•  Diploma Thesis Defense by Mr Haralambos Marazakis

Thesis Title:  «  Numerical investigation of the long-term effects of corrosion on the seismic vulnerability of reinforced concrete bridges »

Tuesday 18  August 2020, at: 9:15, Venue:  https://tuc-gr.zoom.us/j/9742331787?pwd=TjBkZ1ZFUlR1aXkrYkRaeFdQanZYQT09

Examination Committee

• Professor            Yiannis Tsompanakis (advisor)
• Professor            Konstandinos Providakis
• Dr           Prodromos Psarropoulos

Abstract

Under a strong earthquake excitation, a reinforced concrete bridge can be distressed in several ways and damages can occur to its structural members. Nonetheless, such damages are usually more severe when the bridge has been exposed to corrosion. Therefore, the present thesis examines the impact of chloride induced corrosion on the reinforcement of bridge columns, on the seismic vulnerability of typical reinforced concrete bridges which are located in adverse corrosive environment close to the coastline. The parametric investigation is performed by developing elaborate numerical models utilizing a specialized finite element software, both for the pristine and for the "aged" bridge after 50 or 100 years of operation. The pristine bridge is stressed by a seismic sequence consisting of six seismic records that occurred consecutively over a period of three days. In the sequence, the same accelerograms are applied on the "aged" models of the same bridge and the damages are compared for the three scenarios. The purpose of this investigation is to compare the accumulation of damages at the base and the top of the columns of the bridge frames, i.e., the zones in which the plastic hinges are usually formed.

In general, due to corrosion, in addition to the area of ​​the reinforcement cross section, the mechanical properties of the reinforcement are reduced. Based on the simulation of the uniform corrosion of the reinforcements, their geometric and mechanical properties are modified in the computational model of the "aged" bridge. The corrosion simulation is based on the fact that the reinforcement of the bridge columns starts to deteriorate at different times. Initiation of corrosion depends on the concrete type, the thickness of the concrete cover of the reinforcement and the distance of the column from the coastline. The gradual propagation of corrosion, as well as the damage caused to the reinforcement, also depends on these parameters.

To investigate the above critical factors, characteristic cases of bridge columns were examined, both in terms of their position in the bridge bents and the other parameters mentioned above. By examining the columns in three different time phases of their operation, it is concluded that the corroded columns exhibit increased damage levels. Whether the damage is capable of leading to the collapse of the bridge depends on the degree of aging / corrosion, but also on the level of seismic intensity. Furthermore, any preventive or repair interventions that are usually performed during the life of large bridges play also a crucial role in their seismic vulnerability. Certainly, the complex phenomenon of corrosion in conjunction with the dynamic distress of a bridge under a seismic sequence involves many parameters and several uncertainties, thus, it needs special attention due to the importance of such infrastructure.