complexity and limited exposure. To help overcome these issues, this study integrates calcareous nannoplankton and foraminifera biostratigraphy with isotopic age dating (U-Pb) of volcaniclastic zircons, and sedimentological and structural observations/interpretations. Our study was carried out along an ~6-km-long section made from a series of outcrops along the Bizdidel River which exposes several formations such as the Pucioasa, Fusaru, Vinețișu, Starchiojd and Slon. We show that the Fusaru Formation consists of coarse-grained rocks deposited as confined longitudinal channel successions that migrated laterally. It is bounded by the mud-rich Pucioasa and Vinețișu formations which are lateral equivalents of the Fusaru confined channels deposited as levee/overbank units. These genetically related formations appear to reach younger ages – of the lower to middle Burdigalian based on calcareous nannoplankton and foraminifera biostratigraphy – than previously thought (upper Oligocene to lower Burdigalian). The dominant organic-rich mudstones of the Starchiojd Formation represent pelagites/hemipelagites deposited in anoxic conditions. Their middle Burdigalian age is established by a 17.41 ±0.27 Ma zircon U-Pb age of zircons from the Bătrâni Tuff in the Starchiojd Formation. Based on the similar phenocryst content, zircon U-Pb age and zircon trace element composition, the source of the tuff is suggested to be the 17.3 Ma Eger ignimbrite-forming eruption, which has proximal, near-caldera deposits in the Bükkalja Volcanic Field, Hungary. The mud-rich Slon Formation seems to be related to shelf edge/upslope failure that formed cohesive debrite avalanches resulting from foreland propagation of compression. The Slon Formation extends in this area to at least the upper part of the lower Miocene to middle Miocene. These results highlight the need to revise ages of those parts of the sequence which are poorly constrained or different in other parts of the Carpathian Basin. Such revised ages help to better constrain the understanding of the deformation history of the Carpathians.

Study on action mechanism between rated working re-sistance of support and overburden strata movement

Based on the pressure regulating test curve describing support–surrounding rock relationship, the relationship between rated working resistance (RWR) and overburden movement is investigated. It is discov-ered that between RWR and movement of direct roof strata, the relationship is “must control and must be controlled”, which is qualitatively expressed as Pze=hzγz; between movement of main roof strata and RWR, the relationship is “degree-controlling and degree controlled”, which is hyperbolic and qualitatively expressed as Pre=QSm/2Sx; between RWR and movement of bend zone strata, the relationship is that of “unable to control and unable to be controlled”, which is qualitatively expressed as Pb=0. Finally, the author examines the characteristics of the “hyperbola”, the prerequisite for its existence, and the influence of main roof fault block movement parameters on the position of the hyperbola in the coordinate system, the degree of support control, and the degree of roof movement. This research outcome represents an innovation and a breakthrough on the basic mine pressure theory. It has great academic significance to the discipline of mine pressure and stratum control and provides theoretical basis for the application of strata control.

Enhancement of RC T‐beams toughness using laced stirrups reinforcement for blast response predictions

AbstractThe dynamic behavior of laced reinforced concrete (LRC) T‐beams could give high‐energy absorption capabilities without significantly affecting the cost, which was offered through a combination of high strength and ductile response. In this paper, LRC T‐beams, composed of inclined continuous reinforcement on each side of the beam, were investigated to maintain high deformations as predicted in blast resistance. The beams were tested under four‐point loading to create pure bending zones and obtain the ultimate flexural capacities. Transverse reinforcement using lacing reinforcement and conventional vertical stirrups were compared in terms of deformation, strain, and toughness changes of the tested beams. The inclination angles of the used lacing reinforcement with respect to the longitudinal reinforcement were 45° and 60°. The lacing reinforcement was efficient and participated actively in resisting the bending moments and shear forces at the same time. For the same diameter of lacing reinforcement, the 60° inclination angle imposed more ductility before failure than beams with lacing reinforcement of a 45° inclination angle. Moreover, the lacing bar diameter was more effective in improving the load‐carrying capacities when using the inclination angle of 45°. A finite element (FE) model was developed and validated using the experimental results based on the measured deformations and strains to conduct a parametric study. The investigated parameters included the effect of the arrangements of the applied loads, laced rebar diameter, inclination angle, tension reinforcement ratio, and concrete strength.

