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Title: Accounting for bridge dynamic loads using moving force identification system (MFIS)
Authors: Yu, Ling
Degree: Ph.D.
Issue Date: 2002
Abstract: Bridge dynamic loads are very important for pavement and bridge design. A large number of studies indicate that bridge dynamic loads increase responses and road surface damage by a factor of 2 to 4. Many researchers have investigated the effects of bridge dynamic loads on bridges and pavements. However, these traditional methods can only measure static axle loads and are therefore, subject to bias. These all prompt the need to develop a system that can not only measure the static but also the dynamic wheel loads, the moving force identification system (MFIS). The main objective of this study is to develop the MFIS system to identify moving time-varying axle loads on bridges. The secondary objective is to account for the dynamic axle loads with the aid of the MFIS developed. In this study, the moving force identification system (MFIS) developed, consists of four methods which are the interpretive method I (IMI), interpretive method II (IMII), time domain method (TDM) and frequency-time domain method (FTDM). The MFIS is developed using both MATLAB and FORTRAN languages. A preliminary comparison of the four methods involved in the MFIS has been carried out. The merits, disadvantages and limitations of each method have been understood. The effects of various parameters on each method have been critically investigated based on the laboratory tests of a two-axle vehicle model. Some suggestions have been made in order to use the MFIS system correctly. In order to improve the accuracy of the MFIS, the singular value decomposition (SVD) technique has been introduced to solve the over-determined equation sets established in both TDM and FTDM. By contrast to the previous pseudo inverse (PI) solution, the SVD technique can effectively enhance the identification methods and improve the accuracy, particularly in the case of FTDM. Besides identification of two axle loads of the vehicle from bending moment responses, the acceleration responses of the bridge are also employed to identify the moving forces. Both the simulations and laboratory tests are used to investigate the feasibility. Furthermore, in order to assess the robustness and applicability of the MFIS to multiple axle loads on bridges, a comparative study scheme has been planned and performed. Different multiple axle vehicles have been designed and constructed in the laboratory and three suspension systems and two connection ways between tractor and trailer simulated. Various multiple axle loads have been identified. The effects of parameters of both vehicle and bridge, and the characteristics of bridge-vehicle system have been assessed based on the identified results. Much effort has concentrated on investigating the correlation of impact factors with different parameters of bridge-vehicle system. The laboratory study was conducted to investigate parameters that will cause high impact factor. Two kinds of bridge-vehicle systems were simulated in the laboratory. One is different multiple axle vehicles and beam-like bridge system, and the other is the short span multi-girder plate bridge and vehicle system. It is concluded that the MFIS developed is a successful moving force identification system. After introducing the SVD technique, the system has been significantly improved, particularly for the FTDM method involved in the system. The SVD makes the system more stable and effective. In addition, the MFIS can be effectively used to account for bridge dynamic loads. The impact factors of the bridge can be evaluated and the bridge-friendly vehicles can be distinguished with the aid of MFIS.
Subjects: Hong Kong Polytechnic University -- Dissertations
Bridges -- Live loads
Structural dynamics
Pages: 1 v. (various pagings) : ill. (some col.) ; 30 cm
Appears in Collections:Thesis

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