Appendix-7. Presentation material of JICA study team

Transcription

1 Appendix-7 Presentation material of JICA study team

2 Large scale RC building Survey Outline What kinds of study we have done? How large the intensity of ground motion at this earthquake. What is found from Structural Analysis of surveyed building in Padang What is found from the viewpoint of the Design Code What is the main reason of those large damage of buildings. Is repair possible for partially damaged buildings / Is strengthening possible without reconstruction Why our target is Large scale RC building? Large-scale RC buildings were damaged and collapsed by this earthquake on Sep 30, It will minimize the damage of the earthquake to occur in future to reinforce the large-scale RC building which many people use. Large-sized RC building is damaged in Banda Aceh and Yogyakarta in the past. This is an overall problem in Indonesia, and immediate improvement is necessary. Questionnaire survey of Seismic intensity Because seismometers did not operate in this time, accurate seismic intensity is unidentified. It is necessary to know a more accurate seismic intensity to analyze seismic intensity and relations of the damage level. Each item of questionnaire is prepared as answered even if interviewee does not have special knowledge concerning the earthquake. Therefore the questionnaire survey of seismic intensity is useful.

3 Characteristic survey of Earthquake-Damaged Buildings Study Results

4 What we must know We must know the feature of the shaking of the Padang Pariaman Earthquake in order to achieve better engineering. Following three components should be known: 1. Intensity 2. Predominant period 3. Duration Questionnaire Intensity Survey Each questionnaire sheet contains 35 easy multiple-choice questions including the response of the house and the human feeling. We translated the questions into Bahasa Indonesia and distributed more than five hundred sheets to the residents of Padang. JMA intensity was extracted from the count of the answers using an empirical formula. Then, JMA intensity was converted to the MM intensity empirically. Intensity of the shaking "Intensity" is to represent the strength of shaking which begins to damage structures. In Japan, we use the JMA Intensity, and in Indonesia, you use the MM Intensity. These "Intensitys" are the sets of the index values defined from the mechanical strength of shaking (acceleration etc.) modified by its effectiveness to destruction and by the human feeling. We used a questionnaire method to get the intensity distribution in Padang. Results of the Intensity Survey MM intensity was in the city area of Padang. The peak acceleration of the shaking was estimated to be gal. intensity empirically.

5 Questionnaire MM Intensity (Provisional) Questionnaire JMA Intensity (Provisional) UNP UNP BAPPENDA BPKP BAPPENDA BPKP PU PU Predominant Period The vibration response of structures can vary one by one depending on the predominant period of earthquake and the structure scale. Scale of building Sensitive period (second) Low building (one or two-story) Middle scale building (for example, 5-story) High-rise building (for example, 20-story) < >2.0 RC frame with brick wall building Discussion on the Intensity The questionnaire intensity survey method is effective in Indonesia. Whereas the data seems to have a discrepancy which comes from the personal difference of some interviewers and the confusion of some translated questions. Some of the questions should be modified to fit to the circumstances of Indonesia and standardization of interviewer's role should be defined. Predominant Period Survey The predominant period of earthquake depends on mainly two factors: 1. Source (Seismic fault) mechanism Magnitude, Depth, Stress drop, Directivity etc. many varieties and difficult for forecast 2. Surface soil layer depositing on the base rock Stiffness and depth of soil layer, Irregularity of base rock depth etc. Not simple, but predictable Ground microtremor was observed by sensitive seismometer and analyzed to get H/V spectrum.

6 Results of Ground Microtremor Observation 0.83 sec. 1.5 sec. 2.3 sec. PU site H/V BPKP site H/V UNP site H/V Prof. Kiyono (Kyoto Univ.) et al. had surveyed the predominant period of microtremor and the shear wave velocity distribution (velocity structure) of surface soil layer at many points of Padang. Above results are consistent with their results. Discussion on the Predominant Period The predominant period of the earthquake is supposed to be more than 1 second in the flat area of Padang. That was hard for the middle and large scale buildings, and was mild for the low buildings. It is necessary to get the shear wave velocity distribution of deeper layer for understanding and modeling better of the Padang ground vibration. The microtremor observation with a large scale array, the deep bowling and the seismic reflection profiling are required. Discussion on the Predominant Period The predominant period of ground microtremor of Padang becomes longer from the south (PU site) to the north (UNP site) as well as from the inland to the coast line. The shear-wave velocity of the surface layer of these areas is m/s, and the thickness is meter and below it a layer of 500m/s follows (from Prof. Kiyono, et al.). This the shear wave velocity distribution (velocity structure) interprets the predominant period of microtremor well. Duration of the Earthquake Duration of earthquake will increase the damage especially of large scale building. Duration of an earthquake is affected by the magnitude and the deep velocity structure, and the latter is unknown in case of Padang. Questionnaire survey: the duration of the destructively strong shaking was 1. about 10 seconds 2. about 30 seconds 3. about 1 minute 4. about 5 minutes

