ECCE Conference, Istanbul SEISMIC REHABILITATION STRATEGY FOR SOUTHERN EUROPE

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ECCE Conference, IstanbulSEISMICREHABILITATION
STRATEGYFOR SOUTHERN EUROPE

• A. T. Tankut, Chair
• Professional Engineering Committee
• Turkish Chamber of Civil Engineers

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OUTLINE

• Introduction - Concepts definitions
• Bases of rehabilitation strategy
• - Common problems deficiencies
• - Performance levels
• - Rehabilitation technologies available
• Rehab strategy for southern Europe

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INTRODUCTION

• A huge seismically unsafe building stock
• A systematic assessment will reveal
• - A small number seismically safe,
• - A certain portion to be demolished,
• - The majority to be rehabilitated.
• ?Seismic rehabilitation of the existing building
  stock is one of the most critical aspects of
  damage mitigation efforts, if not the most
  important one.

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TERMINOLOGY

• Repair Post-damage intervention to bring the
  performance back to the pre-damage level or
  higher
• Strengthening Intervention to improve the
  existing performance of an undamaged
  structure/member
• Damage The key concept

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SEISMIC REHAB STRATEGY

• Rehab strategy is essential for
• - The single building or
• - The building stock in a certain area
• - The country or region considered.
• An efficient strategy development requires
  careful considerations of
• - Common deficiencies observed
• - Performance levels to aim at
• - Rehab technologies available.

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COMMON DEFICIENCIES

• Reinforced concrete framed building structures
  with hollow brick masonry infill are common in
  southern Europe.
• Low-rise (1?2 floor) are not vulnerable
• High-rise (gt 10?12 floor) buildings are
• carefully designed and constructed
• Mid-rise (3?10floor) bldgs of inferior
• material, design and construction
• quality present the major problem.

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COMMON DEFICIENCIES

• Mid-rise buildings of inferior quality
• Constitute the majority in small towns
• Collapse in the pancake mode thus
• Are responsible from the high number of human and
  material losses,
• Are generally too good for demolition
• Are greatly in need of rehabilitation.

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COMMON DEFICIENCIES

• Common deficiencies of such buildings
• Insufficient lateral stiffness
• Deficient reinforcement detailing
• - Insufficient confinement anchorage
• - Inadequate joint reinforcement etc.
• Deficient design practice
• - Horizontal/vertical irregularities
• - Short columns soft storeys etc.
• Poor concrete poor workmanship etc.

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PERFORMANCE LEVELS

• Generally accepted performance levels
• Functional Slight or no damage (in the
  code prescribed earthquake) continued
  serviceability
• Immediate occupancy Light damage
  serviceability after inspection
• Life safety Moderate damage
• Collapse prevention Severe damage, no collapse,
  no casualties

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PERFORMANCE LEVELS

• Most of the current seismic codes
• Were developed for new structures
• Aim at a performance level above life safety
  without explicitly mentioning
• Expect repair and strengthening interventions to
  comply with them
• Do not provide any flexibility for performance
  level and remaining service life
  considerations.

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PERFORMANCE LEVELS

• Special code provisions are definitely needed for
  rehabilitation applications
• providing flexibility for
• - Performance level and
• - Remaining service life considerations.
• Designer should be given the choice of
• - Life safety or collapse prevention
• - 20 or 40 or gt60 yrs service life.

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SEISMIC REHAB TECHNOLOGY

• Member strengthening techniques are available
  (to increase their capacities) for
• Columns (axial load bending)
• Beams (bending shear)
• Beam-column joints (shear)
• Slabs (diaphragm action)

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SEISMIC REHAB TECHNOLOGY

• System behaviour imrovement techniques are also
  available
• - Lateral stiffness increasing elements
• (To relieve members from seismic effects)
• - Base isolation, dampers etc.
• (To minimise seis action transfer to structure)

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COLUMN STRENGTHENING

• Reinforced concrete jacketing
• - Effective for axial load, complicated
• and not recommended for bending
• - Full jacket is best, partial is acceptable
• - Well confinement in jacket is essential
• - Bar welding is recommended

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COLUMN STRENGTHENING

• Steel jacketing
• - Only for axial load, never for bending
• - Tight connection with base plates and
• - Well confinement are essential

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COLUMN STRENGTHENING

• CFRP confinement
• - Effective as confinement, especially
• in circular columns to a lesser
• extent in rectangular ones
• - Effective to improve lap splice
• performance and capacity

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BEAM STRENGTHENING

• Additional layers with new steel
• - Effective for bending
• - Bar development is critical
• - Welding is advisable
• - Stirrups or Z-bars are essential
• CFRP applications to the same effect are also
  possible.

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BEAM STRENGTHENING

• External clamps as shear reinforcement
• - Effective for shear
• - Limited prestressing is recommended
• CFRP applications to the same effect are being
  investigated (anchorage is critical).

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BEAM STRENGTHENING

• Beams connected to new lateral stiffness
  elements become coupling beams and receive
  enormous bending and shear.
• - Hinging is unavoidable let it be, and
• - Make sure it is properly confined to
• tolerate hinging, and
• - Make sure shear capacity is higher than
• bending cap to prevent shear failure.

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JOINT STRENGTHENING

• Joints are critical under seismic action, and
  they are generally deficient (Required
  confinement is not usually provided).
• - An effective and practical strengthening
• technique is not yet available (Techniques
• suggested are ineffective or impractical).
• Another reason to endorse the system
• behaviour improvement approach

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SLAB STRENGTHENING

• Major contribution of the slab to the seismic
  performance is diaphragm action.
• Additional layers with new steel
• - Effective for bending in-plane stress
• - Rough connection surface and
• - Shear connectors are essential
• - Def recovery is not recommended

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SYSTEM IMPROVEMENT

• Lateral stiffness increasing elements
• Cast-in-place reinf conc infilled frames
• Reinforced masonry infilled frames
• Steel cross bracing
• Post tensioning
• External rigid frame to support the str
• Masonry infills reinforced with
• - CFRP diagonals
• - High strength precast concrete panels

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SEISMIC REHAB STRATEGY

• Member strengthening is preferred when
• - Structural weakness is localised or
• - A small number of members are deficient.
• Member strengthening is not feasible when
• - Deficiencies are widespread and
• - Lateral stiffness is insufficient

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SEISMIC REHAB STRATEGY

• Remembering the common deficiencies mentioned
  above (ie, insufficient lateral stiffness and
  widespread deficiency),
• System behaviour improvement is
• essential and should be accompanied by
• Strengthening of a limited number of
• deficient members, whenever needed