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8/12/2019 Presentation Athens

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ATHENS 12thof April, 2013 1

M. Eng. Velyan Petkov

The European Center for Risk Prevention, Sofia,

Bulgaria

Bulgarian seismic design codes andcivil construction practice. Infilled RC

frames - Application and assessment of

their resistance to lateral forces

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

ATHENS 12thof April, 2013

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 1947No Seismic Design Code

1947First Seismic Design Requirements

1957First Seismic Design CodeLow Level Seismic Design Codes

1964New Seismic Design CodeMedium Level Seismic Design Codes -

Introduction of Dynamic factors

1987Modern Bulgarian Seismic Design Code and preceding events (1977

Vrancea Earthquake and 1987 Strazhica Earthquake)

2007, 2009 and 2012 Editions

2012 - Introduction of Eurocode 8

20122014Joint Application of Codes

Post 2014Planned retirement of Bulgarian Seismic Code





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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 ConstructionMedium 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





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3.Pernik Earthquake 2012





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3.Pernik Earthquake 2012Pernik RegionUndamaged buildings





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3.Pernik Earthquake 2012Pernik RegionDamaged buildings





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3.Pernik Earthquake 2012Sofia regionElastic Spectrum soil type C





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3.Pernik Earthquake 2012Sofia regionDamages




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3.Pernik Earthquake 2012Sofia regionDamages




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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.

4.1Masonry-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 60sapplication in low rise buildings with up to 4-5stories (usually 3-

4)

60spresentuse in low rise residential houses up to 2(max 3) stories high

Use of masonry as nonstructural material

60spresentapplication in low, middle and high rise buildings with RCas primary structural material (usually RC shear walls are used)

Positives of the early designs:

Usually regular buldings

Use of bricks with no openings




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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 detailinglack 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.






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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)






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4.2Assessment 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




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Micromodels






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Comparison of Analysis Results






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Nonlinear Strut Models

Importance and field of application

Data input requirements




SEISMOSTRUCT Software Package nonlinear model



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4.3 Application of infill modeling in assessment and retrofit

Linear Strut Models

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Nonlinear Strut Models






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Nonlinear Strut ModelsCapacity CurvesBase Shear vs. Top displacement




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Nonlinear Strut ModelsStrengthening of existing structures




Nonlinear Micromodels

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CONCLUSIONS

1. BDS EN 1998-3:2005 Assessment and Retrofitting of Buidings is the first

complete structural code of this type in Bulgaria.

2. Contradictions between the old and the new code exist- Completely different principles

- Different definition of seismically resistant structure

3. 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.

4. Masonry-infills influence the behavior of structures.






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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 1998-3:2005

8. But the last doesnt mean that they really arent.

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TNANK YOU FOR YOUR ATTENTION

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