土建專業(yè)外文翻譯---二層預(yù)制混凝土結(jié)構(gòu)物的抗震測(cè)試

1、<p>　　一個(gè)未完工的二層預(yù)制混凝土結(jié)構(gòu)物的抗震測(cè)試</p><p>　　這篇文章是關(guān)于地震和預(yù)制混凝土建筑物設(shè)計(jì)的試驗(yàn)性的研究。墨西哥市里一個(gè)帶有雙重系統(tǒng)和代表了一個(gè)停車場(chǎng)結(jié)構(gòu)的未完工的兩層的預(yù)制混凝土建筑物被調(diào)查研究。這個(gè)結(jié)構(gòu)物在實(shí)驗(yàn)室里用模擬地震荷載測(cè)試，結(jié)果失敗了。在一些梁和柱的接頭處，粱底部的縱筋由于尺寸的限制不能屈服。這項(xiàng)研究所強(qiáng)調(diào)的是提高所測(cè)試結(jié)構(gòu)物的可觀察的綜合性能。這種性能表現(xiàn)為所測(cè)

2、試結(jié)構(gòu)物的墻控制傳力途徑而且能顯著地減少預(yù)制結(jié)構(gòu)所要求的側(cè)向變形。源自于這項(xiàng)研究的預(yù)制混凝土結(jié)構(gòu)抗震設(shè)計(jì)標(biāo)準(zhǔn)和規(guī)范細(xì)節(jié)被討論。這項(xiàng)研究的最終結(jié)果是能更好地理解這種類型的建筑物的已得知的性能。</p><p>　　在墨西哥，一個(gè)兩層的預(yù)制混凝土構(gòu)件建成的預(yù)制混凝土建筑物，在其上加上模擬的地震荷載。在這里描述的是其結(jié)果。在測(cè)試結(jié)構(gòu)物中所選擇的結(jié)構(gòu)系統(tǒng)是所謂的雙重類型，其定義就是構(gòu)造墻的結(jié)合點(diǎn)以及梁-柱框架。測(cè)試結(jié)構(gòu)物

3、中預(yù)制梁柱之間的結(jié)合是窗型的。這種類型的建設(shè)顯著地用在低的或中等高建筑物中，在這種建筑中在每一樓層中柱子和窗子連在一起。這些“窗”包含頂部和底部的鋼筋。圖1所示的是在墨西哥市中這種類型的一個(gè)商業(yè)建筑物。</p><p>　　大多數(shù)的預(yù)制混凝土結(jié)構(gòu)如圖1中所示，縱梁底部的鋼筋不能完全屈服。這是由于在梁-柱接頭中柱的尺寸限制所造成的。為了盡力克服這種缺陷，正如在后面所描述的，在墨西哥一些工程師嘗試著這樣設(shè)計(jì)這些接頭，

4、就是通過用箍筋圈住這些鋼筋，這樣做是為了達(dá)到所要求的連續(xù)性。然而，這種嘗試在ACI建筑規(guī)范和MCBC中都沒有提到。這些研究的一部分是為了闡述這個(gè)觀點(diǎn)。</p><p>　　這項(xiàng)研究的目的是為了提高在實(shí)驗(yàn)室里的預(yù)制混凝土結(jié)構(gòu)屋的可觀察的性能以及為利用諭旨構(gòu)件或預(yù)制結(jié)構(gòu)建議了一個(gè)可接受的期望的抗震性能以及從建設(shè)能力的觀點(diǎn)所得出的有吸引力的特征。這篇文章中強(qiáng)調(diào)的所測(cè)試結(jié)構(gòu)物中預(yù)制構(gòu)件間的連接處的可觀察的性能以及預(yù)制樓層

5、系統(tǒng)的性能將會(huì)詳細(xì)講述。</p><p>　　在過去的地震中，在建筑物中造成的可觀察的構(gòu)造和非構(gòu)造的破壞顯示了通過控制結(jié)構(gòu)的側(cè)向位移來降低由地震造成的建筑物的破壞的重要性。在這里還要提到的是，在中等程度的地震中有一些情況下非結(jié)構(gòu)構(gòu)件的破壞相當(dāng)大，盡管構(gòu)造構(gòu)件只有一點(diǎn)破壞或根本就沒有破壞。這種性能和結(jié)構(gòu)物中所要求的過多的側(cè)向位移有關(guān)。</p><p>　　為了減少地震所造成的破壞，以上的討論

