【正文】 g in California, are examples of segmental structures。 ? Short and longterm pier shortenings and foundation sum of the various de?ection values for the successive sections of the deck allows the construc tion of a camber diagram to be added to the theoretical pro?le of the bridge. A construction camber for setting the elevation of the traveler at each joint must also be developed. Precast Segments Opposite to the precast girder concept where the bridge is cut longitudinally in the precast segmental methods, the bridge is cut transversally, each slice being a segment. Segments are cast in a casting yard one at a time. Furthermore, the new segment is cast against the previously cast segment so that the faces in contact match perfectly. This is the matchcast principle. When the segments are reassembled at the bridge site, they will take the same relative position with regard to the adjacent segments that they had when they were cast. Accuracy of segment geometry is an absolute priority, and adequate surveying methods must be used to ensure followup of the casting of the segments is a prerequisite for the application of glued joints, achieved by covering the end face of one or both of the meeting segments with epoxy at the erection. The epoxy serves as a lubricant during the assembly of the segments, and it ensures a watertight joint in the?nished structure. Full watertightness is needed for corrosion protection of internal tendons (tendons inside the concrete). The tensile strength of the epoxy material is higher than that of the concrete, but, even so, the strength of the epoxy is not considered in the structural behavior of the joint. The required shear capacity is generally provided by shear keys, single or multiple, in bination with longitudinal the introduction of external posttensioning, where the tendons are installed in PE ducts,outside the concrete but inside the box girder, the joints are relieved of the traditional requirement of watertightness and are left dry. The introduction of external tendons in connection with dry joints greatly enhanced the ef?ciency of precasting. Casting Methods There are two methods for casting segments. The ?rst one is the longline method, where all the segments are cast in their correct position on a casting bed that reproduces the span. The second method, used most of the time, is the shortline method, where all segments are cast in the same place in a stationary form, and against the previously cast segment. After casting and initial curing, the previously cast segment is removed for storage, and the freshly cast segment is moved into place. Geometry Control A pure translation of each segment between cast and matchcast position results in a straight bridge(Figure ). To obtain a bridge with a vertical curve, the matchcast segment must ?rst be translated