鋼筋混凝土外文翻譯

1、<p><b>　　附錄一</b></p><p><b>　　論文原文</b></p><p>　　ACI STRUCTURAL JOURNAL TECHNICAL PAPER</p><p>　　Title no. 107-S61</p><p>　　Creep Effects in

2、Plain and Fiber-Reinforced Polymer-Strengthened Reinforced Concrete Beams</p><p>　　by M. M. Reda Taha, M. J. Masia, K.-K. Choi, P. L. Shrive, and N. G. Shrive</p><p>　　The long-term deflection b

3、ehavior of two reinforced concrete (RC) beams with similar dimensions and material properties was monitored. One beam was externally strengthened with fiberreinforced polymer (FRP) strips, whereas the other was used as a

4、 control specimen. Both beams have been subjected to sustained loading for over 6-1/2 years. The objective of the experiments was to assess the significance of creep in the epoxy adhesive and whether such creep might all

5、ow the FRP strips to unload over t</p><p>　　The experimental deflections have been compared to deflection predictions using ACI 209R-92 and CEB-FIP MC 90. The creep deformations of the FRP-strengthened beam

6、are not as predicted from the control beam. Two analytical approaches are used: a step-by-step in-time analysis and finite element (FE) modeling. Both techniques demonstrate that creep of the adhesive layer can account

7、for the differences observed between the predicted and actual behaviors of the beams.</p><p>　　Keywords: creep; deflection; epoxy adhesive; fiber-reinforced polymer(FRP); reinforced concrete.</p><

8、p>　　INTRODUCTION</p><p>　　In recent years there has been much research on the use of fiber-reinforced polymers (FRPs) to strengthen existing concrete structures. One popular application, used widely in pr

9、actice, is to bond FRP strips externally to the tension face of reinforced concrete (RC) beams to increase flexural capacity.</p><p>　　The FRP strips are typically bonded directly to the prepared concrete su

10、rface using an epoxy adhesive. The strips may be anchored mechanically near their ends or supported by additional shear reinforcement, usually in the form of U-shaped FRP sheets. If the beam is subsequently loaded with s

11、ustained loads, creep in the epoxy adhesive could take place and would allow the FRP strips to unload, leaving them ineffective against the sustained load. Similarly, if the strips are prestressed as recentl</p>

12、<p>　　Research into the time-dependent behavior (creep and shrinkage) of concrete beams strengthened with externally bonded FRPs is scarce. Analytical models were verified against limited experimental observations o

13、f RC2 and timber3 beams externally reinforced with FRP strips. Similar approaches were used for a composite glass fiber-reinforced polymer (GFRP) box girder with concrete in the compression flange and a carbon fiber-rein

14、forced polymer (CFRP) strip bonded to the tension face.4 In all of the </p><p>　　Herein, the results of an experimental investigation and accompanying analytical predictions of immediate and timedependent be

15、am deflections are described. The construction of the RC beams and the experimental program for observing their time-dependent deflection are presented. The measured deflections are compared to deflection predictions usi

16、ng the ACI and CEB-FIP methods implemented according to the recommendations of Hall and Ghali.6</p><p>　　The long-term deflection data show that the timedependent (creep) deformation of the CFRP-strengthened

17、 beam is a larger proportion of its immediate deformation than the same deformation ratio for the unstrengthened beam. The creep of the beam with the FRP strips could not be predicted from the creep measured on the plain

18、 beam when creep of concrete alone was considered. Because CFRPs have not been observed to creep at the stress levels generated,7,8 the additional creep may have occurred in the </p><p>　　The creep mechanism

19、 is expected to be a simple flow of the epoxy under the shear stress,5 which develops to create tension in the FRP strip. While models exist for predicting long-term deformation of RC beams strengthened with FRP (for exa

20、mple, Charkas et al.9), these models do not account explicitly for creep of epoxy adhesives. Herein, we use two different approaches to determine if creep in the epoxy can account for the different behaviors observed in

