【導(dǎo)讀】然而，對(duì)于一般實(shí)踐的詳細(xì)設(shè)計(jì)規(guī)則當(dāng)前還處于發(fā)展階段。等方面進(jìn)行聯(lián)合研究。這種框架是應(yīng)用密歇根大學(xué)最近發(fā)展的基于能量的塑性設(shè)計(jì)。程序設(shè)計(jì)而成的。%到10%荷載50年設(shè)計(jì)范圍中的%到2%）和總體的屈曲原理。是對(duì)這種最新成熟設(shè)計(jì)方法的最好候選者。性響應(yīng)結(jié)果進(jìn)行了對(duì)比。由密歇根大學(xué)設(shè)計(jì)的框架對(duì)臺(tái)灣和美國(guó)的地面運(yùn)動(dòng)。屈曲約束支撐極好的地震反應(yīng)激勵(lì)了臺(tái)灣地震工程研究中心的實(shí)驗(yàn)計(jì)劃，也鼓勵(lì)了密歇根大學(xué)的研究者們對(duì)分析和設(shè)計(jì)之間結(jié)合的進(jìn)一步研究。荷載實(shí)驗(yàn)的三層三跨框架提供了最基本的抗力結(jié)構(gòu)。針對(duì)實(shí)驗(yàn)?zāi)康?，假定這些跨中的兩。內(nèi)外側(cè)柱子采用不同的型材，隨著建筑物高度的。當(dāng)?shù)囊蛩剡M(jìn)行測(cè)量來(lái)表示為真實(shí)的地面運(yùn)動(dòng)。SDOF系統(tǒng)中考慮5%的衰減模擬加速度譜線進(jìn)行的。的地震事件相關(guān)規(guī)則相對(duì)應(yīng)。這兩個(gè)測(cè)試結(jié)果分別有和的地震。采用這種延展性和有效目標(biāo)位移δeff，系統(tǒng)的有效周期將。準(zhǔn)中，第二個(gè)標(biāo)準(zhǔn)的底部剪力起支配作用，等于415千磅。

　　

【正文】 rlier, the braced bay of the frame was designed to resist 80% of the total lateral forces. Design of the braced frame involved design of the braces, the interior beams and the interior columns. Since all connections in the braced frame were assumed pinned, the applied shear force in each story was resisted by the pair of braces only. Because the bases of the interior columns were assumed to be fixed, these columns act as cantilevers and carry some amount of shear as the frame undergoes lateral drift. However, for simplicity and to be conservative, this effect was neglected. Thus, crosssection area of the braces in each story was obtained by simply considering the horizontal ponent of the design yield forces of the two braces and equating that to the corresponding story shear, as shown in Figure 6. The interior beams were assumed as pin connected to the interior columns at both ends, while the braces connect at the beam midspan. The beams were designed for a bination of axial force and bending moment. As the frame drifts, one brace goes into tension and the other into pression. Horizontal ponents of these forces represent the axial load applied at the midspan of the interior beam. Vertical ponents of these forces tend to cancel each other. However, since the yield strength of the pression brace is assumed to be 10% higher than that of the tension brace, an unbalanced upward force remains once both braces have yielded, causing bending moment in the beam. Thus, the interior beams were designed as simply supported beams with an axial load and a transverse load applied at the center, as shown in Figure 6. The wide flange sections used in the exterior beams were checked against this bined loading following the provisions of the AISC steel design manual [6], and were found adequate for use in the braced frame. P s θ in θ Ps in θ in θ θ Figure 6: Forces in braced frame after yielding Design of the interior columns was done primarily from axial load consideration (Figure 6). Columns in any story carry the vertical ponents of the brace forces from the stories above. Thus, interior columns in the 1st story were designed for an axial force which is the sum of the vertical ponents of the brace forces from the 2nd and 3rd stories. Brace forces were calculated at the point when the frame is at its assumed target drift of %. Also, the higher yield load of the pression brace pared to that of the tensile brace, as mentioned earlier, was considered. However, there are some other factors that affect the load on the interior column. These are: 1. Shear force on the exterior beams is transferred through the pinned connection and acts as axial load on the interior columns. From the deflected shape of the frame, it is seen that this shear force always acts in the opposite direction to the force ing from the braces, thus reducing the load on the column. 2. Shear force on the interior beams adds a small tensile load on both interior columns. P P θ Psinθ 3. Interior columns carry some shear and bending moment by virtue of their bent shape. For simplicity of design, the above factors were neglected. COMPARISON OF UM FRAMES WITH TAIWAN FRAME The crosssection areas of various members obtained from the two UM designs and from the Taiwan design are shown in Table 1. It can be seen that the UM Frame 1 had almost identical member sizes as those in the Taiwan frame. Some differences can be seen in the sizes of the beams at all three floors those in the UM frame being lighter than those in the Taiwan frame. While the difference is small at the 1st and 2nd levels, the beams at the 3rd (roof) level in the UM frame were significantly lighter than those in the Taiwan frame. The UM Frame 2, being designed for a significantly smaller base shear, was much lighter than the other two frames. Table 1: Member crosssection areas (in2) of frames for Taiwan site Taiwan Frame UM Frame 1 UM Frame 2 1st Floor 2nd Floor Braces 3rd Floor 1st Floor 2nd Floor Exterior Columns 3rd Floor 1st Floor 2nd Floor Interior Columns 3rd Floor 1st Floor 2nd Floor Beams 3rd Floor FRAME DESIGNED FOR . EARTHQUAKES To further the study on applicability of the energybased approach to calculate design base shear, the same frame was redesigned for a . location (UMUS). Seattle was chosen as the site for the frame. For design purpose, an increased triangular profile of lateral forces, as specified in IBC 2020 [5], was used. The frame was designed to meet the performance criterion of % target roof drift in a 2/50 seismic event. Using a spectral acceleration of for a 2/50 event, the design base shear Vd was puted as 680 kips. Table 2 shows the member sizes obtained for this frame. Table 2: Member crosssection areas (in2) of frame for Seattle site Braces Exterior Columns Interior Columns Beams 1st Floor 2nd Floor 3rd Floor PUSHOVER ANALYSIS Static pushover analyses were performed on the first three frames as a first step in evaluating and paring their behavior. SNAP2DX program, developed at the University of Michigan for nonlinear static and dynamic analysis of 2D frames (Rai [7]), was used for this purpose. The pushover analysis was done under displacementcontrol mode and the frames were pushed to about 3% roof drift with the lateral loads being applied at three floors in the same ratio as the design distribution of the base shear. This ratio was maintained while the controlling roof displacement applied to the frame was increased. The displacement of the roof was increased in steps of inch. Lateral load at any floor was distributed equally at all five nodes. ., four beamcolumn joints and one bracebeam join