Effects of Specimen Shape and Size on Water Loss and Drying Shrinkage of Cement-based Materials

The effects of specimen size and shape on development of water loss and shrinkage of mortar and concrete respectively were investigated. The experimental results showed that the effects of specimen size and shape on water loss ratio were consistent with those on drying shrinkage strain. It is also indicated that drying shrinkage strain has obvious linear correlation with water loss ratios independent of specimen size and shape. The effects of specimen size and shape on the water loss ratio were embodied in established model of averaged relative humidity improved by considering effects of sequential hydration and calculated by finite difference method. Furthermore, the effects of specimen size and shape on drying shrinkage strain of concrete were experimentally deduced and applied to modify criterion EB-FIP1990. The comparison between experimental and calculated results shows that the modified EB-FIP1990 can be adopted to predict drying shrinkage strain of concrete with reasonable accuracy.

Pre-reinforcement grout in fractured rock masses and numerical simulation for optimizing shrinkage stoping configuration

Proper room and pillar sizes are both critical factors for safe mining and high ore recovery rate in shrinkage stoping mining of underground metal mines. The rock masses of Tangdan copper mine of China are fractured, which needs much reinforcement and support prior to mining. Cement-sodium silicate grout technology was selected, then its related parameters such as grout pressure, diffusion radius and time were calculated and proposed. In order to test the effect of the pressured grout in the fractured No.4 ore block, field experiments were conducted. To optimize stoping configuration, three-dimensional numerical simulation with ANSYS and FLAC 3 D softwares was proposed. The results show that the drilling porosity and mechanical properties of the rock masses are increased obviously. After grout, ore recovery rate is increased by 10.2 % employing the newly designed stoping configuration compared with the previous. Last, analyzed from the surface movements, roof subsidence and the maximum principal stress of the pillars, the mining safety is probable of being ensured.

Influences of Reinforcement on Differential Drying Shrinkage of Concrete

Shrinkage strain of concrete specimen with different reinforcement configuration was measured at various depths from the exposed surface by using several pairs of displacement sensors. Only one surface of the concrete specimen was exposed to dry condition during the experiment. The results show that differential shrinkage strain occurs in both plain and steel reinforced concrete specimens according to depths from the exposed surface. A higher reinforcement ratio results in a greater restraint against shrinkage of concrete nearby reinforcement rebar and a worse differential shrinkage strain distribution in the concrete specimen. The restraint against shrinkage of concrete becomes lower with the increasing distance from reinforcement rebar. Under the same reinforcement arrangement, a higher free shrinkage of concrete leads to a stronger restraint against shrinkage and a higher shrinkage stress formation in local concrete. The relationship between shrinkage strain and reduction of relative humidity in reinforced concrete structure is far different from that in plain concrete.

抗结核固定剂量复合剂对初治活动性肺结核患者病灶吸收效果的影响

目的探讨抗结核固定剂量复合剂对初治活动性肺结核患者病灶吸收效果的影响。方法便利选取2021年2月—2023年1月福州结核病防治院收治的初治活动性肺结核患者64例为研究对象,按照随机数表法分为两组。对照组(32例)给予常规抗结核药物治疗,观察组(32例)实施抗结核固定剂量复合剂治疗。对比两组治疗总有效率、痰菌阴转率、病灶吸收情况、不良反应。结果观察组总有效率为93.75%,高于对照组的75.00%,差异有统计学意义(χ^(2)=4.267,P<0.05)。观察组第2、5、6个月的痰菌阴转率均高于对照组,差异有统计学意义(P均<0.05)。治疗第2、6个月,两组患者病灶吸收情况相比,差异无统计学意义(P>0.05)。两组不良反应发生率相比,差异无统计学意义(P>0.05)。结论在初治活动性肺结核患者中应用抗结核固定剂量复合剂治疗效果显著,能够增强病灶吸收率,提高痰菌阴转率。