21、the beams: a step-by-step in-time analysi</p><p>　　RESEARCH SIGNIFICANCE</p><p>　　The potential effects of creep on RC beams strengthened with externally applied FRP strips are considered. It wa

22、s thought that creep in the epoxy resin might relieve stress in the FRP, making the FRP less effective from a serviceability point of view under sustained loads. Thus, FRP strips used to strengthen a beam, which was then

23、 subject to increased sustained load, might end up with the extra sustained load being carried by the original concrete and steel reinforcement, not the FRP. The experi</p><p>　　EXPERIMENTAL PROGRAM</p>

24、;<p>　　Test specimens and materials</p><p>　　Two similar RC beams were cast from the same concrete batch (Fig. 1). Each beam was 3500 mm (137.8 in.) long, 280 mm (11.02 in.) wide, and 180 mm (7.09 in.

25、) high, reinforced with four longitudinal bars (Canadian 10M-11.3 mm [0.445 in.] diameter, 100 mm2 [0.155 in.2] area) at an effective depth of 135 mm (5.31 in.) from the top surface of the beam. Seven 10M stirrups were s

26、paced uniformly in each shear span of each beam. The 28-day compressive strength of the concrete, as determined from 100 mm (</p><p>　　Fig. 1—Test specimens, test setup, and strain distribution.</p>&

27、lt;p>　　The two beams were cast together and stored—fully supported—for 10 months before the CFRP strips and GFRP wraps were applied. One beam (Beam 1) was designated as a control ·specimen. Two CFRP strips were b

28、onded to the tension face of the second beam (Beam 2) using an epoxy adhesive. The strips are 100 mm (3.94 in.) wide, 1.2 mm (0.047 in.) thick, and 2970 mm (116.9 in.) long. Over the shear spans at each end of Beam 2, G

29、FRP sheets were wrapped in a U-shape to cover the two side faces and the te</p><p>　　Test setup and procedure</p><p>　　The beams were simply supported (pin-roller) over a span of 3200 mm (125.98

30、 in.) (Fig. 1). The midspan deflection due to self-weight was recorded using a dial gauge (least count 0.01 mm [0.000394 in.]) mounted on a lightweight steel frame over the 3200 mm (125.98 in.) span. For Beam 2, electron

31、ic spring gauges were mounted on the concrete adjacent to each end of one of the CFRP strips. The deflected tip of the spring gauge was carefully positioned to touch the exposed end of the CFRP strip. Thes</p><

32、;p>　　Experimental results and discussion</p><p>　　Upon loading, the immediate midspan deflections of the beams relative to the measured self-weight deflections were 10.01 and 3.76 mm (0.394 and 0.148 in.)

33、 for the control and CFRP-strengthened beams, respectively. Numerous flexural cracks were observed extending from the tension face of the control beam, predominantly over the region of constant bending moment between the

34、 point loads. No flexural cracks were observed in Beam 2 at first loading. Such cracking would be hard to see unless significa</p><p>　　The long-term midspan deflections (total deflection minus the initial d

35、eflection) of both beams are shown in Fig. 2, plotted versus time after loading up to 2470 days of loading. The relative slip movements versus time at each end of one of the CFRP strips bonded to Beam 2 are shown in Fig.

36、 3. Several observations can be made:</p><p>　　1. The long-term deflection of Beam 2 is significantly less than that of Beam 1. Long-term deflection due to concrete creep is a function of the immediate defle

37、ction, which depends on cross-sectional stiffness and cracking status. Beam 1 cracked much sooner than Beam 2.</p><p>　　2. The long-term deflection of Beam 2 constitutes a larger proportion of its immediate

38、deflection compared with Beam 1. Plevris and Triantafillou2 observed a similar response in beams externally reinforced with FRP strips compared to their control specimen (no FRP).</p><p>　　3. The midspan def

39、lection for Beam 2 does not appear to be “catching” that of Beam 1. That is, at first appearance, there is no indication that the CFRP reinforcement is unloading, thereby becoming ineffective against the sustained load.&

