超高压- frp非预应力预制大跨度桥梁主梁研究

S. Chao, Venkatesh Kaka, Missagh Shamshiri
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引用次数: 2

摘要

超高性能纤维增强混凝土(UHP-FRC)的特殊抗压强度和延性可以彻底改变钢筋混凝土结构构件的设计。现行设计规范(ACI 318建筑规范和AASHTO LRFD桥梁设计规范)假设普通素混凝土的最大可用压缩应变εcu为0.003,而UHP-FRC的εcu则高出5至10倍。低估UHP-FRC的抗压延性限制了允许的最大纵向配筋量,从而导致构件的抗弯能力有限。传统的钢筋混凝土构件是用少量的钢筋来设计的,以满足张力控制的性能。这种设计方法反过来导致1)小的极限抗弯能力,2)在使用荷载下大量裂缝和更宽的裂缝宽度,这导致构件刚度降低,3)裂缝在超载后不太可能关闭,4)小的压缩区深度允许裂缝深入扩展,这进一步降低了刚度,5)钢筋中的大应变,这降低了骨料联锁和抗剪强度,6)钢筋的相当大的屈服。这会导致粘结恶化。与传统的设计理念相反,本文研究了一种新的延性强钢筋混凝土(DCSR)设计理念。考虑到UHP-FRC的最大可用压缩应变为0.015,这允许混凝土构件在使用大量钢筋时保持张力控制行为。因此,截面的抗弯能力增加。这种方法可以使UHP-FRC的高抗压强度在压缩区得到有效利用。强钢与UHP-FRC抗拉强度的协同作用显著提高构件的抗裂性能。此外,由于高钢量的强桥接作用,初始微裂纹的数量和大小受到限制。因此,构件在服务荷载下保持其刚度和小挠度。这一特点允许消除预应力的桥梁梁,其中一个未开裂的部分是期望在服务载荷下。除了实验证据外,还使用DCSR概念设计了一个250英尺长的非预应力超高压- frc桥面球形三通梁原型。基于AASHTO加载的有限元分析证实,新型UHP-FRC梁满足规范要求。试验和分析结果表明,新型非预应力面板UHP-FRC梁可以替代传统预制预应力混凝土梁。
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Toward A Non-Prestressed Precast Long-Span Bridge Girder Using UHP-FRC
The exceptional compression strength and ductility of ultra-high-performance fiberreinforced concrete (UHP-FRC) can revolutionize the design of reinforced concrete structural members. While the maximum useable compressive strain, εcu, for conventional plain concrete is assumed to be 0.003 in current design codes (ACI 318 Building Code and AASHTO LRFD Bridge Design Specifications), UHP-FRC’s εcu is 5 to 10 times higher. Underestimating the compressive ductility of UHP-FRC limits the allowable maximum amount of longitudinal reinforcement, which in turn leads to limited flexural capacity of the members. Conventional reinforced concrete members are designed with a smaller amount of reinforcement to meet tension-controlled behavior. This design approach in turn leads to 1) a small ultimate flexural capacity, 2) a large amount of cracking and wider crack widths under service loads, which lead to a reduced member stiffness, 3) cracks that are less likely to close after overloading, 4) a small compression zone depth that allows cracks to propagate deeply, which further reduces the stiffness, 5) large strains in rebars, which reduce aggregate interlock and shear strength, and 6) considerable yielding of rebars, which causes bond deterioration. Contrary to the conventional design concept, a new ductileconcrete strong-reinforcement (DCSR) design concept is investigated in this study. A maximum useable compressive strain of 0.015 is considered for UHP-FRC, which allows a concrete member to maintain tension-controlled behavior while using a high amount of steel rebars. Accordingly, the flexural capacity of the section increases. This approach allows the UHP-FRC’s high compressive strength to be effectively utilized in the compression zone. The synergistic interaction of strong steel and tensile strength of UHP-FRC considerably increases the cracking resistance of the member. In addition, the number and size of initial microcracks are limited due to the strong bridging effect of a high amount of steel. Therefore, the member maintains its stiffness and small deflection under service loads. This feature permits eliminating prestressing in bridge girders, where an uncracked section is desired under service loads. Besides experimental evidence, a prototype single-span 250-ft long non-prestressed UHP-FRC decked bulb-tee (DBT) girder was designed using the DCSR concept. Finite element analysis with AASHTO loading confirms that the new UHP-FRC girder satisfies code requirements. The experimental and analytical results show that conventional precast prestressed concrete girders can be replaced by the new nonprestressed decked UHP-FRC girders.
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