动力定位系统与单波束测深仪在科考船定点作业中的应用

科考船定点作业时会受到海洋风、涌、浪、流等外界环境因素影响，导致工作效率降低，原位测量精度下降，甚至影响作业安全。动力定位系统 （DP） 具有自动定位功能，能够抵抗外界环境因素的影响，可实现科考船高精度定点控位。 单波束测深仪不仅可以测量水深，也可反映水下设备深度信息，可以起到辅助监控水下设备功能。本文在介绍定点作业施工现状与局限性的基础上，分析 DP 系统与单波束测深仪工作原理，以“向阳红 01”船为载体，在定点作业时开启 DP 系统与单波束测深仪，发现该方法可以提高科考船定点作业工作效率、原位测量精度并保障作业安全，可为其他科考船定点作业提供参考。     

基于单波束测深资料的海底冷泉动力学特征反演方法研究

为了准确理解冷泉水体中甲烷气体的分布规律,综合运用单波束测深数据和冷泉水体流场数据,建立了冷泉气泡上升、溶解速率的定量反演方法,利用现场海试资料对反演方法进行了验证,并对海试区域的冷泉气体溢出、溶解通量以及冷泉水体的甲烷浓度进行了估算。计算结果表明,考察船航向与冷泉水体流向的差异会对声学探测结果产生影响,当航向与流向的夹角大于±60°时,声学成像中冷泉倾角的误差将超过50%。同时,冷泉气泡上升速率的衰减与溢出口水深显著相关,相关系数可达0.9,并且冷泉上升流对上升速率的提升效果明显。水合物稳定带的分布对冷泉气泡的收缩速率影响显著,稳定带内、外收缩速率的差异可达3～4倍。冷泉气体通量的计算结果表明,调查区域内冷泉的溢出强度整体较大,同时溶解通量与水深之间呈现明显的分段效应。根据冷泉气体溶解通量估算的冷泉水体甲烷浓度与色谱分析结果具有较好的一致性。相关研究有助于实现对冷泉水体中甲烷气体分布的定量评估,为潜在海底冷泉区的圈划和海域天然气水合物的调查提供技术支撑。     

桩锚支护中锚杆张拉顺序对预应力影响的试验研究

以北京某深基坑支护工程为背景,结合现场桩锚支护体系预应力锚杆的实测数据,综合分析不同张拉顺序下锚杆预应力损失率变化规律。认为相同条件下依次张拉锁定的顺序,锚杆预应力值损失率最小。     

声惯一体单波束测深系统在长江河道勘测中的应用

现如今单波束测深系统及多波束测深系统已经在长江河道水下地形测绘中广泛应用,人们对于内河航道水下地形数据的精度要求也越来越高,声惯一体单波束测深系统很好地解决了传统单波束测深精度不高及多波束测深系统安装操作复杂且对测量水域条件要求较高等问题。本文针对声惯一体单波束测深系统在长江河道勘测中的实际应用情况,与传统单波束及多波束测量数据进行对比分析,结果表明声惯一体单波束测深系统能够很好地满足长江河道高精度测量的需求。     

Single precast concrete rocking walls as earthquake force‐resisting elements

Precast concrete walls with unbonded post‐tensioning provide a simple self‐centering system. Yet, its application in seismic regions is not permitted as it is assumed to have no energy dissipation through a hysteretic mechanism. These walls, however, dissipate energy imparted to them because of the wall impacting the foundation during rocking and limited hysteretic action resulting from concrete nonlinearity. The energy dissipated due to rocking was ignored in previous experimental studies because they were conducted primarily using quasi‐static loading. Relying only on limited energy dissipation, a shake table study was conducted on four single rocking walls (SRWs) using multiple‐level earthquake input motions. All walls generally performed satisfactorily up to the design‐level earthquakes when their performance was assessed in terms of the maximum transient drift, maximum absolute acceleration, and residual drift. However, for the maximum considered earthquakes, the walls experienced peak lateral drifts greater than the permissible limits. Combining the experimental results with an analytical investigation, it is shown that SRWs can be designed as earthquake force‐resisting elements to produce satisfactory performance under design‐level and higher‐intensity earthquake motions. Copyright © 2016 John Wiley & Sons, Ltd.     

Biaxial testing of unbonded post‐tensioned rocking bridge piers with external replacable dissipaters

The biaxial response of two bridge piers is experimentally investigated. A post‐tensioned precast bridge pier with external replaceable mild‐steel dissipaters is tested under biaxial loading. The performance of the post‐tensioned bridge pier is compared with a conventionally reinforced monolithic bridge pier. The experimental biaxial response is then compared with previous uniaxial experimental testing of identical bridge piers to understand the influence of biaxial loading, specifically concerning post‐tensioned rocking sections. A 3‐dimensional moment–curvature and moment–rotation analysis program is created to generate the monotonic section response of a conventional and post‐tensioned bridge pier. After comparing the accuracy of the section analysis program to the experimental testing of the monolithic pier, the program is validated against the experimental testing of the post‐tensioned bridge pier. This section analysis program is then used in the calibration of a macro‐model to capture the entire cyclic response of the post‐tensioned bridge pier. The macro‐model adopts multiple linear‐elastic compression‐only springs at the rocking interface, combined with non‐linear inelastic springs for each of the mild‐steel dissipaters and returns encouraging results at both local and global levels. The paper concludes with a number of biaxial moment‐interaction design charts for monolithic and post‐tensioned bridge piers as a function of mechanical and geometric section properties. The design charts define the biaxial yield surface at nominal yield and at the design section capacity defined by one of three material limit states. Copyright © 2011 John Wiley & Sons, Ltd.     

