簡支梁布局外文資料翻譯-其他專業(yè)-資料下載頁
2025-01-19 01:07本頁面
【導(dǎo)讀】要時(shí)其他部位也要單獨(dú)調(diào)查。最大彎矩截面在以下兩種荷載階段為。而端截面則由抗剪強(qiáng)度、支承墊板、錨頭間。距和千斤頂凈空所需要的面積來決定。多個(gè)上述要求，根它們與上述兩種危險(xiǎn)截面的距離來控制。形的截面，而在接近梁端處逐漸過渡到簡單的矩形截面。們通常所說的后張構(gòu)件的端塊。對于用長線法生產(chǎn)的先張構(gòu)件，為。在第5、6和7章節(jié)中已經(jīng)闡明了個(gè)別截面的設(shè)。通過調(diào)整這些變化因素，布置方案可能。有許多組合，以適應(yīng)不同的荷載情況。這一點(diǎn)是與鋼筋混凝土梁是。供最大力臂而提供最大的內(nèi)部抵制力矩。而不致在傳遞時(shí)在頂部纖維中引起拉應(yīng)力。無論如何，如果張應(yīng)力在最后不能承受，放。由于預(yù)應(yīng)力在整個(gè)光纖內(nèi)受到負(fù)面彎曲。能獲得最適合于荷載情況的曲線。少力筋的彎曲所引起的預(yù)應(yīng)力的摩擦損失。要通過井然有序且沒有張應(yīng)力的過程。據(jù)推測，布局的具體方法和地區(qū)的預(yù)應(yīng)力鋼已經(jīng)確定時(shí)。只有形象的位置。
【正文】 e beams, but it also serves as an introduction to the solution of more plicated layouts, such as cantilever and continuous spans, where cable location cannot be easily determined by inspection. The method is a graphical one。 giving the limiting zone within which the c. g. s. must pass in order that no tensile stresses will be produced. Compressive stresses in concrete are not checked by this method. It is assumed that the layout of the concrete sections and the area of prestressing steel have already been determined. Only the profile of the c. g. s. is to be located. Referring to Fig . 89, having determined the layout of concrete sections, we proceed to pute their kern points, thus yielding two kern lines, one top and one bottom, ( c ) . Note that for variable sections, these kern lines would be curved, although for convenience they are shown straight in the figure representing a beam with uniform cross section. For a beam loaded as shown in ( a ), the minimum and maximum moment diagrams for the girder load and for the total working load respectively are marked as MG and MT in ( b ). In order that, under the working load, the center of pressure, the Cline, will not fall above the top kern line, it is evident that the c. g. s. must be located below the top kern at least a distance a1=MT/F (81) Fig 89. Location of limiting zone for c. g. s. If the c. g. s. falls above that upper limit at any point, then the Cline corresponding to moment MT and prestress F will fall above the top kern, resulting in tension in the bottom fiber. Similarly, in order that the Cline will not fall below the bottom kern line, the c. g. s. line must not be positioned below the bottom kern by a distance greater than which gives the lower limit for the location of c. g. s. If the c. g. s. is positioned above that lower limit, it is seen that the Cline will be above the bottom kern and there will be no tension in the top fiber under the girder load and initial prestress F0. Thus, it bees clear that the limiting zone for c. g. s. is given by the shaded area in Fig. 89( c ), in order that no tension will exist both under the girder load and under the working load. The individual tendons, however, may be placed in any position so long as the c. g. s. of all the cables remains within the limiting zone. The position and width of the limiting zone are often an indication of the adequacy and economy of design, Fig. 810. If some portion of the upper limit falls outside or too near the bottom fiber, in ( a ), either the prestress F or the depth of beam at that portion should be increased. On the other hand, if it falls too far above the bottom fiber, in ( b ), either the prestress or the beam depth can be reduced. If the lower limit crosses the upper limit, in ( C ), it means that no zone is available for the location of c. g. s. , and either the prestress F or the beam depth must be increased or the girder moment must be increased to depress the lower limit if that can be done. On the other hand, as will be discussed later, the case shown in Fig. ( c ) may be very satisfactory when are allowing tensile stress in concrete. Fig 810. Undesirable positions for c. g. s. zone limits.
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