Stability evaluation method of large cross-section tunnel considering modification of thickness-span ratio in mechanized operation

Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.

Assistant pullback technique for main span closure of Sutong Bridge

Sutong Bridge is a cable-stayed steel box girder bridge with a main span of 1 088 m.The erection of upper structure adopts geometry control method and requires no change to the unit's size and the structure's none-stress geometry.Before main span closure,the cantilever of girder reaches 540.8 m,the structure state is noticeably influenced by external circumstances,the main span closure face great difficulty.By abstracting the advantage of the pullback method abroad and the domestic temperature-cutting method,a new assistant pullback method have put forward and bring into practice actually.In this paper,the analysis key point of practice conditions,key parameter of practice,main measures of the method and the performance is introduced.

Effects of salinity on egg and fecal pellet production, development and survival, adult sex ratio and total life span in the calanoid copepod, A cartia tonsa:a laboratory study

The ef fects of salinity on the copepod, A cartia tonsa in terms of daily egg production rate(EPR), hatching success, fecal pellet production rate(FPR), naupliar development time and survival, sex ratio, and total life span were determined in laboratory conditions through three experiments. In experiment 1, EPR, hatching success, and FPR of individual females were monitored at salinities of 13, 20, 35 and 45 during short-periods(seven consecutive days). Results show EPR was aff ected by salinity with the highest outputs recorded at 20 and 35, respectively, which were considerably higher than those at 13 and 45. Mean FPR was also higher in 35 and 20. In experiment 2, the same parameters were evaluated over total life span of females(long-term study). The best EPR and FPR were observed in 35, which was statistically higher than at 13 and 20. In experiment 3, survival rates of early nauplii until adult stage were lowest at a salinity of 13. The development time increased with increasing of salinity. Female percentage clearly decreased with increasing salinity. Higher female percentages(56.7% and 52.2%, respectively) were signifi cantly observed at two salinities of 13 and 20 compared to that at 35(25%). Total longevity of females was not af fected by salinity increment. Based on our results, for mass culture we recommend that a salinity of 35 be adopted due to higher reproductive performances, better feeding, and faster development of A. tonsa.

Experimental research on shear carrying capacity of H-steel concrete composite beam with small shear span ratio

In order to investigate shear carrying capacity of H-steel concrete beam with small shear span ratio,shear test on 5 H-steel concrete composite beams with small span ratio (from 0.7 to 1.1) are reported,including test design,test scheme,test method,failure characteristics and test results. Influences of shear span ratio,web of H steel and concrete on shear carrying capacity of this kind of beam are investigated. The main components comprising shear bearing capacity are analyzed. The results show that with the shear span ratio increasing,the contribution of web of H steel and concrete on shear carrying capacity decrease. Based on test data,the calculation formula of shear carrying capacity for this beam is established by curve fitting.

Dynamic behavior of single-layer latticed cylindrical shells subjected to seismic loading

The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.

Characteristics of response spectra for long-periods of main-shock recordings of the Chi-Chi earthquake

Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not reliable, which means that the seismic design code cannot accurately define seismic design requirements for long-period structures. The near-field recordings in the main-shock of the Chi-Chi earthquake have a large signal-to-noise ratio （SNR）, which makes them suitable for studying the long-period acceleration response spectrum up to 20 sec. The acceleration response spectra from 246 stations within 120 km of the causative fault are statistically analyzed in this paper. The influence of distance and site conditions on long-period response spectrum is discussed, and the shapes of the amplification spectra are compared with the standard spectra specified in the seismic design code of China. Finally, suggestions for future revisions to the code are proposed.

Dynamic genetic analysis for body weight and main length ratio in turbot Scophthalmus maximus

The objective of this study was to estimate genetic parameters of body width(BW)to body length(BL)ratio(BW/BL)and of body weight traits(BWT)in turbot,and to elucidate the genetic mechanism of the two traits during ontogeny by dynamic genetic analysis.From 3 to 27 months,BW,BL and BWT of each communally stocked fish were measured every 3 months.The BW/BL ratio was measured at different sampling ages.A twotrait animal model was used for genetic evaluation of traits.The results showed that the heritability values of BW/BL ratio ranged from 0.2168 to 0.3148,corresponding to moderate heritability.The BWT heritability values ranged from 0.2702 to 0.3479 corresponding to moderate heritability.The heritability of BW/BL ratio was lower than that of BWT,except at 3 months of age.Genetic correlation between BW/BL ratio and BWT decreased throughout the measurement period.Genetic correlations were higher than the phenotypic correlations.The current results for estimating genetic parameters demonstrate that the BW/BL ratio could be used as a phenotypic marker of fast-growing turbot,and the BW/BL ratio and BWT could be improved simultaneously through selective breeding.

