Lehigh University researchers have been on the forefront of field instrumentation and testing of bridges, buildings and other structures for over 50 years. They have developed a vast database and considerable experience in the field testing and evaluation of highway and rail structures. Field testing and evaluation is a particularly challenging area of structural research. It is the only method to accurately evaluate the true behavior of a structure in real-time under actual loads. Field measurements are the link that connects and validates laboratory testing and computer modeling to the behavior of real structures.
众所周知，对结构行为的准确解释需要准确的数据。但是，很明显，比在实验室中收集几百英尺在河上的空气中的数据要困难得多。除了环境障碍之外，在对测量结果进行准确的解释之前，必须解决许多变量。因此，对数据采集系统，传感器和结构行为进行彻底低估至关重要。最重要的是一个数据采集系统，可以在这些不利条件下持续执行。Lehigh大学的研究人员发现，Campbell Scientific CR9000测量和控制系统非常强大，并且能够承受最严重的现场环境。它们是我们基础架构监控计划的工作主场。
一个最近完成的现场测试项目的一个例子包括现场测量和对纽约州纽约市威廉斯堡桥的长期远程监控，该监视目前正在进行重大康复。该项目的很大一部分涉及用钢对型甲板上的南部，北部和外部道路上的现有混凝土填充甲板更换。除了一项全面的实验室测试计划外，还在南部外道路上进行了深入的现场仪器和测试计划。进行这项研究是为了研究原位应力范围，并更好地表征了这种复杂的结构系统及其与实验室反应的关系。使用CR9000收集数据。在受控的负载测试期间，从82个应变量计收集数据，以高达200 Hz的采样速率收集数据。所有数据均临时存储在数据词架中安装的PCMCIA卡上。随后在每个测试结束时将这些数据复制到笔记本电脑进行处理和备份。在整个测试程序中，紧凑型和坚固的CR9000表现出色。在测试期间，实时观察和审查数据的能力是无价的。
A second portion of the program consisted of nearly seven months of remote monitoring. Data were collected using the CR9000 system described above. Program upload and data download were achieved with two modems specially configured by Lehigh University’s Advanced Technology for Large Structural Systems (ATLSS) researchers. One modem was placed at the site, the other in an office at the ATLSS laboratory. The data were downloaded to a desktop PC every one to 14 days. The entire data acquisition system was stored in a steel box that was bolted to the west face of floorbeam 64E.
进入结构非常困难。记录器的恒定流量和远程位置给监视程序带来了一个特殊的问题。很方便，定期访问根本是不可能的。CR9000允许Lehigh的研究人员远程收集大量数据，从而消除了反复的桥梁本身的旅行。
为了最大程度地减少收集的数据量，未连续记录时间历史。相反，将CR9000进行编程以开始记录当活载荷超过预定的触发器时的应力时。确定触发器的适当大小Apriori从受控的负载测试中。
例如，假设确定在给定位置观察到的重型卡车会产生6.0 KSI的峰值应力。然后将软件触发器设置为5.9 ksi，用于这些量具。如果压力超过该值，则记录时间历史记录。还记录了在触发事件之前记录的数据，例如五秒钟（即维持五秒钟的缓冲区）。CR9000继续记录额外的指定时间段，说五秒钟，然后停止记录。这些通道通过数字平衡算法在整个半小时内自动重新归零，被监测为触发时间的历史。在现场确定缓冲区和总记录时间的适当长度。该技术提供了足够的时间依赖性数据和对高应力范围事件的验证方法，以确保将虚假信号排除在应力范围直方图之外。
应力范围直方图开发使用rainflow cycle counting method contained in the CR9000’s instruction set. The stress-range histograms were generated continuously and did not operate on triggers, thus all cycles were counted. In addition, the histogram was updated every 10 minutes. Thus, in the event of a power failure, a minimal amount of data were lost. The stressrange bins were divided into 0.5 ksi intervals. The results of the research will be incorporated in the AASHTO LRFD Bridge Design Specifications.