7 The Next Earthquake Many scientist are saying that the next earthquake will be from the Mentawai Gap. It will be true. As for the Mentawai Gap earthquake - the intensity of will be same level or higher, - the predominant period will be longer, - the duration will also be longer than the earthquake. Namely, the shaking will be harder one against the large scale building in Padang. A tsunami must accompany too. When City area of Istanbul When? Troy Istanbul Anatolia peninsula Ankara North Anatolia Fault Turkey Athens 1941 (7.9) 1881 (7.9) (M9.15) 1907 (~M7.8) 2005 (M 8.7) 1935 (M7.7) 1797 (M8.4) 1833 (8.9) 1861 (M~8.5) 2000 (M7.8) 2007 (M 8.4) Malaysia Currently locked, end of typical cycle Jakarta Un known section, No large eartquakes in Historical records Danny Hilman Natawidjaja, LabEarth, Geoteknologi-LIPI, Indonesia The Next Earthquake The large scale building in Padang must serve as the vertical evacuation place from the tsunami. So, they must be rehabilitated or retrofitted to withstand the next earthquake. The next big one can burst tomorrow or can burst 10 years later. Nobody knows the exact time. But, it will surely occur. Your mission is competing with time.

8 Large scale RC building Survey What kinds of study we have done? Questionnaire survey of Seismic intensity Characteristic survey of Earthquake-Damaged Buildings Study for retrofitting Why our target is Large scale RC building? Large-scale RC buildings were damaged and broken by this earthquake on Sep 30, It will minimize the damage of the earthquake to occur in future to reinforce the large-scale RC building which many people use. Large-sized RC building is damaged in Banda Aceh and Jogjakarta in the past. This is an overall problem in Indonesia, and immediate improvement is necessary. Study Results

9 Questionnaire survey of Seismic intensity Because seismometers did not operate in this time, accurate seismic intensity is unidentified. It is necessary to know a more accurate seismic intensity to analyze seismic intensity and relations of the damage level. Therefore the questionnaire survey of seismic intensity is useful. BPKP Building Jl Rasuna Said No. 69 Buildings surveyed: Numerical models of the buildings Seismic Loading Analysis Structural Safety Analysis Study for Retrofitting Built in 2003 In 2007 earthquake, the roof top was falling down The roof was altered from terracotta roof to lighter thin-steel roof There were some minor damage at the column at Floor-3 (Floor-4 if no ground floor). The column was repaired

10 FEM model: (a) First Mode, Sway X, T1 = 1.02 s (b) Second Mode, Sway Y, T2 = 1.00 s (c) Third Mode, Torsion Z, T3 = 0.91 s Column model: Dimension of Column Floor 2 E-5 Dimension of Column Floor-2 C-2 Dimension of Column Floor-G E-5 Microtremor Measurement: Floor-4 Longitudinal Floor-4 Lateral Column capacity: P-M Interaction Diagram of Column at Floor-G up to Floor-1 P-M Interaction Diagram of Column at Floor-2 up to Floor-4

11 Seismic Loading: Seismic Static Equivalent Loading (based on SNI ) Axial Force at Columns: 504 kn.m 865 kn 1525 kn 792 kn.m Axial Force at columns due to Dead and Life Load Seismic Demand: 504 kn.m 792 kn.m Moment demand at columns due to Seismic Loading Safety of Columns: Axial load at column Floor-G = 1525 kn: Therefore, moment capacity is 515 kn.m The seismic demand of 792 kn.m at the base at one column is beyond the moment capacity From the survey, the column shows little damage at the base floor Photo of Column at Floor-G

