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

22 STORIES

CAUSES OF DAMAGE (DIAGNOSIS) 1. CREEP 2- TEMPERATURE DROP Climate of Ankara: In winter temperatures drop to -15 o to -20 o C. Inside the building the temperature is about 20 o 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. P o = ø (0.85f’ c A c + A st f y ) P d = Design axial load on the column P o = kN (For ø = 0.65) P d = 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: -AXIAL LOAD CAPACITY -CONFINEMENTDECISION: -STEEL JACKET ( services should not be interrupted )

COLUMN HYDRAULIC RAM PLAN STEEL ANGLES STEEL PLATES STEEL BRACKET HYDRAULIC RAM

Steel Jacket (2 pieces) Column Special mortar Steel Jacket Welding

DIAGNOSIS: MAIN CAUSE OF DAMAGE IS TEMPERATURE DROP. INDICATIONS: -COLUMN CONCRETE CRUSHING. -BRICK INFILL CRUSHING. - BOTH INDICATING STORY SHORTENING.

DECISION: -INSTRUMENT THE BUILDING TO MONITOR CHANGES IN TEMPERATURE AND STRAINS IN 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 Crack

REHABILITATION OF A PRECAST INDUSTRIAL BUILDING (1998)

SLAB MOMENT (M) and TORQUE (Mt) DISTRIBUTION

CRACK PATTERN PRIOR TO ULTIMATE

To (kN.m)