Dissertations / Theses on the topic 'Rotational stiffness'

Polyethylene (PE), particularly linear medium density PE (LMDPE), is the most widely used thermoplastic in the rotational moulding (RM or rotomoulding) industry, possessing a balance between melt flow characteristics and mechanical properties best suited to the RM process relative to alternative thermoplastics. Reliance of the RM industry on LMDPE limits the application envelope for manufacturers due to the inherently low modulus of the material; manufacturers overcome this low modulus by increasing the wall thicknesses of their products which is costly and energy intensive. The addition of filler particles to PE as a method of modulus enhancement was considered a feasible alternative to increasing the wall thickness. The resulting composite material could down gauge part thickness and potentially expand the application envelope of RM. Phase 1 of this study observed the behaviour of RM grade PE’s with the introduction of filler particles in order to double the modulus (namely garnet, sand, cenospheres or fly-ash and the latter two combined). The PE/filler composites were mixed by dry blending or melt compounding, moulded and mechanically tested in tensile, flexural and Charpy impact mode. The aim of doubling the tensile modulus of rotomoulding grade PE was achieved by the melt compounded, rotomoulded PE/fly-ash composites. The introduction of maleic anhydride grafted linear low density polyethylene (MA-g-LLDPE) coupling agent also increased the modulus and tensile yield stress of LMDPE with the addition of fly-ash. However, the beneficial melt flow rate and impact toughness of PE decreased significantly with the addition of fly-ash. The latter was especially true for rotomoulded samples. As the RM industry typically uses finite element analysis (FEA) to numerically approximate the stress or deflection of load-bearing parts, phase 2 of this study focused upon developing numerical material properties for FEA of the new PE/fly-ash composites. Physical measurements from compression tests on rotomoulded PE/fly-ash safety steps were close to FEA approximations (confirming the practical value of the numerical materials data), except in the case of the unfilled and highest filled PE samples. The significant differences observed between physical measurements and FEA were probably due to complex factors such as the non-linear behaviour of PE and the variation in wall thickness of rotomoulded parts, highlighting the importance of properly understanding the finite element method (FEM) for RM.

Shallow embedded steel column connections are widely used in steel buildings; however, there is insufficient research about this connection type to understand the actual rotational stiffness that the connection provides. Shallow embedded steel columns are when a steel column is anchored to the foundation slab and then unreinforced concrete is poured around the base plate and the base of the column. This thesis seeks to further quantify the rotational stiffness available in this type of connection due to the added concrete and improve an existing model in order to represent the rotational stiffness. Existing data from two series of experiments on shallow embedded columns were used to validate and improve an existing rotational stiffness model. These two data sets were reduced in the same manner so that they could be compared to one another. In addition, the rotational stiffness for each test column was determined so they could be evaluated against the outputs of the model. The existing model was improved by evaluating each parameter in the model: the modulus of subgrade reaction, exposed column length, modulus of concrete for the blockout and the foundation slab, flange effective width, embedment depth, and effective column depth. It was determined that the model was sensitive to the subgrade reaction, modulus of concrete, embedment depth and effective column depth. The exposed length was not a highly sensitive parameter to the model. Flange effective width was determined to not be needed, especially when the other parameters were altered.

Finite element models were created in Abaqus 6.14 to characterize the rotational stiffness of shallowly embedded column-foundation connections. Scripts were programmed to automate the model generation process and allow study of multiple independent variables, including embedment length, column size, baseplate geometry, concrete modulus, column orientation, cantilever height, and applied axial load. Three different connection types were investigated: a tied or one part model; a contact-based model; and a cohesive-zone based model. Cohesive-zone modeling was found to give the most accurate results. Agreement with previous experimental data was obtained to within 27%. Baseplate geometry was found to affect connection stiffness significantly, especially at lower embedment depths. The connection rotational stiffness was found to vary only slightly with cantilever height for typical column heights. Results from varying other parameters are also discussed.

Despite the crucial role they play in transferring loads from the superstructure to the foundation, steel column-to-footing connections have received little attention in research. Though shallow embedded connections are typically characterized as pinned, studies have shown that they exhibit significant rotational stiffness. The objective of this thesis is to quantify the rotational stiffness of such connections. A method named the continuum model is developed by which the rotational stiffness of embedded connections may be calculated. Outputs from this model are compared with experimental data on steel connections embedded in concrete. The continuum model is shown to be capable of reasonably predicting the rotational stiffness of such connections. Results from the model were consistent with those of previous experimental studies that showed that embedment lengths greater than twice the column depth fail to significantly increase stiffness. Plots of rotational stiffness vs. embedment length developed from the continuum model are provided such that rotational stiffness may be calculated for any wide flange shape at any embedment length. Simplified equations provide a simpler way for engineers to estimate the same information.

Shallowly embedded column base connections with unreinforced block out concrete are a common method of connecting steel columns to their foundation. There has been little research done to accurately quantify the effects of this block out concrete on the connection strength and rigidity, and therefore there is nothing to aid the practicing engineer in accounting for this in structural analysis. Due to this lack of understanding, engineers have typically ignored the effects of shallow block out concrete in their analysis, presumably leading to a conservative design. Recent research has attempted to fill this gap in understanding. Several methods have been proposed that seek to quantify the effects of shallow block out concrete on a column base connection. Barnwell proposed a model that predicts the strength of a connection. Both Jones and Tryon used numerical modeling to predict the rotational stiffness of the connection. An experimental study was carried out to investigate the validity of these proposed models. A total of 8 test specimens were created at 2/3 scale with varying column sizes, connection details, and embedment depths. The columns were loaded laterally and cyclically at increasing displacements until the connection failed. The results show that the strength model proposed by Barnwell is reasonable and appropriate, and when applied to this series of physical tests produce predictions that have an observed/predicted ratio of between 0.95 to 1.39. The results also show that methods for estimating the rotational stiffness of the connection at the top of the block out concrete, as proposed by Jones and Tryon also produce reasonable values that had observed/predicted ratios of between 0.93 to 1.47. An alternative model for determining a design value for the rotational stiffness of a shallowly embedded column base plate is also proposed. When the embedment depth to column depth ratio is greater than 1.22, the connection is sufficiently rigid and at small deflections (less than 1% story drift) may be accurately modelled with infinite rotational stiffness (a "fixed" connection) at the base of the column.

