桥梁外文文献

A BALANCED CANTILEVER CONCRETE BRIDGE by Olivier BURDET， Ph。D。

Swiss Federal Institute of Technology， Lausanne, Switzerland

Institute of Reinforced and Prestressed Concrete SUMMARY There is a need for reliable monitoring systems to follow the evolution of the behavior of structures over time。

Deflections and rotations are values that reflect the overall structure behavior. This paper presents an innovative approach to the measurement of long-term deformations of bridges by use of inclinometers。 High precision electronic inclinometers can be used to follow effectively long-term rotations without disruption of the traffic。 In addition to their accuracy， these instruments have proven to be sufficiently stable over time and reliable for field conditions。 The Mentue bridges are twin 565 m long box-girder post—tensioned concrete highway bridges under construction in Switzerland. The bridges are built by the balanced cantilever method over a deep valley。 The piers are 100 m high and the main span is 150 m。 A centralized data acquisition system was installed in one bridge during

its construction in 1997。 Every minute, the system records the rotation and temperature at a number of measuring points. The simultaneous measurement of rotations and concrete temperature at several locations gives a clear idea of the movements induced by thermal conditions. The system will be used in combination with a hydrostatic leveling setup to follow the long-term behavior of the bridge. Preliminary results show that the system performs reliably and that the accuracy of the sensors is excellent。

Comparison of the evolution of rotations and temperature indicate that the structure responds to changes in air temperature rather quickly。

1. BACKGROUND

All over the world， the number of structures in service keeps increasing. With the development of traffic and the increased dependence on reliable transportation， it is becoming more and more necessary to foresee and anticipate the deterioration of structures。 In particular，

for structures that are part of major transportation systems, rehabilitation works need to be carefully planned in order to minimize disruptions of traffic。 Automatic monitoring of structures is thus rapidly developing。

Long—term monitoring of bridges is an important part of this overall effort to attempt to minimize both the impact and the cost of maintenance and rehabilitation work of major structures。 By knowing the rate of deterioration of a given structure, the engineer is able to anticipate and adequately define the timing of required interventions. Conversely, interventions can be delayed until the condition of the structure requires them, without reducing the overall safety of the structure.

The paper presents an innovative approach to the measurement of long—term bridge deformations。 The use of high precision inclinometers permits an effective， accurate and unobtrusive following of the long—term rotations. The measurements can be performed under traffic conditions。 Simultaneous measurement of the temperature at several locations gives a clear idea of the movements induced by thermal conditions and those induced by creep and shrinkage。 The system presented is operational since August 1997 in the Mentue bridge, currently under construction in Switzerland。 The structure has a main span of 150 m and piers 100 m high。

2。 LONG—TERM MONITORING OF BRIDGES

As part of its research and service activities within the Swiss Federal Institute of Technology in Lausanne (EPFL)， IBAP -

Reinforced and Prestressed Concrete has been involved in the monitoring of long—time deformations of bridges and other structures for over twenty-five years [1, 2, 3, 4］。 In the past, IBAP has developed a system for the measurement of long-term deformations using hydrostatic leveling [5, 6］。 This system has been in successful service in ten bridges in Switzerland for approximately ten years [5，7］. The system is robust， reliable and sufficiently accurate, but it requires human intervention for each measurement， and is not well suited for automatic data acquisition. One additional disadvantage of this system is that it is only easily applicable to box girder bridges with an accessible box。

Occasional continuous measurements over periods of 24 hours have shown that the amplitude of daily movements is significant, usually amounting to several millimeters over a couple of hours。 This is exemplified in figure 1， where measurements of the twin Lutrive bridges， taken over a period of several years before and after they were strengthened by post—tensioning， are

shown along with measurements performed over a period of 24 hours. The scatter observed in the data is primarily caused by thermal effects on the bridges. In the case of these box—girder bridges built by the balanced cantilever method, with a main span of 143。5 m， the amplitude of deformations on a sunny day is of the same order of magnitude than the long term deformation over several years.

