Dissertations / Theses on the topic 'Structural analysis (Engineering) Structural engineering'

Uncertainty involved in the safe and comfort design of the structures is a major concern of civil engineers. Traditionally, the uncertainty has been overcome by utilizing various and relatively large safety factors for loads and structural properties. As a result in conventional design of for example tall buildings, the designed structural elements have unnecessary dimensions that sometimes are more than double of the ones needed to resist normal loads. On the other hand the requirements for strength and safety and comfort can be conflicting. Consequently, an alternative approach for design of the structures may be of great interest in design of safe and comfort structures that also offers economical advantages. Recently, there has been growing interest among the researchers in the concept of structural control as an alternative or complementary approach to the existing approaches of structural design. A few buildings have been designed and built based on this concept. The concept is to utilize a device for applying a force (known as control force) to encounter the effects of disturbing forces like earthquake force. However, the concept still has not found its rightful place among the practical engineers and more research is needed on the subject. One of the main problems in structural control is to find a proper algorithm for determining the optimum control force that should be applied to the structure. The investigation reported in this thesis is concerned with the application of active control to civil engineering structures. From the literature on control theory. (Particularly literature on the control of civil engineering structures) problems faced in application of control theory were identified and classified into two categories: 1) problems common to control of all dynamical systems, and 2) problems which are specially important in control of civil engineering structures. It was concluded that while many control algorithms are suitable for control of dynamical systems, considering the special problems in controlling civil structures and considering the unique future of structural control, many otherwise useful control algorithms face practical problems in application to civil structures. Consequently a set of criteria were set for judging the suitability of the control algorithms for use in control of civil engineering structures. Various types of existing control algorithms were investigated and finally it was concluded that predictive optimal control algorithms possess good characteristics for purpose of control of civil engineering structures. Among predictive control algorithms, those that use ARMA stochastic models for predicting the ground acceleration are better fitted to the structural control environment because all the past measured excitation is used to estimate the trends of the excitation for making qualified guesses about its coming values. However, existing ARMA based predictive algorithms are devised specially for earthquake and require on-line measurement of the external disturbing load which is not possible for dynamic loads like wind or blast. So, the algorithms are not suitable for tall buildings that experience both earthquake and wind loads during their life. Consequently, it was decided to establish a new closed loop predictive optimal control based on ARMA models as the first phase of the study. In this phase it was initially established that ARMA models are capable of predicting response of a linear SDOF system to the earthquake excitation a few steps ahead. The results of the predictions encouraged a search for finding a new closed loop optimal predictive control algorithm for linear SDOF structures based on prediction of the response by ARMA models. The second part of phase I, was devoted to developing and testing the proposed algorithm The new developed algorithm is different from other ARMA based optimal controls since it uses ARMA models for prediction of the structure response while existing algorithms predict the input excitation. Modeling the structure response as an AR or ARMA stochastic process is an effective mean for prediction of the structure response while avoiding measurement of the input excitation. ARMA models used in the algorithm enables it to avoid or reduce the time delay effect by predicting the structure response a few steps ahead. Being a closed loop control, the algorithm is suitable for all structural control conditions and can be used in a single control mechanism for vibration control of tall buildings against wind, earthquake or other random dynamic loads. Consequently the standby time is less than that for existing ARMA based algorithms devised only for earthquakes. This makes the control mechanism more reliable. The proposed algorithm utilizes and combines two different mathematical models. First model is an ARMA model representing the environment and the structure as a single system subjected to the unknown random excitation and the second model is a linear SDOF system which represents the structure subjected to a known past history of the applied control force only. The principle of superposition is then used to combine the results of these two models to predict the total response of the structure as a function of the control force. By using the predicted responses, the minimization of the performance index with respect to the control force is carried out for finding the optimal control force. As phase II, the proposed predictive control algorithm was extended to structures that are more complicated than linear SDOF structures. Initially, the algorithm was extended to linear MDOF structures. Although, the development of the algorithm for MDOF structures was relatively straightforward, during testing of the algorithm, it was found that prediction of the response by ARMA models can not be done as was done for SDOF case. In the SDOF case each of the two components of the state vector (i.e. displacement and velocity) was treated separately as an ARMA stochastic process. However, applying the same approach to each component of the state vector of a MDOF structure did not yield satisfactory results in prediction of the response. Considering the whole state vector as a multi-variable ARMA stochastic vector process yielded the desired results in predicting the response a few steps ahead. In the second part of this phase, the algorithm was extended to non-linear MDOF structures. Since the algorithm had been developed based on the principle of superposition, it was not possible to directly extend the algorithm to non-linear systems. Instead, some generalized response was defined. Then credibility of the ARMA models in predicting the generalized response was verified. Based on this credibility, the algorithm was extended for non-linear MDOF structures. Also in phase II, the stability of a controlled MDOF structure was proved. Both internal and external stability of the system were described and verified. In phase III, some problems of special interest, i.e. soil-structure interaction and control time delay, were investigated and compensated for in the framework of the developed predictive optimal control. In first part of phase III soil-structure interaction was studied. The half-space solution of the SSI effect leads to a frequency dependent representation of the structure-footing system, which is not fit for control purpose. Consequently an equivalent frequency independent system was proposed and defined as a system whose frequency response is equal to the original structure -footing system in the mean squares sense. This equivalent frequency independent system then was used in the control algorithm. In the second part of this phase, an analytical approach was used to tackle the time delay phenomenon in the context of the predictive algorithm described in previous chapters. A generalized performance index was defined considering time delay. Minimization of the generalized performance index resulted into a modified version of the algorithm in which time delay is compensated explicitly. Unlike the time delay compensation technique used in the previous phases of this investigation, which restricts time delay to be an integer multiplier of the sampling period, the modified algorithm allows time delay to be any non-negative number. However, the two approaches produce the same results if time delay is an integer multiplier of the sampling period. For evaluating the proposed algorithm and comparing it with other algorithms, several numerical simulations were carried during the research by using MATLAB and its toolboxes. A few interesting results of these simulations are enumerated below: ARM A models are able to predict the response of both linear and non-linear structures to random inputs such as earthquakes. The proposed predictive optimal control based on ARMA models has produced better results in the context of reducing velocity, displacement, total energy and operational cost compared to classic optimal control. Proposed active control algorithm is very effective in increasing safety and comfort. Its performance is not affected much by errors in the estimation of system parameters (e.g. damping). The effect of soil-structure interaction on the response to control force is considerable. Ignoring SSI will cause a significant change in the magnitude of the frequency response and a shift in the frequencies of the maximum response (resonant frequencies). Compensating the time delay effect by the modified version of the proposed algorithm will improve the performance of the control system in achieving the control goal and reduction of the structural response.