单束张拉和多束张拉工艺在斜坡治理中的联合应用

格构梁的锚索张拉大多采用多束张拉工艺。在甘肃陇南消防支队后山不稳定斜坡锚索格构梁防护施工中,遇到钢绞线外露工作长度不足,多束张拉难以进行的问题。提出了单束张拉工艺与多束张拉工艺联合应用治理不稳定斜坡的方案。详细介绍了施工工艺以及治理效果。     

Quasi‐static and pseudo‐dynamic testing of unbonded post‐tensioned rocking bridge piers with external replaceable dissipaters

It has been well documented that following a major earthquake a substantial percentage of economic loss results from downtime of essential lifelines in and out of major urban centres. This has thus led to an improvement of both performance‐based seismic design philosophies and to the development of cost‐effective seismic structural systems capable of guaranteeing a high level of protection, low structural damage and reduced downtime after a design‐level seismic event. An example of such technology is the development of unbonded post‐tensioned techniques in combination with rocking–dissipating connections. In this contribution, further advances in the development of high‐performance seismic‐resistant bridge piers are achieved through the experimental validation of unbonded post‐tensioned bridge piers with external, fully replaceable, mild steel hysteretic dissipaters. The experimental response of three 1 : 3 scale unbonded, post‐tensioned cantilever bridge piers, subjected to quasi‐static and pseudo‐dynamic loading protocols, are presented and compared with an equivalently reinforced monolithic benchmark. Minimal physical damage is observed for the post‐tensioned systems, which exhibit very stable energy dissipation and re‐centring properties. Furthermore, the external dissipaters can be easily replaced if severely damaged under a major (higher than expected) earthquake event. Thus, negligible residual deformations, limited repair costs and downtime can be achieved for critical lifeline components. Satisfactory analytical–experimental comparisons are also presented as a further confirmation of the reliability of the design procedure and of the modelling techniques. Copyright © 2008 John Wiley & Sons, Ltd.     

Precast concrete wall with end columns (PreWEC) for earthquake resistant design

An innovative seismic resisting system consisting of a Pre cast W all with E nd C olumns (or PreWEC) has been developed, and its performance has been verified using large‐scale cyclic testing. The wall and end columns in the PreWEC system are anchored individually to a foundation using unbonded post‐tensioning. A newly designed, low‐cost mild steel connector is used to connect the wall and end columns horizontally along the vertical joint. The connectors are easily replaceable and provide additional hysteretic energy dissipation to the system. The PreWEC system can be economically designed to have a lateral load carrying capacity similar to that of a comparable reinforced concrete wall, while minimizing damage and providing self‐centering capability. In addition to confirming these benefits, the large‐scale test demonstrated that the PreWEC system: (i) would provide superior seismic performance compared to other currently available structural wall systems especially for the precast industry; and (ii) meets all the mandatory acceptance criteria established by the American Concrete Institute (ACI) for special unbonded post‐tensioned precast structural walls and building frame special reinforced concrete shear wall systems, as defined in the American Concrete Society of Civil Engineers (ASCE) 7‐05. Copyright © 2015 John Wiley & Sons, Ltd.     

Shaking table test on small‐scale retrofitted model of Sefid‐rud concrete buttress dam

Sefid‐rud concrete buttress dam with a height of 106 m was damaged during the devastating 1990 Manjil earthquake. The dam was repaired and strengthened using epoxy grouting of cracks and the installation of post‐tensioned anchors. In a previous study, nonlinear seismic response of the highest monolith with empty reservoir was investigated experimentally through model testing. A geometric‐scaled model of 1:30 was tested on a shaking table to study dynamic cracking of the model. As a result of the similarity between model and prototype cracking pattern, the model was retrofitted according to prototype retrofitting plan after the Manjil earthquake and re‐tested on shaking table to estimate the current safety of the prototype. Experimental test results showed that the post‐tensioning resulted in a significant decrease in dynamic responses in terms of crest displacement and measured strains of the retrofitted model in comparison with its corresponding responses at the first test. No cracking was observed in the retrofitted model when the base motion peak acceleration exceeded a value that was 22% higher than the one caused cracking in the first model. This can be interpreted as the efficiency of prototype post‐tensioning system in evaluating the seismic safety of Sefid‐rud dam. Copyright © 2009 John Wiley & Sons, Ltd.