Investigation of the Flexural Behavior of Preloaded and Pre-Cracked Reinforced Concrete Beams Strengthened with CFRP Plates

This paper investigates the flexural behavior of preloaded reinforced concrete (RC) beams, strengthened with Carbon Fiber Reinforced Polymer (CFRP) plates using an experimental program, analytical procedure, and Finite Element Method (FEM) simulation. The RC beams were subjected to preloads of 30%, 50% and 70% of the yielding load, prior to installation of the strengthening system. The eight RC-strengthened beams with a reinforcement configuration of 3Ø12 and two CarboDur S512 plates have been evaluated using bending tests. The failure modes of all the RC-strengthened beams were governed by the widening of flexural cracks within a constant bending zone, followed by debonding of the CFRP plates. The plates were debonding simultaneously or one plate prior to the other plate. The ultimate moment capacity is not significantly reduced while increasing preload levels from 0% to 70%. The moment capacity is increased by 70% to 80% in the CFRP strengthened beams, compared with un-strengthened beams indicating the potential of capacity enhancement that can be attained by externally bonded CFRP.

Study on grain deformation in bending zone of SUS304 stainless steel foil

In this paper, the grain deformation of SUS304 stainless steel foil under small fillet bending was studied. First, bending experiments were performed on 50 and 100μm thick foils, and the results showed that when the bending radius was close to the thickness of the foil, the surface grains in the bending zone collapsed and extruded, resulting in a rough surface. Then, Crystal Plastic Finite Element Method (CPFEM) was used to simulate the bending of different thickness foil (20, 50 and 100μm), in which the grains are hexagonal and the opposite edge distance is 20μm. Simulation results showed that when the relative fillet radius (the ratio of fillet radius to thickness) is similar, the surface layer of fillet becomes coarser with the increase of the foil thickness-grain size ratio. In addition, the uncoordinated intergranular deformation is caused by orientation difference, which leads to high density Geometric Necessary Dislocation (GND) in grain boundary region. Electron Backs-Scattered Diffraction (EBSD) experiments on recrystallized annealed foils with a thickness of 100μm showed that the GND density of the grain boundary after bending is significantly higher than that of the intragranular, which has the same distribution characteristics as the simulation results.

Shear behavior of composite stone beams reinforced with NSM longitudinal CFRP bars

Employing near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) bars in the tensile zone of bare stone beams can effectively improve their flexural performance. Meanwhile, shear failure could occur when excessive amount of flexural reinforcement is adopted. Seven composite stone beams were tested to study the shear behavior of composite stone beams reinforced with NSM CFRP bars. The test variables included the shear span to depth ratio and the reinforcement ratio. Digital Image Correlation (DIC) technology was used to capture the full-field strain of the beams. The results indicated that the composite stone beam exhibited ductile failure mode with visible deflection and multiple cracks formed in both constant bending zone and flexural-shear zone. With the decrease of shear span to depth ratio, the cracking load and shear capacity increased linearly but the deformation capacity decreased. For the same shear span to depth ratio of 2.5, the composite beam with a higher CFRP reinforcement ratio observed higher shear load-carrying capacity. DIC results demonstrated the shear force was mainly provided by the arch action before failure. A shear-resistance theoretical model based on Rankine's failure criteria, sectional mechanical analysis and experimental observations was proposed and verified with the current and previous test results.

Numerical investigation of the parameters that may seriously impact the ship control lability in restricted bending channels

Inland waterway transport is now playing a significant role thanks to its various advantages over the other transportation modes, for example, low cost, low environmental pollution, and large capacity, etc. However, inland waterways are not only naturally curved but also narrow and shallow, which causes complex flow environments and navigational conditions. Inland ships are consequently susceptible to accidents in restricted curved waterways. Especially during these years, this mode of transport has seen significant progress by the arrival of the new generation of ships (larger size and more powerful), and this makes ships' maneuverability in such sensitive waters severer. The aim of the present work is firstly to well understand the flow behaviors around a ship in bending zones, and secondly to study the variation of hydrodynamic forces (bank cushion and suction phenomena) in these zones. To conduct this investigation, the CFD model based on an unsteady Navier-Stokes solver in STARCCM+ is used. The verification and validation of this model are realized by respecting the ITTC recommendations. The latter is then used to perform a series of simulations by testing the following parameters: channel angle, water depth to draft ratio, ship speed, channel bottom width and drift angle on ship hydrodynamics in restricted curved fairways. The obtained results of this work provide an interesting idea about the ship's hydrodynamics variation and characterize the parameters that seriously impact the ship controllability in restricted bending channels.

