The influence of lift frequency,lift duration and work experience on discomfort reporting

Discomfort surveys are commonly used to assess risk in the workplace and prioritize jobs for interventions before an injury or illness occurs. However, discomfort is a subjective measure and the relationship of discomfort to work-related factors is poorly understood. The objective of this study was to understand how reports of discomfort relate to work-related risk factors for the low back. A total of 12 novice and 12 experienced manual materials handlers performed repetitive, asymmetric lifts at different load levels and at six different lift frequencies throughout an 8-h exposure period. Discomfort was recorded hourly throughout the day. Analyses were performed to determine which experimental factors influenced reporting of discomfort and if discomfort trends matched spine loading trends. Novice lifters reported significantly higher discomfort levels than experienced subjects. They also reported increases in discomfort as moment exposure increased and as the exposure time increased. Novices lifting at 8 Nm load moment level reported increased discomfort from 0.07 to 0.63 by the end of the day, at 36 Nm they reported an increase from 0.04 to 0.40 and at 85 Nm they reported an increase from 0.37 to 3.06. Experienced subjects, on the other hand, reported low levels of discomfort regardless of moment exposure, lift frequency or exposure duration. The reported discomforts were generally unrelated to the biomechanical loading on the spine. Discomfort reporting appears to be more a reflection of experience than of work risk factor exposure. Experienced subjects may have more efficient motor patterns, which reduce spinal load and thus discomfort. Novice subjects seemed to have a lower threshold of discomfort. Caution is needed when using discomfort reporting as a means to identify jobs in need of interventions, in that biomechanical loading may not be accurately represented. Discomfort should only be used as a supplement to objective measures, such as spinal loading, to assess the risk of low back disorders.     

Wind buckling of tanks with conical roof considering shielding by another tank

Oil storage tanks are usually arranged in groups in tank farms, and this configuration may affect their buckling and postbuckling strength under wind loads. The assessment of wind action on tank structures is performed in this work by means of wind tunnel experiments to evaluate the pattern of pressure distribution for a tank which is shielded by another tank under various configurations and separation between them. The experimental results show significant changes in pressures due to shielding effects. In a second stage the structural response under the pressures previously evaluated is performed by finite element analysis using both linear bifurcation and geometrically nonlinear analysis. Results of two-tank interaction are compared with those of an isolated tank. Based on the results, it is concluded that the changes in wind pressures due to group effects induce changes in buckling loads and in the associated deflected patterns.     

Automated extraction and classification of thunderstorm and non-thunderstorm wind data for extreme-value analysis

Design wind loads are partly based on extreme value analyses of historical wind data, and limitations on the quantity and spatial resolution of wind data pose a significant challenge in such analyses. A promising source of recent wind speed and direction data is the automated surface observing system (ASOS), a network of about 1000 standardized US weather stations. To facilitate the use of ASOS data for structural engineering purposes, procedures and software are presented for (a) extraction of peak gust wind data and thunderstorm observations from archived ASOS reports, (b) classification of wind data as thunderstorm or non-thunderstorm to enable separate analyses, and (c) construction of data sets separated by specified minimum time intervals to ensure statistical independence. The procedures are illustrated using approximately 20-year datasets from three ASOS stations near New York City. It is shown that for these stations thunderstorm wind speeds dominate the extreme wind climate at long return periods. Also presented are estimates based on commingled data sets (i.e., sets containing, indiscriminately, both non-thunderstorm and thunderstorm wind speeds), which until now have been used almost exclusively for extreme wind speed estimates in the US. Analyses at additional stations will be needed to check whether these results are typical for locations with both thunderstorm and non-thunderstorm winds.     

Seismic retrofit of GLD shear wall structures in Singapore

This study is concerned with the experimental investigation into the seismic behaviour and retrofitting of gravity-load-designed reinforced-concrete (RC) shear wall structures in Singapore. These structures are designed according to the British Standard (BS8110 1985 BS8110. 1985. Structural use of concrete parts 1, 2 and 3, London: British Standards Institution.  [Google Scholar]). For this purpose, 1/5 scaled models (with and without retrofitting), representing the lower critical regions of a 25-story RC shear wall structure, were tested under cyclic loadings. Test results showed that the shear wall failed at the base due to shear and that the pushover test provides a simplified representation of the cyclic test. Retrofitting the wall with GFRP (glass fibre reinforced polymer) system resulted in improved performances of up to 20% to 30% higher ultimate load capacity and displacement. The study provides an insight into the seismic behaviour of such structures and the mechanism of the proposed retrofitting scheme for improving the structural resistance to seismic loads.     

