Advancement of technology to improve seismic performance of concrete bridge after Kobe earthquake Hikaru NAKAMURA Nagoya University, Japan

Transcription

1 TECHNICAL CHAMBER OF GREECE HELLENIC CONCRETE SECTION JAPAN SOCIETY OF CIVIL ENGINEERS 20th November 2009, ELECTRA PALACE Hotel Advancement of technology to improve seismic performance of concrete bridge after Kobe earthquake Hikaru NAKAMURA Nagoya University, Japan

2 Hanshin-Awaji (Kobe) Earthquake Date : January 17, 1995 Magnitude : 7.2 Type : inland type due to active fault Depth of epicenter : 14km Max. Acc. : 818cm/s 2 The dead persons : 6425 Economic Loss 100billion Euro Collapsed highway piers the supporting columns collapsed over 600m

3 Earthquakes in Japan from over magnitude Earthquake history Earthquake map Strong earthquakes occurred many times and in all area Impossible to avoid damage due to earthquake!

4 Economy loss forecast due to future earthquakes Economy loss forecast and occurrence probability Economy loss (billion Euro) Inland earthquake in Tokyo Tonankai and Nankai earthquake Tokai Earthquake Probability during 30 years 70% 50% 86% Probability map of earthquake Big earthquake risk Loss of huge money Loss of many human life

5 CONTENTS Damage of concrete structures due to recent earthquakes in Japan Advancement of seismic design - JSCE Standard Specifications for Seismic Performance Verification - Advancement of seismic performance - Seismic Retrofit method, Seismic isolation and Vibration Control Technique -

6 CONTENTS Damage of concrete structures due to recent earthquakes in Japan Advancement of seismic design - JSCE Standard Specifications for Seismic Performance Verification - Advancement of seismic performance - Seismic Retrofit method, Seismic isolation and Vibration Control Technique -

7 Recent strong earthquakes concrete structures were damaged 1: Kobe, , M7.2 2: Tottori, , M7.3 3: Geiyo, , M : South of sanriku-oki, , M7.1 5: Miyagi-oki, , M6.2 6: Tokachi-oki, , M8.0 7: Niigata-ken chuetsu, , M6.8 8: fukuoka-oki, , M7.0 9: Noto Hanto, , M6.9 10: Niigata-ken chuetsu-oki, , M6.8 After Kobe Earthquake, the concrete structures have been damaged due to several earthquakes in Japan.

8 Mechanism of earthquakes Inland type: occur at fault and epicenter is near ground surface Kobe(M7.2), Tottori(M7.3), Off miyagi(m6.2), Niigata(M6.8) Interplate type: occur at interplate and epicenter is relatively deep Off Tokachi(M8.0) Intraslab type: occur inside plate and epicenter is deep Geiyo(M6.7), South of sanriku-oki(m7.1) 0 Japan sea 50km 100km 150km magma reservoir Eurasian plate mantle Outbreak of magma volcano Inland Japan trench Intraslab Interplate Pacific plate

9 Mechanism of earthquakes

10 Kobe Earthquake on January 17, 1995 Kobe Earthquake occurred at Hyogo Prefecture in Magnitude : 7.2 Type : inland Depth of epicenter : 14km Max. Acc. : 818cm/s 2 Many Concrete Structures were collapsed. First experience of big Inland type earthquake at city area.

11 Damage due to Kobe Earthquake on January 17, 1995

12 Geiyo Earthquake on March 24, 2001 The Geiyo Earthquake occurred at Aki-nada in the Seto Inland Sea Magnitude : 6.7 Type : intraslab Depth of epicenter : 50km Max. Acc. : 830cm/s 2

13 Damage due to Geiyo Earthquake on March 24, piers in RC elevated bridges of Sanyo Shinkansen were damaged. The shear failure with the spalling of cover concrete was observed by 12 piers among these. Photo shows a damaged two story RC rigid frame elevated bridge. The feature of damage is that severe diagonal shear crack was observed in the middle layer beam.

