Effect of a cervical collar on optic nerve sheath diameter in trauma patients

BACKGROUND:As advocated in advanced trauma life support and prehospital trauma life support protocols,cervical immobilization is applied until cervical spine injury is excluded.This study aimed to show the difference in optic nerve sheath diameter(ONSD)between patients with and without a cervical collar using computed tomography(CT).METHODS:This was a single-center,retrospective study examining trauma patients who presented to the emergency department between January 1,2021,and December 31,2021.The ONSD on brain CT of the trauma patients was measured and analyzed to determine whether there was a difference between the ONSD with and without the cervical collar.RESULTS:The study population consisted of 169 patients.On CT imaging of patients with(n=66)and without(n=103)cervical collars,the mean ONSD in the axial plane were 5.43±0.50 mm and 5.04±0.46 mm respectively for the right eye and 5.50±0.52 mm and 5.11±0.46 mm respectively for the left eye.The results revealed an association between the presence of a cervical collar and the mean ONSD,which was statistically significant(P<0.001)for both the right and left eyes.CONCLUSION:A cervical collar may be associated with increased ONSD.The effect of this increase in the ONSD on clinical outcomes needs to be investigated,and the actual need for cervical collar in the emergency department should be evaluated on a case-by-case basis.

Added value of ratio of cross diameters of the appendix in ultrasound diagnosis of acute appendicitis

BACKGROUND The maximum outer diameter(MOD)of the appendix is an essential parameter for diagnosing acute appendicitis,but there is space for improvement in ultrasound(US)diagnostic performance.AIM To investigate whether combining the ratio of the cross diameters(RATIO)of the appendix with MOD of the appendix can enhance the diagnostic performance of acute appendicitis.METHODS A retrospective study was conducted,and medical records of 233 patients with acute appendicitis and 112 patients with a normal appendix were reviewed.The MOD and RATIO of the appendix were calculated and tested for their diagnostic performance of acute appendicitis,both individually and in combination.RESULTS The RATIO for a normal appendix was 1.32±0.16,while for acute appendicitis it was 1.09±0.07.The cut-off value for RATIO was determined to be≤1.18.The area under the receiver operating characteristic curve(AUC)for diagnosing acute appendicitis using RATIO≤1.18 and MOD>6 mm was 0.870 and 0.652,respectively.There was a significant difference in AUC between RATIO≤1.18 and MOD>6 mm(P<0.0001).When comparing the combination of RATIO≤1.18 and MOD>6 mm with MOD>6 mm alone,the combination showed increased specificity,positive predictive value(PPV),and AUC.However,the sensitivity and negative predictive value decreased.CONCLUSION Combining RATIO of the appendix≤1.18 and MOD>6 mm can significantly improve the specificity,PPV,and AUC in the US diagnosis of acute appendicitis.

Simulation of Haloxylon Ammodendron Stand Basic Diameter Structure Based on Fuzzy Distribution Function

Based on the investigation data of 12 Haloxylon ammodendron plots in the south edge of Gurbantunggut Desert, Fuzzy distribution was introduced into the study of Haloxylon ammodendron base diameter structure fitting according to the consistency between the characteristics of Fuzzy distribution function and the distribution series of cumulative percentage of stand base diameter, and the fitting precision and effect of Fuzzy distribution function were discussed. The root mean square error RMSE and determination coefficient R2 values showed that Fuzzy-Γ1, Fuzzy-Γ2, Fuzzy-Γ3, Fuzzy-Γ4 had good fitting performance, among which Fuzzy-Γ1 had relatively high fitting precision, and its parameters were closely related to stand age and density, Fuzzy-Γ2 distribution function was the second, and Fuzzy-Γ4 distribution function had the worst fitting effect. By introducing a parameter c from the similarity of four distribution function formulas, a generalized Fuzzy distribution function Fuzzy-Γ5 is obtained. This function shows the highest fitting accuracy. Most of the values of parameter c are near 1 or 2, which shows that the diameter distribution is mainly approximate to Fuzzy-Γ1 and Fuzzy-Γ2.

