Bending Section Research Articles

Experimental research on fatigue behavior of prestressed concrete beams under constant-amplitude and variable-amplitude fatigue loading

This paper presents the experimental and analytical results of the fatigue behavior of prestressed concrete (PC) beam used in a heavy-haul railway under constant-amplitude and variable-amplitude fatigue loading. The fatigue behaviors including mid-span displacement, bending stiffness and strains of classical materials were investigated comprehensively. Moreover, the residual strain of concrete in compression zone was mainly analyzed and fitted, and the S-N relationships of bottom tensile steel bar and the test beam related to prestressing force were given. The experimental result shows that the fatigue failure mode of PC beam is the fatigue fracture of bottom tensile steel bar in the pure bending section. The main crack width, stiffness degradation and the maximum displacement all show development law of three stages under the constant-amplitude fatigue loading. The fatigue characteristic parameters (stiffness, displacement and strain of concrete in compression zone) of variable-amplitude fatigue test beams exhibit the multi-stage development law due to the addition of multi-level fatigue load. Further, on the basis of the fatigue characterization model of classical materials and the stress analysis of fatigue cracking cross-section, a nonlinear numerical analysis method for the whole fatigue process is proposed. The numerical simulation results are in good agreement with the test data, which shows that the proposed numerical analysis method can simulate the fatigue behavior of PC beams under constant-amplitude and multi-level variable-amplitude fatigue loading. The results of this research provide a reference for fatigue design and fatigue life evaluation of PC beams in heavy-haul railway.

Suppression of Cavity Resonant Coupling by L-Shaped Metal Plate on Microwave Module Lid

This article proposes and implements a novel technique for high spatial isolation that includes the placement of L-shaped metal-plate resonator shunt open-circuited stubs as a band-rejection filter on the lid of a microwave/radio frequency (RF) module. The low-cost, lightweight resonators are realized using a thin metal plate, which is patterned, with high design flexibility, and bent. This article demonstrates that the resonator is equivalent to a quarter-wavelength shunt open-circuited stub in a parallel-plate waveguide, which effectively suppresses the cavity resonant mode in the housed microwave/RF module. In addition, the robust design of the bent section and the determination of the resonator size, from the common ground to the open-circuited end, are presented. The suppression of the coupling level via cavity resonance is demonstrated by the $X$ -band measurements, where the suppressed fractional bandwidth is 46.8% of −63 dB, which is the highest reduction level achieved with an absorber model in this frequency band. These measurement results are in good agreement with the theoretical and electromagnetic simulation results.

Experimental investigation of turbulent flow in a two-pass channel with different U-shaped bends

Time-resolved particle image velocimetry is used to study internal flow field characteristics in U-shaped channels of square cross section and different structures of the bend section. The Reynolds number based on the hydraulic diameter of the channel is 8888, 13 333, or 17 777. The mean flow and Reynolds stress are considered, and proper orthogonal decomposition (POD) is used to investigate the flow characteristics. A series of important conclusions are drawn from the results. For the main flow, the structure of the bend section has an obvious influence on the flow field characteristics. The size and number of vortices in the corner area are significantly reduced because the increase in the Reynolds number makes the impact of the influx stronger. It can be seen from the clear differences in the Reynolds stress for different bend sections that the fluctuations caused by the mixing of the main flow and the vortices are significantly stronger than those at the boundary. The flow in the bend section is complex, there is a relatively high proportion of turbulent kinetic energy in the low-order modes, and there is an obvious stripe-like structure in the bend section of the channel in which the bend has both inner and outer circular walls, which matches the velocity field from the POD.

