Large roofs and sports stadiums Wind loading and structural response Lecture 20 Dr. J.D. Holmes Large roofs and sports stadiums

Large roofs and sports stadiums Entertainment centres, exhibition centres, sports arenas etc Quasi-steady approach is not applicable Resonant effects can be significant Bending moments in arches and domes are sensitive to distribution of wind load

Large roofs and sports stadiums General flow characteristics : Separation “bubble” Stagnation Point Fluctuating re-attachment point Shear layer positions: High turbulence Low turbulence Mainly attached flow on large roofs

Large roofs and sports stadiums General flow characteristics : Separation point On arched roof, separation occurs downstream of apex

Large roofs and sports stadiums Mean pressure distributions : U.W.O. Wind-tunnel tests Fluctuations in pressure will generate downwards pressures for short times

Large roofs and sports stadiums Mean net pressure distributions (cantilevered stadium roof): blocked at rear -1.3 -1.2 -1.1 -1.0 -0.7 -0.6 -0.4 -0.2 -0.1 -0.8 0.0 0.2 0.1 -1.4 C/L gap at rear reduces net pressures

Large roofs and sports stadiums Arched roof : L S R he wind loads depend strongly on R/S (rise/span) less strongly on L/S and he/S

Large roofs and sports stadiums Arched roof (Cp) : +0.4 -0.4 -0.8 +0.3 +0.2 -0.3 -0.6 +0.5 -0.5 -0.25 R/S = 0.2 he/R = 0.45 L/S = 1.0  = 0o increasing L/S  pressures on roof become more negative

Large roofs and sports stadiums Arched roof (Cp) : -0.3 -0.7 +0.2 -1.0 -0.4 -0.5 +0.4 +0.3 -0.2 -0.6 +0.1 -0.45 -0.9 higher negative values

Large roofs and sports stadiums Arched roof (Cp) : -0.2 -0.25 -0.3 -0.4 -0.5 -0.7 -0.9 +0.4 +0.2 +0.5 -0.15 positive lower negative values R/S = 0.5 he/R = 0.45 L/S = 1.0  = 0o

Large roofs and sports stadiums Structural loads - effective static load distributions Instantaneous pressure distributions vary greatly from time to time due to turbulence, vortex generation etc. Shapes may vary greatly from the mean pressure distribution Need to identify those distributions which produce maximum load effects

Large roofs and sports stadiums Structural loads - effective static load distributions Wind-tunnel methods for design wind loads : 1) Direct approach : simultaneous time histories from the whole roof are recorded and stored. Later weighted with structural influence coefficients to obtain time histories of load effects. Instantaneous pressure distributions are identified and averaged. 2) Correlations between pressure fluctuations at different parts of the roof are measured and used to determine effective static load distributions (Lecture 13, Chapter 5) Correlations for separated parts of a large roof are low: hence potential for significant reduction in peak effective loads and peak load effects (b.m.’s, axial forces etc.)

Large roofs and sports stadiums Structural loads - effective static load distributions Arch roof (Kasperski,1992) :

Large roofs and sports stadiums Structural loads - effective static load distributions Sydney Olympics, 2000 Superdome Stadium Australia

Large roofs and sports stadiums Structural loads - effective static load distributions Sydney Olympics, 2000 - 1/500 wind-tunnel model Stadium Australia Superdome

Large roofs and sports stadiums Structural loads - effective static load distributions Stadium Australia (Sydney Olympics, 2000) Panel layout for wind-tunnel testing

Large roofs and sports stadiums Structural loads - effective static load distributions Stadium Australia (Sydney Olympics, 2000)

Large roofs and sports stadiums Structural loads - effective static load distributions Stadium Australia (Sydney Olympics, 2000)

Large roofs and sports stadiums Structural loads - effective static load distributions Superdome (Sydney Olympics, 2000)

Large roofs and sports stadiums Structural loads - effective static load distributions Superdome (Sydney Olympics, 2000) Effective static load distributions for axial loads in a particular roof member

Large roofs and sports stadiums Structural loads - contribution from resonant modes Usually not significant for roofs supported all round or on two sides May be significant for cantilevered roofs : Time Vertical upwards Very large roofs may have several modes below 1 Hertz - contributions to load effects depend on similarity of mode shapes with influence lines

End of Lecture 20 John Holmes 225-405-3789 JHolmes@lsu.edu