APPENDIX G SUMMARY SHEETS OF EMERGING TECHNOLOGY AND DEFORMABLE ELEMENT CONNECTIONS

Transcription

1 APPENDIX G SUMMARY SHEETS OF EMERGING TECHNOLOGY AND DEFORMABLE ELEMENT CONNECTIONS

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3 NCHRP Connection Evaluations Appendix G G-1 APPENDIX G SUMMARY SHEETS OF EMERGING TECHNOLOGY AND DEFORMABLE ELEMENT CONNECTIONS

4 NCHRP Connection Evaluations Appendix G G-2 Location: Foundation to column Type: Special: Precast segmental column, unbonded PT, mild steel, Title: Connection S-1 elastomeric bearing pad, DE and ED Elastomeric Bearing TRL: Maximum TRL: 6 Source: University of Nevada - Reno TRL Gaps: Levels 3

5 NCHRP Connection Evaluations Appendix G G-3 BACKGROUND Title: Connection S-1 (Elastomeric Bearing) History / Description: An elastomeric bearing pad assembly is cast into footing, using studs. The first column segment is cast in place. Subsequent column segments are precast, stacked on top of one another, and connected with an unbonded PT bar. Seismic performance tested at University of Nevada Reno in shake table tests. References: Motaref et al. (Accepted for publication) Contact Information: Prof. Mehdi Saiidi (University of Nevada Reno) saiidi@unr.edu EVALUATION Constructability: Risk Value: -2 Seismic Performance: Value: +2 Inspectability: Durability: Elastomeric bearing pad assembly needs to be cast into footing and first column segment. Needs to be located accurately and supported rigidly during footing pour. Many extra construction steps compared with CIP Bearing assembly adds to cost. Practical field details for PT anchorage at base of column need to be developed. Erection sequence poses difficulties: either the precast segments must be lowered over the PT bar(s), the PT bar(s) must be threaded blind after segment installation, or a coupler must be used at each interface. The bearing assembly is a critical component. Replacement appears difficult. Energy dissipation, shared by elastomer and mild steel, was comparable to plastic hinge zone with only mild steel and concrete. Lower initial stiffness than conventional CIP concrete column. Low damage in plastic hinge region. Achieved high drift levels with low residual drift. No reinforcement is provided between upper column segments, so segments are held together solely by the clamping force of the PT. Difficult to inspect PT anchors after an earthquake. Inspection and repair of bars passing through bearing would be difficult. PT tendon introduces possibility of corrosion. Time Saving Potential: The many additional steps would slow down construction. Value: -2 TRL Comments: Most experience with high deformations in bearings occurs with isolation bearings in shear. Here the bearings are subjected to rotations. Additional Comments: Specimens with different natural periods were compared on shake table

6 NCHRP Connection Evaluations Appendix G G-4 Location: Foundation to column Type: Special: Precast segmental column with shape memory alloy ED bars Title: Connection S-2 ED and DE Shape Memory Alloy Bars TRL: Maximum TRL: 4 Source: State University of New York - Buffalo TRL Gaps: Level 3

7 NCHRP Connection Evaluations Appendix G G-5 BACKGROUND Title: Connection S-2 (Shape Memory Alloy Bars) History / Description: PT tendons and T-threaded studs for SMA bars are cast into footing. The first column segment placed on the footing. Unbonded SMA bars are screwed into the T-threaded studs in the footing and anchored with a nut to the top of the first segment. Subsequent column segments are placed and clamped to the previous. Analytical testing performed at SUNY Buffalo. References: Roh and Reinhorn (2010) Contact Information: Prof. Andrei Reinhorn (SUNY Buffalo) reinhorn@buffalo.edu EVALUATION Constructability: Risk Value: -2 Seismic Performance: Value: +1 Difficult mechanical connection for SMA bars if they are to be spliced to conventional steel screw lock couplers are an option (see Alam et al. 2008). Need to use a template to align T-thread studs in footing with bar anchorages at top of first segment. Segment clamping mechanism and force transfer is unclear. Practical field details for PT anchorage at base of column need to be developed. Erection sequence poses difficulties: either the precast segments must be lowered over the PT bar(s), the PT bar(s) must be threaded blind after segment installation, or a coupler must be used at each interface. (Estimated) Seismic damage minimized by rounding corners at column base. Segmental column with rigid links concentrates rotation and energy dissipation at base. SMA bars dissipate energy with low residual strains (superelasticity). Energy dissipation is less than conventionally reinforced column. Needs physical testing only studied analytically. Inspectability: Engagement of PT bar nuts/couplers might be difficult to inspect. Durability: Time Saving Potential: Value: -2 Potential water infiltration at clamped joints. Corrosion protection system for PT cables unclear. SMA bars have high corrosion resistance. Many extra pieces to connect (clamp joints, SMA bars, PT). Accurate alignment needed. TRL Comments: SMA is a relatively new and expensive material in earthquake engineering. Additional Comments: Are the #11 bars in the upper segments to be developed to the SMA bars?