Free vibrations of a taut cable with an attached linear viscous damper are investigated in detail using an analytical formulation of the complex eigenvalue problem. This problem is of considerable practical interest in the context of stay-cable vibration suppression in bridges. An expression for the eigenvalues is derived that is independent of the damper coefficient, giving the range of attainable modal damping ratios and corresponding oscillation frequencies in every mode for a given damper location without approximation. This formulation reveals the importance of damper-induced frequency shifts in characterizing the response of the system. New regimes of behavior are observed when these frequency shifts are large, as is the case in higher modes and for damper locations further from the end of the cable. For a damper located sufficiently near the antinode in a given mode, a regime of solutions is identified for which the damping approaches critical as the damper coefficient approaches a critical value. A regime is developed to indicate the type of behavior in each mode for any given damper location.

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and Technology is to use metric units in all its published materials. Because this report is intended for the U.S. building construction industry which uses in-pound units, it is more practical and less confusing to use inch-pound units, in some cases, rather than metric units within quoted text. However, in most cases, units are presented in metric and the inch-pound system. DisclaimerCertain commercial entities, equipment, products, or materials are identified in this document in order to describe a procedure or concept adequately or to trace the history of the procedures and practices used. Such identification is not intended to imply recommendation, endorsement, or implication that the entities, products, materials, or equipment are necessarily the best available for the purpose.iii ABSTRACT This report presents an experimental and computational study of two steel beam-column assemblies, each comprising three columns and two beams. The two beam-column assemblies represent portions of the structural framing system of two ten-story steel frame buildings, which were designed as part of the National Institute of Standards and Technology research program aimed at prevention of disproportionate structural collapse. One building was designed for Seismic Design Category C (SDC C) and the other for Seismic Design Category D (SDC D). The beam-column assemblies were taken from the exterior moment-resisting frames of these buildings. One test specimen, which was part of the SDC C building, had welded unreinforced flange-bolted web (WUF-B) connections, and the other, which was part of the SDC D building, had reduced beam section (RBS) connections. The specimens were subjected to monotonically increasing vertical displacement of the unsupported center stub column to observe their behavior under a simulated column removal scenario, including the development of catenary action in the beams. The test was terminated when a collapse mechanism of each assembly was developed and the vertical load-carrying capacity was depleted. The primary test specimen response characteristics were measured. These included vertical and horizontal displacements at specific locations, rotations at beam ends, strains at various locations, and the applied load. In addition, a high speed video camera was used to record the specimen response, including the failure mode and sequence of the beam-to-column connections at the center column.For both the WUF-B and RBS test specimens, the beam-column assemblies remained initially in the elastic range at small displacements of the center column, where the behavior of the beams was dominated by flexure. With increased vertical displacement, the beam connections exhibited yielding and large tensile axial forces developed in the beams. The axial tension in the beams increased until the connections could no longer sustain the combined bending and axial stresses, and the beam-column assemblies failed.The failure of the WUF-B test specimen was characterized by the following sequence: (1) local buckling of the top ...

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