外文翻譯--鋼板包裹的鋼筋混凝土柱受沖力影響下的性能

1、<p>　　中文7700字,5400單詞，2.5萬(wàn)英文字符</p><p>　　出處：Griffith M C, Wu Y F, Oehlers D J. Behaviour of Steel Plated RC Columns Subject to Lateral Loading[J]. Advances in Structural Engineering, 2005, 8(4):333-348.&l

2、t;/p><p><b>　　原文</b></p><p>　　Behaviour of Steel Plated RC Columns Subject to Lateral Loading</p><p>　　Griffith M C, Wu Y F, Oehlers D J.</p><p>　　Abstract: Th

3、e main focus of this paper is to describe the behaviour of RC columns that are</p><p>　　retrofitted with an alternative technique to “jacketing” or wrapping. This new technique consists of attaching steel pl

4、ates to the tlexural faces of a concrete column using bolts. It is envisaged that this technique would be suitable primarily for columns having rectangular cross-sections and in situations where lateral loading induces p

5、redominately a single plane of bending (as opposed to biaxial bending). Effectiveness of this new technique has been demonstrated by experimental testing and num</p><p>　　Keywords: reinforced concrete, colum

6、ns, numerical model, retrofitting, partial interaction, slip.</p><p>　　INTRODUCTION</p><p>　　Theoretical and experimental studies have demonstrated that external jacketing can be highly effectiv

7、e in preventing existing columns from premature shear, lapspltce or flexural failure in the case of circular columns. Therefore, this kind of retrofitting work has already been widely used in engineering (Chai et al. 199

8、1, 1994; Priestley et al. 1994a,b).However,it is not quite as clear-cut for rectangular RC columns where the success of the retrofit procedure depends on</p><p>　　the degree to which jacketing increases conf

9、inement. For example, Park (2001) states “A rectangular thin steel jacket would not be so effective, due to the sides bowing out when dilation of the concrete occurs during a major earthquake, resulting in confinement ap

10、plied mainly in the column corners”. Although rectangular jacketing can still be effective in certain circumstances, the relative poor performance of rectangular jackets in confining the concrete core has been experiment

11、ally verified (C</p><p>　　Efforts to improve the confinement effectiveness rectangular jackets have been reported in the literature. One technique was to enhance the out-of-plan flexural stiffness of the jac

12、ket by using additional stiffeners in the cross-section. However, test results showed that the improvement was not satisfactory (Chai et al. 1990). The use of anchor bolts to enhance the confinement from rectangular stee

13、l jacket was shown (Aboutaha et al.1996) to also provide limited improvement. Another technique use</p><p>　　There has been much research into the use of advanced composite materials such as fiberglass and c

14、arbon fiber jackets/wrapping to replace steel jackets in recent years (Katsumata et al. 1988; Saadatmanesh et al.1994, 1996; Priestley and Seible 1995; Seible et al. 1997; Xiao and Ma 1995, 1997;Mirmiran and Shahawy 199

15、7; Hanna and Jones 1997; Xiao et al. 1999; Liu et al. 2000; Pantelides et al. 2000; Karbhari 2001; Theriault and Nealc 2000; Yao et al. 2001; Lau and Zhou 2001; Pessiki et al. 2001; </p><p>　　In contrast to

16、“jacketing” retrofit schemes, the form of composite plating developed by the authors is a new concept for retrofitting rectangular RC columns. It works, essentially, by delaying the onset of concrete crushing through the

17、 addition of external steel plating that acts only in compression on the flexural faces of the concrete column. By delaying concrete crushing, additional curvature can be sustained by the column before substantial loss o

18、f strength occurs, resulting in substantially</p><p>　　RETROFIT SCHEME BY PARTIAL INTERACTION PLATING</p><p>　　A schematic of the new scheme is given in Figure l where a length of column between

19、 its end and midheight is shown. Steel plates in the shape of an “L” (as in Figure l (a) are bolted to both the tension and compression faces of the column and also to the foundation or beam / slab (Figure l (a) and l (d

