【正文】 %, with a summertime average of approximately 35% and a wintertime average of approximately 10%. The observed changes in creep rate are thus believed to be seasonal and depend on changes in relative humidity.Fig. 2—Experimentally measured longterm midspan deflection versus time after loading (recorded up to 2470 days) and as predicted for both beams using CEBFIP10 and ACI11 models.Fig. 3—Relative slip versus time at each end of one CFRP strip (Beam 2) as measured and as predicted using FE model.5. Some relative slip occurred between the concrete and CFRP strip at the strip ends soon after loading, as shown in Fig. 3. Since then, the movement at one end of the strip has essentially stabilized and only a relatively small gradual movement has occurred at the other end. The significant scatter in the slip readings, particularly late in the data record, is thought to result from temperature variations in the strain gauges between dates of reading (the beams are beside an airconditioning outlet) and repeated reconnection/disconnection of the measurement instrumentation for these gauges. The maximum relative slip at the ends of the gauged CFRP strip within 2470 days was in the order of mm ( in.)—an average of approximately 60 microstrain over the length of the strip—which implies an average loss of tensile stress of approximately 9 MPa ( psi) in the strips, and translates to an average loss of tensile force of approximately 1 kN ( kips) per strip. Fifty percent of this movement occurred in the first 3 weeks after loading. This observation agrees with those reported by Choi et al.,confirming that the majority of epoxy creep occurs in a relatively early time period.ANALYTICAL PREDICTION OF DEFLECTIONSAnalytical predictions of the beam deflections were made in an attempt to identify any features of the behavior not obvious from the experimental results alone. First, the simplified procedures of CEBFIP10 and ACI11 were used. These procedures focus on accurate modeling of concrete creep—and thus deflection—without considering the effect of creep of epoxy. A stepbystep intime analysis and an FE model were therefore developed to examine the bined effect of creep of the concrete and of the epoxy on the longterm deflection.Analytical prediction of deflections using CEBFIP and ACIApproaches based on the CEBFIP Model Code 1990 and the ACI Committee 209 remendations11 were used by Hall and Ghali6 with the former being shown to achieve good agreement with experimental results for concrete beams reinforced with steel bars and concrete beams with GFRP bars in place of the steel bars. Both approaches aim at estimating longterm deflections due to the effects of creep and shrinkage in the concrete. The methodologies are described in detail by Hall and Ghali6 and Masia et al. Fig. 4—Deflections predicted by stepbystep in time model versus experimentally measured deflections for Beam 1 (reinforced with steel only), including effect of concrete creep and tension stiffening of concrete (238。