12 Safety of Columns: Axial load at column Floor-2 = 865 kn: Therefore, moment capacity is 230 kn.m The seismic demand of 504 kn.m at the upper part of column at Floor-2 is beyond the moment capacity From the survey, the column shows severe damage at the upper part Photo of upper part column damage at Floor-2 PU Building Jl Batang Arau No. 86 Built in 1970 s Concluding Remarks: The damage of columns at Floor-2 is due to the too early reduction of column size at Floor-2 The reduction of column size should be at Floor-3 where the seismic demand is smaller FEM model: (a) First Mode, Sway Y, T1 = 0.81 s (b) Second Mode, Sway X, T2 = 0.38 s (c) Third Mode, Torsion Z, T3 = 0.37 s

13 Microtremor Measurement: Fifth Floor at Center, Longitudinal Fifth Floor at Center, Lateral Column capacity: P-M Interaction Diagram of Column Longitudinal Direction P-M Interaction Diagram of Column Lateral Direction Column model: Dimension of Column at PU Building Seismic Loading: Seismic Static Equivalent Loading (based on SNI )

14 Seismic Demand: 504 kn.m 792 kn.m Moment demand at columns due to Seismic Loading Safety of Columns: Axial load at column Floor-1 is 450 kn, therefore the moment capacity is 180 kn.m The demand of 198 kn.m at the base at one column is beyond the moment capacity From the survey, the column shows soft-story mechaniscm Photo of Column at Floor-1 Axial Force at Columns: 504 kn.m 865 kn 1525 kn 792 kn.m Axial Force at columns due to Dead and Life Load Safety of Columns: Beams dimension in longitudinal direction is 300 x 300 mm2 (The same dimension with columns width of 300 mm) However, seismic demand at beams is smaller than that of columns This led to soft story mechanism Photo of Beam at Floor-4

15 Things to know: Column height: 4.4 m; Column inclination: 4 (0.07 rad), Moment caused by the weight = 10341x0.07x4.4 = 3185 kn.m. Moment capacity of 35 columns = 35x180 = 6300 kn.m. Therefore: The building can stand at this tilting position because the demand moment caused by P-delta effect is 51% the capacity of the columns. The building theoretically starts to collapse when the tilting degree becomes 6300/(10341x4.4) = 0.14 rad (or 7.9 ). Note: The weight is by structural component only. The weight may increase (by about 50%) due to existence of masonry walls and life loads. BAPPEDA Building Jl Khotib Sulaiman No. 1 Built in... Concluding Remarks: Seismic demand at beams is lower than the seismic demand at columns Since the beam width is the same as column width, it led to soft story mechanism of columns Moreover, since the columns dimension is the same along the height of structure, the damage is concentrated at first floor FEM model: (a) First Mode, Sway Y, T1 = s (b) First Mode, Side View (c) Third Mode, Torsion Z, T3 = s

16 Column model: Dimension of Column at BAPPEDA Building The beam dimension is h = 500 mm and b = 300 mm. Seismic Loading: Seismic Static Equivalent Loading (based on SNI ) Column capacity: P-M Interaction Diagram of Column Seismic Demand: 504 kn.m Maximum Moment (206 kn.m) at Column Base Under Seismic Equivalent Static Loading (SNI ) 792 kn.m

17 Axial Force at Columns: 504 kn.m 865 kn 1525 kn 792 kn.m Axial Force Diagram at Column under Dead Load (largest axial force is 403 kn) Safety of Columns: The column could not develop its full capacity (it collapsed because of pull out of rebars): The overlappings of rebars were at the large moment area the rebars were the smooth type the stirrups were too small ( 5.5 mm) Photo of Column Rebar and Stirrups at Floor-1 Safety of Columns: Axial load at column Floor-1 is 403 kn, therefore the moment capacity is 400 kn.m The demand of 206 kn.m at the base at one column is lower the moment capacity However, the column shows heavy damage and soft-story mechaniscm Photo of Columns at Floor-1 Concluding Remarks: Real column capacity is lower than the calculated capacity: Column rebars were overlapped at maximum moment region Smooth type of rebars Too-small stirrups. Soft story failure mechanism: High columns at first floor Additional ballustrade at upper floors Large beam dimension

18 Large scale RC building Survey From the View Point of Design Code Base Shear Force V = CD W t Where W t :Total weight of dead load and reduced live load CD = C I K C : Base shear coefficient I : Importance factor K : Structure type factor (K = 1.0 for reinforced concrete) SNI :Peraturan Pembebanan untuk Rumah dan Gedung For Padan Firm ground Soft ground C : Base shear coefficient is 0.07