Research on the Construction Characteristics of Stone-Built Folk Houses in Jiarong Tibetan Area <br/>—Take the Stone-Built Houses in Xisuo Village as an Example

The Jiarong Tibetan traditional residence is a characteristic regional architecture, located in a high-intensity, high-altitude and cold area, with geographic identification, and is a typical representative of this ethnic group. It has also become an important tourist destination and has important research value. The research used the methods of field survey surveying and mapping to conduct field survey and surveying on 20 buildings in Xisuo Village, a traditional village in the Jiarong Tibetan area. Measure building plans, elevations, and building sections, and collect measurement data for statistical analysis. The results show that the average total height of the building is 10.08 m, the average total building span is 12.44 m, the average total depth is 10.87 m, and the squareness is 0.87. The square shape of the building is more in line with the seismic requirements of high-intensity areas and the local terrain environment. The maximum window-wall ratio in the building is 0.18 south for the second floor, and 0.025 west for the first floor. Smaller window-to- wall ratios have better adaptability to high-altitude cold areas. The height of the building beam section is generally from 0.17 m to 0.32 m, and the average Beam span-depth ratio is 0.10. The building space construction has a good match with the properties of wood materials. These conclusions quantitatively analyze the characteristics of stone-built houses in high-intensity, high-altitude and cold areas, supplement the research on ethnic regional architecture, and provide materials and references for the design, repair and update of related buildings.

深井松软围岩煤巷采动增跨效应及防控技术

针对深井松软煤巷围岩变形严重、巷道支护困难等问题,以城郊煤矿LW21106工作面沿空巷道为工程背景,建立了采动巷道增跨模型,揭示了采动增跨效应演化机理。通过构建巷道顶板横纵弯曲梁模型,指出顶板横向受力、巷道等效跨度、煤岩强度是巷道围岩损伤破坏的主控因素,提出了采动增跨效应防控对策并进行工业性试验。研究结果表明:受采动影响,巷道经历“初始围岩稳定—围岩裂隙发育扩展—围岩剪切破坏加剧—等效跨度增加”过程;巷道顶板最大正应力与应力集中系数、顶板等效跨度、巷道断面尺寸及埋深成正相关关系;巷道顶板在高应力环境下易发生拉剪破坏,增加顶板锚索数量以及锚索预紧力有利于增强顶板初期完整性。基于巷道变形破坏主控因素,提出“围岩加固–卸压–强化支护”协同防控策略;针对现场条件,采用煤柱侧向切顶+注浆加固并对破碎区域补充锚索强化支护的防控技术。现场监测结果表明,煤柱帮最大移近量为18.89cm,顶板下沉量为25.86cm,两帮移近量为29.65 cm,有效控制了煤巷围岩变形,为深井松软围岩巷道变形控制提供了参考。

复合空间索对大跨度铁路悬索桥横向刚度影响的研究

为提升大跨度铁路悬索桥的横向刚度,提出一种由主、副斜拉索组成的复合空间索结构。然后,基于材料有效利用率和静力分析,对复合空间索的直径、主斜拉索在加劲梁和地表的锚点位置、副斜拉索的数量等参数进行了优化。最后,采用风-车-桥耦合振动分析法,基于行车性能得到了桥梁横向挠跨比限值,分析了主、副斜拉索对横向挠跨比限值提升率的影响。结果表明:基于材料有效利用率,主斜拉索与加劲梁的锚点位置宜设在1/4主跨附近,且主斜拉索的地表锚点、加劲梁锚点与桥塔的垂直距离相等时最优,每组复合空间索中副斜拉索设置1根即可;在复合空间索的最优布置形式下,桥梁横向挠跨比可降低14.18%,横向挠跨比限值可提升16.79%。

考虑硬化历史的圆筒形件二次拉深极限拉深比的解析模型

以圆筒形件二次拉深成形为例,基于主应力法和板料弯曲理论,考虑材料硬化历史、壁厚比t_(min)/t_(max)、凹模圆角半径和摩擦因数的影响,建立了一种预测圆筒形件二次拉深极限拉深比的解析模型,并对SUS304不锈钢板料进行了拉深试验验证。结果表明:解析模型的预测值与试验结果吻合较好;考虑硬化历史的解析模型与未考虑硬化历史的模型相比二次拉深极限拉深比相差约10%;摩擦因数、凹模圆角半径对二次拉深极限拉深比有显著影响,摩擦因数越大,二次拉深极限拉深比越小;凹模圆角半径越大,二次拉深极限拉深比越大。

