【正文】 the reinforcement process . Cracking and deflection are therefore essentially irrecoverable in reinforced concrete once the member has reached its limit state at service load . The reinforcement in the reinforced concrete member does not exert any force of its own on the member , contrary to the action of prestressing steel . The steel required to produce the prestressing force in the prestressed member actively preloads the member , permitting a relatively high controlled recovery of cracking and deflection . Once the flexural tensile strength of the concrete is exceeded , the prestressed member starts to act like a reinforced concrete element . Prestressed members are shallower in depth than their reinforced concrete counterparts for the same span and loading conditions . In general , the depth of a prestressed concrete member is usually about 65 to 80 percent of the depth of the equivalent reinforced concrete member . Hence , the prestressed member requires less concrete , and about 20 to 35 percent of the amount of reinforcement. Unfortunately , this saving in material weight is balanced by 濰坊學(xué)院本科畢業(yè)論文 6 the higher cost of the higher quality materials needed in prestressing . Also, regardless of the system used , prestressing operations themselves result in an added cost : formwork is more plex ， since the geometry of prestressed sections is usually posed of flanged sections with thin webs . In spite of these additional costs, if a large enough number of precast units are manufactured, the difference between at least the initial costs of prestressed and reinforced concrete systems is usually not very large. And the indirect longterm savings are quite substantial, because less maintenance is needed, a longer working life is possible due to better quality control of the concrete, and lighter foundations are achieved due to the smaller cumulative weight of the superstructure. Once the bean span of reinforced concrete exceeds 70 to 90 feet ( to m), the dead weight of the beam bees excessive, resulting in heavier membersand,consequently,greater longterm deflection and cracking. Thus,for larger spans,prestressed concrete bees mandatory since arches are expensive to construct and do not perform as well due to thesevere longterm shrinkage and creep they large spans such as segmental bridges or cablestayed bridges can only be constructed through the use of prestressing . Prestressed concrete is not a new concept, dating back to 1872,when . Jackson ,an engineer from California, patented a prestressing system that used a tie rod to construct beams or arches from individual block. After a long lapse of time during which little progress was made because of the unavailability of highstrength steel to overe prestress losses, . Dill of Alexandria, Nebraska , recognized the effect of the shrinkage and creep(transverse material flow) of concrete on the loss of prestress. He subsequently developed the idea that successive posttensioning of unbonded rods would pensate for the timedependent loss of stress in the rods due to the decrease in the length of the member because of creep and shrinkage. In the early 