Effects of strain reversal on elastic and viscoelastic properties of early age cement paste beams
Effects of strain reversal on elastic and viscoelastic properties of early age cement paste beams
复制标题
应变反转对早期水泥浆梁弹性和粘弹性的影响
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
Z. Grasley
中科院分区：
文献类型：
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作者：
Christopher L. Galitz;Z. Grasley
混凝土早期特性的表征是一个正在进行的研究领域，对于理解预应力和传统混凝土构件在不同荷载历史下的长期行为尤其重要，包括应变逆转，例如在预应力梁上放置混凝土甲板时可能发生的情况。目前广泛使用的模型特别排除了存在应变逆转的情况。本文的研究是为了完善水泥浆体在早期受应变逆转时的粘弹性行为的理解。对一系列小尺度梁进行了中心点不规则位移的三点加载试验。在某些时间间隔，梁被负位移，引起应变反转。结果表明，在最初几天，负载损失显著，随后在整个测试过程中稳定松弛。结果进一步表明，反转后的载荷松弛明显慢于载荷同方向增加时的松弛。最后，在整个测试过程中，杨氏弹性模量的测量表明，与相同龄期的未加载梁相比，持续加载导致梁的刚度明显增加。对这些现象的解释和意义进行了探讨。
Characterization of the early age properties of concrete is an ongoing area of research particularly important in understanding longer-term behavior of pre-stressed and conventional concrete members subjected to varying load histories, including strain reversals, such as may occur during placement of a concrete deck atop pre-stressed girders. Models currently in widespread use specifically exclude cases where strain reversals are present. Research presented in this paper was undertaken to refine the understanding of the viscoelastic behavior of cement paste at an early age when subject to strain reversals. A series of small-scale beams were tested in 3-point loading with the center point displaced at irregular time intervals. At some time intervals, beams were displaced negatively, inducing a strain reversal. Results indicate significant load loss in the first few days followed by steady relaxation throughout the length of testing. Results further indicate that load relaxation after reversal is significantly slower than that with same-direction increases in load. Finally, measurements of Young’s modulus of elasticity throughout the testing program indicate that sustained loading leads to an apparent increase in beam stiffness compared to unloaded beams of the same age. The explanation and significance of these phenomena are explored.