Fiber Beam Research Articles

Performance and damage states assessment of thin-walled steel bridge piers with end-corrosion under earthquake loading

End-corrosion is typical damage to steel bridge piers, which will reduce the seismic performance. Unlike overall uniform corrosion, end-corrosion results in more complex stresses on bridge piers, however, there are few related studies. This study aims to analyze the mechanical performance of corroded bridge piers and to establish a method for evaluating the seismic damage status of steel piers considering circumferential uniform end-corrosion. Firstly, the effect of corrosion parameters on key performance points of bridge piers is quantitatively analyzed using the validated finite element model. The calculation method of critical displacement value corresponding to different damage states of the end-corroded bridge pier is proposed. A high-precision fiber beam element analysis model is developed to simultaneously consider the effects of end-corrosion and shear stiffness variation. The results show that the degradation degree of yield displacement of the end-corroded bridge pier is relatively small. In contrast, the ultimate displacement, capacity point displacement and bearing capacity are significantly affected by corrosion parameters, and the degradation degree after corrosion can reach more than 30%. The pier damage ratio formula proposed in this study can accurately describe the degradation of the ultimate value, and the calculation error is almost controlled within 15%. The multi-node variable section (MNVS) fiber beam model proposed in this study has higher analysis accuracy, which can be improved by more than 16% compared with the traditional fiber beam model. In addition, the accuracy of the MNVS model in the dynamic analysis is verified by inputting the seismic records under three site conditions. Finally, considering the characteristics of end-corrosion, an evaluation method and procedure for seismic damage status of the steel pier with end-corrosion is established.

Dynamic imaging of three-dimensional temperature field via three-directional wavelength modulated lateral shearing interferometry

A three-directional wavelength modulated lateral shearing interference system was proposed for the dynamic three-dimensional visualization of a temperature field. The laser emitted from a distributed feedback (DFB) laser was divided into three beams by a fiber beam splitter. The beams were spatially expanded and passed through the flame in three directions of 0°, 120° and 240°, respectively. The three interferograms formed by reflections from the front and back surfaces of the parallel glass plates were spatially converged into the lens of a high-speed camera. Multiple plane mirrors were utilized to reflect the beams. The size of the region of interest (ROI) was −20 ∼ 20 mm in both x and z directions and 5 ∼ 30 mm in y direction, with a spatial resolution of 200 μm in all directions. A three-dimensional sensitivity matrix was modeled, and the simultaneous algebraic reconstruction technique (SART) was used for layer-by-layer imaging to achieve three-dimensional flame monitoring. Numerical simulations verified the effectiveness of the algorithm qualitatively and quantitatively. In experiments, the temperature distributions of four cases of flames, namely, steady diffused flame, partially blocked diffused flame, dynamic acoustically excited flame and the flame after ignition, were reconstructed at 1k frames per second (fps). The flame structures and temporal variations of temperature distributions were clearly visualized, demonstrating the ability of the system in fast monitoring of three-dimensional dynamic temperature fields.

The Effect of SMA Fiber Content on the Bending and Self-Recovery Performance of ECC Beams.

The addition of superelastic shape memory alloy fibers (SMAF) into engineering cementitious composites (ECC) can create a new type of SMAF-ECC composite material with good self-recovery and energy dissipation performance, which is very suitable for seismic structures. In this study, 10 groups of beam specimens with different volume contents of SMAF were fabricated, and the bending performance, deflection recovery and energy dissipation ability of these beams were studied through three-point bending cyclic loading tests. The failure mode, peak load, load-deflection curve, crack width and other indicators of the specimens were analyzed, and the relationship expression between fiber content and bending strength was established by fitting analysis. The results show that adding SMA fibers can significantly improve the peak load of ECC beams, with a maximum increase of 48.31%. The knotted SMA fibers can fully exert their superelasticity, providing the beam specimens with crack self-closing and deflection recovery ability. When the volume content of SMA fibers is 0-0.6%, the bending strength, energy dissipation ability and deflection recovery ability of the composite material beams increase with the increase in fiber content. When the volume content of SMA fibers is 0.6-1.0%, the above indicators decrease with the increase in fiber content. The suggested equations can well reflect the relationship between fiber content and beam bending strength. The research results of this paper provide theoretical support for the engineering application of SMAF-ECC composite materials.

