Span Length Research Articles

Fatigue condition assessment of subsea pipelines under vortex induced vibration and cyclical lateral displacement

ABSTRACT Subsea pipeline may suffer from vortex-induced vibration (VIV) and cyclical lateral displacement (CLD), which can result in fatigue failure of subsea pipeline. This paper presents a fatigue damage assessment of subsea pipelines under VIV and CLD. A finite element model of pipeline considering the pipe–soil coupling action is developed, and dynamic response of subsea pipeline under VIV and CLD is implemented to obtain time history of equivalent stress. The integrated fatigue damage of subsea pipeline under VIV and CLD is estimated using Palmgren–Miner linearly cumulative fatigue damage theory. The effect of pipe diameter, span length, pipe length and tidal period on fatigue damage of subsea pipelines under CLD is analyzed. A case study of a subsea pipeline in the strong tide area is performed. The results show the fatigue life of pipeline under VIV and CLD is 14.1 years, which is 2.3 years lower than the pipeline under VIV alone. The study can support more accurate estimation of fatigue life of subsea pipelines.

Management of bridge with non-rigid connectors in cases with pier abutments

The type of denture bridge with pier abutments where there are stand-alone abutment teeth between the abutment terminals, requires the dentist to pay special attention. One crown is attached to a natural tooth, and the other crown is attached to a dental implant or other type of abutment, known as the pier abutment that can become a class I fulcrum if restored using a 5-unit bridge with rigid connectors, which can cause excessive force to be received by the retainer at the abutment terminal, leading to debonding of the retainer or even damage to the periodontal tissues of the abutment teeth. In addition to these problems, long-span bridges have a poor prognosis due to the mobility difference between the anterior and posterior teeth, which may cause excessive stress on the connector. The use of a non-rigid connector can overcome this problem, as it can be a stress breaker by allowing micro-movements in the connector. The design of semi-rigid bridge with pier abutments must consider factors such as span length, anticipated occlusal load, and mastication factor. Proper consideration of these factors ensures the safety and longevity of the bridge.

Performance Against Direct Lightning on 10-kV Overhead Distribution Lines With Counterpoise Wires

This article investigates the lightning performance of a 10-kV overhead distribution line equipped with grounding counterpoise wires under extremely low soil conductivity conditions. A partial element equivalent circuit model with the lossy ground being considered is adopted for lightning surge investigation. The Monte Carlo method considering natural lightning randomness is used for the flashover rate evaluation. It is found that under extremely low soil conductivity conditions, the simple vertical grounding rod is not effective in lightning protection, while the performance is significantly improved with extended counterpoise wires. The single-row counterpoise wire with a length of line span performs best. The single-row counterpoise wire with a half-length of line span is a competitive one, due to a half-cost reduction and a competitive performance. If a higher performance of lightning protection is expected, further extending the length of counterpoise wires would be ineffective. Increasing the CFO level or installing surge arresters on all poles would be the possible solution.

Comparative Analysis of Steel Structure with Rigid and Semi Rigid Joint using Analysis Tool ETABS

Generally, in steel structure the connection between beam and column are designed as moment connection and pinned connection, but in actual condition the structure behaves between these two conditions, resulted into semi-rigid condition which is intermediate stage between rigid and pinned joints. Effect of semi-rigid connection on multi-story multi-bay frame is accomplished in this Study. The present study introduces the effect of static and dynamic loading on high rise steel structure of G+12 story with 4m, 6m and 8m three bay span length. Structure is analyzed under two different condition of partial release of semi-rigid connections which is derived by fixity factor of values 0.5 and 0.75 in this study. The analysis is done commercially available software ETABS. From the non-linear analysis, the story displacement and story drift are obtained. The overall performance of the structure from the analysis, semirigid joints display more story displacement and story drift compared to rigid joints. To overcome the results, bracing system is introduced at different location of periphery of structure. These brace frame structure consist of X- bracing and diagonal bracing. Again, comparative analysis is to be performed in ETABS on these three-bay span lengths. It is found that braced semi-rigid frame structure perform quite well as compared to unbraced frame structure.