Increased retinal venule diameter as a prognostic indicator for recurrent cerebrovascular events:a prospective observational study

Microvasculature of the retina is considered an alternative marker of cerebral vascular risk in healthy populations.However,the ability of retinal vasculature changes,specifically focusing on retinal vessel diameter,to predict the recurrence of cerebrovascular events in patients with ischemic stroke has not been determined comprehensively.While previous studies have shown a link between retinal vessel diameter and recurrent cerebrovascular events,they have not incorporated this information into a predictive model.Therefore,this study aimed to investigate the relationship between retinal vessel diameter and subsequent cerebrovascular events in patients with acute ischemic stroke.Additionally,we sought to establish a predictive model by combining retinal veessel diameter with traditional risk factors.We performed a prospective observational study of 141 patients with acute ischemic stroke who were admitted to the First Affiliated Hospital of Jinan University.All of these patients underwent digital retinal imaging within 72 hours of admission and were followed up for 3 years.We found that,after adjusting for related risk factors,patients with acute ischemic stroke with mean arteriolar diameter within 0.5-1.0 disc diameters of the disc margin(MAD_(0.5-1.0DD))of≥74.14μm and mean venular diameter within 0.5-1.0 disc diameters of the disc margin(MVD_(0.5-1.0DD))of≥83.91μm tended to experience recurrent cerebrovascular events.We established three multivariate Cox proportional hazard regression models:model 1 included traditional risk factors,model 2 added MAD_(0.5-1.0DD)to model 1,and model 3 added MVD0.5-1.0DD to model 1.Model 3 had the greatest potential to predict subsequent cerebrovascular events,followed by model 2,and finally model 1.These findings indicate that combining retinal venular or arteriolar diameter with traditional risk factors could improve the prediction of recurrent cerebrovascular events in patients with acute ischemic stroke,and that retinal imaging could be a useful and non-invasive method for identifying high-risk patients who require closer monitoring and more aggressive management.

One-year results for myopia control of orthokeratology with different back optic zone diameters: a randomized trial using a novel multispectral-based topographer

AIM:To present the 1-year results of a prospective cohort study investigating the efficacy,potential mechanism,and safety of orthokeratology(ortho-k)with different back optic zone diameters(BOZD)for myopia control in children.METHODS:This randomized clinical study was performed between Dec.2020 and Dec.2021.Participants were randomly assigned to three groups wearing ortho-k:5 mm BOZD(5-MM group),5.5 mm BOZD(5.5-MM group),and 6 mm BOZD(6-MM group).The 1-year data were recorded,including axial length,relative peripheral refraction(RPR,measured by multispectral refractive topography,MRT),and visual quality.The contrast sensitivity(CS)was evaluated by CSV-1000 instrument with spatial frequencies of 3,6,12,and 18 cycles/degree(c/d);the corneal higher-order aberrations(HOAs)were measured by iTrace aberration analyzer.The one-way ANOVA was performed to assess the differences between the three groups.The correlation between the change in AL and RPR was calculated by Pearson’s correlation coefficient.RESULTS:The 1-year results of 20,21,and 21 subjects in the 5-MM,5.5-MM,and 6-MM groups,respectively,were presented.There were no statistical differences in baseline age,sex,or ocular parameters between the three groups(all P>0.05).At the 1-year visit,the 5-MM group had lower axial elongation than the 6-MM group(0.07±0.09 vs 0.18±0.11 mm,P=0.001).The 5-MM group had more myopic total RPR(TRPR,P=0.014),with RPR in the 15°–30°(RPR 15–30,P=0.015),30°–45°(RPR 30–45,P=0.011),temporal(RPR-T,P=0.008),and nasal area(RPR-N,P<0.001)than the 6-MM group.RPR 15–30 in the 5.5-MM group was more myopic than that in the 6-MM group(P=0.002),and RPR-N in the 5-MM group was more myopic than that in the 5.5-MM group(P<0.001).There were positive correlations between the axial elongation and the change in TRPR(r=0.756,P<0.001),RPR 15–30(r=0.364,P=0.004),RPR 30–45(r=0.306,P=0.016),and RPR-N(r=0.253,P=0.047).The CS decreased at 3 c/d(P<0.001),and the corneal HOAs increased in the 5-MM group(P=0.030).CONCLUSION:Ortho-k with 5 mm BOZD can control myopia progression more effectively.The mechanism may be associated with greater myopic shifts in RPR.

