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