and given a rotation in the vertical plane (Figure ). Practically, the bulkhead is left ?xed and the mold bottom under the conjugate unit adjusted. To obtain a horizontal curvature, the conjugate unit is given a rotation in the horizontal plane (see Figure ). To obtain a variable superelevation, the conjugate unit is rotated around a horizontal axis located in the middle of the top slab (Figure ).All these adjustments of the conjugate unit can be bined to obtain the desired geometry of the bridge. Erection The type of erection equipment depends upon the erection scheme contemplated during the design process。 起拱需要 通常 10年到 15年，所有徐變撓度全部產(chǎn)生后的結(jié)構(gòu)永久變形會令使用者行駛不舒適或者令公眾失去信心。比如，AASHTO規(guī)范規(guī)定除了行人使用情況外，懸臂梁撓度取決于活載撓度加上橋跨的3001 。對后張拉的正面和負(fù)面的彎矩， 10%是合理的。 一些節(jié)段性結(jié)構(gòu)抗震設(shè)計的知道提供在最新版本的 AASHTO的設(shè)計與施工節(jié)段性混凝土橋梁規(guī)范 [2]中 ,該規(guī)范有一章致力于抗震設(shè)計。由于大多數(shù)的測試都是在就地澆筑的連接處進(jìn)行的，在這些情況下這都是首選。此外 ,這些軸承將增加結(jié)構(gòu)的齡期 ,從而在整體上減小感應(yīng)力 (對高頻結(jié)構(gòu)有益 ),隔離軸承也會提供一些結(jié)構(gòu)阻尼。 對于后者 ,我們可以看到柱面在四分之三 Mp范圍變化，但是中跨有鉸鏈時，只能在二分之一范圍變化。 適中塑性鉸鏈開口需要限制器，適當(dāng)?shù)闹ё鶎挾群玩i定裝置 簡單的懸臂結(jié)構(gòu) 后者影響顯然不適用于現(xiàn)澆柱 ,但適用于彎矩轉(zhuǎn)換。盡量減少橫隔板和加勁肋的數(shù)量，并且模板中出現(xiàn)銷釘 現(xiàn)澆懸臂梁 傳統(tǒng)起重機(jī) 傳統(tǒng)形式的起重機(jī)通過縱梁或者最后一段外伸框架的形式支撐新鮮混凝土。在寒冷天氣，可以通過各種加熱裝置來加速固化。在每個連接處設(shè)置起重機(jī)標(biāo)高也必須得到發(fā)張。環(huán)氧樹脂在組裝節(jié)段時充當(dāng)潤滑劑，并且它保證結(jié)構(gòu)完成時連接處的水密性。第二種方法是短線法，大多數(shù)時間用這種方法，即所有的節(jié)段在一個靜止的地方挨著前一個節(jié)段澆筑。 圖 典型短線預(yù)制操作 圖 平曲線橋 圖 帶超高的橋 安裝 安裝設(shè)備的類型取決于設(shè)計節(jié)段的安裝方案構(gòu)思，當(dāng)?shù)厮懬闆r，安安裝速度和總體建造安排。這種方法很慢。這種方法同樣很慢，但是，這不需要就地使用又貴又重的卷揚機(jī)，特別是在節(jié)段很重的時候。 第二種類型構(gòu)臺有典型跨兩倍的長度 (見圖 )。這大概用 7到10天，但根據(jù)項目的細(xì)節(jié)和推進(jìn)梁的改進(jìn)有不同的變化。在夏威夷橋的雙線箱梁是通過兩條平行線建造的，但又有獨立的構(gòu)架 (見圖 )，典型跨度是 ，節(jié)段重量 70噸；兩座橋結(jié)構(gòu)以不同的高度和縱坡相距 。懸臂施工過程中，中心支腿依賴于橋墩而后部支腿依賴于前面豎起跨的懸臂端，該支腿必須承受相對運動。卷揚機(jī)安裝在適合節(jié)段的梁上。懸臂端連接處的閉合施工到位并且連續(xù)鋼筋安裝和受力。實際上在隔離壁是保持直的。 通過外部后張的采用，鋼筋安裝在聚乙烯管內(nèi)部，混凝土外面和箱梁內(nèi)部，連接處達(dá)到傳統(tǒng)的保證水密性的要求。這就是配合澆筑原則。建造時施加后張節(jié)段的重量下懸臂梁的撓度 灌注期間需要頂起模板來避免這些裂縫。但也有共同特點，就是必須記住設(shè)計階段應(yīng)保證方案簡單，經(jīng)濟(jì)和效率。從其他方面的研究推斷墩的預(yù)制節(jié)段可以通過未粘接的錨固的預(yù)應(yīng)力鋼筋連接。 適度的塑性開端需要結(jié)尾部分有充分的間隔 整體墩 不適用 單跨標(biāo)準(zhǔn)解決方法 上部結(jié)構(gòu)必須抵抗最后的合力 (使用適當(dāng)?shù)臏p力因素 ),而在下部結(jié)構(gòu)中可以產(chǎn)生屈服。大跨度和高大的圓柱、空心柱部分會更合適。 對于其他抗震設(shè)計和細(xì)化問題 ,讀者應(yīng)參考加州交通部提供的現(xiàn)澆結(jié)構(gòu)的設(shè)計資料 [58]。通常情況下 ,這種屈服通常是柱子產(chǎn)生可塑性屈服 (巨大的板或者上部結(jié)構(gòu)連接 )或 者軟支撐系統(tǒng)屈服達(dá)到的 [6]。外部后張很容易在結(jié)構(gòu)的任何時期檢查，消除內(nèi)部鋼筋的問題和避免在各現(xiàn)澆塊間使用昂貴的環(huán)氧膠黏劑。 活載引起的整體變形 由于活載的影響，大多數(shù)設(shè)計規(guī)范對橋跨的整體變形都有限制。 the two bridge structures are m apart with different elevations and longitudinal slopes. This system is a re?nement of the ?rst type of gantry applied to twin decks with variable , the balanced cantilever method is used for spans from 60 to 110 m, with a launching girder.