7 research outputs found
STRUCTURAL INTEGRITY ASSESSMENT USING VIBRATION DATA
Engineering structures need to be assessed as part of activities to ensure their continued
serviceability. Global methods of assessment which also give an indication of local
conditions are most attractive since they are cost effective and flexible. A suitable method
with these attributes is vibration monitoring which involves relating dynamic properties, or
changes in them, to the integrity of the assessed structure. The present study investigates
the application of vibration testing to structural integrity assessment of civil engineering
structures.
A survey of existing methods of damage detection, location and quantification in structures
using vibration testing was conducted. Evaluation of the performance of some of the more
promising methods was conducted using both simulated and experimental data. The results
revealed that the damage identification process could be enhanced if appropriate modes are
used. To this end, a new function, called Modal Sensitivity Values, has been proposed for
identifying damage sensitive modes to be included in damage detection and location
methods. It was also found that some success could be achieved if system identification
and model updating procedures are applied to the problem of damage detection in
structures. The literature survey revealed that most of the available methods are not
applicable to general structural systems and are often limited by the damage model
assumed. A new method, called Integrity Index Damage Location method, of assessing
structural integrity using vibration data has also been proposed. The method is applicable
to any structure and any damage type that affects the integrity/stiffness of the structure.
Performance evaluation of the method using both numerical and experimental data is
presented.
Full-scale forced vibration tests were conducted before and after repairs on two reinforced
concrete highway bridges. The vibrator used during the tests was developed during the
research project and details of its development and operation are given in the thesis. As
a background to the tests, a review of full-scale dynamic testing of bridge structures was
conducted. Results from the tests were used to investigate the effectiveness of forced
vibration testing as an integrity monitoring tool. It was found that the repair works caused
slight (less than 5%) changes in the natural frequencies while there was no definite trend
in the changes to the modal damping ratios. Comparison of frequency response functions
and mode shapes, using modal analysis procedures, was found to give an indication of the
presence and location of the repairs. The integrity assessment method proposed was also
able to identify some of the affected parts of the structures.
Results from the full-scale tests were also compared with predictions from finite element
analysis. Good correlation was obtained between the measured and calculated natural
frequencies and mode shapes, thus enabling validation of the analytical models within
limits of the model assumptions and experimental errors. The results demonstrate the
importance of accurate representation of boundary conditions. They (results) also showed
that the vertical stiffness of new bearings installed on one of the bridges is not as high as
was assumed in the design
INVESTIGATION OF THE DYNAMIC BEHAVIOUR OF NON-UNIFORM THICKNESS CIRCULAR PLATES RESTING ON WINKLER AND PASTERNAK FOUNDATIONS
The study of the dynamic behaviour of non-uniform thickness circular plate resting on elastic foundations is very imperative in designing structural systems. This present research investigates the free vibration analysis of varying density and non-uniform thickness isotropic circular plates resting on Winkler and Pasternak foundations. The governing differential equation is analysed using the Galerkin method of weighted residuals. Linear and nonlinear case is considered, the surface radial and circumferential stresses are also determined. Thereafter, the accuracy and consistency of the analytical solutions obtained are ascertained by comparing the existing results available in pieces of literature and confirmed to be in a good harmony. Also, it is observed that very accurate results can be obtained with few computations. Issues relating to the singularity of circular plate governing equations are handled with ease. The analytical solutions obtained are used to determine the influence of elastic foundations, homogeneity and thickness variation on the dynamic behaviour of the circular plate, the effect of vibration on a free surface of the foundation as well as the influence of radial and circumferential stress on mode shapes of the circular plate considered. From the results, it is observed that a maximum of 8.1% percentage difference is obtained with the solutions obtained from other analytical methods. Furthermore, increasing the elastic foundation parameter increases the natural frequency. Extrema modal displacement occurs due to radial and circumferential stress. Natural frequency increases as the thickness of the circular plate increases, Conversely, a decrease in natural frequency is observed as the density varies. It is envisioned that; the present study will contribute to the existing knowledge of the classical theory of vibration
Review of Classical Methods in Supersaturated Designs (SSD) for factor Screening
Supersaturated designs are fractional factorial designs that have too few runs to allow the estimation of the main effects of all the factors in the experiment. There has been a great deal of interest in the development of these designs for factor screening in recent years. A review of supersaturated design is presented, including criteria for design selection, with reference to the popular E(s2) criterion and classical methods for constructing supersaturated designs. Classical methods have been suggested for the analysis of data from supersaturated designs and these are critically reviewed and illustrated. Keywords: Supersaturated, Classical method, Screening, fractional factorial and E(S2
Response surface methodology assessment of osmotic pre-drying and convective dehydration processes on the anti-oxidant property of Hausa variety of tomato
This study was conducted to determine the effect of osmotic pre-drying treatment on the vitamin C content of Hausa variety of tomato. The tomatoes used were sliced to a uniform diameter of 10 mm, deseeded and then osmotically pre-treated with sugar and honey solution at different osmotic concentrations (20, 30, 40, 50, 60 °Bx), osmotic time (10, 20, 30, 40 and 50 min) and osmotic temperature (10, 20, 30, 40, 50 °C). Experimental design was done using the Central Composite Design (CCD) methodology of Design Expert software version 6.0.6. Drying of the samples was done at 65 °C in a cabinet dryer operating mainly on convectional heat transfer. Drying process was completed and terminated when the samples reached their equilibrium moisture content between 3-5% after total drying time of 10 hours. The data obtained were analysed statistically using analysis of variance (ANOVA) and regression analysis at p≤0.05 significance level. The developed model was significant and has goodness of fit with an R2 value of 71.29% and lack of fit test was insignificant at p≤ 0.05. Optimized process conditions for producing the best quality of tomato product with vitamin C content of 22 mg/100 g were 35.43 °Bx osmotic concentration, 11.10 min osmotic time and 23.86 °C osmotic temperature having a desirability function of 1. These conditions were considered to be advantageous as they were more economical, time and energy saving
Оценка гибридного метода исследования динамического поведения изотропных прямоугольных пластин, опирающихся на двухпараметрическое основание
Dynamic behaviour of isotropic rectangular plate resting on two-parameter foundation
is investigated. The governing partial differential equation is transformed to ordinary differential
equation due to Galerkin method of separation. The hybrid method of Laplace transform and
variation parameters method is used to analyze the ordinary differential equation. Introduction of
exact method helps in fast convergence of the results. Obtained analytical solutions are compared
with existing literature and confirmed as accurate. They are used to examine the effect of
controlling parameters on the plate natural frequencies. Due to obtained results it is obvious that,
the increase of both elastic foundation parameter and aspect ratio results in increasing the natural
frequency. The solution is found immediately by means of a few iterationsИсследовано динамическое поведение изотропной прямоугольной пластины,
опирающейся на двухпараметрическое основание. Основное дифференциальное уравнение
в частных производных преобразуется в обыкновенное дифференциальное уравнение с
использованием метода разделения Галеркина. Для анализа обыкновенного дифференциального
уравнения применен гибридный метод преобразования Лапласа и параметров вариации.
Введение точного метода помогает в быстрой конвергенции результатов. Полученные
аналитические решения сравниваются с существующей литературой и подтверждаются с
хорошей точностью. Их используют для изучения влияния управляющих параметров на
собственные частоты пластины. Из полученных результатов видно, что рост параметров
упругого основания и соотношения сторон увеличивает собственную частоту. Решение находят
быстро с несколькими итерациям