178 M.Majowiecki STEP LOAD PROELE-A-A Rce Fig.4.Sliding and wind snow accumulations step loads magnitude of the leopardized accumulations in the roof are of 4-15 kN!;local overdi- mensioning was necessary in order to avoid progressive collapse of the structural system. 2.2 Wind Loading-Experimental Analysis on Scale Models:Rigid Structures-Quasi Static Behaviour The Cp factors:the Olympiakos Stadium in Athens Tests have been performed in two distinct phases,the first phase has been devoted to the characterization of the appropriate wind profile in the BLWT,the second one has been dedicated to the identification of the pressure coefficients on the roofing of the new stadium.Because of the great number of pressure taps on the roofing(252), the second phase consisted of three distinct measurement sets. The stadium is located near to the sea,as a consequence a "sea wind profile" with the parameters listed below and taken from literature and laboratory expertise, seems to be a good approximation of the wind profile in the area(Fig.5): profile exponent a =0.15/0.18 (level ground,with few obstacles,sea), roughness length zo =5/15 cm (cultivated fields), integral length scale Lw=50/100m. In the following paragraph the characteristics of the wind profile actually ob- tained in the BLWT are examined,and the consistency of the choice in the chosen geometric scale (1:250)
178 M. Majowiecki Fig. 4. Sliding and wind snow accumulations step loads magnitude of the leopardized accumulations in the roof are of 4-15 kN!; local overdimensioning was necessary in order to avoid progressive collapse of the structural system. 2.2 Wind Loading-Experimental Analysis on Scale Models: Rigid Structures-Quasi Static Behaviour The Cp factors: the Olympiakos Stadium in Athens Tests have been performed in two distinct phases, the first phase has been devoted to the characterization of the appropriate wind profile in the BLWT, the second one has been dedicated to the identification of the pressure coefficients on the roofing of the new stadium. Because of the great number of pressure taps on the roofing (252), the second phase consisted of three distinct measurement sets. The stadium is located near to the sea, as a consequence a “sea wind profile” with the parameters listed below and taken from literature and laboratory expertise, seems to be a good approximation of the wind profile in the area (Fig. 5): profile exponent α = 0.15/0.18 (level ground, with few obstacles, sea), roughness length z0 = 5/15 cm (cultivated fields), integral length scale LU = 50/100 m. In the following paragraph the characteristics of the wind profile actually obtained in the BLWT are examined, and the consistency of the choice in the chosen geometric scale (1:250)
Widespan Membrane Roof Structures 179 XA△AP ADABAPBAPA AOHNA KEPATIINI KAIEAPIANH MOEXATO BYPONAE NE AnOE AHMHTP例DE AIOYnOAH 233.699 3KM APANETEONA AAAIO中AAHPO RK孙A 910.906 1.830.93010KM EAAHNIKO Fig.5.Geographic location of the stadium The model has been made in a geometric scale of 1:250 and includes:the roofing, the stands,all the structures of the stadium,and other private and public buildings not far then 250 m (in full scale)Figs.10-11 from the centre of the stadium.The geometric scale has been chosen in order to fulfil the similitude laws (Figs.6-9). In turn the extension of the model around the stadium was dictated by the chosen scale and by the diameter(2m)of the rotating platform over which the model has been placed in the wind tunnel. Fig.6.Profile of mean wind velocity Fig.7.Profile of the turbulence intensity
Widespan Membrane Roof Structures 179 Fig. 5. Geographic location of the stadium The model has been made in a geometric scale of 1:250 and includes: the roofing, the stands, all the structures of the stadium, and other private and public buildings not far then 250 m (in full scale) Figs. 10-11 from the centre of the stadium. The geometric scale has been chosen in order to fulfil the similitude laws (Figs. 6-9). In turn the extension of the model around the stadium was dictated by the chosen scale and by the diameter (2m) of the rotating platform over which the model has been placed in the wind tunnel. Fig. 6. Profile of mean wind velocity Fig. 7. Profile of the turbulence intensity 14 16 18 20 22 24 26 0 10 20 30 40 50 60 70 80 90 approx esponenziale approx logaritmica
180 M.Majowiecki 1o" Fig.8.Spectral density of the longi- Fig.9.Integral length scale at differ- tudinal component of the wind veloc- ent levels(“fitting”with Von Karman ity(“fitting'”with Von Karman spectral spectral density) density) Fig.10.Circle which identifies the location of the buildings included in the model The roofing has been equipped with 252 pressure taps,of which 126 at the extrados and 126 at the intrados.in order to get the net pressures on the roofing.In the model the roofing of the stadium (Fig.12)has a box structure in order to allow for the settlement of the pressure taps inside.A minimum thickness of about 7 mm has been required for the roofing structure to allow for the insertion of the pneumatic
180 M. Majowiecki Fig. 8. Spectral density of the longitudinal component of the wind velocity (“fitting” with Von Karm´an spectral density) Fig. 9. Integral length scale at different levels (“fitting” with Von Karm´an spectral density) Fig. 10. Circle which identifies the location of the buildings included in the model The roofing has been equipped with 252 pressure taps, of which 126 at the extrados and 126 at the intrados, in order to get the net pressures on the roofing. In the model the roofing of the stadium (Fig. 12) has a box structure in order to allow for the settlement of the pressure taps inside. A minimum thickness of about 7 mm has been required for the roofing structure to allow for the insertion of the pneumatic 10-1 100 101 102 103 10 -2 10 -1 100 15 20 25 30 35 0 10 20 30 40 50 60 70 80 90