ATHENS 12 th of April, M. Eng. Velyan Petkov 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 THE EUROPEAN CENTER FOR RISK PREVENTION, SOFIA, BULGARIA

2 1.INTRODUCTION Eurocode 8 and Eurocode 8 Part 3 in Bulgaria Eurocode 8 and Eurocode 8 Part 3 in Bulgaria Assessmen and retrofit programs in Bulgaria Assessmen and retrofit programs in Bulgaria Type of existing buildings structures. Type of existing buildings structures. - large panel systems - large panel systems - masonry and masonry infilled structures ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

3 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 Introduction of Eurocode – 2014 – Joint Application of Codes Post 2014 – Planned retirement of Bulgarian Seismic Code ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

4 Type of Buildings, classified by the reference Seismic Design Code at the time of design and construction Pre 1947 Construction Construction Construction 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 Seismic Design Code -1990s period present Comparison between the codes Seismic Assessment of buildings designed according to Bulgarian codes ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

5 3.Pernik Earthquake 2012 ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

6 3.Pernik Earthquake 2012 – Pernik Region – Undamaged buildings ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

7 3.Pernik Earthquake 2012 – Pernik Region –Damaged buildings ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

8 3.Pernik Earthquake 2012 – Pernik Region –Damaged buildings ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

9 3.Pernik Earthquake 2012 – Pernik Region –Damaged buildings ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

10 3.Pernik Earthquake 2012 – Sofia region – Elastic Spectrum soil type “C” ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

11 3.Pernik Earthquake 2012 – Sofia region – Damages ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

12 3.Pernik Earthquake 2012 – Sofia region – Damages ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

13 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 ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

14 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. ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

15 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) ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

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 ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

17 Micromodels ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

18 Comparison of Analysis Results ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

19 Nonlinear Strut Models Importance and field of application Data input requirements ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria SEISMOSTRUCT Software Package nonlinear model

Application of infill modeling in assessment and retrofit Linear Strut Models ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

Application of infill modeling in assessment and retrofit Nonlinear Strut Models ATHENS 12 th of April, 2013 M. Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

Application of infill modeling in assessment and retrofit Nonlinear Strut Models – Capacity Curves – Base Shear vs. Top displacement ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

Application of infill modeling in assessment and retrofit Nonlinear Strut Models – Strengthening of existing structures ATHENS 12 th of April, 2013 M. Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria Nonlinear Micromodels

24 CONCLUSIONS 1.BDS EN :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” Pernik Earthquake conclusions: -The event in Pernik may be classified as a strong one (ref 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. ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

25 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 : But the last doesn’t mean that they really aren’t. ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria

26 ATHENS 12 th of April, 2013 M.Eng. Velyan Petkov The European Center for Risk Prevention, Sofia, Bulgaria TNANK YOU FOR YOUR ATTENTION