Axial Load Capacity Model - Civil Engineering

Axial Load Capacity Model - Civil Engineering

Update of ASCE 41 Concrete Provisions Kenneth Elwood, Univ. British Columbia Craig Comartin, CDComartin Inc. Jon Heintz, ATC Dawn Lehman, Univ of Washington Adolfo Matamoros, Univ of Kansas Andrew Mitchell, Degenkolb Jack Moehle, UC Berkeley Mark Moore, Forell/Elsesser Michael Valley, MKA John Wallace, UCLA SEAONC 2007 Excellence in Structural Engineering Awards Scope of Work Concrete Chapter of ASCE 41 Research from PEER and elsewhere EERI/PEER seminars New Information on the Seismic Performance of Existing Concrete Buildings Compelling and urgent findings Components addressed Columns Slab-Column Connections Joints Walls Onset of column shear failure P Ag f c ' 1.0 v 3 fc ' FEMA 356 0.8 Proposed, ( =0.0005) 0.6 Proposed, ( =0.006) 0.4 0.2 0 0 0.01 0.02 0.03 0.04 0.05 plastic rotation (rad)

0.06 0.07 Example: Improved reliability, clearly expressed Parameter a for flexure-shear columns: p meas p calc Proposed 10 FEMA 356 5 conservative 1 0 0.0 0.2 0.4 P Ag f c ' 0.6 unconservative Examples of other changes Proposed / FEMA 356 2 1.5 1 0.5 0 column stiffness for low axial load max steel stress for typical lap splice slab-column qp p at punching (Vg/Vo=0.2, continuity) wall drift at shear failure (low axial load)

wall drift at axial failure (high axial load) Impact on REAL projects V V shear-critical captive columns Elevation Impact on REAL projects Shear-Critical Columns Life Safety BSE-1 Collapse Prevention BSE-2 2,000 1,000 0 0.000 0.002 0.004 0.006 Total Hinge Rotation (rad) 0.008 4,000 3,000 2,000 1,000 0 0.010 0.000 ASCE 41 Supp. CP 3,000 5,000 FEMA 356 CP 4,000 ASCE 41 Supp. LS 5,000 Hinge Moment (kip-in) 6,000 FEMA 356 LS

Hinge Moment (kip-in) 6,000 0.002 0.004 0.006 Total Hinge Rotation (rad) 0.008 0.010 Impact on REAL projects Impact on bottom line: New stiff shear wall or column strengthening needed based on FEMA 356 No retrofit needed to address columns based on ASCE 41 Supplement. = less disruption and $$$$ Savings End result = more retrofit projects done and reduced seismic risk!! Acknowledgments American Society of Civil Engineering Chris Poland Jim Rossberg Federal Emergency Management Agency Cathleen Carlisle PEER Center Laura Lowes University of Washington Update of ASCE 41 Concrete Provisions Columns: Highlights: Highlights: New development length model. Lap splices typical of older columns: fs Supp / fs FEMA 356 = 1.45 Low axial-load columns and beams: EIeff FEMA 356 = 0.5EIg EIeff Supp = 0.3EIg v 3 f c ' v 6 f c '

v 6 f c ' v 3 f c ' 16 0.8 0.7 0.6 0.5 Accounts for shear deformations in B-C joints. Beam-Column Joints: FEMA 356: rigid zone Supplemental: Dependent on Mnc/Mnb Rigid end zone Rigid end zone Rigid end zones b) Mnc/Mnb < 0.8 c) 0.8 Mnc/Mnb 1.2 kcalc/kmeas FEMA 356 Mean 1.22 2.59 Min 0.19 0.41 Max 2.52 5.18 cov 0.36 0.36 Walls: 4 2 0.1 0 0.0 0 0.01 Flexure-shear failure mode. p depends on axial load and and v 0.02 0.03 0.04 0.05 No penalty for walls with one curtain of reinforcement. Secondary shear-critical columns. Low axial loads: FEMA 356 (CP) p = 0.004 rad Supp. (CP) p = 0.006 to 0.06 rad Highlights: d Specific parameters for PT slabcolumn connections. g B C F D f E c A RC modeling parameters and acceptance criteria revised based on new data. -continuity reinforcement values -no continuity reinforcement values h 3 2 0.3 0.7 0.6 0.5 0.4 @ axial failure 7 6