“孤岛效应”:大都市穿孔式收缩空间联系研究——基于武汉青山区的实证

以武汉青山区(含化工区)为例,采用定性定量相结合的方式,测度物质和社会空间联系,对大都市穿孔式收缩空间联系展开探讨,并验证其“孤岛效应”的存在。结果表明:1)青山区存在路网可达性低和交通设施不均衡分布等问题,内外物质空间联系相对薄弱,是导致“孤岛效应”产生的重要因素;2)青山区存在基础设施弱化且不均衡分布、对外吸引力差及政策层面独立发展等特征,内外社会空间联系相对不足。上述因素间相互影响,共同推动青山区“孤岛效应”的产生;3)因大都市穿孔式收缩常伴随着“孤岛效应”出现,各城市在后续发展过程中应加快推进交通网络连通和公共空间建设,规避空间联系层面的孤立和封闭。同时应重视不均衡发展问题,加快推动区域间合作及人才引进等相关政策落实。

基于热分析技术的球墨铸铁球化率和收缩特性预测

针对球铁生产中存在的缩孔、缩松和球化不良等铸造缺陷导致废品率较高的问题,开展基于热分析技术的球铁球化率和收缩特性的预测研究。使用特定的热分析样杯进行铁液取样分析,在浇注目标成分铁液后,多路温度采集系统记录试样凝固温度曲线,计算了液相线温度TL、共晶最低温度TEU、共晶最高温度TER特征温度,并以这些特征值为变量,通过多元线性回归方法建立了预测收缩率和球化率的数学模型。经现场试验测试,采用模型预测收缩率和球化率的平均误差分别不超过1%和2%。

Evolution and Determinants of Population Agglomeration in Less Developed Metropolitan Areas:A Case Study of the Taiyuan Metropolitan Area,China

It is of importance to enhance the urban areas'capacity for population aggregation in underdeveloped regions,aiming to rectify the imbalanced and insufficient pattern of economic development in China.Taking the Taiyuan Metropolitan Area(TMA)in central China as a case study,this paper examines the evolutionary process and characteristics of population agglomeration from 2000 to 2020,and identifies factors associated with agglomeration and their spatial effects.The findings indicated that:1)against the background of sustained population shrinkage in the provincial area,the TMA showed a demographic trend of steady increase,albeit with a decelerated growth rate.In the metropolitan area,urban population size continued to grow rapidly,whereas the rural areas endured sustained losses.Disparities in city size continued to widen,and the polarization of concentrated population in the core cities kept increasing.2)Agglomerations in both secondary and service industries had significant positive effects on local population agglomeration,with the former effect being stronger.Regional economic development,government fiscal expenditure,and financial advancement all contributed to facilitating local population clustering.From a spatial spillover perspective,service agglomeration and financial development promoted population agglomeration in surrounding areas.Conversely,fiscal expenditure inhibited such agglomeration.As for industrial agglomeration and regional economic development,their spatial spillover effects were non-significant.The results obtained reveal several policy implications aimed at enhancing the population agglomeration capacity of the metropolitan area in underdeveloped regions during the new era.

Influence of cutterhead opening ratio on soil arching effect and face stability during tunnelling through non-uniform soils

Tunnelling has increasingly become an essential tool in the exploration of underground space.A typical construction problem is the face instability during tunnelling,posing a great threat to associated infrastructures.Tunnel face instability often occurs with the soil arching collapse.This study investigates the combined effect of cutterhead opening ratio and soil non-uniformity on soil arching effect and face stability,via conducting random finite-element analysis coupled with Monte–Carlo simulations.The results underscore that the face stability is strongly associated with the evolution of stress arch.The obtained stability factors in the uniform soils can serve as a reference for the design of support pressure in practical tunnelling engineering.In addition,non-uniform soils exhibit a lower stability factor than uniform soils,which implies that the latter likely yields an underestimated probability of face failure.The tunnel face is found to have a probability of failure more than 50%if the spatial non-uniformity of soil is ignored.In the end,a practical framework is established to determine factor of safety(FOS)corresponding to different levels of probability of face failure considering various opening ratios in non-uniform soils.The required FOS is 1.70 to limit the probability of face instability no more than 0.1%.Our findings can facilitate the prediction of probability of instability in the conventionally deterministic design of face pressure.

