【正文】 h values, the crosssectional area was calculated by using Eq. (4). The dependencies of the effective engineering yield and ultimate stress on the duration of salt spray exposure are displayed in Fig. 6 and Fig. 7 as well. As it can be seen in the figures, the corrosion attack causes a moderate tensile strength reduction which increases with increasing duration of the corrosion exposure, even though for the calculation, the reduced nominal specimen diameters have been used. This result is consistent to the observation of the performed corrosion characterization. It should be remembered that the indentations of the corrosion attack that remained on the specimen surface after removal of the oxide layer and hence, the associated notch effects during tensile loading were found to increase in dimensions and depth with increasing duration of the exposure. Furthermore, as corrosion attacks the surface of the bars, the specimen crosssection which is reduced by corrosion damage refers to material rich in high strength martensite. The experimentally observed reduction of yield and ultimate stress with increasing time of corrosion exposure can be fitted by the set of equations: Rp(t)=A1+B1 t+B2t2 (6) and Rm(t)=A2+B3 t+B4t2. (7) The constants A1, B1, B2, A2, B3 and B4 in Eqs. (6) and (7) were derived to , ?, , , ? and , respectively. (23K) Fig. 6. Effect of the duration of corrosion exposure on yield strength. (23K) Fig. 7. Effect of the duration of corrosion exposure on ultimate stress. Table 4. Mechanical property degradation during salt spray corrosion Property Exposure to salt spray corrosion environment 0 10 20 30 40 60 90 Effective yield strength (MPa) Apparent yield strength (MPa) Effective ultimate stress (MPa) Apparent ultimate stress (MPa) Elongation to failure (%) Energy density (N/mm2) Even though the actual effect of corrosion on the tensile engineering strength properties of the reinforcing steel is moderate, the corrosion damage problem for the integrity of an older reinforced concrete structure remains significant. It is noticeable that the effective engineering strength of the corroded specimens Rmeff drops below the limit set by the standards as the minimum requirement for the stress value at about 40 days salt spray corrosion exposure. As it is shown in Fig. 8, it represents a corrosion damage situation which is not unrealistic for older buildings. Furthermore, as the loads of a reinforced concrete structure remain the same during the service time of the structure, the reduction of the load carrying crosssection of the bars due to corrosion damage results to an increase of the stress applied to the bars. By considering Eqs. (3) and (4), the values of the applied stress on the reinforcing bars can be calculated as (8) with σ0 being the applied stress for the uncorroded material. For the case under consideration, it refers to a bar with d0 = 8 mm. An example of the increase on applied stress as a result of the reduction of the load carrying crosssection with increasing duration of the salt spray exposure is shown in Fig. 8. The values taken for σ0 for the two curves in Fig. 8 were 280 and 320 MPa, respectively. The synergistic effect of the observed decrease on the effective strength values of the material and the increase of applied stresses due to the crosssection reduction may reduce appreciably the safety factors involved in the calculations of a reinforced concrete structure. Note that the safety factor normally used when designing reinforced concrete structures is . Furthermore, it should be noted that the reduction of the crosssection of a reinforcing bar also reduces the moment of inertia of the steel bar. (22K) Fig. 8. Applied stress increase as a function of the duration of corrosion exposure. The effects of increasing corrosion damage on the tensile ductility of the investigated steel bars are shown in Fig. 9 and Fig. 10. Both elongation to fracture, Fig. 9, and energy density, Fig. 10, decrease appreciably with increasing duration of the salt spray exposure. The value of elongation to fracture meets the requirement fu 12%, as requested by the standards in [1], for exposures to salt spray of up to 35 days. As discussed above, the corrosion damage referring to 35 days laboratory salt spray exposure is not unrealistic for corroded reinforcing steels of older buildings at coastal sites. Fig. 9 and Fig. 10 have been approximately fitted using the Weibull function. The Weibull constants C1 to C4 are given in Table 2. (19K) Fig. 9. Effect of the duration of corrosion exposure on elongation to fracture. (16K) Fig. 10. Effect of the duration of corrosion exposure on energy density. The standards do not require for the evaluation of the energy density W of the reinforcing steel. Energy density is a material property which characterizes the damage tolerance potential of a material and may be used to evaluate the material fracture under both, static and fatigue loading conditions [26]. Note that energy density may be directly related to the plain strain fracture toughness value, KIC, . [27], which evaluates the fracture of a cracked member under plain strain loading conditions. The observed appreciable reduction on tensile ductility may represent a serious problem for the safety of constructions in seismically active areas. As during the seismic erection, the reinforcement is often subjected to stress events at the region of low cycle fatigue, the need for a sufficient storage capacity of the material is imperative. 4. Conclusions ? The exposure of the steel bars S500s tempcore to salt spray environment results to an appreciable mass loss which increases with increasing duration of exposure. Durations of laboratory salt