Instantaneous measurements， as those made by hydrostatic leveling, are not necessarily representative of the mean position of the bridge. This occurs because the position of the bridge at the time of the measurement is influenced by the temperature history over the past several hours and days。 Even if every care was taken to perform the measurements early in the morning and at the same period every year， it took a relatively long time before it was realized that the retrofit performed on the Lutrive bridges in 1988 by additional post-tensioning ［3，

7，11］ had not had the same effect on both of them。 Figure 1: Long—term deflections of the Lutrive bridges， compared to deflections measured in a 24—hour period Automatic data acquisition， allowing frequent measurements to be performed at an acceptable cost， is thus highly desirable. A study of possible solutions including laser—based leveling， fiber optics sensors and GPS-positioning was performed, with the conclusion that， provided that their long-term stability can be demonstrated, current types of electronic inclinometers are suitable for automatic measurements of rotations in existing bridges ［8]。

3。 MENTUE BRIDGES

The Mentue bridges are twin box-girder bridges that will carry the future A1 motorway from Lausanne to Bern。 Each bridge, similar in design， has an overall length of approximately 565 m, and a width of 13.46 m， designed to carry two lanes of traffic and an emergency lane. The bridges cross a deep valley with steep sides (fig. 2）。 The balanced cantilever design results from a bridge competition。 The 100 m high concrete piers were built using climbing formwork, after which the construction of the balanced cantilever started （fig. 3).

4. INCLINOMETERS

Starting in 1995， IBAP initiated a research project with the goal of investigating the feasibility of a measurement system using

inclinometers。 Preliminary results indicated that inclinometers offer several advantages for the automatic monitoring of structures. Table 1 summarizes the main properties of the inclinometers selected for this study。

One interesting property of measuring a structure’s rotations， is that， for a given ratio of maximum deflection to span length， the maximum rotation is essentially independent from its static system ［8]. Since maximal allowable values of about 1/1，000 for long-term deflections under permanent loads are generally accepted values worldwide， developments made for box—girder bridges with long spans， as is the case for this research, are applicable to other

bridges， for instance bridges with shorter spans and other types of cross—sections. This is significant because of the need to monitor smaller spans which constitute the majority of all

bridges。

The selected inclinometers are of type Wyler Zerotronic ± 1° [9］. Their accuracy is 1 microradian (μrad)， which corresponds to a rotation of one millimeter per kilometer， a very small value. For an intermediate span of a continuous beam with a constant depth, a mid—span deflection of 1/20，000 would induce a maximum rotation of about 150 μrad， or 0。15 milliradians （mrad）.

One potential problem with electronic instruments is that their measurements may drift over

time. To quantify and control this problem, a mechanical device was designed allowing the inclinometers to be precisely rotated of 180° in an horizontal plane （fig. 4). The drift of each inclinometer can be very simply obtained by comparing the values obtained in the initial and rotated position with previously obtained values. So far， it has been observed that the type of

inclinometer used in this project is not very sensitive to drifting。 5。 INSTRUMENTATION OF THE MENTUE BRIDGES

Because a number of bridges built by the balanced cantilever method have shown an unsatisfactory behavior in service [2, 7,10]， it was decided to carefully monitor the evolution of the deformations of the Mentue bridges. These bridges were designed taking into consideration recent recommendations for the choice of the amount of posttensioning

［7,10,13]。 Monitoring starting during the construction in 1997 and will be pursued after the bridges are opened to traffic in 2001。 Deflection monitoring includes topographic leveling by the highway authorities， an hydrostatic leveling system over the entire length of both bridges and a network of inclinometers in the main span of the North bridge. Data collection is

coordinated by the engineer of record, to facilitate comparison of measured values。 The information gained from these observations will be used to further enhance the design criteria for that type of bridge， especially with regard to the amount of post—tensioning [7, 10, 11， 12， 13].