Chloride transport behavior in bending-shear section of reinforced concrete beam under combined effect of load and environment

This paper investigated the combined effects of different sustained loads and environmental conditions on chloride transport behavior in bending-shear section of reinforced concrete beam. It also compared the chloride transport pattern between bending-shear section and pure bending section based on published literatures. In this study, the tested reinforced concrete beams were subjected to 10%, 16%, 22% and 28% of ultimate bending load using spring-loaded system. For each load, the chloride content was measured on different depths of two specimens under chloride immersion and drying-wetting cycle conditions for 60 days, respectively. The results show that for the given depth and load, the specimens under drying-wetting condition had higher chloride content than those under immersion. The drying-wetting condition facilitated the chloride transport in concrete. The restrictive effect of depth on chloride transport in tension zone was larger than in compression zone. Experimental condition is the most effective factor on chloride transport in compression zone, comparing with depth and load. The corrosion of chloride was mainly on bending-shear section when the load is within 10–16% of the ultimate flexural capacity, while it was on pure bending section when the load is from 22 to 28% of the ultimate flexural capacity.

Isogeometric iFEM Analysis of Thin Shell Structures.

Shape sensing is one of most crucial components of typical structural health monitoring systems and has become a promising technology for future large-scale engineering structures to achieve significant improvement in their safety, reliability, and affordability. The inverse finite element method (iFEM) is an innovative shape-sensing technique that was introduced to perform three-dimensional displacement reconstruction of structures using in situ surface strain measurements. Moreover, isogeometric analysis (IGA) presents smooth function spaces such as non-uniform rational basis splines (NURBS), to numerically solve a number of engineering problems, and recently received a great deal of attention from both academy and industry. In this study, we propose a novel “isogeometric iFEM approach” for the shape sensing of thin and curved shell structures, through coupling the NURBS-based IGA together with the iFEM methodology. The main aim is to represent exact computational geometry, simplify mesh refinement, use smooth basis/shape functions, and allocate a lower number of strain sensors for shape sensing. For numerical implementation, a rotation-free isogeometric inverse-shell element (isogeometric Kirchhoff–Love inverse-shell element (iKLS)) is developed by utilizing the kinematics of the Kirchhoff–Love shell theory in convected curvilinear coordinates. Therefore, the isogeometric iFEM methodology presented herein minimizes a weighted-least-squares functional that uses membrane and bending section strains, consistent with the classical shell theory. Various validation and demonstration cases are presented, including Scordelis–Lo roof, pinched hemisphere, and partly clamped hyperbolic paraboloid. Finally, the effect of sensor locations, number of sensors, and the discretization of the geometry on solution accuracy is examined and the high accuracy and practical aspects of isogeometric iFEM analysis for linear/nonlinear shape sensing of curved shells are clearly demonstrated.

Flow processes of the interaction between turbidity flows and bottom currents in sinuous unidirectionally migrating channels: An example from the Oligocene channels in the Rovuma Basin, offshore Mozambique

A number of unidirectionally migrating channels have been interpreted as the result of the interaction between turbidity flows and bottom currents. Based on the analysis of the morphology and internal architecture of channels, different conceptual models of unidirectionally migrating channels were built to reveal the flow process of the interaction between turbidity flows and bottom currents. Most previous studies mainly focused on the straight section of channels, however, the relevant models did not elucidate the flow process in sinuous sections, limiting the knowledge on the formation mechanism and evolution of the whole unidirectionally migrating channels. By using 3D seismic data, the current study not only depicted the geomorphology and internal architecture of a sinuous unidirectionally migrating channels in the Rovuma Basin, offshore Mozambique, but also quantitatively analyzed the flow processes in the straight and bend sections of the channels. The results show that the interaction between turbidity flows and the northward-flowing Antarctic Bottom Water (AABW) led to the unidirectional migration of the turbidite channels. In the straight section of channels, fine-grained material from the upper parts of turbidity flows was deflected northward via flow stripping induced by the AABW, and this material was finally deposited as sandy lateral accretion packages and muddy drifts. The lateral deposits steepened northern channel banks and forced the southward migration of channel axes. However, in the bend section of channels, the upper parts of turbidity flows were forced towards the inner (southern) bank due to the helical flow induced by centrifugal forces, which probably offset the effect of the AABW, and therefore no lateral drifts developed. The effect of bottom currents on turbidity flows is related to the relative direction of turbidity flow and bottom currents. The lateral deposition and corresponding erosion induced by bottom currents influence the formation of the unidirectionally migrating channels, and the channels migrate towards the erosional side but away from the lateral deposition. Our results can help reveal the complete flow processes and sedimentation in the unidirectionally migrating channels in deep water basins around the world.

