A DETERMINISTIC ESTIMATION OF EARTHQUAKE-RESISTANCE SHORTAGE OF RC FRAMES

Abstract

Earthquake-resistance reserves for a 4-storey reinforced concrete frame were investigated; the frame was in-situ tested in 1968 by TSNIIEP zhilishcha with application of a powerful vibration machine В-2 type. It is taken that erected in Ashgabat on a site characterized average soil conditions and 9 points at the MSK–64 scale. A computational experiment under the frame had been recently conducted by the author; estimations were performed with calculations procedures of the non-linear static Pushover analysis methodology in SAP2000 software. An estimation of earthquake-resistance shortage (further Id) caused by insufficient ability of study objects to reduce seismic forces is consi-dered. It is noted that existing definitions of earthquake-resistance shortage do not contain clear rela-tionship between an Id and safe-limit-state damages at a severe earthquake. A procedure for quantita-tive estimation of Id using the frame Pushover curve is explained. It is pointed out that an estimation of earthquake-resistance shortage for study objects should cover a large displacement region on a Pushover curve. An earthquake-resistance shortage at an action event satisfied with response acce-leration spectrum Sa(T) which was obtained from a β(T)-curve of Seismic Building Design Code SNiP II-A.12–62 for the frame is absent. In this case seismic-force-reduction factor (an analogue of K1-factor) for the frame is equal to 0.34. Computational estimates have shown that the frame can withstand a horizontal seismic loads similar to main shock parameters of the 1948 Ashgabat Earth-quake. Checking of earthquake-resistance for the frame with a response spectrum Sa(T) was ob-tained from a β(T)-curve of Seismic Building Design Code SP 14.13330 has led up to overly con-servative estimation of the Id. It is noted that a value of seismic-force-reduction factor K1 factor can affect formation on an Id value only in non-ductile reinforced concrete frame buildings and struc-tures. Having of earthquake-resistance shortage in the study objects is mainly due to poor trans-verse/web reinforcement parameters in hinge zones.