In a typical light metal building, the structural members are designed for the forces and moments obtained from the wind drift analysis, which assumes pinned connections at the base. The pinned connections provide no moment at the base and have zero rotational stiffness. However, in reality every connection provides some restraint and has some rotational stiffness. Hence, by considering a modeling assumption of pinned condition, the actual behavior of the connection is not captured and this results in overestimation of lateral drifts and appearance of larger moments at the knee of the gable frames. Since the structural components are designed on the basis of these highly conservative results, the cost of the project increases. This thesis investigates the real behavior of the column base connection and tries to reduce the above stated conservatism by developing a computer program or â wizardâ to calculate the initial rotational stiffness of any column base connection. To observe the actual behavior of a column base connection under different load cases, a number of finite element models were created in SAP2000. Each finite element model of the column base connection contained base plate, column stub, anchor bolts and in some cases grout as its components. The model was mainly subjected to three load cases, namely gravity, wind and gravity plus wind. After performing many analyses, the influence of flexibility of each component on the flexibility of the connection was observed and a list of parameters was created. These parameters are the properties of above mentioned components which characterizes any column base connection. These parameters were then used as inputs to model any configuration of the column base connection in the developed wizard. The wizard uses OpenSees and SAP2000 to analyze the modeled configuration of the connection and provides values of the initial rotational stiffness and maximum bearing pressure for the provided loads. These values can be further used in any structural analysis which is done to calculate the lateral drift of a frame under lateral loads. This will also help in getting results which are less conservative than the results which one gets on assuming pinned condition at the base.
Master of Science

Cross Laminated Timber (CLT) has in recent years become a more important building material. This means that the demand for accurate calculation methods in building standards such as Eurocode 5 has increased. There is limited knowledge about the connections in CLT buildings which is an important part of a CLT structure. This thesis was therefore focused on investigating a wall-floor-wall type connection commonly found in platform type buildings.  An experimental and numerical study on typical wall-floor-wall connections was carried out in this thesis. In the experimental part 60 tests with 8 different configurations were conducted to investigate the influence of different parameters on the connection, moment capacity and rotational stiffness. During the tests the deformation of the specimens under four load levels were investigated. Compression tests were also performed on the specimens to determine the compressive strength and stiffness of the elements. In the numerical part two different models for the connection were created. One simplified model with rotational springs and one more complex model with compression springs. With these models the influence from the number of stories, span and thickness of the wall on the global behavior of a structure was investigated.  The result from this thesis shows that there is both moment capacity and rotational stiffness in the wall-floor-wall type connection that can be utilized in the design phase of a structure. This was proven by both the experimental and the numerical study. The parameters that influence the behavior of the connection most were the load level applied on the wall and the wall thickness. The model created in the numerical study showed great potential regarding the replication of the connection behavior observed in the experimental study.

L’impact de la perte racinaire sur l’ancrage d’Eugenia grandis Wight et de Pinus pinaster Ait ainsi que la capacité de trois différentes espèces d’arbres (Fagus sylvatica L, Abies alba Mill et Picea abies L) à résister au déracinement ou à la rupture sous l’effet d’un éboulement en pente raide ont été étudiés au moyen de tests de treuillage et le creusement de tranchées (tree winching and trenching tests) et les résultats ont été corrélés avec la structure du système racinaire. Aucune différence n’a été observée entre TMcrit et la distance de creusement de tranchée sur E. grandis. Les résultats obtenus ont révélé qu’en termes de rigidité rotationnelle de l’ancrage des arbres (TARS) et de TMcrit, la stabilité mécanique n’a pas été significativement affectée par le creusement de tranchées en sol argilo-sableux en raison de la profondeur d’enracinement des racines pivotantes (« sinker roots ») qui se sont formées près du tronc et en raison de la taille de la plaque racinaire qui augmente la rigidité et constitue donc une composante importante de l’ancrage d’E. grandis. Toutefois, pour P. pinaster, la stabilité mécanique a été significativement affectée par le creusement de tranchée, probablement en raison de la coupe des racines latérales qui a considérablement altéré la taille de la plaque racinaire et, en conséquence, la somme des surfaces en section (CSA= cross-sectional area) de la plupart des racines latérales et d’un certain nombre de racines traçantes, ce qui constitue une des composantes essentielles de l’ancrage d’arbres P. pinaster adultes plantés en podzol sableux. Pour les espèces forestières de protection plantées en pente raide, les résultats obtenus ont révélé que les espèces d’arbre présentant un système racinaire profondément enfoui et fortement ramifié avec une grande proportion de racines obliques (par exemple, le hêtre et le sapin pectiné) seront mieux ancrées et auront une meilleure fonction anti-éboulement que epicéa commun qui possède un système racinaire superficiel et peu profond. Les connaissances apportées par cette étude peuvent être utilisées pour la sélection et la production d’arbres qui résistent aux risques naturels ainsi qu’aux risques provoqués par l’Homme
The impact of root loss on tree anchorage on Eugenia grandis Wight and Pinus pinaster Ait and the ability of three different trees species (Fagus sylvatica L, Abies alba Mill and Picea abies L) to resist uprooting or breakage due to rockfall on steep slopes were investigated using tree winching and trenching tests and results correlated to root system architecture. No differences were found between TMcrit and trenching distance in E. grandis trees. The results showed that in terms of Tree Anchorage Rotational Stiffness (TARS) and TMcrit, mechanical stability was not significantly affected by trenching on sandy clay soil, due to rooting depth of the sinkers which occurred close to the trunk and root plate size which provide greater stiffness thus play a major component of anchorage in E. grandis. However, in P. pinaster, mechanical stability was significantly affected by trenching, possibly due to severing of lateral roots greatly altered the size of the root plate and subsequently root CSA of major lateral roots and number of sinkers, which are crucial components in anchorage of mature P. pinaster trees grown on sandy podzol soil. For protection forest species grown on steep slopes, the results showed that tree species with deep, highly branched root systems with a higher proportion of oblique roots (e.g. European beech and Silver fir) will be better anchored and provide better protective function against rockfall as compared to Norway spruce that possessed a superficial plate-like root system. The knowledge gained from this study can be utilized in selection and production of trees which are resistant to both man made or natural hazards