A fiber beam element based on plastic and damage models for prestressed concrete structures

Modeling of prestressed concrete beams and their degrading processes are relevant issues in the assessment of existing structures and infrastructures, particularly for bridges. This work focuses on the formulation and validation of a fiber beam finite element for prestressed concrete structural elements that accounts for nonlinear material behavior and time-dependent phenomena. The element is a 3D Timoshenko beam that follows a force-based approach. A fiber discretization of the cross-section is used to model concrete, steel reinforcements and prestressing cables based on damage and plasticity for concrete, and plasticity for steel through three-dimensional constitutive laws. The steel fibers are fully bonded. Strain-softening in the concrete requires an appropriate regularization procedure. The tendons are treated as additional fibers with prestressing applied as initial strain of the relevant fibers. No additional discretization is required except for the description of the tendons’ profile. Time-dependent phenomena such as creep, shrinkage and cable relaxation are taken into account. The proposed model is implemented in the OpenSees computational framework to carry out specific validation tests and demonstrate the element potential.

Performance analysis of photonic crystal fiber structure based on different highly nonlinear materials

Generally, fiber with a large mode area is desired for fiber laser and beam delivery applications. But the use of these fiber types is restricted to linear optical applications due to the lower value of the nonlinear coefficient. This paper investigates a single material-based photonic crystal fiber (PCF) with improved optical characteristics, applicable for linear and nonlinear optics. The light propagation in the structure is explored by applying finite element solver-based COMSOL multiphysics software. Five nonlinear optical materials are utilized as background material to get the optimized material with high performance PCF. Using this PCF, the improved optical properties of PCF such as moderate effective mode area of 115.85 [Formula: see text], chromatic dispersion, confinement loss of 10[Formula: see text] dB/m, the nonlinear coefficient of 543W[Formula: see text]Km[Formula: see text], splicing loss of 2.013 dB, and numerical aperture are numerically analyzed. This single-mode PCF also shows the low bending loss for the bending radius of 7[Formula: see text]mm. The amended PCF structure is found to be suitable for high-power fiber laser, supercontinuum generation, wavelength conversion, and slow-light generation.

Performance-based blast-resistant design of RC bridge piers under vehicular bombs

Bridge piers are the critical components to support the superstructures and the blast resistance of piers has attracted extensive attention considering the ever growing deliberate and accidental explosion attacks on bridge structures. However, most of the existing studies focus on the blast-induced dynamic response of a single pier without considering the bridge redundancy, even less the actual traffic performance of the entire bridge. This paper aims to propose a performance-based blast-resistant design approach of RC bridge piers under explosions of vehicular bombs. Firstly, the distribution model of blast impulse on bridge piers is proposed with considering both the ground reflections and diffractions of piers based on the validated finite element analysis (FEA) approach. Then, the fiber beam element-based model and the above blast impulse distribution model were validated based on the dynamic monotonic loading test and the explosion test on RC frame column. Furthermore, the simplified fiber element beam-based prototype RC bridge was established and the parametric studies were performed. Finally, the response surface methodology was adopted and the performance-based blast-resistant design procedure for three design basis threats specified in FEMA, i.e., cargo van bomb, small moving van bomb, moving van bomb, was proposed with utilizing the relative vertical displacement of the mid-bent as the performance index. It derives that, (i) the proposed distribution model of blast impulse is applicable to explosions at scaled distances of 0.5–2.1 m/kg1/3; (ii) the fiber beam element-based model can well describe the global response of the blast-exploded columns/piers; (iii) the proposed performance-based blast-resistant design approach can provide an efficient tool for bridge engineers.