Historical Review on Resonance and Cancellation of Simply Supported Beams Subjected to Moving Train Loads: From Theory to Practice

The advent of railways and especially highspeed railways marks great strides in human transportation history. To guarantee exclusive right-of-way, highspeed railways are often built on equal simply supported beams resting on piers. In this paper, a historical review will be given of the resonance and cancellation phenomena observed for simply supported beams traveled by a set of moving loads, as they are typical of highspeed railways. The phenomenon of resonance was observed by early investigators including Timoshenko, Bolotin, Frýba, Matsuura, etc. However, the phenomenon of cancellation was noted lately in 1997 by Yang et al. By letting the conditions of resonance and cancellation coincident, they proposed the optimal span length for suppressing the resonance of simple beams, which is equal to 1.5 times the car length. This 1.5 times rule has been verified and adopted in the design of some highspeed railways. In this article, the theoretical solution for the problem will be revisited for unveiling the key parameters such as the resonance speed (in temporal domain) and resonance wavelength (in spatial domain). Then a rather in-depth review will be given of existing works on the resonance and cancellation of railway bridges from the waves perspective. Some new developments along these lines will also be identified.

Numerical Studies on Flexural Behaviour of Graded Multi-Layer Puf Cored Sandwich Panels

The present numerical investigation was mainly concerned with the evaluation of flexural properties of graded multi-layered polyurethane foam cored (MLCC) sandwich panels using a novel approach through the medium of general purpose program i.e. FEM/ANSYS. Aiming to the goal, three-point bending analysis was performed on sandwich beam models assumed to be made up of composite face sheets (GFRP) and graded multi-layer polyurethane foam cores of different layer densities. Finite element models of sandwich beams were obtained successfully using nonlinear shell 91 elements for face sheets (orthotropic material) and 8-noded shell 98 elements for core (isotropic material).Various multi-layer core configurations in a stack of three layered core were studied with great care. Prior to actual task, the proposed evaluation technique was verified using bench marks. Series of multi-layered cored beam models of different core configurations and span length were analysed in order to study the influence of different graded (density) layer configuration on flexural properties. The present studies reveals that use of MLCC panels for sandwich construction can provide improved flexural properties and hence these panels could be the better choice for structures under non uniform bending and shear loads due to their higher shear stiffness values compared to soft PUF cored panels. Furthermore the MLCC-2 panels in which layers arranged in order of higher to lower density between compression face and tension face stand better among all the possible core configurations.

Are Children Performing Better on the Digit Span Backward Task Than the Digit Span Forward Task? An Exploratory Analysis.

This research note was motivated by community speech-language pathologists (SLPs) who have expressed concerns about how to interpret the unexpected observation of higher performance on the Digit Span Backward task than the Digit Span Forward task on the Test of Integrated Language and Literacy Skills (TILLS). We therefore conducted an exploratory analysis to examine the pattern of digit span performance in children to help clinicians interpret their findings. We investigated performance on the Digit Span Forward and Digit Span Backward subtests using the TILLS normative sample (N = 1,262). Raw scores, standard scores, and percentile ranks were systematically compared. In addition, we were able to estimate span length (longest number of items that can be accurately recalled) for 69 participants and evaluated the relation between performance and span length. Our exploratory analyses revealed that "better" performance on the backward than forward task was rare. Instead, the pattern that SLPs are reporting can be explained by three factors: (a) a statistical phenomenon exacerbating small differences, (b) comparing standard scores or percentile ranks instead of raw scores or span length, and (c) better backward scores can still mean longer forward span length. It is likely that community SLPs tended to report cases of better backward than forward recall because it is the more remarkable and interesting finding, leading to the perception that the pattern is common, when it is not. Overall, we caution clinicians against overinterpreting their own client's performance on the digit span tests.

