【正文】 d 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 midspan total。板柱結構與框架結構非常相似，不同之處僅是用板代替了梁。 6． 為了更精確地驗算構件強度和位移，利 用 計算機對結構進行整體分析，需要時則近一步調(diào)整構件截面尺寸。 剪力使框架結構每層的柱產(chǎn)生雙曲率彎曲，其反彎點大約在層高的中間部位。因此，高層框架結構變形型式為剪切型。 框架的尺寸取決于柱子在水平荷載 作用下面將討論在重力荷載作用下構件內(nèi)力計算的兩種方法。 3． 當構件尺寸尚未確定時，每個節(jié)點的分配系數(shù)取 1/n， n 是框架平面內(nèi)連接在各節(jié)點上的構件總數(shù)。表 7. 3中 a組分配為邊支座 A和 E。 第二循環(huán)包括節(jié)點 A 的釋放和平衡。將第 5 行的彎矩相加后就得出節(jié)點 B的兩端最大負彎矩。實際結構的節(jié)點處應該能夠轉動，所以需要對跨中彎矩加以修正 。 。該值計算的最簡便方法是將兩次循環(huán)彎矩分配組合起來，如表 。計算過程類似于 a組分配，但首次循環(huán)應平衡兩相間節(jié)點 A和 C，同時僅將它們的傳遞彎矩記錄在節(jié)點 B。這些計算可不作記錄，而將修正彎矩的一半即 (U/4)/2傳于 MAB。計算梁在支座處最大彎矩時必須考慮不同的荷載組合，而每種荷載組合作用都應進行一次計算。 彎矩分配法的分析假定如下 : 1． 梁端約束彎矩以反時針方向為正，順時針方向為負 。 框架結構是多次超靜定結構，因此，只有在確定了構件截面尺寸后才能進行精 確分析。而梁在內(nèi)柱附近產(chǎn)生的最大負彎矩只會在活荷載作用于相鄰跨時才能發(fā)生，如圖 B點。其結果在建筑的最頂部整體彎曲對層間位移的貢獻會大大超過剪切變形對層間位移的貢獻。 框架結構的側向剛度主要取決于梁、柱及節(jié)點的抗彎能力，在較高的框架中主要取決于柱子的軸向剛度。 4． 檢驗位移并對構件截面尺寸做必要的調(diào)整 ?？蚣芙Y構對于25層以內(nèi)的建筑是經(jīng)濟的，超過 25層由于要限制其位移而花費的代價高，顯得很不經(jīng)濟。7 RigidFrame Structures A rigidframe highrise structure typically prises parallel or orthogonally arranged bents consisting of columns and girders with moment resistant joints. Resistance to horizontal loading is provided by the bending resistance of the columns, girders, and joints. The continuity of the frame also contributes to resisting gravity loading, by reducing the moments in the girders. The advantages of a rigid frame are the simplicity and convenience of