The dynamics of wrist rotations are dominated by joint stiffness, which the neuromuscular system must account and compensate for when controlling wrist movements. Because wrist stiffness is anisotropic, movements in some directions require less torque than movements in others, creating opportunities to follow "paths of least resistance." Forearm pronation-supination (PS) can combine with wrist flexion-extension (FE) and radial-ulnar deviation (RUD) to allow the wrist to rotate in directions of least stiffness. Evaluating this hypothesis, and understanding the control of combined wrist and forearm rotations in general, requires a knowledge of the stiffness (the dominant mechanical impedance) encountered during combined wrist and forearm rotations. While wrist and forearm stiffness have been measured in isolation, there are no measurements of coupled wrist and the forearm stiffness. This study characterizes the passive stiffness of the wrist and forearm in combinations of FE, RUD, and PS. Using a wrist and forearm robot, we measured coupled wrist and forearm stiffness for 15° movements from neutral position in 10 young, healthy subjects. We found the stiffness in PS to be significantly smaller than the stiffness in RUD, but similar in magnitude to the stiffness in FE, indicating that the torque required to overcome stiffness in combinations of PS and FE is significantly smaller than the torque required to overcome stiffness in combinations of FE and RUD (assuming equal displacements). The coupled stiffness measured here will enable future studies to determine optimal paths and to compare these optimal paths to observed movements involving wrist and forearm rotations.

The doctoral thesis focuses on problem of stability of steel thin-walled beams with lateral and torsional restraints along the spans. Theoretical background of lateral-torsional buckling of an ideal beam with and without restraints preventing out-of-plane buckling is briefly described. In the following chapters the problem of stabilization of steel thin-walled beams by planar members is dealt with. The state of the art in this field is summarized and some open questions are identified. The research in this field could bring new findings about actual behavior of these structural systems. The rate of stabilization can be quantified using values of shear and rotational stiffness provided to a thin-walled member by a planar member. In the frame of the thesis the problem of torsional restraint given to steel cold-formed members by sandwich panels under load is discussed. In case of the uplift load applied on the sandwich panels the torsional restraint should be verified by experimental analysis. To contribute to this field, experimental verification of rotational stiffness provided to steel cold-formed beams by sandwich panels was proposed and performed. Torsional restraint under no external load as well as under uplift load applied on the panels was investigated. The purpose was to obtain the values of the rotational stiffness provided by planar members. The performed tests indicate significant and practically applicable rate of the torsional restraint even in case of the uplift load on the surfaces of the panels. Utilization of the values of the rotational stiffness might result in more economical, effective and reliable structural design. Selected problems were investigated using numerical modeling in a finite element method based software.

Wrist orthoses are the most common upper limb orthoses, being used by thousands of individuals each year to stabilize, immobilize, or support the wrist joint. Wrist orthoses achieve their function by altering the stiffness of the wrist joint (Figure 1-1). However, there is no quantitative understanding of how wrist orthoses affect wrist stiffness, and consequently, wrist orthosis development often relies on feel, intuition, or empirical heuristics rather than a methodical, quantitative approach. Because wrist movement control is dominated by wrist joint stiffness (Charles and Hogan 2011) a quantitative understanding of how wrist orthoses alter the stiffness of the wrist is imperative to the development of improved wrist orthoses with properties tailorable to the needs of the thousands of individuals who use them. In order to begin bridging this gap, our research characterized the stiffness of four common groups of wrist orthosis in two degrees of freedom: flexion-extension (FE) and radioulnar deviation (RUD) which are the degrees of motion most affected by wrist orthoses. We used a wrist robot to measure how twelve orthoses altered the passive wrist stiffness of twenty healthy subjects (three orthoses and five subjects per orthosis group). To perform these measurements we designed a unique wrist-mounting fixture (Figure 3-2) which allows the wrist robot to manipulate the hand inside an orthosis without interfering with orthosis motion (more accurately simulating the actual hand-orthosis interaction). Our results showed that (1) three out of four orthosis groups significantly altered the stiffness of the wrist joint, (2) orthoses in the same group are not generally significantly different than one another, and (3) there are important differences in stiffness between different orthosis groups. An interesting implication of our research is the result that in many cases orthoses with volar stays may be interchanged with orthoses with both volar and dorsal stays without significant changes in orthosis performance (Table 4-2). We anticipate this work will prove fruitful toward the future study of wrist orthoses' effects on wrist movement behavior and the future improvement of wrist orthosis design.

The aim of my master’s thesis was to create models of the damping device and observing their behavior in interaction with the structure. First was the construction separately modeled with Java application named FyDiK2D like a model with one degree of freedom. Model of construction takes form like a high, thin rod with full circular cross section. The lower part was restrained into the subsoil. The design was to verify the correct functionality of the model by comparing the analytical and numerical solutions. For capturing the precise behavior of the structure was converted to a multi-stage model. Then the pendulum damper was applied on this construction and found amplitude lies in highest point of multi-stage model. He was then replaced by tuned mass damper. By comparing these amplitudes from both dampers was found which kind of damper is efficient for multi-stage model.

