Structural damage identification: influence of model incompleteness and errors

This paper presents a study of the influence of model incompleteness and errors in a structural damage identification technique based on modal data, leading to a set of linear equations. To deal with the incompleteness three methods are used: (1) dynamic and (2) static expansions of measured degrees of freedom and (3) replacement of unmeasured degrees of freedom by their undamaged counterparts. These methods are applied on damage identification of a laminated rectangular plate. The numerical tests show that the best accuracy is obtained with the dynamic expansion, followed by the static expansion and finally, the replacement of unmeasured degrees of freedom. It is also demonstrated that for small damage the errors are the main influence, whereas for large damage the incompleteness becomes the most important factor in the results. The identification of small and large damages is performed by deleting non-reliable equations, i.e., equations that contain large errors.     

A formal notation for specifying static semantic rules

The syntax rules of programming language are generally fairly well understood and may easily be expressed formally as a grammar using BNF. However, the static semantic rules are less well understood and considerably more difficult to express formally. All notations for expressing static semantic rules either formally or informally involve actions being associated with the productions of the grammar. This paper presents such a formal notation which has been applied to various languages and found to be very useful both for the designer and the compiler writer.     

Characteristics of joining inserts for composite sandwich panels

Composite sandwich constructions are widely employed in various light weight structures, because composite sandwich panels have high specific stiffness and high specific bending strength compared to solid panels. Since sandwich panels are basically unsuited to carry localized loads, the sandwich structure should provide joining inserts to transfer the localized loads to other structures.In this work, the load transfer characteristics of the partial type insert for composite sandwich panels were investigated experimentally with respect to the insert shape. The static and dynamic pull out tests of the composite sandwich panels composed of an aluminum honeycomb core, two laminates of carbon fiber/epoxy composite and aluminum insert, were performed. From the experiments, the effect of the insert shape on the mechanical characteristics of composite sandwich panels was evaluated.     

Fatigue Life Assessment and Static Testing of Structural GFRP Tubes Based on Coupon Tests

Fiber-reinforced polymer (FRP) hollow tubes are used in structural applications, such as utility poles and pipelines. Concrete-filled FRP tubes (CFFTs) are also used as piles and bridge piers. Applications such as poles and marine piles are typically governed by cyclic bending. In this paper, the fatigue behavior of glass-FRP filament-wound tubes is studied using coupons cut from the tubes. Several coupon configurations were first examined in 24 tension and five compression monotonic loading tests. Fatigue tests were then conducted on 81 coupons to examine several parameters; namely, loading frequency as well as maximum-to-ultimate (σmax/σult) and minimum-to-maximum (σmin/σmax) stress ratios, including tension tension and tension compression, to simulate reversed bending. The study demonstrated the sensitivity of test results and failure mode to coupon configuration. The presence of compression loads reduced fatigue life, while increasing load frequency increased fatigue life. Stiffness degradation behavior was also established. To achieve at least one million cycles, it is recommended to limit (σmax/σult) to 0.25. Models were used to simulate stiffness degradation and fatigue life curve of the tube. Fatigue life predictions of large CFFT beams showed good correlation with experimental results.     

Stability enhancement of wind energy integrated hybrid system with the help of static synchronous compensator and symbiosis organisms search algorithm

Conventional proportional integral derivative (PID) controllers are being used in the industries for control purposes. It is very simple in design and low in cost but it has less capability to minimize the low frequency noises of the systems. Therefore, in this study, a low pass filter has been introduced with the derivative input of the PID controller to minimize the noises and to improve the transient stability of the system. This paper focuses upon the stability improvement of a wind-diesel hybrid power system model (HPSM) using a static synchronous compensator (STATCOM) along with a secondary PID controller with derivative filter (PIDF). Under any load disturbances, the reactive power mismatch occurs in the HPSM that affects the system transient stability. STATCOM with PIDF controller is used to provide reactive power support and to improve stability of the HPSM. The controller parameters are also optimized by using soft computing technique for performance improvement. This paper proposes the effectiveness of symbiosis organisms search algorithm for optimization purpose. Binary coded genetic algorithm and gravitational search algorithm are used for the sake of comparison.     

湖北省棉花检验中心实验楼加固改造技术

本工程在部分楼层正常使用的情况下,通过对基础进行锚杆静压桩加固;柱、梁采用粘钢和粘碳纤维的加固方法以及植筋技术达到房屋加层。     

Structural assessment of current steel design models for transmission and telecommunication towers

The usual methods of structural analysis involved in the design of steel telecommunication and transmission towers tend to assume a simple truss behaviour where all the steel element connections are considered hinged. Despite this fact, the most commonly used tower geometries possess structural mechanisms that could compromise the assumed structural behaviour. A possible explanation for the structure stability is related to the actual behaviour being close to semi-rigid connections instead of the assumed hinged connections. This paper proposes an alternative structural analysis modelling strategy for the steel tower design considering all the actual structural forces and moments combining three-dimensional beam and truss finite elements. Comparisons of the two above-mentioned design methods with a third method based on the use of spatial beam finite elements to model the main structure and the bracing system on two actually built steel telecommunication towers (40 and 75 m high steel towers) are described. The comparison is based on an extensive parametric study of the tower geometry in order to access the structural tower ultimate and serviceability limit states.     

锚杆静压桩的设计及应用

本文介绍了锚杆静压桩的设计、应用及工作机理 ,总结出锚杆静压桩托换技术的许多优点 ,阐明了该技术用于地基加固、托换和纠偏等方面具有较高的使用价值 ,是值得在地基加固方面推广使用的。     

索穹顶结构在静力荷载作用下的失效分析

索穹顶结构中压杆起着十分重要的作用,压杆的失稳将导致整体结构的失效。故本文研究了索穹顶结构在静力荷载作用下,基于压杆失稳的失效机理,提出了具体的失效判别依据,求得了相应的极限荷载。     

静止进相机工作特性及其电气联锁

介绍了静止式进相机的工作原理、特性并对应用中的静止式进相机与电动机的电气联锁进行了探讨。