Thesis (PhD)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Structural analysis is examined in order to identify its essential information requirements, its fundamental tasks, and the essential functionalities that applications which support it should provide. The special characteristics of the information content of structural analysis and the algorithms that operate on it are looked into and exploited to devise data structures and utilities that provide proper support of the analysis task within a local environment, while presenting the opportunity to be extended to the context of a distributed network-based collaboratory as well. Aspects regarding the distribution of analysis parameters and methods are analysed and alternatives are evaluated. The extentions required to adapt the local data structures and utilities for use in a distributed communication network are developed and implemented in pilot form. Examples of collaborative analysis are shown, and an evaluation of the overhead involved in distributed work is performed.
AFRIKAANSE OPSOMMING: 'n Ondersoek van die struktuuranalise-taak word uitgevoer waarin die kerninligtingsbehoeftes en fundamentele take daarvan, asook die vereisde funksionaliteit van toepassings wat dit ondersteun bepaal word. Die besondere eienskappe van struktuuranalise-inligting en die algoritmes wat daarop inwerk word ondersoek en benut om data strukture en metodes te ontwikkel wat die analise-taak goed ondersteun in In lokale omgewing, en wat terselfdertyd die moontlikheid bied om sodanig uitgebrei te word dat dit ook die taak in 'n verspreide samewerkingsgroepering kan ondersteun. Aspekte van die verspreiding van analiseparameters en metodes word ondersoek en alternatiewe oplossings word evalueer. Die uitbreidings wat nodig is om die datastrukture en metodes van die lokale omgewing aan te pas vir gebruik in verspreide kommunikasienetwerke word ontwikkel en in loodsvorm toegepas. Voorbeelde van samewerking-gebasseerde analise word getoon, en die oorhoofse koste verbonde aan analise in 'n verdeelde omgewing word evalueer.

Computer-aided structural analysis processes are highly dependent on the use of computer graphics. The objective of this work is to evolve techniques that allow structural analysts, designers and architects to work with computer graphics in a convenient manner. The formex approach of data generation is explained through a number of examples. This approach enables data to be generated very conveniently for the purposes of structural analysis. Also, introduced are the main features of an interactive programming language which acts as a vehicle to implement the concepts of formex algebra. An attempt to investigate the possibility of using the concepts of formex graphics in postprocessing stages of structural analysis is presented. This enables output of structural analysis programs to be graphically displayed so that plots of structural configurations can be shown in both their deformed and undeformed shapes. It is also shown that it is possible to employ the concepts of formex graphics in order to produce axial force, shear force, bending moment and torque diagrams in a manner that they can be visualized conveniently.

