Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 1 Northridge Earthquake - Concrete Structures

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 2 Outline Introduction Types of Structures Typical Failure Modes Code Development Conclusions

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 3 Types of Structures Parking Garages –Large plan areas – number of lateral systems minimized –Not limited to a specific type of parking garage: Precast Steel components Cast in place concrete – post tensioned Hybrid systems

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 4 Types of Structures Parking Garages –Ramps have the effect of shortening and stiffening adjacent columns –Precast elements often difficult to tie together –Performance far worse than other structures –9 parking garages collapsed

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 5 Types of Structures Parking Garages –California State University –Moment resisting frame –Cast in place Ductile – lateral –Precast Brittle - gravity

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 6 Types of Structures Parking Garages

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 7 Types of Structures Office Buildings –Fared better than parking garages –Shear walls performed reasonably well Cracked but did not collapse Most could use epoxy grouting –Non-ductile structures showed brittle failure in columns and piers

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 8 Types of Structures Office Buildings

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 9 Types of Structures Residential Housing –Apartments –Precast concrete used in basement parking experienced mixed results –Concrete and wood structures above did not fare well –Post-tensioned slab failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 10 Types of Structures Residential Housing

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 11 Typical Failure Modes Column Failure –Tie failure –Tie distribution –Shear failure –Spiral columns Steel to Concrete Connections Tilt-up Buildings

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 12 Typical Failure Modes Joints –Beam hinging –Corner joints –Roof joints Beam Alignment Waffle Slab Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 13 Column Failure Spalling Vertical Reinforcement Concentrated in Corners Inadequate Cover Older Structures – Non-ductile

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 14 Column Failure Tie Failure –Occurred in numerous buildings

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 15 Column Failure Tie Distribution

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 16 Column Failure Shear Failure –Holiday Inn built in 1966 –Minor damage during 1971 earthquake –Red tagged, temporary shoring installed –Vertical column reinforcement between ties buckled – added confinement not provided by the concrete –Most severe damage between 4 th and 5 th floors

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 17 Column Failure Shear Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 18 Column Failure Shear Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 19 Column Failure Shear Failure –Champaign Tower –15 story building in Santa Monica –Non-ductile moment frames & shear walls –Column spans shortened by balconies –Experienced full length shear cracks –Typical short column behavior –Structure did not collapse

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 20 Column Failure Shear Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 21 Column Failure Spiral Reinforced Columns –Spiral ties are more effective than rectangular ties –Need about 30% more link steel –Columns in following pictures do not have adequate confinement –Concrete outside of steel is lost

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 22 Column Failure Spiral Columns

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 23 Steel to Concrete Connections

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 24 Tilt-up Building Failure Commonly Used for Industry, Warehouses 300 Structures Damaged Poor Connection Between Roof & Tilt-up Panels Caused Failures 1976 UBC – Minimum Tie Reinforcement –Post 1976 construction fared better Passed Retrofit Ordinance after Northridge –2,100 structures need to be retrofitted

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 25 Tilt-up Building Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 26 Tilt-up Building Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 27 Tilt-up Building Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 28 Joint Failure Beam Hinging

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 29 Joint Failure Corner Joint –No transverse reinforcement –Insufficient anchorage for hooked bars –Widely spaced ties in members outside of the joint –No intermediate ties in column –Adequate confinement of concrete necessary

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 30 Joint Failure Corner Joint

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 31 Joints Roof Joint

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 32 Beam Alignment Failure Inadequate Connection of Beam to Column Most Cases Experienced Concrete Spalling

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 33 Beam Alignment Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 34 Beam Alignment Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 35 Waffle Slab Failure Few Bars Passing Through Columns Punching Failure Transfer of Moment From Slab to Column No Secondary Resistance Progressive Failure

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 36 Code Development Various Code Changes Over Last 40 Years Varying Seismic Resistances 1976 UBC Code Is First Code Similar to Current Codes –Separates “modern” and “older” buildings

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake Ductile Detailing in Frames Revised Detailing for Tilt-up Structures Design Forces Increased (Development of UBC) Improved Detailing of Shear Walls Shear Wall Design Provisions Introduced Code Development

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake New Requirements for Welded & Mechanical Splices for Precast Structures Provisions for Seismic Design of Precast Concrete Structures Requirements for Frame Members That Are Not Part of LFR System Must Be Detailed for Maximum Inelastic Response Code Development Since Northridge

Villanova University Dept. of Civil & Environmental Engineering CEE 8414 – Structural Dynamics Northridge Earthquake 39 Conclusions Ductile Structures Fared Better Parking Garages Suffered the Most Damage Columns Lacked Confinement Shear Failures Prevalent Code Changes Seem to be Working