Parameters Affect Flexural Mechanism to Prevent Progressive Collapse of RC Buildings

This study investigates the effect of spans length, reinforcement ratio and continuity of flexural reinforcement on the progressive collapse performance of double span beams over failed columns. The investigations focus on initial flexural resisting mechanism to prevent the progressive collapse. Detailed nonlinear finite element simulation of double span beam-column sub-assemblages subjected to residual gravity loads that initially carried by the failed column is adopted for the investigations. Nonlinear static pushover analysis is conducted in which capacity curves are derived and compared with demanded capacities. The effect of spans length, reinforcement ratio and number of continuous bottom flexural reinforcement on progressive collapse are considered in the investigations. Analysis results show that the strength to resist progressive collapse has decreased by 25.4 % and the ductility increased by 103 % following the increasing in span length from 5 m to 7 m. On the other hand, increasing reinforcement ratio of top flexural reinforcement from 0.447 to 1.089 leads to 26.27 % increasing in strength accompanied with a decrease in ductility equal to 16.42 %. In addition, extending all bottom bars rather than the minimum specified two bars resulted in 12 % increasing in strength and 40.28 % decreasing in ductility.

BENDING RESISTANCE OF HIGH STRENGTH HOT-ROLLED STEEL UNIVERSAL COLUMN SECTION

The most commonly found steel grades in the market are S 275 and S 355 However, recent advancement in the welding techniques allows for the development of high-strength steel for higher grades up to S 700 with reasonable cost and quality to construct heavy-loaded and long spanned structures. To facilitate the selection of the section sizes in accordance to Eurocode 3 Standard, this research focusses on investigate and validate the bending resistance, Mc,Rd and lateral torsional buckling resistance, Mb,Rd of a hot-rolled steel universal column section (UKC) from common steel grades (S 275 and S 355) up to high strength steels (S 460, S 550 and S 650). This study employed Microsoft Excel spreadsheet to develop a program for design calculation for UKC in accordance with Eurocode 3 Standard and compared with the available results provided in SCI P363. The validated program was further applied to develop selection data for high strength UKC steels (S 460, S 550 and S 650). The study outcome suggests that the classification, Mc,Rd and Mb,Rd of the steel is greatly affected by the steel grade. The parametric study in this research also shows that C1 factor, section size and span length can also affect the Mc,Rd and Mb,Rd of the steel, aside from steel grade. Further analysis of high strength UKC steels was done and tabulated since the program developed was validated and employed in the study

Preoperative thalamus volume is not associated with preoperative cognitive impairment (preCI) or postoperative cognitive dysfunction (POCD)

A growing body of literature suggests the important role of the thalamus in cognition and neurodegenerative diseases. This study aims to elucidate whether the preoperative thalamic volume is associated with preoperative cognitive impairment (preCI) and whether it is predictive for postoperative cognitive dysfunction at 3 months (POCD). We enrolled 301 patients aged 65 or older and without signs of dementia who were undergoing elective surgery. Magnetic resonance imaging was conducted prior to surgery. Freesurfer (version 5.3.) was used to automatically segment the thalamus volume. A neuropsychological test battery was administered before surgery and at a 3 month follow-up. It included the computerized tests Paired Associate Learning (PAL), Verbal Recognition Memory (VRM), Spatial Span Length (SSP), Simple Reaction Time (SRT), the pen-and-paper Trail-Making-Test (TMT) and the manual Grooved Pegboard Test (GPT). Using a reliable change index, preCI and POCD were defined as total Z-score > 1.96 (sum score over all tests) and/or Z-scores > 1.96 in ≥ 2 individual cognitive test parameters. For statistical analyses, multivariable logistic regression models were applied. Age, sex and intracranial volume were covariates in the models. Of 301 patients who received a presurgical neuropsychological testing and MRI, 34 (11.3%) had preCI. 89 patients (29.5%) were lost to follow-up. The remaining 212 patients received a follow-up cognitive test after 3 months, of whom 25 (8.3%) presented with POCD. Independently of age, sex and intracranial volume, neither preCI (OR per cm3 increment 0.81 [95% CI 0.60–1.07] p = 0.14) nor POCD (OR 1.02 per cm3 increment [95% CI 0.75–1.40] p = 0.87) were statistically significantly associated with patients’ preoperative thalamus volume. In this cohort we could not show an association of presurgical thalamus volume with preCI or POCD.Clinical Trial Number: NCT02265263 (https://clinicaltrials.gov/ct2/show/results/NCT02265263).