Comparative Analysis of Energy Characteristics of Two Southwest Vortices in Sichuan Under Similar Circulation Backgrounds

Based on ERA5 reanalysis data,the present study analyzed the thermal energy development mechanism and kinetic energy conversion characteristics of two extreme rainstorm processes in relation to the shallow southwest vortex in the warm-sector during a“rain-generated vortex”process and the deep southwest vortex in a“vortex-generated rain”process.The findings were as follows:(1)During the extreme rainstorm on August 11,2020(hereinafter referred to as the“8·11”process),intense surface heating and a high-energy unstable environment were observed.The mesoscale convergence system triggered convection to produce heavy rainfall,and the release of latent condensation heat generated by the rainfall promoted the formation of a southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy preceded the increase(decrease)in vorticity.By contrast,the extreme rainstorm on August 16,2020(hereinafter referred to as the“8·16”process)involved the generation of southwest vortex in a low-energy and highhumidity environment.The dynamic uplift of the southwest vortex triggered rainfall,and the release of condensation latent heat from rainfall further strengthened the development of the southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy exhibited a delayed progression compared to the increase(decrease)in vorticity.(2)The heating effect around the southwest vortex region was non-uniform,and the heating intensity varied in different stages.In the“8·11”process,the heating effect was the strongest in the initial stage,but weakened during the vortex's development.On the contrary,the heating effect was initially weak in the“8·16”process,and intensified during the development stage.(3)The available potential energy of the“8·11”process significantly increased in kinetic energy converted from rotational and divergent winds through baroclinic action,and the divergent wind energy continued to convert into rotational wind energy.By contrast,the“8·16”process involved the conversion of rotational wind energy into divergent wind energy,which in turn converted kinetic energy back into available potential energy,thereby impeding the further development and maintenance of the southwest vortex.

异种胶原基质在种植体周角化黏膜增宽中的美学效果评价

目的评价异种胶原基质在种植体周角化黏膜增宽中的稳定性及美学效果,为异种胶原基质材料的临床应用提供参考依据。方法获得医院伦理委员会审批及患者知情同意,收集2020年7月至2022年9月于滨州医学院附属烟台口腔医院因种植位点颊侧角化黏膜宽度(keratinized mucosa width,KMW)<2 mm行角化黏膜增宽的20例患者,共纳入36颗种植体,年龄(52.0±10.4)岁,其中女性18例,男性2例。根据移植材料的不同分为游离龈移植(free gingival graft,FGG)对照组和异种胶原基质试验组。测量术后1、3个月种植体颊侧KMW的增量效果及黏膜收缩率,评价术后黏膜瘢痕指数(mucosal scarring index,MSI)。结果术后3个月对照组的KMW为(3.67±1.06)mm,试验组的KMW为(2.96±0.98)mm,差异有统计学意义(t=2.076,P<0.05)。术后1个月试验组KMW收缩率为(33.34±16.30)%,对照组为(22.05±15.47)%,差异有统计学意义(P<0.05);术后3个月试验组KMW收缩率为(51.95±12.60)%,对照组为(37.44±16.30)%,差异有统计学意义(P<0.05)。术后3个月试验组在瘢痕5项指标中(瘢痕宽度、瘢痕凸度、瘢痕颜色、缝合痕迹、整体外观)均优于对照组,差异具有统计学意义(P<0.05)。结论异种胶原基质在种植体周角化黏膜增宽中可以增加KMW,同时获得更加自然协调的软组织美学效果,但具有较大的收缩率。

超深竖井封底混凝土浇筑温度效应研究

南京沉井式智能停车设施建设项目采用新型超深装配式竖井建造技术,依托该工程,采用理论分析及有限元计算方法,对超深竖井封底混凝土浇筑温度效应进行研究,探讨温度收缩对封底混凝土与竖井结构接触面的影响,并结合工程特点提出合理化的设计施工控制措施。结果表明:对于超深竖井结构,封底混凝土浇筑温度效应会引起水平收缩变形,进而影响封底混凝土与竖井结构接触面的咬合;采用理论计算封底混凝土浇筑因温度效应引起的水平收缩变形量与有限元计算所得结果基本一致,最大值相差约为8%;封底混凝土因温度效应引起的水平收缩变形会影响封底混凝土与竖井结构接触面的抗剪性能及防水性能,需采取控制措施。