四主缆大跨悬索桥抗震性能分析及减震措施优化

以燕矶长江大桥为工程背景,首先,采用动力非线性时程法分析了燕矶长江大桥抗震性能,并研究了设置电涡流-摩擦组合型阻尼器和黏滞阻尼器对大跨悬索桥抗震性能的影响;然后,对附加电涡流-摩擦组合型阻尼器摩擦力、阻尼系数和阻尼指数开展了参数敏感性分析;最后,从耗能角度分析地震作用下电涡流-摩擦组合型阻尼器减震特点.结果表明:在E2地震作用下,桥塔关键截面抗弯能力均大于弯矩需求;在“纵向+竖向”地震作用下梁端纵向位移较大.设置塔梁处纵桥向阻尼器后,可有效降低主桥梁端纵向位移;增大摩擦力、阻尼系数与降低阻尼指数均可提升梁端纵向地震响应的控制效果,但参数变化对桥塔控制截面的地震响应影响较小.阻尼系数较大时,电涡流阻尼主导了电涡流-摩擦组合型阻尼器耗能,相较于黏滞阻尼器,电涡流-摩擦组合型阻尼器对梁端纵向位移控制效果更好.

深江铁路洪奇沥公铁大桥主桥设计关键技术

研究目的:洪奇沥公铁大桥是深江铁路的控制性工程,主桥采用主跨808 m公铁合建斜拉桥一跨跨越洪奇沥水道,上层布置8车道城市快速路,下层布置4线铁路。结合建设条件、结构特点及使用性能,对主桥结构体系、主梁横断面及结构形式、索-塔锚固结构、施工方法等关键技术展开研究,确定技术合理可行和经济节约的设计方案。研究结论:(1)首创了短边跨叠合板-桁组合梁斜拉桥结构体系,主桥长度减少20%,节省工程投资;(2)首次在4线铁路公铁合建斜拉桥上采用倒梯形双主桁截面,桥面布置紧凑、受力明确;(3)提出的边跨主梁采用矩形钢管混凝土叠合板-桁组合结构,集结构受力和锚固压重于一体,施工便捷;(4)发明了“自平衡交叉锚固+齿块锚固”的索-塔混合锚固方式,技术经济性高;(5)钢主梁创新采用“纵向大节段+横向分块”施工方法,解决了超宽超高超重整节段钢桁梁运输受既有桥净空限制的难题;(6)本研究成果可为公铁合建桁梁斜拉桥设计提供参考或借鉴。

水平往复荷载作用下钢箱提篮拱弹塑性力学性能研究

目的 探究倾角、矢跨比及宽跨比三个参数对钢箱提篮拱在水平往复荷载作用下力学性能的影响,为钢提篮拱桥抗震设计提供理论基础。方法 通过改变参数,建立54个钢箱提篮拱有限元模型,在水平往复荷载作用下进行滞回分析,研究钢箱提篮拱水平力-位移滞回性能、极限承载力和拱顶横撑内力、变形在不同参数条件下的变化规律。结果 随着拱肋倾斜角度、宽跨比的增加或矢跨比的减小,结构初期刚度、极限承载能力均有较大提高,但横撑内力也随之增加,并会产生局部失稳破坏,影响结构的承载能力。结论 增加拱肋倾斜角度对钢箱提篮拱横向力学性能有较大改善,但在设计时应注意横撑内力增加带来的不利影响。

大跨度铁路桥附属构件对不同宽高比矩形断面涡振性能的影响

在已建成的大跨度鳊鱼洲长江大桥原设计宽高比为6.7∶1的四线铁路桥矩形箱型主梁断面的基础上,通过调整断面宽高比,设计宽高比为4∶1的二线铁路和宽高比为9∶1的六线铁路桥矩形箱梁断面。通过节段模型风洞试验,在0°,±3°和±5°风攻角的均匀来流下,对以上3种常用二线、四线和六线铁路桥矩形箱梁断面与对应相同宽高比纯矩形断面之间的涡振特性关系,以及铁路桥附属构件对不同宽高比矩形断面涡振性能的影响进行研究。结果表明:在宽高比分别为4∶1和6.7∶1的矩形断面上布置铁路桥附属构件能增大断面在负风攻角下的涡振振幅,在-5°风攻角下竖向涡振振幅增大率高达277.5%,但对正风攻角下的涡振响应起到一定的抑制作用,而在宽高比为9∶1的矩形断面布置六线铁路桥附属构件则能明显增大该断面在各风攻角下的涡振振幅,其扭转涡振振幅增大率均在48.3%以上;铁路桥附属构件对矩形断面涡振性能的降低作用随着断面宽高比的增大而提升,针对气动外形较钝的二线和四线铁路桥箱梁,可参考相似宽高比矩形断面涡振特性,并重点考察箱梁在负风攻角下的涡振响应,而针对宽高比较大的六线铁路桥箱梁,由于附属构件影响较大,参考相似宽高比矩形断面涡振特性的意义较小,均应详细研究其在各风攻角下的涡振性能。