40、lt;/p><p>　　4. The rate of increase of deflection changes with time. This is particularly evident when compared to the smooth curves of predicted long-term deflections discussed and presented in the following s

41、ections (Fig. 2, 4, and 5). Similar trends occur for both beams. The periods of reduced rate of increase of deflection coincide with the summer months and those of increased creep coincide with the winter months. In the

42、 calculation of creep coefficient using CEB-FIP,10 the creep coefficient reduces a</p><p>　　Fig. 2—Experimentally measured long-term midspan deflection versus time after loading (recorded up to 2470 days) an

43、d as predicted for both beams using CEB-FIP10 and ACI11 models.</p><p>　　Fig. 3—Relative slip versus time at each end of one CFRP strip (Beam 2) as measured and as predicted using FE model.</p><p&

44、gt;　　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 rel

45、atively 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 betw

46、een dates of reading (the beams are beside an air-conditioning ou</p><p>　　ANALYTICAL PREDICTION OF DEFLECTIONS</p><p>　　Analytical predictions of the beam deflections were made in an attempt to

47、 identify any features of the behavior not obvious from the experimental results alone. First, the simplified procedures of CEB-FIP10 and ACI11 were used. These procedures focus on accurate modeling of concrete creep—and

48、 thus deflection—without considering the effect of creep of epoxy. A step-by-step in-time analysis and an FE model were therefore developed to examine the combined effect of creep of the concrete and of the </p>&

49、lt;p>　　Analytical prediction of deflections using CEB-FIP and ACI</p><p>　　Approaches based on the CEB-FIP Model Code 1990 and the ACI Committee 209 recommendations11 were used by Hall and Ghali6 with the

50、 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 long-t

51、erm 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</p><p>　　Fig. 4—Deflections predicted by step-by-step i

52、n time model versus experimentally measured deflections for Beam 1 (reinforced with steel only), including effect of concrete creep and tension stiffening of concrete (? = 0.9) and Beam 2 (reinforced with steel and FRP),

53、 including effects of concrete creep, tension stiffening of concrete (), and stress relaxation of FRP-epoxy composite (anddays).</p><p>　　Results of analytical deflection predictions using CEB-FIP10 and ACI1

54、1</p><p>　　The CEB-FIP10 approach was first used to predict the immediate midspan deflections of both beams. The model predictions were calibrated against the experimental results by adjusting the cracking m

55、oment for each beam. These cracking moments are best-fit values representing the observed deflections (immediate midspan deflection measured relative to the self-weight deflection) in the beams and not derived from the c

56、racking strength of concrete. The cracking moments were determined in this way becau</p><p>　　The long-term midspan deflections of each of the beams were then predicted for all times after loading, at which

57、experimental readings were recorded. The ultimate creep coefficients for concrete were adjusted to provide a leastsquares best fit between the predicted and experimental deflection values for the Control Beam 1. The same

58、 ultimate creep coefficients were then used to predict the long-term deflections for Beam 2, assuming no creep in the adhesive bonding of the CFRP to the concrete. The</p><p>　　Fig. 5—Long-term deflections a

59、t midspan of beams using FE method: (a) Beam 1, considering creep of concrete; and (b) Beam 2, considering combined effect of creep of concrete and creep of epoxy adhesive.</p><p><b>　　論文翻譯</b>&l

60、t;/p><p>　　普通鋼筋混凝土梁和纖維增強(qiáng)聚合物加固的鋼筋混凝土梁的徐變效應(yīng)</p><p>　　監(jiān)測(cè)了兩根具有相同尺寸和材料性能的RC梁的長(zhǎng)期繞度行為。其中一根梁的外部用纖維加固材料條加固，而另一根梁是用來(lái)作為對(duì)照樣本。兩根梁均持續(xù)負(fù)荷超過(guò)6-1/2年。本實(shí)驗(yàn)的目的是評(píng)估環(huán)氧膠粘劑的蠕變的重要性，以及這樣的蠕變是否允許玻璃鋼條隨著時(shí)間的推移有卸載荷載的作用。在玻璃鋼條的兩端的滑移也被監(jiān)