Numerical modeling of deteriorated concrete bridge bent caps with externally bonded CFRP retrofit

Deterioration of old concrete bridge bent caps due to spalling and rebar corrosion is a common occurrence. Carbon fiber-reinforced polymer (CFRP) laminate external retrofit is a viable option for regaining such bent cap capacity and serviceability. In this study, a three-dimensional numerical modeling of significantly deteriorated bent caps from a 78-year old cast-in-place bridge in Forney, Texas, was performed. The purpose was to determine the effectiveness of the repair and strengthening process. Numerical models of the bent caps in the original undamaged, damaged, epoxy mortar repaired and CFRP strengthened states were created and calibrated using strain data obtained from full-scale live load testing. The calibrated model strains showed good agreement with those from the load testing. With short span lengths and deep sections, the model strains were small and the effect of the repair/strengthening at modest levels. The neutral axes of the bent cap sections, found from numerical modeling, moved slightly downward after the repair/strengthening process. The model with no section loss showed the highest tensile capacity, and subsequent levels of concrete spalling resulted in progressively smaller capacity. After the first crack initiation, inelastic behavior set in along with crack opening, which explains the increased rate of strains. Truck live loads were adequately represented in the developed numerical models.

Design and optimization of beam optics for a superconducting gantry applied to proton therapy

PurposeProton therapy (PT) is a precise and effective radiotherapy method for tumors. To reduce the weight and footprint of normal conducting gantries applied to PT, a lightweight superconducting (SC) gantry with large momentum acceptance is studied at Huazhong University of Science and Technology. MethodsTo limit the frequency of field changing in SC magnets, a local-achromaticity beamline is designed with large momentum acceptance. Based on the analysis of high order aberrations, the lattice of the gantry beamline is composed of two symmetric bending sections to limit high-order aberrations, and sextupole fields are superimposed to further eliminate dispersion up to second order. ResultsWe presented a second order beam optics design of a SC gantry. The optics fitting is completed with COSY Infinity and the result of particle tracking shows a momentum acceptance of ±8%. Alternating gradient canted-cosine-theta (CCT) magnets are applied to implement combined functions of beam bending and focusing. Some methods are proposed to minimize the field distortion in curved CCT magnets. ConclusionsThe beam optics with high order considerations of a lightweight SC gantry with large momentum acceptance is presented.

Correlation of Standing Work Position and Musculoskeletal Disorders (MSDs) Complaints on Rack Frame Bending Section Workers in Informal Industry of Rack Making in Surabaya, Indonesia

This research was conducted to analyze the correlation between standing work position and complaints of musculoskeletal disorders on rack frame bending workers in the informal industry of rack making in Surabaya, Indonesia. When doing rack bending, standing work position was affected by work position. The jobs forced workers to work with non-ergonomic standing work position. This caused workers to experience complaints on the skeletal system (MSDs) faster. This research was an observational research with cross sectional design. The sample used a total population of 5 workers. Data obtained by interview, measurement of height and weight and observation of work position. The data analysis method used was descriptive statistics. It was known that due to non-ergonomic standing work position, 40% of rack frame bending workers had a moderate and high MSDs risk category while 20% of other workers were in the low category. In addition, it was known that 40% of workers had low and moderate MSDs complaints category and 20% of other workers had high MSDs complaints category. Based on the results, the standing work position on the rack frame bending workers had a strong and positive correlation with a correlation coefficient of 0.655. In addition to the work position, there was a strong correlation between age, working period, and BMI with MSDs complaints of rack frame bending workers. It was recommended that the employer adjust the frame size on each bending machine and provide seat for workers to rest.

