悬臂式桥梁预力损失评估模式研究

本研究目的拟针对大跨径悬臂式预力桥梁,提出一套分析方法与流程期能快速预测桥梁预力损失及其安全性,分析方法以相关理论基础搭配 SAP2000N 分析软件并运用其静力分析功能预测其预力损失所造成桥梁结构的力学行为,其中以节点力法与钢腱模拟来等效模拟预力的行为,且根据A桥监测数据与水平测量予以比对,并利用桥梁设计数据与挠曲应力分析来评估预力损失对桥梁安全性的影响,并验证评估模式的可靠性与准确性。结果显示,此分析方法对于后拉式预力桥梁能有效的预测其预力损失与长期变位的行为,并依据预拱损失、预力损失与时间三者之间的关系,则能推估其桥梁的安全性与破坏模式。

基于应变监测的预应力混凝土梁桥安全评估

主要探讨了某早期建设的预力混凝土I型梁桥。经过几十年的变化,桥梁已有迈向老劣化的趋势,为确认老劣化对桥梁的影响,利用数值模拟与健康监测数据来确保桥梁是否仍然保持在安全范围内。使用Midas Civil软件进行梁桥建模,并搭配监测资料与荷载试验来做比对。通过数值仿真分析得到的数据与实桥测得数据对比后,将数值模型调校成符合桥梁现状,掌握桥梁结构的应力应变,评估整体桥梁受老劣化影响的程度,并且建立监测管理阈值以便于掌控桥梁未来的安全性。

NUMERICAL PREDICTION OF AIRCRAFT HYDRAULIC SYSTEM BASED ON THERMAL DYNAMIC ANALYSIS

A mathematical model of principal elements of the aircraft hydraulic system is presented based on the heat transfer theory. The dynamic heat transfer process of the hydraulic oil and the pump shells within an aircraft hydraulic system are analyzed by the difference method. A kind of means for the prediction to variational trends of the aircraft hydraulic system temperature is provided during operation. The numerical prediction and simulation under the operational conditions are presented for ground trial running and the decelerated operation in flight. Computational results show that there is a good coincidence between the experimental data and the numerical predictions.

Test analysis of stress characteristics on reinforcing rock slope with group anchorage cable

To research the reinforcement effect of a rock slope with group anchorage cables and the stress characteristics of pre-stressed anchorage cables in the fractured surface, the rock slope calculated model of a wedge block within the double-slide face was established by using the finite difference software according to the actual slope project combined with indoor model test. The pre-stress loss rule of the anchorage cable and the distribution of axial force and the force-transferring mechanism of the anchorage cable were analyzed during simulation. Also, based on the displacement contour and the safety factor of the calculated results, the quantitative analysis for the reinforcement ef- fect of the rock slope with group pre-stressed anchorage cable was discovered. The results computed by the software conform with the data in the experiment, which can prove the effectiveness and correctness of parameter selection and model building. Keywords group anchorage reinforcement, rock slope, joint fissure, pre-stressed anchorage cable, stress characteristics

Simulation and Numerical Analysis on Anti-float Anchor by Field Rock and Soil Tests

This paper introduces the stress and deformation of anti floating anchor rod and explained the damage. Through field testing and numerical analysis, the article were studied the displacement and internal force of a basement tensile anti float anchor, results showed that： the axial force of bolt tension transfer is top-down transfer, axial force decreases, the stress concentrate on the end. When a force is applied to a certain load, end firstly generate damage, but with the deepening of the axial force, it is greatly reduced, which indicates that the anchor force is an effective length, rather than the longer the anchor pullout force is bigger; anchor group effect is a problem that can not be ignored, because the engineering community for its attention degree is not enough, so that the design of anti floating anchor the lack of a reliable basis, the test results can provide a reference for the future design of anti floating anchor. Prestressed anchors in the tension lock, prestressed loss are regularly.

Coupling model for calculating prestress loss caused by relaxation loss,shrinkage,and creep of concrete

The calculation model for the relaxation loss of concrete mentioned in the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts(JTG D62—2004) was modified according to experimental data. Time-varying relaxation loss was considered in the new model. Moreover, prestressed reinforcement with varying lengths(caused by the shrinkage and creep of concrete) might influence the final values and the time-varying function of the forecast relaxation loss. Hence, the effects of concrete shrinkage and creep were considered when calculating prestress loss, which reflected the coupling relation between these effects and relaxation loss in concrete. Hence, the forecast relaxation loss of prestressed reinforcement under the effects of different initial stress levels at any time point can be calculated using the modified model. To simplify the calculation, the integral expression of the model can be changed into an algebraic equation. The accuracy of the result is related to the division of the periods within the ending time of deriving the final value of the relaxation loss of prestressed reinforcement. When the time division is reasonable, result accuracy is high. The modified model works excellently according to the comparison of the test results. The calculation result of the modified model mainly reflects the prestress loss values of prestressed reinforcement at each time point, which confirms that adopting the finding in practical applications is reasonable.

Research on Stability Calculation Methods for Grillage Supporting Structure with Pre-stressed Anchor

Aiming at prestressed anchor cable frame in the presence of reinforcement landslide problem, through the selection of test points, the paper study and tested soil pressure, frame internal force and prestress losses under prestressed anchor cable frame beam, reveal the law of internal force distribution, and provides a theory basis for the rational design of prestressed anchor cable in landslide.

Natural Ageing Tests to Study In-service Different Facade Solutions--ETICS and Premixed One-Coat Rendered Walls

In situ testing provides accurate characterization of existing degradation mechanisms of materials and building systems which helps reducing the subjectivity of visual inspections especially when ageing under natural ageing conditions is carried out over significant periods of time. In this work, data collected from field experimental campaigns over 10 years after construction using several premixed one-coat rendered walls and over 4 and 6 years after construction in the case of ETICS （external thermal insulation composite systems） are presented and discussed. The influence of hydrophobic agents on the performance of both types of facades in terms of surface condition and water penetration was assessed by visual inspections, Karsten test and capillary tests. Additionally, adhesion tests and subsequent evaluation of porosity were also carried out for premixed one-coat mortars. The results obtained have shown that ageing of the rendering solutions, especially after 5 or 6 years in-service, results from the loss of resistance to liquid water penetration, especially at the surface. Yet, additional mechanisms such as leaching of hydrophobic agents and photochemical degradation are thought to be involved, too. Moreover, the results obtained using the Karsten test proved to be the most reliable method to determine the loss of water penetration resistance and predict the ageing of facade solutions. The information collected and the correlations established can help developing solutions to prevent early ageing and implement appropriate maintenance plans to delay their effect.