14 Tokachi-Oki Earthquake on September 26, 2003 The Tokachi-Oki Earthquake occurred at southeast offshore of Hokkaido and the magnitude was 8.0. Tsunami was also observed. It was typical inter-plate type earthquake. Magnitude : 8.0 Type : inter-plate Depth of epicenter : 42km Max. Acc. : 972cm/s 2 The feature of the earthquake ground motion was that long-period wave is dominant and the duration time is long. A fire of the oil storage tank occurred due to sloshing and the effect of the longperiod wave have been paid to attention.

15 Damage of Toshibetsu-gawa railway bridge Damage of a pier Typical Damage Damage of floor slab For pier, the spalling of the concrete cover and the buckling of the longitudinal re-bars occurred. For the floor slab at the end of girder, damage occurred due to the collision between girders.

16 Damage of Chiyoda highway bridge Damage of a pier Damage at a support Left photo shows the flexural failure in the piers in which spalling of concrete cover and buckling of the longitudinal re-bars were observed. Right photo shows the punching shear failure at support due to horizontal force from anchor.

17 Damage of Uroho-gawa railway bridge Capacity Moment The spalling of the concrete cover and buckling of the longitudinal re-bars occurred at cut-off plane of the longitudinal re-bars.

18 South of Sanriku-Oki Earthquake on May 26, 2003 The South of Sanriku-Oki Earthquake occurred at Off Miyagi Prefecture in Magnitude : 7.1 Type : intraslab Depth of epicenter : 71km Max. Acc. : 1106cm/s 2 The feature of the earthquake ground motion is that short-period wave is dominant.

19 Damage due to South of Sanriku-Oki Earthquake on May 26, 2003 damaged one story RC elevated bridges The severe damages were observed in 5 one story RC viaduct of Tohoku Shinkan-sen constructed in 1977 to The feature of these damages was that the end columns are mainly damaged.

20 Damage of four bay one story RC viaduct of Shinkan-sen a b SB(spalling of cover concrete) SC(crack width > 1mm) SD(crack lwidth < 1mm) No observed crack (a) damage of end column (view from a) (b) damage of intermediate column (view from b) Two of the end columns failed in shear with the spalling of the cover concrete, while others were observed diagonal cracks. The damage due to flexure hardly observed. The feature of structures is that the end columns has severe condition for shear failure, because they are shorter than intermediate columns to support simple beam between elevated bridges.

21 Process of repair and strengthening of damaged structures Restoration procedure was (1) injection of epoxy resin to cracks, (2) restoration of cross section by shrinkage compensating mortar, and (3) steel jacketing. May 26: earthquake occur May 27: shinkan-sen start to drive slow speed May 29: shinkan-sen drive normal speed again Restoration finished only in 3 days

22 Niigata-ken Chuetsu Earthquake on October 23, 2004 The Niigata-ken Chuetsu Earthquake occurred at Mid Niigata Prefecture. It was caused by inland active fault. Magnitude : 6.8 Type : inland Depth of epicenter : 13km Max. Acc. : 1722cm/s 2 The earthquake occurred when a Shinkan-sen was running. Then, Shinkansen was derailed.

23 Damage of three bay one story RC frame elevated bridge of Shinkan-sen Dai-san Wanazu Bridge R1 of Joetsu Shinkansen Damage of end column Column strengthened by the steel jacketing Left photo shows damage of end columns failed in shear. The end columns show severe damage more than intermediate columns. This failure is the same as the one explained in the South of Sanriku-Oki Earthquake.

24 Damage of Uono-gawa Bridge of Joetsu Shinkansen (a) Panorama of Uono-gawa bridge (b) Close-up of damaged portion The spalling of the concrete cover and buckling of the longitudinal re-bars occurred at the mid height. Failure occurred at the cut-off plane of the longitudinal re-bars. Lateral ties at that location detached.

25 Niigata-ken Chuetsu-oki Earthquake on July 16, 2007 The Niigata-ken Chuetsu-oki Earthquake occurred at Mid Niigata Prefecture. It was caused by inland active fault. Same type earthquake occurred 3 years ago near the place. Magnitude : 6.8 Type : inland Depth of epicenter : 17km Max. Acc. : 1018cm/s 2 The earthquake occurred near nuclear power station.