6、建議了在結(jié)構(gòu)物中可以方便地使用能控制惻向位移的構(gòu)造系統(tǒng)。這種類型的解決方法就是所謂的雙重系統(tǒng)。Paulay和 priestly的關(guān)于雙重系統(tǒng)的地震反映的研究表明墻的出現(xiàn)降低了框架微系統(tǒng)中結(jié)構(gòu)構(gòu)件的動(dòng)力要求。同時(shí)，在一個(gè)現(xiàn)澆的鋼筋混凝土雙重系統(tǒng)上所做的搖擺測(cè)試顯示了雙重系統(tǒng)能達(dá)到良好的抗震性能的潛力。在這次調(diào)查研究中，雙重系統(tǒng)應(yīng)用在預(yù)制混凝土構(gòu)件上。</p><p><b>　　雙重系統(tǒng)的柔性要求<

7、/b></p><p>　　為了使這個(gè)工程所研究的被測(cè)試結(jié)構(gòu)物的能觀測(cè)到的抗震反應(yīng)的以后的分析打好基礎(chǔ)，一個(gè)簡(jiǎn)單的分析模式被用來提高雙重系統(tǒng)中主要柔性特征要求。</p><p>　　圖2所示的是一個(gè)簡(jiǎn)單的分析作用在雙重系統(tǒng)側(cè)向荷載反映的結(jié)果。側(cè)向荷載從這種方式標(biāo)準(zhǔn)化，將任一系統(tǒng)中最大的側(cè)向抵抗力聯(lián)合起來。比如，墻和框架導(dǎo)致綜合系統(tǒng)的側(cè)向抵抗力。假設(shè)任一微系統(tǒng)的總的位移量為4和2。在第

8、二種情況下，框架系統(tǒng)假設(shè)為彈性，墻微系統(tǒng)的剛度為框架微系統(tǒng)的4倍。</p><p>　　圖2所示，聯(lián)合系統(tǒng)的側(cè)向變形兼容性由墻微系統(tǒng)的側(cè)向變形量控制，在第一種情況下，假設(shè)雙重系統(tǒng)的總側(cè)向反應(yīng)有一個(gè)塑料封套，相應(yīng)的位移系數(shù)是3.3在第二種情況下，框架微系統(tǒng)在彈性力下，起位移系數(shù)是2.5。</p><p>　　這些簡(jiǎn)單的例子說明，在以上分析的情況下，由于在雙重系統(tǒng)中框架微系統(tǒng)與墻微系統(tǒng)相比彈性

9、大的多，框架微系統(tǒng)柔性要求更小比墻微系統(tǒng)的該項(xiàng)要求有價(jià)值。這項(xiàng)分析結(jié)果在被測(cè)試結(jié)構(gòu)物上所做的研究上被證實(shí)了，這個(gè)證明在這篇文章的后面會(huì)討論。有趣的是圖2所示的類型的結(jié)果，Bertero在一個(gè)搖擺測(cè)試的雙重系統(tǒng)中也發(fā)現(xiàn)了。</p><p><b>　　測(cè)試結(jié)構(gòu)物的描述</b></p><p>　　在這次調(diào)查中所用到的被測(cè)試結(jié)構(gòu)物是一個(gè)兩層的預(yù)制混凝土建筑，是一個(gè)位于墨西

10、哥市高地震發(fā)生地帶的有代表的低層的停車結(jié)構(gòu)。原型還未完工，為了簡(jiǎn)單起見，一個(gè)停車場(chǎng)結(jié)構(gòu)物所需的扶梯在所選的結(jié)構(gòu)物中沒有考慮。如果考慮的話，將占有樓層系統(tǒng)的大面積空間，為了進(jìn)行結(jié)構(gòu)物的線性或非線性分析，將需要一個(gè)非常復(fù)雜的樓層系統(tǒng)模型。</p><p>　　關(guān)于所測(cè)試結(jié)構(gòu)物的詳細(xì)的尺寸，材料，設(shè)計(jì)步驟和建設(shè)描述到處都可以發(fā)現(xiàn)，下面給出了這些信息的一個(gè)總結(jié)。</p><p>　　所測(cè)試結(jié)構(gòu)物的

11、尺寸和一些特征如圖3所示，其縱向以及相反方位如圖3所示，同時(shí)，外部框架包含墻被定義為側(cè)向框架，內(nèi)部框架和單個(gè)T梁被定義為中間框架。</p><p>　　縱向的兩個(gè)T梁由相反方向的L型預(yù)制梁支撐如圖3所示，該結(jié)構(gòu)物用預(yù)制框架和預(yù)制構(gòu)造墻組成，后面構(gòu)件的功能是作為主要的側(cè)向荷載抵抗系統(tǒng)，圖4所示的是所測(cè)試結(jié)構(gòu)物建設(shè)的早期階段。我們可以看到，在柱和墻上留下了一些窗，是為了以后的預(yù)制梁的裝配。</p>&