As the average American age increases, there is a need to study the spine biomechanics of adults with scoliosis. Most studies examining the mechanics of scoliosis have focused on in vitro testing or computer simulations, but in vivo testing of the mechanical response of a scoliotic spine has not yet been reported. The purpose of this study was to quantitatively define the passive stiffness properties of the in vivo scoliotic spine in three principle anatomical motions and identify differences relative to healthy controls. Scoliotic (n=14) and control (n=17) participants with no history of spondylolisthesis, spinal fracture, or spinal surgery participated in three different tests (torso lateral side bending, torso axial rotation, and torso flexion/extension) that isolated mobility to the in vivo lumbar spine. Scoliotic individuals with Cobb angles ranging 15-75 degrees were accepted. Applied torque was measured using a uni-directional load cell, and inertial measurement units (IMU) recorded angular displacement of the upper torso relative to the pelvis and lower extremities. Torque-rotational displacement data were fit using a double sigmoid function, resulting in excellent overall fit (R2 > 0.901). The neutral zone (NZ) width, or the range of motion where there is minimal internal resistance, was then calculated. Stiffnesses within the NZ and outside of the NZ were also calculated. Stiffness asymmetries were also computed within each trial. These parameters were statistically compared between factor of population and within factor of direction. There was an interaction effect between populations when comparing axial twist NZ width and lateral bend NZ width. The lateral bend NZ width magnitude was significantly smaller in scoliotic patients. NZ stiffness in the all three directions was greater in the scoliotic population. There was no significant difference in asymmetrical stiffness between populations. The present study is the first investigation to quantify the in vivo neutral zone and related mechanics of the scoliotic lumbar spine. Future research is needed to determine if the measured lumbar spine mechanical characteristics can help explain progression of scoliosis and complement scoliosis classification systems.
Master of Science

Fluorocarbons are known to be stiffer than their hydrocarbon analogues, a property that underlines the extensive industrial application of fluorocarbon materials. Although there has been previous studies on the rotational barrier of molecules having fluorocarbon centers, a detailed systematic study is necessary to quantify flurocarbon stiffness. The molecules, Pyrene-(CF2)n-Pyrene, Pyrene-(CF2)n-F, Pyrene-(CH2)n-Pyrene and Pyrene-(CH2)n-H were therefore synthesized to enable the determination of the barrier to rotation of the carbon backbone in fluorocarbons. Conformational studies will be completed with steady-state and time-dependent emission spectroscopy.

Railway foundations play an integral role in controlling the stability of the overlying track structure and the maintenance of the overall track geometry. Premature failures of railway track foundation are likely to result in frequent maintenance, which may entail significant costs since railway track foundations are less easily accessible than the other layers of railway track. Premature failures of track foundations may arise if the service loads exceed the design specifications, but may also develop as a result of the shortcomings of the design codes to simulate in situ stress paths, which involve cyclic stress changes in the horizontal as well as vertical direction, which result in principal stress rotation (PSR). Laboratory investigations have suggested that cyclic changes in the horizontal as well as vertical direction may result in a higher rate of plastic strain accumulation than cycling the vertical stress only. The effect of PSR on the soil stiffness is less certain however. Furthermore little consideration has been given to how the gradation of different soils may affect in situ drainage conditions and therefore influence the rate of railway track deterioration during PSR. A knowledge gap exists as to how cyclic changes in the directions of principal stresses may affect the pore pressure and stiffness of soils under different drainage conditions. In order to improve our understanding of the effects of PSR on the long term performance of railway track foundations, a series of laboratory tests were conducted which investigated the effects of cyclic changes in the direction of principal stresses on the pore pressure, stiffness and susceptibility to failure of saturated railway track foundation soils under different drainage conditions. The investigated sand-clay mixes were selected so as to replicate the gradation of an in situ railway track foundation. It was found that even small additions of clay to the volume of a sand significantly affected the response of the mixes during cyclic changes in principal stress direction. Moderate additions of clay in the pore space of a sand reduced the susceptibility to principal stress rotation by reducing the tendency for excess pore pressure generation and by increasing the cyclic shear stress the mixes were able to sustain before rapid plastic strain accumulation occurred. Increases in principal stress rotation below the cyclic shear threshold increased the resilient stiffness of the sand-clay mixes, however once this threshold was exceeded rapid stiffness degradation occurred. Below the cyclic shear threshold, the response of the mixes was stable over a high number of loading cycles and no abrupt fatigue failures were observed. The sand-clay mixes were sensitive to even small changes in the magnitude of PSR near the cyclic shear threshold. Small increases in PSR could trigger the sudden collapse of a previously stable sand-clay mix. Under conditions where the rate of pore pressure dissipation was regulated by the permeability and the volumetric compressibility of the soil, the sand clay mixes with moderate additions of fines were stable over a range of cyclic increases in PSR which correspond to the maximum expected changes in magnitude within the depth of a ballasted railway track foundation.

In this thesis is wrote up a complete procedure of stator core stiffness determination using finite element method (FEM), subsequently, the stator core stiffness database was created according to this procedure. In the next chapter is carried out a sensitivity analysis of one chosen stator core, which led to identifying parameters that affected its stiffness the most. Finally, a modal analysis of one synchronous machine was performed using FEM, in order to determine the effect of stator core stiffness on modal characteristics of the machine. Several modal shapes and corresponding natural frequencies were computed in this analysis, then only a few shapes with the highest core effect were chosen and compared.

Concrete-filled tubular (CFT) columns have been widely adopted in building structures owing to their superior structural performance, such as enhanced load bearing capacity, compared to hollow tubes. Circular, square and rectangular hollow sections are most commonly used in the past few decades. Elliptical hollow section (EHS) available recently is regarded as a new cross-section for the CFT columns due to its attractive appearance, optional orientation either on major axis or minor axis and improved structural efficiency. The state of the research in terms of elliptical columns, tubular joints between EHSs and connections with CFT columns, etc., are reviewed in this thesis, showing a lack of investigations on EHSs, especially on beam to elliptical column connections which are essential in framed structures. The structural behaviour of elliptical column to I-beam connections under bending is studied in this thesis to fill the research gap. Overall ten specimens with various joint assemblies were tested to failure to highlight the benefits of adopting concrete infill and stiffeners in the columns. A three-dimensional finite element model developed by using ABAQUS software is presented and verified against obtained experimental results, which shows acceptable accuracy and reliability in predicting failure modes of the connections and their moment capacities. Parametric studies were performed to access the main parameters that affecting the bending behaviour of the connections. A simple hand calculation method in terms of ultimate moment capacity is proposed according to experiments conducted for connections with concrete-filled columns.