The automatic monitoring system is driven by a data acquisition program that gathers and stores the data. This system is able to control various types of sensors simultaneously， at the present time inclinometers and thermal sensors. The computer program driving all the instrumentation offers a flexible framework, allowing the later

addition of new sensors or data acquisition systems. The use of the development environment LabView [14］ allowed to leverage the large user base in the field of laboratory instrumentation and data analysis. The data acquisition system runs on a rather modest computer, with an Intel 486/66 Mhz processor， 16 MB of memory and a 500 MB hard disk, running Windows NT. All sensor data are gathered once per minute and stored in compressed form on the hard disk. The system is located in the box-girder on top of pier 3 (fig。 5）. It can withstand severe weather conditions and will restart itself automatically after a power outage， which happened frequently during construction。

6. SENSORS

Figure 5(a) shows the location of the inclinometers in the main span of the North bridge。 The sensors are placed at the axis of the supports (①and⑤）， at 1/4 and 3/4 (③and④) of the span and at 1/8 of the span for ②. In the cross section， the sensors are located on the North web, at a height corresponding to the center of gravity of the section (fig。5a）。 The sensors are all connected by a

single RS—485 cable to the central data acquisition system located in the vicinity of inclinometer ①. Monitoring of the bridge started already during its construction。 Inclinometers ①, ② and ③ were installed before the span was completed。 The resulting measurement were difficult to interpret, however, because of the wide variations of angles

induced by the various stages of this particular method of construction.

The deflected shape will be determined by integrating the measured rotations along the length of the bridge (fig。5b）。 Although this integration is in principle straightforward， it has been shown [8, 16］ that the type of loading and possible measurement errors need to be carefully

taken into account。

Thermal sensors were embedded in concrete so that temperature effects could be taken into account for the adjustment of the geometry of the formwork for subsequent casts. Figure 6 shows the layout of thermal sensors in the main span。 The measurement sections are located at the same sections than the inclinometers （fig。 5). All sensors were placed in the formwork before concreting and were operational as soon as the formwork was removed, which was required for the needs of the construction。 In each section， seven of the nine thermal sensor （indicated in solid black in fig。 6) are now automatically measured by the central data acquisition system。

7. RESULTS

Figure 7 shows the results of inclinometry measurements performed from the end of

September to the third week of November 1997。 All inclinometers performed well during that period. Occasional interruptions of measurement， as observed for example in early October are due to interruption of power to the system during construction operations。 The overall symmetry of results from

inclinometersseem to indicate that the instruments drift is not significant for that time period。 The maximum amplitude of bridge deflection during the observed period， estimated on the basis of the inclinometers results, is around 40 mm. More accurate values will be computed when the method of determination of deflections will have been further calibrated with other measurements. Several periods of increase, respectively decrease， of deflections over several days can be observed in the graph。 This further illustrates the need for continuous deformation monitoring to account for such effects. The measurement period was 。busy. in terms of construction， and included the following operations: the final concrete pours in that span， horizontal jacking of the bridge to compensate some pier eccentricities， as well as the stressing of the continuity

post—tensioning， and the de-tensioning of the guy cables (fig. 3）. As a consequence， the interpretation of these measurements is quite difficult。 It is expected that further measurements, made after the completion of the bridge, will be simpler to interpret。

Figure 8 shows a detail of the measurements made in November， while figure。9 shows temperature measurements at the top and bottom of the section at mid—span made during that same period。 It is clear that the measured deflections correspond to changes in the temperature。

The temperature at the bottom of the section follows closely variations of the air temperature

（measured in the shade near the north web of the girder）. On the other hand， the temperature at the top of the cross section is less subject to rapid variations。 This may be due to the high elevation of the bridge above ground， and also to the fact that, during the measuring period, there was little direct sunshine on the deck。 The temperature gradient between top and bottom of the cross section has a direct relationship with short-term variations. It does not， however,

appear to be related to the general tendency to decrease in rotations observed in fig。 8.

8. FUTURE DEVELOPMENTS

Future developments will include algorithms to reconstruct deflections from measured rotations. To enhance the accuracy of the reconstruction of deflections， a 3D finite element model of the entire

structure is in preparation [15]。 This model will be used to identify the influence on rotations of various phenomena, such as creep of the piers and girder， differential settlements, horizontal and vertical temperature gradients or traffic loads。

Much work will be devoted to the interpretation of the data gathered in the Mentue bridge. The final part of the research project work will focus on two aspects: understanding the very complex behavior of the structure， and determining the most important parameters, to allow a simple and effective monitoring of the bridges deflections.

