Kết cấu có hình dạng đơn giản, ƯSBD thường phân bố khá đồng đều trong kết cấu, trị số không lớn và thường dao động trong miền đàn hồi của VL, nên phép đo thường không có sai số đáng kể. - Kết cấu có hình dáng phức tạp hoặc ghép từ nhiều phân tử với nhau việc khảo sát trạng thái ƯSBD có khó khăn vì ở đây sự phân bố ƯSBD thường thay đổi lớn, những điểm lân cận nhau có thể có trị số rất khác nhau (do giai đoạn làm việc là đàn hồi hay biến dạng dẻo) | TRUCK POSITION ft. Figure 29 Measured and Computed Stresses - Floor Beam at Midspan. TRUCK POSITION ft. 8 1 __8_ 2_ x 8 1 x x 8 2 Figure 30 Measured and Computed Stresses - Floor Beam at Quarter Span. Bai giang Thí nghiện2Cẫu - Page 154 of 168 Appendix A - Field Testing Procedures The motivation for developing a relatively easy-to-implement field testing system was to allow short and medium span bridges to be tested on a routine basis. Original development of the hardware was started in 1988 at the University of Colorado under a contract with the Pennsylvania Department of Transportation PennDOT . Subsequent to that project the Integrated technique was refined on another study funded by the Federal Highway Administration FHWA in which 35 bridges located on the Interstate system throughout the country were tested and evaluated. Further refinement has been implemented over the last several years through testing and evaluating several more bridges lock gates and other structures. The real key to being able to complete the field testing quickly is the use of strain transducers rather than standard foil strain gages that can be attached to the structural members in just a few minutes. These sensors were originally developed for monitoring dynamic strains on foundation piles during the driving process. They have been adapted for use in structural testing through special modifications and have a 3 to 4 percent accuracy and are periodically re-calibrated to NIST standards. In addition to the strain sensors the data acquisition hardware has been designed specifically for field use through the use of rugged cables and military-style connectors. This allows quick assembly of the system and keeps bookkeeping to a minimum. The analog-to-digital converter A D is an off-the-shelf-unit but all signal conditioning amplification and balancing hardware has been specially designed for structural testing. The test software has been written to allow easy configuration test length
