Behavior of Fully Encased Steel-concrete Composite Columns Subjected to Monotonic and Cyclic Loading

The paper describes experimental aspects for composite steel-concrete columns, with steel encased profile. In composite columns with HSC case, even if elastic displacement vy decreases, the value of the lateral force Hy corresponding to the vy displacement and the maximum lateral loading Hmax indicates a significant increase. Failure modes were different, characterized by sudden and violent concessions due to cracking developments through aggregate in columns with HSC, while columns with NSC shows a “slow” failure mode characterized by gradual decline of bearing capacity with the growth of the displacements. It is well known that the high strength concrete is more susceptible to fragile failure than the normal concrete, so it is, in a way, the presumed result. On the other hand, from the graphics and parameters analysis we can conclude that the columns with HSC have a higher energy absorption capacity, which can recommend this solution to the construction in seismic areas, even the failure mode was brittle. In structural terms, composite columns with concrete class C70/85 provide obvious better performances to structures, having significant increases to almost all analyzed parameters.The solution of fully encased composite column is a competitive solution for seismic and non-seismic zones, due to the excellent seismic performances (resulted from the presented experimental tests) and also because of improved fire protection. The results obtained on the columns made with high strength concrete showed improved performances, especially resistance. Due to the brittle fracture of the high strength concrete more experimental and numerical research must still be made.