2nd Croatian Conference on Earthquake Engineering 2CroCEE

Shock Transmission Units (STU) also known as temporary connection devices or lock-up devices are mechanical devices that offer a simple, economical way to improve the resistance of existing bridges. They are mainly used for retrofitting existing bridges to accommodate higher-intensity earthquake and breaking loads defined by new design codes for which existing bridges have insufficient bearing capacity. The basic idea of a shock transmission unit is to only distribute seismic or other suddenly applied impact loads between different substructural elements of the bridge so that bridge behaves as a rigidly connected structure. For slowly applied loads such as temperature, creep, and shrinkage, shock transmission units are not activated so the different parts of the bridge-bearing structure can move independently. They behave like “seatbelts for bridges” because they restrain bridge movement for sudden dynamic loads but allow free movement for slowly applied static loads. In order 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, the modal parameters such as natural frequency, modal shapes, and damping were obtained on the pedestrian bridge which has been strengthened with shock transmission units. In this paper, the difference between experimental and numerical modal parameters is shown from which conclusions about the impact of shock transmission units on global bridge stiffness are made. Also, the proposition for numerical modeling of shock transmission units and their influence on overall seismic action will be given.