Single-mode Bragg ring laser diodes.

We have designed and fabricated a monolithic semiconductor ring laser based on a Bragg waveguide structure. Through careful control of the waveguiding, we have overcome the inherent "leaky" nature of this waveguide mode and demonstrated a ring laser lasing in the Bragg mode. Best behavior was obtained from lasers with a diameter of 400 µm, where they exhibited output power ${ \gt }{1}\;{\rm mW}$>1mW, in continuous wave (CW) operation. A tangent waveguide provided access to the ring cavity using two ports through evanescent coupling. To meet the stringent waveguiding requirements imposed by the Bragg structure, a two-step etching process, consisting of a shallow-etched coupler and a deep-etched bend section of the ring, was developed in order to reduce the bend and scattering losses. The laser showed a threshold current density of ${\sim}{2.2}\;{{\rm kA/cm}^2}$∼2.2kA/cm2 in CW operation with single longitudinal mode operation with a signal-to-noise ratio of 30 dBm obtained at 1.5 ${I_{\rm th}}$Ith. Broadband phase-matching of $\chi ^{(2)}$χ(2) nonlinearity is observed, offering self-pumped parametric C-band conversion ${ \gt }{40}\;{\rm nm}$>40nm with efficiency of ${142}\% \;{{\rm W}^{ - 1}}\;{{\rm cm}^{ - 2}}$142%W-1cm-2.

Investigation of abutment effect on scouring around inclined pier at a bend

In this paper, in order to investigate the effects of abutments in presence of a pier on scour depth and bed topography alteration, a series of tests were carried out considering abutments with a length twice that of the pier and vertical and inclined piers with their inclination towards upstream, downstream, inner and outer banks. The results show that the maximum scour depth is formed at the upstream side of the outer abutment in all tests. Maximum scour depths are formed at the angle of 89 degrees if the bend section between 92% and 94% of the channel’s width from the inner bank in all tests except in the case of abutments with one pier which is inclined towards downstream. In the latter case, maximum scour depth is formed at the angle of 90 degrees and at the point 88% of the channel’s width from the inner bank.

Advanced FE model validation of cold-forming process using DIC: Air bending of high strength steel

Recent advances in mechanical and civil engineering are noticed in many innovative designs that frequently employ cold-formed High Strength Steels (HSS). Typical mobile cranes benefit from the advanced properties of these steel grades in a bent configuration. Here, the majority of load-carrying members are produced through cold-bending and subsequent welding procedures. These cold-foring processes induce residual stresses and strains that must be considered when assessing the structural integrity and service life of bent sections in an assembly. Finite Element Analysis (FEA) offers a unique solution here to reproduce the bending process accurately. However, this analysis must be verified using representative validation methods. If these methods remain scarce, basic or incomplete, the credibility of a sensitive FE model may be compromised. In the present paper, a series of model validations are proposed that rely on the global and local response of the material during or after bending. A benchmark specimen and an air bending set-up have been developed from a numerical design of concepts and fine-tuning of tool dimensions, ensuring the appropriate bending conditions. Local validation is pursued using stereo Digital Image Correlation (DIC) to capture the strain fields, generated during plastic bending of a 12 mm thick S690QL plate. The crux of the problem is twofold: firstly, strain calculation methods used in DIC and FEA are fundamentally different, hampering a correct and honest comparison. Secondly, consistent point-to-point comparisons of experimentally acquired (DIC) and numerically computed (FEA) strains are more susceptible to uncertainties related to processing settings and differences in coordinate frame. Moreover, the main advantage of the introduced ground truth validation is the ability to level the FEA data through identical filters as the DIC experiment. Unlike a direct comparison, this levelling approach auto-adopts an unconditionally equal strain calculation, based on nodal displacement fields, independently of a local (shell) or global (solid) element formulation. This paper aims at clarifying the need for this ground thruth validation in pursuance of higher fidelity FE-models for metal forming simulations.

