Dynamic performance requirements for permanent grandstands

Side and Plan views of the Barclay Stand with Accelerometer orientation

Vibration Test Equipment

Engine Hoist Crane

Vibration

Norwich City Football Stadium

Project: 2010
Location: Norwich
Country: United Kingdom
Sector: Vibration Assessment

Following the previous vibration survey carried out by Civil Engineering Dynamics in 2004, a need for measurements to include the response of the roof component of the Barclay Stand was identified. Impulses due to the crowd simultaneously rising to their feet were reported by catering staff working inside the Barclay stand. The Jarrold Stand was under construction at the time of our previous survey.

Hence, the Norwich City Football Stadium commissioned a vibration test to find the fundamental frequencies of vibration for seating decks of the Barclay Stand and the Jarrold Stand. Civil Engineering Dynamics undertook vibration measurements at strategic locations on the two stands to determine their lowest natural frequencies of vibration in vertical and horizontal directions.

The Barclay Stand (East) has a steel structure with concrete decks with two tiers of seating. The Jarrold Stand (South) is supported by a reinforced concrete structure and has one tier of seating. The stadium is currently used only for sporting events so rhythmic synchronization is likely to be limited to intermission musical events, chanting, singing, clapping and foot stamping during football matches.

The weather during the survey was dry, with minimal wind. The stadium itself was not in any use by the public and there were no maintenance works taking place during the day of the test.

The Dynamic performance requirements for permanent grandstands subject to crowd action specify the lowest frequency of vibration allowable for a permanent grandstand. As the Norwich City Football Stadium is currently used only for sporting events, with possible use of incidental music during matches, the guideline suggests that the fundamental frequency of the seating stand should be above 5Hz.

To provide adequate levels of comfort for all types of events including music concerts, the grandstands should have vertical natural frequencies greater than 6Hz.

An eight channel PC-based vibration monitoring system was used to measure vibration. The system comprised of four Brel and Kjr 4378 accelerometers and four Lance Piezoelectric accelerometers. Brel and Kjr 4378 accelerometers were connected to Brel and Kjr 2635 Charge Amplifiers. Similarly, Lance Piezoelectric accelerometers were connected to 4 channel Brel and Kjr NEXUS signal conditioner.

The signals from Brel and Kjr 2635 Charge Amplifiers and NEXUS signal conditioner were fed into a 16-bit Data Acquisition card, with all data being logged and processed in Virtual Instrument designed using LabVIEW. A sampling rate of 1280 Hz and sample length of 10 seconds were used for simultaneous measurement of 8 channels.

The NEXUS signal conditioner was set to low pass filter the data at 100 Hz with the high pass filter set to 0.1 Hz. This filtering therefore included information in the frequency range of interest between 0.1 Hz and 100 Hz. During calibration the low pass filter was set to 1 kHz. A Brel and Kjr 4294 Calibration exciter was used for the pre/post calibration of the accelerometers. MATLAB was used for processing the time histories and spectra.

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