【正文】 these structures. Podolny’s caution regarding placency was warranted, as were Poston’s concerns for lack of diagnostic nondestructive tools which would have provided a more reliable means for judging condition of post tensioned structures. In 1999, corrosionrelated failure of an external (unbonded) post tensioning tendon in Florida DOT’s 20year old Niles Channel Bridge focused attention on posttensioned bridges. Three other Florida bridges including the MidBay Bridge in Destin, Sunshine Skyway (St. Petersburg), and I75/I595 Sawgrass Interchange in Broward County were later investigated. Investigations of these structures highlighted the critical role that tendon grouting and plementary corrosion barriers take in successful construction. The root causes of reinforcement deterioration in these bridges were identified as grouting procedure ineffectiveness for controlling entrapment of bleed water in tendons, and poor tendon duct detailing creating access for aggressive solutions. These incidents prompted rigorous review of the durability issues related to corrosion of posttensioned concrete structures. Corrosion – Mechanisms and Threats Corrosion is defined as the degradation of a metal’s integrity and strength by interaction with its environment. Because the metals used in construction are refined from their naturallyoccurring oxides, the refined metal is less thermodynamically stable than its oxide. When corrosion occurs, the refined metal’s structure reverts to its naturallyoccurring state through an electrochemical reaction. Initiation and sustenance of the reaction require existence of an electrolytic cell. Each corrosion cell requires three elements。 these are positioned outside the mass of the concrete girder elements, although these are nearly always incorporated within the interiors of cellular construction. Unbonded tendons are also grouted, principally for corrosion protection Common among these bridge ponents is the role of the prestressing reinforcement, which can take the form of colddrawn high strength wire, or wire helically wound to form 7wire strand, and rolled high strength threaded bars. Prestressing strand for bridge construction is presently supplied with a tensile strength of 1860 MPa, and bar reinforcement in 1030 to 1100 Mpa tensile strength. Prestressing wire (parallel wire systems) has also been used for prestressed bridges, though not in this country for more than two decades. In bridges, the prestressing reinforcement element provides the concrete structure a means for counteracting tensile stress resulting from service loads, and provides the needed capacity for the strength limit state. As such, the prestressing reinforcement must reliably and continuously sustain, over the life of the structure, a minimum stress level on the order of 60% of its nominal strength. In the realm of engineering design, this demand on material performance is very substantial. Consequently, the prestressing reinforcement39。幾何截面和使用的設(shè)計(jì) /施工程序代表的范圍廣泛的可能結(jié)構(gòu)設(shè)計(jì)配置、 預(yù)制和強(qiáng)制轉(zhuǎn)換的地方 ；有興趣的讀者應(yīng)該鼓勵(lì)從預(yù)應(yīng)力 /預(yù)制混凝土研究所、 后張法研究所和美國(guó)節(jié)段橋梁研究所深入設(shè)計(jì)和施工指導(dǎo)對(duì)這一技術(shù)，等組織獲得的信息，因?yàn)樘剿魉膹?fù)雜性是超出了本文的范圍。對(duì)這些 特點(diǎn) 的認(rèn)識(shí) 是對(duì)建設(shè)持久的預(yù)應(yīng)力 橋梁和延長(zhǎng) 舊 的 可用結(jié)構(gòu) 壽命 的 一個(gè)關(guān)鍵 因 素。 This paper discusses considerations necessary for achieving the potential low maintenance service life these bridges can offer. These observations are derived from the author’s experience in investigating and evaluating prestressed, posttensioned concrete bridges, and developing investigative and rehabilitation solutions at the CTL Structural Engineering Laboratory since 1988. While the durability of prestressed concrete can be influenced by behaviors of both the concrete and reinforcement, recent construction trends and post tensioned concrete bridge performance observations have focused more attention on preserving the condition of prestressing steel. Consequences of prestressing steel deterioration are most serious. Awareness of these features is a key element to construction of long lasting prestressed bridges and extending life of older, serviceable structures. 本文討論了實(shí)現(xiàn)這些橋梁潛在的低維護(hù) 使用 壽命 所需的考慮。 the pace of acceptance for this construction technology accelerated rapidly。這些問(wèn)題可能繼續(xù) 危害結(jié)構(gòu) 。 Abstract The impact on bridge reliability, of prestressing steel deterioration and tendon rupture created by corrosion mechanisms, is much more critical and rapid than that of any other ponent of a prestressed concrete bridge. Additionally, deterioration of embedded prestressing reinforcement in these structures may not necessarily be made visible through manifestation of external distress in the Concrete. 摘要 腐蝕機(jī)制 引起 預(yù)應(yīng)力 鋼筋的 惡化和 斷裂，進(jìn)而對(duì) 橋梁 的 可靠性 產(chǎn)生 影響 ，這比對(duì) 預(yù)應(yīng)力混凝土橋 的 其他 部分的影響更加嚴(yán)重，也更加迅速。 此外， 在這些結(jié)構(gòu)中 ，有粘結(jié) 預(yù)應(yīng)力鋼筋的惡化 也 不 必要 通過(guò) 混凝土外部糟糕的 狀況 表現(xiàn)出來(lái)。因此， 我將對(duì) 預(yù)防 腐蝕 的 方法和 施工 與 維護(hù) 期間 的 檢測(cè) 進(jìn)行介紹。 most all concrete bridge superstructures in existence today were built in that fashion. Assuring success in new construction and extending service life of prestressed and post tensioned concrete bridges requires attentiveness to the distinctive characteristics and behaviors inherent to this particular construction technology. 介紹 美國(guó)的第一個(gè)預(yù)應(yīng)力混凝土橋建于 1950 年 ； 接受這種施工技術(shù) 的步伐迅速 加快 。 自 1988 年以來(lái) ， 作者 在 CTL 結(jié)構(gòu)工程實(shí)驗(yàn)室 調(diào)查和 評(píng)估 預(yù)應(yīng)力 、 后張法預(yù)應(yīng)力混凝土橋梁、開發(fā)檢測(cè) 和 加固 解決方案 ， 這些 觀測(cè)結(jié)論 就源于 這期間 的 經(jīng)驗(yàn) 。 Function of Prestressing Reinforcement in Bridge Design and Construction Most concrete highway bridges are prised of prestressed concrete in two predominant fabrication/construction categories。 Prestressed (less monly known as pretensioned) concrete is made by stressing the reinforcement between fixed bulkheads and casting concrete around the steel elements. Following concrete curing, the steel strand is released at the bulkhead, transferring pressive stress and added stiffness into the concrete. Most all pretensioned concrete bridge ponents are precast in specialized fabrication yards, then shipped an