Sub-stand diameter distribution types vary along an old-growth Douglas-fir chronosequence into the horizontal diversification development stage

Managing mature Douglas-fir[Pseudotsuga menziesii(Mirb.)Franco]stands to emulate the structural complexity of natural old-growth forest requires identifying structural targets at the sub-stand level at which neighborhood dynamics and patchy disturbance shape structure.We therefore sought to describe the archetypal shapes of predominant sub-stand diameter distribution types(DDTs)observed in natural tree neighborhoods in stands comprising a chronosequence(ca.120-450+yrs)encompassing mature,vertical diversification,and horizontal diversification development stages.The ten 1.0 ha stands are located in the southcentral Oregon Cascades,USA.Building on the known spatial position of each tree,natural tree neighborhoods were identified using the floating neighborhood approach based on spatial tessellation connecting neighboring trees at the first-(mean 61 m2)through fifth-(mean 2058 m2)order scales.Cluster analysis was then used to objectively identify the most predominant DDTs among the relative tree size distributions observed in the trans-scale neighborhoods within each stand.Repeated measures regression was used to classify each DDT to one of six observed archetypal shapes:negative exponential,unimodal,rotated sigmoid,bimodal,concave,or multi-modal.Only three of the 81 observed DDTs deviated by<10%from the stand average,while every stand had at least one DDT that deviated by>50%(maximum 83%).Within each stand,five to ten predominant DDTs were observed,which deviated from the stand average by 30-48%and were characterized by two to five different archetypal shapes.Consequently,in some stands the majority of tree neighborhoods were best characterized by a different shape from that assigned at the stand level.Deviation from the stand average increased from the youngest stand in the mature development stage through the middle stands in the vertical diversification stage to the oldest stands in the horizontal diversification stage.The complexity of DDT shapes tended to increase along the chronosequence(from negative exponential and uniform toward concave and multi-modal),with shape richness highest mid-sequence and evenness peaking in the oldest stands.The high diversity of sub-stand structural complexity reduces the utility of standlevel diameter distributions as old-growth restoration targets.However,the presence in early-sequence stands of sub-stand diameter distributions common to later-sequence stands may facilitate active management at the neighborhood level to promote future old-growth condition.Restoration of substand diameter structures would likely require combining spatial perspectives,such as by augmenting tree-level croptree management with diameter distribution targets for the resulting tree neighborhoods.

Alternative expressions for stand diameter in complex forests

Quadratic mean diameter is the most frequently reported descriptor of the diameter distribution of forests.As such,it is often used as an indicator of forest stand structure,developmental stage,and ecological and economic potential.However,quadratic mean diameter can be heavily influenced by the presence or absence of large numbers of small stems in lower canopy strata,and it is also sensitive to left-truncation of the diameter distribution,making its interpretation across inventories with different protocols challenging.Here,we examine three alternative expressions of stand diameter:the arithmetic and quadratic mean diameter of the thickest 100 trees per hectare,and the basal area-weighted mean diameter.Using data from the United States Forest Inventory and Analysis program for New York and New England,these alternative expressions showed closer correlation with multiple stand structural variables than did quadratic mean diameter,including merchantable cubic and board foot volume per hectare,aboveground live tree carbon per hectare,and total number of live and dead standing trees greater than 40 cm diameter at breast height per hectare(previously proposed as an index of old-growth structure).Arithmetic and quadratic mean diameter of the thickest 100 trees per hectare showed nearly identical performance,and the strongest correlations across the board.We develop closed-form expressions for these variables when the diameter distribution is a Weibull,and illustrate their behavior relative to quadratic mean diameter for that situation.While the reasons for prevalence of quadratic mean diameter as an indicator remain valid,we suggest that these alternative measures should be more widely reported and analyzed to give a more informative depiction of stand structure and development in complex forests.

