Real time structural damage assessment from vibration measurements

Damage identification in civil engineering structures using vibration measurements has become an important area of research. A reliable and cost effective method is required to detect and quantify local damage in the structures. The objective of this new proposed method is to identify structural damage in real time at a more detailed level directly from the vibration measurements. Structural damage is assumed to be associated with a proportional reduction of element stiffness matrix. Dynamics characteristics of the structure are calculated by using Newmark's numerical integration method based on measured acceleration data. The change in the stiffness matrix caused by structural damage is implemented into the equation of motion of the dynamic system. A system of governing equations is derived, where the difference between the vibration data of undamaged and damaged structures can be directly adopted. The changes in the stiffness matrix are represented by the changes in the coefficients associated with element stiffness matrixes. Those coefficients can be used as damage parameters in structural damage detection. Both the location and extent of the damage are then determined based on the inverse calculations of damage parameters of the individual elements. Finally, a numerical example is utilised to demonstrate the effectiveness of the proposed approach for on-line structural damage assessmen

Effect of Social Capital Endowment on the Welfare of Farming Households in Kwara State, Nigeria

This study examines the effect of social on welfare of farming households in Kwara state, Nigeria. It focused on household food security status and nutritional status of under-five children as measure of household welfare. A three stage random sampling was employed to collect primary data from 160 farming households in Kwara State. The data was analysed using descriptive statistics, ordinary least square regression (OLS) and probit regression analyses. The regression analysis result shows that educational level, household size, household monthly income, dependency ratio and social capital index were significant in explaining variation in household food security status and in addition, number of friends of household head and status of household members in social groups are also significant in explaining nutrition status of under-five children in the households. The study showed that household’s per capital calories intake increases with increase decision making index and heterogeneity index. Children nutrition status increase as density of membership and heterogeneity indices increase. The study concludes that social capital has a positive effect on household food security and children nutrition status thereby improving household welfare. The study therefore recommended that farmer should be encouraged to join social group so as to increase their social capital endowment. Also, social groups need to be strengthened and supported to improve household social network so as to improve household welfare

Multi-failure mode assessment of buried concrete pipes subjected to time-dependent deterioration, using system reliability analysis

This article presents a reliability-based methodology for assessment of corrosion-affected, reinforced concrete sewers, considering serviceability and ultimate strength as limit state functions for multi-failure mode assessment. A stochastic model for system failure analysis is developed, which relates to key factors that affect concrete corrosion in a concrete sewer system in Harrogate in the United Kingdom. A time-dependent Monte Carlo simulation method is employed to quantify the probability of failure of concrete sewers with 70-cm diameter due to two categories of failure modes (serviceability and ultimate strength). Factors that affect the failure due to concrete corrosion are also studied by way of parametric sensitivity analysis

Modelling suction caisson installation in sand using FLAC3D

Suction caisson foundations have been very popular in oil and gas industry and the current trend is to extend their use to offshore wind farms. A suction caisson is an upturned ?bucket? of cylindrical shape made from steel. Seepage conditions play a pivotal role in suction caisson installation process in sand. Pressure gradients generated by the imposed suction inside the caisson cavity cause an overall reduction in the soil resistance around the caisson wall and tip. This transient soil loosening around the caisson wall helps caisson penetration into the seabed. However, these effects must be controlled to avoid soil failure due to critical conditions such as piping or loss of soil shear strength. In this paper, we endeavour to study the role of seepage on the suction caisson installation process in sand. We investigate the effect of seepage conditions on soil resistance to caisson penetration with a particular focus on how frictional and tip resistance are differently affected. For this purpose a series of finite difference simulations of suction caisson installation process are performed using FLAC3D models. The required suction is predicted using an explicit strategy which consists of updating current suction based on displacement history available after the previous prescribed displacement increment. The results of FLAC3D models show that this approach provides an insight on how soil resistance evolves under suction during the installation process and confirm the effect of seepage on total reduction of shear resistance around the caisson wall during installation in sand

Representation of capillary forces in polydisperse granular assemblies in the pendular regime

In this paper, the equations governing capillary forces between polydisperse spheres in the pendular regime are presented. These equations are adopted within the Laplace-Young framework using a Toroidal approximation of the liquid bridge geometry. Based on the numerical solution of the fundamental problem and a novel evolutionary computing technique (EPR), an analytical expression is developed for the prediction of capillary force. The analytical expression accounts for the effects of intrinsic parameters such as inter-particle separation distance, ratio of particle radii and liquid volume. Such a representation of capillary forces is shown to mimic the real behaviour with a good accuracy. The developed model can be implemented in discrete element computer simulations as it does not require any iterations to update contact forces at particle level

