大跨度钢结构人行悬索桥受力性能对比分析

为了提高大跨度钢结构人行悬索桥的安全性能,以某实际工程为依托,采用有限元软件Midas/Civil建立整体空间模型,分析单缆体系和双缆体系在人群荷载和风荷载作用下的受力特点以及自振频率特性。结果表明:人群荷载作用下,双缆体系的底缆承担更多荷载,主梁挠度相比单缆体系减小约15%;风荷载作用下,两种结构体系主梁弯矩和挠度的变化趋势比较相似,双缆体系的弯矩和挠度均小于单缆体系;双缆体系的侧弯频率、竖弯频率、竖振频率以及侧振频率相比单缆体系均有所增加。双缆体系具有更优的力学性能,提高了工程安全性,并为类似工程的桥型选择提供有力参考。     

The impact of traffic barrier geometric features on crash frequency and injury severity of non-interstate highways

Introduction: The main objective of this research is to investigate the effect of traffic barrier geometric characteristics on crashes that occurred on non-interstate roads. Method: For this purpose, height, side-slope rate, post-spacing, and lateral offset of about 137 miles of traffic barriers were collected on non-interstate (state, federal aid primary, federal aid secondary, and federal aid urban) highways in Wyoming. In addition, crash reports recorded between 2008 and 2017 were added to the traffic barrier dataset. The safety performance of traffic barriers with regards to their geometric features was analyzed in terms of crash frequency and crash severity using random-parameters negative binomial, and random-parameters ordered logit models, respectively. Results: From the results, box beam barriers with a height of 27–29 inches were less likely to be associated with injury and fatal injury crashes compared to other barrier types. On the other hand, the likelihood of a severe injury crash was found to be higher for box beam barriers with a height taller than 31 inches. Both W-beam and box beam barriers with a post-spacing between 6.1 and 6.3 inches reduced the probability of severe injury crashes. In terms of the crash frequency, flare traffic barriers had a lower crash frequency compared to parallel traffic barriers. Non-interstate roads without longitudinal rumble strips were associated with a higher rate of traffic barrier crashes.     

2003—2018年全国酸雨状况变化趋势研究

基于2003—2018年全国291个城市降水监测结果的分析表明:全国降水酸度明显降低,其中,2003—2006年有所升高,2006年之后呈降低趋势;酸雨区面积呈减小趋势,共减少约97万km²,酸雨发生频率超过5%的面积减少了20.9个百分点;全国酸雨城市比例为21.3%～40.9%,2009年开始总体呈下降趋势,2018年降为21.6%,重酸雨城市比例在2005年之后总体呈下降趋势;全国平均酸雨频率为11.7%～25.6%,2006年之后总体呈下降趋势,2018年酸雨频率在50%以上的城市比例较2006年下降了13.9个百分点。基于174个城市的降水离子组分分析结果显示:我国降水中的主要阴离子为硫酸根,其离子当量浓度占比为19.4%～32.9%,2003年以来年平均降低0.6个百分点;降水中的主要阳离子为钙离子和铵离子;硫酸根沉降通量年平均下降0.68 t/km²,硝酸根沉降通量年平均降低0.05 t/km²,全国SO₂浓度变化趋势与硫酸根沉降通量变化趋势基本一致;我国降水中的硝酸根与硫酸根离子当量浓度比值总体呈升高趋势,表明硝酸根离子对降水酸度的影响逐渐增加,酸雨类型正由硫酸型向硫酸-硝酸混合型转变。     

大断面高铁隧道掘进爆破振动传播规律研究*

为研究隧道爆破掘进振动规律并合理控制爆破振动危害,对京张高铁大断面南口隧道爆破掘进过程进行实时监测,并对监测结果进行线性回归分析,求得3个监测方向的场地系数K和衰减系数α值以及爆破振动峰值速度衰减回归方程,通过FFT法计算出主振频率和爆破振动波的振动频率范围,利用ANSYS/LS-DYNA对爆破工程进行数值模拟。结果表明:喷锚支护和监测方向对爆破振动衰减回归分析影响较大;主振频率和爆破振动波的振动频率分布范围为50~300 Hz,无需考虑周边建筑共振情况,与周边古建筑和临近隧道的最小安全距离分别为147 m和12 m;数值模拟与实际结果对比发现二者振动峰值略有差别但整体趋势基本相同,证明建立模型的有效性。     