61、測(cè)了。實(shí)驗(yàn)繞度已經(jīng)和ACI 209R-92 and CEB-FIP MC 90前期預(yù)估的繞度作了對(duì)比。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。使用了兩種分析方法：一種是時(shí)程分析，另一種是有限元（FE）模型。兩種分析方法表明：粘結(jié)層蠕變能解釋預(yù)測(cè)和實(shí)際行為之間差異的現(xiàn)象。</p><p>　　關(guān)鍵詞：蠕變，撓度，環(huán)氧樹(shù)脂粘接劑，纖維增強(qiáng)復(fù)合材料（玻璃鋼），鋼筋混凝土</p><p

62、><b>　　簡(jiǎn)介</b></p><p>　　在最近幾年出現(xiàn)了對(duì)使用（FRPs）纖維增強(qiáng)聚合物加強(qiáng)現(xiàn)有混凝土結(jié)構(gòu)的大量研究。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。玻璃鋼條通常直接用環(huán)氧膠粘劑粘結(jié)于精制的混凝土表面。這些玻璃鋼條可能被機(jī)械的錨固于RC梁梁端附近或者被附加抗剪鋼筋支撐于梁端附近，通常采用U字型的玻璃鋼條。如果隨后給

63、梁加以持續(xù)負(fù)荷，環(huán)氧膠粘劑可能發(fā)生蠕變，也允許玻璃鋼條卸載，使他們不能承受持續(xù)荷載。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。因此，雖然玻璃鋼條仍然可以協(xié)助承受額外的活荷載，增加的持續(xù)荷載可能超過(guò)使之成為原加固梁的能力。</p><p>　　對(duì)（用玻璃鋼條加固于混凝土梁外表面的）梁的隨時(shí)間發(fā)生的行為（蠕變和收縮）的研究還很少。分析模型已被證實(shí)與用玻璃鋼條加固于外表面的R

64、C2和timber3梁的有限的實(shí)驗(yàn)觀測(cè)相違背。類(lèi)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)。在所有上述的模型，不管怎樣，發(fā)生在玻璃鋼條與梁受拉面之間粘結(jié)層的蠕變的影響被忽視了。也就是說(shuō)，假定梁的受拉面和玻璃鋼條之間是理想的約束和協(xié)調(diào)的應(yīng)變。Choi et al最近做的試驗(yàn)說(shuō)明，當(dāng)加載后7天之內(nèi)，在剪應(yīng)力作用下發(fā)生顯著的蠕變，位于混凝土和玻璃鋼條界面之間的環(huán)氧基樹(shù)

65、脂。</p><p>　　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。為了觀察鋼筋混凝土梁隨時(shí)間而發(fā)生的繞度，它的制作過(guò)程和實(shí)驗(yàn)步驟都被呈現(xiàn)出來(lái)了。Hall and Ghali的提議把實(shí)測(cè)繞度和用ACI and CEB-FIP的方法預(yù)測(cè)的繞度進(jìn)行比較。</p><p>　　長(zhǎng)期撓度的數(shù)據(jù)顯示,碳纖維復(fù)合材料加固的梁的隨時(shí)間發(fā)生的蠕變變形占瞬時(shí)變形的比例比沒(méi)有加

66、固的梁大。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。因?yàn)樵谝旬a(chǎn)生的應(yīng)力水平下還沒(méi)有觀察到碳纖維復(fù)合材料的蠕變，可額外蠕變可能已經(jīng)在玻璃鋼條和混凝土梁界面之間產(chǎn)生。蠕變機(jī)理被期待為環(huán)氧基樹(shù)脂的一種簡(jiǎn)單的流體剪切應(yīng)力，即發(fā)展到在玻璃鋼條和混凝土之間產(chǎn)生應(yīng)力的程度。當(dāng)模型的存在為預(yù)測(cè)用玻璃鋼條加固的RC梁的長(zhǎng)期變形（例如，Charkas et al.9），這些模型沒(méi)有明確的考慮到環(huán)氧樹(shù)脂膠粘劑蠕變。在