定向钻井MWD工具面角数据分析

定向钻井过程中,正确地判断滑动钻进和复合钻进井段分析钻井过程是非常必要的。通过对大量实际MWD工具面角数据的观察和归纳总结,发现了滑动钻进和复合钻进的工具面角数据特征:当滑动钻进时,工具面角是围绕均值小幅波动的平稳序列;当复合钻进时,工具面角无规则地剧烈震荡。对于给定的一个数据窗口,使用频数分析方法求出了井段工具面角均值的近似值;通过定义最小波动值,求出了偏离均值的例外点集合。根据最小井段长度限制、最多例外点个数、最小波动值等参数,提出了滑动井段的判别算法。对于MWD工具面角的历史数据或者实时数据,使用数据窗口扫描方法,能从MWD工具面角数据中正确地划分出滑动钻进井段和复合钻进井段。实际钻进数据算例表明,该算法是快速、有效的。该算法既能对MWD工具面角数据做事后分析,也能用于实时在线分析。

MWD磁干扰的判断和矫正

在定向井和水平井施工过程中,用于轨迹控制的随钻测量(MWD)无线随钻测斜仪器是不可缺少的。该仪器通过探管内的磁通门传感器和重力加速的传感器测量井眼状态(井斜、方位、工具面等)。在介绍MWD仪器测量原理的基础上,分析了磁干扰的原因,并进一步的分析了施工过程中遇到磁干扰时的判断方法,以及径向轴向矫正磁干扰的简单方法,可为现场工程师提供一定的指导建议。

Measuring tree stem diameters and straightness with depth-image computer vision

Current techniques of forest inventory rely on manual measurements and are slow and labor intensive.Recent developments in computer vision and depth sensing can produce accurate measurement data at significantly reduced time and labor costs.We developed the ForSense system to measure the diameters of trees at various points along the stem as well as stem straightness.Time use,mean absolute error(MAE),and root mean squared error(RMSE)metrics were used to compare the system against manual methods,and to compare the system against itself(reproducibility).Depth-derived diameter measurements of the stems at the heights of 0.3,1.4,and 2.7 m achieved RMSE of 1.7,1.5,and 2.7 cm,respectively.The ForSense system produced straightness measurement data that was highly correlated with straightness ratings by trained foresters.The ForSense system was also consistent,achieving sub-centimeter diameter difference with subsequent measures and less than 4%difference in straightness value between runs.This method of forest inventory,which is based on depth-image computer vision,is time efficient compared to manual methods and less computationally and technologically intensive compared to Structure-from-Motion(SFM)photogrammetry and ground-based LiDAR or terrestrial laser scanning(TLS).

Accuracy of Trans-Cerebellar Diameter and Placental Thickness in Third Trimesteric Pregnant Women for Calculation of Gestational Age: A Cross Sectional Study

Background: Accurate determination of gestational age has become important for deciding the appropriate time for termination of the pregnancy as well as to monitor the fetal growth during the entire period of pregnancy. Objective: The aim of the study was to assess whether the trans-cerebellar diameter, placental thickness or combining both of them is more accurate for assessment of gestational age in the 3rd trimester of pregnancy. Patients and Methods: This is a cross sectional study conducted at outpatient Clinic and Obstetric ward, Ain Shams University Maternity Hospital, over a period of six months from March 2019 to September 2019. One hundred pregnant women were recruited according to inclusion criteria either from outpatient clinic or were admitted in obstetric ward Ain Shams Maternity Hospital to find out the most accurate fetal biometric measurement in the third trimester either trans-cerebellar diameter placental thickness or both compared to reliable LMP (last menstrual period) dates confirmed by crown rump length (CRL) in the first trimester. Results: Trans-cerebellar diameter mean ± SD was 46.0 ± 3.5 with range 38.2 - 51.7. The mean of placental thickness was 39.6 ± 7.1 with range 22.8 - 54.3. Placental thickness had highest determination (0.813) for last menstrual period followed by trans-cerebellar diameter (0.802). Combining trans-cerebellar diameter and placental thickness increased determination (0.902) for last menstrual period. Conclusion: Combined use of trans-cerebellar diameter and placental thickness in the third trimester of pregnancy is a reliable indicator for gestational age in women whose last menstrual period is unreliable or unknown, but placental thickness had higher accuracy than trans-cerebellar diameter.

