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懸索橋施工期主纜—貓道系統(tǒng)馳振及靜風(fēng)穩(wěn)定性的干擾效應(yīng)

發(fā)布時(shí)間:2018-08-17 14:13
【摘要】:在強(qiáng)風(fēng)作用下,部分大跨懸索橋施工期主纜在繩索的張拉下振動(dòng)幅度較大,嚴(yán)重影響施工工期;且因施工期主纜并非成橋時(shí)圓形截面形式,存在馳振失穩(wěn)的可能性;同時(shí),貓道的存在對(duì)施工期大尺度尖頂型主纜靜風(fēng)系數(shù)存在氣動(dòng)干擾效應(yīng)問(wèn)題,可能影響主纜的馳振性能。因此,進(jìn)行大跨徑懸索橋暫態(tài)結(jié)構(gòu)抗風(fēng)性能具有較高的理論和實(shí)際意義。鑒于此本文進(jìn)行了如下主要研究工作:1.本文采用CFD數(shù)值模擬方法,參考某大橋施工期貓道和主纜設(shè)計(jì)參數(shù),首先結(jié)合貓道風(fēng)洞試驗(yàn)的結(jié)果,驗(yàn)證了數(shù)值模擬參數(shù)設(shè)置的正確性;然后分別研究了不考慮貓道和考慮貓道影響時(shí),施工期三角形、五邊形和尖頂型形狀主纜的阻力和升力系數(shù);最后利用登哈托準(zhǔn)則,計(jì)算了施工期主纜不同工況的馳振力系數(shù)。結(jié)果表明:隨著主纜索股層數(shù)的不斷增加,施工初期呈倒三角形形狀的主纜阻力系數(shù)不斷減小,升力系數(shù)逐步增加;施工中期呈五邊形形狀的主纜阻力系數(shù)不斷增加,升力系數(shù)逐步減小;施工后期呈上尖頂型形狀的主纜阻力系數(shù)不斷增加,升力系數(shù)總體上有減小趨勢(shì);通過(guò)與無(wú)貓道工況的對(duì)比可知,考慮貓道時(shí)會(huì)造成施工期主纜阻力和升力系數(shù)相應(yīng)地減小,且計(jì)算主纜馳振力系數(shù)時(shí),不能忽略貓道的氣動(dòng)干擾效應(yīng)。2.研究表明,懸索橋施工期暫態(tài)主纜存在馳振失穩(wěn)的可能性,且因施工期主纜處于主纜施工腳手架貓道的半包圍之中,貓道設(shè)計(jì)參數(shù)的變化勢(shì)必對(duì)施工期主纜的馳振性能產(chǎn)生重要影響。為研究貓道設(shè)計(jì)參數(shù)對(duì)施工期主纜馳振性能的影響,本文以某大跨徑懸索橋施工期不同工況大尺度尖頂型主纜為研究對(duì)象,以貓道風(fēng)洞試驗(yàn)結(jié)果為參照,以流體力學(xué)軟件Fluent為工具,首先驗(yàn)證了數(shù)值模擬參數(shù)設(shè)置的正確性;進(jìn)而研究了貓道高度、貓道寬度、貓道側(cè)網(wǎng)透風(fēng)率、貓道底網(wǎng)透風(fēng)率,以及貓道面層與主纜底部間距等參數(shù)影響下施工期主纜的氣動(dòng)力系數(shù);最后運(yùn)用登哈托準(zhǔn)則分析了貓道設(shè)計(jì)參數(shù)對(duì)施工期主纜馳振性能的影響。研究結(jié)果表明:(1)貓道寬度、貓道護(hù)欄高度以及貓道面層與主纜底部間距對(duì)施工期主纜阻力系數(shù)影響不大,但會(huì)導(dǎo)致升力系數(shù)變大;當(dāng)主纜與貓道面層間距為84cm、貓道寬度為4.5m、貓道護(hù)欄高度為1.3m時(shí),對(duì)馳振失穩(wěn)預(yù)防較為有利;(2)貓道側(cè)網(wǎng)透風(fēng)率可導(dǎo)致施工期主纜阻力系數(shù)變小,但升力系數(shù)較無(wú)規(guī)律;當(dāng)貓道側(cè)網(wǎng)透風(fēng)率為50%時(shí),對(duì)馳振失穩(wěn)預(yù)防較為有利;(3)貓道底網(wǎng)透風(fēng)率對(duì)施工期主纜阻力和升力系數(shù)影響較為敏感;當(dāng)貓道底網(wǎng)透風(fēng)率為70%時(shí)對(duì)馳振失穩(wěn)預(yù)防較為有利;(4)當(dāng)貓道面層與主纜底部間距為0.84m、貓道高度為1.3m、貓道寬度為4.5m、貓道側(cè)網(wǎng)透風(fēng)率為50%和貓道底網(wǎng)透風(fēng)率為70%時(shí),主纜發(fā)生馳振失穩(wěn)可能性最小。3.由于大跨徑懸索橋施工期尖頂型主纜與貓道間存在氣動(dòng)干擾效應(yīng),且主纜索股層數(shù)在施工期不斷增加,因此,貓道的氣動(dòng)性能和靜風(fēng)穩(wěn)定性也隨之變化。本文以某大跨徑懸索橋施工期尖頂型主纜和貓道為背景,研究了施工期尖頂型主纜對(duì)貓道靜風(fēng)穩(wěn)定性影響問(wèn)題。首先,參照該橋貓道風(fēng)洞試驗(yàn)的結(jié)果,驗(yàn)證了數(shù)值模擬參數(shù)設(shè)置的正確性;進(jìn)而計(jì)算了施工期尖頂型主纜不同階段貓道的三分力系數(shù);最后對(duì)ANSYS軟件進(jìn)行了二次開(kāi)發(fā),考慮了貓道的幾何非線性和風(fēng)荷載非線性,進(jìn)行了施工期尖頂型主纜不同階段貓道靜風(fēng)穩(wěn)定性分析。研究結(jié)果表明:考慮施工期尖頂型主纜影響時(shí),(1)貓道阻力系數(shù)和扭矩系數(shù)呈先增大后減小的趨勢(shì);(2)貓道升力系數(shù)在負(fù)攻角范圍內(nèi)呈先減小后增大趨勢(shì),但在正攻角范圍內(nèi)變化不大;(3)隨尖頂型主纜的施工進(jìn)程,貓道失穩(wěn)臨界風(fēng)速呈先減小后增大,成橋階段又減小的趨勢(shì)。其中,15#工況失穩(wěn)臨界風(fēng)速接近大橋施工階段和成橋狀態(tài)10米高度處的空氣靜力穩(wěn)定性檢驗(yàn)風(fēng)速,施工時(shí)應(yīng)注意加強(qiáng)觀測(cè),必要時(shí)須采取抗風(fēng)保護(hù)措施。
[Abstract]:Under the action of strong wind, the vibration amplitude of the main cable of some long-span suspension bridges under the tension of the cable is large, which seriously affects the construction period; and because the main cable is not a circular section when the bridge is completed during the construction period, there is the possibility of galloping instability; at the same time, the existence of catwalk has the aerodynamic interference effect on the static wind coefficient of the large-scale pointed main cable during the construction period. Therefore, it is of great theoretical and practical significance to study the wind resistance of the transient structure of long-span suspension bridges. In view of this, the following main research work has been carried out in this paper: 1. In this paper, CFD numerical simulation method is used to refer to the design parameters of catwalk and main cable during the construction period of a bridge. The test results verify the correctness of the numerical simulation parameters. Then the drag and lift coefficients of triangle, Pentagon and cusp-shaped main cables during construction without considering catwalk and catwalk are studied. Finally, the galloping force coefficients of main cables under different working conditions during construction are calculated by using Denharto criterion. As the number of strands of the main cable increases, the resistance coefficient of the main cable in the inverted triangle shape decreases and the lift coefficient