67、此，我們使用兩種不同的方法來(lái)確定環(huán)氧基樹(shù)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(shù)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。</p><p><b>　　研究意義</b></p><p>　　蠕變對(duì)用玻璃鋼條加強(qiáng)于梁外表面的RC梁的潛在影響被考慮到了。它被認(rèn)為能消除玻璃鋼條的壓力，在持續(xù)荷

68、載作用下，一個(gè)適用性的觀點(diǎn)認(rèn)為它能使玻璃鋼條效應(yīng)減弱。因此，玻璃鋼條被運(yùn)用于加固梁，它便受到增加的持續(xù)的荷載，可能最終所受的額外持續(xù)荷載是原始的混凝土和鋼筋所帶來(lái)的，而不是玻璃鋼條所帶來(lái)的。實(shí)驗(yàn)和分析工作的執(zhí)行顯示：情況更加復(fù)雜。然而，蠕變變形比單從混凝土徐變預(yù)測(cè)的更大，表面這都緣于環(huán)氧樹(shù)脂的蠕變變形。已報(bào)道的實(shí)驗(yàn)方案的目的是確認(rèn)環(huán)氧樹(shù)脂蠕變的存在，而不是復(fù)制一個(gè)實(shí)用的改造方案。研究結(jié)果強(qiáng)調(diào)，在實(shí)踐中環(huán)氧樹(shù)脂蠕變可影響玻璃鋼條長(zhǎng)期性能的

69、潛力。</p><p><b>　　實(shí)驗(yàn)項(xiàng)目</b></p><p><b>　　測(cè)試樣品和材料</b></p><p>　　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）。每根梁長(zhǎng)3500mm，梁寬280mm，梁高180mm，從箱梁頂部至底部135mm位置處有4根縱向鋼筋（直徑11.3mm，單根面積100mm&#

70、178;）加強(qiáng)。每跟梁的每個(gè)剪跨均勻布置7道直徑11.3mm的箍筋?；炷琉B(yǎng)護(hù)28天的抗壓強(qiáng)度值為34.3 ± 2.3 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。</p><p>　　兩根混凝土梁是同時(shí)澆筑的，且在碳纖維貼片和玻璃纖維增強(qiáng)塑料帶運(yùn)用前10個(gè)月，它們是平放于地面的（完全支撐）。梁一被設(shè)計(jì)為參照樣本，采用環(huán)氧粘合劑把兩根碳纖維

71、復(fù)合材料條粘于梁二的受拉面表面。碳纖維貼片100mm寬，1.2mm厚，2970mm長(zhǎng)。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。碳纖維貼片纖維方向的單向性與梁長(zhǎng)方向?qū)R。碳纖維貼片在順纖維方向的彈性模量為165Gpa，抗拉強(qiáng)度為2800Mpa（生產(chǎn)廠家提供的數(shù)據(jù)）。</p><p><b>　　測(cè)試設(shè)置和步驟</b></p><p>　　簡(jiǎn)支梁的

72、支座跨度為3200mm（如圖1）。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。對(duì)于梁二，電子彈簧儀表被安置在靠近每個(gè)具體的碳纖維帶的梁端。小心地把彈簧儀表的偏移尖端定位于碳纖維貼片暴露的末端。這些測(cè)量?jī)x表主要用于測(cè)量碳纖維貼片末端相對(duì)于混凝土粘結(jié)表面的縱向相對(duì)位移。每根梁在距支座930mm處加10.34KN的集中荷載，使之產(chǎn)生4個(gè)點(diǎn)的彎曲。這種荷載水平的目的是要使兩根梁達(dá)到工作的范圍。對(duì)于梁一，