Three components, a pallet, packaging, and material handling equipment, of the unit load portion of the supply chain are physically and mechanically interacting during product storage and shipping. Understanding the interactions between two primary components, a pallet and packaging, in a unit load is a key step towards supply chain cost reduction and workplace safety improvement. Designing a unit load without considering physical and mechanical interactions, between those two components, can result in human injury or death caused from a unsafe workplace environment and increased supply chain operating costs, due to product damage, high packaging cost, disposal expense, and waste of natural resources. This research is directed towards developing predictive models of the compressive stress distributions using the principle of the beam on an elastic foundation and experimentally quantifying the compressive stress distributions. The overall objective of this study is to develop a model that predicts compressive stress distributions at the interface between a pallet deck and packaging as a function of: pallet deck stiffness, packaging stiffness, and pallet joint fixity. The developed models were validated by comparison to the results of physical testing of the unit load section. Design variables required for modeling included Modulus of Elasticity (MOE) of pallet deckboards, Rotation Modulus (RM) for nailed joints, and packaging stiffness. Predictive models of the compressive stress distributions were non-uniformly distributed across the interface between pallet deckboards and packaging. Maximum compressive stresses were observed at the deckboard ends over stringer segments. All predictive compressive stress distributions were influenced by pallet deck stiffness, packaging stiffness, and joint fixity. The less the joint fixity the greater the pallet deck deflection. The stiffer deckboards are more sensitive to joint fixity. For predictive compressive stress distribution models, the measure of the stress concentrations was the Compressive Stress Intensity Factor (SIF), which was the ratio of the estimated maximum compressive stress to the applied stress. Less stiff pallets and stiffer packaging resulted in greater SIF for all end condition models. SIF was reduced by stiffer joint, stiffer pallet deck and more flexible packaging. The stiffer the pallet deck and pallet joint the greater the effective bearing area. The lower stiffness packaging resulted in the greater effective bearing area with all three packages. The predicted effective bearing area was more influenced by pallet deck stiffness than the packaging stiffness. The developed prediction models were validated by comparison to experimental results. All prediction models fell within 95% confidence bounds except the 3/8-inch deck with free ends and 3/4-inch deck with fixed ends. The difference between predicted and measured results was due to a limitation in pressure sensor range and test specimen construction for the free end model and fixed end model, respectively. The results show effects of pallet deck stiffness and packaging stiffness on SIFs with percentage changes ranging from 2 to 26% (absolute value of change) for all three end conditions. The sensitivity study concluded that changing both pallet deck stiffness and packaging stiffness more significantly influenced the SIFs than bearing areas.
Ph. D.

The concept of energy production through the fusion of two light nuclei has been studied since the 1950’s. One of the major problems that fusion scientists have encountered is the confinement of the hot ionised gas, i.e. the plasma, in which the fusion process takes place. The most common way to contain the plasma is by using at magnetic field configuration, in which the plasma takes a doughnut-like shape. Experimental devices of this kind are referred to as tokamaks. For the fusion process to proceed at an adequate rate, the temperature of the plasma must exceed 100,000,000C. Such a high temperature forces the plasma out of thermodynamical equilibrium which plasma tries to regain by exciting a number of turbulent processes. After successfully quenching the lager scale magnetohydrodynamic turbulence that may instantly disrupt the plasma, a smaller scale turbulence revealed itself. As this smaller scale turbulence behaved contrary to the common theory at the time, it was referred to as anomalous. This kind of turbulence does not directly threaten existents of the plasma, but it allows for a leakage of heat and particles which inhibits the fusion reactions. It is thus essential to understand the origin of anomalous turbulence, the transport it generates and most importantly, how to reduce it. Today it is believed that anomalous transport is due to drift-type waves driven by temperature and density inhomogeneities and the theoretical treatment of these waves is the topic of this thesis.

The first part of the thesis contains a rigorous analytical two-fluid treatment of drift waves driven solely by density inhomogeneities. Effects of the toroidal magnetic field configuration, the Landau resonance, a peaked diamagnetic frequency and a sheared rotation of the plasma have been taken into account. These effects either stabilise or destabilise the drift waves and to determine the net result on the drift waves requires careful analysis. To this end, dispersion relations have been obtained in various limits to determine when to expect the different effects to be dominant. The main result of this part is that with a large enough rotational shear, the drift waves will be quenched.