Flexural and Serviceability Behavior of Concrete Beams Reinforced with Ribbed GFRP Bars

Glass fiber-reinforced polymer (GFRP) bars are used as internal reinforcement in many structural applications. The structural performance of GFRP-reinforced concrete elements is dependent on the physical and mechanical properties of GFRP reinforcement. There is a lack of experimental data on the flexural behavior of concrete beams reinforced with ribbed GFRP bars. This study evaluates the flexural strength and serviceability performance of concrete beams reinforced with ribbed GFRP bars. A total of 11 GFRP-reinforced concrete beams with dimensions of 4,350 × 400 × 200 mm (length × height × width) were constructed and tested under a four-point loading test setup. The main test parameters were the concrete cover, reinforcement ratio, bar spacing, and confinement due to the transverse reinforcement in the bending zone. The results uantify the effect of increasing the reinforcement ratio on the increase in the ultimate capacity and the reduction in deflection at the service and ultimate stages. In addition, the results showed that the increase in the confinement in the bending zone due to closely spaced stirrups resulted in a higher ductility index and ultimate capacity with no considerable effect on the postcracking stiffness of the beams. Moreover, based on the experimental results, the accuracy of deflection equations available in design codes and guidelines is evaluated and discussed.

Fragility curves for road embankments exposed to adjacent debris flow

Studies of recent decades have shown thousands of kilometers of transportation networks that have presented damage or failure from different types of flows, causing important traffic disruptions. Debris flows running adjacent (or in parallel) to river channels often explain the structural damage to road embankments caused by slope erosion. The probability of expected structural damage caused by a natural hazard may be modeled using fragility curves, which have been developed for transportation infrastructures like bridges and roads exposed to debris flows and are used in risk assessment. There are even fragility curves available to estimate the fragility of road embankments exposed to perpendicular debris flows. However, currently no model is available to estimate the road damage probability of embankments exposed to adjacent debris flows despite their important effects on traffic. This paper aimed to develop fragility curves for road embankments exposed to adjacent debris flows, considering mechanisms of exposed slopes subject to erosion and subsequent embankment instability. Models were calibrated considering flow characteristics in straight and bend channels including three damage states in terms of road traffic capacity loss. Monte Carlo simulations were performed to model potential damage, obtaining fragility curves for two types of roads. Curves were fit to log-normal distributions with a 99.5% confidence level. The analysis demonstrated that the geometric characteristics of road embankments explain their fragility, wherein lower heights and platform widths result in more probable expected damage. The analytical model developed confirmed that the erosive process intensifies in bend zones of channels, resulting in higher damage probability.

Gravimetric analysis of tomato stems in the perception of a gravitational signal

The dynamics of the content of various groups of cell wall polysaccharides in the cells of tomato stems during the development of the plant’s response to gravitational stimulation and phytohormonal treatment was studied. It has been shown that gravitational stimulation causes changes in the relative content of stem cell wall polysaccharides in the zone of gravitropic bending over a period of 3–6 hours. At the same time, predominantly multidirectional changes occur in the upper and lower halves of the stem, which ultimately leads to noticeable biochemical differences between the two parts of the stem, which allows it, in all likelihood, to bend due to an uneven growth of cells in different parts of the stem. Under the action of gravitational stimulation and epibrassinosteroid epine, changes in the polysaccharide composition appear earlier (already 1 hour after exposure) in time than with a single gravitational stimulation, and under the influence of ethephon and gravitational stimulation later (only from 6 hours of exposure).

Method for calculating the forces required when bending pipes of small cross-section with a rectangular profile

Curved pipes of small cross-section rectangular profile (3,6x1,8 – 11x5,5 mm) are widely used in antenna-feeder devices of spacecraft. They are required to ensure dimensional accuracy, in the bending zone no more than ±0,05 mm, for this a choice of methods of technological modes is necessary. The object of the study is a small-section pipe billet made of copper M4, which must be bent to obtain a bending angle of 90°. The purpose of the study is to develop calculation methods necessary for the implementation of the technological process of bending small-section pipes, with justification of bending efforts. The paper analyzes the methods of bending rectangular pipes. The most rational method was chosen, bending using a rigid mandrel. Based on the selected bending method, a calculation model was compiled. The methodology and calculation algorithm have been developed and the analysis of the calculation results has been carried out. As a result of theoretical studies, with the help of calculations, the degree relationship of the effort of bending from the bending radius was revealed, the bending forces from the bending radius – the larger the bending radius, the less effort is required for bending. The calculation can be used to determine the size of the bending equipment and the bending force of the pipe of small cross-section, allows you to choose the most optimal mode of the technological process.

Numerical study on flexural behaviour of FRP reinforced concrete beams with compression yielding blocks

Fibre-reinforced polymer (FRP) bars are used in concrete structural members to tackle the corrosion problem of steel bars. However, the brittle rupture of FRP bars results in relatively low ductility of such concrete members. This paper numerically investigates the feasibility of using compression yielding (CY) block to enhance the ductility of FRP bar reinforced concrete beams. A finite element model is developed to study the behaviour of beam adopting the CY block, followed by a parametric analysis on the effects of material properties and geometry of the CY block. The results indicate that the adoption of CY block changes the failure mode of the beam from brittle concrete crushing to ductile compression yielding, increasing both the loading capacity and ductility of the beam. Increasing the compressive yield strength of the CY block can effectively increase the loading capacity but decrease the ductility of beams. A higher compressive ultimate strength of the CY block also increases the loading capacity but has limited effect on the beam ductility. In addition, the beam ductility can be increased by reducing the yielding and ultimate strains of the CY block, while the loading capacity can be enhanced by higher yielding strain or lower ultimate strain. It is revealed that sufficient height of the CY block is required to prevent concrete crushing in the compression zone, and an increase in CY block height improves the beam ductility. The CY block length should cover at least the pure bending zone when the section with the block has higher flexural capacity than that without the block, otherwise the length can be controlled as the theoretical plastic hinge length.

