【正文】 , clear of bracing members and structural walls, allows freedom internally for the layout and externally for the fenestration. Rigid frames are considered economical for buildings of up to39。 4． 檢驗(yàn)位移并對構(gòu)件截面尺寸做必要的調(diào)整 。其結(jié)果在建筑的最頂部整體彎曲對層間位移的貢獻(xiàn)會(huì)大大超過剪切變形對層間位移的貢獻(xiàn)。 框架結(jié)構(gòu)是多次超靜定結(jié)構(gòu)，因此，只有在確定了構(gòu)件截面尺寸后才能進(jìn)行精 確分析。計(jì)算梁在支座處最大彎矩時(shí)必須考慮不同的荷載組合，而每種荷載組合作用都應(yīng)進(jìn)行一次計(jì)算。計(jì)算過程類似于 a組分配，但首次循環(huán)應(yīng)平衡兩相間節(jié)點(diǎn) A和 C，同時(shí)僅將它們的傳遞彎矩記錄在節(jié)點(diǎn) B。 。將第 5 行的彎矩相加后就得出節(jié)點(diǎn) B的兩端最大負(fù)彎矩。表 7. 3中 a組分配為邊支座 A和 E。下面將討論在重力荷載作用下構(gòu)件內(nèi)力計(jì)算的兩種方法。因此，高層框架結(jié)構(gòu)變形型式為剪切型。 6． 為了更精確地驗(yàn)算構(gòu)件強(qiáng)度和位移，利 用 計(jì)算機(jī)對結(jié)構(gòu)進(jìn)行整體分析，需要時(shí)則近一步調(diào)整構(gòu)件截面尺寸。 consequently, an accurate analysis can be made only after the member sizes are assigned. Initially, therefore, member sizes are decided on the basis of approximate forces estimated either by conservative formulas or by simplified methods of analysis that are independent of member properties. Two approaches for estimating girder forces due to gravity loading are given here. Girder Forces— Code Remended Values In rigid frames with two or more spans in which the longer of any two adjacent spans does not exceed the shorter by more than 20 %, and where the uniformly distributed design live load does not exceed three times the dead load, the girder moment and shears may be estimated from Table . This summarizes the remendations given in the Uniform Building Code []. In other cases a conventional moment distribution or twocycle moment distribution analysis should be made for a line of girders at a floor level. TwoCycle Moment Distribution []. This is a concise form of moment distribution for estimating girder moments in a continuous multibay span. It is more accurate than the formulas in Table , especially for cases of unequal spans and unequal loading in different spans. The following is assumed for the analysis: 1. A counterclockwise restraining moment on the end of a girder is positive and a clockwise moment is negative. 2. The ends of the columns at the floors above and below the considered girder are fixed. 3. In the absence of known member sizes, distribution factors at each joint are taken equal 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 correctin