In the second part we focus on temperature effects and thus treat reactive drift waves, specifically ion temperature gradient and trapped electron modes. In fusion plasmas the α-particles, created as a by-product of the fusion process, transfer the better part of their energy to the electrons and hence the electron temperature is expected to exceed the ion temperature. In most experiments until today, the ion temperature is greater than the electron temperature and this have been proven to improve the plasma confinement. To predict the performance of future fusion plasmas, where the fusion process is ongoing, a comprehensive study of hot-electron plasmas and external heating effects have been carried out. Especially the stiffness (heat flux vs. inverse temperature length scale) of the plasma has been examined. This work was performed by simulations done with the JETTO code utilising the Weiland model. The outcome of these simulations shows that the plasma response to strong heating is very stiff and that the plasma energy confinement time seems to vary little in the hot-electron mode.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Conventional structural analysis of buildings in reinforced concrete is performed considering beam-column connections as rigid. However, experimental results prove the existence of relative rotations in beam-column connections of reinforced concrete structures, showing the partial transfer of bending moment. In this study the influence of the stiffness of beam-column connections on the structural behavior of multi-storey buildings in reinforced concrete was investigated. On a first stage, the value of the rotation restriction of connections was varied, observing the impact on horizontal displaceability of the structure, on the γz coefficient, on the negative and positive moments of the beams and on the longitudinal reinforcement of the pillars. This analysis was performed for buildings with 05, 10, 15 and 19 floors. The results show that the reduction of the rotation restriction of connections increases the values of the horizontal displacements, of the γz coefficient, of the positive moments and of the reinforcement of the pillars. The increases that occur on the values of the analyzed parameters become larger as the number of floors of buildings increases. On a second stage, the same building was calculated with rigid connections and deformable connections. In order to determine the factor αR of deformable connections, two analytical models available in literature were used, and a comparison between the results obtained by each analytical model was also performed. Based on the results, it is concluded that neglecting the influence of the stiffness of the beam-column connections on the analysis of monolithic reinforced concrete structures may result in different solutions compared to the real behavior of the structure. The stiffness values obtained with the analytical models that were used differ considerably from the condition of rigid connections, suggesting an adjustment on the standard consideration of rigid connections adopted by the computer programs of structural calculation.
A análise estrutural convencional de edificações em concreto armado é realizada considerando as ligações viga-pilar como rígidas. Entretanto, resultados experimentais comprovam a existência de rotações relativas nas ligações viga-pilar de estruturas de concreto armado, evidenciando a transmissão parcial de momento fletor. Neste trabalho foi investigada a influência da rigidez das ligações viga-pilar no comportamento estrutural de edificações de múltiplos pavimentos em concreto armado. Em uma primeira etapa, variou-se o valor de restrição à rotação das ligações observando os impactos na deslocabilidade horizontal da estrutura, no coeficiente γz, nos momentos negativos e positivos das vigas e nas armaduras longitudinais dos pilares. Esta análise foi realizada para edificações com 05, 10, 15 e 19 pavimentos. Observou-se por meio dos resultados que a redução da rigidez à rotação das ligações provoca aumento nos valores dos deslocamentos horizontais, do coeficiente γz, dos momentos positivos das vigas e das armaduras dos pilares. Os acréscimos ocorridos nos valores dos parâmetros analisados são maiores à medida em que se aumentam o número de pavimentos das edificações. Em uma segunda etapa, calculou-se uma mesma edificação com ligações rígidas e com ligações deformáveis. Para determinação da restrição à rotação das ligações deformáveis, utilizaram-se dois modelos analíticos disponíveis na literatura, realizando-se, também, uma comparação entre os resultados obtidos pelos modelos. Com base nos resultados, conclui-se que negligenciar a influência da rigidez das ligações viga-pilar na análise de estruturas monolíticas em concreto armado pode gerar soluções muito diferentes do comportamento real da estrutura na prática. Os valores de rigidez obtidos pelos modelos analíticos utilizados divergem consideravelmente da condição de ligações rígidas, sugerindose a adequação na consideração padrão de ligações rígidas adotada pelos programas computacionais de cálculo estrutural.
Mestre em Engenharia Civil

Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia
This dissertation seeks to evaluate the validity of different procedures to consider rotational stiffness in spread foundations in order to ensure a reliable estimation of their behavior and optimize the design of these elements. The adoption of spread foundations is common, mainly due to economic reasons and to the easiness of their construction. However, their design and of the superstructure are still carried in a non-integrated way, compromising the validity of the internal stresses obtained. The foundation’s behavior when submitted to eccentric loads can be quantified through vertical and rotational stiffness since these loads lead, in addition to the expectable settlements, to the rotation of the foundation. There are different methods to evaluate the rotational stiffness of footings, although the outputs obtained can vary considerably. Besides that, the orientations defined in the reglementary norms about this theme are scarce, unclear and unanimous. They define, for the same conditions, distinct admissible limits for the maximum loads’ eccentricities. In order to understand the limits for the eccentricities of the loads in spread foundations, the validity of the reglementary limits and the formulas usually applied, proposed according to the theory of the elasticity to estimate the rotational stiffness of the footings, it's analyzed the variation of the rotational stiffness standardized with the increase of eccentricities uni- and bi-directional. Foundations with different geometries are object of analysis, founded in dense and loose sand, and clay and submitted to a variable moment and constant vertical load. The analysis is preformed using analytical solutions, discrete spring models (Robot) and models to finite elements of continuous bi- and tri-dimensional (RS2 and RS3). For this last analysis it is applied two constructive models, the elastic perfectly elastic model of Mohr-Coulomb and the hyperbolic model of Duncan-Chang. Although, the analysis with the hyperbolic model of Duncan-Chang was limited by the plane strain state because it did not achieve the convergence of the calculus when applied to tridimensional cases.To conclude, some considerations about the work performed are presented, followed by some suggestions for further works.
Esta dissertação procura fundamentalmente avaliar a validade das diferentes formas de consideração da rigidez rotacional em fundações superficiais, de forma a garantir uma estimativa fiável para o seu comportamento e otimizar o projeto destes elementos. A utilização de fundações superficiais é frequente devido, principalmente, a questões económicas e de facilidade de execução. No entanto, o seu dimensionamento e da superestrutura é ainda realizado de forma não integrada, comprometendo a validade das distribuições de esforços obtidos. A resposta das fundações às cargas excêntricas que lhe são aplicadas pode ser quantificada através da rigidez vertical e rotacional, uma vez que estas cargas conduzem, além dos assentamentos expectáveis, a rotações da fundação. Existem diferentes métodos para avaliar a rigidez rotacional de sapatas fornecendo, todavia, resultados diferentes. Além disso, as orientações definidas nas normas regulamentares acerca deste tema são escassas, pouco claras e pouco unânimes, definindo, para as mesmas condições, limites admissíveis distintos para as excentricidades máximas das cargas.Com o objetivo de compreender os limites para a excentricidade da carga em fundações superficiais, a validade dos limites regulamentares e das fórmulas, recorrentemente utilizadas, propostas com base na teoria da elasticidade para estimar a rigidez rotacional de sapatas, é analisada a variação da rigidez rotacional normalizada com o aumento da excentricidade unidirecional e bidirecional. São alvo de análise fundações com diferentes geometrias, assentes em areia densa, areia solta e argila e submetidas a momento fletor variável e carga vertical constante. A análise é realizada recorrendo a soluções analíticas, modelos discretos de molas (Robot) e modelos de elementos finitos de contínuo bidimensionais e tridimensionais (RS2 e RS3). Para esta última análise são utilizados dois modelos constitutivos, o modelo elástico perfeitamente plástico de Mohr-Coulomb e o modelo hiperbólico de Duncan-Chang. Porém, a análise com o modelo hiperbólico de Duncan-Chang limitou-se ao estado plano de deformação por não se ter atingido a convergência do cálculo quando aplicado a casos tridimensionais. Perfazendo, são tecidas considerações acerca do trabalho realizado e apresentam-se algumas linhas para desenvolvimentos futuros.