简支预应力混凝土箱梁的收缩徐变效应研究

采用有限元方法对60m简支预应力混凝土箱梁的收缩应变、徐变应变与混凝土龄期之间的关系,收缩徐变效应对简支箱梁的竖向变形的影响,以及收缩徐变效应引起的预应力损失对简支箱梁的竖向变形的影响进行了研究。研究结果表明,在浇筑结束至龄期100d范围内,收缩徐变应变随龄期增长呈现出线性快速增长态势;龄期超过100d后,应变增大速度逐渐减缓;在混凝土浇筑结束至龄期25d时间范围内,徐变变形随龄期增长呈线性快速增长趋势;随混凝土龄期进一步增长,徐变变形增速减缓;在混凝土浇筑结束至龄期140d范围内,收缩徐变效应导致的预应力损失引起主梁最大下挠2.3mm,龄期达1000d时的主梁下挠最大值为4.0mm。

公路T梁桥双侧拼宽技术要点及力学效应研究

以青银高速公路太原联络线项目郭家沟大桥双侧拼宽为工程背景,研究了公路T梁桥双侧拼宽时新旧桥间连接型式及拼宽施工工艺等问题,运用midas Civil有限元程序,分析了新旧桥沉降差和新旧混凝土收缩徐变影响下的拼宽桥梁力学性能,提出了设计施工关键技术要点及相应控制措施,为日后类似工程的设计、施工及后期管养提供了参考依据。

Clamped-end effect on static detection signals of DNA-microcantilever

Boundary constraint induced inhomogeneous effects are important for mechanical responses of nano/micro-devices.For microcantilever sensors,the clamped-end constraint induced inhomogeneous effect of static deformation,so called the clamped-end effect,has great influence on the detection signals.This paper is devoted to developing an alternative mechanical model to characterize the clamped-end effect on the static detection signals of the DNA-microcantilever.Different from the previous concentrated load models,the DNA adsorption is taken as an equivalent uniformly distributed tangential load on the substrate upper surface,which exactly satisfies the zero force boundary condition at the free-end.Thereout,a variable coefficient differential governing equation describing the non-uniform deformation of the DNA-microcantilever induced by the clamped-end constraint is established by using the principle of minimum potential energy.By reducing the order of the governing equation,the analytical solutions of the curvature distribution and static bending deflection are obtained.By comparing with the previous approximate surface stress models,the clamped-end effect on the static deflection signals is discussed,and the importance of the neutral axis shift effect is also illustrated for the asymmetric laminated microcantilever.

东北地区人口收缩的经济效应与对策响应

东北地区人口收缩问题具有典型性,全面审视东北地区人口收缩空间格局,科学判断人口收缩程度,探讨人口收缩的经济效应具有重要意义。从人口收缩内涵入手,利用收缩指数对2009—2020年东北地区34个地级市及以上城市进行人口收缩的测度,利用空间自相关分析其空间相关性,并运用多元回归分析探究人口收缩的经济效应。结果表明:东北地区除长春市、沈阳市和大连市外,其他91.18%的城市均存在不同程度的人口收缩现象,资源枯竭型城市是人口收缩最典型的区域;东北地区城市人口收缩空间差异显著,呈现由南向北递增趋势;“高—高”集聚区主要分布在南部哈—大经济带,“低—低”集聚区位于北部资源枯竭型城市,少数“低—高”集聚区主要位于“高—高”集聚区外围,没有形成明显集聚中心;城市人口收缩“高—高”集聚区与“低—低”集聚区随时间变化呈现出“南北”分异现象;沈阳市和大连市是未来东北地区人口集聚的集中区域;东北地区人口收缩引起负面的经济效应;科教投入水平在沿海型和资源型城市对经济产出率的影响作用力相反;人口收缩制约了经济密度、就业密度、能源供应水平的提高,加深了人口老龄化程度。据此,应科学制定人口发展战略、明确精明收缩的发展理念、积极融入城市群以及优化产业结构等,寻求人口收缩地区城市发展的新出路。

Non-uniform,axisymmetric misfit strain:in thin films bonded on plate substrates/substrate systems:the relation between non-uniform film stresses and system curvatures

Current methodologies used for the inference of thin film stress through curvature measurements are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate system. By considering a circular thin film/substrate system subject to non-uniform, but axisymmetric misfit strain distributions in the thin film, we derived relations between the film stresses and the misfit strain, and between the plate system＇s curvatures and the misfit strain. These relations feature a “local” part which involves a direct dependence of the stress or curvature components on the misfit strain at the same point, and a “non-local” part which reflects the effect of misfit strain of other points on the location of scrutiny. Most notably, we also derived relations between the polar components of the film stress and those of system curvatures which allow for the experimental inference of such stresses from full-field curvature measurements in the presence of arbitrary radial non-uniformities. These relations also feature a “non-local” dependence on curvatures making a full-field measurement a necessity. Finally, it is shown that the interfacial shear tractions between the film and the substrate are proportional to the radial gradients of the first curvature invariant and can also be inferred experimentally.