Dynamic Effect of Fluid–Structure Interaction and Modal Analysis of Crude–Pipeline Interaction System Considering the Fluctuating Pressure of Medium

This work explored the fluid–structure interaction (FSI) effect of crude oil and pipeline and the vibration characteristics of the pipe–crude oil structural system. A finite element computational analysis theory and corresponding simulation method were proposed for crude oil pipelines considering the FSI effect. Meanwhile, the spring model of the FSI interface between crude oil and pipeline was proposed. The experimental simulation and neural network were adopted to obtain the flow-excited pulsation pressure (FEPP), and the kinetic equations of the pipe–crude oil FSI were analyzed. The finite element computation (FEC) model for pipe–crude oil bi-directional FSI dynamics was established, which was composed of five support span lengths and four pipe liquid levels and can provide five different crude oil fluid velocities. One hundred orthogonal simulation test conditions were designed. In addition, the displacement response and acceleration response under FSI of the pipe wall were calculated, and the first six orders of inherent frequencies and main vibration patterns of the FEC model were analyzed. The results revealed that the dynamic effect of FSI between the crude oil transport medium and pipeline was complex and was influenced by the length of the pipeline crossing section, medium flow velocity, difference of liquid surface height, and displacement response. The acceleration response possessed prominent vibration decay characteristics, and the response peak in the same condition was about 8.2 times larger than that of the steady-flow state response. Therefore, the effect changed the inherent frequency and vibration pattern of the pipeline, to which the engineering design should pay sufficient attention.

Seismic Resilience and Design Factors of Inline Seismic Friction Dampers (ISFDs)

While damping devices can provide supplemental damping to mitigate building vibration due to wind or earthquake effects, integrating them into the design is more complex. For example, the Canadian code does not provide building designs with inline friction dampers. The objective of this present article was to study the overstrength, ductility, and response modification factors of concrete frame buildings with inline friction dampers in the Canadian context. For that purpose, a set of four-, eight-, and fourteen-story ductile concrete frames with inline seismic friction dampers, designed based on the 2015 National Building Code of Canada (NBCC), was considered. The analyses included pushover analysis in determining seismic characteristics and dynamic response history analysis using twenty-five ground motion records to assess the seismic performance of the buildings equipped with inline seismic friction dampers. The methodology considered diagonal braces, including different 6 m and 8 m span lengths. The discussion covers the prescribed design values for overstrength, ductility, and response modification factors, as well as the performance assessment of the buildings. The results revealed that increasing the height of the structure and reducing the span length increases the response modification factors.

Experimental and numerical investigation on test methods for mode II fracture of composite‐titanium adhesively bonded structures

AbstractThe investigation on fracture test methods for dissimilar materials adhesively bonded structures is urgent. In this study, three mode II fracture test methods for composite‐titanium adhesively bonded structures are experimentally and numerically studied. A manual inverse fitting method is adopted to obtain accurate cohesive models, and sensitivity evaluation of test methods is comprehensively conducted. The results show that GII of the experimental end‐notched flexure (ENF) test is nearly 20% greater than end‐loaded split (ELS). The effect of friction can be ignored, while all methods are highly dependent on the adherend's thickness, especially the maximum deviation of ELS that is 23.74%. In addition, the condition that the adherend with smaller flexural stiffness places outside the bending direction should be avoided to achieve mode II dominant possibly. In summary, the ENF test method with span length of 100 mm and small adherend's thickness is recommended for the mode II fracture test of the dissimilar materials adhesively bonded structures.

Human-Induced Vibration Analysis and Reduction Design for Super Long Span Pedestrian Arch Bridges with Tuned Mass Dampers

With the increasing demands on span length, aesthetics, and urban landscapes of pedestrian bridges, the fundamental frequency of pedestrian bridges is continuing to decrease, and their vibration and walking comfort issues are becoming increasingly prominent. The pedestrian load model of the pedestrian bridge was introduced here referencing current design specifications, and a spatial finite element model was established to study the dynamic characteristics of the case of a long-span pedestrian arch bridge. The comfort of the bridge under human-induced vibration was analyzed using the time history analysis method. According to the optimal damper parameter expression, the design parameters of the damper were obtained. In addition, the vibration reduction effects of different generalized mass ratios were analyzed, and the damping effects of setting the tuned mass damper (TMD) at different positions were compared. The results indicated that setting the TMD on the bridge can enhance the damping effect, and the transverse vibration can be suppressed by setting TMDs on both the arch ribs and the bridge deck. The research content could provide recommended parameters for the vibration reduction design of long-span pedestrian arch bridges.