Cyclic behavior of recycled-lump-concrete-filled GFRP tubular columns: Experimental investigation and numerical modeling

A fiber-reinforced polymer (FRP) tube offers the advantages of lightweight formwork, external confinement, and non-corrosive reinforcement for recycled lump concrete (RLC), creating an attractive opportunity for structural applications of this green material. While prior research has predominantly focused on the axial compressive behavior of RLC-filled FRP tubular columns, this study addresses the implications of using such members in seismic areas. Six large-scale RLC-filled Glass FRP (GFRP) tubular columns were tested under constant axial compression and quasi-static reversed lateral loading to examine the impact of crucial parameters on their cyclic behavior. Additionally, the study discusses the numerical modeling of such columns using a fiber beam element approach. The findings indicate that the replacement rate of recycled lumps (<33%) has limited impact on the cyclic behavior of the columns. Reducing the GFRP tube thickness and simultaneously adding a minimum amount of longitudinal steel reinforcement can improve the hysteretic response. An off-axis tube with a fiber orientation close to 50° appears more suitable for structural use compared to 80°. Moreover, even with a tube diameter-to-thickness ratio of 100, the columns still meet the code requirement for lateral drift limit of flexural-dominated members. Overall, the study contributes to instilling confidence in the scaling-up applications of RLC-filled GFRP tubular columns in earthquake-prone areas.

Damage Analysis of Reinforced Concrete Columns Based on Fiber Beam–Column Element

The method of damage analysis of reinforced concrete columns based on the fiber element model is established by combining the uniaxial damage constitutive model of concrete and steel with the fiber beam–column element model. The quasi-static test and the shaking table test of reinforced concrete columns are simulated and analyzed, respectively. The results show that the established fiber element model can predict nonlinear mechanical behavior and the damage distribution of reinforced concrete columns with good accuracy. Furthermore, the model can effectively simulate the evolution process of damage of columns, and describe weak parts of columns, and has high computational efficiency and solution accuracy, thus providing a practical analysis method for the simulation of building structures during earthquake.

Surgical treatment of the floppy eyelid syndrome

Purpose: to evaluate the effectiveness of surgical treatment of the floppy eyelid syndrome. Material and methods. The clinical group consisted of 23 patients (46 eyes) with the floppy eyelid syndrome (16 men and 4 women), ave. aged 46,0 ± 2.6 years. Of these 20 patients underwent surgery for floppy eyelid syndrome by vertical and horizontal shortening of the upper eyelid with or without correction of blepharoptosis. The observation period ranged from 1 month to 10 years. Fragments resected during the operation were subjected to histological examination. Results. A histological study revealed a reduced quantity or absence of elastin in the tarsal plate, destruction of collagen fiber beams, malformation of hair follicles accompanied by moderate chronic inflammation, In the postoperative period, the complaints caused by involuntary ectropion of the upper eyelid disappeared in all patients, the palpebral fissures became maximally symmetric. Conclusion. Surgeries performed by our technologies result in the best possible anatomical arrangement of the upper eyelid within a single-stage procedure.

Measurement and Analysis of Light Leakage in Plastic Optical Fiber Daylighting System

The daylighting systems via polymethylmethacrylate (PMMA) plastic optical fibers have obvious cost advantages and have been widely studied. However, there is light leakage when PMMA optical fibers transmit concentrated sunlight, resulting in a transmission efficiency lower than the theoretical value. This research aims to quantitatively study the light leakage effect of PMMA optical fibers. Concentrated sunlight was used as the sunlight source instead of a monochromatic laser. An adjustable diaphragm was used to adjust the angle of the incident light, and the infrared filter and heat-absorbing glass were used to solve the overheating problem of PMMA fibers. The results show that when the incident angle is greater than 13°, the relative transmission efficiency of the fibers drops rapidly, which means that the light leakage deteriorates. The data also show that the angle of the output beam of PMMA optical fibers is ±30°, which is independent of the angle of the incident beam. Based on this conclusion, a PMMA optical fiber daylighting system with an incident angle of 13° was developed, which has higher transmission efficiency than previously developed systems. This study indicates that the angle effect of light leakage should be considered in the design of a plastic optical fiber daylighting system.

