Increase Of Span Length Research Articles

Surrogate modeling for aerodynamic static instability of central-slotted box decks using machine learning approaches

Studies on aerodynamic controls of central-slotted box decks primarily focused on mitigating vortex-induced vibrations (VIV), as this type of deck typically performs well against flutter instability. However, as the span length increases, the critical wind speed of aerodynamic static instability ( U cr) might be lower than flutter critical wind speed. Thus, U cr will determine the overall aerodynamic performance of such bridges. Investigating this instability through wind tunnel testing methods and numerical simulation can be expensive and time-consuming. In this paper, surrogate models using machine learning approaches, specifically artificial neural network (ANN) and extreme gradient boosting (XGBoost), were developed and optimized for fast and reliable prediction for U cr based on wind tunnel tests and simulation data. The results demonstrated that the built surrogate models can predict U cr accurately. The parametric study results showed that the height ratio of wind fairing apex ( a/b), wind angle of attack ( α), and length of the main span ( L) have the most influence on the U cr compared with other parameters. Finally, based on the developed ANN surrogate model and the artificial bee colony (ABC) optimization algorithm, an optimized section was proposed to enhance the section’s performance against aerodynamic static instability.

Temperature analysis and prediction for road-rail steel truss cable-stayed bridges based on the structural health monitoring

A growing number of road-rail steel truss bridges have been built worldwide in recent years. Due to the complex cross-sectional structure and increasing span length, these main girders are prone to developing uneven temperature fields and significant local thermal effects, which can lead to excessive temperature stresses and structural damage. An accurate assessment of the temperature distribution in road-rail steel truss girders is critical as it aids in the thermal response analysis of the bridge and the structural safety evaluation. The paper analyses the temperature distribution of the road-rail steel truss girder base on the light conditions and the structure of the main girder. A modified method for calculating the effective temperature (ET) and temperature difference (TD) is also proposed. Comparing with the conventional regional weighted averaging method, the modified method improves the accuracy of ET calculation by 20 %. A prediction method based on the long short-term memory (LSTM) network is proposed, which estimates ET and TD for road-rail steel truss girders based on the environment around the bridge. The deep learning-based method improves accuracy by 40 % compared with the conventional linear regression method for ET prediction. Meanwhile, the proposed method alleviates the current lack of prediction methods for TD of road-rail steel truss girders. A detailed analysis of the temperature of a road-rail steel truss bridge is also presented based on the structural health monitoring (SHM) system. A negative vertical temperature difference was observed in the fringe truss. The maximum transverse temperature difference (TTD) was much greater than the maximum vertical temperature difference (VTD). The above features deserve extra attention from bridge designers.

Effect of Frequency-Amplitude Parameter and Aspect Ratio on Propulsion Performance of Underwater Flapping-Foil.

The propulsion system is the core component of unmanned underwater vehicles. The flapping propulsion method of marine animals' flippers, which allows for flexibility, low noise, and high energy utilization at low speeds, can provide a new perspective for the development of new propulsion technology. In this study, a new experimental flapping propulsion apparatus that can be installed in both directions has been constructed. The guide rail slider mechanism can achieve the retention of force in the direction of movement, thereby decoupling thrust, lift, and torque. Subsequently, the motion parameters of frequency-amplitude related to the thrust and lift of a bionic flapping-foil are scrutinized. A response surface connecting propulsion efficiency and these motion parameters is formulated. The highest efficiency of the flapping-foil propulsion is achieved at a frequency of 2 Hz and an amplitude of 40°. Furthermore, the impact of the installation mode and the aspect ratio of the flapping-foil is examined. The reverse installation of the swing yields a higher thrust than the forward swing. As the chord length remains constant and the span length increases, the propulsive efficiency gradually improves. When the chord length is extended to a certain degree, the propulsion efficiency exhibits a parabolic pattern, increasing initially and then diminishing. This investigation offers a novel perspective for the bionic design within the domain of underwater propulsion. This research provides valuable theoretical guidance for bionic design in the underwater propulsion field.