兩根梁均持續(xù)負(fù)荷超過61/2年。玻璃鋼條加固梁的蠕變變形并不像從控制標(biāo)本梁所預(yù)測(cè)的那樣。一種普及的應(yīng)用，廣泛使用于實(shí)踐之中，那就是在普通鋼筋混凝土受拉面粘結(jié)玻璃鋼條以增加梁的抗彎能力。同樣，正如最近一些研究者推薦的那樣，如果給玻璃鋼條施加預(yù)應(yīng)力，蠕變可以減弱原始的內(nèi)力。類似的方法被用于混凝土箱梁在抗壓凸緣的復(fù)合玻璃碳纖維增強(qiáng)聚合物(GFRP)與和粘結(jié)于張拉面的碳纖維增強(qiáng)聚合物(CFRP)。在這方面，實(shí)驗(yàn)研究結(jié)果以及瞬時(shí)的和伴隨時(shí)間發(fā)生的梁繞度分析預(yù)測(cè)都被描述了。當(dāng)僅考慮混凝土蠕變時(shí)，從測(cè)量簡(jiǎn)單梁的蠕變變形，不能預(yù)測(cè)有玻璃鋼條加固的梁的蠕變變形。在此，我們使用兩種不同的方法來確定環(huán)氧基樹脂的蠕變是否能解釋所觀察到的梁的不同現(xiàn)象：一步一步的時(shí)間分析，允許混凝土和環(huán)氧基樹脂在每個(gè)時(shí)間步內(nèi)的蠕變?cè)隽窟_(dá)到平衡，有限元（FE）與剪切流模型允許在環(huán)氧膠粘劑層。實(shí)驗(yàn)和分析工作的執(zhí)行顯示：情況更加復(fù)雜。實(shí)驗(yàn)項(xiàng)目測(cè)試樣品和材料兩跟相似的鋼筋混凝土梁是由同一批混凝土澆筑而成（圖一）。 MPa，該值是從直徑為100mm，高 200mm的圓柱測(cè)量而得，而這批圓柱是用澆筑梁的同一批混凝土澆筑而成。在梁二的每個(gè)剪跨處，碳纖維貼片以U型形式包裹著梁的兩側(cè)和受拉面。梁由于自重，在跨中產(chǎn)生繞度，該繞度可以用安裝在輕跨度為3200mm鋼架上的千分表測(cè)量。使之產(chǎn)生4個(gè)點(diǎn)的彎曲。荷載是通過懸掛混凝土塊于每根梁上表面。在加載后的第一個(gè)24小時(shí)內(nèi)要多次記錄數(shù)據(jù)，然后在第一個(gè)月內(nèi)要每天記錄一次數(shù)據(jù)，最后逐漸是每3天、每周、每?jī)芍艿礁L(zhǎng)的時(shí)間段記錄一次數(shù)據(jù)。第一次加載的時(shí)候，在梁二上沒有觀察到彎曲裂紋。FRP條必須保持平衡，因此，F(xiàn)RP條大規(guī)?？焖俚暮痛蟮淖兓遣豢赡艿?。碳纖維貼片顯著提高了梁二抗裂彎矩。粘結(jié)于梁二的碳纖維貼片的末端的相對(duì)滑移量與時(shí)間相對(duì)應(yīng)的圖如圖3所示。與梁一相比，梁二的長(zhǎng)期撓度構(gòu)成其直接繞度的比例比梁一大。繞度曾長(zhǎng)率隨時(shí)間是變化的。在徐變系數(shù)計(jì)算中用CEBFIP，當(dāng)相對(duì)濕度增加，徐變系數(shù)降低，意味在相對(duì)濕度大的時(shí)間段徐變?cè)鲩L(zhǎng)率降低。從觀察到的徐變變化率變化，我們相信徐變變化率具有季節(jié)性，并隨相對(duì)濕度而變化。在2470天內(nèi)，貼片整個(gè)長(zhǎng)度范圍內(nèi)的平均滑移量接近60微應(yīng)變，這意味著貼片的應(yīng)力平均損失9Mpa，相當(dāng)于每條帶損失1KN的力。首先，運(yùn)用CEBFIP 和ACI的簡(jiǎn)單程序。兩種方法的目的都是為了評(píng)估梁的長(zhǎng)期繞度受影響于混凝土的徐變和收縮。這些開裂彎矩最佳擬合了代表梁繞度（跨中直接繞度測(cè)量相對(duì)于自重繞度）的測(cè)試值，而不是源于混凝土的開裂強(qiáng)度。m）。用源于梁一的最終徐變系數(shù)去分析梁二是一個(gè)有根據(jù)的設(shè)想，因?yàn)閮筛菏怯猛慌炷镣瑫r(shí)澆鑄而成，且在相同環(huán)境下進(jìn)行加載實(shí)驗(yàn)。澆鑄后，兩根梁負(fù)荷了近300天，總收縮應(yīng)變的90%已經(jīng)完成。對(duì)控制梁一而言，調(diào)整混凝土最終徐變系數(shù)，提供一個(gè)最小二乘方以最佳匹配它的繞度預(yù)測(cè)值和實(shí)驗(yàn)測(cè)試值。開裂彎矩值的巨大差異凸顯了碳纖維貼片的加固效果。后面計(jì)算兩根梁跨中長(zhǎng)期繞度要用最終開裂彎矩。用CEBFIP 和 ACI分析繞度預(yù)言的結(jié)果第一次用CEBFIP方法來預(yù)測(cè)兩跟梁的跨中的直接繞度。所以時(shí)程分析和有限元模型得到發(fā)展，并用他們檢驗(yàn)混凝土徐變和環(huán)氧基樹脂蠕變對(duì)長(zhǎng)期繞度的影響。這份觀察報(bào)告與Choi et ，也證實(shí)了環(huán)氧基樹脂大部分蠕變發(fā)生在相對(duì)比較早的時(shí)期內(nèi)。從加載起，碳纖維貼片一個(gè)末端的運(yùn)動(dòng)就基本穩(wěn)定，只有很小一部分運(yùn)動(dòng)是逐步發(fā)生于另一末端的。然而，在同一實(shí)驗(yàn)室的同一階段，Hall 和Ghali在裂縫試驗(yàn)中記下了相對(duì)濕度。相似的趨勢(shì)在梁跟梁上都有發(fā)生。對(duì)于梁二的跨中繞度并不像梁一那樣被“清楚理解”。長(zhǎng)期繞度是由于混凝土徐變是直接繞度的一個(gè)函數(shù)，它與梁截面的剛度和裂縫情形有關(guān)。兩根梁的跨中長(zhǎng)期繞度（總繞度減去初始繞度）如圖2所示。因此，彎矩值恒定區(qū)段的混凝土必須先有很多的小裂縫以使FRP條的應(yīng)力保持不變。這是因?yàn)樵诮孛鎻澗夭蛔兊膮^(qū)域FRP條的張拉應(yīng)變保持不變。