Fabrication-tolerant Fourier transform spectrometer on silicon with broad bandwidth and high resolution

We report an advanced Fourier transform spectrometer (FTS) on silicon with significant improvement compared with our previous demonstration in [Nat. Commun. 9, 665 (2018)2041-1723]. We retrieve a broadband spectrum (7 THz around 193 THz) with 0.11 THz or sub nm resolution, more than 3 times higher than previously demonstrated [Nat. Commun. 9, 665 (2018)2041-1723]. Moreover, it effectively solves the issue of fabrication variation in waveguide width, which is a common issue in silicon photonics. The structure is a balanced Mach–Zehnder interferometer with 10 cm long serpentine waveguides. Quasi-continuous optical path difference between the two arms is induced by changing the effective index of one arm using an integrated heater. The serpentine arms utilize wide multi-mode waveguides at the straight sections to reduce propagation loss and narrow single-mode waveguides at the bending sections to keep the footprint compact and avoid modal crosstalk. The reduction of propagation loss leads to higher spectral efficiency, larger dynamic range, and better signal-to-noise ratio. Also, for the first time to our knowledge, we perform a thorough systematic analysis on how the fabrication variation on the waveguide widths can affect its performance. Additionally, we demonstrate that using wide waveguides efficiently leads to a fabrication-tolerant device. This work could further pave the way towards a mature silicon-based FTS operating with both broad bandwidth (over 60 nm) and high resolution suitable for integration with various mobile platforms.

Experimental behaviour of steel-concrete composite box girders subject bending, shear and torsion

The results of two unique experimental campaigns carried out on composite box girder sections subjected to moment-shear interaction and moment-shear-torsion interaction are presented. They involve the behaviour of the box sections both in positive and negative bending. The effect of the flexibility of the connection is measured and accounted for. A finite element model is implemented to account for this effect, resulting in an improvement in the accuracy of the stiffness of the sectional behaviour. One of the main results is a significant over-resistance in relation to the shear capacity of the sections, which is very clear in the tests involving bending shear and torsion. This effect is attributed to the contribution to the shear capacity of the concrete slab.

Will a buried composite pipeline system fail at its joints under the effects of overburden soil, pipe operating pressurization, and traffic loads?

In real world applications, buried pipelines span across great lengths. It is inevitable that certain sections of a buried pipeline experience external loads in addition to top soil overburden, such as weights of aboveground buildings and traffic loads located directly above these sections. The present study investigated the effects of overburden soil, pipe internal pressurization, and traffic loads on fiber-reinforced plastic pipelines at various pipe sections with particular emphasis on pipe joints using finite element method. This study includes realistic modeling of traffic loading on service road running across a buried pipeline system, consisting of straight, bent, and joint sections. Our results also revealed that surcharge loading might not be a predominant factor in pipe failure or leakage issues as compared to the cyclic pipe internal pressurization. Moreover, it was also confirmed in our study that the pipe joint remained as the most critical region for pipe failure or leakage issues.

Surgical Robot for Intraluminal Access: An Ex Vivo Feasibility Study.

Early-stage gastrointestinal cancer is often treated by endoscopic submucosal dissection (ESD) using a flexible endoscope. Compared with conventional percutaneous surgery, ESD is much less invasive and provides a high quality of life for the patient because it does not require a skin incision, and the organ is preserved. However, the operator must be highly skilled because ESD requires using a flexible endoscope with energy devices, which have limited degrees of freedom. To facilitate easier manipulation of these flexible devices, we developed a surgical robot comprising a flexible endoscope and two articulating instruments. The robotic system is based on a conventional flexible endoscope, and an extrapolated motor unit moves the endoscope in all its degrees of freedom. The instruments are thin enough to allow insertion of two instruments into the endoscope channel, and each instrument has a bending section that allows for up-down, right-left, and forward-backward motion. In this study, we performed an ex vivo feasibility evaluation using the proposed robotic system for ESD in a porcine stomach. The procedure was successfully performed by five novice operators without complications. Our findings demonstrated the feasibility of the proposed robotic system and, furthermore, suggest that even operators with limited experience can use this system to perform ESD.

