DRAFT: US-JAPAN PBEE PAPER BY CORDOVA ... - PEER

Three of the case study structures are composite moment frames composed of reinforcedconcrete columns and steel beams (referred to as RCS systems), and the forth is a steel spaceframe. An elevation of one of the frames, a six-story RCS perimeter frame, is shown in Fig. 2.Beam sizes in the frames were generally governed by drift requirements while the reinforcedcolumns were governed by the strong column weak beam criterion. As summarized in Table 1,vibration periods for the frames range from T 1 = 1.3 to 2.1 seconds (note – other data reported inTable 1 is discussed later).Inelastic static and dynamic (time history) analyses are conducted using an analysis programdeveloped by El-Tawil et al. (1996) that takes into account second-order geometric behavior andspread-of-plasticity effects in the beam-columns and connections. Inelastic componentproperties are based on the expected (as compared to nominal) material strengths, where theexpected strengths are taken as 1.15 times the nominal strengths. Static pushover and inelastictime history analyses are run simultaneously with gravity loads equal to 100% dead load and25% live load. Summarized in Table 1 are static lateral overstrengths of the frames, defined asΩ o = V u /V d where V u is the ultimate base shear and V d is the IBC design base shear. Theoverstrengths range from roughly Ω o = 2.6 for the six-story RCS perimeter frame up to Ω o = 6.1for the six-story steel space frame. The overstrengths are relatively large compared to the typicalexpected values of Ω o = 2 to 3, due to the following sources of overstrength: (1) expected versusminimum specified material strengths, (2) minimum stiffness (drift) criteria, (3) structuralredundancy, (4) strong column criterion, and (5) discrete member sizing.Frame IDFirstModePeriod,T 1 (sec)V u /V d ,ΩTable 1 – Testbed frame dataσ ln(IDR|Sa)6S_RCS_S 1.3sec 3.9 0.426S_S_S 1.3sec 6.1 0.2712S_RCS_S 2.1sec 4.4 0.246S_RCS_P 1.5sec 2.6 0.30IDA Dispersion Data for Alternative Intensity MeasuresGeneral RecordsNear Fault Recordsσ ln(IDR|SaRsa)(Optimized)0.28(1.9,0.65)0.20(1.2,2.4)0.19(1.6,0.6)0.23(1.65,0.45)σ lnIDR|SaRsa(2.0,0.5)σ ln(IDR|Sa)0.29 0.450.23 0.300.22 0.26σ ln(IDR|SaRsa)(Optimized)0.22(1.8,0.9)0.18(1.6,0.8)0.21(2.4,0.4)σ ln(IDR|SaRsa)(2.0,0.5)0.270.190.220.24 - - -6