Seismic behavior of fifteen years old RC frame

It is known that during the construction process of significant part of rc structure stock, mild steel and agregates coming from sea bed used before the existing code proposals and standards in Turkey. Low concrete quality, mild-nonribbed reinforcement and sea type of aggregates are some of the under design features of those structures. This study mainly focused on seismic behavior of this type of RC frame as experimentally and analytically. Especially in humid environments, reinforcement corrosion probably occurs when the concrete quality is low and it includes agregates coming from sea bed . The reinforcement corrosion can cause a lot of strcutural problems such as cracking of concrete , bond lost and decreasing of effective cross sectional area of rebar durig the service life of rc structure. These destructive corrosion results limit the service life of existing structure stock. Depending on the degree of natural corrosion attack, the adherence between the reinforcement and concrete is adversely affected, the effective reinforcement cross section is reduced as a function of time and the cracking of the concrete cover can be seen as the main structural damages. Within the scope of this study, the fifteen years old RC frames were tested to represent the structures which are naturally corroded and constructed before recent earthquake codes and standards. Nearly 1/3 scale one RC frames and one reference frame (15 years ago) were tested under the cyclic horizontal loads and constant axial forces in the İstanbul Technical University Building and Earthquake Engineering Laboratory. The seismic behavior of reinforced concrete frames has been tried to be explained by analysing the strength development, displacement capacity,ductility, los of effective cross sectional area of reinforcement, stiffness,moment-curvature relations and displacement components obtained under cylic load procedures. The poisson ratio of fifteen years old confined and unconfined concrete in decending branch of stress-strain diagrams was another topic for which only limited amount of literature is available. In the theoretical part of this study; nonlinear pushover analysis of the structural frame was investigated using by DC2B-v2 which include distrubuted plasticity theory , Sap2000 and SeismoStruct that are based on concentrated plasticity theory computer programs. The outputs obtained from these programs by using theoretical models and the results of the experiemental behavior are compared. There is a special purpose computer program has been developed for finding the buckling load parameters of a frame with and without plastic hinges . According to the experiemental and analytical results; strength development,lateral and verical displacement capacity, ductility and moment curvature relationships have been measured, evaluated and compared.The tested frame specimen did not reach its theoretical load capacity and drift level due to decreament of effective cross sectional area of reinforcement and decreament of adherence between the concrete and rebar .Displacement capacity of tested corroded frame was reduced visibily when compared with uncorroded reference frame. Some of the reinforcing bars of stirrups which are closer to the outer joints were ruptured at 4% story drift that indicate a loss in displacement capacity and shear capacity due to high corrosion attack on those outer stirrups reinforcemements.