20、)). The novel aspect of this retrofit solution is that the plate on the tension face can be made to attract very little tension force, in the plastic hinge zone at the base of the column, by positi</p><p>　　

21、The motivation for this alternative retrofit concept is that substantially improved confinement through jacketing is not always achievable for rectangular cross-sections. Further many concrete frame structures in low to

22、moderate earthquake hazard regions have been designed predominately for gravity and wind loading but may have insufficient levels of displacement ductility to withstand significant earthquake shaking. In many instances,

23、the columns have sufficient shear strength for the columns t</p><p>　　single plane. For example, bridge piers whose flexure in the longitudinal direction is restricted due to the axial stiffness of the bridg

24、e deck and displacement constraints of the bridge abutments. In addition, it is not unusual to have columns in a building structure participating in moment frame action under lateral loading only in a single direction. F

25、or all of these situations, it may be feasible to consider retrofit only for uni-directional loading rather than bi-directional loading.</p><p>　　The effectiveness of the new retrofit scheme has been demonst

26、rated experimentally (Wu et al. 2003). Abrief description of the testing is provided here. The test configuration is illustrated in Figure 2 (a) with the axial load N =360 kN being applied in “force control” mode and

27、the lateral load F being applied in “displacement control” mode. In order to get two tests from each specimen, one end was temporarily strengthened by sandwiching the column between large steel channel sections (Figure &

28、lt;/p><p>　　Plots of the lateral load F versus sidesway deflection ? are presented in Figure 3 and</p><p>　　the results are summarized in Table 2. It should be noted that a more useful, n

29、on-dimensional, variable for expressing the sidesway response is in terms of “drift”, defined here as ?</p><p>　　divided by the column height of 1.218 m. The drift response is also shown in Fig

30、ure 3 on the top horizontal axis. To compare the response of the three columns, it is convenient then to use displacement ductility, defined by Eqn 1,</p><p>　　µ? = ?u ? y</p><p><b

31、>　　(1)</b></p><p>　　where ? y</p><p>　　is the yield displacement (the point where the tensile reinforcement first yields</p><p>　　and the maximum strength is reached), an

32、d</p><p>　　?u is the lateral displacement at the point where</p><p>　　the lateral resistance force equals 80% of the maximum lateral force. The displacement ductility factors for the three cu

33、rves in Figure 3 are listed in Table 2 where it can be seen that both the plated columns had greater displacement ductility than the unplated column. Similar behaviour was observed in the cyclic loading tests (Figure 4)

34、where the 6 mm plated column (4ACP6) was significantly more ductile than the bare RC column (3ACR).</p><p>　　BEHAVIOUR OF THE PLATED COLUMNS</p><p>　　A computer-based numerical modeling procedur

35、e was developed in order to study the characteristic behaviour of reinforced concrete (RC) columns that are plated for a range of values for plate thickness and bolt stiffness. For details of the numerical model refer to

36、 Wu et al. (2004). The numerical model was based on a number of assumptions, the most important being: (1) that plane sections remain plane applies to the concrete and plate sections separately with slip between the si

37、de plates and th</p><p>　　A segmental layered approach was used for the numerical modeling to account for non-linear material behaviour for both the concrete and the steel reinforcement and plates as well as

38、 for geometric non-linearity. The accuracy of the numerical model was verified by comparisons with the experimental test results (refer Wu et al.,2004). With this numerical model, the analysis of this complicated column

39、system is made possible. From this numerical study, the effectiveness of this new scheme can be cle</p><p>　　The example columns considered here are similar to that used in the experimental programme (refer

40、Figures 1 and 2). The column reinforcement details are shown in Figure 2(c) and the material properties used in the numerical analysis are listed in Table 3. The bolt shear stiffness was obtained from bolt shear tests as