This thesis investigated the application of seismic analysis methods and the response of idealized shear frames subjected to seismic loading. To complete this research, a Design Basis Earthquake (DBE) for a project site in San Luis Obispo, CA, and five past earthquake records were considered. The DBE was produced per the American Society of Civil Engineers’ Minimum Design Loads for Buildings and Other Structures (ASCE 7-10) and used for application of the Equivalent Lateral Force Procedure (ELFP) and Response Spectrum Analysis (RSA). When applying RSA, the modal peak responses were combined using the Absolute Sum (ABS), Square-Root-of-the-Sum-of-Squares (SRSS), and Complete Quadratic Combination (CQC) method. MATLAB scripts were developed to produce several displacement, velocity, and acceleration spectrums for each earthquake. Moreover, MATLAB scripts were written to yield both analytical and numerical solutions for each system through application of Linear Time History Analysis (THA). To obtain analytical solutions, two implicit forms of the Newmark-beta Method were employed: the Average Acceleration Method and the Linear Acceleration Method. To generate a comparison, the ELFP, RSA, and THA methods were applied to shear frames up to ten stories in height. The system parameters that impacted the accuracy of each method and the response of the systems were analyzed, including the effects of classical damping and nonclassical damping models. In addition to varying levels of Rayleigh damping, non-linear hysteric friction spring dampers (FSDs) were implemented into the systems. The design of the FSDs was based on target stiffness values, which were defined as portions of the system’s lateral stiffness. To perform the required Nonlinear Time History Analysis (NTHA), a SAP2000 model was developed. The efficiencies of the FSDs at each target stiffness, with and without the addition of low levels of viscous modal damping are analyzed. It was concluded that the ELFP should be supplemented by RSA when performing seismic response analysis. Regardless of system parameters, the ELFP yielded system responses 30% to 50% higher than RSA when combing responses with the SRSS or CQC method. When applying RSA, the ABS method produced inconsistent and inaccurate results, whereas the SRSS and CQC results were similar for regular, symmetric systems. Generally, the SRSS and CQC results were within 5% of the analytical solution yielded through THA. On the contrary, for irregular structures, the SRSS method significantly underestimated the response, and the CQC method was four to five times more accurate. Additionally, both the Average Acceleration Method and Linear Acceleration Method yielded numerical solutions with errors typically below 1% when compared with the analytical solution. When implemented into the systems, the FSDs proved to be most efficient when designed to have stiffnesses that were 50% of the lateral stiffness of each story. The addition of 1% modal damping to the FSDs resulted in quicker energy dissipation without significantly reducing the peak response of the system. At a stiffness of 50%, the FSDs reduced the displacement response by 40% to 60% when compared with 5% modal damping. Additionally, the FSDs at low stiffnesses exhibited the effects of negative lateral stiffness due to P-delta effects when the earthquake ground motions were too weak to induce sliding in the ring assemblies.

Thesis (M.S.)--Worcester Polytechnic Institute.
Keywords: structural engineering; fire safety; framework approach; performance-based design; information management; finite element; lumped-parameter; laboratory tests; steel; beam; restrained; plastic analysis. Includes bibliographical references (p. 180-182).

This thesis presents three methods to estimate and locate damage in framed buildings, simply-supported beams and cantilever structures, based on experimental measurements of their fundamental vibration modes. Numerical simulations and experimental essays were performed to study the effectiveness of each method. A numerical simulation of a multi-storey framed building, a real bridge and a real chimney were carried out to study the effectiveness of the methodologies in identifying damage. The influence of measurement errors and noise in the modal data was studied in all cases. To validate the experimental effectiveness of the damage estimation methods, static and dynamics tests were performed on a framed model, a simply supported beam, and a cantilever beam in order to determine the linear behavior changes due to the increase of the level of damage. The structural identification algorithms during this thesis were based on the knowledge type of the stiffness matrix or flexibility matrix to reduce the number of modal shapes and required coordinates for the structural assessment. The methods are intended to develop tools to produce a fast response and support for future decision procedures regarding to structures widely used, by excluding experimental information, thereby allowing a cost reduction of extensive and specific testing

Aspendos Theatre still stands in fairly good condition although it has been constructed about 2200 years ago in Serik village of Antalya, Turkey. Aspendos Theatre is one of the most valuable historical buildings in Turkey. The fact that the structure had overcome numerous possible earthquakes during its lifespan in Antalya and located in second degree earthquake zone, makes the subject an interesting research topic. The earthquake analysis of Aspendos Theatre was conducted using Specification for Structures to be Built in Disaster Areas code and stress levels are investigated using 3D FE modeling. Also, the resonance state of the theatre under sound induced forces due to concerts and exhibitions performed in the theatre has been examined. Structural identification is performed to obtain certain structural characteristics by comparing experimentally measured and analytically obtained natural frequencies. The analytical model is constructed using solid members and the analysis is performed by using SAP2000 software. The elastic modulus of conglomerate used as building blocks in the Theatre is taken as 2350 MPa based on the experimental and analytical studies. The compressive and tensile strength of the theatre wall material is taken as 12 MPa and 1.2 MPa, respectively based on the previous studies conducted on conglomerate. When the maximum stress levels under combined effect of response spectrum and dead load analyses are examined, the level of compressive stress is found to be about 60% of the compressive strength. On the other hand, the tensile stresses developing at upper corners and bottom middle parts of the stage wall and mid-height central location of the exterior wall (on the vicinity of the front door) are calculated to be about 6.6 MPa, which are more than the assumed tensile strength. It has also been calculated that the level of sound that generates tensile failure is about 125 dB as the theatre gets into resonance state.