Finally， the research report will propose guidelines for determination of deflections from measured rotations and practical recommendations for the implementation of measurement systems using inclinometers。 It is expected that within the coming year new sites will be equipped with inclinometers. Experiences made by using inclinometers to measure deflections during loading tests [16， 17] have shown that the method is very flexible and competitive with other high—tech methods.

As an extension to the current research project， an innovative system for the measurement of bridge joint movement is being developed. This system integrates easily with the existing monitoring

system， because it also uses inclinometers, although from a slightly different type。

9。 CONCLUSIONS

An innovative measurement system for deformations of structures using high precision inclinometers has been developed。 This system combines a high accuracy with a relatively simple implementation。 Preliminary results are very encouraging and indicate that the use of inclinometers to monitor bridge deformations is a feasible and offers advantages。 The system is reliable, does not obstruct construction work or traffic and is very easily installed. Simultaneous temperature measurements have confirmed the importance of temperature variations on the behavior of structural concrete bridges。

10。 REFERENCES

[1] ANDREY D., Maintenance des ouvrages d’art: méthodologie de surveillance， PhD Dissertation Nr 679, EPFL, Lausanne， Switzerland, 1987.

［2] BURDET O., Load Testing and Monitoring of Swiss Bridges, CEB Information Bulletin Nr 219, Safety and Performance Concepts, Lausanne, Switzerland, 1993.

［3] BURDET O。, Critères pour le choix de la quantité de précontrainte découlant de l。observation de ponts existants, CUST—COS 96， Clermont—Ferrand， France, 1996.

［4］ HASSAN M.， BURDET O.， FAVRE R。, Combination of Ultrasonic Measurements and Load Tests in Bridge Evaluation, 5th International Conference on Structural Faults and Repair, Edinburgh, Scotland， UK, 1993。

［5] FAVRE R。, CHARIF H。， MARKEY I., Observation à long terme de la déformation des ponts， Mandat de Recherche de l’OFR 86/88， Final Report， EPFL, Lausanne， Switzerland， 1990.

[6］ FAVRE R。， MARKEY I。， Long—term Monitoring of Bridge Deformation, NATO Research Workshop, Bridge Evaluation, Repair and Rehabilitation， NATO ASI series E: vol。 187, pp. 85-100， Baltimore， USA, 1990。

[7］ FAVRE R.， BURDET O。 et al., Enseignements tirés d’essais de charge et d’observations à long terme pour l'évaluation des ponts et le choix de la précontrainte， OFR Report, 83/90, Zürich, Switzerland， 1995.

［8] DAVERIO R。， Mesures des déformations des ponts par un système d’inclinométrie，

Rapport de maîtrise EPFL—IBAP, Lausanne, Switzerland, 1995. [9] WYLER AG。, Technical specifications for Zerotronic Inclinometers, Winterthur， Switzerland， 1996.

［10］ FAVRE R., MARKEY I。， Generalization of the Load Balancing Method， 12th FIP Congress， Prestressed Concrete in Switzerland, pp。 32—37, Washington, USA， 1994。

［11］ FAVRE R。, BURDET O., CHARIF H.， Critères pour le choix d’une précontrainte: application au cas d’un renforcement,

［12］ FAVRE R.， BURDET O., Wahl einer geeigneten Vorspannung, Beton— und Stahlbetonbau, Beton- und Stahlbetonbau， 92/3, 67， Germany， 1997.

[13］ FAVRE R.， BURDET O., Choix d'une quantité appropriée de précontrainte, SIA D0 129, Zürich, Switzerland， 1996。

[14] NATIONAL INSTRUMENTS， LabView User。s Manual, Austin, USA， 1996.