Experimental and numerical investigations of S960 ultra-high strength steel welded I-section beams with in-plane flexural failure

A testing and numerical modelling programme was performed to investigate the in-plane flexural behaviour and cross-section bending capacities of S960 ultra-high strength steel welded I-section beams and presented in this paper. The testing programme included material testing, membrane residual stress measurements, initial local geometric imperfection measurements and eight in-plane four-point bending tests, with four performed about each of the cross-section minor and major principal axes. This was followed by the numerical modelling programme, where finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data over a wide variety of cross-section dimensions and span lengths. The obtained test and numerical data were used to evaluate the applicability of the design rules for cross-section classification and bending capacities, as prescribed in the European code, Australian standard and American specification, to S960 ultra-high strength steel welded I-section beams. The evaluation results revealed that all codified slenderness limits were safe (though conservative to different extents) when used for classifying the constituent plate elements of S960 ultra-high strength steel welded I-sections in bending. Moreover, all three considered design codes were shown to result in accurate and consistent bending capacity predictions for Class 1 and 2 (or compact) S960 ultra-high strength steel welded I-sections, but conservative bending capacity predictions, to different extents, for Class 3 (or non-compact) and Class 4 (or slender) S960 ultra-high strength steel welded I-sections.

Selection of an optimal cable brand for high-voltage overhead power lines based on criterion analysis

This paper is aimed at developing a versatile approach to selecting an optimal cable brand for overhead transmission lines for use in design practice, adapted to conventional and new-generation cable types. To implement multi-criterion evaluation of external factors and limitations when selecting a cable type, the methods of systems, hierarchy and comparative analysis were used. A method for selecting an optimal cable brand based on hierarchy analysis was developed along with an algorithm for its implementation when designing new or modernizing existing overheadlines. The developed approach is demonstrated on the example of construction and modernization of 220 kV overhead lines with the conventional AC cable and such new-generation domestic brands, as АСВТ, АСВП, АСк2у and АСТ. In the considered examples, the technical feasibility of the construction of a new overhead line was limited by the value of the sag. For the modernization project, the specific weight of the cable was of greater importance. The selection criteria included the span length, cable cost and admissible continuous current. The АСВП and АСТ cable brands showed the greatest compliance with the selection criteria (27.5% and 55.9%, respectively). Therefore, at minimum capital investments, the АСВП brand ensures the optimum span length in the construction of a new overhead line, whereas the ACT brand ensures the maximum capacity in the modernization of an existing line. The conducted verification calculations confirmed the feasibility and versatility of the proposed method for selecting a cable brand.

Simulation of the E-Defense 2015 test on a 10-storey building using macro-models

The capabilities of certain standard macro numerical models were evaluated by simulating a shaking table experiment that was performed on a full-scale ten-storey fixed-base building with a frame and dual structural system in two perpendicular directions (denoted as the frame and wall directions) at the largest shaking table in the E-Defense centre in Japan. The lumped plasticity model for columns and beams, the multiple-vertical-line-element model for walls and the scissors model for beam-column joints were evaluated. The results indicated that the experiment was simulated reasonably well. The most significant discrepancy was observed between the maximum drifts along the wall direction in the strongest cycle of the strongest test (calculated drift of 1.9% versus measured drift of 1.5%). In other cycles and tests, these differences were smaller. The calculated and measured maximum accelerations along the wall direction in the strongest test were 13.8 m/s2 and 13.5 m/s2, respectively. The discrepancy between the analysis and experiment results was smaller along the frame direction. The maximum calculated and measured drifts were 2.9% and 3.1%, respectively. The maximum calculated and measured accelerations were 15.8 m/s2 and 19.0 m/s2, respectively. In general, the standard input parameters were used in the evaluated models. However, some parameters required modifications, particularly when modelling weakly reinforced beam-column joints with substandard reinforcement that were considerably damaged. Their yielding rotation and near-collapse strength were, on average, reduced to 55% and 30% of the standard value, respectively. One of the most important parameters influencing the response was the effective width of the slabs, which was increased to the total span length for the highly loaded beams. The ratios of the strength, stiffness and amount of dissipated energy in the joints, beams and columns also significantly influenced the response. The adequate ratio of the dissipated energy was obtained by reducing the standard unloading stiffness in the beams and columns. The initial stiffness considerably influenced the response, particularly under weaker excitations. This stiffness was reduced threefold to account for various factors that typically reduce its value, which, among others, includes the influence of preceding tests on the same building with sliding foundations, as well as the assembly, transportation and handling of the specimen.

