Dynamic properties of Byblos municipality building with soil-structure interaction using geophysical methods

Abstract

Byblos city is located on the coast north of Beirut, Lebanon, and is one of the oldest continuously-inhabited cities in the world. It is exposed to a moderate-up-to-high level of seismic activity, given its proximity to several major faults such as the Yammouneh and the Mount Lebanon Thrust, among others. To mitigate the risk encountered by Byblos buildings facing earthquake threat, a preliminary study of the dynamic properties of the structures is proposed in this paper. The recently-constructed Byblos Municipality building was chosen as a prototype for this study, given its important role as a vital structure for centralizing the emergency response, in the event of a disaster. The approach consists of using the horizontal to vertical ratio method, HVNR. By analysing the ambient noise recordings, one can determine the structural frequency, damping, and other stiffness characteristics, and identify the natural soil frequency. In order to investigate the soil structure interaction and specifically possible resonance occurrence during earthquakes, the values obtained are compared and analysed. In addition to classical geotechnical tests to reveal the type and properties of the considered in-situ soil, the multichannel analysis of surface waves, MASW, is used to investigate the stiffness of the subsurface conditions and determine the shear wave velocities of the layers. In parallel, the Finite Element Model of the structure is analysed and the result of the fundamental resonance frequencies is compared to the HVNR data, and to the computed values using conventional formulae recommended by classical building codes. Results and comparisons of experimental and numerical investigations are presented for the structure and analysed for further resonance analysis.