［15] BOUBERGUIG A., ROSSIER S。, FAVRE R。 et al, Calcul non linéaire du béton armé et précontraint, Revue Français du Génie Civil， vol。 1 n° 3， Hermes, Paris， France, 1997。

［16] FEST E.， Système de mesure par inclinométrie: développement d’un algorithme de calcul des flèches, Mémoire de maîtrise de DEA, Lausanne / Paris, Switzerland / France, 1997。

［17］ PERREGAUX N。 et al。, Vertical Displacement of Bridges using the SOFO System： a Fiber Optic Monitoring Method for Structures， 12th ASCE Engineering Mechanics Conference， San Diego, USA, to be published，1998。

译文

平衡悬臂施工混凝土桥挠度和温度的自动监测 作者Olivier BURDET博士 瑞士联邦理工学院，洛桑，瑞士 钢筋和预应力混凝土研究所

概要：我们想要跟踪结构行为随时间的演化,需要一种可靠的监测系统. 挠度和旋转两个参数反映了结构的整体行为.本文提出了一种测量桥梁长期变形的创新方法，即，使用倾角仪.高精密电子倾角仪可以有效地追踪桥梁的长期旋转而不需要中断交通。除了准确,这些仪器已被证明随着时间的推移是足够稳定,野外条下也非常可靠。 Mentue桥,长565m，双箱双室梁，后张法预应力混凝土公路桥梁，修建于瑞士。该桥由平衡悬臂法修建于一条深谷之上。墩高100m,主跨为150m。一个

集中的数据采集系统于1997年修建该桥时安装在一梁上。每一分钟，系统记录了很多测量点的旋转量和温度值。在多个地点同时测量出的旋转量和混凝土温度给出了热条件引起的变动的清晰概念。该系统将与一水平装置结合使用,用以跟踪桥梁的长期行为。

初步结果表明该系统运行可靠，并且传感器的准确性非常优秀。 对旋转和温度的演变比较表明，结构对气温变化的反应相当快。 1。 背景

遍布世界，服役结构的数量在不断增加.随着交通的发展，我们日益依赖于可靠的交通运输，越来越有必要去预见和预测结构的恶化。特别是，对于主要运输系统的那部分结构,修复工程需要认真规划，以尽量减少交通中断。结构自动监测仪器从而迅速发展。

以尝试减少对主要结构的影响和维 长期桥梁监测是这一全面努力的重要组成部分，

修工程的费用。通过了解某一特定结构的恶化速度，工程师能够预见并充分界定所要求的处理措施的时机.相反，不降低结构的整体安全性，处理可以推迟到结构需要相应措施的时候。

本文提出了一种检测桥梁长期变形的创新方法。高精度倾角仪的使用允许我们可以对长期旋转进行有效、准确和无障碍跟踪。该测量设备可以在正常交通状况下运行.同一时间测量的、多个地点的温度给出了

一个由热、蠕变和收缩导致的变形的清晰概念.提出该系统的可行性是1997年8月开始运营的修建于瑞士的Mentue桥。该桥主跨150m，墩高100m。

2. 桥梁的长期监测

作为其研究和瑞士联邦理工学院（洛桑联邦理工学院）服务活动的一部分，该桥梁和其他结构涉及到的钢筋混凝土和预应力混凝土长期变形的监测已超过二十五年[1，2，3，4］。在过去,IBAP已经制定了一个长期变形测量的水准测量系统［5，6］。该系统已成功的服务于瑞士的十座桥梁约十年［5,7］。该系统强大，可靠和足够准确,但它要求每次测量要人为操作，并没有很好地适合于数据自动采集.该系统另外的一个缺点是，它只是较容易适用于可接触到的箱形梁桥.

偶尔超过24小时的连续测量表明，它日常变形幅度很大，通常一两个小时内几个毫米。这体现在图1中，那里的双箱双室梁Lutrive桥在他们被后张之前和尔后超过数年的测量显示了24小时内的测量结果。观察到的数据散射主要是由桥梁的热效应造成的。用平衡悬臂法建造、1435m主跨的箱形梁，在一个阳光明媚的日子变形幅度是与过去数年的长期变形属于同一量级的。

瞬时测量，如水准测量得出的结果,不一定代表了该桥的平均位置。这是因为在桥梁测量时的位置是受过去几个小时、几天气温的温度历史影响。即使周全的考虑影响监测测量结果的因素并且在每年的同一时期

进行测量,也需要相对较长的时间,我们才能弄清楚Lutrive桥在1988年进行改造时额外桥梁后张［3,7,11]有没有产生与两者相同的影响。

图1:Lutrive桥的长期挠度,与24小时内挠度自动采集的数据，使得我们可以在一个

可接受的成本上进行方便地测量,因此非常可取。一个可能的解决方案研究,进行了包

括基于激光水准，光纤传感器和GPS定位，得出的结论是，只要可以确保它们的长期稳定性，当前类型的电子倾角仪，都适合于自动测量现有桥梁的旋转量［8］.

