共查询到20条相似文献，搜索用时 250 毫秒
1.
张弦桁架结构施工时预应力的施加分为一端张拉及两端同时张拉的方式,通过有限元软件ANSYS分析了可以通过初始缺陷法加载预应力的方式模拟两种张拉形式在结构中引起的内力及位移反映,从而为工程施工中的张拉控制提供辅助。 相似文献
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预应力混凝土结构，以其良好的受力性能被广泛运用于桥梁建设中。预应力混凝土施工分为先张法和后张法。一般以伸长量及张拉应力进行双控，以张拉控制应力为主，伸长值进行校核，实际伸长值与理论伸长值误差控制在6％以内。在实际施工中发现，后张法施工伸长值误差控制在6％以内往往难以实现。就后张法预应力张拉伸长量校核问题进行分析并提出一些看法以供探讨。 相似文献
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预应力砼结构中预应力筋建立的有效预应力除受各种预应力损失因素影响之外还应考虑以下几个重要因素的影响:a.在预应力硅几何尺寸与张拉控制力相同的条件下,结构层数对预应力硅梁的有效预应力的影响;b.同一预应力砼结构中,不同层预应力筋因张拉顺序不同而对预应力筋有效预应力的影响;c.环境温度变化对预应力筋有效预应力的影响。 相似文献
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多层预应力钢筋砼框架结构是比较常见的结构形式。在施工过程中,大多数采用以下四种张拉方案:1.逐层浇筑,逐层张拉;2.整体浇筑,一次张拉;3.数层浇筑,逆向张拉;4.数层浇筑,顺向张拉等施工方案。不同的施工方案,各有其优缺点,应根据具体工程情况来选择。本文仅对常见的前两种方案(第1、2)进行分析。 相似文献
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随着经济的快速发展,建筑行业发展日益增长,预应力技术在混凝土结构工程中使用越来越广泛.本文简单分析了预应力混凝土的主要特点,并从施工方案、材料的检验、张拉设备的校核、板的安装及混凝土浇筑等几个方面,介绍了预应力混凝土施工质量的控制. 相似文献
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预应力钢绞线施工时,采用张拉应力和伸长值双控,实际伸长值与理论伸长值误差不得超过6%,后张预应力技术一般用于预制大跨径简支连续梁、简支板结构,各种现浇预应力结构或块体拼装结构。预应力施工是一项技术性很强的工作,预应力筋张拉是预应力砼结构的关键工序,施工质量关系到桥梁的安全和人身安全,因此必须慎重对待。 相似文献
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预应力张拉是预应力桥梁构件施工极为重要的环节之一,其施工质量如何直接关系着混凝土桥梁张拉应力与伸长量能否得到控制,更事关预应力桥梁结构的使用寿命。所以,在预应力混凝土桥梁施工中,充分做好预应力桥梁构件的张拉施工,对于确保桥梁工程整体施工质量具有十分重要的意义。 相似文献
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《Journal of The Franklin Institute》2023,360(2):1226-1251
For a kind of linear discrete-time-invariant multi-input-multi-output systems with a higher-order relative degree that repetitively operates within a finite time length, the paper exploits a Markov parameters identification method by making use of the multi-operation inputs and outputs obeying a criterion. Simultaneously, an adaptive iterative learning control scheme is architected by formulating the compensator with the sequentially identified Markov parameters and the tracking error in minimizing a performance index consisting of the quadratic tracking error of the next iteration and the compensation cost. Algebraic manipulations including the singular value decomposition of a matrix and the eigenvalues estimation conduct that the identification error of the Markov parameters is monotonically declining as the iteration goes on and a smaller identification ratio in the criterion delivers a faster decline rate. Meanwhile, a rigorous derivation achieves that under the assumption that the initial identification error is within an appropriate range the tracking error is monotonously convergent for the case when the relative degree is unit whilst the tracking error is asymptotically bounded for a positive level for the case where the relative degree is higher. Numerical simulations illustrate the validity and efficiency. 相似文献
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文章在现有金属飞机钢索变形理论的基础上,对复材飞机操纵钢索的设计和应用进行了详细的论述。总结性地提出了软式钢索操纵的设计步骤,在已有钢索变形量计算理论的基础上,考虑热、结构、座舱增压等因素的影响,计算钢索变形量并确定了钢索初始张力的予加原则,并给出钢索张力示例曲线,为钢索张力维护和调节提供理论依据。 相似文献
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无应力索长控制索力,是当下斜拉桥梁段拼装广泛应用的索力监控方法。针对此文章所阐述的中承式系杆拱桥,利用无应力索长控制方法结合温度应变,很好地解决了接近300米中拱在整体提升前临时拉索索力确定问题。 相似文献
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Frederick E. Pernot 《Journal of The Franklin Institute》1920,190(3):323-371
This paper contains the results of experiments performed by members of the Signal Corps Research Laboratory, Bureau of Standards, in an attempt to develop a method or methods of signal transmission over submarine cables which would permit of a more effective use of existing cable systems.In the method proposed and developed, signals are transmitted by means of alternating currents simultaneously with the normal battery of direct-current operation of the cable. Currents of several different frequencies may be used, reserving a given frequency for each message, and by tuning or equivalent methods at the receiving end these messages may be separated, so that the simultaneous transmission of a number of messages is redered possible.Accurate determination of the fundamental physical properties of a particular cable for different frequencies has been accompalished, and the results are given herewith. From these physical properties accurate calculations for any length of cable can be made, so that the design of proper apparatus becomes purely a laboratory problem.Actual trial of the proposed alternating-current method was made covering distances up to approximately 700 kilometres, with results which were in all cases completely satisfactory, indicating that the method is an entirely feasible one, and one which will render cables of this length, and undoubtedly of several times this length, much more useful. 相似文献
