13 th World Conference on Earthquake Engineering Vancouver, B.C.,Canada August 1-6, 2004 Paper No. 2182 SEISMIC PERFORMANCE CAPACITIES OF OLD CONCRETE Vsevolod LEVTCHITCH 1 , Victor KVASHA 2 , Helen BOUSSALIS 3 , Anastasios CHASSIAKOS 4 and Elias KOSMATOPOULOS 5 SUMMERY Static, dynamic and low cycle fatigue testing of 20…30 years old concrete have been carried out. Samples were taken from residential buildings in Cyprus and bridges in Ukraine. Dynamic strengthening factors were 2…4 times lower than those of 28 day concrete. Dynamic strengthening in splitting has been approximately 4 times smaller than that in compression. The static tensile-to-compressive strength ratio of old concrete is more than two times lower than that of young concrete. Modulus of elasticity is increasing with age more significantly than the strength. Elasticity modulus increase has been observed even in cases when there was no increase of strength. Ultimate strains were drastically lower than those of a young concrete. A reduction of approximately 50% has been observed. Up to the stress of 75% of a peak value, old concrete behaves as an elastic material. All these changes in properties are on the alarmingly unsafe side in terms of seismic performance. Concrete with age is evidently getting to be more rigid, less ductile and exhibits a very unhappy tendency to brittle explosive modes of failure. It is becoming seismically fragile .and is an easy target for seismic forces. Old concrete itself is an object of destruction and it triggers damage and destruction of other elements. Contribution of old concrete in resisting shear and torsion is diminishing drastically. Due to a very limited ability to expand laterally, the effectiveness of confinement is also reducing and ultimately cease to have any positive effect. Low cycle fatigue capacity, i.e. seismic capacity, is totally dependant on the available reserve of plastic deformations. Only concrete with a remaining capacity to undergo plastic deformations is able to develop dynamic strengthening and provide a predictable resistance to cyclic loading. Large strength increases, commonly adopted in seismic analysis are absolutely not relevant to the actual phenomenon. INTRODUCTION Old concrete is a mess. At an age of 20…30 years it is not the same material as it was at 28days. It is not just a common mix of bad and good, but a store of bad dynamic properties. In old concrete everything is changing with the course of time, but nothing is getting better, except a possible increase of static short- term compressive strength, which, in itself, is practically of no importance for the dynamic performance. 1 Professor, Frederick Institute of Technology, Nicosia, Cyprus. savvas@research.fit.ac.cy 2 Professor, National University- Lvivska Polytechnica, Lviv, Ukraine. salus@icmp.lviv.ua 3 Professor, Department Chair, California State University, LA, USA. hboussa@exchange.calstatela.edu 4 Professor, California State University, Long Beach, USA. achassk@csulb.edu 5 Professor, University of Crete, Khania, Greece. kosmatop@dssl.tuc.gr