Crack elongation and its width of large depth reinforced concrete beams

In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading levels of serviceability state.The effects of the depth of normal section beams on the crack spacing and crack width were analyzed,and the modified model is proposed for calculating the average crack spacing by thinking about the depth of normal section,the reinforcement arrangement and the effective reinforcement ratio.The relationships of crack widths at any position in the tensile zone and at the reinforcement level on the side surface of beam were studied.By theoretical and statistical analysis,a method is proposed to calculate the ratios of crack widths between any position and the reinforcement level on the side surface of large depth reinforced concrete beams.

The 266-nm ultraviolet-beam generation of all-fiberized super-large-mode-area narrow-linewidth nanosecond amplifier with tunable pulse width and repetition rate

We report on a compact, stable, all-fiberized narrow-linewidth(0.045 nm) pulsed laser source emitting laser beam with a wavelength of 266 nm, and tunable pulse width and repetition rate. The system is based on all-fiberized nanosecond amplifier architecture, which consists of Yb-doped fiber preamplifiers and a super-large-mode-area Yb-doped fiber power amplifier. The fiber amplifier with a core of 50 μm is used to raise the threshold of the stimulated Brillouin scattering(SBS) effect and to obtain high output power and single pulse energy. Using lithium triborate(LBO) crystal and betabarium borate(BBO) crystal for realizing the second-harmonic generation(SHG) and fourth-harmonic generation(FHG),we achieve 17 μJ(1.73 W) and 0.66 μJ(66 mW), respectively, at wavelengths of 532 nm and 266 nm and a repetition rate of 100 kHz with pulse width of 4 ns. This source has great potential applications in fluorescence research and solar-blind ultraviolet optical communication.

Mobility-Aware Adaptive Beam Tracking for Vehicles in Mm Wave Communication Networks

The millimeter wave(mm Wave)is a potential solution for high data rate communication due to its availability of large bandwidth.However,it is challenging to perform beam tracking in vehicular mm Wave communication systems due to high mobility and narrow beams.In this paper,an adaptive beam tracking algorithm is proposed to improve the network throughput performance while reducing the training signal overhead.In particular,based on the mobility prediction at base station(BS),a novel frame structure with dynamic bundled timeslot is designed.Moreover,an actor-critic reinforcement learning based algorithm is proposed to obtain the joint optimization of both beam width and the number of bundled timeslots,which makes the beam tracking adapt to the changing environment.Simulation results demonstrate that,compared with the traditional full scan and Kalman filter based beam tracking algorithms,our proposed algorithm can improve the time-averaged throughput by 11.34%and 24.86%respectively.With the newly designed frame structure,it also outperforms beam tracking with conventional frame structure,especially in scenarios with large range of vehicle speeds.

Periodic Measurements of Passive Proton Beam Width Using Radiochromic Film in Fixed Gantry System

Background and Aim: Irradiation methods such as double scattering method and spot scanning method have been used in proton beam treatment devices. In the scattering method, a ridge filter or a range modulation wheel is used to create a spread-out Bragg peak, but the distribution at the patient position may change due to positional deviation of the incident beam. Therefore, assessment of the incident position of the beam is very important even in the scattering method. To investigate the width and distribution of the proton beam before entering the RMW, a radiochromic film was installed at the outlet of the transport pipe and the entrance of the profile-monitoring detector. Methods: In this study, the distributions of the beam at the exit of the transport pipe and the entrance of the monitor detector were measured using films. The beam width was measured from the full width at half maximum of the profile obtained from the distribution. Measurements were conducted every month for 10 months. Results: Beams of widths ranging from 1.82 to 2.30 mm in the horizontal direction and 4.25 to 5.33 mm in the vertical direction were outputted from the exit of the transport pipe. Beams of widths ranging from 2.16 to 2.67 mm in the horizontal direction and 4.06 to 5.31 mm in the vertical direction were outputted from the entrance of the monitor detector. The maximum width fluctuation for 10 months was 0.55 mm in the horizontal direction and 1.26 mm in the vertical direction at the entrance of the monitor detector. Conclusions: The distribution was obtained before the proton beam was scattered by the scatterer, and then we propose a method to periodically measure and monitor the changes in the beam distributions every month.

Rectangular Microstrip Antenna for Symmetrical 3-D Beam Widths for an Efficient Feed of Reflector Antenna and its Quantitative Analysis

A simple rectangular microstrip antenna on low dielectric constant substrate such as air for improved radiation beam performance is theoretically investigated. The conventional patch antenna fabricated on common substrates always produces quite broader E plane pattern compared to its H plane. In the present investigation, the same microstrip antenna is designed on air substrate with a view to develop an efficient feed for parabolic reflector antenna, which shows an excellent radiation pattern with symmetrical 3 dB beam widths at its both E and H plane. The present antenna compared to conventional structure to show its excellence in the beam performance is presented. The complete quantitative analysis to explore such radiation beam characteristics for both the structures (conventional and the present one) is also presented in this paper. An easy and handful relationship between the length of patch antenna and its fringing length for different types of substrate is established in the background of 3 dB beam widths. The proposed idea has been verified through a commercial software package for a patch operating in X band and a concrete physical insight into the phenomenon is developed.