1920s, of Minneapolis developed the principles of circular prestressing He hoopstressing horizontal reinforcement around walls of concrete tanks through the use of turnbuckles to prevent cracking due to internal liquid pressure , thereby achieving watertightness . thereafter , prestressing of tanks and pipes developed at an accelerated pace in the United States,with thousands of tanks for water,liquid,and gas storage built and much mileage of prestressed pressure pipe laid in the two to three decades that followed. Linear prestressing continue to develop in Europe and in France,in particular through the ingenuity of Eugene Freyssi,who proposed in 192328 methods to overe prestress losses through the use of highstrength and highductility ,he introduced the now wellknown and wellaccepted Freyssi system. . Abeles of England introduced and developed the concept of partial prestressing between the 1930s and 1960s . F. Leonhardt of Germany , V. Mikhailov of Russia, and . Lin of the United States also contributed a great deal to the art and science of the design of prestressed concrete .Lin39?？煞譃閮煞N類型的單層和多層的廠房，民用建筑，工業(yè)建筑是相同的。 房屋是人類居住。多數(shù)首選的一半左右 1英畝的土地，這將提供業(yè)余活動(dòng)空間單戶住宅的家庭。我們主要感興趣的安排和房間 的大小和臥室數(shù)目?！耙埂钡姆块g，臥室組成。然而，它往往很難達(dá)到最佳的要求，同時(shí)對(duì)環(huán)境的考慮和位置，的道路。 由于水泥行業(yè)的天然放射性水平和 輻射危害的評(píng)估抽象被視為水泥行業(yè)的基礎(chǔ)產(chǎn)業(yè)，對(duì)發(fā)展中國(guó)家的國(guó)民經(jīng)濟(jì)中起著重要的作用之一。獲得 226Ra的， 232Th和 40K的活度濃度的平均值，在不同濰坊學(xué)院本科畢業(yè)論文 9 類型的水泥比報(bào)道科委出版物的全球相應(yīng)值低。介紹 對(duì)水泥的需求是如此巨大。根據(jù)化學(xué)成分和每一個(gè)水力特性，有許多類型的水泥。 從天然放射性輻射 影響，是由于身體接觸輻射伽瑪射線和肺組織的照射吸入氡及其子體（ Papastefanou等， 1988）。平均室內(nèi)從地面的放射性源的空氣中吸收劑量率估計(jì)為 70 NGY H？1。 Kumar 等。知識(shí)的發(fā)生與濃度等重要材料的天然放射性是一般檢查其質(zhì)量和對(duì)周圍環(huán)境，特別是水泥生產(chǎn)工廠明知其效果的關(guān)鍵。 2。與其他工廠的產(chǎn)品進(jìn)行比較， 8個(gè)樣品取自普通硅酸鹽水泥（赫勒萬(wàn)基納， ELkawmya，托拉）和白水泥（西奈半島和赫勒萬(wàn)）， 4個(gè)樣本。完全密封的燒杯 4周，以達(dá)到長(zhǎng)期平衡氡子體衰變率等于母公司。密封裝配用的 NaI（ Tl）晶體耦合的 PCMCA（坎培拉 Accuspes）。為了確定探測(cè)器周圍環(huán)境中的背景分布，一個(gè)空的密封燒杯計(jì)算以同樣的方式，在相同的幾何形狀的樣品。 3。所獲得的結(jié)果表明，輻射危險(xiǎn)參數(shù)的平均值為艾斯尤特水泥廠的鐳當(dāng)量 Raeq 的， 1 的水平的的指數(shù) Iγr，外部風(fēng)險(xiǎn)指數(shù)六角≤ 1 和 59（ NGY?低于可接受水平的 370 貝克公斤 1？ 1）吸收劑量率。從選擇合適的材料在水泥生產(chǎn)中使用的角度來(lái)看，結(jié)果可能是重要的。為了減少或防止來(lái)自發(fā)展中國(guó)家如裂縫，同心或偏心的力量施加在縱向方向的結(jié)構(gòu) 元素。涉及的預(yù)應(yīng)力類型，連同它的大小，主要取決于系統(tǒng)建設(shè)跨度和所需的細(xì)長(zhǎng)型的基礎(chǔ)上。在一個(gè)相對(duì)低負(fù)荷時(shí)，在混凝土梁底部的拉應(yīng)力達(dá)到混凝土的抗拉強(qiáng)度，會(huì)形成裂縫。然后創(chuàng)建一個(gè)向上的傾角。張力下兩個(gè)防止和張力裂縫的組合被淘汰?；颉皳肀А钡膱A柱形或球形結(jié)構(gòu)上的壓力，中所載的內(nèi)部壓力所造成的曲線表面的外層纖維的拉伸應(yīng)力。開(kāi)濰坊學(xué)院本科畢業(yè)論文 11 裂和撓度，因此在鋼筋混凝土的成員基本上是無(wú)法挽回的，一旦在業(yè)務(wù)負(fù)荷已達(dá)到其極限狀態(tài)。 預(yù)應(yīng)力成員在深度較淺的比相同跨度和荷載條件下的鋼筋混凝土同行。另外，無(wú)論系統(tǒng)的使用，預(yù)應(yīng)力行動(dòng)本身在增加成本的結(jié)果：模板更為復(fù)雜，因?yàn)轭A(yù)應(yīng)力部分的幾何形狀通常薄腹板法蘭部分組成。因此，較大跨度預(yù)應(yīng)力混凝土成為強(qiáng)制性的，因?yàn)楣伴T(mén)是昂貴的建設(shè)和不執(zhí)行以及由于嚴(yán)重的長(zhǎng)期收縮和徐變，他們?nèi)缍螛蛄夯?。在 20 世紀(jì) 20 年代初，明尼阿波利斯WHHewett循環(huán)發(fā)展的原則預(yù)應(yīng)力他箍強(qiáng)調(diào)圍繞橫向鋼筋混凝土水池的墻壁，通過(guò)螺絲扣的使用，以防止開(kāi)裂由于內(nèi)部液體壓力，從而達(dá)到水密性。五米哈伊洛夫，俄羅斯，德國(guó)，樓倫哈德和 TY美國(guó)林也作出了很大貢獻(xiàn)預(yù)應(yīng)力混凝土設(shè)計(jì)的藝術(shù)和科學(xué)。這有幾個(gè)原因： （ 1）高強(qiáng)度混凝土通常有較高的彈