Diameter distributions in Pinus sylvestris L.stands:evaluating modelling approaches including a machine learning technique

The diameter distribution of trees in a stand provides the basis for determining the stand’s ecological and economic value,its structure and stability and appropriate management practices.Scots pine(Pinus sylvestris L.)is one of the most common and important conifers in Turkey,so a well-planned management schedule is critical.Diameter distribution models to accurately describe the stand structure help improve management strategies,but developing reliable models requires a deep understanding of the growth,output and constraints of the forests.The most important information derived by diameter distribution models is primary data on horizontal stand structure for each diameter class of trees:basal area and volume per unit area.These predictions are required to estimate the range of products and predicted volume and yield from a forest stand.Here,to construct an accurate,reliable diameter distribution model for natural Scots pine stands in the Türkmen Mountain region,we used Johnson’s SBdistribution to represent the empirical diameter distributions of the stands using ground-based measurements from 55 sample plots that included1219 trees in natural distribution zones of the forests.As an alternative,nonparametric approach,which does not require any predefined function,an artificial intelligence model was constructed based on support vector machine methodology.An error index was calculated to evaluate the results.Overall,both Johnson’s SB probability density function with a three-parameter recovery approach and the support vector regression methodology provided reliable estimates of the diameter distribution of these stands.

Bedside ultrasonography of optic nerve sheath diameter for detection of raised intracranial pressure in nontraumatic neurocritically ill patients

BACKGROUND Delay in treatment of raised intracranial pressure(ICP)leads to poor clinical outcomes.Optic nerve sheath diameter(ONSD)by ultrasonography(US-ONSD)has shown good accuracy in traumatic brain injury and neurosurgical patients to diagnose raised ICP.However,there is a dearth of data in neuro-medical intensive care unit(ICU)where the spectrum of disease is different.AIM To validate the diagnostic accuracy of ONSD in non-traumatic neuro-critically ill patients.METHODS We prospectively enrolled 114 patients who had clinically suspected raised ICP due to non-traumatic causes admitted in neuro-medical ICU.US-ONSD was performed according to ALARA principles.A cut-off more than 5.7 mm was taken as significantly raised.Raised ONSD was corelated with raised ICP on radiological imaging.Clinical history,general and systemic examination findings,SOFA and APACHE 2 score and patient outcomes were recorded.RESULTS There was significant association between raised ONSD and raised ICP on imaging(P<0.001).The sensitivity,specificity,positive and negative predictive value at this cut-off was 77.55%,89.06%,84.44% and 83.82% respectively.The positive and negative likelihood ratio was 7.09 and 0.25.The area under the receiver operating characteristic curves was 0.844.Using Youden’s index the best cut off value for ONSD was 5.75 mm.Raised ONSD was associated with lower age(P=0.007),poorer Glasgow Coma Scale(P=0.009)and greater need for surgical intervention(P=0.006)whereas no statistically significant association was found between raised ONSD and SOFA score,APACHE II score or ICU mortality.Our limitations were that it was a single centre study and we did not perform serial measurements or ONSD pre-and post-treatment or procedures for raised ICP.CONCLUSION ONSD can be used as a screening a test to detect raised ICP in a medical ICU and as a trigger to initiate further management of raised ICP.ONSD can be beneficial in ruling out a diagnosis in a low-prevalence population and rule in a diagnosis in a high-prevalence population.