悬浮隧道锚索涡激振动影响因素分析

将锚索运动简化为弹簧质量阻尼系统,锚索周围流场采用RSM(Reynolds Stress Model)结合增强的壁面函数模型计算,利用四阶Runge-Kutta法计算锚索振动方程,并将程序写入FLUENT软件进行流固耦合分析。讨论了锚索质量比、阻尼比、是否考虑流向运动和来流速度对锚索涡激振动的影响,主要结论有：质量比对锚索横向涡激振动幅值影响很小,对约化速度范围影响较大;阻尼比对约化速度范围影响很小,对锚索涡激振动幅值影响较大;在低质量比的情况下,考虑锚索流向运动时,涡激振动幅值比不考虑时偏大。     

强风作用下高耸钢结构输电塔的破坏特征研究

强风作用是输电塔等高耸结构倒塌的潜在威胁,由于不同风场的特征存在很大的差异,导致结构具有不同的破坏形式。本文研究了两种风场下结构不同高度截面抗风能力的验证方法。文中,首先引入了边界层近地风和下击暴流风的设计风荷载;其次,提出了输电塔结构抗风能力的验证方法,即两种风力引起的输电塔结构底部截面弯矩相等,并在达到输电塔结构底部截面抗风能力极限状态时,计算不同高度处输电塔截面的抗风能力是否满足设计要求;最后以一大跨越输电塔为例进行分析,结果表明,当底部达到抗风能力极限状态时,下击暴流可导致结构在40m高度区域内发生破坏,而近地风可导致结构首先从根部发生破坏,从而在理论上验证了下击暴流强风荷载作用下输电塔结构大多不在根部首先发生破坏的现象。     

Bridge user cost estimation – a synthesis of existing methods and addressing the issues of multiple counting,workzones and traffic capacity limitation

Efforts to incorporate the concerns of bridge users in bridge investment evaluation are often stymied by lack of a comprehensive framework for assessing different user costs. There is a need to synthesise and update existing user cost estimation techniques so that the incorporation of user costs in bridge investment evaluation can be more consistent and streamlined. Secondly, a bridge detour may occur for more than one reason, thus there is a danger of multiple counting that could cause overestimation of user costs. Thirdly, user costs during bridge workzones have rarely been considered in the literature. To address these issues, this article presents a framework for comprehensive estimation of bridge user costs, an approach to address the multiple-counting problem, and a methodology for bridge workzone user cost estimation. Furthermore, the article develops a method to estimate bridge user delay cost due to traffic capacity limitation. The methodologies are demonstrated using a case study.     

Monte Carlo simulation of extreme traffic loading on short and medium span bridges

The accurate estimation of site-specific lifetime extreme traffic load effects is an important element in the cost-effective assessment of bridges. A common approach is to use statistical distributions derived from weigh-in-motion measurements as the basis for Monte Carlo simulation of traffic loading. However, results are highly sensitive to the assumptions made, not just with regard to vehicle weights but also to axle configurations and gaps between vehicles. This paper presents a comprehensive model for Monte Carlo simulation of bridge loading for free-flowing traffic and shows how the model matches results from measurements on five European highways. The model has been optimised to allow the simulation of many years of traffic and this greatly reduces the variance in calculating estimates for lifetime loading from the model. The approach described here does not remove the uncertainty inherent in estimating lifetime maximum loading from data collected over relatively short time periods.     

基于FBG传感技术的深海立管涡激振动测试研究

为了探索光纤光栅传感技术在深海立管振动测试中的适用性,采用光纤光栅应变传感器,在大型波流耦合试验水池中进行了阶段流作用下大长细比深海立管的涡激振动测试。试验立管模型长为6.2 m,长细比为310,模型材料采用铜管,立管上部1.2 m处于均匀稳定的流场中,下部5.0 m处于静水之中。沿立管长度四面对称布置48个光栅测点,通过改变外流流速、内流流速和初始顶张力等影响因素,采集应变数据并结合模态分析理论,分析了不同工况下立管的振动频率、幅值及模态等振动特性,研究了阶段流作用下立管的涡激振动规律。结果表明,光纤光栅传感技术能很好地满足大长细比深海立管的涡激振动测试要求,能准确体现立管的应变时程、振幅和频率等振动特性,清晰反映出在不同外流速下立管振动的多模态特征及每阶主导频率下的锁振区间。