钢筋混凝土纯扭构件截面尺寸效应的试验

对适筋的钢筋混凝土实心及空心矩形截面纯扭构件,当取其截面高宽比、纵筋及箍筋配筋率,以及二者的配筋强度比基本相同,而具有不同的截面尺寸,对空心截面并具有不同的有效壁厚时,进行试验研究分析,提出了钢筋混凝土矩形截面纯扭构件截面尺寸对承载力影响的规律性,为今后建立构件受剪扭的统一计算公式,打下基础.

高频超声测量尺神经横截面积在肘管综合征临床分型的应用价值

目的构建基于顾玉东肘管综合征临床分型为基础的尺神经横截面积(cross sectional area,CSA)分度标准,评估高频超声在肘管综合征临床分型判定中的应用价值。方法回顾性分析2021年5月至2022年12月在秦皇岛市第一医院同时完善高频超声和肌电图的拟诊肘管综合征患者60例,依据肌电图诊断结论分为病例组和对照组。病例组44例,男30例,女14例;年龄22~81岁,平均(54.14±2.15)岁。对照组16例,男9例,女7例;年龄22~68岁,平均(43.44±13.17)岁。以顾玉东肘管综合征临床分型为基础将病例组分为轻、中、重三组,轻度11例,中度13例,重度20例。通过分析不同临床分型中尺神经CSA,评估使用尺神经CSA诊断肘管综合征与肌电图诊断结果的一致性,探讨尺神经CSA对于诊断肘管综合征不同分度的临界值。结果高频超声可清晰的显示尺神经及其周围解剖结构,明确肘管综合征病因。病例组尺神经CSA平均值为(18.00±7.92)mm^(2),对照组尺神经CSA平均值为(9.50±3.54)mm^(2);轻、中、重度三组尺神经CSA平均值分别为(11.27±2.69)mm^(2)、(15.46±3.91)mm^(2)、(23.35±8.23)mm^(2)。高频超声诊断结果与肌电图诊断结果一致性中等(kappa系数=0.479,P<0.001)。对尺神经CSA进行受试者工作特征(receiver operating characteristic,ROC)曲线分析,诊断肘管综合征轻、中、重度的临界值分别为11.50 mm^(2)、15.50 mm^(2)、20.00 mm^(2)。结论高频超声检测指标尺神经CSA在肘管综合征患者具有诊断价值,并可用于肘管综合征临床分型预测。

MR在尺神经卡压综合征诊疗中的应用

目的探讨MR在尺神经卡压综合征(CuTS)术前评估、术式选择、术后疗效评估中的应用价值。方法对470例CuTS患者,按Dellon术式对卡压神经行尺神经显微松解减压术。所有患者术前4周病侧组和健侧组尺神经行MR检测对照,术前、术后病侧组尺神经MR检测指标对照。结果 MR显示受累神经肿胀、增粗,信号减低,神经内线状结构消失,肿胀部位(内上髁沟、穿尺侧腕屈肌处)明显受到旋前圆肌、指浅屈肌、肘管、屈肌总腱等组织卡压;神经横截面积(CSA)相比较于健侧差异显著;术前、术后对照:MR尺神经检测结果提示神经卡压明显缓解。结论 MR能够从形态学角度提供神经卡压程度、部位等信息,同时可以清晰显示卡压神经周围解剖,适用于辅助术前评估,指导手术操作,评价手术效果。

螺旋滚筒选煤机滚圈强度设计方法的研究

介绍了螺旋滚筒选煤机的基本结构和滚圈的作用 ,分析了滚圈的受力 ,建立了力学模型 ,利用求解静不定问题的方法算出特殊截面的内力 ,进而算出滚圈的最大弯矩和截面尺 。

The Optimal Cross-section Design of the “Trapezoid-V” Shaped Drainage Canal of Viscous Debris Flow

Debris flow drainage canal is one of the most widely used engineering measures to prevent and manage debris flow hazards.The shape and the sizes of the cross-section are important parameters when design debris flow drainage canal.Therefore,how to design the appropriate shape and sizes of the cross-section so that the drainage canal can have the optimal drainage capacity is very important and few researched at home and abroad.This study was conducted to analyze the hydraulic condition of a Trapezoid-V shaped drainage canal and optimize its cross-section.By assuming characteristic sizes of the cross-section,the paper deduced the configuration parameter of the cross-section of a Trapezoid-V shaped debris flow drainage canal.By theory analysis,it indicates that the optimal configuration parameter is only related to the side slope coefficient and the bottom transverse slope coefficient.For this study,the Heishui Gully,a first-order tributary of the lower Jinsha River,was used as an example to design the optimal cross-section of the drainage canal of debris flow.