19 This seismic load is for method of elastic This seismic load is applied for the method of elastic stiffeness stress analysis. (allowable stress design method) Assumed return period may be about 73 years When base shear coefficient C=0.07 The C value of some example of surveyed buildings are 0.07 If the safety factor assumed in allowable stress is 3.0 Critical member of the building can yield to the horizontal inertia force of 0.21 times gravity =0.21 It is understandable that some RC buildings yield to the earthquake motion at this time. The earthquake motion estimated about 0.3 times gravity assessed acceleration value of the earthquake Result of questionnaire survey was about as I jma this value correspond to as MMI this value correspond to 223 gal (PGA) Building Capacity

20 Indonesian new code for seismic load SNI :Peraturan Base Shear Force C 1 I V = W R t R : Seismic Reduction Factor SNI :Peraturan Pembebanan untuk Rumah dan Gedung For Padan C = 0.83 for medium ground

21 Seismic Reduction Factor C 1 I V = W R t R : Seismic Reduction Factor Seismic capacity index I s Simplified method for estimation of earthquake resistance Inspect outline of the building and damage of structural members at the most severely damaged floor The horizontal shear capacity of the columns and the wall is calculated and totaled. The earthquake-resistance in a building is judged. referring to the distribution of I s -valve in the example of past earthquake. Activity for Existing Buildings at normal times Diagnosis of antiseismic capacity OK Strengthening existing nonqualified Immediately after earthquake Post- Earthquake Temporary Risk Evaluation or ATC-20-Rapid Evaluation OK RESTRICTED USE UNSAFE Rehabilitation period Diagnosis of antiseismic capacity light Repair Repair design Demolish and Reconstruction Repair and Strengthening Is Value ( Seismic Index of structure ) and it s distribution About the entire Japan Damaged Relative frequency Value needed in code Is Value PGA concerning capacity (approximate only)

22 Policy for repair work and strengthening I s value of partially damaged building was calculated That was about medium value of the heavily damaged building in Japanese past earthquake. Policy for repair work and strengthening is not to be damaged seriously even if the same scale of the earthquake occur again. Possibility to achieve this policy depends on procurement of skill and budget

23 Ductility is essential for modern RC structure The ductility of columns of RC frame building is essentially important in the modern earthquake resistant design. If you could utilize this design concept and get its construction technique, you could lower the construction cost as well as improve the earthquake resistance of buildings remarkably. If you applied new design code SNI-2002 to all of the large RC buildings in Padang and carefully follow the structural detail required, all buildings in Padang did not collapse. Beam yield first If the beams yield by bending first, many yielding hinges are generated and vibration energy can be absorbed by their yielding, whereas the yield hinges in the columns can be minimized. Then, the building can avoid collapsing. Yield hinge by bending How to improve the ductility of a RC frame Beams in the frame should yield first. Columns should yield at its top or at its bottom by bending if necessary. Shear failure of columns has to be avoided. The distribution of story stiffness along the vertical axis should be smooth. Piloti without reinforced shear wall should not be used. The planar shape of the building should be symmetry not to generate the excess torsion. Let the shear failure never occur Shear failure of a column will lead the superstructure to a brittle fall down. Shear failure occurs in the following cases: 1. Short column 2. Column with poor lateral rebar 3. Column with excess main reinforcement 4. Column with excess vertical load Seismic load Cracking Sudden fall down Short column Vertical load

24 Columns should yield by bending Excess main reinforcement and poor lateral rebar Inadequate location of rebar lap joint Buildings should be symmetry Rigidity center Seismic force Gravity center Distribution of stiffness should be smooth Seismic load Piloti The columns yielded by bending, but only the yield hinges in the first story columns absorbed the vibration energy and deformed too much. Yield hinge How to improve the ductility of a RC column Load Yield of main rebar Crack by bending End state Safe limit Compression crack of cover concrete Break of rebar and fracture of core concrete Rapid drop of stiffness Deformation It is possible to construct so deformable column if we arrange rebars smartly.

