31 Leveraging Hybrid Simulation for Vibration-Based Damage Detection Studies 335 with destructively testing field structures. Furthermore, in contrast to conventional experiments where damage is unnaturally prescribed using surrogate techniques to mimic structural damage mechanisms, damage can be naturally developed in the experimental substructure under specific prescribed loading scenarios, including historical records of extreme events. 31.2 Hybrid Simulation of Vibration Testing and Damage Progression 31.2.1 Description of Case Study Structure The case study structure used in this paper is a seven story three-dimensional truss comprised of 32 nodes and 91 members (Fig. 31.2). Due to a limitation on the length of the experimental member introduced by the load frame used to prescribe displacements and record restoring forces in the hybrid simulation, the dimensions of the truss are relatively small producing an approximate 3.7 m total height of the structure. For simplicity, all members of the truss were modeled as nominally identical L51x51x4.8 (L2x2x 3 16 ) A36 steel angles. Additionally, the experimental substructure was limited to a single diagonal strut at the first story of the structure (denoted in green in Fig. 31.2 between nodes 4 and 5). This 66 cm (26 in.) long member was bolted to a pair of 9.5 mm (0.375 in) thick steel gusset plates using 1.27 cm (0.5 in.) diameter grade 8 high strength bolts and flat washers. These gusset plates were then used to secure the experimental substructure to a MTS 810 load frame with 250 kN capacity using mechanical wedge grips. This experimental substructure within the load frame is visible in Fig. 31.1. Within the analytical substructure, all members were idealized with linear elastic material properties and pinconnections. However, nonlinear geometric effects were incorporated in the dynamic time history analysis performed within the hybrid simulation routine implemented and described in the following section. Lastly, joint masses were uniformly scaled to produce a fundamental period of approximately 2s for the structure, and Rayleigh damping was prescribed to produce a range of reasonable damping ratios across the first eight modes of the full structural model. a b c Fig. 31.2 Seven story truss structure used for case study: (a) isometric view of truss geometry; (b) elevation views; (c) details of experimental substructure with bolted connection
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