Bibliography: p. 113-123.
This thesis investigates probabilistic and stochastic methods for structural analysis which can be integrated into existing, commercially available finite element programs. It develops general probabilistic finite element routines which can be implemented within deterministic finite element programs without requiring major code development. These routines are implemented in the general purpose finite element program ABAQUS through its user element subroutine facility and two probabilistic finite elements are developed: a three-dimensional beam element limited to linear material behaviour and a two-dimensional plane element involving elastic-plastic material behaviour. The plane element incorporates plane strain, plane stress and axisymmetric formulations. The numerical accuracy and robustness of the routines are verified and application of the probabilistic finite element method is illustrated in two case studies, one involving a four-story, two-bay frame structure, the other a reactor pressure vessel nozzle. The probabilistic finite element routines developed in this thesis integrate point estimate methods and mean value first order methods within the same program. Both methods require a systematic sequence involving the perturbation of the random parameters to be evaluated, although the perturbation sequence of the methods differ. It is shown that computer-time saving techniques such as Taylor series and iterative perturbation schemes, developed for mean value based methods, can also be used to solve point estimate method problems. These efficient techniques are limited to linear problems; nonlinear problems must use full perturbation schemes. Finally, it is shown that all these probabilistic methods and perturbation schemes can be integrated within one program and can follow many of the existing deterministic program structures and subroutines. An overall strategy for converting deterministic finite element programs to probabilistic finite element programs is outlined.

The focus of this work is to advance the theoretical and modeling techniques for the fields of hybrid simulation and multi-slider friction pendulum systems (MSFPs). Hybrid Simulation is a simulation technique involving the integration of a physical system and a computational system with the use of actuators and sensors. This method has a strong foundation in the experimental mechanics community where it has been used for many years. The hybrid simulation experiments are performed with the assumption of an accurate result as long as the main causes of error are reduced. However, the theoretical background on hybrid testing needs to be developed in order validate these findings using this technique. To achieve this objective, a model for hybrid simulation is developed and applied to three test cases: an Euler-Bernoulli beam, a nonlinear damped, driven pendulum, and a boom crane structure. Due to the complex dynamics that these three test cases exhibit, L² norms, Lyapunov exponents, and Lyapunov dimensions, as well as correlation exponents were utilized to analyze the error in hybrid simulation tests. From these three test cases it was found that hybrid simulations are highly dependent on the natural frequencies of the dynamical system as well as how and where the hybrid split is located. Thus, proper care must be taken when conducting a hybrid experiment in order to guarantee reliable results.

Multi-stage friction pendulum systems (MSFPs), such as the triple friction pendulum (TFP), are currently being developed as seismic isolators. However, all current analytical models are inadequate in modeling many facets of these devices. Either the model can only handle uni-directional ground motions while incorporating the kinetics of the TFP system, or the model ignores the kinetics and can handle bi-directional motion. And in all cases, the model is linearized to simplify the equations. The second part of this dissertation presents an all-in-one model that incorporates the full nonlinear kinetics of the TFP system, while allowing for bi-directional ground motion. In this way, the model presented here is the most complete single model currently available. It was found that the non-linear model can more accurately predict the experimental results for large displacements due to the nonlinear kinematics used to describe the system. The model is also able to successfully predict the experimental results for bi-directional ground motions.

University of Central Florida College of Engineering Thesis
This thesis describes the design and development of software to parametrically build three-dimensional aerodynamic objects or shapes for various engineering design and analysis activities. The software is designed to generate and display sufficient geometric output to completely define the object. Parameters are entered through a prompting sequence which determines the type of object and the amount of geometry needed to describe the object. Geometry created by this program will act as the baseline model for aerodynamic , structural, and radar cross-section analysis. An integral part of the program is the complete 3-D viewing capability. Interactive global display capability allows for visualization of the model from any direction. Input of a viewing direction or an eye-point position will automatically shift the viewer to the correct orientation in space while scaling and centering the model on teh display. Once the object geometry has been verified and accepted, it is converted to a surface model by a second program developed at the Martin Marietta Orlando Aerospace Company, and formatted for input into aerodynamic analysis programs such as S-HABP (Supersonic-Hypersonic Arbitary Body Program) for lift and drag calcuations at multiple angles of attack and trim conditions and/or CAMS (Computer Aided Missile Synthesis) for trajectory data calculations under various flight regimes. The geometry may also be formatted for input to the stress and dynamic mode analysis program NASTRAN or the physical optics scattering program POSCAT which is used to predict radar signal returns of an object at any desired frequency. Program design, geometry generation, and data manipulation techniques are presented in detail.
M.S.
Masters
Engineering
Engineering
182 p.
viii, 182 leaves, bound : ill. ; 28 cm.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 113-116). Also available in electronic version. Access restricted to campus users.