Effect of Overlap Stress as Well as Tie Beam Length and Width on Settlement of Isolated Footings Using Finite Element

Effects of tie beam length, width and overlap stress on settlement of foundations have been investigated. In this investigation square concrete footings have been used with dimensions (B × B × d) where (d) is footing depth and (B) is footing width (1, 1.5,2 m). Width of tie beam (b) has been taken equal to 0.25, 0.30, 0.40, 0.50 and 0.75 (m). Tie beam length (L) has been taken varying from B till 3B with same footing depth = 0.50 m. Effect of overlap stress on settlement as well as effect of tie beam width and length on settlement has been determined. Also, the efficiency of tie beam length and width has been obtained. An equation is presented to compute the overlap stress zone in case of existing tie beam. It is found that the settlement increases with increasing the length of tie beam which is clear after the effect of the overlap stresses zone. The width of overlap stress zone case of existing tie beam has been found to be equal to (1.6 -1.75) B. The settlement of footings decreases with increasing tie beam width. It is found that the settlement after the effect of the overlap stress zone increases with increasing the length of tie beam.

Compact and broadband circularly polarized ring antenna with wide beam-width for multiple global navigation satellite systems

A compact and broadband circularly polarized （CP） annular ring antenna with wide beam-width is proposed for multiple global navigation satellite systems （GNSS） in the L1 band. The annular ring is excited by two modified L-probes with quadrature phase difference. It has a 36.3% 10-dB return loss bandwidth and a 13% 3-dB axial ratio bandwidth, because of the orthogonal L-probes with 90° phase difference. The measured peak gain of the antenna is 3.9 dBic. It can detect the satellites at lower elevation as its half power beam-width （HPBW） is 113° in both the x-z and y-z planes, achieving a cross-polarization level of larger than 25 dB. Noticeably, the antenna achieves 89% size reduction compared with the conventional half wavelength patch antennas. It can be used in hand-held navigation devices of multiple GNSS such as COMPASS, Galileo, GPS and GLONASS.

部分充填式窄幅钢箱-UHPC组合梁抗裂性能

为研究部分充填式窄幅钢箱-UHPC组合梁的抗裂性能,开展了4根不同钢纤维掺量的部分充填式窄幅钢箱-UHPC组合梁与1根部分充填式窄幅钢箱-NC组合梁静力加载试验。试验表明:在负弯矩作用下,部分充填式窄幅钢箱-UHPC组合梁裂缝呈现数量多、短小且密集的特点;同等配筋率的条件下,不同钢纤维掺量(0、1%、2%和3%)部分充填式窄幅钢箱-UHPC组合梁与部分充填式窄幅钢箱-NC组合梁相比,在弹性阶段其刚度明显提高,最大裂缝宽度随钢纤维掺量的增加而减少,开裂强度分别提高了36.0%、48.8%、82.0%和112.0%,UHPC显著提高了组合梁的抗裂性能;可以参考按照JTG 3362—2018中裂缝宽度式乘以0.8的修正系数来计算部分充填式窄幅钢箱-UHPC组合梁裂缝宽度。

微波着陆模拟器波束宽度校准方法研究

波束宽度是微波着陆模拟器(Microwave Landing Simulator, MLS)的重要参数,对波束宽度参数进行定期校准非常必要。文中研究了MLS输出的波束宽度参数的校准方法,重点研究了信号的提取与解算。首先,对MLS输出微波信号进行采集和处理,获取模拟器输出的飞行器与着陆设备之间相对位置和角度相关的原始数据,对原始数据进行处理和解算;其次,针对波束宽度参数,实现了往扫描波束和返扫描波束的脉冲3 dB点的提取。最后,通过实际应用验证所提出的方法,评估其在MLS中的有效性和可靠性,并对波束宽度的校准进行了不确定度分析评定。研究成果可为MLS的波束宽度参数校准提供新的方法和技术支持。