长期效应下不同边界钢-混凝土组合梁挠度分析

为了研究长期荷载效应对钢-混凝土组合梁挠度的影响,本文对不同边界钢-混凝土组合梁进行分析。考虑组合梁的剪切变形、层间滑移及剪力滞效应,引入长期荷载下的混凝土收缩徐变作用,运用能量法和变分原理推导出均布荷载作用下不同边界条件的组合梁长期挠度解析解,并通过有限元和试验结果验证了解析解的正确性。通过简支组合梁、固结组合梁和连续组合梁3个算例的挠度分析结果表明:长期荷载作用对组合梁总挠度影响较大,对两跨连续梁尤其显著;除长期荷载影响外,简支组合梁挠度主要受层间滑移作用的影响,两端固结梁挠度主要受剪切变形和层间滑移作用的影响,两跨连续组合梁挠度主要受层间滑移作用的影响;3种不同边界条件的钢-混凝土组合梁挠度受剪力滞效应的影响最小。

考虑孔隙压缩及煤基质收缩效应的煤层气井产能预测模型及影响因素

煤层气井产能预测中仅考虑应力敏感效应而忽略基质孔隙收缩效应导致产能评价误差较大。在分析非达西作用、煤基质收缩作用的基础上,建立了考虑孔隙压缩及煤基质收缩效应的煤层气产能预测模型。结果表明:考虑非达西效应的煤层气井产量明显低于不考虑非达西效应的产量,并且随着生产压差的增大,二者之间的产量差异逐渐扩大;煤层气井井底流压的减小会导致生产压差增加,相应煤层气井的产量增大幅度下降;无论考虑非达西效应与否,随着生产压差的增大,产量差值逐渐增大;随着孔隙压缩系数的增大,煤层相对渗透率逐渐降低,并且相对渗透率与生产压差呈线性关系。实例验证表明,新的产能预测模型比Eclipse模型更接近实际产气量。研究成果可为煤层气井产能预测影响因素分析提供理论指导与技术参考。

温度效应和混凝土收缩对单阶柱计算长度系数的影响分析

对于大体积混凝土结构而言,其计算长度系数受温度效应和混凝土收缩两者的影响很大,在分析计算长度系数时,不能忽略这两种因素的影响。基于此,文中先引入了考虑温度侧向变形Δ和混凝土收缩变形ε_(y)^(0)的独立柱屈曲方程,然后在此基础上,推导出了单阶柱在同时在两者影响下的屈曲方程,最后系统地分析了对计算长度系数μ_(2)的影响。结果表明,当同时考虑温度效应和混凝土收缩时,单阶柱的计算长度系数会增大,且临界力参数η_(1)和线刚度比K_(1)越大或温度侧向变形与混凝土收缩变形之和Δ+ε_(y)^(0)h越大,计算长度系数的差异就越明显。

考虑尺寸效应的大尺寸混凝土干燥收缩预测方法研究

国内外规范均基于小尺寸试件的实测数据提出混凝土的干燥收缩模型,未充分考虑试件尺寸效应的影响,因而其对大尺寸混凝土的干燥收缩的预测精度较低。基于此,首先对典型的混凝土干燥收缩模型(EC2模型及B3模型)的特点进行评述,明晰构件截面形式与尺寸效应对干燥收缩的影响规律;基于收集的15组混凝土收缩试验结果评价规范模型的可靠性,进而提出考虑尺寸效应的大尺寸混凝土干燥收缩模型。研究结果表明,现有的规范模型可有效预测小尺寸混凝土的干燥收缩变形,但会低估大尺寸混凝土的干燥收缩终值,理论厚度大于100 mm(200 mm)时,EC2模型(B3模型)的预测结果平均低于试验结果 33.2%(40.5%);通过引入理论厚度调整系数,得到修正的EC2模型和B3模型,可以有效预测大尺寸混凝土的干燥收缩变形,预测结果与试验结果平均相差15.5%和2.0%。