Seismic events around the globe directly affect all ranges of structures, from complex and expensive ‘skyscrapers’ to simple frame structures, the latter making up a higher proportion of the number of structures affected as they are a much more common type of structure. The impact of a seismic event can be devastating, especially if adequate predictions of their impact and imposed structural response are not made during the design stage of the structure. Knowing what response to expect allows the engineer to design the structure to survive an event and protect the occupants. The structural response to a seismic event is very complex and can be affected by a wide range of structural, geotechnical and environ parameters. While larger, expensive structures make use of expensive, time consuming, finite element analytical procedures to determine their response the cheaper, simpler, frame structures have to make do with existing, simplified, spectral method predictions. This research firstly involves finite element analysis of simple frame structures, considering different structural and geotechnical parameters which may influence the seismic response, namely the stiffness of the structural joints, the geometry of the structure (influencing the individual structural element flexibility) and the foundation conditions (fixed base or shallow foundations with soil structure interaction). A range of frames, of varying geometry, are considered which mobilise different amounts of inter-storey drift, local rotation and global rotation response. The influence of soil structure interaction (SSI) and frame rigidity (i.e. the properties of the joints) on the response behaviour is investigated. The finite element database is then used to validate improved methods for predicting the spectral response parameters, specifically the natural period and damping of equivalent single degree of freedom (SDOF) systems, which include the effects of frame rigidity, geometry and SSI. Dynamic centrifuge testing is also carried out in order to further validate the improved spectral model for the case of real soil with shear dependant stiffness. The physical model testing is also extended to consider how environs, such as other structures in close proximity, influence the response of a structure.

This thesis focuses on the structural behavior of a washer machine cylinder. The cylinder is the component in the washing machine that rotates and keeps the laundry in place. The aim of this thesis is to determine the maximum load applied to the cylinder at which crack propagation occurs. Three experiments are performed to determine the structural behavior of the cylinder. Two experiments are performed to estimate mechanical properties i.e. stress-strain relation and critical fracture energy of the stainless steel sheet in use today. This is to derive a good estimation of the maximum load the cylinder can endure. The third type of experiment is performed to determine the strains on the outer surface of the cylinder when an evenly distributed load, 11 kg, and 2200 revolution per minute are applied on the inner surface of the cylinder. Three numerical models are performed from these three types of experiments which gives an estimation of the work to be done to propagate the crack at 15 kg and 2400 rpm. The question is if this load is overestimated to start crack propagation? This load is considerably higher than the washer machines operating speed.

This thesis examines the fatigue behaviour of FPSO structures. It has been compiled as a result of theoretical, analytical and experimental study. The Finite Element approach has been utilized to analyse the FPSO's structure. It is intended that this particular work will enable further computer simulations for fatigue assessment to be carried out. The thesis starts with the development of the general arrangement, structure and typical details of the City FPSO. The applied loads are then reviewed and this includes the so called static loads due to cargo loading and still water pressure, and the green loads due to dynamic loads induced by the vessel behaviour on waves at sea. Response to local loads such as, external sea pressure, internal pressure due to the cargo and ballast, wave slamming loads, etc. is then determined. The effect of the top structural loads on the FPSO is discussed with some practical calculation of typical topside processing palates loads. SCF evaluation methods are considered together with a discussion of the effect of structural dimensioning of local details, the use of specially performed test results conducted on ship structure. In particular, the structural stress concentration factor at the web-toe associated with the max loading conditions is developed. Confirmation of validity of the SCFs theory is provided from an extensive appraisal of the literature and from laboratory tests of the structure in question. The experimental technique developed in this thesis is based upon geometrical analogy to the simplified Peterson's Neuber notch theory, applied to the system parametric equations of SCFs and the geometric relations. The experimental results are in general accordance with published results. This research includes a calibration method for S-N Curves required for typical fatigue sensitive details in FPSOs. It also provides improved information on the important link between S-N data and finite element analysis for fatigue life assessment using a linear cumulative damage formulation.

In order to be able to undertake an analysis of a component the designer will need to know the properties of the material being used. The aim of this work is help the design engineer such that the mechanical properties of continuous glass fibre reinforced composite material can be determined and used in the design analysis of components manufactured from this material. The literature survey has shown that for the material considered here, then given the constituent properties, the fibre arrangement and the fibre volume fraction, the composite mechanical properties may be determined mathematically by the use of micromechanical equations. The micromechanical prediction of the mechanical properties of uni-directional, random and woven fibre reinforced composites has been examined. The variation of these mechanical properties that may occur in a composite component due to the manufacturing process has been highlighted as being of importance. This has been studied to determine whether such a variation is significant by analysing examples of composite components and plates. The results from these analyses have been correlated with experimental results and investigated to study the importance of such variations in properties. Many micromechanical equations have been found in the literature for the prediction of the mechanical properties of continuous fibre reinforced composite materials. An accuracy of the predicted properties to within 10% of the experimental data was concluded to be acceptable and good enough for initial design purposes as design engineers are not usually able to design to such tight tolerances. This work has shown that further development of the micromechanical theories is not the most important problem concerning the prediction of the mechanical properties. These properties can currently be predicted with acceptable accuracy from the micromechanical equations already available in the literature. However, the design engineer is unlikely to have knowledge of the micromechanical equations necessary to determine the required properties. It is only by undertaking a large literature survey that the designer would be able to find this information. Many of the micromechanical equations require the use of an empirical factor. The knowledge of a value for such a factor is again something that would not be readily available to the designer. Rather than concentrating upon improving the micromechanical predictions, this work shows that effort should be made to understand the influence of other factors upon the mechanical properties of composite materials. In particular, the behaviour and flow of the material during the manufacturing process has been highlighted as being of importance as it can cause a significant variation in the properties. Thus, analyses of composite components cannot assume that the mechanical properties are constant throughout, and it is therefore necessary to first model the manufacturing process to determine the mechanical properties before undertaking a structural analysis.

