SEISMIC REHABILITATION BY SYSTEM IMPROVEMENT (METU APPROACH)

1. SEISMIC REHABILITATION BY SYSTEM IMPROVEMENT (METU APPROACH) UĞUR ERSOY Bogazici University, Civil Engineering Dept. Istanbul - Turkey Presentation atUniversity of Texas and Purdue University November 2008

2. ONE OF THE MAJOR EARTHQUAKES IN ISTANBUL WAS IN 1715 ACCORDING TO SOLAKZADE (HISTORIAN WHO EXPERIENCED THE 1715 EARTHQUAKE) 10000 PEOPLE GOT KILLED A GREAT MAJORITY OF THE BUILDINGS WERE DESTROYED 109 MOSQUES AND 30 CHURCHES EITHER COLLAPSED OR SUFFERED HEAVY DAMAGE A PORTION OF THE CITY WALLS COLLAPSED, WAVES WENT OVER THE CITY WALLS

3. MAJOR CAUSES of SEISMIC DAMAGE TO RC BUILDINGS • MISTAKES MADE IN CHOOSING THE BUILDING CONFIGURATION (ARCHITECTURAL AND/OR STRUCTURAL SYSTEM) • INADEQUATE REINFORCEMENT DETAILING AND DETAILING ERRORS • MISTAKES MADE AT THE CONSTRUCTION STAGE (INADEQUATE INSPECTION) • SOIL PROBLEMS

6. SEISMIC REHABILITATION • MEMBER REHABILITATION • (Column, Beam Jacketing, Wrapping with CFRP Sheets, etc.) • SYSTEM IMPROVEMENT

7. SYSTEM IMPROVEMENT • IN THIS TECHNIQUE , THE EXISTING LATERAL LOAD RESISTING SYSTEM IS REPLACED BY A NEW LATERAL LOAD RESISTING SYSTEM CONSISTING OF RIGID VERTICAL MEMBERS.

8. CASES IN WHICH SYSTEM IMPROVEMENT BECOMES FEASIBLE • WHEN THE LATERAL STIFFNESS OF THE FRAME SYSTEM IS INADEQUATE • WHEN TOO MANY MEMBERS NEED TO BE REHABILITATED • WHEN THE FRAME SYSTEM HAS INHERITED WEAKNESSES SUCH AS SOFT STORY, SHORT COLUMNS, ETC.

9. MOST COMMONLY USED SYSTEM IMPROVEMENT TECHNIQUE IN TURKEY IS “REINFORCED CONCRETE INFILLED FRAME TECHNIQUE”. IN THIS TECHNIQUE: SELECTED BAYS OF THE FRAME SYSTEM IN EACH DIRECTION ARE FILLED WITH CAST IN PLACE REINFORCED CONCRETE WALLS PROPERLY CONNECTED TO FRAME ELEMENTS BY INSERTED DOWELS

11. RC INFILL FOUNDATION SECTION A-A

12. RESEARCH AT METU ON RC INFILLED FRAMES (1969 – 2000)

18. METU INFILLED FRAME TESTS THREE BAY DEFICIENT, DAMAGED FRAME, 1999

19. INFILL WAS INTRODUCED TO DAMAGED FRAME. NO REPAIR WAS MADE DEGREE OF DAMAGE IN THE FRAME: COLUMN LONGITUDINAL BARS YIELDED INFILLED FRAME BEHAVED WELL 90 – 95 % OF LATERAL LOAD WAS RESISTED BY THE WALL

20. RC INFILLED FRAME TECHNIQUE • HUNDREDS OF BUILDINGS HAVE BEEN REHABILITATED USING THIS TECHNIQUE AFTER THE FOLLOWING EARTHQUAKES: • 1969 Bartın • 1992 Erzincan • 1995 Dinar • 1998 Ceyhan • 1999 Marmara • 1999 Düzce

21. THE GREAT TRUTHS OF ENGINEERING ARE SIMPLE... AN ENDLESSLY COMPLEX PRESENTATION OF AN ENGINEERING FACT INDICATES COMPLICATION IN THE BRAIN OF THE PROPOUNDER RATHER THAN COMPLEXITY OF NATURE. Hardy Cross

22. METU RECOMMENDATIONS FOR RC INFILLED FRAMES MINIMUM INFILLED WALL AREA: IN EACH DIRECTION, S Aw >=0.0025 S Api >=0.01 Apt S Aw - SUMMATION OF CROSSSECTIONAL AREA OF INFILLS S Api – SUMMATION OF PLAN AREAS OF ALL FLOORS Apt - FLOOR AREA OF THE BUILDING AT THE BASE IN CASE OF WEAKNESSES SUCH AS SOFT STORY, SHORT COLUMNS, INCREASE THE CONSTANT FROM 0.0025 TO 0.003.