3。 MENTUE道桥

Mentue桥是单箱双室箱梁桥,将衔接从洛桑到伯尔尼的未来A1高速公路.每片梁设计类似，拥有约565m的,整体长度和13。46m的宽度，设计承载两行车线和一个应急车道。桥梁跨越一两侧有陡峭山坡的深谷（图2）。平衡悬臂桥梁施工设计是与另一桥梁方案比选的结果.100m高的混凝土桥墩用爬模施工方法完成后,平衡悬臂施工启动（图

3） 。 4。 倾角仪

从1995年开始，IBAP发起了一个研究项目，目的是调查利用倾角仪的测量系统的可行性。初步结果表明,倾角仪为结构提供自动监测提供了些许优点。表1总结了本研

究选择的

倾角仪的主要特性。

衡量结构转动的有趣属性是,对于一个给定的最大挠度跨度比，最大旋转基本上是于它的静态系统[8］.由于在永久荷载下，最大允许值约1 / 1000的长期挠度已经被全世界普遍接受,就像这项研究中大跨度箱梁桥取得发展，同样适用于其他桥梁,例如跨度较短桥梁和其他类型跨度区域。这是很重要的,因为需要检测那些小跨度梁,他们构成所有桥梁的

大部分结构。

表1 倾角仪的主要特性

选定的倾角仪类型:伟伦Zerotronic ± 1 °［9］。其准确度为1 microradian（μrad），相当于一毫米每公里，是一个非常小的旋转值。对于一个通常高度连续梁的中跨， 1 / 20000的跨中挠度,将导致最大约150μrad的旋转，或

0.15毫弧度（mrad）。 电子仪器潜在的一个问题是他们的测量结果可能随时间漂移。为量化和控制这个问题，设计了一种机械装置,允

许倾角为180 °旋转正是在一水平面上（图4）。每个倾角仪的漂移可以通过比较获得的初始值和旋转位置与以前获得值简单地获得。到目前为止，我们观察到工程中使用的那种倾角仪的类型对漂流不是很敏感。

5。曼图桥的测试设备

一些采用平衡悬臂施工的桥梁,在实际使用中的状态并不理想［2，7，10］，为了查清原因，对曼图桥的变形发展做精密监控。这些桥跨设计时考虑了最近的关于后期张拉量的建议[7，10，13］。监控从1997年建桥时开始，2001年通车后会继续跟踪监控.偏转

监控包含公路部门提供的地形水准、一个覆盖两跨整个跨度的流体静力学水准系统以及北桥主跨上的倾角仪网.为了便于比较测量值，工程师的记录数据要同步收集。观测的信息将用于改善设计标准，尤其是关于后张拉量［7,10,11，12，13］。

一个数据提取程序会驱动自动监控系统，并将数据存储。这个系统可以同步控制不同类型的传感器,目前控制着倾角仪和热传感器。这个电脑程序控制所有的测量设备，它提供了一个灵活的框架模式，允许后期增加新型传感器和数据收集系统。LabView的使用给予使用者实验室级别的设备和分析优势。数据收集系统可以在普通配置的电脑上运行,因特尔486/66兆赫的处理器、16兆内存、500兆硬盘、WindowsNT的系统.所有传感器的数据一分钟收集一次,之后以压缩格式存储在硬盘

里。系统安置在3号墩上部的箱梁里（图5）。它能抵抗严峻的气候条件并且在电力供应后自动工作,断电在施工阶段频频发生.