ENDOSIALOSCOPIC DIAGNOSIS AND TREATMENT OF SIALOLITHIASIS

The aim of the study is to evaluate the effectiveness of endosialoscopy in the diagnosis and treatment of patients with sialolithiasis. Material and methods . 106 clinical observations were analyzed in which computed tomography (multislice spiral computed tomography or cone-beam computed tomography) without contrast, salivary gland ultrasound and endosialoscopy were used to diagnose and treat patients with sialolithiasis. In the process of diagnostic sialoscopy, the patency of the ducts, the presence of strictures and dilatations, the condition of their walls, the severity of the vascular pattern, the integrity of the epithelial lining, the contents of the ducts, the presence of mucus, pus, and, of course, the presence of sialolites, their number, size, shape, density were evaluated. Results and discussion. Endoscopy allows you to get unique information about sialolite and the state of the ductal apparatus, which determines the method of further treatment. Endosialoscopy can be used as a standard diagnostic method for suspected sialolithiasis and for the removal of sialolites (using endoscopic instruments) or as assistance. At the same time, diagnostic endosialoscopy is not an exhaustive method; therefore it should be carried out in conjunction with other methods – computed tomography or ultrasound of the salivary glands. The possibility of endoscopic sialolite removal depends on its mobility, size, location and condition of the duct. Attempts to capture and remove fixed sialolites, which are only partially visible and located in the deep sections of the salivary gland beyond the bend or stenosis section using endoscopic techniques, have been unsuccessful.

Comparative calculation of optimal parameters of channel bent and bent closed profiles

Relevance. A new technical solution for channel bent closed profiles (BCP), distinguished by a composite section and related to light steel thin-walled structures (LSTWS), which are distinguished by high technical and economic indicators and massive demand in industrial and civil construction, is presented. The main results of the comparative calculation of the optimal parameters of bent channels and channel horizontal bending sections are also given. Aim of the research. The purpose of the study is to show that the characteristics of LSTWS can be further improved by shaping modification profiles, combining in its composite section straight and round outlines of closed and open loops. Methods. Through experimental design and optimization and design calculations of channel profiles, their new technical solution has been developed, the originality of which is confirmed by patent examination. Results. Channel BCP consists of two tubular shelves and one wall of double thickness. For its manufacture without welded, bolted or riveted joints, the outer and inner blanks are made along the entire length with serrated longitudinal edges, the teeth of which are staggered relative to each other and mutually bent in grooves after closing a bent profile along its shelves. The bends of the gear mounts increase the collapse thickness, provide an increase in local stability and shear strength of the thin-walled elements, and also allow not to reduce the design sections. A comparative calculation of the optimal parameters of bent channels and channel bending sections for bending showed that in the first of them the strength is maximum when the ratio of the width and height of the cross section is 1/6, and in the second - 1/5.68.

An achromatic gantry for proton therapy with fixed-field superconducting magnets

A novel concept for a superconducting, fixed-field bending section is presented for use in a proton therapy gantry. The large momentum acceptance of this design allows for treatment over the full proton energy range of 70–220 MeV with fixed field in the superconducting magnets, eliminating the technical risks associated with fast-field ramping to match beam energy changes during treatment. A combined study of beam dynamics and magnet design is shown for such a system in which a simple magnet geometry with straight Nb–Ti racetrack coils is used to produce the desired fields. Particle tracking through this design is compared with clinical requirements for beam spot shape and size at isocenter over the full range of proton energy.

On the post‐buckling rotational capacity of square hollow sections in uniform bending – An initial study of the impact of initial imperfections on deformation paths

On the post‐buckling rotational capacity of square hollow sections in uniform bending – An initial study of the impact of initial imperfections on deformation paths