ORIGINAL ARTICLE The effect of ribs on the mechanical behavior of corroded reinforcing steel bars S500s under low-cycle fatigue Ch. Alk. Apostolopoulos Received: 25 January 2006 / Accepted: 17 August 2007 / Published online: 12 September 2007 Ó RILEM 2007 Abstract An experimental study has been carried out to assess the effects of gradually accumulating corrosion damage on the low-cycle fatigue behavior of smoothed concrete reinforcing steel bars S500s. Low-cycle fatigue loading may simulate in a satis- factory way the loading applied to the reinforcement of structures during seismic actions. Profiled (ribbed) concrete reinforcing steel bars have been tested after the removal of the ribs by means of filing. The fatigue behavior of the smoothed bars is compared against that of profiled steel bars, which are widely used as concrete reinforcement. The low-cycle fatigue tests performed indicate that the presence of ribs greatly reduces the performance of the steel bars under cyclic loading. A significant increase of the number of cycles to failure, as well as of the dissipated energy, has been observed, whereas there was only a minor reduction of the load-carrying ability of the bars due to the reduction of the ribs. The results indicate that the use of non-profiled steel bars could be considered in certain areas of reinforced concrete frames, especially for structures located in seismically active areas, which suffer the most from earthquake loadings. Keywords Smooth steel bars BSt 500 s  Salt spray corrosion  Corrosion damage  Low-cycle fatigue  Degradation of useful service life 1 Introduction Steel-reinforced concrete still holds as the most widely used construction material for the load- carrying elements of buildings and structures. Although the many disadvantages that reinforced concrete is known to have, such as its increased weight which leads to bulky constructions, the difficulty of being formed into complex shapes, and the high maintenance costs, advantages such as durability and low construction costs still classify it as the first choice in many constructions. Plain concrete has very high compressive proper- ties, which diminish when the material is subjected to tensile loads. The use of steel bars as concrete reinforcement leads to a composite material with high mechanical properties in both tensile and compres- sive loads. To ensure the cooperation of steel and concrete as a composite material, steel bars are produced with ribbed surfaces. The ribs on the steel surface act as ‘‘anchors,’’ increasing the bond strength between the two materials. A known disad- vantage of ribbed over smooth bars, which had been in use in Greece until the 1960s, concerns the fatigue behavior of the steel bars. When steel bars are subjected to alternating fatigue loads, the fatigue Ch. Alk. Apostolopoulos (&) Laboratory of Technology and Strength of Materials, Department of Mechanical Engineering and Aeronautics, University of Patras, Panepistimioupolis Rion, Patras 26500, Greece e-mail: charrisa@mech.upatras.gr Materials and Structures (2008) 41:991–999 DOI 10.1617/s11527-007-9300-7