Rational concrete cover of prestressed concrete beams and slabs for fire resistance

As the influence of the ratio of the characteristic value of structural resistance to that of frequent combination effect, K, on the thickness of concrete cover of prestressed concrete （PC） beams and slabs for fire resistance is not considered sufficiently in design criteria for concrete structures in China and other countries at present, numerical analyses were carried out by ANSYS software on unbonded prestressed concrete （UPC） oneway simply-supported and continuous slabs and beams, and bonded PC simply-supported and continuous beams subjected to fire in 186 cases. In the analysis, K, section dimensions and the thickness of concrete cover are regarded as independent variables and some calculation parameters determined by trial and error based on test resuits. Calculation formula for fire endurance of UPC simply-supported and continuous slabs was proposed, and the recommended thicknesses of cover of PC beams and slabs was presented in consideration of the influence of K and section dimensions as well as fire endurance requirements. Comparison analysis of relevant design criterions in China and other countries was performed to verify the rationale of the proposed values.

Optimum Determination of Partial Transmission Ratios of Mechanical Driven Systems Using a V-belt and a Three-Step Helical Gearbox

This paper introduces a new study on the optimum calculation of partial transmission ratios of a mechanical drive system using a V-belt and a three-step helical gearbox in order to get the minimum size of the system. The chosen objective function was the cross section dimension of the system. In solving the optimization problem, the design equation for pitting resistance of a gear set was investigated and equations on moment equilibrium condition of a mechanic system including a V-belt and three helical gear units and their regular resistance condition were analysed. From the results of the study, effective formulas for determination of the partial ratios of the V-belt and three-step helical gearboxes were introduced. As using explicit models, the partial ratios can be determined accurately and simply.

Optimum Determination of Partial Transmission Ratios of Three-Step Helical Gearboxes for Getting Minimum Cross Section Dimension

This paper presents a new study on optimum calculation of partial ratios of three-step helical gearboxes. The chosen objective function is the cross section dimension of the gearbox. In solving the optimization problem, the design equation for pitting resistance of a gear set was investigated and equations on moment equilibrium condition of a mechanic system including three gear units and their regular resistance condition are analyses. From the results of the study, effective formula for determination of the partial ratios of three-step helical gearboxes is introduced. As the formulas are explicit, the partial ratios can be calculated accurately and simply.

Aerodynamic Performance of Wind Microturbines and Their Dynamic Response

Wind microturbines typically have rotor diameters of 2 m or less. This paper presents theoretical expressions that can be used to determine the aerodynamic performance of wind microturbines. A commercially-available three-bladed microturbine was tested at the outlet plane of a wind tunnel. The cross-section dimensions of the wind tunnel jet are 2.5 m （horizontal） x 1.5 m （vertical）. The tested microturbine has a diameter of 1.2 m, and it generates a maximum power output of about 300 W. The paper provides the wind tunnel test methodology that was used to determine the mean and fluctuating forces generated by the aforementioned wind microturbine. Both the static and dynamic responses of the turbine were measured, and results from this testing are presented in this paper. These results enable the trends and predictions of the theoretical expressions to be compared with wind tunnel measurements. It is shown that, for this particular microturbine, the behaviours of these test measurements are consistent with the expected theoretical predictions.