26 CONTENTS Damage of concrete structures due to recent earthquakes in Japan Advancement of seismic design - JSCE Standard Specifications for Seismic Performance Verification - Advancement of seismic performance - Seismic Retrofit method, Seismic isolation and Vibration Control Technique -

27 Similar damage due to recent earthquakes Niigata-ken Chuetsu Earthquake Kobe earthquake Shear failure of RC column The damage due to Kobe earthquake is severer, but they are same failure type

28 Similar damage due to recent earthquakes We already observed similar damage for several earthquakes Niigata-ken Chuetsu(2004) Tokachi-oki(2003) Kobe(1995) For all structures, the spalling of the concrete cover and buckling of the longitudinal re-bars occurred at mid height in piers where the longitudinal re-bars are cut off Most major life-line structures were constructed in 1960 s and 1970 s in Japan. Then, the knowledge and design code for seismic performance were insufficient.

29 Change of JSCE Specification for Design Allowable shear stress Effective depth 3m Main bar ratio 0.5% year Allowable shear stress Minimum web reinforcement ratio(%) JSCE Railway Highway Example for square section of 1m length(d32) year Min. web reinforcement ratio Before 1986, the allowable stress design method was applied in JSCE Specification. Then, the allowable shear stress is large value and the minimum web reinforcement ratio is small value. Therefore, structures constructed in 1960 s and 1970 s do not have sufficient shear capacity. This is the reason that many concrete structures failed in shear.

30 Many concrete structures were failed roadways, railways, the port, and other lifelines Three major reasons why many structures were damaged Underestimation of design seismic loads Underestimation of shear capacity Insufficient structural details detaching of lap splices of web re-bar buckling of longitudinal re-bar breaking of longitudinal re-bar at spliced portion New seismic design concept had been adopted in Japanese code after Kobe earthquake

31 Change of JSCE Specification for Design Allowable Stress design Limit state design Structural design Design 1986 Seismic design Design (one chapter) 1995 KOBE earthquake 1996 Seismic design Performance based design Performance based design Structural performance verification Design Seismic performance verification At 1986, limit state design was adopted, then seismic design was described as one chapter in the specification for design. After Kobe earthquake, seismic design code was established based on the performance based design. At 2007, it was included in design code again.

32 Change of JSCE Specification for Seismic Performance Verification 1996 JSCE standard specification for Seismic design The methods for seismic performance verification of concrete structures was described basically. It includes definition of seismic performance, definition of design earthquake ground motion, modeling and analytical method and Structural details 2002 JSCE standard specification for Seismic performance verification 2007 Definition of seismic performance, definition of design earthquake ground motion are same. The items of (1)earthquake ground motion in verification, (2) evaluation for the effect of ground, (3) verification technique(analytical method) were enhanced based on the knowledge of seismic performance and the advancement of the analytical technique. Moreover, it was systematized that the more reasonable seismic performance verification becomes possible.

33 Procedure to verify the seismic performance based on Seismic Performance Verification Setting Ground Motion Setting Structure Modeling of Structure and Ground Response Analysis Estimation of Response Values Nonlinear analysis Setting Seismic Performance Setting Limiting Values Verification END In the specification, the methods how to consider these items are described. nonlinear finite element analysis standard technique to verify seismic performance

34 Seismic Performance 1 Seismic Performance 2 Seismic Performance Seismic performance is classified into 3 cases Function of the structure during an earthquake is maintained, and the structure is functional and usable without any repair after the earthquake. Function of the structure can be restored within a short period after an earthquake and no strengthening is required. Seismic Performance 3 There is no overall collapse of the structural system due to an earthquake even though the structure does not remain functional at the end of the earthquake. Concept The damage is allowable for strong earthquake. Performance 1 : serviceability Performance 3 : safety Performance 2 : serviceability and restoration ability from social and economic points of view Important point is to make clear damage for restoration process

35 Limit values for members When the seismic performances of structures are verified, limit values of response should be determined to assure the defined seismic performance. Seismic Performance 1 Seismic Performance 2 Seismic Performance 3 displacement of a member does not exceed the yield displacement shear and torsional capacity of a member, and ultimate displacement of a member are not reached shear capacity of vertical members and self-weight support capacity is not exceeded Performance 1 Load Performance 2 Performance 3 yield load shear failure after yielding Shear failure flexural failure yield disp. ultimate disp. Disp. An example of skeleton curve of member

36 Earthquake ground motion in verification Before Kobe Earthquake, the design seismic coefficient was assumed as 0.2 and it was considerably small compared with the earthquake ground motion at the location that structures damaged in the Kobe Earthquake. design earthquake ground motion was classified into two level Level 1 Design Earthquake Ground Motion Level 2 Design Earthquake Ground Motion earthquake ground motion that is likely to occur a few times within the lifetime of a structure. very strong earthquake ground motion that has only a rare probability of occurrence within the lifetime of a structure. Level 2 ground motion is chosen from the ground motion caused by an inland type beneath or close to the site and by large scale interplate type occurring in the neighborhood of land.