Effect of polyethylene terephthalate fibres on the structural performance of reinforced concrete beams with openings in the shear region

The provision of transverse openings in the shear region of beams to allow passage of services reduces the cracking and ultimate load capacities of the beams and increases deflection under the openings, especially when the size of the opening exceeds 25 % of the overall beam depth. Strengthening of the pre-planned opening regions by use of special steel reinforcements causes reinforcement congestion and difficulties in compaction, calling for alternative ways of strengthening beams with openings. In this study, concrete material was modified by the use of Polyethylene Terephthalate (PET) fibres produced from waste plastic bottles to improve the tensile properties and hence reduce the cracking around the openings and improve the overall performance of the beams. To evaluate the performance of PET fibres in beams with openings, eight (8) reinforced concrete beams with and without fibres of dimensions (150 × 250 × 2000 mm) were cast with varying opening sizes. The horizontal position of the openings was fixed at 300 mm from the support while the vertical position was maintained at the mid-depth of all beams. This performance was evaluated in terms of ultimate and first cracking loads, mid-span deflections, ductility, crack patterns and failure modes, and strain behavior. Test data showed that incorporating PET fibres in beams with openings resulted in a slight increase in ultimate load of 4.1 % and 5.82 % for 0.25 h and 0.35 h beam opening sizes respectively, beyond which the strength was reduced by 9.57 % for beams with 0.45 h opening size, where h was the overall depth of the beam. The first cracking loads increased by 44.12 %, 48.48 %, and 9.38 % for 0.25 h, 0.35 h, and 0.45 h opening sizes, respectively. In addition, a slight improvement in the ductility of PET fibre beams for all opening sizes was observed. The PET fibre beams exhibited a slight change in the mode of failure from dominant shear failure to combined shear and flexure failure characterized by multiple cracks in the flexure region with minimal spacing. An increase in the concrete compressive and tensile strains accompanied by a reduction in concrete and steel shear strains was observed because of the tension stiffening effects of the fibres. The incorporation of PET fibres, therefore, showed a slight improvement in the ultimate performance of beams with 0.25 h and 0.35 h opening size, with no improvement for the control beam and 0.45 h opening sized beam. However, a significant improvement in the serviceability performance for all PET reinforced beams was observed.

Laguerre-Gaussian Expansion of Step-Index Multimode Fiber Beams in Free-Space

We show that the complex conjugate of the overlap integrals between the fiber end-facet field and the Laguerre-Gaussian modes provides the expansion coefficients for the step-index multimode fiber beams. We also show that the fractional power in different azimuthal mode orders remains unchanged from fiber to free-space propagation.

Experimental and two-scale numerical studies on the behavior of prestressed concrete-steel hybrid wind turbine tower models

Prestressed concrete-steel hybrid (PCSH) wind turbine tower has been recognized as an efficient alternative to traditional steel tube supporting towers for wind farms in harsh sites such as mountain regions. To investigate the global and local mechanical behavior including failure patterns of a full scale PCSH wind turbine towers, an experimental study on a substructure of a scaled PCSH tower is carried out firstly. Then, a material subroutine for three-dimensional (3D) fiber beam elements suitable for implicit analysis on the mechanical behavior of the substructure of the scaled PCSH tower is developed. A two-scale numerical model of the substructure of the scaled PCSH wind turbine tower employing the developed 3D fiber beam elements and solid elements is developed. The accuracy and efficiency of the developed two-scale numerical model for the behavior simulation of the substructure of the scaled PCSH wind turbine tower is illustrated by comparing the numerical results with the experimental measurements. Additional comparison of the simulation results using the developed two-scale numerical model is made with them of a model using sole 3D fiber beam elements and a model using sole solid elements, respectively. Results show that the force–displacement curve determined with the developed two-scale model is close to the test result and coincident well with that of the two models using 3D fiber beam elements and the solid elements. The developed two-scale model can describe the global behavior, the local failure patterns and the stress distribution of the tested specimen accurately with improved simulation efficiency. Finally, the validated two-scale modelling approach is employed to analyze the static behavior, modal parameter, and fatigue of the optimized full-scale PCSH wind turbine tower previously developed by the authors. The simulation results show that the two-scale model can reflect the stress of the PCSH wind turbine tower at the critical position as well as the global mechanical behavior with higher computational efficiency. The fiber beam model can be used for predicting only global, but not local, behavior.