5 4 3 2 1 0 0.0 0 0 0.01 0.02 0.03 0.04 0.05 0.06 0.1 0.2 0.07 plastic rotation (rad) Acceptance Criteria: R C c o n n e c t io n s /S u b a s s e m b lie s E d g e c o n n e c t io n s A S C E 4 1 - C o n tin u ity (C ) A S C E 4 1 - N o C o n t in u it y ( N C ) F E M A 3 5 6 - C /N C 0 .0 5 O n e C u rta in T w o C u r ta in s f y ) m i n = 0 . 1 5 % * 4 1 4 M P a 0 0 1 2 ( fy)M 3 IN (MPa) 4 Modeling recommendations: Guidance on stiffness and nonlinear models to model influence of punching. Allow for secondary nonductile elements to lose lateral load capacity, but still sustain gravity loads.

0 .0 3 0 .0 2 0 .0 1 A C I 3 1 8 -0 5 2 1 .1 1 .5 L im it 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 G ra v ity S h e a r R a tio (V g /V 0 ), w h e re V 0 = 4 f 'c 0 .8 1 /2 b od 0 .9 Elastic column Column plastic hinge Torsional connection element Joint region Elastic slab beam 1 Highlights: R e f: K a n g & W a lla c e , A C I 1 0 3 (4 ), 2 0 0 6 0 M M Plastic hinges for slab beams or for torsional element 0.7 8 0.1 0 .0 4 0.6 Condition ii - propos ed 'controlled b y flexure' - FEM A 356 9

v 3 fc ' 0.3 0.5 Ag f c ' 10 a ( =0.006) b ( =0.006) a ( =0.0005) b ( =0.0005) a - FEMA 356 b - FEMA 356 0.8 0 0.4 P (b) 0.9 Slab-beam plastic hinge f y ) m i n = 0 . 2 5 % * 4 1 4 M P a Shear-controlled walls dependent on axial load. Low axial load: total Supp = 2.0% (Sec. - CP) High axial load: total Supp = 1.0% (Sec. - CP) 0.2 0 .0 6 1.0 V test / V n (F E M A 3 5 6 ) Increase shear stress limits. Deformation capacity approximately v 4 fc ' constant for 0.1 0.07 Proposed Condition ii vs. FEMA 356 Non-Conforming Slab-Column Connections: Highlights: Relax confinement requirements. Considered as confined if: Ash > 0.75Ash ACI s < 8db 0.06 plastic rotation (rad) High axial loads: FEMA 356 (CP) p = 0.004 rad Supp. (CP) p = 0.0 to 0.008 rad e Tri-linear backbone for walls controlled by shear. 6 0.2 0.2 Q Qy 8 0.3 0 D rift R a tio (T o ta l R o ta tio n ) a t P u n c h in g New models provide better estimate of measured stiffness from 57 beamcolumn sub-assembly tests. Proposed @ shear failure 10 0.4 Flexure-controlled columns. p depends on axial load and 1 a) Mnc/Mnb > 1.2 12 a ( =0.006) b ( =0.006) a ( =0.002) b ( =0.002) a - FEMA 356 b - FEMA 356 0.9 Condition ii - propos ed 'controlled by flexure' - FEMA 356 14 (a) 1 p table Accounts for slip

from B-C joints. p meas Stiffness Models: Andrew Mitchell, Degenkolb Kenneth Elwood, Univ of British Columbia Engineers Craig Comartin, CDComartin Inc. Jon Heintz, Applied Technology Council Jack Moehle, UC Berkeley Mark Moore, Forell/Elsesser Dawn Lehman, Univ of Washington Michael Valley, Magnusson Adolfo Matamoros, Univ of Kansas Klemencic Proposed Condition Johni vs.Wallace, UCLA Calibrated to experimental data: FEMA 356 Conforming p table 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 beamcolumn 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. p meas Abstract: Elastic relation for slab beam or column SEAONC 2007 Excellence in Structural Engineering Awards 1 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. 0.3 P 0.4 Ag f c ' 0.5 0.6 0.7

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