37 Earthquake ground motion in verification The earthquake ground motion used for seismic performance verification is expressed as the time history waveform of acceleration. This is examples of simulated earthquake ground motion waveforms at the engineering base layer for inland type and inter-plate type. Inland type has very large acceleration and Inter-plate type has long duration time. Acceleration(gal) Time(S) Max. Acc. 749 gal Examples of an inland type Level 2 earthquake ground motion Acceleration(gal) Max. Acc. 347 gal Time(S) Examples of a off-shore type Level 2 earthquake ground motion

38 Example of combination with seismic performance and earthquake level Moment Maximum moment Damage location Mm My,Mn Yield point Ultimate deformation Railway frame structure θc θy θm θn Rotation angle Level 1 earthquake seismic performance 1 (no repair) Rotation angle of all members should be less than θy Level 2 earthquake seismic performance 2 (short time repair) upper and less than θn underground beam column less than θn pile less than θm Rotation angle of pile is limited to smaller value in comparison with other members, because pile is difficult to repair.

39 Evaluation for the Effect of Ground Methods to analyze the structure with ground The response of a structure during an earthquake is strongly affected by neighboring ground and others. Therefore, the whole structural system including foundation or neighboring ground should be analyzed. ground Engineering base layer Engineering base layer To consider the effect of ground, a coupled analysis modeled for structure and ground should be use to obtain the response of structure. Input place of the earthquake ground motion is at the engineering base layer.

40 Evaluation for the Effect of Ground Methods to analyze the structure and the ground independently According to types or characteristics of structures and ground, dynamic interaction between structures and ground can be neglected. Then, the responses of the structures and the ground may be analyzed independently. Base part of structures Earthquake ground motion at ground surface Engineering base layer Subsurface grounds Input to structures Earthquake ground Motion for verification First, only ground model is solved for input earthquake ground motion at the engineering base layer and obtain the wave form at the base part of structure. Then, only structure is solved for obtained ground motion at the base part of structure.

41 Verification technique (analytical method) The seismic performance is verified by a nonlinear analysis based on finite element method. linear member beam element z y x Fiber model beam element is divided into many cells with fiber technique In which material stress-strain relationships are considered. planar member plate or layered shell element

42 =τ τ γ+γ Mechanical model using nonlinear analysis The constitutive model of concrete, reinforcing bar, and soil should be described with those hysteresis. Hysteresis curve (loading) τ y r ( ) ( τ+τ a) a0a Ga ( G2 y0 ) γ 1r G0 γ y 1 G ( γ a, τ a ) skeleton curve ( γ a, τ a ) Hysteresis curve (unloading) A simplified hysteresis model of concrete dynamic shear stress-strain curve of the soil Stress strain relationship shall include softening branch after peak stress residual plastic strain stiffness degradation on loading and reloading path.

43 Structural Details It was observed many damages that are related to insufficient structural details in Kobe Earthquake. Therefore, structural details were greatly revised from 'Seismic Design(1996). Revised points Development of longitudinal re-bar Splices of longitudinal re-bar Spacing of Lateral Re-bar Splices of Lateral Re-bar Anchorage of Lateral Re-bar

44 Development of longitudinal re-bar Tensile re-bar shall be anchored into concrete sections not subjected to tensile stresses. It may, however, be anchored into concrete sections subject to tensile stresses, when the moment and shear capacity are sufficiently greater than design shear force. Cut off plane V u : shear force V ydl : design shear capacity at termination point of re-bar M u : flexural moment M l : flexural moment at termination point of re-bar M udl : design flexural moment at termination point of re-bar Damage due to insufficient development