大直径盾构隧道成型质量巡检方法研究

针对因工业应用成本限制,中、小盾构隧道成型质量无损检测技术迁移至大直径盾构隧道时精度、速度折损严重的问题,以巡检车为载体,集成二维激光扫描仪、编码器和计算机等设备,研制了大盾构隧道成型质量巡检车,并提出一种基于数字图像的盾构质量非对称巡检方法.分析大直径盾构的施工环境,滤除地面、车体点云,并采用邻域向量法提取中轴线,建立隧道中心坐标系.偏心布置巡检路线,按照点云密度将采样点云分为稠密侧和稀疏侧点云,通过不同方法实现对管片接缝特征的拾取:将稠密侧点云绕中轴线展开为二维灰度图像,并通过缩放、归一化、梯度阈值分割等方法实现接缝图像分割;基于直线方程对接缝进行分类,结合管片结构、布置点位,推导出稀疏侧接缝与稠密侧接缝的线性分布公式,间接拾取稀疏侧接缝.根据接缝特征点计算两侧管片边缘点云簇,计算管片错台量;剔除接缝点云簇,使用最小二乘法拟合隧道点云,计算隧道椭圆度.最后在某大直径盾构隧道进行巡检试验,试验结果表明:成型质量巡检车在十四米盾构隧道中巡检速度为3 km·h-1,与传统方法的错台量检测偏差小于2 mm,椭圆度检测偏差小于0.1%,可以满足大直径盾构隧道成型质量巡检的高速度、高精度、低成本需求.

广西沃柑果实横径生长动态及模型构建

【目的】研究广西沃柑果实横径的生长动态并构建数学模型,为提升其品质和产量提供科学依据。【方法】以沃柑为材料,于稳果后,连续两年每月1日、15日通过“定园、定点、定果、定期”的方法测量并记录广西桂南、桂中、桂北15个果园的沃柑横径数据,直至采收期,研究沃柑横径的变化动态,考察年终横径与各生长节点,月度横径增加值与主要气象信息的相关性并建立数学模型。【结果】各个果园最终的横径差别较大,达到极显著差异水平,多个果园的横径有待提升;对比气象数据,选定2021—2022年度的沃柑横径数据为正常年份数据,翌年1月15日果实横径平均值为69.85 mm,最高的果园达75.33 mm,最小的61.55 mm;以80、75、70、65、60、55 mm为等级,构建桂南、桂北和桂中沃柑果实横径生长动态对照表、横径月度增加值对照表;分别建立年终沃柑横径数值与各生长节点,横径月度增加值与主要月度气象信息的数学模型,年终横径与7月15日呈显著正相关,与8月15日以后呈极显著正相关,至11月1日达到极显著的0.934 0;月度增加值与降雨、温度相关系数分别为显著的0.791 8和极显著的0.879 1。【结论】广西沃柑提质增产仍存在较大空间,可结合当期横径生长对照表、定期差值对照表,科学合理安排水肥药的灌溉来进一步加速果实膨大,从而提升效益。

施氮量对花生结瘤特性的影响

为了探明施氮量对田间栽培花生结瘤特性的影响,以‘桂花36’为研究材料,设置6个氮用量处理:施氮量0%(N0,不施氮)、施氮量25%(N1,少量施氮)、施氮量50%(N2,中量施氮)、施氮量75%(N3,少量减施氮)、施氮量100%(N4,常规施氮67.50 kg/hm^(2))、施氮量150%(N5,大量施氮),大田试验采用随机区组设计,田间取样共33次,研究了不同施氮量对结瘤特性观测值和变化规律的影响。结果表明:在采样前期,根瘤数量与直径的观测值平均数随施氮量的上升而下降;在采样中、后期,根瘤平均数量的最小值都出现在N4处理,平均直径的最小值则均出现在N5处理,既氮对数量的抑制在常规施氮条件下达到最强,对直径的抑制随用量的增加而增强;从N0到N4,以其中任一处理为参照时,参照处理与相邻处理间的变化差异显著概率在各采样期均未达到很可能级别,既当施氮量小于67.50 kg/hm^(2)时,25%幅度的氮用量增减不会导致根瘤数量和直径观测值产生差异显著的变化;相比常规施氮,大量施氮时根瘤直径观测值在采样中、后期很可能显著下降,数量观测值在采样后期很可能显著上升。

