Nicholas P. Jones

Wind engineering as a discipline was previously addressed within ASCE in three primary committees. The Wind Effects Committee, which was part of the Dynamics Technical Activities Committee structure in the Structural Engineering Institute, concentrating on wind effects on structures. This was an active committee, which met regularly at the Structures Congress and supported technical sessions at Structures Congresses; another primary responsibility was the review of articles for the Journal of Structural Engineering. The Aerodynamics Committee in the Aerospace Division focused more generally on wind (atmospheric) flows, sometimes considering fluid structure interaction. This was also an active committee, in fact one of the more active committees in the Aerospace Division. It also had traditionally met at the Structures Congress. Unfortunately, its connection to the missions of the Aerospace Division and other committees within the Division had been rather weak. The ASCE-7 Wind Loads Committee, which has overlap in membership with the above two committees, is also an active and important committee within the SEI.

A database of 4000 vibrations measurements from 1000 buildings was used to derive models for building period and damping. Herein, we focus on the dominant trends in the median and standard deviation of the damping with respect to basic building parameters such as height, material and frame type. We also outline the statistical techniques used to identify the most important building parameters and separate the sources of variability, while avoiding model over-fitting.

The mitigation of in-plane stay oscillation in cable-stayed bridges is commonly addressed by placing an external mechanical damper, linear or nonlinear, on each stay or by introducing transverse cross-ties among cables. Although the problem of a cable with a single external damper has found significant attention in the past and different techniques have been proposed for the solution of the free-vibration problem, limitations are related to the fact that the location of the damper is usually very close to the cable end (on the bridge deck side) due to geometric constraints, leading to inherently low modal damping in the fundamental modes. In this paper the installation of more than one damper on an individual stay is considered to overcome such limitations and to increase the overall performance of the system. An existing procedure, based on the linearized taut-string theory, was modified to allow for the presence of multiple external discrete viscous dampers. The case of two devices with arbitrary locati...

Analytical solutions are used to investigate the free vibrations of tensioned beams with a viscous damper attached transversely near a support. This problem is of particular relevance for stay-cable vibration suppression, but no restrictions on the level of axial load are introduced, and the results are quite broadly applicable. Characteristic equations for both clamped and pinned supports are rearranged into forms suitable for numerical solution by fixed-point iteration, whereby the complex eigenfrequencies and corresponding damping ratios can be accurately computed within a few iterations. Explicit asymptotic approximations for the complex eigenfrequencies are also obtained, subject to restrictions on the closeness of the eigenfrequencies to their undamped values. These asymptotic approximations are expressed in the same “universal” form identified in previous studies. It is observed that the maximum attainable modal damping ratios and the corresponding optimal values of the damper coefficient can be si...

Exact analytical solutions are formulated for free vibrations of tensioned beams with an intermediate viscous damper. The dynamic stiffness method is used in the problem formulation, and characteristic equations are obtained for both clamped and pinned supports. The complex eigenfrequencies form loci in the complex plane that originate at the undamped eigenfrequencies and terminate at the eigenfrequencies of the fully locked system, in which the damper acts as an intermediate pin support. The fully locked eigenfrequencies exhibit “curve veering,” in which adjacent eigenfrequencies approach and then veer apart as the damper passes a node of an undamped mode shape. Consideration of the evolution of the eigenfrequency loci with varying damper location reveals three distinct regimes of behavior, which prevail from the taut-string limit to the case of a beam without tension. The second regime corresponds to damper locations near the first antinode of a given undamped mode shape; in this regime, the loci bend b...