Naslov
Effects of vehicles and railings on aeroelastic behavior of bridge deck

Autori
Buljac, Andrija

Vrsta, podvrsta i kategorija rada
Ocjenski radovi, diplomski rad, diplomski

Fakultet
Fakultet strojarstva i brodogradnje

Mjesto
Zagreb

Datum
05.12

Godina
2014

Stranica
61

Mentor
Kozmar, Hrvoje ; Pospišil, Stanislav

Ključne riječi
Bridge-deck section ; vibrations ; aerodynamics ; aeroelasticity ; small-scale experiments ; climatic wind tunnel

Sažetak
In the last few decades, significant development in building technology has been achieved, which allowed for a major increase in span length of cable-stayed and suspension bridges. Consequently, these structures characterized with low natural frequencies and mechanical damping become particularly sensitive to wind effects. Hence, detailed study of bridge aeroelastic properties has become one of the main parameters in design of long-span cable-stayed and suspension bridges. The focus of this thesis is on analysis of bridge deck susceptibility to movement-induced vibrations due to interaction of airflow and vibrating bridge-deck section. The fundamental aeroelastic phenomena experienced by bridge sections are flutter and galloping. Aerodynamic flutter of the bridge section develops due to fluctuating forces acting on a bridge deck, feeding energy into the system during every bridge-deck oscillation. When this energy cannot be dissipated through the mechanical damping of the system, the flutter instability occurs. Galloping is a low frequency, large amplitude instability in direction normal to the wind flow, which occurs due to a lack of reattachment of the flow on the bridge deck after the flow originally separated at the bluff leading edge of the bridge-deck section. While analysis of aerodynamic flutter requires dynamic tests, galloping can be studied through the quasi-steady approach by applying the Glauert – Den Hartog criterion. Flutter phenomenon has been recognized in the 19th century as a dynamic aeroelastic instability with respect to airfoils, but remained studied in the aerospace community only until the year 1940 and the collapse of the Tacoma Narrows bridge in USA due to torsional flutter, when this physical phenomenon started to be investigated more closely in the wind and structural engineering communities as well. Even though the computational methods have been intensively developing, small-scale wind-tunnel experiments are still the most utilized practice for analysis of this phenomenon. Hence, a comprehensive experimental study on dynamic behavior of bridge deck sections exposed to wind is carried out with a particular focus on the influence of vehicles and railings on aeroelastic behavior of a characteristic bridge-deck section. The effects of vehicles and railings on aeroelastic behavior of the investigated bridge-deck section are analyzed in terms of aeroelastic flutter derivatives. The results are compared to those of the thin plate with high aspect ratio, which proved to be aerodynamically stable with respect to flutter phenomenon. The effects of the dynamic stiffness of the system on flutter derivatives are studied as well. Moreover, in order to determine bridge deck sensitivity to galloping instability, it is necessary to determine the time averaged aerodynamic force coefficients as a function of the wind incidence angle. For this purpose, an experimental stand for the measurement of drag and lift forces acting on a bridge-deck section was accordingly developed. The wind flow around the bridge-deck section was computationally modelled for different wind incidence angles as well, and time averaged aerodynamic force coefficients are calculated. The computational results are in good agreement with the wind-tunnel experiments.

Izvorni jezik
Engleski

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