The effect of span length on the flexural properties of glass and basalt fiber reinforced sandwich structures with balsa wood core for sustainable shipbuilding

The current research aims to analyze the mechanical characterization of sandwich materials through a three-point flexural test. The sandwich structures in question composed of balsa wood as a core and four different types of fiber reinforced vinyl ester composite facesheets, namely Glass, Basalt, Glass/Carbon, and Basalt/Carbon. The sandwich panels were prepared using the vacuum infused processing method. The primary objective of this investigation is to explore the feasibility of utilizing basalt fibers for the production of structural parts in shipbuilding and replacing the already existed glass fibers. The flexural test was carried out with using three-point flexural test with varying the span length from 120 mm, 180 mm, 220 mm. Additionally, an analysis of variance (ANOVA) was then carried out to compare the mean values of properties deduced from these tests. The results showed that using basalt fibers instead of glass fiber reinforced enhanced the flexural stiffness of the sandwich structure. The flexural strength and modulus are shown to depend on span length and fiber type. The flexural modulus increases with an increase in span length. Similarly, flexural strength increases in glass fiber-based structures, while a slight reduction is observed in basalt fiber-reinforced structures the larger span length. The findings of this research suggest that basalt fibers hold potential as a replacement for glass fibers in producing structural components in shipbuilding. These results offer valuable information that can aid in the design and optimization of sandwich materials in shipbuilding.

Collapse resistance analysis of steel frame structures with varying spans using component models

This study aims to expand the current research on the progressive collapse resistance of steel frame structures with welded-flange bolted-web connections (WBCs) by investigating both symmetric and asymmetric structures with varying spans. It focuses on developing and validating a component model for WBCs using relevant experimental data. The collapse resistance of full-scale substructures and steel frame structures with varying spans is comprehensively analyzed and evaluated. The main findings are as follows: A simplified two-bar spring model is proposed for WBCs, representing their resistance, internal force, and large deformation responses. Symmetric substructures exhibit higher bearing capacity and deformation due to the effective collaboration between the two-span beams, whereas the substructure’s resistance progressively decreases as the span length increases. Asymmetric substructures exhibit initial local damage in the beam with higher linear stiffness, resulting in asymmetric trends for internal forces of the two-span beams. The beam with higher linear stiffness plays a dominant role in controlling the anti-collapse performance of asymmetric substructures. A proposed formula for accurately and reliably calculating the ultimate rotation of WBCs was put forward. The critical loads of steel frame structures decrease as the linear stiffness ratios of the two-span beams decrease. Accurate fitted formulas are provided for estimating the critical load of steel frame structures with varying spans, offering insights into their capacity to resist progressive collapse when the middle column is removed. Under critical load conditions, steel frame structures primarily resist external loads through bending and vierendeel mechanisms, with minimal contribution from the catenary mechanism.

Modelling of vortex-induced force and prediction of vortex-induced vibration of a bridge deck using method of multiple scales

With the increase of span length, long-span bridges become more flexible and susceptible to vortex-induced vibrations (VIV). Several models for vortex-induced force (VIF) and various methods for predicting VIV have been developed accordingly but without consensus. This paper uses the method of multiple scales, from a different angle of view, to analyze the general polynomial model for VIF and present a concise polynomial model for VIF and a simple method for predicting VIV of a bridge deck. The aeroelastic vibration of a deck section is simulated by the computational fluid dynamics (CFD) and the results are used to verify the concise polynomial model of VIF. The forced vibration of a deck section is also simulated by CFD to yield the simple method for predicting VIV together with the frequency response equation and the critical equation of VIV derived by the method of multiple scales. The results show that the even and cross terms of aerodynamic damping and stiffness in the general polynomial VIF model are small compared with the odd terms and can be thus omitted. The lock-in region and the amplitude of VIV of the deck section can be accurately predicted by the proposed simple method.