23. DOWELS CONNECTING THE INFILL TO FRAME MEMBERS TOTAL CROSS-SECTIONAL AREA OF DOWELS IN THAT DIRECTION SHOULD NOT BE LESS THAN THE WALL REINFORCEMENT IN THAT DIRECTION: Adx >= S Asx Ady >= S Asy AT FOUNDATION LEVEL, Ady >= 1.5 S Asy ANCHORAGE OF DOWELS: Ld >= 35 BAR DIAMETER (INFILL) >= 15 BAR DIAMETER (FRAME MEMBERS,EPOXY)

24. SHEAR CAPACITY Vr <= fct (Ac) fct = TENSILE STRENGTH OF CONCRETE Ac = SHEAR AREA = txL = SHADED GRAY AREA

27. METU APPROACH

28. Building Model ANALYSİS FILTER DECISION

29. “RC INFILLED FRAME TECHNIQUE” IS PROVED TO BE, ECONOMICAL, PRACTICAL AND SAFE BY TESTS AND NUMEROUS APPLICATIONS AFTER THE EARTHQUAKES DRAWBACK : THE BUILDING HAS TO BE EVACUATED

30. “RC INFILLED FRAME TECHNIQUE” WILL NOT BEFEASIBLE TO REHABILITATE THOUSANDS OF EXISTING BUILDINGS, SINCE IT WILL NOT BEPRACTICAL TO EVACUATE THEM!

31. YEAR 2000, RESEARCHERS AT METU WERE SEARCHING FOR A NEW REHABILITATION TECHNIQUE WHICH WILL NOT REQUIRE EVACUATION AND WILL GIVE MINIMUM DISTURBANCE TO THE OCCUPANTS DURING APPLICATION

32. SOLUTION, TO STRENGTHEN THE EXISTING NON-STRUCTURAL INFILLS AND PARTITION WALLS WHICH WOULD BEHAVE AS STRUCTURAL WALLS

33. STRENGHTHENING OF EXISTIMG NON-STRUCTURAL INFILLS BY, • CFRP SHEETS • PRECAST PANELS • WHICH WILL BE CONNECTED TO THE FRAME MEMBERS

34. METU RESEARCH PROJECTS (2001-2006) • Financed by: • TUBITAK (Turkish Science Foundation) • NATO • BUDGET ≈ $ 1.5 Million

35. Other Contributers: • TURKEY: • Kocaeli and Boğaziçi Universities • and ITU • FOREIGN • USA (University of Texas), Greece and Republic of Macedonia

36. SP – 6, SP – 7

37. TEST SETUP

38. TEST RESULTS

39. PC PANELS

40. LOADING SYSTEM

41. ENVELOPE CURVES

42. PERFORMANCE IMPROVEMENT Relative to masonry Relative to infilled frame bare frame Lateral load capacity2.5 times  15 times Lateral stiffness 3 times  20 times Ductility 2 times  0.2 times

43. SHAKE TABLE TESTS INSTITUTE OF EARTHQUAKE ENGINEERING AND ENGINEERING SEISMOLOGY, SKOPJE, MACEDONIA

44. SEISMIC REHABILITATION REQUIRES A SOUND BEHAVIOR KNOWLEDGE • REHABILITATION MADE WITH LIMITED KNOWLEDGE AND EXPERIENCE CAN MAKE THE STRUCTURE MORE VULNERABLE

45. THE ENGINEER IS FACED WITH MANYUNKNOWNS IN THE ANALYSIS OF AN EXISTING BUILDING PRIOR TO AND AFTER  REHABILITATION. THEREFORE IN MODELING THE STRUCTURE THE ENGINEER HAS TO MAKE NUMEROUS ASSUMPTIONS SUCH AS, MATERIAL STRENGTHS, FLEXURAL RIGIDITY (EI), etc.

46. 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.

47. HISTORY OF SCIENCE IS FULL OF BEAUTIFUL THEORIES, BUTCHERED BY SMALL UGLY FACTS ! Sir S. Thomas