Proposed AASHTO Seismic Specifications for ABC Column Connections (2020) / Chapter Skim
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101 3.1 Introduction Chapter 2 summarized the state-of-the-art literature review of four precast column connections that was conducted for NCHRP Project 12-105 and the knowledge gaps that were identified. After the NCHRP 12-105 project panel reviewed the available test data and connection performance, it selected three types of connection for development of guidelines: mechanical bar coupler connections, grouted duct connections, and pocket/socket connections.
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Type of Connection Test Data to Support Design Equations Objective Experimental Studies (NCHRP 12-105) Experimental Parameters Deliverable Mechanical bar splices No.
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Experimental Programs 103 Details of the model are presented in Tazarv and Saiidi (2016)
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104 Proposed AASHTO Seismic Specifications for ABC Column Connections bars. The average measured yield and ultimate strength of the unspliced No.
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Experimental Programs 105 GSM2 - fu = 99.9 ksi - εu = 23,642 microstrainGSM1 - fu = 97.0 ksi - εu = 31,363 microstrain GSM3 - fu = 104.5 - εu = 73,397 microstrain GSC1 - fu = 100.9 ksi - εu = 24,035 microstrain GSC2 - fu = 96.22 ksi - εu = 51,483 microstrain GSC3 - fu = 96.82 ksi - εu = 45,637 microstrain GSD1 - fu = 107.8 ksi - εu = 64,477 microstrain GSD2 - fu = 106.9 ksi - εu = 51,244 microstrain GSD3 - fu = 107.6 ksi - εu = 68,377 microstrain GSD4 - fu = 100.9 ksi - εu = 23,503 microstrain c) Fracture under dynamic monotonic loading b)
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106 Proposed AASHTO Seismic Specifications for ABC Column Connections Specimen Yield Stress (ksi) Ultimate Stress (ksi)
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Experimental Programs 107 Of the 10 grouted sleeve coupler specimens, four failed at the coupler center in between the spliced bar ends. Note that grouted sleeve couplers include a stopper with a central hole that allows for the grout to flow but prevents the two spliced bar ends to bear directly on each other.
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108 Proposed AASHTO Seismic Specifications for ABC Column Connections The coupler fracture strain was not affected by the loading type. However, when fracture was in the bar (the other six specimens)
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Experimental Programs 109 (a) Static Monotonic Stress–Strain Curves (c)
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110 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-6. Effect of cyclic loading on stress–strain relationships of grouted sleeve splice specimens.
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Experimental Programs 111 monotonic (HBM) , cyclic (HBC)
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112 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-9. Fracture of spliced bars with headed bar couplers.
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Experimental Programs 113 Specimen Yield Stress (ksi) Ultimate Stress (ksi)
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114 Proposed AASHTO Seismic Specifications for ABC Column Connections of improper attachment of the transducer. The curves indicate that the stiffness of the spliced bars was lower than the control bar stiffness because of slight settling with the couplers.
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Experimental Programs 115 (a) Static Monotonic Stress–Strain Curves (c)
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116 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-12. Effect of cyclic loading on stress–strain relationships of headed bar splice specimens.
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Experimental Programs 117 Figure 3-14 shows the test setup for a swaged bar specimen. The tests were conducted according to preliminary testing methods that were developed in the present study and then finalized as presented in Appendix B
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118 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-15. Fracture of spliced bars with swaged couplers.
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Experimental Programs 119 Specimen Yield Stress (ksi) Ultimate Stress (ksi)
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120 Proposed AASHTO Seismic Specifications for ABC Column Connections 3.2.4.2 Effect of Load Type on Headed Bar Couplers The acceptance criteria for spliced bars proposed in Appendix B include monotonic static, half-cyclic, and monotonic dynamic loading, with the latter two intended to evaluate the performance of the splices under earthquake-type loading. The fracture of the specimens with SW couplers was discussed in the previous section.