碩士
國立中正大學
機械工程系研究所
106
Foil gas bearing have wide industrial applications, mainly in micro-turbine engine and the aircraft industry else. Micro-turbine is the small size of gas turbine, and only equipped with single layer compressor and a turbine, which make the machine system having the advantage of small volume and suitable for high- speed rotating application. Turbine engine also have the need for long-time running lubrication system. Most important, air foil have remarkable potential for both aspect. This research project applies a lubrication system to meet the technology vision; developing a 80kg-thrust micro-turbine engine in the use of micro-turbine generator, small high-speed target drone, life propulsion system of standard high speed trap and long high speed rotating operations. In the application of high speed micro-turbine engine, the micro-turbine power system has the long running time requirements with the rotating speed up to 90,000 to 100,000 rpm and life needs ( for 30kW ) over 30,000 hours, so the primary is to choose a proper bearing lubrication system in the need of high speed and long time rotating. From the previous research, knowing spindle rotates in high speed and usually works in the environment of high temperature. Applying rolling or fluid hydrodynamic bearing, we need to use an efficient cooling system to make sure bearing working performance. Foil gas bearing isn’t vulnerable to temperature change, so we don’t need the cooling system in the allowable temperature range of foil material. Therefore we choose foil gas bearing, having high speed rotation and long-time operation, as the lubrication system and hope to enhance power efficiency and life-cycle of micro-turbine generator . We need lots of experience for the bearing design because it’s complicated to manufacture. For the purpose of making shaft lift, we set up a simulation and analysis system. Therefore, it’s needed to use related patent and article as reference and then take the calculation of experiment trend and result of simulation into account to analysis. After, provide the analysis result with reference data for research organization. While the design of the foil is the key aspect of affecting the performance of foil gas bearings, this research start with surface roughness of top foil and use the full-film hydrodynamic lubrication theory to calculate the minimum film thickness used for supporting shaft lifting. Try to reach the stiffness in the theory calculation with the calculation of programming language and design geometry foil for stiffness. Studying research analysis on present bump foil is also necessary. Eventually, hope to enhance the load capacity and reliability of foil gas bearing in real working.

