Proposed AASHTO Seismic Specifications for ABC Column Connections (2020) / Chapter Skim
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152 4.1 Introduction The findings of the state-of-the-art literature review of four precast column connections conducted for this study are presented in Chapter 2. After the available test data and the performance of accelerated bridge construction (ABC)
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Type of Connection Objective Analytical Studies (NCHRP Project 12-105) Analysis Parameters Deliverable Mechanical bar splices 1.
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154 Proposed AASHTO Seismic Specifications for ABC Column Connections Gap 4. Comprehensive test data are needed for couplers under monotonic, cyclic, and dynamic tensile loading using the unified loading protocol (Gap 3)
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Analytical Programs 155 with a coupler length of 15db or less. The literature review confirmed that bridge columns incorporating couplers that cannot develop the stress–strain capacity of the spliced bars fail prematurely (e.g., columns with short shear screw couplers)
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156 Proposed AASHTO Seismic Specifications for ABC Column Connections Mechanical bar couplers that meet the proposed minimum requirements do not alter the strength of spliced bars, because the connection strength is controlled by the spliced bars. Couplers that do not exhibit fracture outside the coupler region are not acceptable.
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Analytical Programs 157 to accommodate the requirements for couplers presented in the previous sections. For example, the California test procedure only allows testing of couplers with a length of 10db or less.
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158 Proposed AASHTO Seismic Specifications for ABC Column Connections mechanical bar splices -- grouted, headed, and swaged -- were tested according to the proposed test methods (Appendix B) , on the basis of which the coupler rigid length ratios were established (Chapter 3, Section 3.2.5)
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Analytical Programs 159 Figure 4-5. Accuracy of proposed stress–strain model for mechanical bar splices.
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160 Proposed AASHTO Seismic Specifications for ABC Column Connections issue, an extensive analytical parametric study was performed to better understand the seismic behavior of spliced columns and to quantify coupler effects. Through the use of the results of the parametric studies, simple design equations were proposed.
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Analytical Programs 161 benefits of shifting the plastic hinge. However, they are included in the present study to provide an alternative for designers.
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162 Proposed AASHTO Seismic Specifications for ABC Column Connections and behavior in the analysis. A modified analytical plastic hinge length is presented later in this chapter for completeness.
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Analytical Programs 163 region and one CIP column as reference model. The grouted coupler column test specimen with pedestal (GCPP)
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164 Proposed AASHTO Seismic Specifications for ABC Column Connections the calculated drift capacity (6.87%) was lower than the measured drift capacity (7.95%)
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Figure 4-10. Effect of coupler length on ductility of columns with aspect ratio = 6 and axial load index = 5%.
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Figure 4-11. Effect of coupler rigid length factor on ductility of columns with aspect ratio = 6 and axial load index = 5%.
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Figure 4-12. Effect of coupler spacing on ductility of columns with aspect ratio = 6 and axial load index = 5%.
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168 Proposed AASHTO Seismic Specifications for ABC Column Connections The effect of double-level couplers on the displacement ductility capacity is shown in Figure 4-12. It was found that the ductility of columns with two couplers on a reinforcing bar was approximately the same as the ductility of columns with single-level couplers when the couplers were vertically spaced at least 2Lsp on center (or 1.0Lsp face to face)
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Analytical Programs 169 The proposed equation is shown in solid curves in Figure 4-13 for different coupler rigid length ratios and is repeated in all the graphs. It can be seen that the combined effect of the three parameters (β, coupler length, and coupler location)
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170 Proposed AASHTO Seismic Specifications for ABC Column Connections fiber-reinforced polymer jackets in the plastic hinges and their coupler rigid length ratios were known. Grouted sleeve couplers were used immediately above the column–footing interface in two of the columns.
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Analytical Programs 171 Table 4-6 presents the calculated and measured displacement ductility capacities for the four spliced columns discussed in Section 4.3.2. The calculated displacement ductility capacities were based on the proposed modified equation for plastic hinge length (Equation 4-2)
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Table 4-6. Verification of proposed plastic hinge length for mechanically spliced columns.