Modal analysis of rigid pavement resting on two-parameter soil foundation model using finite element framework

PurposeThe purpose of this study is to numerically model the rigid pavement resting on two-parameter soil and to examine its modal parameters.Design/methodology/approachThis study is carried out using a one-dimensional beam element with three rotational and three translational degrees of freedom based on the finite element method. MATLAB programming is used to perform the free vibration analysis of the rigid pavement.FindingsCyclic frequency and their corresponding mode shapes were determined. It has been investigated how cyclic frequency changes as a result of variations in the thickness, span length of pavement, shear modulus, modulus of subgrade, different boundary conditions and element discretization. Thickness of the pavement and span length has greater effect on the cyclic frequency. Maximum increase of 29.7% is found on increasing the thickness, whereas the cyclic frequency decreases by 63.49% on increasing span length of pavement.Research limitations/implicationsThe pavement's free vibration is the sole subject of the current investigation. This study limits for the preliminary design phase of rigid pavements, where a complete three-dimensional finite element analysis is unnecessary. The current approach can be extended to future research using a different method, such as finite element grilling technique, mesh-free technique on reinforced concrete pavements or jointed concrete pavements.Originality/valueThe finite element approach adopted in this paper involves six degrees of freedom for each node. Furthermore, to the best of the authors’ knowledge, no prior study has done seven separate parametric investigations on the modal analysis of rigid pavement resting on two-parameter soil.

Proof Load Testing Method by the American Association of State Highway and Transportation Officials and Suggestions for Improvement

Because of the aging of infrastructure, methods are explored by which the reliability of existing bridges and viaducts can be assessed. In cases in which limited information of the structure is available or its condition is of concern, proof load testing may be used to demonstrate sufficient live load carrying capacity. Proof load tests in the U.S.A. are typically performed using the Manual for Bridge Evaluation (MBE) published by the American Association of State Highway and Transportation Officials (AASHTO). The proof load is expressed by the regular live load model magnified by the target proof load factor. The level of reliability obtained using the target proof load factor is not explicitly stated in the MBE, but is of particular interest. In this article, relevant background documents are investigated to uncover the underlying calculations, assumptions, and input data. Current challenges in proof load testing are described in which the considerations of time dependence, stop criteria, available information, and system-level assessment are highlighted. Subsequently, improvements to the MBE proof load testing background are suggested. An example calculation using traffic data from the Netherlands shows that the HL93 load model and Eurocode LM1 provide a reasonably constant proof load factor with span length for bending and shear. However, the HS20 load model does not scale well with increasing span length. It is found that the magnitude of the target load as specified through the proof load factor is directly related to the desired level of reliability. Although the MBE proof load testing method is practical, several challenges remain.

The Performance of Magnetostrictive Material for Wind-Induced Vibration Power Generator

This research investigated the effect of span length variation and capless prismatic structure on the performance of the micropower generator from flow-induced vibration. The vibration response type covers galloping and vortex-induced vibration regimes. The mini harvester energy induced by the harmonic oscillation of prismatic structure was implemented based on the magnetostrictive principle to gain electricity using a galfenol alloy (Fe-Ga). The power generation variations are influenced by the amplitude, frequency, structure displacement, span length, and shape of the bluff body. The optimum power generation is 2.87 mW, and the maximum power generation is 10.63 mW at the resonance velocity Vr of 6.45. Reducing the frequency characteristics of circular cylinders by applying a cap end tip affect power generation characteristics and galloping behaviour for the prism with a span length of 200 mm but not for other span lengths. The effect of span length variation on free vibration and power generation performance for all prism models is similar in that both features are decreased by increasing span length. However, it enhances onset valued power generation. Power generation is considered for the independent electricity supply for specific sensor or wireless devices of an IoT system.

A Review on the Combined Effects of Seismic and Vehicular Vibrations on Long Span Bridges

Long span bridges are massive structures which are subjected to combined loadings. The increase in span length of long span bridges will result in decrease of their natural frequencies that renders them very susceptible to the actions of various combined dynamic forces. Dynamic loads such as vehicular movement and seismic excitations have greater potential in causing increased vibrations in long span bridges. The vehicular loading is highly variable and depends on type of vehicle, number of lane, behaviour of vehicle such as lane changing, traffic congestions and so on. Further, seismic excitations are characterized by its spatial variability parameters such as incoherence effect, wave passage effect and site response effects. From detailed review, it was found that fewer researches have been carried out in the field of dynamic effects of long span arch bridges and thus the study aims in determining the combined effects of seismic and vehicular vibrations on long span arch bridges.