ПРОЧНОСТЬ И ДЕФОРМАТИВНОСТЬ ИЗГИБАЕМЫХ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ, УСИЛЕННЫХ УГЛЕПЛАСТИКОМ

Reinforcement of reinforced concrete flexible elements with polymer composite materials has found wide application in modern construction, so the accumulation of experimental studies of the strength of such structures is relevant. This paper presents the results of experimental studies of the stress-strain state of flexible reinforced concrete elements forced with carbon fiber. Namely, six beams of three types. The first type of beams - reference samples without reinforcement. The second type of beams – beams loaded at the stage corresponding to the standard load, in the presence of cracks and deflections, reinforced with carbon fiber, by gluing it to a stretched zone with a U-shaped anchorage on the supporting areas after unloading. The third type of beams includes samples reinforced, similar to the second type of beams but before the application of loads. In addition, during the experimental study, control images of concrete, rebar and carbon fiber were tested to establish their basic physical and mechanical characteristics. The limit values of experimental bending moments in the middle of the span of samples of all series are obtained. It was found that all samples externally reinforced with carbon fiber were destroyed as a result of increasing the width and height of normal cracks located in the zone of pure bending and increasing deflections, which led to the separation of the composite material from the concrete and the indent of the concrete of the compressed zone

Fibre angle prediction for post-forming of carbon fibre reinforced composite tubular structures

This paper presents a model to predict local fibre angle change due to post-forming of [±60°]4 polyamide 6 carbon (CF/PA6) thermoplastic tubular structures. Fibre angles of the CF/PA6 tubes after forming are predicted based on the initial local fibre angles before forming within their bending zones. Four sets of [±60°]4 CF/PA6 tubes were uniformly heated to 220 °C and formed under isothermal conditions into 45°, 90°, 135° and 180° bends using a rotary draw bender with a bending ratio of 2. A model is derived to predict local post-forming fibre angle changes and validated by experimental fibre angle measurements taken both before and after forming with an optical measurement system. Additionally, micro computed tomography is performed to analyse post-formed tube geometries and determine post-forming strains. The fibre angle prediction model allows laminate mechanical analysis to be performed on post-formed tube, therefore enabling tube laminate design optimisation.

The 21 May 2021 Mw 6.1 Yangbi Earthquake—A Unilateral Rupture Event with Conjugately Distributed Aftershocks

Abstract An Mw 6.1 earthquake occurred in Yangbi, Yunnan province, China, at 13:48:34 (UTC time) on 21 May 2021. It exhibited a typical foreshock–mainshock–aftershock sequence in the northwestern Yunnan rifting area. We used the first P-arrival time from regional broadband seismic stations to check the location of the mainshock’s hypocenter. The updated location of the epicenter is 99.88° E, 25.66° N. The focal mechanisms of nine earthquakes, including the mainshock and the largest foreshock and aftershock, were investigated using the general cut-and-paste method based on regional seismic waveforms to set up the fault geometry and to calculate the static coulomb stress change. The rupture process of the mainshock was constrained by 33 unclipped regional broadband seismic records from 15 stations and nine static displacements from three Global Navigation Satellite System stations. The results showed that the Yangbi earthquake was a unilateral rupture event propagating toward the southeast along-strike direction. The moment was 1.81×1018 N·m, and the corresponding magnitude was Mw 6.1. The peak slip value, the weighted rupture velocity, and the duration time of the mainshock were 0.95 m, 2.2 km/s, and 9.1 s, respectively. At 10 km southeast of the mainshock’s epicenter, the conjugately distributed aftershocks were observed, and the moment density of the mainshock along the strike direction decreased sharply (78% of the total moment released in the first 10 km), suggesting that the sharply decelerating rupture could be the reason for the conjugately distributed aftershocks. The changes in static coulomb stress due to the largest foreshock and mainshock were calculated. The results showed positive Coulomb stress on the major slip zone in the mainshock fault plane triggered by the largest foreshock. Moreover, the 0.01 MPa contour due to the mainshock radiated out of the bend zone of the Weixi–Qiaohou–Weishan fault.