12、lt;p>　　墨西哥城市建筑規(guī)范所要求的設(shè)計(jì)基礎(chǔ)剪力為0.2Wt, Wt是模型結(jié)構(gòu)物的總重，假設(shè)橫載為5.15Kpa，活載為0。2Kpa，模型結(jié)構(gòu)物是按彈性分析的步驟設(shè)計(jì)的，比例是按MCBC要求來的，結(jié)構(gòu)物中構(gòu)件總的慣性都考慮了，結(jié)構(gòu)物中除了中間框架的梁（會(huì)在以后介紹）以外的所有梁都考慮了剛度補(bǔ)償。</p><p>　　這些分析的結(jié)果表明測(cè)試結(jié)構(gòu)物中的構(gòu)造墻將承受65%的設(shè)計(jì)側(cè)向荷載，一個(gè)用MCBC步驟考慮

13、的結(jié)構(gòu)物的名義上的側(cè)向抵抗顯示這個(gè)抵抗力是規(guī)范規(guī)定的側(cè)向抵抗的1。3倍。這只是使結(jié)構(gòu)無承載過度的因素中的其中之一，其它的以后會(huì)討論。</p><p>　　測(cè)試結(jié)構(gòu)物的所有構(gòu)件的縱筋都是從420級(jí)鋼筋開始破壞的，表一是模型結(jié)構(gòu)物中不同構(gòu)件的混凝土壓柱強(qiáng)度。</p><p>　　圖6，7分別是柱，構(gòu)造墻和基礎(chǔ)的鋼筋詳細(xì)情況，應(yīng)提到的是，測(cè)試結(jié)構(gòu)物是按MCBC要求設(shè)計(jì)的適度柔性結(jié)構(gòu)物。由于這些規(guī)

14、定，測(cè)試結(jié)構(gòu)物不需ACI318-02第21章所要求的有邊界部件的特殊的構(gòu)造墻。</p><p>　　預(yù)制的兩層柱是通過埋置在一個(gè)插座連接處與預(yù)制基礎(chǔ)相連接的基礎(chǔ)的配筋情況以及設(shè)計(jì)步驟和性能在相應(yīng)的文章中討論。</p><p>　　測(cè)試結(jié)構(gòu)物的梁-柱接頭是現(xiàn)澆的，為了能安置框架梁中的縱向鋼筋。梁頂部鋼筋是按in-situ分布在預(yù)制梁的頂部.圖8所示的是中間框架中雙T接頭的配筋情況.因?yàn)檫@些T

15、支座和支撐他們的L型梁 在軸A,C上深度相同(見圖3),在雙T座底部的鋼筋不能穿過整個(gè)柱深,因?yàn)槠浔幌喾捶较騼傻牡撞讳摻畲驍嗔?</p><p>　　所以 ,這些帶鉤的鋼筋只有ACI318-02第21章所要求的55%的發(fā)展長(zhǎng)度.為了能錨固住這些帶鉤鋼筋,在墨西哥的一些設(shè)計(jì)師沿著鉤用封閉的箍筋箍住,如圖8所示,這種方法的有效 性在相應(yīng)的文章中回研究.</p><p>　　測(cè)試結(jié)構(gòu)物的側(cè)向框架

16、中的梁-柱接頭中有相反方向的梁比縱梁還要深.這使的縱梁中頂部,底部的鋼筋能穿過整個(gè)接頭,所以這些鋼筋能達(dá)到所需要的發(fā)展長(zhǎng)度.</p><p>　　測(cè)試結(jié)構(gòu)物中頂部的現(xiàn)澆的板層有30mm厚,也形成了結(jié)構(gòu)系統(tǒng)的圖表.WWR被用作頂部的板層的鋼筋,頂部板層中WWR的數(shù)量由MCBC中溫度和收縮要求控制,這與ACI318-02中的控制要求相似.</p><p>　　有趣的是,由這些規(guī)范所給的圖表中的

17、抗剪強(qiáng)度要求與ACI318-89的要求相似,不控制設(shè)計(jì),鋼筋尺寸是6*6,10/10導(dǎo)致在頂層 的鋼筋比率為0.002,WWR的測(cè)試屈服和破壞強(qiáng)度分別是400和720mpa.</p><p>　　測(cè)試程序以及測(cè)試設(shè)備</p><p><b>　　測(cè)試程序</b></p><p>　　測(cè)試結(jié)構(gòu)物在縱向加上了模擬的地震荷載（見圖3a）,周期的側(cè)向荷