Theoretical Analysis of Ultimate Main Span Length for Arch Bridge

The advancement of construction techniques and high-performance sustainable materials enables the increase of span length for arch bridge. It is of great importance to study the theoretical ultimate span length of arch bridge. Based on the parabolic and catenary arch axes, the analytical solutions of ultimate span length of arch bridge are solved using theoretical derivation accounting for the strength, in-plane stability and out-plane stability conditions, respectively. Then, the use of high-performance concrete, reactive powder concrete and high-strength steel is considered to study the relationship between theoretical ultimate span length and rise-span ratio as well as material strength for concrete and steel arch bridges. The results show that the theoretical ultimate span length derived by catenary arch axis is smaller by about 2–6% than that obtained by parabolic arch axis, but the difference is insignificant. When the rise-span ratio is 1/5, the theoretical ultimate span length for concrete arch bridge using R200 reactive powder concrete can reach 2000 m (2161 m for catenary arch axis and 2099 m for parabolic arch axis) while the main span of steel arch bridge using Q690 high-strength steel can be longer than 2500 m (2948 m for catenary arch axis and 2865 m for parabolic arch axis).

Sentence repetition span in primary progressive aphasia and Alzheimer's disease: Insights from preliminary results

Primary Progressive Aphasia (PPA) is a neurocognitive disorder ascribed to cortical atrophy impacting language abilities. It is widely classified into three main variants, logopenic PPA (lvPPA), the semantic variant of PPA (svPPA), and the non-fluent PPA (nfvPPA), showing different impairment patterns across variants. However, in the early phases of PPA, it is not always easy to dissociate different PPA variants and distinguish PPA from other neurodegenerative disorders. One characteristic language symptom that seems to be a distinguishing factor of PPA, especially the logopenic variant, is impaired sentence repetition. Nonetheless, studies examining sentence repetition in PPA, and Alzheimer's disease (AD) more broadly, have resulted in mixed findings. To better understand the working memory-intensive nature of sentence repetition deficits, we designed a sentence repetition span task. We seek to understand (i) whether three diagnostic groups (lvPPA, svPPA, and AD) encounter greater sentence repetition difficulties than the controls, and (ii) whether using a span task design, in which the number of content words increases as the span length increases, would help dissociate PPA variants from AD type dementia. In this study, we administered a sentence repetition span task to four groups of French-speaking individuals with lvPPA (n = 14), svPPA (n = 5), and with AD (n = 13), and their age-matched healthy controls (n = 61). The results showed that all three diagnostic groups (lvPPA, svPPA, and AD) performed equally poorly compared to the controls on the repetition span task virtually in all measures (i.e., sentence span, the number of content words, and the number of omission and substitution errors). One intriguing finding was that the lvPPA group produced an exalted number of phonological errors during repeating sentences, while this type of error was somewhat moderate in the svPPA group and only minimal in the AD group. We conclude that the sentence repetition difficulty in PPA and AD should be modulated by working memory capacity, as our participants undoubtedly demonstrated greater difficulty as the span length increased. However, we note that working memory-intensive sentence repetition deficits based on the number of content words might not reveal critical diagnostic differences between the neurodegenerative groups.

Modal analysis of an RCC long span arch bridge using midas Civil - A validation

Long span bridges are predominantly prone to vibrations when loaded. Structural vibrations are initiated by dynamic periodic forces like wind, people, traffic and even by pedestrian loading. The increase in span length of long span bridges decreases the natural frequencies of the structure thereby subjecting it to the adverse effect of various combined dynamic forces. It is critical to determine the natural frequencies and periods of such structures in order to avoid the formation of resonance, which is hazardous to the structure's safety. This paper exemplify the natural period and mode shapes of a real time long span arch bridge by performing Eigen value analysis of the structure using midas Civil. The software's results are compared to similar work done using ABAQUS. The results obtained with midas Civil are in good agreement with those obtained with ABAQUS, indicating the suitability of employing midas Civil and the acceptance of the generated model for further analysis.