Mechanical properties of engineered cementitious composite using polyvinyl alcohol fibers

Engineered Cementitious Composite (ECC) is an advanced construction material that combines cement, fine aggregates, and specially designed fibers to create a highly ductile and durable building material. ECC is renowned for its exceptional tensile strain capacity, allowing it to undergo significant deformation while retaining its structural integrity. This characteristic makes ECC particularly suitable for applications where flexibility and durability are paramount, such as in earthquake-resistant structures and infrastructure repairs. This study investigates the tensile and flexural properties of ECC using Polyvinyl Alcohol Fibers (PVA) and compares these properties with those of regular mortar. Various sizes of PVA are available, and for this study, we utilized 12mm PVA fibers. The trial concrete mix design used was M30, with a watercement ratio of 0.3. The mixing process for traditional concrete and ECC is similar. Initially, the dry combination of ingredients is mixed for one to two minutes, followed by the addition of High Range Water Reducer (HRWR), and the mixture is further stirred for an additional three minutes. Finally, fibers are incorporated to achieve a stable condition for mixing. The samples used for testing consisted of 15 beams and 15 cylinders. The beam dimensions were (500 X 100 X 100) mm, while the cylinder dimensions were 100 mm in diameter and 200 mm in height. These samples were tested after 28 days of curing. The experimental findings indicate that PVA-enhanced concrete exhibits greater tensile and flexural strength when compared to conventional concrete, with results varying based on the percentage of PVA used. The split tensile strength of 1.5% PVA ECC cylinders was enhanced by approximately 46.8%. In terms of flexural strength, there was a decrease observed in 0.5% and 1% PVA fiber beams compared to ordinary concrete beams. However, the 1.5% PVA fiber beam exhibited a 43.45% improvement over the 0% fiber beam and showed a 9.4% increase compared to the 2% PVA beam. Additionally, the 1% PVA sample in the soundproof test reduced sound by up to 21.2%.

Flexural behavior of printed concrete wide beams with dispersed fibers reinforced

Thanks to the highlighted advantages of the construction method, including digitalization and automation, sustainable materials, and environmental protection, 3D concrete printing technology has been a hot topic for a few decades. This construction method was initially used in small and non-structural applications and is now being adopted for large-scale structures. This transition requires a lot of research on the structural behavior of structures. Therefore, the study focuses on the behavior of wide beams, which is the primary element in the structure system. Nine wide beams with different glass/steel fiber amounts were printed, and 3-point loading tests were conducted. The failure mode, flexural strength, deflection, and ductility were reported in this study. In this study, the girder web was designed in the style of truss beams, and glass/steel fibers were used. The fibers, including glass and steel fiber, will enhance the beams' flexural strength and ductility. The results showed that (1) The adhesion force between the printed layers ensures the overall working of the wide beams; (2) The failure patterns of glass fiber beams were brittle; glass fibers show insignificant improvement in compressive strength; the flexural capacity was significantly enhanced, and the optimal steel fiber amount is 1.0%. (3) The failure patterns of steel fiber beams were ductile; steel fibers showed light improvement in compressive strength. The steel fiber significantly impacted the flexural strength. The optimum amount of steel fibers was determined to be ranged from 1.0% to 1.5%.

Research Progress in Metamaterial Design and Fiber Beam Control Based on Deep Learning

Research Progress in Metamaterial Design and Fiber Beam Control Based on Deep Learning

Spatial mode and wavelength switchable erbium-doped fiber laser based on a fiber beam shaper.