The performance-based analysis methods and evaluation criteria in ASCE 41-06 were used to evaluate a special concentric braced frame building based on the design standards in ASCE 7-05. A rectangular, six-story office building was evaluated using linear static, linear dynamic, nonlinear static, and nonlinear dynamic procedures. The results showed that the linear procedures underestimated damage compared to the nonlinear procedures, with the building performing to Life Safety for the linear procedures, and the nonlinear procedures indicating component damage beyond the intended Life Safety limit for the 2/3 maximum considered earthquake (MCE) hazard. This trend continued to the maximum considered earthquake hazard as well, under which the overall building performance for the linear procedures did not reach the Collapse Prevention level, which occurred in the nonlinear procedures.

This research shows that worst-case methane-air detonation loading on coal mine seals could be more severe than the design loads required by federal regulations, and therefore mine seals should be designed with sufficient ductility beyond the elastic regime. For this study, reinforced concrete mine seals were designed according to traditional protective structural design methods to meet the federal regulation requirements, and then the response to worst-case loads was analyzed in a single-degree- of-freedom model. Coal mine seals designed to resist the regulation loads elastically experienced support rotations up to 4.27 deg when analyzed with the worst-case loads. The analysis showed that coal mine seals designed to satisfy the federal regulations can survive worst-case methane-air detonations if they have sufficient ductility, but will undergo permanent, inelastic deformation.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 935-1001).
Structural failures of bulk carriers continue to account for the loss of many lives every year. Capes are particularly vulnerable to cracking because of their large length, their trade in high density cargos, and the high rates of cargo operations. Rapid loss often occurs allowing little reaction time which has alarmed the industry. The Cape market is extremely volatile with ship values appreciating in some cases by over 500% and then returning to original levels, all within a few years. Recent market changes have rendered conventional pricing methods inaccurate and often inapplicable, resulting in a pressing need for alternate valuation models. Very little research combines the closely interlinked technical and financial elements which are crucial for valuation and decision making by various parties in the shipping industry. The present research involves the collection and analysis of one of the largest ship cracking surveys. It is focused specifically on capes which lie at the core of the problem and is based on the records of ship owners, classification societies and shipyards. A location coding system was specifically designed to analyze the data and present the frequency, size and estimated crack growth rates with respect to location and ship age. The results were compared with existing knowledge based on surveys conducted over the past 50 years, the stress distribution based on an investigation of loading patterns, and theoretical fracture mechanics predictions. They were then combined with the frequency of crack failures, derived from an investigation of an extensive fleet sample, to develop a reliability model which yields the hazard function throughout the ship's life. Repair procedures and design modifications were also examined and a model was designed to assess their cost effectiveness based on the present value of projected crack costs. The crack repair costs were calculated as a function of ship age to be used in conjunction with the safety assessment for decision making by ship owners, insurance companies, classification societies and others. A new state of the art valuation model was developed combining both technical and financial aspects in a fundamental valuation based on risk-adjusted discounting of expected cash flows. A forward view of the main parameters was obtained from derivatives and financial securities that include shipping futures, FFAs, options, interest rate swaps and inflation protected bonds. The inherent risk of cracks is treated as a fictitious credit risk, derived from the reliability model, and is incorporated into the discount rate along with other risk premiums. Other inputs include repair costs and off-hire time, which were calculated with respect to ship age using a database of repairs, while the records of public and private companies were used along with surveys to estimate operating expenses. The resulting valuations were found to be in very close alignment with recent transaction prices across all ship ages. The model also estimates the volatility of the ship value and uses it to price optionalities that are often included in ship transactions. The combination of technical and financial analysis of this thesis is valuable to many involved in the shipping industry including brokers, accountants, analysts, shipping banks and investors interested in valuation; ship owners when making managerial or investment decisions; shipyards when designing ships, setting prices and deciding payment structures and options; insurance companies when covering total loss or emergency repairs; the IMO when setting regulations; and classification societies when scheduling inspections and deciding which areas to focus on.
by Nicholas Andrew Hadjiyiannis.
Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 23).
Although cost effective and environmentally friendly, bicycles are impractical for many users due to the required strength and physical exertion. The GreenWheel is a set of mechanical and electronic devices that provide adjustable amounts of torque to a bicycle wheel to assist the rider in pedaling. This device makes bicycles accessible to a much larger fraction of the population. The device consists of two main modules, one of which is mounted on the handlebar, allowing the user a convenient way to set a desired torque output. It functions to wirelessly convey this information to the second main module, which mounts at the center of the rear wheel of the bicycle and is designed to exert a user-desired amount of torque to the wheel. The inner portion of this module contains a motor layout, including batteries, solenoids, and magnets. The outer portion of this module is a casing that rotates on bearings on the bicycle shaft. It is held in place by the spokes of the wheel that attach to the holes at the circumference of the device. Originally the device was designed to operate using brushed DC motors. Realizing the potential of brushless DC motors, brushed DC motors were abandoned in the design of the actual product that will be released in the market. This change required a complete redesign of the inner casing that stored the motor. This also created the need to redesign the outer casing to provide the device with the proper structural integrity and a more appealing and elegant design. This thesis focuses on the redesign of the outer casing, the analysis of its two critical components, and its aesthetics. One of its two critical components is the material of spoke-holes on the circumference of the outer casing to which the spokes will be attached. It was evaluated for the amount of shear that it will experience as a result of spoke tension. The second critical component is the material of the bicycle shaft to which the motor was attached. It was analyzed to prevent failure from shearing due to the electromagnetic forces created by the motor coils. In addition, aesthetics and ease of assembly and servicing were also considered in the design of the device. The area of the outer casing that surrounds the spoke-holes was analyzed using the largest amount of force that it will experience from the spokes. It was found that these areas that surround the spoke-holes are strong enough to withstand the shear stress from the spokes. The shaft was designed to withstand the torsion generated during the operation of the motor.
by Kashika Sharma.
S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 26).
It is useful for one owning or buying a house to be able to assess its structure and identify the existence and severity of any damage. No previously existing method appears to make this assessment easily available. This thesis predicts that architecture will fail in some combination of eleven predictable ways that a simple robot can observe and distinguish by measuring the slope of select points on the floor. This prediction was tested on a case study house, and the model predicted 78.7% of the observed contour. A compact robot was fabricated and measurements of inclination were compared with those of a standard digital inclinometer. The ratio of the angle measured with the robot to that measured with the inclinometer was found to be 1.034 ± 0.193. This proof-of-concept study indicates that an inexpensive robot could be developed as a commercial product capable of assessing the structural safety of common houses.
by Noah S. Caplan.
S.B.