Evaluation of the effect of shear wall with and without opening on the ductility of RC structure

The ductility of a structure is an important factor that should be taken under consideration in the design against lateral loads like an earthquake. This paper presents the effect of the shear wall on the ductility of the structure and the effects of the presence of opining in it on the ductility. Eighteen 2D moment-resisting frames (MRFs), with the shear wall (SW) and SW with opening structural models, were created and designed. The pushover analyses using ETABS 19 software were performed on the designed models to calculate the ductility of the structural models. The obtained results show that the shear wall in the models increases the ductility of the structures significantly, while the presence of an opening decreases it slightly. Besides, the increase in the number of storeys increases the ductility of MRF models but decreases the ones with SW. Oppositely; the increase in span length reduced the ductility of MRF models and increases the docility of the models with SW

Effect of posterior span length on the trueness and precision of 3 intraoral digital scanners: A comparative 3-dimensional in vitro study.

PurposeThis in vitro study measured and compared 3 intraoral scanners' accuracy (trueness and precision) with different span lengths.Materials and MethodsThree master casts were prepared to simulate 3 different span lengths (fixed partial dentures with 3, 4, and 5 units). Each master cast was scanned once with an E3 lab scanner and 10 times with each of the 3 intraoral scanners (Trios 3, Planmeca Emerald, and Primescan AC). Data were stored as Standard Tessellation Language (STL) files. The differences between measurements were compared 3-dimensionally using metrology software. Data were analyzed using 1-way analysis of variance with post hoc analysis by the Tukey honest significant difference test for trueness and precision. Statistical significance was set at P<0.05.ResultsA statistically significant difference was found between the 3 intraoral scanners in trueness and precision (P<0.05). Primescan AC showed the lowest trueness and precision values (36.8 µm and 42.0 µm; (39.4 µm and 51.2 µm; and 54.9 µm and 52.7 µm) followed by Trios 3 (38.9 µm and 53.5 µm; 49.9 µm and 59.1 µm; and 58.1 µm and 64.5 µm) and Planmeca Emerald (60.4 µm and 63.6 µm; 61.3 µm and 69.0 µm; and 70.8 µm and 74.3 µm) for the 3-unit, 4-unit, and 5-unit fixed partial dentures, respectively.ConclusionPrimescan AC had the best trueness and precision, followed by Trios 3 and Planmeca Emerald. Increasing span length reduced the trueness and precession of the 3 scanners; however, their values were within the accepted successful ranges.

Lateral-torsional buckling behaviour of concrete-filled high-strength steel tubular flange beams under mid-span load

Lateral-torsional buckling (LTB) behaviour of concrete-filled high-strength steel tubular flange beams (HS-CFTFBs) is experimentally and numerically investigated. Six specimens are tested in simple support with a lateral unrestrained concentrated load in mid-span. Among them, two are failure controlled through flexural yielding (FY), whereas the remaining specimens are controlled through LTB. Finite-element (FE) models are then constructed and the comparison with the experimental results indicates that they could reliably and accurately evaluate failure modes, load–displacement relationship and ultimate capacities of HS-CFTFBs. These verified FE models are consequently used to investigate the effect of flange depth, concrete and steel with various span lengths. Results suggest that the ultimate moment capacity evidently decreases as the span length increased, particularly for the high-strength steel beams. The increasing flange depth remarkably improved the LTB strength but merely slightly increased the amount of steel. The infilled concrete could improve the resistance to flange distortion and thus increase the ultimate capacity. However, the strength of concrete exhibits a slight influence on ultimate capacity. Increasing fy could improve the LTB capacity when the span length is relatively small, but the improvements decrease with increasing span length. When the failure mode is elastic LTB, increased fy could substantially improve post-buckling stiffness and ductility

