【正文】 ct to 185。 however, these bridges are all segmentally cast in place, with mild reinforcement crossing the segment joints. Some guidance for the seismic design of segmental structures is provided in the latest edition of the AASHTO Guide Speci?cations for Design and Construction of Segmental Concrete Bridges [2], which now contains a chapter dedicated to seismic design. The guide allows precastsegmental construction without reinforcement across the joint, but speci?es the following additional require ments for these structures: ? For Seismic Zones C and D [1], either castinplace or epoxied joints are required. ? At least 50% of the prestress force should be provided by internal tendons. ? The internal tendons alone should be able to carry 130% of the dead load. For other seismic design and detailing issues, the reader is referred to the design literature provided by the California Department of Transportation, Caltrans, for castinplace structures [58]. Deck/Superstructure Connection Regardless of the design approach adopted (ductility through plastic hinging of the column or through bearings), the deck/superstructure connection is a critical element in the seismic resistant system. A brief description of the different possibilities follows. Monolithic Deck/Superstructure Connection For the longitudinal direction, plastic hinging will form at the top and bottom of the columns. Since most of the testing has been conducted on castinplace joints, this continues to be the preferred option for these cases. For short columns and for solid columns, the detailing in this area can be readily adapted from standard Caltrans practice for castinplace structures, as shown on Figure . The joint area is then essentially detailed so it is no different from that of a fully castinplace bridge. In particular, a Caltrans requirement for positive moment reinforcement over the pier can be detailed with prestressing strand, as shown below. For large spans and tall columns, hollow column sections would be more appropriate. In these cases, care should be taken to con?ne the main column bars with closely spaced ties, and joint shear reinforcement should be provided according to Reference [3 or 7]. The use of fully precast pier segments in segmental superstructures would probably require special approval of the regulating government agency, since such a solution has not yet been tested for bridges and is not codi?ed. Nevertheless, based upon ?rst principles, and with the help of strut– tiemodels, it is possible to design systems that would work in practice [6]. The segmental superstructure should be designed to resist at least 130% of the column nominal moment using the strength reduction factors prescribed in Ref. [2]. Of further interest may be a bination of precast and castinplace joint as shown in Figure , which was adapted from Ref. [8]. Here, the precast segment serves as a form for the castinplace portion that ?lls up the remainder of the solid pier cap. Other ideas can also be derived from the building industry where some model testing has been performed. Of particular interest for bridges could be a system that works by leaving dowels in the columns and supplying the precast segment with matching formed holes, which are grouted after the segment is slipped over the reinforcement [9] Typically, for spans up to 45 m erected with the spanbyspan method, the superstructure will be supported on bearings. For action in the longitudinal direction, elastomeric or isolation bearings are preferred to a ?xedend/expansionend arrangement, since these better distribute the load between the bearings. Furthermore, these bearings will increase the period of the structure, which results in an overall lower induced force level (bene ? cial for higherfrequency structures), and isolation bearings will provide some structural damping as the transverse direction, the bearings may be able to transfer load between super and substructure by shear deformation。 ? De?ection of the concrete cantilever arm during construction under the weight of segment plus posttensioning。 the local conditions, either over water or land。在很大程度上，撓度取決于結(jié)構(gòu)的構(gòu)造，后張是各部分的齡期和使用荷載作用時結(jié)構(gòu)的齡期。即使結(jié)構(gòu)沒有明顯的缺陷，也不會提升公眾的信心。這種限制的目的是避免對使用者的明顯震動和盡量減小活載的影響。 后張布置 外部后張 當(dāng)大多數(shù)混凝土橋使用支架建造或者現(xiàn)澆梁橋使用充滿混凝土截面的預(yù)應(yīng)力鋼束是，其他新方法已經(jīng)用于現(xiàn)澆部分結(jié)構(gòu)。內(nèi)部鋼筋的問題是在結(jié)合處未對準(zhǔn)引起開裂的鋼筋；在結(jié)合部分缺乏覆蓋物；以一定曲率穿過橋跨的鋼筋 (見圖 )。規(guī)定應(yīng)該適用于入口，錨固處和增加鋼筋的偏差。 同樣的原理也適用于節(jié)段性結(jié)構(gòu) ,即分段上層建筑的需要承擔(dān)子結(jié)構(gòu)產(chǎn)生的需求。該規(guī)范允許裝配式預(yù)制結(jié)構(gòu)不需要在結(jié)合處加強(qiáng)，但對這些結(jié)構(gòu)指定的下列附加的要求： 對于地震帶 C和 D，必須使用就地澆筑或者環(huán)氧粘接劑。 板和上部結(jié)構(gòu)連接 無論什么設(shè)計(jì)方法 (通過鉸接或通過軸承 )，板 /上部結(jié)構(gòu)連接在抗震中是一個關(guān)鍵要素。對短柱和實(shí)心柱 ,在這一地區(qū)的詳細(xì)標(biāo)準(zhǔn)可以很容易從加利福利亞運(yùn)輸部對于現(xiàn)澆結(jié)構(gòu)的實(shí)驗(yàn)中實(shí)現(xiàn)，如圖 所示。在這種情況下 ,應(yīng)該小心地主 柱界限 ,并根據(jù)文獻(xiàn) [3或 7]提供結(jié)合處的剪力。 在橫方向，軸承也許能通過剪切變形轉(zhuǎn)移上部結(jié)構(gòu)間的荷載；然而，在某些不肯能的情況下，能如圖 。 圖 板 /頓軸承連接 膨脹鉸鏈 從地震的觀點(diǎn)來看 ,我們希望將膨脹鉸鏈 (EH)的數(shù)量降到最低。 膨脹鉸鏈在一個跨度的位置及其特性 ,也依賴于基礎(chǔ)的剛度和上部結(jié)構(gòu)到墩的連接類型。相鄰橋墩中連續(xù)跨產(chǎn)生適中上部結(jié)構(gòu) 簡單的懸臂結(jié)構(gòu) 懸臂法建造復(fù)雜結(jié)構(gòu) 連續(xù)梁橫截面內(nèi)部 粘接鋼筋上未粘接的優(yōu)勢在于以前，預(yù)應(yīng)力不會再高柱位移要求中顯著增長，因此不會引起導(dǎo)致預(yù)應(yīng)力損失的非彈性屈服。 如果上部柱段是設(shè)計(jì)用來連接到上部結(jié)構(gòu)，加固屈服是有望的。比如： 這些梁連接以前的片段。起重機(jī)的重量大概是一個節(jié)段重量的 60%。 結(jié)構(gòu)曲面控制 最關(guān)鍵的實(shí)際問題是現(xiàn)澆施工撓度控制。懸臂梁建造后到連接前得撓度 預(yù)制塊 橋縱向分塊來預(yù)制大梁的觀念相反的，橋被橫向分割，每一塊是一個節(jié)段。當(dāng)各部分在橋址重新組裝是，他們會依照和澆筑時相同的位置關(guān)系。完全水密性是內(nèi)部鋼筋腐蝕防護(hù)必須的。混凝土內(nèi)干燥連接的外部鋼筋的采用打打提高了現(xiàn)澆的效果。澆筑和初步加工后，前面的節(jié)段移到倉庫，