41、 described in Wu,Giffith and Oehlers (2003).</p><p>　　The bolt spacing was</p><p>　　Li =100 mm c/c except for the first row of two bolts which was</p><p>　　L1 =20

42、0 mm from the bottom of the column (refer Figure 1) with a total number of 8 rows of 2 bolts on each face (tension and compression) of the column.</p><p>　　The plastic hinge length was calculated to be<

43、/p><p>　　Lp =200 mm (Priestley and Park 1987). This</p><p>　　plastic hinge length was found to provide theoretical results in good agreement with the test result of the plated columns (Wu et al. 2

44、003, 2004). Confinement due to the stirrups of R6@100 mm c/c is considered in the calculations. The confinement effect is calculated based on the method reported by Mander et al. (1988). The confined concrete strength is

45、 calculated</p><p><b>　　to be</b></p><p>　　fcc =47 MPa inside the confined core enclosed by the centre line of the stirrups. P- ?</p><p>　　effects were included in th

46、e numerical simulations.</p><p>　　Figure 5 gives the load versus deflection response of the plated column for different plate thickness (from 0 to 30 mm) and constant bolt stiffness ( Kb =23 kN/mm). Figure

47、6 gives the</p><p>　　results for 6mm plated columns with variations in bolt stiffness ( Kb</p><p>　　from 0 to 46 kN/mm). It</p><p>　　should be noted that the descending branch of

48、the curves in Figure 5 and 6 are not perfectly smooth; i.e., they contain some “kinks” (eg., at about 85 mm of displacement). Unless noted otherwise the kinks in these (and subsequent) figures are due to discretisation o

49、f the column cross-section into layers for the purpose of kinks disappear but this requires significantly more computational time than is necessary to study the influence of the parameters affecting plated-column behavio

50、ur. The follow</p><p>　　The lateral stiffness of a column is increased invariably with an increase in plate thickness and/or bolt stiffness in the ascending branches before yielding of the tensile reinforcem

51、ent. The column load at which the tensile reinforcement yields (indicated by ‘+’), and which occurs very close to the peak lateral resistance, also increases invariably with an increase in plate thickness and/or bolt sti

52、ffness.</p><p>　　There is a clear change in the slope of the load deflection curve when the concrete cracks in the tension zone, as indicated by the point ‘ ? ’ in Figure 5 (where the displacement is</p&

53、gt;<p>　　approximately 5 mm) in each of the curves.</p><p>　　The attainment of the compressive strength of concrete at the compressive face (indicated by ‘ × ’) is delayed relative to the yieldi

54、ng of the tension reinforcement (point ‘+’) as the plate thickness increases. For example, point ‘ × ’ occurs before point ‘+’ for</p><p>　　curves with t=0 and 3 mm, while it occurs after yielding f

55、or cases with t = 6 mm and</p><p>　　above. This phenomenon indicates that the compressive resistance of the column increases when the plate thickness increases. Consistently, the increase in plate thickne

56、ss also delays the onset of concrete crushing at the compression face as indicated by the</p><p>　　points ‘◇’ in Figure 5.</p><p>　　The plating reduces the steepness of the post-peak-load descen

57、ding slope, with thicker plates giving a less steep slope, as shown in Figure 5. Similarly, an increase in bolt stiffness also reduces the slope of the descending branch up to the point ‘▲’ where the whole plate section

58、yields, as shown in Figure 6. However, Figure 6 also shows that the bolt stiffness has no effect on the descending slope once the yielding of the whole plate occurs. This is reasonable since changes in bolt stiffness c&l

59、t;/p><p>　　The plating system improves the integrity (drift capacity) of the column. As seen from Figure 5, yielding of the compression reinforcement (‘X’) and crushing of concrete in the vicinity of compressio

60、n bar (-) does not occur for the 6mm and thicker plated columns (drifts up to 8%). This signifies a vast improvement in the behaviour in the compression zone compared to the benchmark, un-plated column (t = 0 in Figure 5

