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SPECIAL CASES OF STRUCTURAL
REHABILITATION
Presentation atUniversity of Texas and Purdue University
November 2008
UĞUR ERSOY
Bogazici University, Civil Engineering Dept.Istanbul - Turkey
REHABILITATION TECHNIQUES SUCH AS COLUMN JACKETING, RC INFILLED FRAME TECHNIQUE ARE WELL KNOWN BY MOST OF THE ENGINEERS.SOME ENGINEERS CALL THESE AS, “STANDARDIZED TECHNIQUES” !!!!!!
IT IS NOT RIGHT TO APPLY THESE SO CALLED “STANDARDIZED TECHNIQUES” TO A BUILDING WITHOUT CONSIDERING THE CHARECTERISTICS OF THAT BUILDING AND THE PROBLEMS INVOLVED.
THE ENGINEER SHOULD ALSO CONSIDER SERVICEABILITY AND FUNCTIONAL REQUIREMENTS IN DECIDING ON THE REHABILITATION TECHNIQUE TO BE USED.
IN CONCLUSION, SO CALLED “STANDARDIZED TECHNIQUES” SHOULD BE REVISED OR NEW TECHNIQUES SHOULD BE DEVELOPED, CONSIDERING THE PROBLEMS ENCOUNTERED IN THAT PARTICULAR BUILDING AND THE FUNCTIONAL REQUIREMENTS.
IF THE STRUCTURE IS DAMAGED, NO REHABILITATION SHOULD BE MADE UNTIL THE CAUSE OF DAMAGE IS UNDERSTOOD (DIAGNOSIS).
IN EVALUATING THE STRENGTENING / REPAIR TECHNIQUE TO BE USED, THE ENGINEER HAS TO DEFINE HIS OBJECTIVES.
“STRENGTENING/REPAIR” IS AIMED TO IMPROVE WHAT?? -LATERAL STIFFNESS OF THE BUILDING ?-AXIAL LOAD CAPACITY OF SOME MEMBERS ?-MOMENT CAPACITY OF SOME MEMBERS ?-CONFINEMENT ?-OTHERS ?
THE ENGINEER IS FACED WITH MANY UNKNOWNS IN THE ANALYSIS OF AN EXISTING BUILDING PRIOR TO AND AFTER REHABILITATION. THEREFORE IN MODELLING THE STRUCTURE THE ENGINEER HAS TO MAKE NUMEROUS ASSUMPTIONS SUCH AS, MATERIAL STRENGTHS, FLEXURAL STIFFNESSES, etc.
DUE TO THESE ASSUMPTIONS, THE NUMBERS WHICH COME OUT AS A RESULT OF THE ANALYSIS ARE BY NO MEANS EXACT OR NEARLY EXACT. THESE NUMBERS, ALTHOUGH NOT EXACT, SERVE AS A GUIDELINE FOR THE ENGINEER IN MAKING JUDGEMENTS AND DECISIONS.
Building Model
ANALYSIS FILTER
DECISION
COLUMN
DAMAGED COLUMN
CROSS - SECTION
1000mm
1000mm
22 STORIES
CAUSES CAUSES OF OF DAMAGE DAMAGE ((DIAGNOSISDIAGNOSIS))
1. CREEP
2- TEMPERATURE DROP
Climate of Ankara: In winter temperatures drop to -15o to -20o C. Inside the building the temperature is about 20o C. Structural walls at each corner shorten due the temperature drop, imposing axial load to columns (story shortening in winter).
3. AXIAL LOAD LEVEL IN MOST OF THE COLUMNS IS VERY HIGH.
Po = ø (0.85f’c Ac + Ast fy) Pd = Design axial load on the
column Po = 19 000 kN (For ø = 0.65) Pd = 23 000 kN Axial load = 120% of the uniaxial
load capacity!
4. DETAILING ERRORS
-Long. reinforcement concentrated on two faces
-Only two ties for 42 large diameter longitudinal bars ( column size 40x40 in.)
-Kink in longitudinal bars
MAIN PROBLEM:MAIN PROBLEM:
-AXIAL LOAD CAPACITY-AXIAL LOAD CAPACITY
-CONFINEMENT-CONFINEMENT
DECISION:DECISION:
-STEEL JACKET-STEEL JACKET
( ( services should not be interruptedservices should not be interrupted ) )
COLUMN
HYDRAULIC RAM
PLAN
STEEL ANGLES
STEEL PLATES
STEEL BRACKET
HYDRAULIC RAM
Steel Jacket
Steel Jacket(2 pieces)
Column
Special mortar
Steel JacketWelding
DIAGNOSISDIAGNOSIS::
MAIN CAUSE OF DAMAGE IS TEMPERATURE MAIN CAUSE OF DAMAGE IS TEMPERATURE DROP.DROP.
INDICATIONSINDICATIONS::
--COLUMN CONCRETE CRUSHINGCOLUMN CONCRETE CRUSHING..
-BRICK INFILL CRUSHING-BRICK INFILL CRUSHING..
--BOTH INDICATING STORY SHORTENINGBOTH INDICATING STORY SHORTENING..
DECISIONDECISION::
--INSTRUMENT THE BUILDING TO MONITOR INSTRUMENT THE BUILDING TO MONITOR CHANGES IN TEMPERATURE AND STRAINS CHANGES IN TEMPERATURE AND STRAINS IN COLUMNSIN COLUMNS
DATE
PLAN
SECTION A-A
Punch Perimeter
RC Brackets
Dowels anchored to the column
PLAN
SECTION
NEW RC LAYER
EXISTING SLAB
ANCHORS
COLUMN 1X1 meter
HOLE DIAMETER = 25mm
Bolts
Steel plate
Steel plate
Steel angles Steel anglesCrack
REHABILITATION OF A PRECAST REHABILITATION OF A PRECAST INDUSTRIAL BUILDING (1998)INDUSTRIAL BUILDING (1998)
SLAB MOMENT (M) and TORQUE (Mt) DISTRIBUTION
CRACK PATTERN PRIOR TO ULTIMATE
To
(kN
.m)
0
5
10
15
20
25
30
0 0,01 0,02 0,03 0,04 0,05 0,06 0,07
UNIT ROTATION (rad/m)
AP
PL
IED
TO
RQ
UE
(kN
.m)
Ro=11 000 kN.m2
R=105 kN.m2
R= 410 kN.m2
rw = 0.0018
rw = 0.0028
PCA TESTS250x380 mm Beams
rw = Aot / s bw
0,0
2,0
4,0
6,0
8,0
10,0
12,0
0,0 10,0 20,0 30,0 40,0 50,0 60,0 70,0 80,0
P (kN)
To (
kN.m
)
PTo
Linear Analy.
Test Results
T=10.7 kN.m
T=5.2 kN.m
Torsion Cracks