18、載F1,F2分別加在結(jié)構(gòu)物的第一第二高度上，F(xiàn)2與F1的比率代表的是轉(zhuǎn)變的三角分布荷載。這種比率與MCBC中大多數(shù)抗震規(guī)范的假定一致。</p><p>　　測(cè)試裝置如圖9所示，結(jié)構(gòu)物在每個(gè)厚板高度處有合頁A、B、C如圖9所示，裝合頁的目的是通過在側(cè)向荷載測(cè)試時(shí)允許厚板的尾部自由轉(zhuǎn)動(dòng)來避免結(jié)構(gòu)物的不真實(shí)的抵制，從圖9中可以看到側(cè)向荷載是通過水力發(fā)動(dòng)機(jī)在拉壓方向施加。</p><p>　　當(dāng)發(fā)

19、動(dòng)機(jī)工作在壓力方向時(shí)，它直接在結(jié)構(gòu)物的一邊施加荷載。但是當(dāng)發(fā)動(dòng)機(jī)在結(jié)構(gòu)物的一邊施加拉力時(shí)，會(huì)通過4個(gè)高強(qiáng)的預(yù)應(yīng)力鋼筋在每一邊轉(zhuǎn)變?yōu)閴毫Γ@些鋼筋的兩端焊在50mm的厚鋼板上，在每一樓層高度處，這些鋼板中的兩個(gè)是合頁A的一部分，在發(fā)動(dòng)機(jī)一邊的另兩個(gè)鋼板是合頁B的一部分（見圖9b）。</p><p>　　如圖9b所示，在用發(fā)動(dòng)機(jī)施加拉力之前，鋼板的尾部留下了放置厚板端部的空間。在側(cè)向荷載為0處該空間大約為50mm，當(dāng)

20、梁中的塑料合頁形成時(shí)，該空間就允許了梁的延長(zhǎng)，在這種發(fā)動(dòng)機(jī)作用在合頁B上一邊的相反方向的梁上產(chǎn)生壓力的情況下（見圖9b），系統(tǒng)也允許50mm的梁的延長(zhǎng)。測(cè)試裝置的這些特殊的特點(diǎn)允許在厚板上的一些點(diǎn)上有壓力而在這些點(diǎn)上不需特別加強(qiáng)。如果拉力已加在厚板上的荷載點(diǎn)上，那么很有可能的是這些荷載將需非真實(shí)的特殊的加強(qiáng)，而在真實(shí)的結(jié)構(gòu)上不需要。</p><p>　　重力荷載是結(jié)構(gòu)物中分布的53個(gè)鋼板的重力。如圖9a所示，每一

21、單元的每一高度出的鋼板重力的是2.79kpa(58.3psf),且加上了厚板的重力，使樓層的橫載為5.73kpa。這是抗震設(shè)計(jì)所需重力.荷載的88%（MCBC,1993）。由于厚板的空間的局限剩下的12%的重力荷載不能應(yīng)用。結(jié)構(gòu)物的總重，不包括基礎(chǔ)的重力，是284.2KN(63.9KIPS)。</p><p>　　結(jié)構(gòu)物的橫向偏移（垂直與荷載方向）可以通過安裝在第二層的A1,A3梁-柱接頭上的剛球來防止。這些球座

22、通過剛框架支撐。如圖10所示，預(yù)制的柱，墻用由基礎(chǔ)支撐的剛梁安置在樓層上，并錨固在樓層上。</p><p>　　測(cè)試結(jié)構(gòu)物上的側(cè)向加載是由結(jié)構(gòu)上的彈性反映的控制力，還根據(jù)屈服階段位移控制，即結(jié)構(gòu)物上屋頂?shù)膫?cè)向位移。最終的側(cè)向荷載是上面的一半。最初應(yīng)用的一個(gè)周期的側(cè)向荷載大約是0.75VR，VR的數(shù)值是198KN（44.5Kips）,能假定為結(jié)構(gòu)物第一階段的屈服強(qiáng)度。</p><p>　　這

23、個(gè)參數(shù)是用可測(cè)量的材料特性計(jì)算出來的，單元的折減系數(shù)和簡(jiǎn)單的加強(qiáng)混凝土部件的抗彎強(qiáng)度的假定。側(cè)向力為0.75VR，其相關(guān)的屋頂側(cè)向位移被定義為0.75▽y’,用這個(gè)數(shù)值和假定為彈性情況下，在第一屈服階段計(jì)算位移為▽y’，即4.5mm(0.18in)。</p><p>　　在0.75▽y’的周期過后，結(jié)構(gòu)物被加上三個(gè)周期的荷載，每一個(gè)周期最大的屋頂位移為2▽y’，4▽y’，6▽y’，13▽y’，20▽y’，與此對(duì)應(yīng)