A simulation-based reliability analysis method is presented and evaluated. This method is intended for problems for which most probable point of failure (MPP) search-based methods fail or provide inaccurate results, and for which Monte Carlo simulation and its variants are too costly to apply. This may occur in the evaluation of complex engineering problems of low failure probability. The method used to address this problem is a variant of conditional expectation and works by sampling on the failure boundary without relying on the MPP. The effectiveness of the method is compared to a selection of other commonly available reliability methods considering a variety of analytical as well as more complex engineering problems. The results indicate that the method has the potential to deliver solutions of high efficiency and accuracy for a wide range of difficult reliability problems.

The form of the energy function (i.e. Total, Hellinger-Reissner, Hu-Washizu or Complementary energy functions) has a significant influence on FEM performance. Motivated by the ability of the force-based method to satisfy the equilibrium equation and ability of the displacement-based method to satisfy compatibility equation, this thesis proposes a mathematical framework, namely the ‘Hybrid Force-Based Method’ which employs two physical concepts; the Total and Complementary Potential Energy functions. Satisfaction of both the Total and Complementary Potential Energy function is critical to the success of the Hybrid Force-Based Method. The Hybrid Force-Based Method is constructed using these two independent energy functions in order to perform inelastic structural analyses. The method has been proposed, implemented and evaluated across the entire structure, element, section and material domains first considering each domain separately and then in combination. The equilibrium and compatibility equations are satisfied simultaneously by discretisation of these two equations, and accuracy is controlled by specifying the upper and lower bounds of the results. Outcomes following evaluation of the proposed method can be classified into the following three categories: (i) structure-level performance (see Chapter 2), (ii) material-level performance (see Chapter 3), and (iii) element level performance (see Chapter 4). The proposed Hybrid Force-Based Method is constructed by deriving the governing equations directly from the Total and Complementary Potential Energy functions, leading to two distinct variants of the hybrid approach (i) the so-called ‘augmented Hybrid Force-Based Method’, and (ii) the so-called ‘unaugmented Hybrid Force-Based Method’. A number of numerical posterior process tests were devised and used to demonstrate the performance of these two variations of the hybrid method (see Sections 2.9.4.1 and 2.9.5.1) to demonstrate those methods ability in convergence in contrast to the Large Increment Method. Due to the occurrence of numerical instabilities experienced when using various established solution algorithms in solving the fundamental equations at the material level, within implicit approach (such as the Standard Implicit Method, the Cutting Plane Method, and the Closest Point Projection Method). A new form of the constitutive equation solver is proposed in Sections 3.9, referred to as the General Implicit Method (GIM). It is shown that the GIM can be implemented both in the strain and stress domains, and is therefore appropriate for use in both the displacement- and the force-based solution family of methods. The GIM is then evaluated by comparing its predictions to those of other common solution algorithms for inelastic analysis. Performance evaluation involves the use of a new error indicator that guarantees the uniqueness and accuracy of a solution in both the stress and the strain domains. Three iso-error maps serve to emphasis the accuracy, reliability, and computational performance of the General Implicit Method as a solution method compared to those are evaluated for the defined Stress Increment Ratio. The fundamental equations at the element level are followed, based on structured fibre discretisation. The decomposition of the various degrees of freedom into deformational and rigid-body motion serve as a mechanism by which independent equilibrium equations can be determined for each element. The subsequent equation is able to involve axial force, torsion, and both in and out of plane moments while a general form of shear strain distribution is also involved. The original form of the solution at the cross section of the elements leads to novel governing equations that are based on the characteristics of the hybrid force-based approach. The numerical evaluation in Section 4.11.7.1 demonstrates the performance of the proposed method. The