钢纤维预应力混凝土梁中早期裂缝的控制

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钢纤维预应力混凝土梁中早期裂缝的控制(中文3800字,英文2300字)
摘要：
德克萨斯州运输部门（TxDOT）及美国各地的类似部门广泛运用预应力混凝土I型梁作为建筑中主要的上层构造元素。 在预应力混凝土I型梁中存在着一个普遍问题，在预应力释放后，或者一段时间后，由于徐变，收缩，温度变化的二次效应，端部表面会产生裂缝。为控制端部的开裂，在此区域布置了大量的横向箍筋。端部加强层的体积在混凝土总体积中所占比例达到了惊人的4.2 %。即使端部有这么高的配筋率，该区域还是会发生开裂，问题依然存在。并且由于密集的端部加强层位于I型梁的薄弱部位，导致传统混凝土的完全固定存在一定困难。因此，端部区域的混凝土质量退化，又使其容易开裂。此外，生产大量钢筋并且将之放置在端部区域，需要花费大量劳力和物力。
自我巩固型混凝土（SCC），也被称为自密实混凝土，因其便于放置在复杂形式中并进行密集加固，因而拥有丰厚的商业利益 1，2。与传统混凝土相比，传统混凝土由于压实较困难，导致不利的孔隙比，从而严重地减少混凝土的强度和耐久性。自密实混凝土(SCC)不仅可以固结，而且可通过自重流动。不用振动，就可使表面光滑。它不需要振动就可以实现充分固结，同时，它必须满足下列可用性标准3

Control of early-age cracks in prestressed concrete beams using steel fibers
H. Dhonde, Y.L. Mo* and Thomas T.C. Hsu
(Department of Civil and Environmental Engineering)
(University of Houston, 4800 Calhoun, Houston, TX 77204, USA)

INTRODUCTION
   The Texas Department of Transportation (TxDOT) and other such agencies throughout the United States extensively use the precast/prestressed concrete I-beams as the primary superstructure element in building. A commonly observed problem in the prestressed concrete I-beams is the appearance of end zone cracking either just after the release of the prestressing forces or after some time due to secondary effects of creep, shrinkage and temperature
variation. To control this end zone cracking, large quantities of transverse stirrups are provided in the end zone.This end zone reinforcement amounts to a staggering 4.2 % by volume of concrete. Even with such a high percentage of reinforcing steel in the end zone, cracking still occurs at the end zone and the problem persists. Moreover, the congested end zone reinforcement placed in the slender web of the I-beam leads to difficulty in consolidating the traditional concrete properly. Hence, the quality of concrete degrades at the end zones, again making it susceptible to cracking. Furthermore, it is also labor-intensive and costly to produce and place the large amount of steel reinforcement in the end zone.