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Bài giảng môn học thí nghiệm cầu part 9

Khảo sát trên đối tượng mô hình thì kết quả tính toán ƯSBD chỉ nhận được qua một quá trình tính toán chuyển đổi tương tự qua các hệ số tỷ lệ của các tham số đo nên có thể có sai số nhỏ, dẫn đến lệch lạc kết quả. Nhưng vì số lượng đối tượng thí nghiệm nhiều, nên tổng hợp nhiều số liệu cũng cho được số liệu đáng tin cậy. | D frame elements were used to represent the truss members stringers and floor beams. The deck was represented by a combination of transverse beam elements and plate elements. The beam elements provided the load transfer characteristics of the corrugated deck while quadrilateral plate elements were used only to receive the wheel loads and distribute the wheel loads to the beams. To provide the ability to represent the actual boundary conditions linear displacement springs were placed at the truss support locations. In order to facilitate comparison of the computed and measured responses strain gage locations were defined that corresponded to the same locations defined in the field. The same gage identifications were used so that comparisons could be made accurately and efficiently. The entire computer model including geometry boundary conditions member cross-sections and gage locations was generated graphically and shown in Figure 7. Even though the geometry of the structure was well defined there were various parameters that were not well known. These parameters included the effective stiffness of the deck I of the transverse beam elements and the effective spring stiffness k required to simulate the truss support conditions. Initial cross-section properties of the truss members stringers and floor beams were obtained directly from AISC property tables. Because the truss members did not exhibit any deterioration it was assumed that those stiffness parameters were accurate. Inspection of the stringers and floor beams did indicate probable section loss. As a conservative starting point all of the support spring constants were initially set to zero. Loading of the model was accomplished by defining a two-dimensional model foot print of the test vehicle consisting of a group of point loads and then placing the truck model on the structure model. Truck crossings were simulated by moving the truck model at discrete positions along the same paths used during the field .