24、的屋頂?shù)钠盥适荄r,0.003,0.006,0.009,0.020,0.031。屋頂偏差率可以這樣計(jì)算Dr=▽/H，H是結(jié)構(gòu)物從第一樓層的端部測(cè)量的，其數(shù)值為2920mm(115in)。</p><p>　　加在結(jié)構(gòu)物上的完整的側(cè)向荷載如圖11所示。這個(gè)加在過程是用位移比來表達(dá)的，▽/▽y’，屋頂偏差率Dr，另外圖11中側(cè)向位移最大值與可測(cè)量的剪力V相關(guān)，用V/VR的比表示。</p><p&

25、gt;<b>　　測(cè)試設(shè)備</b></p><p>　　詳細(xì)的結(jié)構(gòu)物的測(cè)試設(shè)備的描述可以見Rodriguez和Blandon的報(bào)告。結(jié)構(gòu)物的側(cè)向位移是由裝在結(jié)構(gòu)物每一高度處的線性電位計(jì)測(cè)量出來的。12對(duì)電位計(jì)用來測(cè)量結(jié)構(gòu)物的兩個(gè)柱見的臨界截面的平均曲率，9對(duì)電位計(jì)設(shè)置在中心和側(cè)向框架中梁的垂直部分，以及墻的基礎(chǔ)部分。</p><p>　　電阻應(yīng)變測(cè)量器安裝在結(jié)構(gòu)物中一

26、些梁柱和墻中的縱向鋼筋處。還裝在梁-柱接頭出的箍筋出。用著寫測(cè)試設(shè)備所測(cè)的結(jié)果以及電位計(jì)測(cè)量在相關(guān)文章中會(huì)討論。這里帶有不合格的鋼筋信息的梁柱接頭的可觀察的試驗(yàn)反映被計(jì)算出來了。</p><p><b>　　實(shí)驗(yàn)結(jié)果</b></p><p>　　加在試驗(yàn)結(jié)構(gòu)物上的側(cè)向荷載如圖13所示，在這種情況下，側(cè)向位移的最大值與測(cè)試時(shí)大多數(shù)重要構(gòu)件有關(guān)，比如縱向鋼筋的第一屈服階段

27、，墻和頂部厚板剛開始破裂時(shí)，混凝土蓋板倒塌是，縱筋屈服時(shí)。</p><p>　　圖14所示的是可測(cè)量的基礎(chǔ)剪力V，屋頂偏差率。該圖的縱坐標(biāo)代表的是以非尺寸形式表達(dá)的v/VR.如圖14a所示，墻和基礎(chǔ)臨界面處縱筋的第一屈服階段，屋頂?shù)钠盥蕿?.0030，與此相關(guān)的基礎(chǔ)剪力大約為1.4VR，可測(cè)量的最大基礎(chǔ)剪力為549KN（123.4kips）或2.77VR,與此相關(guān)的屋頂偏差率為0.020。</p>

28、<p>　　圖14b所示的是偏差率dr，是在結(jié)構(gòu)物的兩處高度處測(cè)量出來的，結(jié)果顯示的是兩層有相同的偏差值，這是由于構(gòu)造橋?qū)Y(jié)構(gòu)物的總的反映的突出貢獻(xiàn)。結(jié)構(gòu)物的這個(gè)位移特征表示，給定一個(gè)Dr值，偏差值在數(shù)量上相似。</p><p>　　周期側(cè)向荷載以屋頂偏差率0.034以及相應(yīng)的基礎(chǔ)剪力為462KN或2.3VR終止。在這個(gè)側(cè)向位移的高度處，在第一層墻的端部的縱筋的屈服點(diǎn)超過了，這導(dǎo)致了沿著頂部厚板-墻的

29、接頭的裂開處的顯著的超出平面的位移。圖14a也顯示在測(cè)試過程中一些可觀察重要的構(gòu)件。下面介紹的是在結(jié)構(gòu)物的測(cè)試過程中可觀察的破壞構(gòu)件的小結(jié)。</p><p>　　墻的破壞最初是由混凝土蓋板的倒塌以及在第一樓層墻端的縱筋的屈服造成的，這些構(gòu)件的Dr值為0.020，縱筋的屈服是在這些臨界面的混凝土的倒塌后立刻發(fā)生的。</p><p>　　圖15，16所示的是測(cè)試結(jié)束時(shí)側(cè)向框架的破壞的總的概括。

30、圖18提供的是測(cè)試結(jié)束時(shí)第一樓層墻端的縱筋屈服時(shí)的詳細(xì)情況，圖15-18說明了測(cè)試結(jié)束時(shí)，柱，梁柱，梁-柱接頭處可觀察到的破壞情況明顯地比墻要小。</p><p>　　在結(jié)構(gòu)構(gòu)件的臨界面中的塑料合頁的形成，比如在第一樓層柱和墻的末端，在梁的末端，尤其在達(dá)到最大基礎(chǔ)剪力時(shí)被觀測(cè)到了。</p><p>　　剛開始裂開和折斷時(shí)，在厚板的頂部和板-墻接頭處的WWR被觀測(cè)出的值的范圍是從.。4到2.