Relative temperature changes within concrete made with recycled glass aggregate

The focus of much of the published literature on the use of glass in concrete has been on its use as a cement replacement material. Recent studies have shown that recycled glass can be used as an aggregate without compromising concrete strength. However little research has been carried out on the thermal properties of such concretes. The temperature of recycled glass cullet after production using an implosion technique remained high for the next 24 h. Thus, an experimental investigation was undertaken in order to study whether concrete made with such material had significantly different thermal properties in comparison to concrete made with natural aggregates. The process of cement hydration resulted in much higher temperatures being produced in concrete made with glass cullet. Further testing revealed that exposure of concrete to both high (60 ?C) and low (?20 ?C) temperatures produced, greater temperature stability. These findings suggest that concrete made with recycled glass could have two important applications, namely, cold temperature concreting and in buildings to maintain greater temperature stability

GPR applications in mapping the subsurface root system of street trees with road safety-critical implications

Street trees are an essential element of urban life. They contribute to the social, economic and environmental development of the community and they form an integral landscaping, cultural and functional element of the infrastructure asset. However, the increasing urbanisation and the lack of resources and methodologies for the sustainable management of road infrastructures are leading to an uncontrolled growth of roots. This occurrence can cause substantial and progressive pavement damage such as cracking and uplifting of pavement surfaces and kerbing, thereby creating potential hazards for drivers, cyclists and pedestrians. In addition, neglecting the decay of the principal roots may cause a tree to fall down with dramatic consequences. Within this context, the use of the ground-penetrating radar (GPR) non-destructive testing (NDT) method ensures a non-intrusive and cost-effective (low acquisition time and use of operators) assessment and monitoring of the subsurface anomalies and decays with minimum disturbance to traffic. This allows to plan strategic maintenance or repairing actions in order to prevent further worsening and, hence, road safety issues. This study reports a demonstration of the GPR potential in mapping the subsurface roots of street trees. To this purpose, the soil around a 70-year-old fir tree was investigated. A ground-coupled GPR system with central frequency antennas of 600 MHz and 1600 MHz was used for testing purposes. A pilot data processing methodology based on the conversion of the collected GPR data (600 MHz central frequency) from Cartesian to polar coordinates and the cross-match of information from several data visualisation modes have proven to identify effectively the three-dimensional path of tree roots

Road foundation detailing using ground penetrating radar systems with different frequencies

This paper reports on the assessment of the underground construction details of a road pavement using different frequency ground penetrating radar (GPR) antenna systems. In addition to this, the possible presence and location of an underground watercourse was investigated in this work. The existence of the latter problem was perceived due to reoccurrence of longitudinal and traversal road surface cracking as well as subsidence at a particular location of the road. Reoccurrence of this damage was interpreted and related to the possible existence of an underground watercourse. The original design and the construction of the road were as such to prevent this movement. Therefore it seemed necessary to perform a GPR survey to investigate and confirm the underground construction details of the road. To this purpose, the identified area was surveyed using high to low frequency antennas with 2000 MHz, 900 MHz, 600 MHz and 200 MHz central frequencies of investigation. The results were conclusive in terms of construction details provided and evidence of subsidence within the road identified. The maximum depth of penetration achieved by the use of the 600 MHz and the 200 MHz antennas (maximum of 3 m) did not allow to identify or confirm the existence of any underground watercourse

Road foundation detailing using ground penetrating radar systems with different frequencies

This paper reports on the assessment of the underground construction details of a road pavement using different frequency ground penetrating radar (GPR) antenna systems. In addition to this, the possible presence and location of an underground watercourse was investigated in this work. The existence of the latter problem was perceived due to reoccurrence of longitudinal and traversal road surface cracking as well as subsidence at a particular section of the road. Reoccurrence of this damage was interpreted and related to the possible existence of an underground watercourse. The original design and the construction of the road were as such to prevent this movement. Therefore it seemed necessary to perform a GPR survey to investigate and confirm the underground construction details of the road. To this purpose, the identified area was surveyed using high to low frequency antennas with 2000 MHz, 900 MHz, 600 MHz and 200 MHz central frequencies of investigation. The results were conclusive in terms of construction details provided and evidence of subsidence within the road identified. The maximum depth of penetration achieved by the use of the 600 MHz and the 200 MHz antennas (maximum of 3 m) did not allow to identify or confirm the existence of any underground watercourse