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Abstract
Excessive vibrations and deflections of modern flexible structures can be imposed by crowd movements. Human actions impose random loads, but present U. S. codes regard the loads as deterministic statically equivalent quantities that are defined using engineering judgement, experience and load surveys. The peak load values, selected for design, are sufficiently large to insure against structural failure. This is a strength design requirement. However, excessive deflections and human discomfort should be admissible design criteria.
The objective of the research was to define the dynamic loads generated by activities involving motion such as walking, marching and running. In order to measure forces generated by one individual, as well as groups of two and four subjects performing prescribed activities at Fears Structural Engineering Laboratory, we constructed and instrumented a special force platform with a flat transfer function in the frequency range of the imposed forces. We conducted a large number of tests using three loading types: walking at different speeds, marching and running. Individual load-time histories were modeled by several dependent descriptive parameters. The descriptive parameters were treated as functions of one independent variable in a regression model.
A simulation computer program was written to use the experimental information, the simulated time overlap between the right foot and the left foot, and the time phase lag between people in order to extrapolate loads imposed by large groups of various sizes. The simulated results compared closely with the corresponding laboratory-measured data in the frequency domain.
As the final phase of the research, a simulation computer program was written to consider the spatial relation of moving loads. This program is a very effective tool in defining the load-time histories for the nodes of a modeled floor and/or a walkway. A finite element package was used to predict the response of a wood-joist floor using the simulated human loading.
