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4th workshop on irregular and complex structures, Thessaloniki, Greece, 2005

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  2. 2. Overview  Introduction  Features  Problems and opportunities  Diagnosis and mission  Outlook to the European context  Conclusions
  3. 3. Introduction
  4. 4. Features: typical view, load bearing elements
  5. 5. Features: architectural plan
  6. 6. Features: structural details
  7. 7. Features: seismic defficiencies
  8. 8. Problems and opportunities  Seismic vulnerability  Seismic hazard Very Poor Seismic Performance A (High) B Medium C D E Excellent Seismic Performance F (Low) < O > Year Earthquake Epicenter Richter magnitude Maximum Intensity 1940 Vrancea 7.4 7 1977 Vrancea 7.2 8 1986 Vrancea 7 8 1990 Vrancea 6.7 7
  9. 9. Problems and opportunities Building site Vulnerable building
  10. 10. Problems and opportunities: building materials Structural element Building materials Characteristic strength Mix Proportion/ Dimensions Comments Infill walls clay brick compression strength between 2.6MPa (min for mark C50) and 10.0MPa (average for mark C100), bending strength between 1.5MPa (min for mark C50) and 2.1MPa (average for mark C100) 7cm (63mm) x 14cm (115mm) x 28cm (240mm) [brick itself (brick with mortar)] Façade walls: 28/34cm thick, Partition walls 10/16cm. The mark of brick and mortar is unknown; the strength of solid bricks was determined experimentally by Lungu. Columns Reinforced concrete (RC) 7-15MPa (mean 12) round smooth steel reinforcement [Bălan] ‘ F i e n i ’ [ 6 ] c e m e n t 2 4 0 - 270kg/m³ w i t h a g g r e g a t e s 0 - 3 m m ( [ P r a g e r ] , p . 3 9 4 , 1 9 4 - 1 9 9 ) , m i x p r o p o r t i o n o f 1 , 5 m ³ g r a v e l / m ³ 1 : 3 m o r t a r ( 7 0 0 k g c e m e n t + 1 m ³ s a n d ) 1 0 0 - 1 2 0 k g s t e e l / m ³ c o n c r e t e . R e - b a r s : s p a c i n g 2 5 - 3 0 c m , d i s t r i b u t e d g e o m e t r i c a l l y . S t i r r u p s : d i a m e t r e 6 - 8 m m , s p a c i n g 2 5 - 3 5 c m . R e i n f o r c e m e n t o f t e n l e s s t h a n 0 , 5 % . I n s u f f i c i e n t l a p s p l i c i n g a n d s t i r r u p s . S t i r r u p s o n l y c o n n e c t t h e c o r n e r R e - b a r s , s p a c e d u p t o 1 m i n b a d l y e x e c u t e d c o n s t r u c t i o n s [Bălan]. T h e ‘ F i e n i ’ c e m e n t h a d 1 0 d a y s h a r d e n i n g t i m e . W o o d s c a f f o l d i n g Beams RC see above reinforcement distribution - no data Roof/ Floors RC see above
  11. 11. Problems and opportunities Structural Element Seismic Deficiency Earthquake Resilient Features Earthquake Damage Patterns Wall additional loads for the structure, especially in case of facade consoles increasing frame stiffness out-of-plane (leading to further torsion) and rifts (especially X). Columns poor reinforcement (<0.6%, bars of 10mm diameter, sparse stirrups), evtl. low cement quantity in concrete; non-verticality, poor section conformation (long rectangles), don’t form moment resisting frames with beams. - Soft storey: concrete spalling till destruction and buckling of Re-bars at plastic hinges. Mezzanine: brittle breaks with rifts at 45°. In the oblique sections resulted the stirrups detached. This sever damage can lead directly to collapse. Current storey: damage along plastic hinges: horizontal and oblique (brittle) X rifts, concrete spalling, buckling of longitudinal reinforcement. Beams Low cement quantity in concrete and low reinforcement in speculatively built blocks, don’t form moment resisting frames with columns (numerous secondary beams) execution usually careful Long beams: rifts and concrete spalling on the bottom in the plastic articulation (near the beam- column-node). Short beams: 0°-45° brittle but undangerous rifts open the beam in whole height at plastic hinges. Roof and floors Low cement quantity in concrete and low reinforcement in speculatively built blocks; simple slab floors are too elastic sufficient stiffness of embedded bricks waffle system In room slabs, balconies some rifts, at change of stair flights some more rifts.
  12. 12. Diagnosis and mission: relationship diagram among the features Structural element Building materials Structural element Seismic defficiency Earthquake resilient features Earthquake damage patterns Seismic defficiency Seismic strengthening provision Characteristic strength Mix proportion/ dimensions
  13. 13. Diagnosis and mission: analysis of a retrofit model project Structural Deficiency Seismic strengthening provision “Wilson” high-rise: 2 basement levels, ground floor with commercial spaces and 11 upper floors at the corner tower RC skeleton structure, with facade walls out of brick masonry and interior walls from plates irregular shape in plan, with inequal wings, a sharp angle at the tower and an interior courtyard The building was heavily affected by the 1940 earthquake and retrofitted afterwards with concrete walls between some columns and jacketing of some columns. Retrofit solution after 1977: rebuilding the collapsed corner zone, set-back at all levels (fig.). The damaged reinforced concrete members were repaired and strengthened through concrete recasting or reinforced concrete jacketing on ground floor, first floor and locally on the other floors, especially at the ‘brand walls’ to the north.
  14. 14. Diagnosis and mission: contemporary preventive retrofit (2003)
  15. 15. Outlook to the European context Buildings of the Modernism in Vienna
  16. 16. Conclusions  France  Portugal  Greece  Austria  Spain  Italy  Potential for comparative studies of inner city housing in areas of variate seismicity  architectural language  urban development policies  preservation requirements
  17. 17. THANK YOU!