Seismic Design of Geosynthetic-Reinforced Soil Bridge Abutments with Modular Block Facing (2012) / Chapter Skim
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From page 92... ...
CHAPTER 4 BEARING PAD DESIGN INTRODUCTION The design of the bearing pads for the shake table experiment was based on Method B from AASHTO LRFD Bridge Design Specifications (2007)
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From page 93... ...
89 Design Calculations Trial Pad Initially, the dimensions of the steel reinforced elastomeric pad are assumed to be 305 mm x 457 mm x 52 mm (See Figures 4.1 and 4.2) The shape factor of a layer of an elastomeric bearing, Si, shall be taken as the plan area of the layer divided by the area of perimeter free to bulge.
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From page 94... ...
90 Initial Dead Load Compressive Deflection ∑= ridid hεδ (Eqn.14.7.5.3.3-2)
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91 Although the maximum allowable deflection of half the pad thickness was used in calculating the design shear force, laboratory tests reviewed show negligible damage to elastomeric bearings translated 100 percent of their design thickness (100 percent shear strain)
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From page 96... ...
92 W = Width of the bearing in the transverse direction 067.0 457 3050.2 1 305 29.14 92.1 A = × + = ( ) 272.0 4570.4 305 10.24.6 67.2 B = × ++ = 272.0B134.0A2 =≤= Okay, bearings are considered stable; no further investigation of stability is required.
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From page 97... ...
93 =φ 0.75 to nominally account for tension ksi) (60kPa685,413=uF for F1554 Gr.36 anchor bolt 46.75685,413 4 0254.0 48.075.0 2 =× × ××= π F kN →=<= kN46.75kN5.44 FFSU Use 2 anchor bolts per bearing pad Top Bearing Plate Design Reference Figure 3.7.4-19 on Page 3-271 Illinois DOT Bridge Manual (See Appendix B)
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From page 98... ...
94 Bottom plate reaction, R 25.1114/445 ==R kN (24.25 kips) Elastomeric pad length, Le 457=eL mm Bottom bearing pad length, Lb Lb = 660 mm Bottom bearing plate width, Wb 356=bW mm Bottom bearing plate thickness, Tb ( )
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From page 99... ...
95 Figure 4.1: Elevation View of Bearing Pad Details
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From page 100... ...
96 Figure 4.2: Plan View of Bearing Pad Details BEARING PAD NATURAL FREQUENCY The natural frequency of the bearing pads significantly effect the performance of a GRS bridge abutment. The design procedure of the bearing pads presented in Section 4.2, adopted from Method B in AASHTO LRFD Bridge Design Specifications (2007)
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From page 101... ...
97 Calculations In reference to Figure 4.3, the shear force, F, can be calculated as: T GA F Δ = Where: G = Shear modulus of elastomer A = Plan area of elastomer T = Total thickness of elastomer Δ = Shear deformation The elastomeric pad used in the shake table test has the following characteristics: G = 689 kPa, A = 0.14 m2, and T = 0.043 m Figure 4.3: Shear Deformation of Elastomeric Pad The shear stiffness, K, of the elastomeric pad can be determined as K = F/Δ, where Δ = 1 unit of displacement. 243,2 043.0 14.0689 = × == ∆ = T GAF K kN/m Therefore, the horizontal natural frequency, f, of the bearing pad-bridge system can be determined using: M K f π2 1 = Where: M = Mass supported by the bearing ( )
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