Basic Dynamic Parameters Research Articles

Floor response of yielding structures

The New Zealand loading code, NZS 4203:1976, specifies design forces for parts and portions determined on the assumption that maximum floor accelerations are related to the yield level for ordinary structures. The code committee were aware that there was a scarcity of factual information on the subject and suggested that studies be carried out. The work described in this paper is aimed at investigating floor motions in buildings responding elastically and inelastically to earthquake motions and thus obtaining a basis for the design of parts and portions and also ancillary services. Twelve structures ranging in height from one to eight storeys and of varying structural type were analysed using a dynamic computer program for elastic response and for two different levels of structure yield strength. Time histories of floor acceleration were obtained at each floor level and from these the maximum absolute values were obtained. To derive loadings on flexible and flexibly mounted components, response spectra were calculated for upper floors and thus the amplification factors relating floor spectra to ground spectra were derived. The basic dynamic parameters used were the El Centro 1940 N-S earthquake record, with constant damping and material strain hardening ratios. The effect of variations in these parameters was studied on a limited number of the structures. From results obtained, tentative equations have been formulated for the design of both rigid and flexible components. For flexible components the floor amplification function was found to be very complex and due allowance must be made for uncertainties in dynamic parameters such as component damping and for factors such as higher mode effects influencing the response.

Frequency response and electronic testing for constant-temperature hot-wire anemometers

The author aims to identify theoretically and to measure electronically the basic dynamic performance parameters of the constant-temperature hot-wire anemometer. It is found that a well designed anemometer behaves as a third-order control system which allows for a two-parameter optimization of its dynamic response. The cut-off frequency of the anemometer and related dynamic parameters can be estimated by means of electronic square- and sine-wave tests.

Longitudinal Dispersion in Open Channels

The effects of cross-sectional geometry and velocity distribution on the dispersion process in straight, uniform open channels with large width-to-depth ratio are investigated. The method of investigation follows Taylor’s approach and thus the results apply after the elapse of an initial period during which a constant dispersion coefficient has developed. The results of the analysis show that under the assumed conditions the longitudinal dispersion coefficient can be described by the general expresion \IK\N = \ICRu\N\D*\N; in which \IR\N = the hydraulic radius, \Iu\N\D*\N = the shear velocity, and \IC\N = a factor. The variation of \IC\N with basic geometric and dynamic parameters is presented in the form of equations and diagrams for two velocity profiles (logarithmic and power law), and two cross-sectional shaped (triangular and circular arc). It is found that \IC\N varies significantly with cross-sectional shape, width-to-hydraulic radius ratio, and the Reynolds number. The calculated values of \IC\N and its pattern of variation are compared to available data for open channels with irregular cross section.