73、預(yù)計(jì)荷載將使梁受拉區(qū)混凝土開(kāi)裂，但是受壓區(qū)混凝土的應(yīng)力和受拉區(qū)鋼筋的應(yīng)力還處在彈性階段。對(duì)于梁二，預(yù)期荷載造成的破壞遠(yuǎn)沒(méi)那么大，但從長(zhǎng)遠(yuǎn)來(lái)看任然導(dǎo)致值得注意的繞度。荷載是通過(guò)懸掛混凝土塊于每根梁上表面。荷載的轉(zhuǎn)移是用液壓千斤頂逐漸降低混凝土塊到梁上。然后拿走液壓千斤頂。每根梁的跨中繞度與自重有關(guān)，也與加載之后一開(kāi)始和每隔一段時(shí)間記錄的碳纖維貼片的縱向滑移量有關(guān)。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)

74、，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)。加荷載的梁位于裝有空調(diào)的實(shí)驗(yàn)室地下室，在這里平均溫度</p><p><b>　　實(shí)驗(yàn)結(jié)果與討論</b></p><p>　　一經(jīng)加載，控制梁和用碳纖維貼片加固的梁因自重在跨中產(chǎn)生的瞬時(shí)繞度分別是10.0mm和3.76mm。在控制梁上，可以看到很多彎曲裂紋從其受拉區(qū)表面開(kāi)始擴(kuò)展，這主要集中在彎矩不變的兩集中荷

75、載作用點(diǎn)之間。第一次加載的時(shí)候，在梁二上沒(méi)有觀察到彎曲裂紋。這樣的裂縫很難看到，除非有值得注意的寬度，是因?yàn)橛袕埦o的碳纖維貼片。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。如果有一些寬裂紋，F(xiàn)RP條的變形和彎曲應(yīng)力在與混凝土粘結(jié)的FRP條段和FRP條延伸過(guò)裂縫段之間有很大的變化。FRP條必須保持平衡，因此，F(xiàn)RP條大規(guī)模快速的和大的變化是不可能的。因?yàn)闆](méi)有任何原理適應(yīng)這種壓力的變化。因此，彎矩值恒定區(qū)段的混凝土必須先有很多的

76、小裂縫以使FRP條的應(yīng)力保持不變。加載后幾個(gè)月，在梁二上可以看到細(xì)小裂縫從梁跨中開(kāi)始延伸。碳纖維貼片顯著提高了梁二抗裂彎矩。雖然沒(méi)有測(cè)試，但額外增加的碳纖維貼片有望增加梁極限抗彎承載力。</p><p>　　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。繪制時(shí)間為加載后2470天。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?？傻贸鋈绺捎^察結(jié)果：</p><p&g

77、t;　　1、梁二的長(zhǎng)期撓度明顯減少梁比一的。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)。梁一早于梁二開(kāi)裂。</p><p>　　2、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。Plevris和Triantafillou2在用玻璃鋼條加固的鋼筋混凝土梁和較對(duì)參照標(biāo)本（無(wú)玻璃鋼）梁上觀察到類(lèi)似的外部響應(yīng)。</p><p>　　3、對(duì)于梁二的跨中繞度

78、并不像梁一那樣被“清楚理解”。 也就是說(shuō)，初看起來(lái)，沒(méi)有跡象表明碳纖維布加固能卸載，從而對(duì)持續(xù)負(fù)載不能起效。</p><p>　　4、繞度曾長(zhǎng)率隨時(shí)間是變化的。當(dāng)與下面所討論和呈現(xiàn)的較平穩(wěn)的長(zhǎng)期繞度曲線（圖2、4、5）相比，這一點(diǎn)尤其明顯。相似的趨勢(shì)在梁跟梁上都有發(fā)生。繞度增長(zhǎng)率降低時(shí)間段與夏季月份相對(duì)應(yīng)，徐變?cè)黾拥臅r(shí)間段與冬季月份相對(duì)應(yīng)。在徐變系數(shù)計(jì)算中用CEB-FIP，當(dāng)相對(duì)濕度增加，徐變系數(shù)降低，意味在相對(duì)

