3.Evaluation of the strength of damaged reinforced concrete underground structures
  • Proposal of a method to evaluate the strength of damaged underground reinforced concrete structures in consideration of cracks and reinforcing bar corrosion
  • Confirmation of the approximate correlation between the results of analysis using the proposed method and those of a survey on cracked structures and model tests simulating reinforcing bar corrosion, partial loss of area and other types of damage
  •    Some reinforced concrete (RC) underground structures represented by railway cut-and-cover tunnels suffer from reinforcing bar corrosion and cracks. Such damage is caused by water leakage arising from the ground conditions and the execution technologies adopted during construction. To properly maintain and manage these structures, it is necessary to ascertain whether the damage will affect the strength or durability of the structure, and urgent countermeasures are required if it becomes clear that the strength is affected. Unfortunately, however, there are no methods of quantitatively evaluating dynamic behavior specific to RC underground structures to determine the situation.
       To evaluate the strength of RC underground structures, therefore, the RTRI proposed a method of applying FEM analysis to express non-linear behavior caused by cracking, taking into account the characteristics of adhesion between concrete and reinforcing bars and those of concrete tensile softening. By implementing model tests to simulate reinforcing bar corrosion and partial loss of area, and then surveying cracks on actual structures, the RTRI confirmed that the actual conditions of stress in reinforcing bars/concrete and cracks on the concrete surface correspond approximately to those analytically obtained using the proposed method (Fig. 1). This method has been applied in evaluating the strength of railway cut-and-cover tunnels constructed 50 years ago or more (Fig. 2). This study was promoted with a subsidy from the Ministry of Land, Infrastructure and Transport.

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