DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES - IISEE

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Chapter 16 Unseating Prevention System 16.1 General (1) Unseating prevention systems consist of a seating length of the girder at the support, unseating prevention structure, excessive displacement stopper, and structure for protecting superstructure from subsidence. These components shall be appropriately selected in accordance with the bridge type, type of bearing supports, ground conditions, and others. (2) As for unseating prevention systems in the longitudinal direction to the bridge axis, the seating length specified in Section 16.2 and unseating prevention structure specified in Section 16.3 shall be provided at the girder-end supports and at the movement joints. The unseating prevention structure can be omitted for a bridge in which longitudinal displacement is unlikely to occur in the bridge axis due to its structural characteristics, except those bridges shown in 2) of Section 16.5 (1), or those located on seismically unstable ground, as specified in Chapter 8. (3) As for the unseating prevention systems in the transverse direction to the bridge axis, excessive displacement stoppers shall be installed at girder-end supports, and movement joints of a bridge specified in Section 16.5 (1), and at intermediate supports of a continuous girder of a bridge specified in Section 16.5 (2). (4) When a tall bearing support is used for Class B bridges specified in Section 2.3, special consideration, including the introduction of a structure for protecting the superstructure from subsidence as specified in Section 16.4, shall be given. 16.2 Seat Length (1) The seating length of a girder at its support shall not be less than the value obtained from Equation (16.2.1). In the case where the length is shorter than that obtained from Equation (16.2.2), the design seating length shall not be less than the value from the latter equation. When the direction of soil pressure acting on the substructure differs from the longitudinal direction to the bridge axis, as in cases of 83
a skew bridge or a curved bridge, the seat length shall be measured in the direction perpendicular to the front line of the bearing support. S E = u R + u G ≧ S EM ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (16.2.1) S EM = 0.7+0.005 l ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (16.2.2) u G = ε G L ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (16.2.3) where SE : Seating length of a girder at the support (m). SE is the girder length from the girder end to the edge of the substructure crown, or the girder length on the movement joint, as shown in Fig. 16.2.1. uR : Maximum relative displacement between the superstructure and the substructure crown due to Level 2 Earthquake Ground Motion (m). In calculating uR, the effects of the unseating prevention structure and the excessive displacement stopper shall not be considered. When soil liquefaction and liquefaction-induced ground flow as specified in Chapter 8 may affect displacement of the bridges, such effects shall be considered. uG : Relative displacement of the ground caused by seismic ground strain (m) SEM: Minimum seating length (m) ε G : Seismic ground strain, ε G can be assumed as 0.0025, 0.00375 and 0.005 for Ground Types I, II and III, respectively. L : Distance between two substructures for determining the seating length (m). l : Span length (m). When two superstructures with different span lengths are supported on one bridge pier, the longer one shall be taken as l. Seating Length on Pier Seating Length on Abutment Seating Length Fig16.2.1 (a) Girder End Support Seating Length (b) Movement Joint of Girders (2) In case of verifying seismic performance of a bridge with complicated dynamic structural behavior by a dynamic analysis as specified in Chapter 7, the maximum 84
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DESIGN SPECIFICATIONS FOR HIGHWAY B
Page 3 and 4:
6.3 Verification of Seismic Perform
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12.6 Design of Members of Pier Foun
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construction site, and is normally
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Chapter 2 Basic Principles for Seis
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Chapter 3 Loads to be considered in
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Table 4.2.1 Standard Acceleration R
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4.4 Modification Factor for Zones M
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Chapter 5 Verification of Seismic P
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Chapter 6 Verification Methods of S
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T 2.01 ・・・・・・・・
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6.2.5 Seismic Hydrodynamic Pressure
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Ground Surface Average Section Fig.
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Table 6.3.1 Standard Values of the
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6.4.3 Design Horizontal Seismic Coe
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khc0 : Standard value of the design
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6.4.6 Performance Verification for
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the shear strength based on Section
Page 37 and 38: Chapter 7 Verification Methods of S
Page 39 and 40: 2) Steel piers and steel superstruc
Page 41 and 42: Chapter 8 Effects of Seismically Un
Page 43 and 44: k hg : Design horizontal seismic co
Page 45 and 46: design shall be assumed to be actin
Page 47 and 48: H L : Thickness of liquefying layer
Page 49 and 50: (6) When an isolation bearing is us
Page 51 and 52: 9.3.3 Equivalent Linear Model of Is
Page 53 and 54: 9.4 Basic Performance Requirement f
Page 55 and 56: 10.2 Evaluation of Failure Mode, La
Page 57 and 58: 10.3 Calculation of Lateral Strengt
Page 59 and 60: Horizontal force P Horizontal displ
Page 61 and 62: d : Effective length (mm) of latera
Page 63 and 64: 10.6 Structural Details for Improvi
Page 65 and 66: h i = h M yi 1 D ・・・・
Page 67 and 68: 1.0 on the effects of alternative c
Page 69 and 70: (2) Failure mode of an Reinforced C
Page 71 and 72: Chapter 11 Verification of Seismic
Page 73 and 74: Chapter 12 Verification of Seismic
Page 75 and 76: 12.5 Ductility and Displacement Cap
Page 77 and 78: 13.5 Design of Members of Abutment
Page 79 and 80: 14.3 Reinforced Concrete Superstruc
Page 81 and 82: Girder Girder Girder Pier Fig. 14.4
Page 83 and 84: Chapter 15 Verification of Sesmic P
Page 85 and 86: horizontal seismic coefficient spec
Page 87: provided in Section 6.3.3. Rd : Dea
Page 91 and 92: length of the unseating prevention
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DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES - IISEE

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