79、濕度大的時(shí)間段徐變?cè)鲩L(zhǎng)率降低。在當(dāng)前的測(cè)試中沒(méi)有記錄相對(duì)濕度。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。他們的結(jié)果顯示相對(duì)濕度在5%—50%之間變化，夏季平均相對(duì)濕度大約為35%，冬季的平均相對(duì)濕度大約為10%。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。</p><p>　　5、加載后不久，發(fā)生于混凝土和碳纖維貼片末端的相對(duì)滑移如圖3所示。從

80、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?；谱x數(shù)中的顯著分散，特別是后期數(shù)據(jù)記錄中，被認(rèn)為是由于應(yīng)變表在讀數(shù)日和反復(fù)重連或測(cè)量?jī)x器斷線期間溫度變化所致。在2470天內(nèi)，標(biāo)準(zhǔn)的碳纖維貼片末端最大相對(duì)滑動(dòng)大約為0.17mm，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。50%的滑移發(fā)生在加載后的3個(gè)星期內(nèi)。這份觀察報(bào)告與Choi e

81、t al.所報(bào)道的相符合，也證實(shí)了環(huán)氧基樹(shù)脂大部分蠕變發(fā)生在相對(duì)比較早的時(shí)期內(nèi)。</p><p><b>　　撓度的分析預(yù)測(cè)</b></p><p>　　單從實(shí)驗(yàn)結(jié)果，試圖通過(guò)梁的繞度分析預(yù)測(cè)來(lái)找出任何不明顯的反應(yīng)特征。首先，運(yùn)用CEB-FIP 和ACI的簡(jiǎn)單程序。這些程序集中在混凝土徐變變形的標(biāo)準(zhǔn)模型上，因此沒(méi)有考慮到環(huán)氧基樹(shù)脂的蠕變影響。所以時(shí)程分析和有限元模型得

82、到發(fā)展，并用他們檢驗(yàn)混凝土徐變和環(huán)氧基樹(shù)脂蠕變對(duì)長(zhǎng)期繞度的影響。</p><p>　　運(yùn)用CEB-FIP 和 ACI進(jìn)行繞度分析預(yù)測(cè)</p><p>　　為了實(shí)現(xiàn)與鋼筋混凝土梁和用碳纖維貼片加固的鋼筋混凝土梁實(shí)驗(yàn)結(jié)果相吻合，Hall 和 Ghali便用了分別基于CEB-FIP1990年的標(biāo)準(zhǔn)守則和ACI委員會(huì)第209號(hào)推薦規(guī)范的方法。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

83、變和收縮。Hall 、 Ghali 和 Masia et al詳細(xì)地描述了該方法論。</p><p>　　用CEB-FIP 和 ACI分析繞度預(yù)言的結(jié)果</p><p>　　第一次用CEB-FIP方法來(lái)預(yù)測(cè)兩跟梁的跨中的直接繞度。通過(guò)對(duì)每根梁的開(kāi)裂彎矩調(diào)整，該模型的預(yù)測(cè)對(duì)實(shí)驗(yàn)結(jié)果進(jìn)行了校核。這些開(kāi)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(kāi)裂強(qiáng)

84、度。用這種方法確定開(kāi)裂彎矩，因?yàn)榭箯垙?qiáng)度和混凝土的設(shè)計(jì)收縮變形要求直接估算開(kāi)裂彎矩，而不是通過(guò)實(shí)驗(yàn)測(cè)得的。后面計(jì)算兩根梁跨中長(zhǎng)期繞度要用最終開(kāi)裂彎矩。梁一和梁二的極限開(kāi)裂彎矩分別是4.53KN·m和9.12KN·m。開(kāi)裂彎矩值的巨大差異凸顯了碳纖維貼片的加固效果。這種差異也與觀察到的梁二裂縫較小，梁一具有明顯裂縫的現(xiàn)象相符合（值得注意的是兩跟梁的最大彎矩都是由自重和實(shí)施的集中荷載所產(chǎn)生，其值為11.13KN·