Effects of Slab Types on the Seismic Behavior and Construction Cost of RC Buildings

Reinforced concrete-framed buildings are commonly preferred to other types of buildings in Turkey. In these types of buildings, a two-way slab with beams, flat, waffle, and ribbed slab types are widely used. In building design, determining the best slab type that will perform well under gravity and lateral loads, with the least cost, is required. However, the proper selection of slab type has generally been overlooked by designers due to the emphasis on other structural members, such as beams, columns and structural walls. For this reason, the structural contribution of floors to building design has not been adequately examined. This shortcoming must be inspected in detail starting from the very first step of the design stage of a building. This study assesses the effects of different slab types on multi-story reinforced concrete buildings by investigating their structural behaviors while trying to optimize their overall cost. For this purpose, a total of 36 structural models were constructed, analyzed, and designed according to the current Turkish Building Codes and Standards. The type of slab system (a two-way slab with beams, flat, waffle and ribbed), the number of floors (10, 20 and 30), and span length (6, 7.5, and 9 m) were selected as the key parameters in these analyses. The buildings were assumed to be office buildings located in a seismically-active zone in Istanbul. The results indicated that a two-way slab with beams was the most economical slab type for 6-meter spans, while the waffle slab was the most economical for spans larger than 7.5 meters. Based on these results, the flat slab was found to be the most expensive slab type in all cases. Out of all slab types, the two-way slab with beams exhibited better earthquake performance, while the waffle and flat slabs provided relatively poor earthquake performances.

Experimental investigation of sandwich panels using foam filled corrugated cores

Sandwich panels are commonly based on honeycomb core, which provides lightweight, high strength applications such as aero plane fuselage. These panels having metallic corrugated cores have distinctly different attributes from those having corrugated foam core. Corrugated core provides high specific stiffness and strength, whereas metallic core provides superior energy absorption. Foam corrugated core was fabricated according to ASTM standards C393M-11 with the length of 265 mm and span of 170 mm and analytical tests were made for flexural Strength and Compressive Strength for three different core types, and the results were compared with each other. In the end, compared results showed better potential in foam-filled panels than other core types.

Structural Optimization of a Longitudinally Moving Layered Web Based on a Multi-Criteria Approach

The longitudinal motion at a constant speed of a thin continuous elastic web through a system of roller bearings under the action of a given constant tension is considered. One span between adjacent supports is considered. The web is modeled by a thin layered plate hinged on two opposite edges, the remaining two sides of the plate are free. It is assumed that the plate in the process of longitudinal movement can perform small transverse vibrations. The layers of the plate from a given set of materials are arranged symmetrically to the middle surface and fit tightly to each other. The total thickness of all layers is given and is small compared to the span length and plate width. Analytical expressions are derived for the effective characteristics of the plate, as a result of which the initial composite structure can be considered as an isotropic homogeneous plate, for which the known equations for calculating the critical velocity are applied. Within the framework of multi-criteria Pareto optimization, using a numerical method of non-local optimization, the order of the layers and their thickness are determined in order to satisfy a number of selected criteria: the maximum critical divergence rate, the maximum flexural stiffness, and the minimum unit weight of the layered web. An example of the found optimal structure of the plate and the constructed Pareto front for a given set of defining parameters of the problem are given.