31、1，測(cè)試結(jié)束時(shí)，每一樓層的裂縫形式，在Rodriguez和Blandon的相關(guān)文章中有介紹，如這兒所見，在厚板頂部,尤其是板-墻接頭處的鋼絲的折斷可以觀察到，接頭出折斷的寬度是15mm和30mm。</p><p>　　圖19所示的是結(jié)構(gòu)物的失效模式，描述的是微弱的梁-強(qiáng)大的強(qiáng)的失效機(jī)理，該假定的機(jī)理以可觀察的塑料合頁的安置為基礎(chǔ)。</p><p>　　在一些柱，梁，墻的臨界截面處的潛在的塑

32、料合頁的曲率可通過電位計(jì)的讀數(shù)計(jì)算出來的一些截面的張應(yīng)力可以從電阻應(yīng)變測(cè)量?jī)x上得到。關(guān)于預(yù)制梁的詳細(xì)的測(cè)量的討論在相關(guān)的文章中有陳述。</p><p>　　從這些測(cè)量結(jié)果可推斷出側(cè)向框架中的梁柱，梁墻連接設(shè)計(jì)在做為傳統(tǒng)的現(xiàn)澆連接的意義上是成功的，然而中間框架中梁柱接頭不是這樣，正如以前提到的，梁底部鋼筋沒有符合規(guī)范所要求的發(fā)展長(zhǎng)度。</p><p>　　Tests on a Half-Sc

33、ale Two-Story Seismic-Resisting Precast Concrete Building</p><p>　　This paper describes experimental studies on the seismic behavior and design of precast concrete buildings. A half-scale two-story precast c

34、oncrete building incorporating a dual system and representing a parking structure in Mexico City was investigated. The structure was tested up to failure in a laboratory under simulated seismic loading. In some of the be

35、am-to-column joints, the bottom longitudinal bars of the beam were purposely undeveloped due to dimensional constraints.</p><p>　　Emphasis is given in the study on the evaluation of the observed global behav

36、ior of the test structure. This behavior showed that the walls of the test structure controlled the force path mechanism and significantly reduced the lateral deformation demands in the precast frames. Seismic design cri

37、teria and code implications for precast concrete structures resulting from this research are discussed. </p><p>　　The end result of this research is that a better understanding of the structural behavior of

38、this type of building has been gained results of simulated seismic load tests of a two story precast concrete building constructed with precast concrete elements that are used in Mexico are described herein. The structur

39、al system chosen in the test structure is the so called dual type, defined as the combination of structural walls and beam-to-column frames. Connections between precast beams and columns </p><p>　　In most pr

40、ecast concrete frames such as those shown in Fig, 1, longitudinal beam bottom bars are not fully developed due to constraints imposed by the dimensions of file columns in beam-to-column joints. In an effort to overcome t

41、his deficiency, and as described later, some practicing engineers in Mexico design these joints by providing hoops around the hooks of that reinforcement in order to achieve its required continuity. However, this practic

42、e is not covered in the ACI Building Code (ACI318-</p><p>　　The objectives of this research were Io evaluate the observed behavior of a precast concrete structures in the laboratory and to propose the use of

43、 precast structural elements or precast structures with both an acceptable level of expected seismic performance and appealing features from the viewpoint of construction Emphasis is given in this paper on the global beh

44、avior of the test structure. In the second part of this research which gill be presented in a companion paper, the observed behavior </p><p>　　Structural and non structural damages observed in buildings duri

45、ng past earthquakes throughout the world have shown the importance of controlling lateral displacement in structures to reduce building damage during earth- quakes. It is also relevant to mention that there are several c

46、ases of structures in moderate earthquakes in which the observed damage in non-structural elements in buildings was considerable even though the structural elements showed little or no damage. This behavior is also r<

47、/p><p>　　To minimize seismic damage during earthquakes, the above discussion suggests the convenience of using a structural system capable of controlling lateral displacements in structures. A solution of this

48、type is the so-called dual system. Studies by Paulay and Priestley4 on the seismic response of dual systems have shown that the presence of walls reduce the dynamic moment demands in structural elements in the frame subs

49、ystem. Also in conjunction with shake table tests conducted on a cast-in-place </p><p>　　DUCTILITY DEMAND IN DUAL SYSTEMS</p><p>　　In order to develop a base for a later analysis of the observed

50、 seismic response of the test structure studied in this project a simple analytical model is used to evaluate the main features of ductility demands in dual systems. </p><p>　　Fig 2 shows the results of a si

