Learning from Earthquakes to Improve Rehabilitation of Reinforced Concrete Buildings. James O. Jirsa The University of Texas at Austin

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2 Learning from Earthquakes to Improve Rehabilitation of Reinforced Concrete Buildings James O. Jirsa The University of Texas at Austin

3 Objectives of NATO SfP Seismic evaluation and retrofitting of existing buildings in Turkey and Greece. Transfer, adapt, and implement and/or develop innovative technologies and methodologies for both countries.

4 Requirements for rehabilitation to be implemented Demand/need for rehabilitation Availability of techniques that are Constructible Cost-effective Convincing

5 Buildings in Turkey

6 Buildings in Mexico City

7 Approaches for reaching objective Reconnaissance studies after recent earthquakes Little documentation of performance of rehabilitated buildings Field experience applicable to typical buildings in region Mexico City after 1984 Experimental studies NATO Project Other reports in this Workshop Demonstration projects

8 Widespread damage to concrete construction Waffle slab systems Column failures Reinforcement details Infill walls

9 Experience Reconnaissance studies Codes & Standards Documentation Design guidelines Analytical studies Experimental studies Shortcut

10 Demonstration projects New approaches must be sold to potential users Implementation depends on the user s perception of technique Seeing is believing Field application and demonstration projects may be most convincing Education of owners and engineers

11 Mexico City after 1985 Characteristics of damage Lake bed zone foundation limitations Construction types Rehabilitation activities Affected zone was a laboratory for rehab Documentation NSF/CONACyT Workshop Case study Cable-bracing techniques

12 Mode of Failure Observed Shear, compression, or other failure of columns Shear in beams Shear in waffle slabs Flexure in beams Beam-column joints Shear walls, shear or bending Other modes Could not be identified % of cases

13 Damage statistics Severe Collapse No. of Buildings RC Frames Steel Frames Waffle Slabs Bldgs w/shear walls Masonry

14 Damage/height of buildings No. of Buildings <5 6 to to 15 >15 No. of Stories Severe Collapse

15 Following the earthquake Owners and occupants were concerned about potential hazards in future events Buildings needed by users Repair and strengthening proceeded with very few design guidelines or standards for construction in place Engineers met challenge with creative solutions

16 Rehab prior to 1985 Some buildings repaired following earthquakes in 1957 and 1979 Almost no information available about those buildings Exception--Two buildings strengthened before 1985 performed well and were extensively studied after the earthquake

17 Building braced pre-1985 Foundation effects

18 1989 Workshop Site visits to buildings under rehab Discussions with engineers in charge of rehabilitation design and construction Review of approval process for rehab projects Participants defined the need to document rehab work

19 Beam and column jacketing

20 New bracing systems

21 New walls

22 Mixed systems

23 Removal of top stories

24 Rehabilitation of Existing Reinforced Concrete Buildings in Mexico City: Case Studies

25 Case study: Layout of building Stairway BUILDING PLAN Stairway A 8.00 C2 C4 C7 C7 C6 C6 C6 C6 C6 C6 C6 C6 C7 C7 C4 C2 B 3.75 C9 C3 C8 C8 C5 C5 C5 C5 C5 C5 C5 C5 C5 C5 C3 C1 30 for h=100 cm. 25 for h=85 cm (meters) ELEVATION LINE A TYPE 1 TYPE 2 TYPE m TYPE 4 TYPE 5 TYPE 6 ELEVATION LINE B MAIN BARS ADDITIONAL #4 BARS

26 Cable braces NEW STEEL BEAMS CABLE BRACING NEW STEEL BEAMS

27 Details EXISTING COLUMN CABLE CABLE A A WAFFLE SLAB (SOLID ZONE AROUND COLUMN) SLAB ZONE TO BE DEMOLISHED EXISTING COLUMN REINFORCEMENT DETAIL A INTERIOR CABLES NEW CONCRETE = f c 5000 psi CABLE ANCHOR MECH EXTERIOR CABLES SECTION A-A STEEL PLATE 6-IN. X 6-IN. X 12-IN. DETAIL A

28 Additional Modifications Column Compression Continuity of horizontal elements

29 Computed response

30 Cable bracing for 2-story school

31 Anchorage and cable details

32 Cable bracing for 12-story steel frame

33 Concluding remarks Future actions to improve learning from earthquakes Documentation of rehabilitation projects for evaluation of performance in future earthquakes. Instrumentation of buildings to enable more detailed evaluation of performance.

34 Challenges Focus efforts on areas where need is greatest Marginal residential construction Determination and enforcement of minimum requirements Maintain and create interest in earthquake mitigation Competition with other political and social exigencies No well-defined industry to pressure policy makers

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