Design and Testing of a Structural Monitoring System in an Almería-Type Tensioned Structure Greenhouse

Greenhouse cultivation has gained a special importance in recent years and become the basis of the economy in south-eastern Spain. The structures used are light and, due to weather events, often collapse completely or partially, which has generated interest in the study of these unique buildings. This study presents a load and displacement monitoring system that was designed, and full scale tested, in an Almería-type greenhouse with a tensioned wire structure. The loads and displacements measured under real load conditions were recorded for multiple time periods. The traction force on the roof cables decreased up to 22% for a temperature increase of 30 °C, and the compression force decreased up to 16.1% on the columns or pillars for a temperature and wind speed increase of 25.8 °C and 1.9 m/s respectively. The results show that the structure is susceptible to daily temperature changes and, to a lesser extent, wind throughout the test. The monitoring system, which uses load cells to measure loads and machine vision techniques to measure displacements, is appropriate for use in different types of greenhouses

The application of parallel computer technology to the dynamic analysis of suspension bridges

This research is concerned with the application of distributed computer technology to the solution of non-linear structural dynamic problems, in particular the onset of aerodynamic instabilities in long span suspension bridge structures, such as flutter which is a catastrophic aeroelastic phenomena. The thesis is set out in two distinct parts:- Part I, presents the theoretical background of the main forms of aerodynamic instabilities, presenting in detail the main solution techniques used to solve the flutter problem. The previously written analysis package ANSUSP is presented which has been specifically developed to predict numerically the onset of flutter instability. The various solution techniques which were employed to predict the onset of flutter for the Severn Bridge are discussed. All the results presented in Part I were obtained using a 486DX2 66MHz serial personal computer. Part II, examines the main solution techniques in detail and goes on to apply them to a large distributed supercomputer, which allows the solution of the problem to be achieved considerably faster than is possible using the serial computer system. The solutions presented in Part II are represented as Performance Indices (PI) which quote the ratio of time to performing a specific calculation using a serial algorithm compared to a parallel algorithm running on the same computer system

Structural Optimization of Cable-Stayed Bridges Considering the Action of Permanent and Transitory Loads

Cable-stayed bridges are complex structures with several advantages such as aesthetical appeal, economic use of materials, and efficient construction method. Due to these advantages and the extensive knowledge gained from projects over the years, longer cable-stayed bridges are being constructed. As span lengths increase, structures become more flexible, which makes the accurate evaluation of wind loads critically important in the design of cable-stayed bridges. A large number of variables are involved in the design of cable-stayed bridges. Those include overall geometric dimensions, cross-sectional dimensions, number of stay-cables and pre-tensioning forces to be applied to the cables. Taking all variables into account, and considering the need to conduct multiple moving load analyses and to calculate accurately aerodynamic wind forces, a design optimization process for such bridges becomes challenging. In this thesis, a numerical model capable of achieving this design optimization task is developed. The numerical model uses a structural system in which the deck is composite steel-concrete with two I main girder. The developed numerical model is based on the Finite Element Method (FEM), the Real Coded Genetic Algorithm (RCGA), and the Discrete-Phases Design Approach. The latter classifies variables into two categories: (i) main variables: number of stay-cables, I-girder inertia, concrete slab thickness, tower cross-section external dimensions, tower height above the deck; (ii) secondary variables: I-girder dimensions, stay-cable areas and pre-tensioning forces. The main variables are design variables optimized directly by the RCGA, while the secondary variables are indirectly optimized by the discrete phases. Buffeting wind loads are considered as equivalent static forces, which were validated through a theoretical-experimental correlation. This powerful tool is used to assess the importance of considering truck versus lane loads, as well as wind buffeting loads and various aeroelastic instabilities in the design optimization process. Results show that the most critical load combination include the wind effect, and that the critical wind velocities of aeroelastic phenomena play a significant role for high values of basic wind speeds

Experimental Study on the Performance of Negative Stiffness Dampers for Cable Vibration Control

Due to the superior performance of negative stiffness damper (NSD), its application to the vibration control of bridge stay cables attracts much research attention in recent years. Nevertheless, the effect of various system parameters on NSD performance has not been fully studied, especially the impact of damper support stiffness. In the current study, an experimental study on the dynamic response of a cable-NSD system is conducted to investigate the effect of negative damper stiffness and damper support stiffness on the efficiency of NSD. A numerical simulation is performed to not only validate the experimental results, but also evaluate the influence of various system parameters on NSD performance. A NSD design tool is developed to predict optimum damper size and the corresponding maximum achievable modal damping ratio of a cable-NSD system. Results show that when the stability criterion is satisfied, choosing stronger negative damper stiffness would enhance NSD efficiency. The impact of support stiffness on NSD performance depends on the magnitude of damper stiffness. Attach a NSD to a cable having larger sag and/or higher bending stiffness would yield a lower maximum achievable system modal damping ratio