newly defined error indicators demonstrate the accuracy and computational performance of the method and the uniqueness of the solution in satisfying both the equilibrium and compatibility equations for Euler-Bernoulli, Timoshenko, and Reddy strain distributions across the element section. Further to the structured fibre, distributed, semi-distributed and concentrated inelastic approach elements, as a simplified form of the element are implemented and evaluated. Although performance of those original formulations is evaluated independently in in comparison with the conventional approaches, compatibility of those as an important issue is followed as well. The numerical evaluation demonstrates higher accuracy and reliability by following the proposed method, further to the higher computational performance respect to the conjugate approaches.

The ability to predict the effect of dimension and thickness variability on the dynamic response of realistically uncertain engineering structures is examined in this thesis. Initially, available methods for predicting key response statistics and probabilities, for both low and high frequencies are examined to establish their strengths and limitations for specified levels of random dimension variability. For low frequency applications, the ability of Direct Integration (DI) and the First-Order Reliability Method (FORM) to predict exceedance probability is examined. For high frequency applications, the ability of the methods of Statistical Energy Analysis (SEA) and DI to predict the mean and standard deviation of the energy response is examined. The use of Extreme Value (EV) theory is included as a way to bound responses using simulated or measured responses. The strengths and limitations of Monte Carlo simulation methods are explored for both low and high frequency responses of randomly uncertain structures using both simple mode superposition plate-structure solutions and (commercially available) finite element solutions for coupled plate structures. To address, without the need to undertake expensive Monte Carlo simulation, the problem of predicting response bounds for structures with varying levels of uncertainty, a novel DI-EV method is developed and examined. It is tested first on a simple plate structure, then on a coupled plate structure, with low-level and high-level random dimension and thickness uncertainty. In addition, the method is compared with the SEA-EV method. The thesis shows that the results from the existing SEA-EV bounding approach gives good bounds only at particular frequencies and mainly for low levels of dimension variability. In contrast, the proposed DI-EV bounding approach compare extremely well with Monte Carlo simulations, which is not only at all frequencies but also with both low-level and high-level uncertainties, for simple and coupled plate structures with dimension and thickness variation.

Bi-Steel panels are a new composite construction system developed by Corus formerly British Steel Plc. The comprise of steel plates permanently coupled by a matrix of transverse friction welded rods with a concrete in-fill. Numerical modelling using finite element analysis has been conducted on Bi-Steel plates with and without in-filled concrete. The results of non-linear analysis are compared with new and existing experimental data. Both material and geometrical non-linearity were considered in the computer analysis. The shear strength and deformation capacity of the Bi-Steel unit subject to push-out load is discussed. The steel and concrete interface is considered extensively in a series of contact studies. A range of element types is used to examine the effect of modelling the interface as a smeared or discrete contact. Mathematical modelling is used in conjunction with experimental data to validate solution accuracy. The inclusion of a smeared cracking and crushing mechanism has allowed the accurate modelling of concrete. A new method of differential smeared element reinforcement is proposed to maximise accuracy and numerical stability. The failure of a panel subject to an applied bending force is analysed to determine the combined effect of flexure and shear. Finally, a design model has been suggested to calculate the shear strength and deformation capacity of any section size. This research has indicated that Bi-Steel bars and plates have significant shear strength. The shear strength is affected by several important parameters. These include plate spacing, bar spacing and bar diameter. From load-deformation relationships it can be seen that Bi-Steel plates have high ductility and deformation capacity. For very thick plates (>12mm), the failure can be brittle if bar numbers are small. The failure will be initiated by shear failure at the weld interface.