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。

温度变化对CPⅢ平面测量结果的影响

目前我国高速铁路建设里程已达3万余公里,在全球首屈一指。在高铁建设过程中,轨道控制网(CPⅢ)测量是一项必不可少的工作。某高铁CPⅢ建网测量过程中,相同点位搭接时两次测量结果坐标较差较大,不满足规范搭接要求,需进行外业补测。本文对搭接不成功处的数据进行了分析,认为两次测量温差较大可能是导致搭接不成功的原因之一,温度变化会对CPⅢ测量结果产生影响。同时,梁体宽度确定时引入混凝土膨胀系数计算得到的梁体宽度变化值与实测值互差较小,均未超过0.7 mm,验证了本文的观点。根据气温变化调整补测时间后,数据成果满足规范要求。最后通过定量分析得出,若将梁体宽度变化阈值设置为±2 mm,梁体宽度为9.25 m时,两次测量温差不应超过-21.6℃~21.6℃;梁体宽度为12.20 m时,两次测量温差不应超过-16.4℃~16.4℃。

翼缘尺寸对地聚物混凝土T形梁抗弯性能的影响

通过对5根不同翼缘尺寸的地聚物混凝土T形梁和1根普通混凝土T形梁进行四点弯曲试验,研究了翼缘宽度和厚度对地聚物混凝土T形梁抗弯性能的影响,以及与普通混凝土T形梁的差异。研究结果表明:地聚物混凝土T形梁的抗弯极限荷载、屈服荷载、裂缝行为及失效模式与普通混凝土T形梁相似,且延性更优,但其跨中受拉纵筋应变较大,刚度、开裂荷载和最大裂缝宽度限值下的承载力较低。随着翼缘宽度从200 mm增大到500 mm,地聚物混凝土T形梁的刚度、屈服荷载、抗弯极限荷载、延性和在最大裂缝宽度限值下的承载力均增大,跨中受拉纵筋应变减小,开裂荷载无明显变化,但越宽的翼缘宽度能有效承担荷载的也只是靠近腹板的一部分宽度。增大翼缘厚度对地聚物混凝土T形梁抗弯性能的影响与增大翼缘宽度基本一致,但其对最大裂缝宽度限值下的承载力提高效果显著。规范GB 50010—2010和ACI 318—19的正截面受弯承载力设计公式适用地聚物混凝土T形梁,GB 50010—2010的预测更精确,ACI 318—19的安全储备更高。

基于空间光调制器的激光光束宽度调节装置

为了满足激光产业对光束宽度测量装置的溯源要求,提升激光光束宽度校准能力,针对400~700 nm波段的激光器不同光束宽度校准的需求,设计了一套基于空间光调制器的激光光束宽度可调节装置,用于光束质量分析仪或激光光斑测量仪的校准。实验结果表明该装置在0.1~5.0 mm的宽度范围连续可调;利用部分相干光束抗环境扰动能力强的特点,其短期稳定性达99.5%,长期稳定性达99.1%,优于参考激光器96.8%的短期稳定性和96.3%的长期稳定性。此外,基于空间光调制器优越的光束整形能力,该装置可将输入的非规则光束输出为高斯光束。

GaAs基高性能MEMS微波功率检测芯片

为了提高电容式MEMS微波功率检测芯片的性能,设计了一种GaAs基高性能MEMS微波功率传感芯片。通过建立双导固支梁电容模型,分析了传感芯片的传输特性、过载功率与灵敏度特性。在双导固支梁电容模型中提出了平行极板的两个等效条件;同时提出了一种新的梁宽等效方式,解决了双梁结构等效梁宽的失配问题,减小了模型的相对误差。双导固支梁电容模型很好地解释了导向梁的厚长比与初始高度对传感器过载功率和灵敏度的影响。测试结果表明,双导固支梁MEMS微波功率传感芯片在200 mW输入功率内的灵敏度为14.3 fF/W,而灵敏度的理论值为13.5 fF/W,两者的相对误差仅5.6%。因此,该理论模型对固支梁MEMS微波功率传感芯片的设计具有一定的借鉴意义。

不等间距拼宽T梁桥拼接段传力机理分析

为了验证广义梁格法计算的精确性,通过空间梁格法分析主梁非等间距拼宽对拼宽直梁桥受力性能的影响,并开展不同拼宽横梁间距对拼宽直梁桥内力横向分布的影响研究。结果表明:拼宽直梁桥广义梁格法计算内力横向分布的结果与空间梁格法计算所得的结果非常接近,各主梁挠度横向分布影响线计算结果最大偏差Δ_(dmax)在10%以内。主梁非等间距拼宽会使拼宽直梁桥的主梁内力横向分配变得不均匀,主梁拼宽间距(bc)<主梁一般间距(b0)时各主梁内力横向分布系数最大值与最小值的差值为0.533,比主梁等间距拼宽的差值大87.0%;bc>b0时各主梁内力横向分布系数最大值与最小值的差值为0.350,比主梁等间距拼宽的差值大23.2%。拼宽直梁桥的拼宽横梁受力性能分析可得:bc0时,拼宽横梁的弯矩影响线数值主要分布在负弯矩区;bc=b0时,拼宽横梁的弯矩影响线数值在正负弯矩区几乎均匀分布,bc>b0时,拼宽横梁的弯矩影响线数值主要分布在正弯矩区。因此在设计计算时,须考虑正弯矩和负弯矩的绝对值的最大值进行设计。

