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首页> 外文期刊>Materials and structures >Rapid heat-activated post-tensioning of damaged reinforced concrete girders with unbonded near-surface mounted (NSM) NiTiNb shape-memory alloy wires
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Rapid heat-activated post-tensioning of damaged reinforced concrete girders with unbonded near-surface mounted (NSM) NiTiNb shape-memory alloy wires

机译：快速热激活损坏钢筋混凝土梁的张紧后张紧，具有未粘附的近表面安装（NSM）NitinB形状记忆合金电线

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摘要

Concrete girders can suffer from serviceability issues due to excessive cracking and deflection. In response to this problem, a novel heat-induced post-tensioning technique utilizing unbonded near-surface mounted nickel-titanium-niobium (NiTiNb) shape-memory alloy (SMA) wires was proposed and evaluated. SMAs are a class of smart materials that can recover seemingly permanent plastic deformation when heated. The post-tensioning forces, thus, can be generated by restrained heat-induced shape recovery of SMA wires. Material characterization tests showed that 3.92-mm diameter NiTiNb wires with 2.5% prestrain can generate recovery stress of approximately 500 MPa when actuated via Ohmic heating in a restrained condition. The proposed post-tensioning system was experimentally evaluated in reinforced concrete girders measuring 2.3 m in length and 23 x 41 cm in cross-sectional dimensions. The girders were initially cracked to simulate typical girder damage. NiTiNb wires were then installed in the bottom cover of the girders and anchored at both ends. Subsequently, the wires were actuated via Ohmic heating, which triggered shape-recovery and generated post-tensioning stresses in the girder. The post-tensioning technique reduced the crack widths by up to 74% (370 urn) and recovered the residual midspan deflection by up to 49% (1.52 mm) in the cracked girders. Following post-tensioning, flexural loading up to failure showed that the cracked stiffness and ultimate moment capacity of the girders had increased by up to 31% and 45%, respectively, with a relatively small NiTiNb reinforcement ratio of up to 0.17%.
机译：由于过度开裂和偏转，混凝土梁可以遭受可维护性问题。响应于这个问题，提出了一种新的热引起的张紧技术，利用未粘结的近表面安装镍 - 钛 - 铌 - 铌（NITINB）形状记忆合金（SMA）线被评估。 SMA是一类智能材料，可以在加热时恢复看似永久的塑性变形。因此，可以通过抑制SMA线的抑制热诱导的形状恢复来产生后张紧力。材料表征试验表明，3.92毫米直径的NitinB导线，其中2.5％PRestain可以在受限制条件下通过欧姆加热致动时产生约500MPa的恢复应力。在钢筋混凝土梁上进行实验评估了所提出的张紧系统，其长度为2.3米，横截面尺寸为23×41厘米。最初裂开梁以模拟典型的梁损伤。然后将NitinB导线安装在梁的底盖中并在两端锚定。随后，通过欧姆加热致动线，该欧姆加热致动，该欧姆加热触发形状回收并在梁中产生张紧后应力。后张紧技术可将裂缝宽度降低至74％（370瓮），并在裂纹梁中恢复高达49％（1.52毫米）的残留中间挠度。后张力后，弯曲加载失败表明，梁的裂纹刚度和最终电量分别增加了高达31％和45％，具有相对较小的NitinB增强比率高达0.17％。

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