The Izmit Bay Bridge
FORCE Technology has been strongly involved in the aerodynamic investigations for the Izmit Bay Bridge ranging from the early design considerations for the bridge deck to details of the wind screens in the vicinity of the pylons.
With a main span of 1,550m, the Izmit Bay Bridge is one of the longest suspension bridges in the world by the length of the main span. The total length of the bridge including side spans is approximately 3km. The approximately 36m wide bridge deck is of the closed box girder type with cantilevered service lanes along both sides.
The investigations were conducted for IHI Infrastructure Systems Co., Ltd.
Wind screen tests
A number of alternatives were investigated for wind shielding aiming at reducing the side force gradients for a vehicle passing the towers of the Izmit Bridge. The investigation included visualisation of the air flow, mapping of the wind speed, static measurement of the side load and overturning moment and yawing moment on three types of vehicles for a range of wind directions. In addition, the feasibility of performing the load and moment measurements on a moving vehicle was investigated. These results were very promising and will be followed up in a research project.
A large, impressive model constructed in scale 1:30 was used for the tests. The model included all the details of the deck, tower, maintenance gantry, cantilevered service lanes and other details around the tower which could have an influence on the flow. The tests demonstrated that tapered wind screens may effectively reduce the gradient in wind effects on a vehicle passing the tower in strong side wind and thus reduce the risk of accidents.
Section model tests
In the design phase, FORCE Technology conducted two section model test campaigns which led to the final deck cross section. In these section model tests, various configurations of the bridge deck were tested. The configurations included variations of parapets, barriers, wind screens and equipment on the deck. In addition, the bridge deck was tested with and without a simulation of congested traffic as well as the lightweight construction stage condition where railings and parapets were not installed.
The section model tests included investigation of aerodynamic stability and vortex-shedding characteristics. Further, the static force coefficients and the so-called aerodynamic flutter derivatives were established. All these parameters are important in the assessment of a bridge’s wind loading and aerodynamic behaviour.
Aerodynamic flutter derivatives are important in connection with the design of flexible structures such as long-span bridges. FORCE Technology has developed a unique 3D-forced motion test rig that can provide data for determination of the aerodynamic flutter derivatives in a fast and efficient manner.
With the method previously applied, FORCE Technology could provide a set of eight derivatives corresponding to a two-degree-of-freedom motion. With this new test rig, we are able to provide the full set of eighteen derivatives that describe motion in three-degrees-of-freedom.