Bridge aerodynamics in skew winds: Generalized buffeting load modelling and response analysis

PhD thesis in Mechanical and Structural Engineering and Materials ScienceThis thesis deals with the modelling of wind loads on bridges. When turbulent wind blows past a bridge deck, the deck experiences fluctuating loads, i.e., buffeting loads. Most buffeting theories concern straight bridge decks subjected to normal wind action, i.e., winds perpendicular to the bridge deck. This thesis initially reproduces the normal wind buffeting theory in a format that can be easily generalized to skew winds (i.e., non-perpendicular). The thesis then revises the state-of-the-art of the skew wind buffeting theory and proposes novel corrections, significant simplifications, and generalizations to that theory. Since the preferred skew wind load formulation requires the estimation of yaw- and inclination-angle-dependent aerodynamic coefficients, the thesis also provides a generalization and improvements to the traditional approach using only inclination-angle-dependent aerodynamic coefficients. Multiple challenges arise when putting into practice the skew wind buffeting theory. An ongoing floating bridge project, whose details are described in the thesis, is considered an ideal case for this application. The long, curved, continuous and flexible structure is planned to span a record 5000 m wide section of the Bjørnafjord in Norway, where it will be subjected to strong winds from multiple directions. Wind tunnel experiments were conducted by a third party, where a sectional model of the bridge girder was tested under skew winds for a large domain of yaw angles. Six aerodynamic coefficients are estimated for 30 combinations of yaw and inclination angles. Four different approaches to fit and extrapolate the coefficients are compared and discussed, enabling a 360-degree assessment of the skew wind buffeting response of the bridge. The proposed approach uses continuous and differentiable piecewise constrained bivariate polynomial functions covering the spherical domain of possible wind directions while respecting symmetries and imposing physical principles at certain angles. A simplified numerical model of the bridge is developed, whose properties, assembling process, modal analysis and sensitivity results are presented in the thesis. The numerical model is then used to assess the novel and the traditional buffeting load formulations. The bridge displacement response is compared for different fits of the aerodynamic coefficients and for different buffeting and quasi-steady motion-dependent force formulations. Both frequency- and time-domain analyses are performed to increase confidence in the results. Methods that neglect the three-dimensionality of the wind-structure interaction and only consider the two-dimensional normal-plane projection of the wind are shown to underestimate the bridge response under skew winds. The exceptionally long span of the case study makes it an equally good candidate for examining the wind field homogeneity assumption and its implications. A full long-term response analysis is performed considering all strong wind events in a 20-year-long wind field simulation period. Inhomogeneous (i.e., space-varying) wind speeds and directions were provided by a high-resolution Weather Research and Forecasting (WRF) model. Inhomogeneous wind turbulence intensities are estimated using a hybrid method combining formulations given in a European standard with an artificial neural network, trained with five years of relevant measurement data. An analogous database of equivalent homogeneous wind fields is created to compare the associated bridge responses. The long-term response is analysed, demonstrating a varying accuracy of the homogeneity assumption. On average, the bridge response under inhomogeneous winds is larger than that under homogeneous winds, but to a different extent for different response components. Large underestimations and overestimations of the response are obtained for particular wind events. The use of a state-of-the-art skew wind formulation in combination with comprehensive wind tunnel tests and careful long-term inhomogeneous wind buffeting analyses is encouraged in the design of wind-sensitive bridges subjected to strong skew winds

Performance of Wind Exposed Structures

PERBACCO (a free Italian acronym for Life-cycle Performance, Innovation and Design Criteria for Structures and Infrastructures Facing Æolian and Other Natural Hazards) is a research project partly funded by the Italian Ministry for University (MIUR) in the PRIN (Progetti di Ricerca di Interesse Nazionale) framework, for the years 2004-05.Within the project, a first attempt has been made to integrate different disciplines aiming at an overall optimization of the performance of a wide range of wind exposed structures and infrastructures, with consequent benefi cial impact on the society.The overall objectives were (a) to provide unifi ed concepts for "expected performance" and "risks induced by æolian and other natural hazards", to be applied to structures and infrastructures over their whole life-cycle, such to be acceptable to stakeholders in the construction process (i.e. from the owner to the end-user), (b) to provide models and methodologies for dynamic monitoring of the performance of structures and infrastructures, to be integrated in appropriately designed procedures, and (c) to collect, refi ne, fi le and disseminate the knowledge available on a European basis, concerning the performance of wind-exposed structures and facilities, in a way such to be of use to Construction Industry. This volume summarises the main results obtained during the Project, with each Section addressing a different class of problems, to which many research Units have contributed. A list of papers containing the main results of the research activities carried out within the Project is also provided in each Section