The Effects of Cross Sectional Dimensions on the Behavior of L-Shaped RC Structural Members

The behavior of L-Shaped RC （reinforced concrete） shear walls was investigated in the Erciyes University Earthquake Investigation Laboratory under the influence of constant axial load together with reversed cyclic lateral load. The objective of this study was to evaluate the effects of cross sectional dimensions on the behavior of L-shaped structural members and to assess their earthquake performance. In order to investigate L-shaped RC structural members, the special experiment setup and four type of 1/2 scaled specimens which have different aspect ratio were constructed. The specimens were loaded in line with the major principal axes direction laterally. Axial load ratio was 0.1 and cross section height to thickness ratios were＇ 3：1, 5：1, 8：1, 10：1. Cross section thickness was 120 mm which corresponds to （360：120）, （600：120）, （960：120）, （1,200：120） wall legs cross sectional dimensions in mm. The specimens height was 1,500 mm, together with upper and lower slabs overall height was 2,000 mm. Concrete compression strength was 30 N/mm2, steel yield stress 420 N/mm2 and vertical reinforcement ratio was 1% for all specimens. According to the test results, the specimen of which the aspect ratio is 3 （360：120） has shown column behavior, the specimen of which the aspect ratio is 5 （600：120） has shown slender wall behavior and last two specimens of which the aspect ratios are 8 （960：120） and 10 （1,200：120） have shown squat wall behavior. When considering the cracking patterns and hysteretic behavior, since the aspect ratio 8, the specimens show flexure-shear interaction behavior and prone to brittle failure.

The Investigation on Flow Boiling Heat Transfer of R134a in Micro-channels

The present study reports an experimental evaluation of heat transfer characteristic of R134a flow boiling in mi- cro-channel heat sink. The heat sink is composed of 30 parallel rectangular micro-channels with cross-sectional dimensions of 500μm width and depth, as well as total length 30ram. Experiments were conducted with heat flux up to 80.212 W/cm2, mass velocity ranging from 373.33 to 1244.44 kg/m2s, vapor quality ranging from 0.06 to 0.9. The wall temperature of heat sink heated could be controlled at around 50℃. Heat transfer coefficient could be up to 180 kW/mZK. Two dominating flow patterns were observed by analyzing boiling curves. The heat trans- fer characteristics of nucleate boiling and convective boiling were presented in the study. Revised correlations of R134a flow boiling in micro-channel heat sink were carded out with the consideration of nucleate boiling and convective boiling mechanisms.

The Effect of Heating Direction on Flow Boiling Heat Transfer of R134a in Microchannels

This paper presents effects of heating directions on heat transfer performance of R134 a flow boiling in micro-channel heat sink. The heat sink has 30 parallel rectangular channels with cross-sectional dimensions of 500mm width 500mm depth and 30 mm length. The experimental operation condition ranges of the heat flux and the mass flux were 13.48 to 82.25 W/cm^2 and 373.3 to 1244.4 kg/m^2 s respectively. The vapor quality ranged from 0.07 to 0.93. The heat transfer coefficients of top heating and bottom heating both were up to 25 k W/m^2 K. Two dominate transfer mechanisms of nucleate boiling and convection boiling were observed according to boiling curves. The experimental results indicated that the heat transfer coefficient of bottom heating was 13.9% higher than top heating in low heat flux, while in high heat flux, the heat transfer coefficient of bottom heating was 9.9%.higher than the top heating, because bubbles were harder to divorce the heating wall. And a modified correlation was provided to predict heat transfer of top heating.

Energy transfer between components of a cable stayed beam model under the concentrated excitation:1:2 modal resonance

The present study aims to investigate the dynamic behaviors and energy transfer between components of a cable stayed beam structure subjected to a concentrated load,in which the primary resonance of the beam and one-to-two internal resonance between modes of the beam and the cable occur.Galerkin discretization and multiple time scales method are applied to derive the modulation equations of the system governing the amplitude and phase.Two sags of span ratios are defined to modulate the internal resonance.Frequency response,amplitude response,phase diagram,Poincare map,and time history curves are calculated and used to investigate the modal resonance dynamics.The results demonstrate that the beam and the cable have two resonant peaks in frequency responses,where the beam always shows hardening spring property and the cable may present hardening and softening spring properties affected by sag to span ratio.The system is prone to complex dynamic behavior with the small amplitude excitation in the primary resonance region.