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Experimental Programs 121 (a) Static Monotonic Stress–Strain Curves (c)
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122 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-18. Effect of cyclic loading on stress–strain relationships of swaged splice specimens.
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Experimental Programs 123 β Sample Failure Type Measured Recommended GSM1 In coupler 0.64 0.55 GSM2 In coupler 0.59 GSM3 Outside coupler 0.51 Average -- 0.51 HBM1 Outside coupler –0.42 0.5HBM2 Outside coupler –0.89 Average -- –0.65 SWM1 Outside coupler 0.85 0.9 SWM2 Outside coupler 0.97 SWM3 Outside coupler 0.84 Average -- 0.89 Table 3-15. Measured and recommended coupler rigid length ratios.
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124 Proposed AASHTO Seismic Specifications for ABC Column Connections also includes acceptance criteria and a material model for couplers. Overall, it was found that consistent and reliable measurement could be obtained with the proposed testing method.
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Experimental Programs 125 Figure 3-22. Column cage after installation of grouted sleeves.
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126 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-25. Close-up of lowering column onto footing dowels.
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Experimental Programs 127 Figure 3-27. Completed GC10 column.
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128 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-28. Test setup for GC10 column model.
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Experimental Programs 129 Figure 3-29. Strain gauge layout in GC10 column model.
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130 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-30. Displacement transducer layout in GC10 column model.
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Experimental Programs 131 D ri ft (% )
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132 Proposed AASHTO Seismic Specifications for ABC Column Connections Drift Ratio (%) Observed Damage +3.00 Widening of cracks above coupler region Initiation of spalling of concrete in coupler region on west face of column –3.00 Initiation of spalling of concrete in coupler region on east face of column +4.00 Vertical cracks in coupler region Extensive spalling in coupler region on east and west faces of column Spalling of concrete on top of coupler region Multiple transverse bars visible on west face of column Widening of flexural cracks along coupler region –4.00 Widening of flexural cracks +5.00 Fracture of one coupler Multiple transverse bars visible on east face of column More minor cracks in footing Wide gap between column and footing –5.00 Extensive spalling of concrete on east face of column Wide gap between column and footing +6.00 Coupler visible at lower part of column (east face)
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Experimental Programs 133 (a) Southeast face (b)
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134 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) Southeast face (b)
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Experimental Programs 135 (a) Southeast face (b)
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136 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-39. Fractured coupler as seen under 8% drift ratio (fracture occurred under 5% drift)
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Experimental Programs 137 The maximum longitudinal bar and coupler strains under low drift ratios of up to 2% and high drift ratios of 3% or more are plotted in Figures 3-42 and 3-43. Under low drift ratios, the strain increased gradually with an expected trend.
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138 Proposed AASHTO Seismic Specifications for ABC Column Connections levels. In the reference CIP column, the longitudinal bars yielded under 1% drift ratio.
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Experimental Programs 139 Figure 3-46. Force-drift envelope and idealized curve for GC10 column model.
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140 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-47. Normalized pushover response for cast-in-place, GCNP, and GC10 column models.
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Experimental Programs 141 Group No.
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142 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-48. Pullout grouted duct test specimen detail for single bars (Groups G1 and G3)
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Experimental Programs 143 Figure 3-49. Pullout grouted duct test specimen detailing for bundled bars (Groups G2 and G4)
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144 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-50. Formwork prior to casting concrete for grouted duct specimens.
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Experimental Programs 145 (a)
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146 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 3-53. Instrumentation details for grouted duct specimens.
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Experimental Programs 147 Figure 3-55. Photograph of grouted duct test setup.
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148 Proposed AASHTO Seismic Specifications for ABC Column Connections Table 3-22. Mode of failure in grouted duct specimens.
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Experimental Programs 149 Figure 3-56. Damage in Group G1 of grouted duct specimens.
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150 Proposed AASHTO Seismic Specifications for ABC Column Connections (a)
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Experimental Programs 151 Table 3-23. Measured peak loads and displacements at failure of grouted duct specimens.
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