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Analytical Programs 173 4.3.4.1 Bar Debonding Model Experimental studies have shown that the bond strength of plain bars is less than 30% of that of deformed bars (Mo and Chan 1996; Verderame et al.
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174 Proposed AASHTO Seismic Specifications for ABC Column Connections db = diameter (in.) of the bar; Lemd = embedment length (in.)
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Analytical Programs 175 force-drift relationship of HCS. The calculated relationships include the response of analytical models with (1)
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176 Proposed AASHTO Seismic Specifications for ABC Column Connections the bar debonding effect. The displacement capacity of debonded spliced columns (Dsp−deb)
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Analytical Programs 177 4.3.5 Summary of Modeling Methods for Mechanically Spliced Columns A mechanically spliced column can be analyzed by three different modeling methods, as summarized in Table 4-7. The design of conventional (CIP)
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178 Proposed AASHTO Seismic Specifications for ABC Column Connections 4.3.7 Testing Method for Mechanically Spliced Columns ACI 374.2R-13 presents guidelines for testing of RC members for seismic applications (ACI Committee 374 2013)
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Analytical Programs 179 the bar pulls out when the embedment length is insufficient (Figure 4-18c)
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180 Proposed AASHTO Seismic Specifications for ABC Column Connections Note that the unit of the normalized bond strength defined here is the square root of the stress unit and is different from the bond strength unit, which has the unit of stress. Normalized bond strength is an intermediate parameter used in deriving the design equations and does not appear in the final equations.
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Table 4-8. Preliminary pullout test database for grouted duct connections.
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182 Proposed AASHTO Seismic Specifications for ABC Column Connections A statistical analysis was carried out to determine the design bond strength, which was defined as the average bond strength less 1 standard deviation. This statistical method was previously used in studies by Brenes et al.
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Table 4-9. Updated pullout test database for grouted duct connections.
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184 Proposed AASHTO Seismic Specifications for ABC Column Connections strength obtained from this specimen would constitute a lower bound value, which is conservative. The bars in the other nine test specimens were fully developed and fractured outside the duct; thus, the data for these specimens were excluded from the database that was used in the derivation of the design equation.
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Analytical Programs 185 lad = anchored length (in.) of longitudinal reinforcing bars into ducts installed in cap or footing on basis of duct bond strength; dbl = nominal diameter (in.)
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186 Proposed AASHTO Seismic Specifications for ABC Column Connections However, the plots for the proposed equations and AASHTO are for dd = 4 in., db = 1.41 in.
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Analytical Programs 187 Figure 4-22 shows the design embedment length for a No. 10 Grade 60 ASTM A706 bar in a grouted duct connection based on different studies for two cases: Case A, a 3.2-in.
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188 Proposed AASHTO Seismic Specifications for ABC Column Connections 4.5 Grouted Duct Column Connections Four precast column connections were introduced and reviewed in previous chapters, and knowledge gaps for each type of connection were identified. The state-of-the-art literature review indicated that the main gap for grouted connections is the minimum embedment length of bars in ducts and the minimum size and detailing of the column adjoining members.
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Analytical Programs 189 simulate load transfer across the cracks as well as strain penetration in the reinforcement. The CDP material model was used to model grout in the ducts separately.
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190 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) Cast-in-place detail (c)
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Analytical Programs 191 The length to the maximum moment in the pile shaft (or the point of fixity) should be sufficiently short to ensure maximum demand on the joint while causing minimal distortion to the stress at the lower part of the pile.
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192 Proposed AASHTO Seismic Specifications for ABC Column Connections range of the maximum moment occurring at 1.25 to 1.4 times the shaft diameter (Dshaft)
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Analytical Programs 193 (a) Shaft-GD-t16 (b)
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194 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) Shaft-GD-t16 (b)
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Analytical Programs 195 Crack in shaft Crack in shaft and interface (a) Shaft-GD-t16 (c)
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196 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 4-31. Moment–drift relationships for shafts with cast-in-place and grouted duct connections.