施工过程中人因差错控制效率分析

以一个钢筋砼单筋梁受弯构件正截面承载力失效概率为例,通过数值模拟发现:检查抽样率为100%的首次检查对控制人因差错非常有效,提高取样率可以有效减少和降低人因差错的发生及其影响程度,但随检查次数增加检查效率直线下降。当对各种工序进行比较细致的检查时,适当提高结构参数设计值可有效防止由较难检查出来的微小人因差错引起的结构失效。显然,质检方法、检查次数、取样率和提高结构参数设计值对人因差错控制效率的提高是十分重要的;人因差错控制效率与检查人力、物力投入成正比。上述结论对合理控制施工过程中人因差错的方案选择具有一定的现实意义。     

城市大跨度隧道爆破对地面建筑物影响的研究

以嘉华隧道工程开挖为研究对象,应用安全系统工程中的事故树法对爆破振动影响区域内的地面建筑物进行定性分析,找出影响地面建筑物稳定的最小割集;求出各基本事件的结构重要度,为后续监测和施工方案的调整提供理论依据。结合现场实际情况,制定合理的爆破地震波的振动监测方案。同时,对爆破振动监测结果的回归分析,确立振动传播衰减规律。分别从振动速度和峰值频率两个方面对地面建筑物的安全性进行评价。笔者研究成果对指导隧道工程开挖爆破施工和保证地面建筑物安全有重要指导作用。     

Occupational noise exposure and hearing loss among pulse processing workers

Occupational noise exposure and noise-induced hearing loss (NIHL) has been recognised as a problem among workers in Indian industries. The major industries in India are based on the processing of agricultural products. There are appreciable numbers of pulse processing units spread throughout the country. The purpose of this study was to determine the prevalence of hearing loss among pulse processing workers. As a part of hearing protection intervention, audiometric tests were conducted at the binaural low (250–1,500 Hz), the binaural mid (1,500–4,000 Hz) and the binaural high (3,000–8,000 Hz) frequency averages. The prevalence of hearing loss was determined based on hearing threshold levels (HTLs) with a low fence of 25 dB. Over 50% of pulse processing workers (dana bazaar and dal mill) showed hearing loss in the noise-sensitive higher (binaural mid and high) frequencies. The rate of hearing loss was particularly high among workers in the dal mill. The analyses show a higher risk of prevalence of hearing loss among the dal mill workers compared to the workers associated with the grain preprocessing activities. The study shows alarming signals of NIHL, especially in the dal mill workers. The occupational exposure to noise could be minimised by efficient control measures through engineering controls, administrative controls and the use of personal protective devices. Applications of engineering and/or administrative controls are frequently not feasible in developing countries for technical and financial reasons. A complete hearing conservation programme, including training, audiometry and the use of hearing protection devices, is the most feasible method for the protection of industrial workers from prevailing noise in workplace environments in the developing countries.     

大跨人行过街天桥利用MTMD减振控制的理论分析

大跨人行天桥的自振频率通常比较低,与人行走时的频率接近,因此行人通过天桥时容易产生竖向共振,影响天桥的正常使用。本文研究多重调谐质量阻尼(MTMD)系统对大跨人行过街天桥竖向振动的控制作用,首先建立起天桥-MTMD系统的分析模型,推导出系统的传递函数及动力放大系数的数学表达式,继而分析了TMD的数量、阻尼比和频带宽等参数对结构的动力放大系数的影响,为实际工程结构设计MTMD减振系统时提供参考。以沈阳某大跨人行天桥为例,进行MTMD优化设置后,能有效减小天桥的受迫振动和自由振动,从而将振动控制在人体的舒适度范围之内。     

巨型减振结构体系风振效应的参数影响研究

巨型结构风激振动特性非常复杂,其动力性能受多种参数的影响。为合理考虑这些因素的影响,以某48层巨型钢结构为研究对象,针对无控、设置粘滞阻尼器和粘弹性阻尼器三种分析工况,系统研究了其在平均风和脉动风荷载共同作用下的动力响应。通过结构顺风向侧移响应、构件内力响应及顶层加速度响应等一系列数据,揭示了风速攻角、基本风压、附加阻尼比及二阶效应等对此类结构体系风振控制动力性能的影响规律与变化趋势,并依据分析结果对其抗风分析与设计提出了相应的建议,因而具有实用参考价值。     

快速轨道交通运行引起的场地振动反应分析

在运输业高度发达的当今社会,轨道交通运行引起的环境振动已经引起了越来越多的关注和研究。本文以ABAQUS软件为计算平台,基于轨道几何不平顺理论荷载模型,采用基于Davidenkov骨架曲线的非线性动粘弹塑性模型描述土的动力特性,以南京典型场地条件为研究对象,对快速轨道交通运行引起的场地地表振动特性进行了分析,得到了不同列车车速下地表振动的强度、频谱特性及其衰减规律,并分析了场地振动强度的影响因素,为进一步研究和控制快速轨道交通运行引起的地面振动提供了基础性资料。