7Impact on REAL projects VVshear-critical “captive” columnsElevation
8Impact on REAL projects Shear-Critical ColumnsBSE-1BSE-2FEMA 356 LSASCE 41 Supp. LSFEMA 356 CPASCE 41 Supp. CP
9Impact on REAL projects Impact on “bottom line”:New stiff shear wall or column strengthening needed based on FEMA 356No retrofit needed to address columns based on ASCE 41 Supplement.= less disruption and $$$$ SavingsEnd result = more retrofit projects done and reduced seismic risk!!
10Acknowledgments American Society of Civil Engineering Chris PolandJim RossbergFederal Emergency Management AgencyCathleen CarlislePEER CenterLaura Lowes – University of Washington
11Update of ASCE 41 Concrete Provisions Abstract: A supplement to ASCE/SEI 41 Seismic Rehabilitation of Existing Buildings has been developed for the purpose of updating provisions related to existing reinforced concrete buildings. Based on experimental evidence, the proposed supplement includes revisions to stiffness models for beams, columns and beam-column joints, and substantive revisions to acceptance criteria for reinforced concrete columns, structural walls, and slab-column frames. These revisions will result in substantially more accurate, and in most cases more liberal, assessments of structural capacity of concrete components in seismic retrofit projects.Kenneth Elwood, Univ of British ColumbiaCraig Comartin, CDComartin Inc.Jon Heintz, Applied Technology CouncilDawn Lehman, Univ of WashingtonAdolfo Matamoros, Univ of KansasAndrew Mitchell, Degenkolb EngineersJack Moehle, UC BerkeleyMark Moore, Forell/ElsesserMichael Valley, Magnusson KlemencicJohn Wallace, UCLAStiffness Models:Accounts for slip from B-C joints.Columns:Proposed Condition i vs. FEMA 356 ConformingCalibrated to experimental data:Highlights:New development length model. Lap splices typical of older columns: fs Supp / fs FEMA 356 = 1.45Flexure-controlled columns. qp depends on axial load and r”Flexure-shear failure mode. qp depends on axial load and r” and vSecondary shear-critical columns. Low axial loads: FEMA 356 (CP) qp = rad Supp. (CP) qp = to 0.06 rad High axial loads: FEMA 356 (CP) qp = rad Supp. (CP) qp = 0.0 to radHighlights:Low axial-load columns and beams: EIeff FEMA 356 = 0.5EIg EIeff Supp = 0.3EIgBeam-Column Joints: FEMA 356: ”rigid zone” Supplemental: Dependent on SMnc/SMnbNew models provide better estimate of measured stiffness from 57 beam-column sub-assembly tests.@ shear failureAccounts for shear deformations in B-C joints.Proposed Condition ii vs. FEMA 356 Non-Conforming@ axial failurekcalc/kmeasProposedFEMA 356Mean1.222.59Min0.190.41Max2.525.18cov0.36Walls:cQQy1.0ABCDEfFdeg∆hSlab-Column Connections:Acceptance Criteria:Highlights:Tri-linear backbone for walls controlled by shear.Relax confinement requirements. Considered as confined if: Ash > 0.75Ash ACIs < 8dbIncrease shear stress limits. Deformation capacity approximately constant forNo penalty for walls with one curtain of reinforcement.Shear-controlled walls dependent on axial load. Low axial load: qtotal Supp = 2.0% (Sec. - CP) High axial load: qtotal Supp = 1.0% (Sec. - CP)Highlights:Specific parameters for PT slab-column connections.RC modeling parameters and acceptance criteria revised based on new data. -continuity reinforcement m values -no continuity reinforcement m-s valuesModeling recommendations: Guidance on stiffness and nonlinear models to model influence of punching.Highlights:Allow for secondary nonductile elements to lose lateral load capacity, but still sustain gravity loads.Facilitate development of more liberal acceptance criteria of other materials.“Alternative Acceptance Criteria” Backbone created using peak of first cycle of each increment of loading (or deformation) less exaggeration of rate of degradation. - more realistic backbone.(MPa)SEAONC 2007 Excellence in Structural Engineering Awards