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This study deals with the stability analysis of a flexible structure with one and only one boundary control. The system is composed of three parts: a cart (motorized platform), a flexible cable, and a load mass attached to the lower part of the cable. This situation leads to a hybrid system as a mathematical model for the cable dynamics: one partial differential equation coupled to two ordinary differential equations. Despite the presence of a time-delay in the top-end of the cable, we are able to prove that the hybrid system is well-posed in the sense of semigroups theory and more importantly, only one boundary control can guarantee the exponentially decay of the energy of the system under reasonable conditions on the parameters of the system. This outcome considerably improves the result recently established in [17], where two more controls are required: one interior (Kelvin–Voigt) damping which acts over the entire cable and another boundary control which is exerted on the lower-end of the cable. Furthermore, we provide an estimate of the exponential decay of the system by means an appropriate Lyapunov functional. Lastly, numerical examples are presented in order to ascertain and highlight our theoretical outcomes. 相似文献
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基于复杂理论的知识创造机理研究 总被引：6，自引：0，他引：6
本文把复杂理论与知识创造相结合,提出基于复杂理论的知识创造机理。文章运用这一机理分别对促进知识创造的正例和抑制知识创造的反例进行了分析。分析表明:在影子系统和合法系统的作用下,清华同方核技术公司占据了创造性空间,获得知识创造;而不适应性学习的存在、影子系统和合法系统对创新的规避,致使成都某电缆公司不能占据创造性空间,从而抑制知识创造。 相似文献
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对于非严格重复线性时变连续系统,初始迭代条件和参考轨迹在一定带宽范围内都是迭代变化的.提出一种非严格的迭代学习方法来控制跟踪整流.通过该方法所获得的控制器,能保证闭环系统的所有信号是全局有界的,能够使超出初始时间间隔的输出跟踪误差收敛到一个小的残差集内,该残差集大小取决于输入矩阵的估测误差.尤其是当输入矩阵已知的情况下,能够让超出的初始时间间隔输出跟踪误差趋近于零. 相似文献
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Ivan Bradaric Athina P. Petropulu Konstantinos I. Diamantaras 《Journal of The Franklin Institute》2002,339(2):161-187
Higher-order statistics (HOS) are well known for their robustness to additive Gaussian noise and ability to preserve phase. HOS estimates, on the other hand, have been criticized for high complexity and the need for long data in order to maintain small variance. Since rank reduction offers a general principle for reduction of estimator variance and complexity, we consider the problem of designing low-rank estimators for HOS. We propose three methods for choosing the transformation matrix that reduces the mean-square error (MSE) associated with the low-rank HOS estimates. We also demonstrate the advantages of using low-rank third-order moment estimates for blind system estimation. Results indicate that the full rank MSE corresponding to some data length N can be attained by a low-rank estimator corresponding to a length significantly smaller than N. 相似文献
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应用能量的方法，研究了简支梁的几何参数对动荷载系数的影响，作出了动荷载系数随几何参数变化的曲线。通过实例得到梁在受到横向冲击时，考虑与不考虑梁自身质量情况下，动载荷系数误差较大。结果表明：动荷载系数随梁的高度增大而增大，随梁的长度、质量增大而减小。 相似文献
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《Journal of The Franklin Institute》2023,360(9):6425-6462
This article proposes a novel explicit-time and explicit-accuracy adaptive fuzzy control for a state-constrained nonlinear nonstrict-feedback uncertain system. This method can explicitly parameterize the upper bound of settling-time with low initial control input under a bounded initial condition. Meanwhile, this method can also explicitly parameterize the upper bound of accuracy while achieving low control input based on the adaptive fuzzy dynamic-approximation theorem. Firstly, a novel generalized explicit-time stability system is proposed by introducing the boundary gain term to render the time-parameter explicit, this method can solve the input conservatism problem caused by the unbounded-state gain term of traditional fixed/prdefined-time function. Then, according to the universal fuzzy approximation theorem, the novel dynamic relationship of adaptive fuzzy logic system between approximation error and adaptive parameters is presented. This relationship can lead to the adaptive fuzzy dynamic-approximation theorem, and an adaptive law designed by this theorem can realize the Lyapunov stability of adaptive control system under a Lasalle invariant set. In the end, a novel adaptive fuzzy control scheme is proposed by the generalized explicit-time function and adaptive fuzzy dynamic-approximation theorem. This scheme can achieve the explicit-time stability by the human-like activation function, and the accuracy can be parameterized by Lyapunov synthesis. Compared with other existing fixed/prdefined-time adaptive fuzzy control methods, the proposed explicit-time and explicit-accuracy controller achieves a significant reduction in the initial control input. Theoretical analysis and simulation results validate the effectiveness of the proposed method. 相似文献