一种基于ASME V的管状校准试块的优化

通过结合ASME V第4章中关于超声波检测对于管状校准试块的技术要求,介绍了一种基于ASME V的管状校准试块的优化,主要优化了管状校准试块的样式、管径及其加工、试块厚度、反射体、长度、端头型式等参数,优化设计后能够减少试块的数量和质量,利于携带,对工程实践应用有一定的实用价值。

抗拔桩承载能力影响因素与群桩变形规律试验研究

利用自主研发的桩基室内抗拔测试装置,结合数值模拟技术对抗拔桩的承载破坏过程及影响因素、群桩的协同工作特征展开了深入研究。结果表明:抗拔桩的承载破坏经历4个阶段,承载初期,桩顶侧摩阻力最先发挥作用,桩顶土体发生塑性破坏;随上拔荷载不断增大,桩体产生相对位移,桩周土体由于桩身侧摩阻力产生塑性破坏;当桩身轴力自桩顶传递至桩底时,桩身底端产生抗拔“吸附力”,并伴随局部土体塑性破坏;随着桩周土体塑性区的拓展、连通,抗拔桩承载能力达到极限;桩身长径比、桩-土界面摩擦因数、桩侧土体压力与其承载极限呈正相关关系,其中桩身长径比对桩端“吸附力”具有重要影响;群桩抗拔过程中,角桩侧摩阻力发挥最充分,桩身位移量最小,极限承载力最大,中心桩桩身位移最大,极限承载力最低;距径比影响抗拔桩的群桩效应,当距径比从2增大至8时,桩身侧摩阻力提高30%,将距径比8作为群桩工程的推荐值,6~10作为群桩距径比的推荐范围。

纵向钢筋C型卡槽连接单向拉伸力学性能

为提高装配式纵向钢筋连接的施工效率,提出了C型卡槽连接方式,制作9个连接件并进行单向拉伸试验,观察其破坏形态,研究试件荷载-位移曲线、应变发展过程,分析不同锚固板直径对连接件连接性能的影响;基于混凝土局部受压计算公式,推导出C型卡槽连接钢筋的承载力计算公式,并给出不同锚固板直径与带锚固板钢筋直径的适配表。结果表明:锚固板直径为43 mm和48 mm的连接件发生带锚固板钢筋拉断破坏,荷载-位移曲线与单根钢筋拉伸的荷载-位移曲线相似,均能满足JGJ 107—2016和ACI 318对接头的强度要求;锚固板直径为38 mm的连接件是依据JGJ 256—2011选取锚固板直径,试验过程中发生带锚固板钢筋拔出破坏,证明按照规程取值,锚固板直径偏小,无法满足连接要求;锚固板直径为38 mm的连接件其荷载-位移曲线呈现波浪形,承载力虽小于前两者,但仍具有较好的延性和较高的残余承载力;所有连接件的C型卡槽在整个受力过程中应变值较小,始终处于弹性阶段,C型卡槽环向应变表现为压应变,C型卡槽连接钢筋承载力的理论计算结果与试验结果相符。

桩端岩溶三维超声成像方法及应用研究

研究目的:岩溶地区大直径桩基础受桩端岩溶的威胁大,探查不清或处理不当时可能会出现桩基承载力不足等严重工程质量问题,现有探测方法难以在桩底复杂泥水环境下实现桩端三维精细化探测。本文基于超声相控阵全聚焦成像原理,提出一种全新的桩端岩溶三维探测方法,以实现对桩端一定范围内地质结构进行三维高精度成像。研究结论:(1)本方法和装备在桩底采集超声数据并成像,可对桩端一定深度和冲切角范围内岩溶三维高精度成像;(2)足尺模型试验表明本装备可探测桩端10 m以内溶洞且探测精度优于0.1 m;(3)工程实践表明本装备可有效查明桩端岩溶、破碎裂隙,探测结果准确可靠;(4)本装备能适应桩底各种恶劣的环境,探测过程简单高效,时效性强,对保障岩溶区桩基施工安全与质量控制具有重要的意义。