Eccentric Lattice Tower Response to Human Induced Dynamic Loads

An excessive lateral vibration of the lightweight pedestrian bridges has initiated worldwide interest of the researchers in phenomenon known as the human and structure synchronization. Recently built slender sightseeing tower in Latvia experiences vibrations that are not con-nected with the wind induced one. The lattice steel tower is 36 m high, has low damping ratio and natural frequency of the structure is close to the natural frequency of the human pacing. This paper analyses experimentally measured response of the tower’s structure to the excita-tion caused by the human movement upstairs and downstairs. The study compares the human walking ground reaction force harmonic frequencies with the frequencies of the tower at its maximum response. It is concluded that the human movement on the stairs generates significant longitudinal and transverse force components. Even a small number of tower’s visitors cause a low frequency torsional vibration combined with transverse displacements. In the case of eccentric structure of the tower where two of critical mode shapes from the first three are the torsional ones. The results illustrate the human and structure interaction must be considered when designing the slender and lightweight sightseeing tower ensure safe exploitation and acceptable comfort levels during the exploitation. In conclusion there is a necessity to define the coupling model and synthetic formulas in order to predict tower’s sensitivity to the human movement. The given vibration acceleration limits of design guidelines are not applicable for the torsional vi-brations and should be developed a new human comfort criteri