A fiber-based beam shaper to adjust the distribution of spatial modes in a few-mode fiber (FMF) is theoretically and experimentally investigated in this work. A compact and robust device, composed with a single mode fiber-graded index multimode fiber-few mode fiber (SMF-GIMF-FMF), is fabricated by simply fusion splicing of the fibers. Switchable spatial modes and multi-wavelength comb are obtained by the combination of the beam shaper and the few-mode fiber Bragg grating (FM-FBG). This combination acts as a filter to select the wavelength and spatial mode in the laser. A spatial mode switchable fiber laser with high mode purity is extended among LP01, LP11 and cylindrical vector beam (CVB) by adjusting the pressure applied on the beam shaper. Five-discrete wavelengths and their free combination wavelength comb are emitted with a slope efficiency higher than 10%. The fiber laser can be used in the spatial- and wavelength-division multiplexing (SWDM) fiber communication networks requiring particular structure light field.

Distributed Optical Fiber Strain Sensors Packaged with Polyurethane and GFRP

To apply optical fiber sensors in an extreme environment and fulfill the rapid curing requirement of the thermosetting packaging process on glass fiber reinforced polymers (GFRP) prepreg, a novel fabricating method is proposed in this paper. It packages optical fiber by pouring and brushing the waterborne polyurethane into dry weave GFRP clothes that have bare optical fibers on one side. A special mold with a slot for laying and fixing package materials is designed. The sample with the size of 20 mm × 80 mm × 1 mm is made by adopting the developed mold. The GFRP side of the sample was pasted on the carbon fiber beam with a constant section, and a static loading test was conducted. The strain of the cantilever beam was collected by the packaged distributed optical fiber sensor and demodulated by the OFDR system. According to the Ko theory, the measured strain was converted into the displacement of the cantilever beam. The displacement of the free end of the cantilever beam was compared with the position measured by the machine vision, and the error between the two was small. The experimental results show that the ultra-thin distributed optical fiber strain sensor obtained by rapid packaging can be used for the deformation monitoring of large structures such as wind turbine blades.

FREE TRANSVERSE VIBRATIONS OF CANTILEVER BEAM FOR TAPERED THICKNESS PREPARED FROM VARIANT FIBERS REINFORCED POLYESTER

The natural frequency of the cantilever beam for the tapered thickness in the current paper is estimated using a Raleigh-Ritz approach. The study explores the effect of different parameters on the behavior of the beam such as the length of beam “L”, thickness at clamped end “hc”, width “b”, the ratio of thickness at free end to thickness at clamped end “hf/hc”, types of fibers and the concentration of fibers “f” in the resin of unsaturated polyester representing the matrix. The resin can be reinforced by aligned long fibers such as E-fibers glass, Kevlar-49 and carbon fibers. When a tapered beam is formed from a composite material, the natural frequency decreases when the length of the beam and the ratio of the thickness “hf/hc” increase; however, the frequency increases as the width of the beam increases. The thickness at the clamped end likewise increases as the volume fraction of fibers in the resin increases. The carbon fiber beam has a higher natural frequency than the other types of fibers. Finally, the results were compared to other available results and were determined to be consistent.

Experimental study on shear performance of basalt fiber concrete beams without web reinforcement

In this study, we report the results of an experimental investigation conducted under a four-point bending loading in order to evaluate the shear performance of concrete beams reinforced with basalt fiber without web reinforcement. According to the experimental results, it is evident that the final failure morphology of concrete-basalt fiber concrete composite beams and conventional concrete beams was shear failure, whereas the failure morphology of concrete beams reinforced with full basalt fiber was bending failure. Moreover, the results also indicate that the cracking load and ultimate bearing capacity of concrete composite beams reinforced with concrete-basalt fiber are lower than those of conventional concrete beam. This is mainly due to the interface between ordinary post-cast concrete and concrete reinforced with hardened basalt fiber. Due to the superior tensile properties of fiber, composite beams and all basalt fiber concrete beams exhibit a higher degree of ductility than conventional concrete beams. Utilizing the existing calculation theory for concrete beams reinforced with fiber, it was calculated that the cracking load and ultimate load of basalt fiber beams were calculated, and the calculation results were consistent with the experimental results. Based on the results of the evaluation and the theoretical analysis, this study proposes a finite element modeling method for basalt fiber composite beams. The results of the analysis were consistent with the experimental results of all investigated beams. The established model was employed in order to investigate the influence of shear span ratio on the shear performance of basalt fiber beams.