Rehabilitation of RC Concrete Buildings
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Learning from Earthquakes
to ImproveRehabilitation of Reinforced
Concrete Buildings
James O. JirsaThe University of Texas at Austin
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.
Requirements for rehabilitation to
be implemented
• Demand/need for rehabilitation
• Availability of techniques that are
–Constructible
–Cost-effective
–Convincing
Buildings in Turkey
Buildings in Mexico City
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
Widespread
damage to
concreteconstruction
• Waffle slab systems
• Column failures
• Reinforcement details
• Infill walls
Reconnaissance studies
Documentation
Analytical studies
Experimental studies
Designguidelines
Codes & Standards
Experience
Shortcut
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
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
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
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
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
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
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
Building braced
pre-1985
Foundation
effects
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
Beam and column jacketing
New bracing
systems
New walls
Mixed systems
Removal of top stories
Rehabilitation of Existing Reinforced Concrete Buildings in Mexico City: Case Studies
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
Cable braces
NEW STEEL BEAMSNEW STEEL BEAMS CABLE BRACING
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
Additional
Modifications
Column Compression
Continuity of horizontal elements
Computed response
Cable
bracing for
2-story
school
Anchorage and cable details
Cable bracing for 12-story steel frame
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.
• 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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