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Analytical Programs 197 (a) Shaft-CIP-t12 (b)
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198 Proposed AASHTO Seismic Specifications for ABC Column Connections Crack in shaft Crack in shaft (a) Shaft-CIP-t12 (b)
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Analytical Programs 199 2014) ; Caltrans SDC (Caltrans 2013)
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200 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) Bridge elevation (b)
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Analytical Programs 201 (a) Elevation (b)
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202 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) Full-bridge model and loading (b)
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Analytical Programs 203 (b)
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204 Proposed AASHTO Seismic Specifications for ABC Column Connections (b)
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Analytical Programs 205 The information provided in this section should be treated as the background for the final proposed specifications. Refer to Appendix C for the design of actual bridge columns incorporating grouted duct connections.
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206 Proposed AASHTO Seismic Specifications for ABC Column Connections Source: Tran (2015)
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Analytical Programs 207 Figure 4-42. Measured moment–drift relationship for pile shaft pocket connections.
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208 Proposed AASHTO Seismic Specifications for ABC Column Connections plastic hinge (springPH) -- the plastic hinge was modeled with a zero-length spring and an elastic beam element elsewhere.
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Analytical Programs 209 was used to model the interaction between the outer surface of the precast column and the pocket in the shaft. Since both specimens and loadings were symmetric about the xz plane (Figure 4-43)
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210 Proposed AASHTO Seismic Specifications for ABC Column Connections the measured and calculated peak moments were 8% and 10% in springPH and fullPH, respectively. While the overall calculated moment–drift relationships were close to those of the test data, the cracking patterns obtained in the fullPH model were closer to the observed pattern (Figures 4-46 to 4-48)
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Analytical Programs 211 (a) DS1 - fullPH (b)
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212 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) DS2 - fullPH (b)
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Analytical Programs 213 Figure 4-48. Comparison of calculated cracking patterns on the symmetry plane in DS2.
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214 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) DS2-fullPH (b)
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Analytical Programs 215 Figure 4-52. Effect of shaft mesh density on cracking pattern for DS2 (b)
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Figure 4-53. Horizontal cracks in DS1 (left)
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(a) DS1 FE model (b)
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218 Proposed AASHTO Seismic Specifications for ABC Column Connections (a) DS1 finite element model (b)
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Analytical Programs 219 (a) DS1 finite element model (b)
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Figure 4-58. Typical pile shaft details.
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Analytical Programs 221 models with four shaft diameters while keeping the column diameter constant. Table 4-12 presents the key parameters.
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222 Proposed AASHTO Seismic Specifications for ABC Column Connections 4.6.2.2 Results of Pile Shaft Parametric Study Figure 4-60 shows the moment–drift relationships for different pile shaft diameters. The increase in the thickness of the concrete from 10 in.
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Analytical Programs 223 Figure 4-61. Reinforcement strains at failure for different shaft diameters with pocket connections.
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224 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 4-62. Cracking pattern at failure for different shaft diameters with pocket connections.
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Analytical Programs 225 Figure 4-63. Large vertical cracks in Shaft-t10 with pocket connections at failure.
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226 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 4-64. Cast-in-place bridge bent.
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Analytical Programs 227 Figure 4-65. Cap beam pocket connection using Alt-2 detailing.
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228 Proposed AASHTO Seismic Specifications for ABC Column Connections elements with embedment constraint, in which the translational degrees of freedom of the reinforcement are constrained to those of the concrete elements. The box girders were modeled by using elastic beam elements with the gross cross-sectional properties of the concrete box.
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Analytical Programs 229 Figure 4-67. Moment–drift relationship for different cap beam width.
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230 Proposed AASHTO Seismic Specifications for ABC Column Connections Figure 4-69. Cracking pattern at failure cap beam pocket connections.
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Analytical Programs 231 (a)
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232 Proposed AASHTO Seismic Specifications for ABC Column Connections 4.6.4 Design and Detailing Guidelines for Pocket Connections The AASHTO SGS, Sections 8.9 to 8.13 (2014) , provides a comprehensive design and detailing method for CIP capacity-protected members such as cap beams and joints.
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Analytical Programs 233 Dassault Systèmes.
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234 Proposed AASHTO Seismic Specifications for ABC Column Connections Tazarv, M and Saiidi, M
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