Verification of Crowd Dynamic Excitation Estimated from Image Processing Techniques

Dynamic structural responses of a major UK stadium have been measured during a series of high-profile events. In order to verify and validate recent approaches to the determination of vibration responses, a series of models have been developed and comparisons between measured and predicted results made. Using advanced image recognition and data processing techniques, video records of the events were used to determine approximations to the real forces induced by the crowds. The image processing is based on a digital correlation method and on post-processing aimed at decreasing image noise disturbance (due for example to camera flashes in the video). The output is the velocity field of the grabbed area. These data are further exploited to estimate the load on the structure. The forces estimated from the image processing have then been used, in conjunction with a highly detailed and accurate FE model, to determine improved estimates of the responses. Comparisons are made between design, measured and back-analysis results using both codified and real crowd forces. The accuracy of the crowd dynamic forces determined from image processing is assessed.