increases gradually in the initial stage of the construction; the resistance coefficient of the main cable in the pentagon shape increases and the lift coefficient decreases gradually in the middle stage of the construction; the resistance coefficient of the main cable in the upper cusp shape increases and the lift coefficient increases continuously in the later stage of the construction. Comparing with the working condition without catwalk, the drag and lift coefficients of the main cable will decrease correspondingly when the catwalk is considered, and the aerodynamic interference effect of the catwalk can not be neglected when the galloping force coefficients of the main cable are calculated. In order to study the influence of catwalk design parameters on the galloping performance of main cables during construction period, a large-scale pointed main cable of a long-span suspension bridge under different construction conditions is selected as the main cable in this paper. Based on the wind tunnel test results of catwalk and the fluid dynamics software Fluent, the validity of numerical simulation parameters was verified firstly, and then the influence of catwalk height, width, side net ventilation rate, bottom net ventilation rate and the distance between surface layer and bottom of main cable on the main cable under construction was studied. The results show that: (1) the width of the catwalk, the height of the catwalk guardrail and the distance between the catwalk surface layer and the bottom of the main cable have little effect on the drag coefficient of the main cable during the construction period, but the lift coefficient will become larger when the main cable and the catwalk surface are used. When the distance between layers is 84cm, the width of catwalk is 4.5m, and the height of catwalk guardrail is 1.3m, it is more advantageous to prevent galloping instability; (2) the ventilation rate of catwalk side net can reduce the resistance coefficient of main cable during construction period, but the lift coefficient is irregular; when the ventilation rate of catwalk side net is 50%, it is more advantageous to prevent galloping instability; (3) the ventilation rate of catwalk bottom net is beneficial to the construction period. The main cable resistance and lift coefficient are more sensitive; when the ventilation rate of catwalk bottom net is 70%, it is more advantageous to prevent galloping instability; (4) when the distance between catwalk surface layer and main cable bottom is 0.84m, the height of catwalk is 1.3m, the width of catwalk is 4.5m, the ventilation rate of catwalk side net is 50% and the ventilation rate of catwalk bottom net is 70%, the main cable is most likely to gallop instability. 3. The aerodynamic performance and static wind stability of the catwalk vary with the increase of the number of layers of the main cables during the construction period because of the aerodynamic interference effect between the pointed main cables and the catwalk during the construction period of the long-span suspension bridge. The influence of main cable on the static wind stability of catwalk is studied. Firstly, the correctness of numerical simulation parameters is verified by referring to the wind tunnel test results of the catwalk of the bridge; then the three-component coefficients of the catwalk at different stages of the construction period are calculated; finally, the ANSYS software is redeveloped, considering the geometric nonlinearity and wind load of the catwalk. The results show that: (1) the resistance coefficient and torque coefficient of catwalk increase first and then decrease; (2) the lift coefficient of catwalk decreases first and then increases in the range of negative angle of attack, but in the case of positive angle of attack. (3) With the construction process of the top-type main cable, the instability critical wind speed of catwalk first decreases and then increases, and then decreases at the bridge completion stage. Wind protection measures must be taken.
【學(xué)位授予單位】:鄭州大學(xué)
【學(xué)位級(jí)別】:碩士
【學(xué)位授予年份】:2015
【分類(lèi)號(hào)】:U448.25

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