The following article appeared in the Research Focus, Issue No.33, May 1998

Design for Safety of Structures Subject to Dance Type Loads

Practising engineers find it difficult to predict structural response to dynamic crowd loads and there is a general lack of understanding of these loads. Research at UMIST, sponsored by EPSRC and supported by BRE, has led to a better understanding of the loads and to methods of determining structural response to these crowd loads.

Dance is movement with rhythmic steps and actions, usually to accompanying music. Similar movements include jumping, stamping and aerobics. The loading is thus related to the dance frequency and is periodical. These loads are here termed as dance type loads. The maximum response produced by dancing occurs when jumping is involved, and it is this situation which is of concern in this project.

The safety of structures subject to dance type loads not only relates to the loads but also the structure itself. Using pre or post-stressing techniques and high strength materials, long span structures can be built to accommodate static loads and thereby provide clear space and viewing. This leads to structures which have relatively low natural frequencies and which are dynamically sensitive. In the extreme this has produced structures like cantilevered grandstands which are desirable for watching sports matches but are particularly vulnerable to dynamic loads which leads to a potential safety problem. Structural vibrations induced by dance type loads is primarily a concern for floors used for dance, aerobics, keep-fit exercise and pop concerts, and grandstands used for pop concerts.

The project is a continuation of previous research and one of the main aims is to investigate the dynamic crowd effect when a crowd of people is involved, i.e. attenuation of loading due to the lack of synchronisation of the crowd. This is required to deal with practical situations and is important for the calibration of calculation methods with full-scale measurements, which is seen as an important aspect of the work. A unique feature of this project is to use the combined resources of UMIST and BRE. Large scale controlled experiments, with crowds of up to 64 students were conducted at the BRE’s Cardington steel test building in October 1997, and these tests produced a significant amount of useful information.

Dynamic crowd loads have been considered in BS 6399 part 1: Loading for Buildings which came into effect on 15 September 1996. BRE Digest 426, Response of Structures Subject to Dynamic Crowd Loads, provides background information to the related clauses in the code.