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第十二讲 实验和方法作用：1让同领域的研究者在必要时可重复和验证2 证明所采用的方法是能被认可的正确方法实验和方法部份应包括以下内容1）对所用的材料、仪器、设备和系统的详细介绍2）对实验程序的说明如有必要，还需对以下内容说明3）对整个实验的概述4）选用特定材料、设备或方法的理由5）实验的特殊条件或工况，如温度、速度、压力等6）特殊设备或方法的详细介绍7）实验所应用的分析方法的描述Example oneTEST PROCEDURE（对整个实验的概述）When a structure to be analyzed is of considerable size, it is possible to test only some subsets, using substructuring procedures. Pseudo-dynamic techniques are an attractive tool for this purpose. The test specimen, assumed to be detached from a global structure, now has compatibility nodes or contact matching surfaces, which are assigned to internal degrees of freedom. In the experimental steps of the analysis, these nodes or surfaces are available to receive the installation of displacement actuators, as previously described. Furthermore, as only degrees of freedom along contact surfaces or matching nodes will be selected in this analysis, the test specimen is equivalent to a structure where condensation of internal degrees of freedom was carried out.（对所用的材料、仪器、设备和系统的详细介绍）The overall dimensions are given in Table 1 and the mechanical properties in Table 2. The test rig used for this purpose is schematically represented in Fig. 2. It consists of a simple and rigid L-shaped HEB beam arrangement with fixtures to receive two pairs of position motors. The position motors consist essentially of a precision worm gear-type speed reducer. Each pair can be driven simultaneously, therefore inducing a nodal displacement to the substructure test specimen, or they can be operated separately, generating an angular nodal rotation. （对实验程序的说明）Both superimposed motions will complete the displacement field, compatible with the kinematics state of the global structure at each time step. At each position of a clamping ring pair a load cell is inserted between the clamping rings and the screw actuator in order to measure the internal reaction force, prescribing a displacement set as shown in Fig. 2. Figures 7 show the schematic diagrams of the data acquisition system and the automated driving block to activate the set of position motors.Table 1 Dimension of structure partsElbow curvature angle (deg) 90Transverse-section mean radius r (mm)50Mean curvature radius R (mm)200Pipe thickness h (mm) 2(overall)Length of vertical and horizontal straight runs, L (mm)8000Length of elbow tangent terminations, Lt (mm)1000Table 2 Mechanical properties of structure partsMaterial Stainless steel, ASTM 204 (overall)Youngs modulus 200 GPaPoissons ratio0.3Specific mass 7850 kg/m3The external force is applied at node 4 along the vertical direction; this force depends on time t as depicted in Fig. 8. Its variation consists in uniformly increasing as a ramp until t = 0.6s, reaching a top value of 10 N and then suddenly vanishing after that time. The basic time step lengths are Dt = 200ms. It is noted that the external force does not represent any standard action; the aim of this shape function for the external load is only to investigate the accuracy of the method, once slow and sudden load changes are involved.Example twoLarge Scale Real Time Dynamic Hybrid TestingDynamic Force Control（概述）The implementation of advanced seismic testing techniques such as the effective force method and real-time dynamic hybrid testing require the implementation of dynamic force control in the hydraulic actuators. This control is sensitive to the acceleration and force measurements, to the modeling of the compressibility of fluid, to the non-linearities of the servo control system (servo-valves) and other stiffness issues as indicated by Dimig et al. (1999) and Shield et al. (2001).Proposed solution（实验所应用的分析方法的描述）Motivated by these observations and by the fact that causality requires a flexible component in order to apply a force (Paynter, 1961), in the force control scheme described here, a spring is introduced between the actuator and the structure as shown in Fig. 8. The actuator behaves as a displacement device. The tuning of the hydraulic actuator in displacement control can be done relatively easily, very precisely and independent of the structure and leads to a well behaved closed-loop transfer function with good force disturbance rejection. Hence the actuator in the control scheme of Fig. 8 is operated in closed-loop displacement control with a PIDF controller. The resulting block diagram is shown in Fig. 9. Although the system as a whole controls force input, internally the actuator operates in closed-loop displacement control. Hence, there is no need for an additional force feedback loop to ensure stability. Besides, this would prevent the actuator responding to spurious force errors caused by the sources listed above. The force transfer function is given by: (7)In the ideal case where C = 1/G, the transfer function has the value of one. The advantages of using the series spring are also now apparent: (1) the actuator can be well tuned and operated in displacement control, (2) it provides for one more parameter than can be altered in the control design (the oil stiffness cannot be) and (3) the term KLC(1-CG) in the transfer function indicates that the smaller the value of KLC the less sensitive is the transfer function to deviations of C from 1/G. Hybrid Testing（对实验程序的说明）A hybrid test was performed at University at Buffalo on a two-story structure with the first story built on the shake table and the second story simulated. The hybrid test setup is shown in Fig. 15b. Fig. 15a shows the two stories model tested for reference placed on a 5-dof (degree of freedom) 50 tons capacity shake table, while Fig 15b shows the hybrid test set-up placed on a 6- dof 50 tons capacity shake table. The model was a 1:3 scaled model with separated lateral and gravity load resisting systems consisting of 2m x 3m, 4.5 tons, steel floors (representing the scaled mass) supported by double hinged 1.2m high “gravity columns” and two portal lateral moment resisting steel frames (Kusumastuti et al., 2005). The force in the hybrid test set-up was delivered with an MTS 244.51S 100tons capacity, 0.6m stroke actuator