土木工程畢業(yè)設(shè)計外文翻譯3-建筑結(jié)構(gòu)-文庫吧資料
2025-05-22 13:49本頁面
【正文】 ual to 1 /n, where n is the number of members framing into the joint in the plane of the frame. TwoCycle Moment Distribution— Worked Example. The method is demonstrated by a worked example. In Fig, , a fourspan girder AE from a rigidframe bent is shown with its loading. The fixedend moments in each span are calculated for dead loading and total loading using the formulas given in Fig, . The moments are summarized in Table . The purpose of the moment distribution is to estimate for each support the maximum girder moments that can occur as a result of dead loading and pattern live loading. A different load bination must be considered for the maximum moment at each support, and a distribution made for each bination. The five distributions are presented separately in Table , and in a bined form in Table . Distributions a in Table are for the exterior supports A and E. For the maximum hogging moment at A, total loading is applied to span AB with dead loading only on BC. The fixedend moments are written in rows 1 and 2. In this distribution only .the resulting moment at A is of interest. For the first cycle, joint B is balanced with a correcting moment of (867 + 315)/4 = U/4 assigned to MBA where U is the unbalanced moment. This is not recorded, but half of it, ( U/4)/2, is carried over to MAB. This is recorded in row 3 and then added to the fixedend moment and the result recorded in row 4. The second cycle involves the release and balance of joint A. The unbalanced moment of 936 is balanced by adding U/3 = 936/3 = 312 to MBA (row 5), implicitly adding the same moment to the two column ends at A. This pletes the second cycle of the distribution. The resulting maximum moment at A is then given by the addition of rows 4 and 5, 936 312 = 624. The distribution for the maximum moment at E follows a similar procedure. Distribution b in Table is for the maximum moment at B. The most severe loading pattern for this is with total loading on spans AB and BC and dead load only on CD. The operations are similar to those in Distribution a, except that the T first cycle involves balancing the two adjacent joints A and C while recording only their carryover moments to B. In the second cycle, B is balanced by adding (1012 + 782)/4 = 58 to each side of B. The addition of rows 4 and 5 then gives the maximum hogging moments at B. Distributions c and d, for the moments at joints C and D, follow patterns similar to Distribution b. The plete set of operations can be bined as in Table by initially recording at each joint the fixedend moments for both dead and total loading. Then the joint, or joints, adjacent to the one under consideration are balanced for the appropriate bination of loading, and carryover moments assigned .to the considered joint and recorded. The joint is then balanced to plete the distribution for that support. Maximum MidSpan Moments. The most severe loading condition for a maximum midspan sagging moment is when the considered span and alternate other spans and total loading. A concise method of obtaining these values may be included in the bined twocycle distribution, as shown in Table . Adopting the convention that sagging moments at midspan are positive, a
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