61、). The points of ‘-’</p><p>　　and ‘ Ξ ’ for the 3mm plated column also occur much later than that for the benchmark</p><p><b>　　column.</b></p><p>　　The plating system

62、 improves the displacement ductility of the column. The ductility factors for the curves in Figures 5 and 6 were calculated using Eqn 1 and are shown in</p><p><b>　　Table 4.</b></p><p&

63、gt;　　From Table 4 it can be seen that the plating generally improves the ductility, with displacement ductility factors of up to 8 being calculated for retrofit columns compared to a value of 1.9 for the bare RC column (

64、t = 0). However, increasing plate thickness or bolt stiffness does not always increase the ductility of the column. Generally, a response curve has a larger ductility factor when yield of the plates or bolts is delayed.

65、It is ironic that in contrast to RC beams where ductility relies </p><p>　　P- ? EFFECTS</p><p>　　The steepness of the descending branch is an important factor affecting ductility in columns and

66、is largely decided by the P- ? effect. Without the P- ? effect, the response curve of a column has a less steep descending branch, as shown in Figure 7. It has been previously</p><p>　　shown (Wu 2002; Bernal

67、 1987; Aschleim and Montes 2003) that the P- ? effect causes a drop</p><p>　　of slope of the response curve by an additional slope of</p><p><b>　　θ = N</b></p><p><b

68、>　　L</b></p><p><b>　　(2)</b></p><p>　　as shown in Figure 7, where N is the axial load, L is the cantilever length and in this case the axial load was 22.5% of the ultim

69、ate axial load.</p><p>　　Therefore, and not surprisingly, columns with a larger axial load N have a larger drop in post-peak strength (due to larger value of θ from Eqn 2), and hence, a steeper descending sl

70、ope. However, so too do columns with a shorter length L . This latter observation with regard to the length of a column is counter-intuitive to engineering common sense that says</p><p>　　P- ?effects are

71、more prominent for longer members. For example, two columns of length</p><p>　　L =1.218 m and L =0.609 m were analysed with and without P- ? effects. The results are shown in Figure 8 where it can be seen th

72、at while the shorter column was much stronger, it</p><p>　　also had a much steeper post-peak softening slope than the longer column.</p><p>　　Strength Stiffening</p><p>　　As seen in

73、 Figure 7, the descending branch from the point ‘+’ to the point ‘▲’ is less steep</p><p>　　than the curve after the point ‘ ▲ ’. This less steep part of the curve, which extends from yielding of the tension

74、 reinforcement (point ‘+’) to yielding of the plating system, as defined</p><p>　　by either full yielding of the plate (point ‘▲’) or full yielding of the bolts (point ‘ ? ’), is called</p><p>　

75、　the “strength stiffened” range of response. It is this part of curve that produces the most important advantage of the new retrofitting scheme of composite plating.</p><p>　　In order to understand what is h

76、appening in the column during the “strength stiffened” range of response, consider the cantilever column shown in Figure 9. The column is subject to an axial load N and a lateral load F . As F increases, the h

77、orizontal displacement at the</p><p>　　top of the column, ? , increases. In the ascending part of Figure 7 before the yielding point</p><p>　　‘+’, the moment resisted at the bottom cross-sectio

78、n, M? , is given by</p><p>　　M? = F? L+ N ? ?</p><p><b>　　(3)</b></p><p>　　and keeps increasing, leading to the monotonic increase of F . After yielding of the colu

79、mn</p><p>　　at a moment capacity, M(that is,</p><p>　　which is given by</p><p>　　M? = M ), if Mremains constant or reduces, F ,</p><p>　　F = M ? N? ?</p&g

80、t;<p><b>　　L</b></p><p><b>　　(4)</b></p><p>　　must decrease because the column displacement ? further increases. Therefore, to keep the</p><p>　　

81、lateral resistance F constant or to reduce its rate of decrease, M must increase all the time.</p><p>　　To counter balance the increase in the second term</p><p><b>　　N ? ? L

82、</b></p><p>　　in Eqn 4, and achieve a</p><p>　　horizontal “strength stiffened” slope (i.e. , maintain a constant strength F ), the increase in</p><p>　　M must equal N ?