6。传感器

图5（a)给出了北桥主跨上倾角仪的位置。①和⑤传感器安置在支撑轴上,③和④号分别在1/4和3/4跨，②号在1/8跨处。从横截面看，传感器安置在北腹板，高度与节目的重心对应(图5)。传感器通过单根RS-485电缆与位于①号倾角仪附近的数据中心相连.早在桥梁施工阶段就已经开始监控。①、②和③号倾角仪安装于桥跨合龙前。在这种特殊施工方法的不同施工阶段，角度的变化范范围较宽，因此测量的结果不是很直观。

通过合成桥长方向测量的旋转,可以确定偏转的形式。尽管合成方法在原理上简明易懂，但必须仔细计入荷载类型和可能的测量误差［8,16］。

热传感器埋置在混凝土内,这样可以计入模板后来浇筑几何调整的温度作用。图6是热传感器在主跨中的布置图。与图5倾角仪测量不同,温度测量时针对同一个截面.根据施工的需要，传感器在浇筑前预置在模板内,在拆模后即可进行测量。在每个截面上，九个传感器中的七个(图6中的黑色）由数据集成系统自动控制测量。

7。检测结果

图7是倾角仪从1997年九月底导十一月的第三个星期的测量结果。所有倾角仪在这段时间内工作良好，其中测量间断的部分，如十月初，是因为在施工操作中系统暂时断电所致。结果整体的对称，见①和⑤、③和④,表面设备在那段时间里的偏动并不明显。根据倾角仪的测量结果,在观察阶段，桥的最大挠曲在40毫米左右.在以后其他测量结果的辅助下，更精确的数值可以计算出来。在图上可以看到在几天内偏差的几个上升阶段及对应的下降阶段。这意味着需要对变形持续的监测，以解释这现象.从施工的角度来说,测量阶段很繁忙，这个阶段进行着以下工作：混凝土的最后浇筑、实施千斤顶对桥的水平顶撑以补偿一些墩的离心以及张拉连续预应力筋和支索缆的留置（图3）,因此，解读测量结果有一定的难度。将来的测量对解读测量结果会有很大的帮助.

图8是九月份的详细测量结果，图9是同时期中跨梁顶部和底部的温度测量结果。显然,变形与温度的变化想对应。梁底的温度变化与空气温度（测量点位于北腹板边的背阴处）变化一致。另一方面，截面上部的温度变化剧烈程度较低。这可能是因为梁体相对地面高程较大，除此以外，与测量阶段桥面受到较少的阳光直射也有关系.顶板和底板的温度梯度与短期的变化有直接的关系，但并不表明旋转的总体变化是图8所示的下降趋势。

图9 1997年11月温度 8。发展前景

将来会发展出跟据旋转的测量结果去推算挠曲的算法。为了提高推算挠曲的准确度，现在正在研究整个结果的三维有限元模型［15］。这个模型将用来鉴定不同因素对旋转的影响，例如，柱和梁的徐变、不均匀沉降、横向和竖向温度梯度、车辆荷载。

彻底分析曼图桥的测量结果还需要大量的工作.这项研究项目的最终部分集中在两个方面：一、解读结构的复杂行为；二、确定最重要的参数，以便于简单有效的测量桥梁的挠曲.

最后,研究报告会给出根据测量的旋转去确定挠曲的大体方法以及安装倾角仪测量设备的可操作性建议。预计来年会在新点位增加倾角仪。在荷载试验阶段使用倾角仪测挠曲的经验证明这种方法较其他高科技方法有很多的灵活性和竞争性。

作为当前这个研究项目的扩展,测量桥梁伸缩缝运动的系统正在研发,这个系统与已有的监控系统兼容性很好,因为其也使用倾角仪，只是倾角仪的类型稍有差别。

9。结论

一个创新的测量结构变形的系统已经产生，这个方法使用高精确度的倾角仪。这个系统把高精度与简单的设备有机结合起来.早期的结果很理想，表明使用倾角仪测量桥梁变形的方法是可行的，而且有一定的优势。这个系统是可靠的，

它不会干扰施工和交

通，设备安装简单。对温度的同步测量结果确认温度的变化对混凝土桥梁结构有很多的影响。