大跨径桥梁挠度测量新方法研究

提出了一种以测量机器人为采集器,通过获取合作目标的几何信息进行桥梁挠度测量的新方法,从测量系统误差、偶然误差两个方面分析了测量机器人的测角及测距误差,并探讨了竖直角、视距对挠度测量误差的影响,同时依据最小二乘原理分析了该方法的测量精度.经分析得知:如果仪器至后视点距离小于150 m,至目标点距离小于200 m,挠度测量精度将优于±1 mm.在实际工程中,该方法测量的挠度值与电子水准仪测量的挠度值差异小于0.22 mm,相对误差小于3.3%,表明该方法在大跨径桥梁检测中完全能满足测试要求.     

荷载模型对沥青路面路表弯沉计算的影响

弯沉作为我国沥青路面设计和竣工验收的重要指标之一,规范规定采用单轴单侧双圆均布荷载进行理论计算,而用贝克曼梁法实地量测时的标准车荷载为单轴双侧四圆荷载。文中采用1层状弹性理论计算结果表明二者差值达25%～45%,并进一步对双轴和三轴荷载模型下弯沉值的影响进行分析。     

Effect of Deflection Characters on Self oscillating Water Jet

The deflective mechanism of the oscillating water jet is analyzed and the effects of jet deflection on the self oscillating water jet are investigated. It is experimentally shown that the deflective angle may reach 9.53 degree, the pressure fluctuation is more intensive and more regular and the jet can efficiently eliminate the water cushion effect and increase the ability in cutting.     

宝兴百合花柱偏转促进延迟自交试验研究

2011年7~8月对云南香格里拉高山植物园的宝兴百合(Lilium duchartrei Franch.)种群进行了传粉生物学研究实验,以期找到这种花朵开放初期雌雄异位的植物传粉生物学特点。结果表明,记录到的178次昆虫对宝兴百合的访问中能触碰到柱头的仅有蝴蝶类1次,有效传粉者传粉频率严重不足;单花期5.5~6.5 d,花开放的前3天,柱头远离花药,从花开放的第二天起花柱缓慢向上偏转,第四天将柱头从远离花药位置送到刚好可以接受自花花粉的位置,利于早期没有昆虫传粉的花朵延迟自交,自花授粉发生在花期末期,自交之前仍然保持异交传粉机制;自然状态(92.3%)及完全套袋处理(90%)的结实率接近,说明宝兴百合传粉存在花柱偏转促进的延迟自交,但2种处理的每果实种子数自然状态(121)显著高于完全套袋处理(78),又说明由昆虫传粉的异交更利于宝兴百合结实。延迟自交避免了自交与异交竞争造成的花粉或者种子的折损,为宝兴百合在有效访花昆虫不足导致异交失败时提供繁殖保障。     

冷弯薄壁型钢-稻草板组合楼盖抗振性能

为研究冷弯薄壁型钢-稻草板组合楼盖抗振性能,对2块单跨组合楼盖进行静载和动载试验,结果表明:在相同用钢量下,减少楼盖梁的数量、增加楼盖梁截面尺寸能有效提高组合楼盖的抗振性能;组合楼盖在1 kN静载作用下的跨中挠度均小于1.0 mm,动力荷载作用下自振频率均大于15 Hz,满足楼盖舒适度的要求。采用有限元软件ANSYS对试验模型进行数值分析,有限元计算结果与试验结果吻合较好。在此基础上,对楼盖跨度、楼盖梁间距和型钢厚度等因素进行参数分析,结果表明:增加组合楼盖边界条件、减小楼盖跨度等能有效地提高组合楼盖抗振性能。提出了该组合楼盖自振频率的简化计算公式,为其在工程中推广和应用提供依据。     

Theoretical and experimental deflections of glued laminated timber beams made from a tropical hardwood

Abstract

Nondestructive testing (NDT) can play an important role in improving the quality and reliability of tropical hardwood as an engineering material. By means of these methods, the stiffness of the material can be determined and the information used to improve its structural performance. Although, it is a usual approach for qualifying the material used to manufacture engineered wood products made mainly from softwoods, it is not so common for tropical hardwoods. Additionally, the lack of information regarding properties of glulam beam made from these kinds of wood is evident. In this context, the paper aimed at evaluating the theoretical and experimental deflection of glulam beams made from the Brazilian hardwood louro-vermelho (Sextonia rubra). Initially, the stiffness of each lamina was determined nondestructively using transverse vibration method (E _dtv), which has been demonstrated to be the most suitable method for this wood species. Then, ten 5-lamina glulam beams were assembled according to descending lamina E _dtv values. The experimental evaluation was performed using a four-point bending schedule. In general, the theoretical values of deflection were 2% higher than the experimental ones. The transverse vibration showed to be a suitable method to both measure lamina stiffness and predict glulam beam deflection.     

Perturbation Solution to Large DeflectionProblem of Cantilever Beams

The large deflection problem of cantilever beams is studied by means of pseudolinear approach and the result is compared with that by algorithm of nonlinear governing equation. It indicates that large deflection problem solved by pseudolinear analysis can lead to simple and precise results.     

变应传感器在甜菜根茎测定中的应用

将变应传感器应用在甜菜根茎生长测定中,测定地表下5cm处甜菜块根直径以期观测甜菜根部生长状态。试验结果表明,2点法测量的误差小于1点法,年度间差异变化不大,并且没有在甜菜表面造成损伤和形成生育障碍,说明2点法可以在生产中应用。     

一类非线性不确定中立型延迟系统的鲁棒滑模控制

基于等效变形区长度提出了极限状态下混凝土梁跨中挠度的简化计算方法,继而根据梁的跨中挠度推导了体内和体外无粘结预应力筋极限应力增量的通用计算公式.以受力钢筋的配筋率、预应力筋布置形式、预应力度、跨高比、荷载形式等为参数,对无粘结预应力混凝土梁的受力性能进行了参数分析,依据分析结果,提出了以综合配筋指标和预应力度为参数的等效变形区长度的计算公式.结果表明 :所提出的无粘结预应力筋极限应力增量的计算方法及公式具有较好的适用性;多种荷载形式作用时的等效变形区长度,可取为各种荷载单独作用时等效变形区长度的加权平均值,权值为各类荷载产生的跨中弯矩.     

弹性薄板大挠度问题两类变量的广义变分原理

应用变积方法,按照广义力和广义位移之间的对应关系,将弹性薄板大挠度问题的平衡方程和几何方程乘上相应的虚量,然后积分,代数相加,代入本构关系,建立弹性薄板大挠度问题两类变量的广义势能原理。通过代入另一类本构关系,再应用类似如上的方法,建立弹性薄板大挠度问题两类变量的广义余能原理。再将这两种两类变量的广义变分原理分别退化到弹性薄板大挠度问题的势能原理和余能原理。