Automating Preliminary Column Force Calculations In Multy-Storey Buildings

In civil engineering practice, values of column forces are often required before any detailed analysis of the structure has been performed. One of the reasons for this arises from the fast-tracked nature of the majority of construction projects: foundations are laid and base columns constructed whilst analysis and design are still in progress. A need for quick results when feasibility studies are performed or when evaluating the effect of design changes on supporting columns form other situations in which column forces are required, but where a detailed analysis to get these forces seems superfluous. Thus it was concluded that the development of an efficient tool for column force calculations, in which the extensive input required in a finite element analysis is to be avoided, would be highly beneficial. The automation of the process is achieved by making use of a Voronoi diagram. The Voronoi diagram is used a) for subdividing the floor into influence areas and b) as a basis for automatic load assignment. The implemented procedure is integrated into a CAD system in which the relevant geometric information of the floor, i.e. its shape and column layout, can be defined or uploaded. A brief description of the implementation is included. Some comparative results and considerations regarding the continuation of the study are given

Vortex-induced vibrations of a freely vibrating cylinder near a plane boundary: experimental investigation and theoretical modelling

This work reports on experiments that were performed with a freely vibrating cylinder exposed to currents and placed near a plane boundary parallel to the cylinder axis. It is observed that the proximity of the boundary affects the vertical response of the cylinder in two ways: (i) for gaps between 0.75 and 2 diameters (D), the amplitude of oscillation is reduced; (ii) for gaps smaller than 0.75D, the cylinder impacts the boundary, resulting in an increase of amplitudes and frequencies of oscillations as the flow is accelerated. The in-line force acting on the cylinder is also examined, and the dependency of its harmonic components on the flow velocity and distance to the boundary is evaluated. Besides the typical amplification of the mean component inside the lock-in region, it is also observed that as the cylinder is placed closer to the boundary, the harmonic component with the frequency of the vertical oscillations increases, while the component with twice that frequency decreases in similar amount. Based on the experimental observations, an existing wake-oscillator model for vortex-induced vibrations is enhanced in order to account for the effect of the boundary. The proposed model introduces an effective damper that is activated when the cylinder reaches a certain distance from the boundary, and a damper/spring set representing the rigidity of the boundary and the dissipation of energy due to impact

CAD-supported preliminary column force calculations in multi-storey buildings

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2006.The predominately manual, time-consuming and error-prone procedure currently used in engineering offices for the calculation of preliminary column forces in multi-storey buildings constitutes the motive for the research described in this study. Identifying the current procedure as in need of improvement, techniques and prototype software posing a semi-automated alternative, are developed. Influence areas used for load-assignment are established with the use of a Voronoi diagram calculated for a specific floor geometry. The forces transferred to the columns are based solely on the size of the influence areas thus calculated. The definition of the floor geometry, as well as the definition of loads and other necessary input parameters, are performed in a CAD-system, into which the Voronoi functionality is integrated. The accuracy of the forces obtained with the implemented procedure and, consequently, the accuracy of the forces as they are calculated in current practice, is determined through comparison with the results of finite element analyses. The comparative analysis of a sample of typical floor geometries allows an evaluation of the results and the identification of tendencies observed regarding the errors obtained. It is concluded that calculating column forces based on influence areas, i.e. solving a geometrical problem without taking any stiffness properties into account, is unsafe. The implication hereof is twofold. Firstly, it serves as a warning concerning the technique currently used in practice and secondly, it steers the investigation in the direction of a finite element analysis: using the influence areas as a basis for automatic meshing, a semi-automated analysis can be performed relatively inexpensively, using plate elements

Force Identification in Structural Dynamics (Krachtidentificatie in structuurdynamica)

Dynamic force identification is a specific type of inverse problem where the time-varying force distribution on a structure is reconstructed from measured vibration response data. During the past few decades a wide variety of techniques has been suggested for the solution of such indirect force reconstruction or input estimation problems. The problem can besolved in either the time or frequency domain; it can be solved in batch mode, recursively, or, as sometimes done when the force has to be localized, iteratively. In this work the focus is on time-domain techniques,with preference given to recursive solutions. It is assumed that a description of the structural system is available, hence limiting the discussion to model-based identification. Based on the type of model used for the identification, the methodologies treated in the text aredivided into deterministic and combined deterministic-stochastic formulations of the problem. Some classical deterministic methods are reviewed, compared, and in some cases improved, whilst a number of new combined deterministic-stochastic techniques are developed. All presented force identification techniques are validated by means of various numerical and/or experimental analyses. The degree to which the accuracyof the identified forces is influenced by the accuracy of the model, the type of data used, and the locations of the sensors, depends on the formulation used. It can generally be concluded that the quality of the results deteriorates with an increase in the distance between the sensors and the applied forces. Also, if some components of the force do not have a distinguishable influence on the measured data, these components cannot be recovered in the identification - consider, for instance, the insensitivity of acceleration data to static or low-frequency components of the force. Finally, the spatial accuracy with which multiple or distributed loads can be identified is shown to be dependent on the number of modes contributing to the measured response. As opposed to the deterministic approaches, the combined or filtering methods involve an estimation of the forces as well as the states (displacements, velocities) of the structure, enabling them to be used also for response prediction in the structure at unmeasured locations. It is concluded that certain response quantities can be estimated even if the model is known with only limited accuracy and no information is available on the location of the input forces. These estimates can be used for a variety of purposes, including the prediction of stresses and fatigue loading.nrpages: 152status: publishe

Estimation of the dynamic response of a slender suspension bridge using measured acceleration data

Suspension bridges with very long spans and slender designs are susceptible to large-amplitude dynamic excitation. Monitoring systems installed on bridges can provide measurement data (e.g. accelerations) and therewith valuable information on the true dynamic behaviour. This pilot study examines the possible use of recently developed methods for real-time response estimation at unmeasured locations. The methodology for response estimation is tested in a case study on the Hardanger Bridge, a 1310 m long suspension bridge in Norway, which has a network of twenty accelerometers. Two techniques, a joint input-state estimation algorithm (JIS) and a dual Kalman filter (DKF), are used to estimate the full-field dynamic response using data measured at the bridge and a reduced order structural model. The results show that the DKF is able to estimate accelerations fairly accurately. The JIS estimate, however, suffer from ill-conditioning and consequently show severe errors. Possible reasons for this ill-conditioning are briefly discussed

An adapted dynamic programming algorithm for the identification of moving forces

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Wind load identification on a tower structure

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