Seismic Design of Geosynthetic-Reinforced Soil Bridge Abutments with Modular Block Facing (2012) / Chapter Skim
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CHAPTER 3 LRFD SEISMIC DESIGN OF GEOSYNTHETIC-REINFORCED SOIL (GRS) BRIDGE ABUTMENTS INTRODUCTION Load and Resistance Factor Design (LRFD)
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67 The external stability of the sill is checked twice: (1) assuming that the sill is a separate entity, and (2)
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68 Figure 3.1: LRFD Example Problem Configuration External Stability Verifying external stability is done in two steps. In the first step, the stability of the sill is examined with respect to sliding, overturning, and bearing capacity.
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69 component, Fl, would have tendency to increase the factor of safety for sliding and have little or no effect on overturning and are therefore omitted. The force Fd is calculated as follows and is applied at the location of bearing as shown in Figure 3.2.
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70 pressure, FT, (Figure 3.2) is calculated using Rankine analysis; and the dynamic (pseudo-static)
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71 Apply a seismic horizontal load Fd (Figure 3.2)
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73 Sill Overturning. (Ignore Ql)
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74 For the eccentricity and bearing stability calculations at the base of the sill, 50% of the bridge live load, Ql is included while the inertia of the dead load and reduced live load, Fd+l, is applied horizontally. From Figure 3.2: ( )
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75 heffEQmeffEQir kWAWP γγ == (Reinforced Soil Mass) heffEQmeffEQI kWAWP 222 γγ == (Overlying Fill)
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76 The calculated weight of the reinforced fill, W, includes the weight of the facing blocks which are assumed to have the same unit weight as the reinforced fill.
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77 Figure 3.4: Static and Dynamic Forces Acting on Soil Mass Sliding of Reinforced Mass. (Article 10.6.3.4)
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78 Overturning of Reinforced Mass. Moments are taken about point C in Figure 3.4: Factored driving moments ( )
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79 Factored resistance nbR qq φ= (Eqn.
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81 [ ] msldai AWQQWP +++= 5.067.0 Figure 3.6: Assumed Active Zone for Calculating Dynamic Forces in the Reinforcement Layers Refer to Figures 3.6 and 3.7: Maximum reinforcement load VHmax ST σ= Factored horizontal stress at each reinforcement level is: )
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82 vv z σγσ ∆+= 11 1D Pv V =∆σ Consider 100% of Ql for reinforcement force calculations: 40.8792.82048.4 =++=++= dlsv QQWP kN/m For 1121 ' zBDzz +=→≤ (See Figure 3.7)
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83 1 40.87 Dv =∆σ Take 1= a r K K (Figure 11.10.6.2.1-3)
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84 cv e CRF T L ασφ *
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85 For this example use a reinforcement with ultT = 70 kN/m (GEOTEX 4x4 fabric) DCRID RFRFRFRF ××= Use 1.1=== DCRID RFRFRF 331.1=→ RF 59.52 331.1 70 === RF T T ultal kN/m Use 9.0=φ and 1=cR ( )
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86 ∑ = = ej m j ej md L L T 1 )
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