45 Splices of longitudinal re-bar For the splices of longitudinal re-bar, the longitudinal re-bar shall be spliced in a manner that the splices perform satisfactorily even under repeated stress in plastic hinge zone. Lap splices shall not be provided in plastic hinge zones subjected to repeated stress. Longitudinal reinforcement broke at pressure welding portion in Kobe earthquake. Therefore, provision about splices greatly revised. Damage due to insufficient splices

46 Spacing of lateral re-bar For spacing of lateral re-bar, it is necessary to provide sufficient amount of lateral re-bar, because the lateral re-bars restrain the progress of diagonal cracks, increase shear capacity, prevent buckling of longitudinal re-bars, and also provide confinement of core concrete. a b s a/2 and s 12φ l ties ties(diameter φ t ) (diameter φ l ) Shear failure Buckling Damage due to insufficient amount of lateral re-bar

47 Anchorage and splices of lateral re-bar The ends of ties shall be acute-angle hooks enclosing the longitudinal re-bars and anchored in the core concrete. For splices of ties, the ties should transmit full strength, even if the spalling occurs. Considering this requirement, flare welding or mechanical coupler are recommended. Acute-angle hook lap splices with standard hooks flare welding Shear crack open greatly Ties are detached Damage due to insufficient details web re-bar did not transmit stress after spalling

48 CONTENTS Damage of concrete structures due to recent earthquakes in Japan Advancement of seismic design - JSCE Standard Specifications for Seismic Performance Verification - Advancement of seismic performance - Seismic Retrofit method, Seismic isolation and Vibration Control Technique -

49 CONTENTS Seismic Retrofit Technique of Concrete Piers Seismic Isolation and Vibration Control Technique

50 Seismic Retrofit Technique of Concrete Piers We observed three typical damage. Shear Failure of Reinforced Concrete Columns Shear Strength Enhancement Buckling and Fracture of Re-bar Ductility Enhancement(Confinement Effect) Damage from Re-bar Cut Off Plane Ductility and Shear Strength Enhancement

51 Seismic Retrofit Technique of Concrete Piers There are three major methods for seismic retrofit of reinforced concrete piers. reinforced concrete jacketing steel plate jacketing fiber sheets jacketing (Carbon / Aramid) The best method is determined among them considering cost, vicinity of construction site, and handling of jacketing materials etc.

52 RC jacketing Steel plate jacketing FRP jacketing superstructure pier Rebar Injected mortar Steel plate longitudinal direction Hoop direction Top coat Fiber footing RC jacket RC jacket at the root t=250mm Cheep for construction and maintenance. Thick additional cross section is need for retrofitting. t= 40mm Additional cross section is thin. t= 10~20mm Additional cross section is thin. Retrofit materials is light ( possible to transport by human power )

53 Crane Examples of Retrofit Measure Girder Girder Steel plate 2m Light, High- Strength Fiber Scaffold Cofferdam Cut-off Section 2m Scaffold River River Anchor Steel Jacketing FRP Jacketing

54 Purpose of Seismic Retrofit Retrofit of Cut-off Zone Enhancement of Ductility Vertical Gap between Jacket and Top of Footing H-beam Retrofit in Plastic Hinge Zone Enhancement of Flexural Strength by Anchor Bars In order to enhancement only shear strength and ductility, there is vertical gap between jacket and top of footing. In order to enhancement of flexural strength, jacket is anchored to footing. Then, the effect of basement should be considered.

55 RC Jacketing Reinforced concrete jacketing has the advantage of cost for construction and maintenance compared with the other two methods. So if there is no restriction, reinforced concrete jacketing will be adopted. Usual method

56 Steel Jacketing MERIT Additional cross section is thin Construction period is short DEMERIT Retrofit materials is heavy It will be often adopted to piers in urban site considering the merits

57 FRP Jacketing Additional cross section is thin Retrofit materials is light and possible to transport by human power. It will be adopted to narrow site, cut-off section in middle height of piers, or high-pier.

58 Special Technique for Seismic Retrofit of Concrete Piers There are three major methods for seismic retrofit of reinforced concrete piers. reinforced concrete jacketing steel plate jacketing fiber sheets jacketing (Carbon / Aramid) Several special technique have been proposed considering construction work.

