engleski

Determination of the dynamic behavior of a bridge strengthened with shock transmission units

Shock Transmission Units (STU), also known as Temporary Connection Devices (TCD) or Lock-up Devices (LUD), are mechanical devices that provide a simple and economical way to improve the resistance of existing bridges. They are mainly used for retrofitting existing bridges to accommodate higher-intensity earthquakes and breaking loads defined by new design codes for which the existing bridges do not have sufficient load-bearing capacity. The basic idea of a shock transmission unit is to distribute seismic or other sudden impact loads only to different substructure elements of the bridge so that the bridge behaves as a rigidly connected structure. In the case of slowly acting loads such as temperature, creep, and shrinkage, the shock transmission units are not activated, so that the different parts of the bridge-bearing structure can move independently of each other. They behave like "seatbelts for bridges" because they restrain bridge movement for sudden dynamic loads but allow free movement under slowly acting static loads. To determine the real contribution of STU to the bridge stiffness and consequently, to the global dynamic behavior of the bridge in regular operating conditions, modal parameters such as natural frequency, mode shapes, and damping were determined on the pedestrian bridge, which had been strengthened with shock transmission units. The modal parameters were determined using operational modal analysis and the numerical model. This paper shows the difference between the experimental and numerical modal parameters and draws conclusions about the impact of the shock transmission units on global bridge stiffness. A proposal is also given for the numerical modeling of shock transmission units and their influence on the overall seismic action.

shock transmission units, bridges, dynamic parameters, operational modal analysis

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