25 Lateral confinement improve the ductility Main reinforcement Lateral confinement A B C A D E F Load E F Deformation Lateral confinement improve the ductility (2) Main reinforcement Lateral confinement Hoop closed by welding A B C Square spiral hoop Circle spiral hoop Diameter of hoop Both ends Middle Hoop rebar ratio A B C D Hoop pitch Ductility of beam column connection 90 fock bond Required bond length Location of joint should be middle of column and be dispersed. Top story corner Ductility of beam column connection

26 Excess vertical load ruins the ductility Floor and beam load Dead load Seismic load Moment due to dead load Crushed concrete drops down. Bending moment Vertical load large Vertical load small Curvature General remarks (2) The fundamental knowladge to construct ductile reinforced-concrete structures should be transferred to citizens and students, too. For example, excess water must not be used to mix fresh concrete, fresh concrete in a form must be compacted well, lateral (transverse) rebar layout must be dense, and so on. Mass media and school education can be utilized. Then, under-construction buildings will be evaluated by the many eyes of the public, and the bottom of the construction technique will improve. General remarks The field engineer as well as the structure designer must be trained to understand the vital importance of the proper arrangement of rebars. Deformed rebar should be used for both of the main reinforcement and the lateral confinements, and the detail of rebar joints and the anchorage must be exactly follow the requirements. These implementations will demand cost up, but it is not so large compared to the total cost of building. It is a smart choice in the view from the cost benefit.

27 Case study of repair and seismic retrofitting method in the BPKP building Repair damaged structure (column) Minimum seismic retrofitting (upper structure) Cost estimation (Re-construction vs Repair and Seismic retrofitting) Repair damaged structure Damage-level Most severe damaged floor is 2 nd floor as below, Number of Column DAMAGE LEVEL V DAMAGE LEVEL IV DAMAGE LEVEL III DAMAGE LEVEL II DAMAGE LEVEL I DAMAGE LEVEL 0 Number of Column Repair damaged structure Repair of damaged columns Damage level of distribution of column on each floor is as follow, Damage level Damage description for column I Visible narrow cracks on concrete surface (crack width is less than 0.2 mm) II Visible cracks of concrete cover (cracks width is about mm) III Local crush of concrete cover Remarkable wide cracks (crack width is about 1-2 mm) IV Remarkable crush of concrete with exposed re-bars Pilling off of concrete cover (crack width is more than 2 mm) V Buckling of re-bars, cracks in core concrete, visible vertical /horizontal column deformation, building inclination/settlement Repair damaged structure Damaged structure Damage Level Damage Level Damage Level Damage Level

28 Repair damaged structure Judgment by damage ratio of structure Damage level of column of 2 nd floor is Severe Damage because of D=77.371>50. Truct Repair damaged structure Restore a column by replacing main bar and casting concrete. Construction step 1. Taking off the damaged concrete 2. Grouting to the cracked portion 3. Repair of existing hoops (Damaged re-bars should be welded if necessary.) 4. Setting up the mould 5. Mortar filling or concrete casting Vertical load supporter Welded joint Lapped splice Necessary length for lapped splice Concrete casting Shear re-bar Removal of vertical load supporter Repair damaged structure The columns of damage level IV and V pushes them back to original height by jacks. To install supporters under the beam-bottom to sustain vertical load of the column. To install supporters under the beam-bottom to sustain vertical load of the shear fractured column. Repair damaged structure The columns of damage level and repair cracks by pressing-fit non-shrink mortar, and casting concrete after repair hoop bar. Existing concrete Repair of cracks Grouting or casting Wire-mesh Dia. mm concrete Taking off the damaged concrete Repair of hoops Repair of cracks Repair of existing damaged hoop Wire-mesh Dia. mm Low-shrink mortar or concrete Low-shrink mortar grouting or concrete casting Construction step 1. Taking off the damaged concrete 2. Grouting to the cracked portion 3. Repair of existing hoops (Damaged reinforcing bars should be welded if necessary.) 4. Setting up the mould 5. Mortar filling or concrete casting pressing-fit non-shrink mortar

29 Minimum seismic retrofitting To increase the stiffness of the building by installing earthquake-resistant walls of RC. Single arrangement Double arrangement More than 200 mm Post-installed anchor More than 200 mm Post-installed anchor Grouted mortar Grouted mortar Strengthening bar against splitting Strengthening bar against splitting Wall thickness Wall thickness RC earthquake resistant wall Minimum seismic retrofitting Evaluation of Seismic Capacity By the above-mentioned method, the earthquakeresistant performance of the building which repaired and reinforced is as follows, Is: seismic capacity index of structure considering damaged member capacity Minimum seismic retrofitting To make the building light weight replace a brick wall with the panel wall. remove top-floor. Cost estimation Cost estimation for re-construction and repair & retrofitting The construction cost of the existing BPKP building is approximately Rp 18.3 billion. (excluding Design, Management and supervise by Consultants) The repair and retrofitting cost of existing BPKP building is approximately Rp XX billion.