rehabilitation of rc concrete buildings
TRANSCRIPT
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Learning from Earthquakes
to ImproveRehabilitation of Reinforced
Concrete Buildings
James O. JirsaThe University of Texas at Austin
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Objectives of NATO SfP977231
• Seismic evaluation and retrofitting of
existing buildings in Turkey and
Greece.
• Transfer, adapt, and implement
and/or develop innovative
technologies and methodologies for
both countries.
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Requirements for rehabilitation to
be implemented
• Demand/need for rehabilitation
• Availability of techniques that are
–Constructible
–Cost-effective
–Convincing
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Buildings in Turkey
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Buildings in Mexico City
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Approaches for reaching objective
• Reconnaissance studies after recent earthquakes– Little documentation of performance of
rehabilitated buildings
• Field experience—applicable to typical buildings in region– Mexico City after 1984
• Experimental studies– NATO Project
– Other reports in this Workshop
• Demonstration projects
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Widespread
damage to
concreteconstruction
• Waffle slab systems
• Column failures
• Reinforcement details
• Infill walls
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Reconnaissance studies
Documentation
Analytical studies
Experimental studies
Designguidelines
Codes & Standards
Experience
Shortcut
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Demonstration projects
• New approaches must be “sold” to potential users
• Implementation depends on the user’s perception of technique
• Seeing is “believing”
• Field application and demonstration projects may be most convincing
• Education of owners and engineers
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Mexico City after 1985
• Characteristics of damage– Lake bed zone—foundation limitations
– Construction types
• Rehabilitation activities– Affected zone was a “laboratory” for rehab
• Documentation– NSF/CONACyT Workshop
• Case study– Cable-bracing techniques
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25Could not be identified
7Other modes
1.5Shear walls, shear or bending
8Beam-column joints
2Flexure in beams
9Shear in waffle slabs
9Shear in beams
43Shear, compression, or other failure
of columns
% of casesMode of Failure Observed
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Damage statistics
0
20
40
60
80
100
120
No. of
Buildings
RC
Frames
Steel
Frames
Waffle
Slabs
Bldgs
w/Shear
walls
Masonry
Severe
Collapse
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Damage/height of buildings
0
20
40
60
80
100
120
No. of
Buildings
<5 6 to 10 11 to 15 >15
No. of Stories
Severe
Collapse
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Following the earthquake
• Owners and occupants were concerned about potential hazards in future events
• Buildings needed by users
• Repair and strengthening proceeded with very few design guidelines or standards for construction in place
• Engineers met challenge with creative solutions
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Rehab prior to 1985
• Some buildings repaired following
earthquakes in 1957 and 1979
• Almost no information available about
those buildings
• Exception--Two buildings strengthened
before 1985 performed well and were
extensively studied after the earthquake
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Building braced
pre-1985
Foundation
effects
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1989 Workshop
• Site visits to buildings under rehab
• Discussions with engineers in charge
of rehabilitation design and
construction
• Review of approval process for rehab
projects
• Participants defined the need to
document rehab work
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Beam and column jacketing
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New bracing
systems
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New walls
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Mixed systems
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Removal of top stories
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Rehabilitation of Existing Reinforced Concrete Buildings in Mexico City: Case Studies
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Case study: Layout of building
Stairway
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A
B
8.00
3.75
Stairway
C1
C2
C3
C4
C5
C6C7
C8C9 C8
C7 C6 C6 C6 C6 C6 C6 C6
C5 C5 C5 C5 C5 C5 C5 C5 C5
C7 C7C2
C3
C4
3.50
ELEVATION LINE B
3.50
13 @ 7.20 m.
(meters) ELEVATION LINE A
BUILDING PLAN
TYPE 4 TYPE 5 TYPE 6
30 for h=100 cm.
TYPE 2TYPE 1 TYPE 3
25 for h=85 cm.
MAIN BARS
ADDITIONAL #4 BARS
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Cable braces
NEW STEEL BEAMSNEW STEEL BEAMS CABLE BRACING
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Details
EXTERIOR CABLES
NEW CONCRETE
STEEL PLATE6-IN. X 6-IN. X 12-IN.
ANCHOR MECHANISMCABLE
DETAIL A
SLAB ZONE TO BEDEMOLISHED
EXISTING COLUMNREINFORCEMENT
INTERIOR CABLES
CABLE
EXISTING COLUMN
DETAIL A
WAFFLE SLAB(SOLID ZONE AROUNDCOLUMN)
CABLE
A A
SECTION A-A
′
′ =fc psi5000
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Additional
Modifications
Column Compression
Continuity of horizontal elements
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Computed response
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Cable
bracing for
2-story
school
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Anchorage and cable details
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Cable bracing for 12-story steel frame
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Concluding remarks
• Future actions to improve “learning from earthquakes”–Documentation of rehabilitation
projects for evaluation of performance in future earthquakes.
–Instrumentation of buildings to enable more detailed evaluation of performance.
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• Challenges–Focus efforts on areas where need is
greatest• Marginal residential construction• Determination and enforcement of
minimum requirements
–Maintain and create interest in earthquake mitigation• Competition with other political and
social exigencies • No well-defined industry to pressure
policy makers
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