83、 ? .</p><p>　　For an unplated RC column, the increase in moment resistance due to the strain hardening of the tension reinforcing bars is limited. Therefore, a sufficient increase in M is not possible u

84、nless the axial load is very small, in which case the required increase in M to</p><p><b>　　balance</b></p><p><b>　　N ? ?</b></p><p>　　is also sma

85、ll. However, it is possible to gain an adequate increase in M for</p><p>　　a plated column even with a large axial load, as illustrated by Figure 10.</p><p>　　To better understand the fundam

86、ental mechanism of the strength-stiffening phenomenon, the following analysis is conducted. Based on the force diagram shown in Figure 11, the resisting moment of a cross-section is given by</p><p>　　M = ec

87、 ? Ncomp + et ? Nst</p><p><b>　　(5)</b></p><p><b>　　where ec</b></p><p><b>　　and et</b></p><p>　　are eccentricities of<

88、/p><p><b>　　Ncomp</b></p><p><b>　　and</b></p><p>　　Nst , respectively, with respect to the</p><p>　　centriod of the cross-section and</p>

89、<p>　　Ncomp = Nconc + Nsc + Nplt = N + Nst</p><p><b>　　(6)</b></p><p>　　When the tensile reinforcement yields,</p><p><b>　　Nst</b></p&g

90、t;<p>　　can be considered as constant, hence based on</p><p>　　Eqn 6 Ncomp</p><p>　　is also then constant. Therefore, the only variable that changes in Eqn 5 is</p><p><

91、b>　　ec ,</b></p><p>　　which means that any increase in the resisting moment M can only come from an increase</p><p>　　in ec . This increase in the eccentricity ec</p>

92、<p>　　of the compressive resultant is due to the transfer</p><p>　　of compressive axial force from the RC column to the plate as shown in Figure 12. Once the plate has fully yielded in compression (po

93、int ‘ ▲ ’ in Figure 12), no further transfer of compression force can take place. This represents the end of the “strength-stiffened” range of</p><p><b>　　response.</b></p><p>　　In

94、 reality, strain hardening of the tensile reinforcement increases</p><p><b>　　Nst</b></p><p>　　slightly, which also</p><p>　　has an effect in increasing the moment resi

95、stance. However, the contribution from strain hardening of the tension bars is small compared to the effect of the lever arm increase in the compressive resultant.</p><p>　　The descending slope of the streng

96、th-stiffened region, as illustrated in Figure 7, is closely related to the stiffness of the plating system, i.e. the stiffness of the plate and bolt. Increasing the stiffness of the plating system reduces the descending

97、steepness of the strength-stiffened region, which can be seen from Figures 5 and 6. This is because the increase in the resisting moment M of the cross-section due to the strength stiffening, i.e.the transfer of axial lo

98、ad from the RC column to t</p><p><b>　　fast as</b></p><p><b>　　N ? ?</b></p><p>　　does, then M - N ? ?</p><p>　　and hence F remains constant

99、, leading to a horizontal</p><p>　　slope for the post-peak strength-stiffened region of the F - ? curve. Therefore, in order to</p><p>　　get a small descending steepness, the plating syst

100、em must be able to increase the moment resistance of the bottom cross-section at a similar rate as the P - ? effects increases the moment at the base of the column.</p><p>　　Once full yielding of either the

101、plate or all bolts occurs, defined by the points ‘▲’ and ‘ ? ’</p><p>　　respectively in Figures 5 and 6, no further extension of the strength stiffening region can take place, because no more transfer of axi

102、al load is then possible (as shown in Figure 12). Therefore, increasing the strength of the plate or bolts, by using thicker plates (or higher yield plates or FRP plates), or stronger or greater numbers of bolts, can ext