59 Special Technique Coupler Joint Steel jacket Quality of steel jacket method depend on welding work. Merit No welding work Good joint quality No scaffold short construction time

60 Special Technique Rib Plate Method Steel plate with coupler joint is is arranged out side of of column Steel Jacket 補強鋼板 Steel plate モルタル材 mortar Steel plate Coupler かみ合わせ継手 joint 鋼板取付け用弾性 rubber ( ゴム ) 材等辺山形鋼 かみ合わせ Coupler 継手 joint Steel plate 補強鋼板 The method is possible to construct by human. It will be applied to narrow site.

61 Special Technique retrofit underground or underwater parts When bottom part of piers is retrofitted, the parts are usually underground or underwater. Then, excavation work is needed. RC jacket RC jacket cofferdam water soil Therefore, the retrofit technique without excavation work is required for easy and quick construction work.

62 Special Technique Steel Pipe Strut Method RC jacket Hold concrete of steel pipe Steel pipe driving in a ground to footing Construction of hold concrete and RC jacket on the ground Strut ( steel pipe) The retrofit of pier bottom in a ground is constructed without excavation work. Steel pipe between hold concrete and footing is played as compression strut to increase neutral axis and to reduce compressive deformation.

63 Special Technique Steel Pipe Strut Method hold concrete Steel pipe Steel pipe driving Hold concrete construction

64 Special Technique Steel Sheet Pile Method Steel Sheet Pile RC 巻き RC Jacket Infilled concrete River surface Pier in water is enclosed by steel sheet piles. The space between pier and steel sheet piles is excavated and is filled by concrete. River bed Construction of RC jacket on the water surface. footing The retrofit of pier bottom in a water is constructed without cofferdam and excavation work.

65 Special Technique Steel Sheet Pile Method RC jacket cofferdam water RC jacket Steel sheet piles water soil soil The method will be applied to the case of piers in water or the difficult location of excavation.

66 Special Technique Steel Sheet Pile Method RC jacket Steel sheet piles

67 Special Technique Girder Collision Method BIG Damage small damage Usual method Jacket Several retrofit methods are proposed for pier in the water. Easiest method is no-retrofit of pier in water. Permit collision of Girder to abutment using energy absorption material. Then, the deformation of pier in water can be decrease. Reduce damage of pier in water

68 Other feature of damage at Kobe Earthquake Unseating caused by bearing failures were observed. Unseating Prevention System (Fail-safe System)

69 Unseating Prevention Devices Connection cable Restrainers PELDAMPER HONEYCOMB TYPE CELL TYPE Girders are connected by cable, and restrainers of displacement are set. Peldampers are set at several place in order to reduce the effect of collision.

70 Unseating Prevention Devices Connection cable peldamper Increase of seat width Restrainers

71 Utilization of Seismic Isolator Retrofit Concept Elongation of natural period Enhancement of damping Seismic Isolation

72 Seismic Isolator Several isolators as bearing have been proposed. Pb Rubber Bearing Super-High Damping Rubber Bearing 72

73 Vibration Control System Usual Design Isolation bearing Expansion joint unseating prevention device Reduction of displacement Scale down of expansion joint Vibration Control Isolation bearing Vibration control dumper is applied Dumper Expansion joint Omission of unseating prevention device Reduction of seismic force Scale down of isolation bearing Scale down of piers

74 Example of Damper Several isolators have been proposed for buildings. The technique is applied to bridge. Bingham material damper Damping using the effect of filler(silicon resin) Low yield stress steel damper Damping using yielding behavior Combination with bucking prevention system

75 Vibration Control of Railway Viaduct X shape damper brace method Brace and damper are combined. brace The method was developed in order to control of displacement of railway viaduct. damper

76 CONCLUSION Following contents were presented. Damage of concrete structures due to recent earthquakes in Japan Advancement of seismic design Advancement of seismic performance Japan has big earthquake risk and it is difficult to prevent the damage due to earthquake perfectly. As fundamental aspects of design method, accurate evaluation of dynamic response and design system from construction to restoration after earthquake are required. Seismic retrofit greatly advanced after KOBE earthquake. Isolation and vibration control technique will be important topic.

77 Thank You Very Much for Your kind Attention!