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    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Research in Progress (RIP)</title>
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      <title>Super-Elastic Copper-Based and Iron-Based Shape Memory Alloys and Engineered Cementitious Composites for Extreme Events Resiliency</title>
      <link>https://rip.trb.org/View/1903711</link>
      <description><![CDATA[Displacement capacity and energy dissipation in conventional RC columns comes at the cost of severe damage to concrete and steel and permanent displacement of the bridges and other structures including marine structures during extreme events such as earthquake, ice load, collision by vessels and vehicles, tsunamis, check floods, and blasts. The resiliency of these structures can be significantly increased if these problems can be eliminated using shape memory alloy (SMA) and engineered cementitious composite (ECC). Comparison of residual displacement in laboratory testing of column models demonstrated that residual displacement was 86% lower than that the columns with conventional materials. The Washington State Department of transportation (WSDOT) implemented SMA/ECC in the columns of the SR-99 on-ramp bridge in downtown Seattle. With the price of Nickel-Titanium SMA (NiTi) being 90 times the mild steel cost, bridge owners may be reluctant to adopt the material. To offset SMA material costs, a new generation of Copper-Aluminum-Manganese (CAM) SMA bar that is approximately 80-90% less expensive than NiTi is emerging. The alloy is composed of 72% Copper, 17% Aluminum, and 11% Manganese. No. 10 CAM bars have been developed and were recently tested along with Headed Reinforcement Corp’s (HRC) couplers at University of Nevada – Reno (UNR) with good results, i.e. large-diameter bars for use in actual bridges have already proven to be feasible. CAM bars are connected to steel bars that extend into the column and footings or cap beams. No CAM-reinforced columns incorporating the (HRC) splice has yet been studied, however, an exploratory study was conducted by shake table testing of a column model incorporating threaded CAM bars. These bars had to be machined to a dog bone shape to avoid fracture at the threaded ends. Engineered Cementitious Composite (ECC) was used in the plastic hinge region. ECC is a fiber-reinforced cement-based concrete which has high tensile ductility and high compressive and tensile strengths.. The column performed very well in limiting residual displacement while eliminating plastic hinge damage. Another SMA type, the low-cost iron-based SMA is also emerging, although its performance under extreme loads is yet to be studied. The advantage of Fe-SMA over CAM, should it prove successful, is having material characteristics that are similar to those of conventional steel that is readily used in bridge construction while being at a low cost.
The objective of this research project is to: 
(1) evaluate and test several innovative columns which have self-centering feature to provide minimum residual displacement after earthquake. 
(2) improve column serviceability after earthquake by decreasing damage and spalling of concrete within column plastic hinge region; and 
(3) provide cost comparison among columns having different engineered materials; and 
(4) develop self-centering column design specifications. Particularly, in this proposed research, the low-cycle fatigue characteristics, corrosion resistance, machinability and coupling mechanisms with traditional steel rebar, and cost of CAM and Fe-SMA super-elastic alloy (SEA) bars will be studied. 
Direct comparisons will be made with Nickel-Titanium (NiTi) SEAs (and traditional steel reinforcing bars as applicable) to illustrate the advantages/disadvantages of each material. If successfully demonstrated for their suitable characteristics, the CAM and Fe-SMA SEA bars could replace their NiTi counterparts at a significantly lower (up to ten times) cost and accelerate their applications in bridges. Therefore, the outcomes of this project are directly relevant to state departments of transportation and bridge and structural engineers and designers. This proposed project will build on the success of previously implemented WSDOT’s application of shape memory alloy/engineered cementitious composite (SMA/ECC) in the columns of the SR-99 on-ramp bridge in downtown Seattle while making a direct impact on advancing and securing the national transportation network.]]></description>
      <pubDate>Thu, 13 Jan 2022 17:36:01 GMT</pubDate>
      <guid>https://rip.trb.org/View/1903711</guid>
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      <title>Material Characteristics of Cu-Based Superelastic Alloys for Applications in Bridge Columns to Improve Seismic Performance</title>
      <link>https://rip.trb.org/View/1599217</link>
      <description><![CDATA[Due to the internal reversible martensitic transformation, Shape Memory Alloys (SMAs) can recover large (up to 10-12%) inelastic strains upon stress removal (referred to as the superelastic effect, SE) or with external heat stimuli (referred to as the shape memory effect, SME). The SE are particularly advantageous for dissipating seismic energy and protecting bridges in earthquake prone regions by substantially reducing permanents under near-fault earthquakes. Previous research on superelastic alloys (SEAs) mainly focused on the nickel-titanium (NiTi) composition, which showed stable behavior at or near room temperature. NiTi SEAs have been shown to have the necessary characteristics (strength, ductility, and energy dissipation capacity, among others) to be used as plastic hinge reinforcement in bridge columns. The first successful implementation of the NiTi SEAs in the SR99 Alaskan Viaduct Bridge in Seattle has been completed in 2017. However, certain properties of the NiTi based SEAs such as the difficulty in machining, potential loss of superelasticity at low temperature, and the high cost still drive the search for alternate materials. As an alternative material to NiTi, this research investigated the use of Cu-Al-Mn (CAM) SEAs, which are known to be cheaper and easier to machine. Considering both the manufacturing and machining, the total cost of CAM SEAs is expected to be one-half to one-quarter of that of NiTi based ones. More importantly, the CAM SEAs show comparable or even better superelasticity and a wider temperature application range than NiTi ones. In the low-cycle fatigue tests, it was found that the single crystal CAM SEAs show excellent superelasticity and fatigue resistance at all test temperatures: -40℃, room temperature, 25℃, and 50℃. The fatigue life of single crystal CAM SEAs was found to be as high as 50,000 cycles under 5% strain, and almost no deterioration was observed in the superelastic properties of single crystal CAM SEAs in the initial 100 cycles. In the long-term corrosion and electrochemical tests, it was found that the mass loss and corrosion rate of CAM SEAs is around 1/3 of mild steel. After around three years of natural corrosion, the CAM SEAs still showed excellent superelasticity: its strain recovery and energy dissipation capacity showed negligible degradation. A cost estimation study indicated that columns reinforced with CAM SEAs show economic advantage over the NiTi SEA reinforced columns particularly if machining is used to connect the SEA bars with the steel rebar. The additional cost associated with using CAM SEAs in the column was only about 1/4 of that of NiTi SEAs, indicating the cost effectiveness of CAM SEA resulting from its excellent machinability. This is confirmed by previous research by the PIs, which showed that incorporating CAM SEAs in the column plastic hinges of earthquake-prone bridges increased the overall initial cost of the bridge by only a few percent, a cost that is more than offset by not needing to conduct major bridge repair or replacement after strong earthquakes. The only major impediment for real life implementation of CAM SEAs in bridges is the mechanical splicing, which is recommended for future research.]]></description>
      <pubDate>Mon, 08 Apr 2019 17:40:45 GMT</pubDate>
      <guid>https://rip.trb.org/View/1599217</guid>
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