An Experimental Study on Damage Affecting Aseismatic Behavior of Structural Walls Under Chloride Attack Environment in the Semitropical Region

Numerous investigations on corrosion and corrosion protection of steel in concrete have been carried out until today. However, most of these studies are almost limited in the field of materials engineering, for example, main subjects are as follows. 1) Mechanics and mechanisms of steel corrosion, and evaluation of corrosion data. 2) Corrosion monitoring in field structures and corrosion protection. 3) Prediction of service life and repair methods.On the other hand, the influence of corrosion on flexural, shear and bond strength of reinforced concrete members has been discussed on beams and floor slabs. Japan is located in the seismic hazard zoning area. Therefore, in this paper the damage affecting aseismatic behavior of reinforced concrete structural members due to corrosion of steel reinforcing bars is discussed through experiments under the constant axial load and alternately repeated lateral loads.As the first step, structural walls were adopted as the test specimens. Because the coverage thickness, namely, the concrete protective covering for reinforcement is small and the corrosion area is large for reinforcing bars in structural walls. Furthermore, a new fiber reinforced composite material (NFM) instead of steel bars was used in order to investigate durability of the structural walls under chroride attack environment in the semitropical region.A wall panel size was 800x950mm and its thickness was 80mm. The rigid edge beams were attached to the top and bottom of the wall panel. The shear-span ratio M/Qd was 1.43. The weight of a test specimen was about 1tonf. The reinforcing bars, whose diameter was 6mm, were arranged as likely mesh by double layered reinforcement. The reinforcement ratio of the wall panel was 0.8%. In order to prevent from corrosion, epoxy coated steel bars were used in the top and bottom rigid edge beams. These test specimens were offered to the electrolytic corrosion test and exposure test in high salty environment in the semitropical and marine region at the coast in Okinawa Prefecture, Japan.The concrete cylinder average strength was about 250kgf/cm^2. The 11 test specimens were provided. The 8 ones contained the soldium chloride solution (NaCl 3.3% sol.). Now, among them the 6 test specimens, in which the 3 NFM test specimens are included, are exposed at the coast in Okinawa. These exposed test specimens will be loaded laterally by a set of hydraulic jacks after one or several years. The other 5 test specimens were tested under the constant gravity load and alternately repeated lateral forces. One of them was the standard test specimen. The 2 specimens were arranged by the new fiber reinforced composite mesh. An electrolytic corrosion test was applied to the other 2 specimens with the steel reinforcing bars contained the soldium chloride solution. In this case, a steel mesh wrapped in gelatin was adopted as an electrode. This electrode was the same size as a wall panel and was attached on it. The loading apparatus was a cantilever type. As a result of this experimental investigation, the following conclusions were obtained.1) The failure mode of normal test specimen was a flexural compressive failure type. The maximum lateral capacity was kept until a drift ratio reached approximately 1.0%. Then some loss of the lateral load due to the crushing at the bottom corner of the wall panel occurred gradually. 2) The ultimate lateral load of test specimens with electrochemical corrosion damages was obtained after the drift ratio reached over 0.5%. Especially. the ultimate loads were almost same regardless of corrosion damages. The cover concrete at the neighborhood of the bottom of wall panel spalled off and the buckling of the longitudinal reinforcing bars was observed at conclusion of loading. These test specimens, whose failure mode was similar to the brittle shear failure, resulted in the significant deterioration of the ductility. 3) The ultimate lateral load of the test specimens, which were arranged by the new fiber reinforced composite material (NFM), was superior to the other test specimens with reinforcing steel bars.After drift ratio reached over 1.0%, the reinforcing bars made of NFM were partially broken. And the degradation of the lateral load capacity was observed in the hysteretic loops. The energy absorption capacity of these test specimens was slightly smaller than the other specimens because of lacking of the plastic range for the NFM. However, the durability of these test specimens will be expected in chloride attack environment