51、mple approach to analyze the lateral load response iii a dual system. The lateral load has been normalized in such a manner that the combination of maximum lateral resistance in both subsystern i.e. walls and frames--lea

52、ds to a lateral resistance of the global system equal to unity b is also assumed that both subsystems have the same maximum lateral resistance. In the first case (Fig 2a), it is assumed that the wall and frame subsystems

53、 have global displacement duc</p><p>　　As shown in Fig 2, the lateral deformation compatibility of the combined system is controlled by the lateral deformation capacity of the wall subsystem. In the first ca

54、se Fig 2ak an elastic-plastic envelope for the lateral global response of the dual system is assumed, and the corresponding displacement ductility (u) is equal to 33.For the second case (Fig. 2b) with an elastic behavior

55、 of the frame subsystem, this ductility is equal to 25. </p><p>　　These simple examples illustrate that in the analyzed cases, due to the higher flexibility in the frame subsystems as compared to those of th

56、e wall subsystern, in a dual system, the ductility demands in the frame subsystem result in smaller ductility values than those of the wall subsystem. This analytical finding was verified in this study from the experimen

57、tal studies conducted on the test structure. This verification is later discussed in the paper It is of interest to note that results of th</p><p>　　The test structure used in this investigation is a two-sto

58、ry precast concrete building, representative of a low-rise parking structure located in the highest seismic zone of Mexico City. The prototype was constructed at one-half scale. For the sake of simplicity, ramps required

59、 in a parking structure have not been considered in the selected prototype structure. Their use, requiring large openings in the floor system, would have required a very complex model of the floor system for both linear

60、an</p><p>　　A detailed description of the dimensions, materials, design procedures, and construction of the test structure can be found elsewhere.6 A summary of this information is given below. </p>&

61、lt;p>　　The dimensions and some characteristics of the test structure are shown in Fig. 3. The longitudinal and transverse are shown in Fig3a. Also, the exterior (longitudinal) frame containing the wall (Column Lines 1

62、 and 3) are termed the lateral frame (see Fig, 3b), and the internal (longitudinal) frame with the single tee (Column Line 2) are termed the central frame. </p><p>　　Doable tees spanning in the longitudinal

63、direction are supported by L-shaped precast beams in the transverse direction as shown in Fig3a. The structure uses precast frames and precast structural walls, the latter elements functioning as the main lateral load re

64、sisting system. Fig. 4 shows an early phase of the construction of the test structure. As can be seen, the "windows'' in the columns and walls are left in these elements for a later assemblage with the preca

65、st beams.</p><p>　　The unfastened design base shear required by the Mexico City Building Code (MCBC, 1993)2 is 0.2WT, where WT is the total weight of the prototype structure, assuming a dead load of 5,15 KPa

66、 (108 psi) and a live load of 0.98 KPa (20.5 psi). The prototype structure was designed using procedures of elastic analyses and proportioning requirements of the MCBC, In these analyses, the gross moment of inertia of t

67、he members in the structure was considered and rigid offsets (distances from the joints to t</p><p>　　Results from these analyses indicated that the structural walls in the test structure would take about 65

68、 percent of the design lateral loads. A review of the nominal lateral resistance of the structure using the MCBC procedures showed that this resisting force was about 1.3 times the required code lateral resistance (0,2Wr

69、), This is one of several factors, later discussed, that contributed to the over-strength of the structure.</p><p>　　The longitudinal reinforcement in all the structural elements of the test structore was de

70、formed bars from Grade 420 steel. Table 1 lists the concrete compressive cylinder strengths for different members of the prototype structure. Fig. 5 shows typical reinforcing details for precast beams spanning in the dir

71、ection of the applied lateral load (see Fig. 3). </p><p>　　Figs. 6 and 7 show reinforcing details for the columns, and for the structural wails and their foundation, respectively. It should be mentioned that

72、 the test structure was designed with the requirements for moderately ductile structures specified by the MCBC. According to these provisions, the test structure did not require special structural walls with boundary ele

73、ments such as those specified in Chapter 21 of AC1 318 02.</p><p>　　The precast two-story columns were connected to the precast foundation by unthreading them in a grouted socket type connection. The reinfor

74、cing details of the foundation, as well as its design procedure and behavior in the test structure are discussed in the companion paper? Tae beam-to-cadmium joints in file test structure were cast-in-place to enable posi

75、tioning the longitudinal reinforcement of the framing beams. The beam top reinforcement was placed in sum on top of the precast beams. Fig. 8</p><p>　　As a result, these hooked bars possessed only about 55 p