嵌入式H型钢梁柱节点受力性能研究

为解决传统标准梁柱节点施工复杂、节点强度低等一系列问题,提出一种嵌入式H型钢梁柱节点结构形式,并设计4个梁柱节点试件(1个标准现浇梁柱节点试件,3个嵌入式H型钢梁柱节点试件)进行试验研究,设置型钢翼缘宽度、剪跨比为主要参数,对4个试件的破坏形态、承载力、变形能力进行对比分析。结果表明:嵌入式H型钢梁柱节点试件的节点核心区柱端混凝土裂缝较少,裂缝分布和破坏位置基本上发生于梁端,充分满足了“强柱弱梁”的设计要求;相较于标准现浇梁柱节点试件,嵌入式H型钢梁柱节点试件峰值承载力、极限承载力、变形能力均显著提高,当型钢翼缘加宽时,试件峰值承载力和极限承载力提升较为有限,当剪跨比大于2.7时,承载力将会明显降低。

超大跨劲性骨架拱桥缩尺模型试验方案设计研究

为对超大跨劲性骨架拱桥缩尺模型试验方案进行合理设计,以计算跨径600 m的劲性骨架拱桥——天峨龙滩特大桥为背景,围绕模型缩尺比、结构设计、材料及加载系统等关键环节,开展主拱圈缩尺模型试验方案设计研究。最终确定模型拱缩尺比为1∶10,劲性钢骨架采用单肋形式,采用与实桥主拱圈性能相近、便于施工的材料,采用阵列式滑轮组加载系统实现模型拱和实桥主拱圈的应力等效,还原外包混凝土分环分段浇筑施工,并简化劲性钢骨架与管内混凝土施工。将模型拱外包混凝土应力实测值、ANSYS建模计算得到的模型拱理论值及实桥主拱圈理论值进行对比,结果表明:模型拱和实桥主拱圈外包混凝土在施工阶段的应力变化趋势基本相同,最大绝对误差在2 MPa以内,模型拱应力实测值和理论值也吻合较好,缩尺模型试验方案设计合理。

我国乡村老龄化现状及其对粮食生产的影响与应对

根据2020年最新人口普查数据,我国乡村老龄化率为17.72%,先于城市步入中度老龄化社会。我国乡村老龄化整体呈现出老年抚养比增速快、低龄老人务农比例高等特征,与国际主要发达国家相比我国乡村老龄人口就业占比相对较高。分区域看,粮食主产区乡村老龄化增幅更多、老年抚养比更重、老龄就业比重更高;全国乡村老年抚养比28.13%,但粮食主产省份达31.28%。通过定性梳理乡村老龄化对农户参与粮食种植及其粮食生产行为效率等的影响,提出积极应对乡村老龄化、保障粮食安全的思路与对策建议。

大跨度桥梁超低频调谐液体质量阻尼器研发及应用

大跨度桥梁在运营过程中易发生较为明显的超低频振动问题,采用调谐质量阻尼器(TMD)进行控制时,由于箱梁内部空间有限,常规TMD在结构上无法满足要求。基于此,提出一种基于浮力和流固耦合作用的超低频调谐液体质量阻尼器(TLMD)。为研究TLMD对结构的阻尼减振效果,进行模型试验,分析安装TLMD前、后主结构加速度幅值和阻尼比;将该新型超低频TLMD在贵州龙里河大桥上进行实桥应用,测试主梁频率特性和阻尼比。模型试验及实桥应用结果表明:TLMD减振技术可实现0.283 Hz乃至更低频率的超低频阻尼减振;采取TLMD控制后,模型试验主结构的阻尼比从0.038%提高至2.2%,主结构的加速度幅值从减振前的0.41 m/s2降低至0.01 m/s2;贵州龙里河大桥超低频TLMD当采用0.31%的质量比时,主梁一阶竖弯模态实测阻尼比从0.20%提高至0.82%,阻尼比提高了3.1倍。超低频TLMD参数稳定、性能可靠,有效降低了阻尼器的安装高度,显著提升了结构阻尼比,增强了桥梁的抗风性能。