Response analysis of pipeline crossing structure with earthquake

Pipeline spanning structure has the characteristics of small overall stiffness, poor resistance to deformation, and large slender-length ratio with poor stability. It is a vulnerable part of long distance pipeline engineering under earthquake action, so it is necessary to analyze the response of pipeline spanning structure under earthquake action. In this paper, the structure model of pipeline span is established through ANSYS, and numerical simulation analysis is carried out under seismic action to explore the influence law of pipeline span structure under seismic action of different pipeline span length and different pipeline span form. The results show that the middle span is the most unfavorable position for pipeline crossing. In the same span, with the increase of span length, the natural frequency of pipeline decreases and the period increases. When the span length of pipeline is fixed, the natural frequency of straight pipeline is obviously higher than that of other pipelines, and the seismic performance is the best. It provides a theoretical basis for seismic design of pipeline crossing structure.

Fatigue strength enhancement by structural modification of transverse to longitudinal rib connections in orthotropic steel decks with open ribs

This paper describes an investigation of fatigue strength enhancement for transverse to longitudinal rib connections in orthotropic steel decks with open ribs by structural modification. A structural hot-spot stress approach was used to evaluate the fatigue strength. The results of a finite-element analysis revealed that the fatigue strength decreased with increasing span length of the longitudinal ribs. The structural modifications to the connection, which reduced the stiffness of transverse ribs due to section loss, absorbed the local deformation of the deck plate and consequently reduced the structural hot-spot stress.

Influence of sample thickness, curvature and notches on the Charpy impact strength - An approach to standardise the impact strength of curved test specimens and biological structures

The specimen geometry has a significant influence on the Charpy impact strength. This is often a problem when it comes to the analysis of materials that can only be prepared with a curved shape, or which, like some biological structures, are naturally given in curved form like nutshells. The question repeatedly arises to what extent the curvature influences the impact strength. Hence, the present study deals with the dependence of the specimen geometry like specimen thickness, curvature and notches on the impact properties of concrete, gypsum, polyurethane (PUR) and epoxy-based (EP) samples. Increasing sample thickness from 2 to 10 mm resulted in increased toughness for brittle materials, whereas more ductile materials did not show any significant change in toughness. Increasing span length showed an increase of the unnotched impact strength for brittle gypsum, while toughness increased for a more ductile PUR sample. For the curved specimens both, the unnotched and the notched Charpy impact strength could be shown to increase with a reduction of the specimen radius (higher curvature) while the notch-sensitivity was not significantly affected. Material-specific linear relationships between the impact strength and the curvature of the samples were found. These relationships were used to create a model to calculate the influence of the curvature on the impact strength. For all materials, the characteristic values of a normalised flat standard sample could be well predicted from measured values of curved specimens. This calculation approach was used to predict the impact strength of an isotropic biological sample (sweet potato) concerning a flat sample and different curved specimens. The results show a good trend with the measured values.

Efficacy Analysis of Thickness and Camber Size of Cross Section of the Stator on Hydrodynamic Parameters in Linear Jet Propulsion System

The linear jet propulsion system, unlike pump-jets which are widely used in underwater bodies, is installed inside a tunnel under the vessel and can be used for high-speed crafts, tugs, and service boats. However, this system has not received adequate attention by researchers, which is the subject of the current study. In the present paper, hydrodynamic performance of the linear jet propulsion system is numerically investigated. Accordingly, the Ansys-CFX software is utilized and RANS equations are solved using the SST turbulent model. The results of the proposed numerical model, in the form of thrust and torque coefficient as well as efficiency, are compared with available experimental data for a ducted propeller, and good compliance is achieved. Considering the importance of stator cross section on the performance of the linear jet propulsion system, the influence of thickness and camber size of the stator on linear jet propulsion systems are examined. Based on the numerical findings, it is determined that at constant advance ratio, with increasing thickness of stator, the efficiency increases. It is also observed that as the span length increases, the maximum and minimum of the pressure coefficient increase for different thicknesses. Furthermore, it is seen that positive and negative pressure coefficients decrease with an increase in foil thickness.