76、ercent of the development length required by Chapter 21 of ACI 318-02. In an attempt to anchor these hooked bars, some designers in Mexico provide closed hoops around the hooks, as shown in Fig. 8. The effectiveness of t

77、his approach was also studied in the companion paper.3 Beam to-column joints in the lateral frames of the test structure had transverse beams that were deeper than the longitudinal beams. This made it possible for the to

78、p an</p><p>　　Cast-in-place topping slabs in the test structure were 30 mm (1.18 in.) thick and formed the diaphragms in January-February 2005 Fig. 3. Plan and elevation of test structure: (a) Plan; (b) Late

79、ral frame; (c) Transverse frame. Dimensions in mm. Note: 1 mm - 0.0394 in. the structural system. Welded wire reinforcement (WWR) was used as reinforcement for the topping slabs. The amount of WWR ill the topping slabs w

80、as controlled by the temperature and shrinkage provisions of the MCBC. which are simila</p><p>　　It is of interest to mention that the requirements for shear strength in the diaphragms given by these provisi

81、ons, which are similar to those of ACI 318-89, did not control the design. A wire size of 6 x 6 in. 10/10 led to a reinforcing ratio of 0.002 in the topping slab. The strength of the WWR at yield and fracture obtained fr

82、om tests were 400 and 720 MPa(58 and 104 ksi),respectively.</p><p>　　TEST PROGRAM AND INSTRUMENTATION</p><p>　　Test Program</p><p>　　The test structure was subjected to simulate sei

83、smic loading in the longitudinal direction (see Fig. 3a). Quasitatic cyclic lateral loads FI and F2 were applied at the first and second levels of the structure, respectively (see Fig. 3b). The ratio of F2 to FI was held

84、 constant throughout the test., with a value equal to 2.0. This ratio represents an inverted triangular distribution of loads, which is consistent with the assumptions of most seismic codes including the MCBC.</p>

85、<p>　　The test setup is shown in Fig. 9.The structure had Hinges A, B, and Cat each slab level as shown in Fig. 9b.The purpose of the hinges was to avoid unrealistic restrictions in the structure by allowing the en

86、ds of the slabs to rotate freely during lateral load testing. As can be seen in Fig 9, the lateral loads were applied by hydraulic actuators that work in either tension or compression.</p><p>　　When the actu

87、ators worked in compression, they applied the loads directly at one side of the structure. However, when the actuators applied tensile loads at one side of the test structure, they were convened to compression loads at t

88、he other side by means of four high strength reinforcing bars for each actuator [see D32 ((~1~ in) reinforcing bars in Fig. 9]. Both ends of these bars were attached to 50 mm (2 in.) thick steel plates At each of the flo

89、or levels, two of these plates were part of Hin</p><p>　　As can be seen in Fig 9b before the application of tensile loads in the actuators, the latter end of the plates left a clear space with the end of the

90、 slab. This space at zero lateral load was about 50 mm (2 in.), and it allowed for beam elongation of the structure which occurs during the formation of plastic hinges in the beams? For the case of compressive loads on t

91、he actuators acting on the transverse beam at the side of Hinge B (see Fig. 9b), the system also allowed 50 mm (2 in.) of beam elo</p><p>　　The gravity load was represented by 53 steel ingots, acting at each

92、 level of the structure, with the layout shown in Fig. 9a, The weight per unit area of the ingots per level was 2.79 KPa (58.3 psf), which added to the self-weight of tile slab, leading to a total floor dead load of 5.37

93、 KPa (112 psf). This is 88 percent of the code required gravity load for seismic design (MCBC, 1993). It was not possible to apply the remaining 12 percent of gravity load due to space limitations in the slabs. Th</p&

94、gt;<p>　　Transverse displacements in the structure (perpendicular to the loading direction) were precluded by using steel ball hearings installed in the lateral faces of beam to-column joints of the second level a

95、t Column Lines A1and A3 (see Fig. 9a). These ball bearings were supported by a steel frame. As shown in Fig. 10, the precast columns and wails were fixed to the strong floor using steel beams supported by the foundation

96、and anchored to the floor. The lateral loading history used in the test stru</p><p>　　The target lateral load or top displacement was typically reached by incremental loading of both actuators in which the b

97、ottom actuator was fore-contrived to half the load value of the top actuator. A cycle of lateral load of about 0.75Vg was initially applied, where VR is the nominal theoretical base shear strength computed using the ACI

98、318 02 provisions. The value of VR, 198 KN (44.5 kips), can be assumed to correspond to first yield in the structure.</p><p>　　This parameter was computed using measured material properties, a strength reduc

99、tion factor (1) equal to unity and common assumptions for flexural strength of reinforced concrete sections. For the lateral force of 0.75VR, the corresponding lateral roof displacement was defined as 0.75▽y’. Using this