条带充填绿色开采回收压覆煤炭资源支巷宽度研究

以山西三元煤业3号煤条带充填工作面为工程背景,基于固支梁理论模型,分析了条带充填开采支巷顶板的变形与受力特征;并采用数值模拟方法揭示了循环间隔条带充填开采支巷间的相互作用及支巷围岩的塑性区分布特征,综合理论解析研究结果并结合三元煤业充填工作面实际条件,确定多轮循环间隔条带充填开采支巷的合理宽度为5 m;最后,通过工程实践验证了支巷宽度的合理性,实现了压覆煤炭资源的安全采出,促进了三元煤业的绿色可持续开采。

多向振动俘能器设计及能量收集实验研究

针对线性、单一的振动能量俘能器存在工作频带狭窄、只能采集单向振动等问题,该文提出了一种适应货运列车等多向振动应用场景的新型多向振动俘能装置,以增强对环境中振动能量的俘获。该装置结合压电和电磁俘能器,通过螺旋圆柱弹簧和顶端质量有效捕获多向振动,并通过磁力传递振动能量至压电梁。合理设计了弹簧-质量结构,使其在较低的频率范围内可实现多种振动模态,拓宽了俘能器的谐振频带。为了充分利用压电材料,采用了变宽度压电悬臂梁,使应力均匀分布。压电梁自由端的永磁体随着压电梁的振动而产生变化的磁场,在线圈中产生感应电压。通过有限元分析和实验测试,验证了复合式俘能器可以采集多向振动能量,并测试了在z向振动激励下压电、电磁及复合式俘能器的最大输出功率。在频率9.5 Hz、z向振幅2 mm的正弦波激励下,复合式俘能器输出最大功率为3.276 mW。该系统在理论上可为低功耗传感器提供持续电力,为机械能收集与能量转换领域提供技术支持。

聚焦离子束工艺参数对单像素线刻蚀的影响

单像素线刻蚀是制备微纳米器件中的基本单元及加工其他复杂结构的基础,对聚焦离子束(FIB)加工具有重要的意义。通过改变离子束流的大小、驻留时间、扫描步长百分比及离子剂量等参数,对硅表面进行单像素线刻蚀的研究。结果表明,在聚焦离子束加工中,离子剂量与刻蚀线条宽度和深度之间呈正相关,与宽深比之间呈负相关;离子束流大小的变化对刻蚀深度影响不明显,但刻蚀宽度和宽深比随离子束流的增大而增大。此外,随着离子束流驻留时间增加,刻蚀宽度增大而深度减小;随着扫描步长百分比的增大,刻蚀深度增大,刻蚀宽度减小,分析结果表明这些变化与加工过程中再沉积作用有关。本研究成果为后续复杂图形的精密加工提供了重要参考依据。

基于不等宽摩擦型叠梁模型的平行钢丝索层间滑移有限元分析

斜拉桥结构中,斜拉索锚固端往往存在强制转角,索内钢丝可能因此产生分层滑移,导致截面整体性被破坏、抗弯刚度退化。为探究平行钢丝索锚固端的分层滑移现象,基于不等宽摩擦型叠梁模型,通过引入非线性弹簧单元,提出一种模拟钢丝分层滑移的算法。依据该算法建立一个11层叠梁模型,对其在跨中集中力作用下的滑移扩展和变形规律进行进一步研究。结果表明:随着外荷载增加,叠梁接触层沿梁高方向从中性轴位置向两侧逐层产生滑移,沿梁长方向从固定端和跨中集中力作用点向两侧对称扩展;与此同时,该叠梁的全截面抗弯惯性矩呈指数衰减,最终约为初始状态的1/100,整体刚度也随滑移开展而加速衰减;受滑移效应影响,叠梁整体挠度呈非线性加速增长,但在低荷载水平时,叠梁锚固端附近位置接触层会全部滑移,从而导致该区域挠度按照线性规律增加,且增长幅度最大;此外,叠梁轴力会影响接触层的剪力传递效率,轴力越大,剪力传递效率越低,沿梁高方向产生滑移的接触层越少,沿梁长方向接触层滑移扩展速度越慢。

非对称荷载下基坑支护结构变形计算方法

文章针对非对称受荷基坑的位移特点,基于弹性地基梁模型,以支撑轴力联系两侧墙体,提出非对称受荷基坑的整体计算模型。通过有限宽度土体的土压力求解公式计算,引入墙土摩擦角和土体内摩擦角随墙体位移的发挥公式,考虑墙体变形与坑外主动土压力的耦合作用。根据非对称受荷计算模型,得到了非对称受荷下支护结构变形控制方程,最后结合实际工程验证了算法。