M. Eng. Velyan Petkov

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THE EUROPEAN CENTER FOR RISK PREVENTION, SOFIA,
BULGARIA
Bulgarian seismic design codes and civil
construction practice. Infilled RC frames -
Application and assessment of their resistance to
lateral forces

• M. Eng. Velyan Petkov
• The European Center for Risk Prevention, Sofia,
  Bulgaria

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• 1.INTRODUCTION
• Eurocode 8 and Eurocode 8 Part 3 in Bulgaria
• Assessmen and retrofit programs in Bulgaria
• Type of existing buildings structures.
• - large panel systems
• - masonry and masonry infilled structures

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• 2.Bulgarian Seismic Codes and Eurocode 8
  (Eurocode 8-3)
• Pre 1947 No Seismic Design Code
• 1947 First Seismic Design Requirements
• 1957 First Seismic Design Code Low Level
  Seismic Design Codes
• 1964 New Seismic Design Code Medium Level
  Seismic Design Codes - Introduction of Dynamic
  factors
• 1987 Modern Bulgarian Seismic Design Code and
  preceding events (1977 Vrancea Earthquake and
  1987 Strazhica Earthquake)
• 2007, 2009 and 2012 Editions
• 2012 - Introduction of Eurocode 8
• 2012 2014 Joint Application of Codes
• Post 2014 Planned retirement of Bulgarian
  Seismic Code

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• Type of Buildings, classified by the reference
  Seismic Design Code at the time of design and
  construction
• Pre 1947 Construction
• 1947-1957 Construction
• 1957-1964 Construction
• 1964-1987 Construction Medium and high rise
  residential buildings. Large Panel Systems, Lift
  Slab method, prestressed reinforced concrete
  buildings, climbing shuttering RC system, and
  others. Mass construction period.
• 1987 Seismic Design Code
• 1990s period
• 2000-present
• Comparison between the codes
• Seismic Assessment of buildings designed
  according to Bulgarian codes

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012
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Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012 Pernik Region
Undamaged buildings
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012 Pernik Region Damaged
buildings
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012 Pernik Region Damaged
buildings
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012 Pernik Region Damaged
buildings
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Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012 Sofia region Elastic
Spectrum soil type C
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012 Sofia region Damages
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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3.Pernik Earthquake 2012 Sofia region Damages
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• 4.Assessment of masonry-infilled reinforced
  concrete frames and buildings
• Masonry together with reinforced concrete is the
  most widely used material in Bulgarian cuvil
  practice.
• In Bulgaria masonry is used as
• Structural material
• Non-structural material
• Until now the effects of the infill on the
  behavior of the structures were usually neglected
  in seismic analysis of RC/masonry buildings.
• 4.1 Masonry-infills in Bulgarian civil
  construction practice
• Use of masonry as primary (structural) material
  in combination with wood, steel etc.
• Use of masonry as primary (structural) material
  in combination with RC.
• 50s 60s application in low rise buildings with
  up to 4-5stories (usually 3-4)
• 60s present use in low rise residential
  houses up to 2(max 3) stories high
• Use of masonry as nonstructural material
• 60s present application in low, middle and
  high rise buildings with RC as primary structural
  material (usually RC shear walls are used)
• Positives of the early designs
• Usually regular buldings
• Use of bricks with no openings

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• Quality control of the masonry
• Conservative design
• Usually low height
• High safety against premature out of plane
  failure of the masonry
• Deficiencies of the early designs
• Designed according to low-level Design codes and
  usually lower seismic design acceleration
• Poor detailing lack of enough transverse rebar
• Use of smooth rebar steel rods.
• Low-strength concrete
• Unknown quality of the mortar
• Possible degradation of strength due to removed
  internal walls.
• Brittle failure is expected
• Positives of later designs
• Designed according to better Design codes
• Better detailing
• Use of textured rebar steel rods (especially in
  the last decades)
• High-strength concrete.

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• Neglecting the strength of infill is often on the
  safe side
• Better performance might be expected (especially
  in buildings designed according to 1987 Seismic
  Design Code)
• Deficiency of late designs
• Use of bricks with high percentage of openings
• Less conservative designs
• Neglecting the stiffness of infill might be
  dangerous
• Low quality control of the masonry construction
  due to the understanding that it is not important
  for the overall behavior of the structure.
• Design and construction of irregular structures
  (especially after 1990)
• 1990s period when overall control was not strict
  enough
• Possible premature collapse of internal masonry
  walls (due to lack of connection between the
  frame and the masonry)

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• 4.2 Assessment of the behavior of in-filled RC
  frames
• Importance
• Lack of modeling techniques, prescribed in
  Seismic codes (either Bulgarian or Eurocode 8)
• Types of infill models
• Macromodels
• Bare frame
• Single-strut
• Double Strut
• Multi-Strut
• EQUIVALENT WIDTH OF THE STRUT

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• Micromodels

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Risk Prevention, Sofia, Bulgaria
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• Comparison of Analysis Results

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• Nonlinear Strut Models
• Importance and field of application
• Data input requirements

SEISMOSTRUCT Software Package nonlinear model
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• 4.3 Application of infill modeling in assessment
  and retrofit
• Linear Strut Models

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• 4.3 Application of infill modeling in assessment
  and retrofit
• Nonlinear Strut Models

M. Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• 4.3 Application of infill modeling in assessment
  and retrofit
• Nonlinear Strut Models Capacity Curves Base
  Shear vs. Top displacement

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• 4.3 Application of infill modeling in assessment
  and retrofit
• Nonlinear Strut Models Strengthening of
  existing structures

• Nonlinear Micromodels

M. Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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• CONCLUSIONS
• BDS EN 1998-32005 Assessment and Retrofitting of
  Buidings is the first complete structural code of
  this type in Bulgaria.
• Contradictions between the old and the new code
  exist
• Completely different principles
• Different definition of seismically resistant
  structure
• 2012 Pernik Earthquake conclusions
• The event in Pernik may be classified as a strong
  one (ref. 1987 code)
• The event in Pernik may be classified as moderate
  or even low
• Almost all buildings properly designed and
  constructed withstood the earthquake without
  severe damages.
• Many of the Buildings that were constructed
  without proper designs and in contradiction to
  good construction practices were heavily
  damaged.
• Some deficiencies of old local codes designs
  were detected.
• Danger of falling non-structural elements of
  buildings during an earthquake exists.
• Masonry-infills influence the behavior of
  structures.

M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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CONCLUSIONS 5. Modeling of masonry requires a lot
of information and knowledge. 6. Introduction
of national application handbooks is
required. 7. Many of the buildings in Bulgaria
may be rated as not seismically resistant if
checked in accordance to BDS EN 1998-32005 8.
But the last doesnt mean that they really
arent.
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria
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TNANK YOU FOR YOUR ATTENTION
M.Eng. Velyan Petkov The European Center for
Risk Prevention, Sofia, Bulgaria