Tese de Doutoramento em Construção Metálica e Mista, apresentada ao Departamento de Engenharia Civil da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
No contexto das estruturas porticadas de edifícios ou similares vêm sendo investigados elementos com secção tubular bem como dispositivos mecânicos de ligação entre vigas e pilares adaptados a tal tipo de secção no sentido da validação de regras para controlo do respectivo comportamento estrutural, atendendo à problemática subjacente à necessidade de implementação de regulamentação apropriada por instituições e organismos oficiais. Nesta Tese apresenta-se um estudo com base em experimentação, análise numérica e teórica para caracterização da resposta estrutural de juntas viga I – pilar SHS com ligações utilizando o parafuso do tipo hollo-bolt como sistema de fixação ao perfil tubular adoptado nos pilares, enquanto exemplo representativo dos diversos blind-bolt-systems. A primeira parte do programa experimental, realizado no Laboratório de Mecânica Estrutural do DEC da FCTUC, incluiu oito ensaios de arrancamento de parafusos hollo-bolt, considerando diferentes valores para o aperto e dois diâmetros comercialmente disponíveis. Com os diagramas força-deslocamento foi avaliada a rigidez axial para cada uma das situações consideradas e identificada a capacidade resistente à tracção para os referidos parafusos ensaiados directamente nos perfis tubulares através de um esquema tipo T-Stub. A segunda parte da investigação incluiu 14 ensaios correspondentes ao tipo de juntas inicialmente indicado em nós externos, de canto e internos, considerando-se protótipos à escala real sob o efeito de carga estática monotónica na(s) viga(s). Foram realizados ensaios uni- e multiplanares, tendo sido elaborados diagramas momento-rotação e determinadas as propriedades estruturais como a rigidez rotacional inicial, o momento plástico resistente e a rigidez pós-elástica para as tipologias com placa rasa e estendida, contempladas na Parte 1-8 da actual versão do Eurocódigo 3. É apresentada, também, a classificação das juntas ensaiadas quanto à rigidez e quanto à resistência à flexão no âmbito das regras estabelecidas no citado Eurocódigo. Complementarmente, foram processados três modelos de elementos finitos no software ANSYS® representando as correspondentes juntas e ligações anteriormente testadas, os quais foram elaborados e calibrados segundo as geometrias reais das secções transversais adoptadas nos protótipos ensaiados e respeitando as propriedades mecânicas referentes aos aços efectivamente utilizados nas diversas componentes das ligações em questão. As principais conclusões experimentais evidenciaram a tendência para um certo comportamento do tipo membrana para a parede do pilar tubular no caso de pequenos rácios espessura/largura, a influência dos hollo-bolts nas áreas dos furos mais traccionados do perfil tubular, a rotura das patilhas associadas ao cilindro daquele parafuso e consequente arrancamento sob esforços de tracção e corte, bem como a plastificação da face solicitada da secção SHS (tanto mais notória quanto menor a espessura), para além da flexão plástica das placas de extremidade estendidas quando inseridas em juntas com pilares de maior espessura, reflectindo, neste caso, uma relação tp/tc de 1,7. Os modelos numéricos conseguiram reproduzir as várias deformabilidades encontradas nos protótipos testados verificando-se, para muitos pontos homólogos das juntas modeladas, uma similitude de resultados comparativamente ao que havia sido registado e determinado a nível experimental, designadamente no que diz respeito a deslocamentos (verticais e horizontais) mas também em relação a tensões equivalentes/principais e ainda a extensões. O estudo teórico igualmente apresentado culminou com a proposta de dois modelos analíticos para o momento resistente plástico das referidas juntas no contexto das referências de suporte à temática das forças resistentes, bem como das normas estipuladas pelo Eurocódigo 3 e pelo CIDECT. Para o caso da rigidez rotacional inicial, foi também aplicada uma dimensão alternativa na zona traccionada do pilar para o cálculo do respectivo coeficiente de rigidez da componente proposta, cuja fórmula original de cálculo havia sido anteriormente avançada por aquela mesma associação internacional. Uma comparação entre resultados teóricos e experimentais foi, ainda, realizada através dos respectivos rácios. Tendo sido observado um efeito tridimensional em nós de canto ou internos sujeitos a carga no mesmo sentido, foi também apresentada uma proposta de correcção do momento resistente e da própria rigidez em juntas localizadas na face ortogonal à face 1 do pilar bi-articulado.
Tubular section elements as well as connection mechanical devices between beams and columns, adapted to that type of section and applied in buildings’ framed structures or similar, have been investigated in order to validate rules to control their behaviour, in compliance with the regulations issued by institutions and official organizations. This thesis presents an experimental, numerical and analytical study to characterize the structural behaviour of I beam – SHS column joints connected using hollo-bolts, a representative example of blind-bolt systems. The first part of the experimental program, carried out at FCTUC´s DEC Structural Mechanics Laboratory, included eight hollo-bolts pull-out tests, considering different values for the tightening moment and two commercial diameters. With force-displacement diagrams the axial stiffness was evaluated for each of the considered situations as well as identified the tensile strength for the bolts, directly tested on the SHS profiles through a T-Stub type scheme. The second part of the experimental investigation included 14 tests corresponding to I beam – SHS column joints at external, corner and internal node´s configuration, considering real-scale prototypes under the effect of a monotonic static load applied on the beams. Uni- and multiplanar tests were performed and the respective force-displacement and moment-rotation diagrams were obtained, as well as determined the corresponding structural properties, such as initial rotational stiffness, plastic resistant moment and post-elastic stiffness for flush and extended endplate typologies, contemplated in the current version of Part 1-8 of Eurocode 3. It was presented the classification of the tested joints regarding to stiffness and resistance to bending, within the scope of that Eurocode. Furthermore, three finite element models were processed in the ANSYS® software representing the corresponding joints and connections previously tested, which were developed and calibrated according to the actual geometries of the cross sections adopted in the tested prototypes and respecting the mechanical properties of the steels actually used in the components of that connections and joints. The main experimental results evidenced the tendency of the tubular column’s wall for a membrane type behaviour, in the case of small thickness/width ratios. The results also showed the influence of the hollo-bolts in the areas corresponding to the more tensioned holes of tubular profile, moreover the hollo-bolt legs rupture, associated to the cylinder and consequent pull-out under a tensile and shear force combination, as well as the plastification of the loaded face of the SHS section (as more remarkable as lower its thickness). In addition to experimental observations mentioned before, it was also verified the plastic bending of the extended endplates when included in joints with thicker columns (reflecting a tp/tc ratio equal to 1,7). The numerical models reproduced the different deformabilities found in the tested prototypes, and for many homologous points of the modeled joints a results’ similarity was observed compared to what had been registered and determined experimentally, not only regarding to the vertical and horizontal displacements, but also in relation to equivalent/principal stresses and strains. The theoretical study culminated with a proposal of two analytical models for the plastic moment of those joints in the context of the main supporting references of the thematic subjected to the resistant forces as included in the established rules by Eurocode 3 and CIDECT. In the case of initial rotational stiffness, an alternative dimension was also proposed in the tensioned area of the column to calculate the respective stiffness coefficient of the new component proposed, which original formula was previously advanced by that institution. A comparison between theoretical and experimental results was made through the respective ratios. Having a three-dimensional effect on corner or internal nodes subjected to loads in the same direction and sense, a proposal of correction to the resistant moment and the rotational stiffness in joints, located on the orthogonal face concerning to the face number one in the simply supported column, was also presented.

Η παρούσα διατριβή ανήκει στο γενικότερο θεματικό πεδίο της σεισμικής αποτίμησης, σχεδιασμού ή ανασχεδιασμού κατασκευών οπλισμένου σκυροδέματος με βάση τις μετακινήσεις. Οι σύγχρονες μέθοδοι αυτού του τύπου, στηρίζονται σε έλεγχο και σύγκριση της σεισμικής απαίτησης με την ικανότητα των μελών της κατασκευής σε όρους μετακινήσεων παρά σε όρους δυνάμεων. Δημιουργείται επομένως η ανάγκη για απλό και αξιόπιστο υπολογισμό της συμπεριφοράς μελών οπλισμένου σκυροδέματος σε κάμψη και διάτμηση, σε όρους μετακινήσεων. Το αντικείμενο της παρούσης διατριβής είναι η ανάπτυξη προσομοιωμάτων για τον υπολογισμό των βασικών χαρακτηριστικών της συμπεριφοράς καμπτόμενων μελών οπλισμένου σκυροδέματος και συγκεκριμένα: της ροπής διαρροής, της παραμόρφωσης στη διαρροή, της ενεργού δυσκαμψίας, της παραμόρφωσης στην αστοχία, της διατμητικής αντοχής σε ανακυκλιζόμενη φόρτιση, της αντοχής μελών με χαμηλό λόγο διάτμησης και της συμπεριφοράς υπό διαξονική καταπόνηση. Εξετάζονται μέλη διαφόρων τύπων και διαφορετικής διατομής, μέλη με ενίσχυση μανδύα οπλισμένου σκυροδέματος ή μανδύα σύνθετων υλικών, καθώς επίσης και μέλη με μάτιση του διαμήκους οπλισμού στην περιοχή πλαστικής άρθρωσης. Για την ανάπτυξη των προσομοιωμάτων, καθώς και για τον έλεγχο άλλων παλαιότερων, αναπτύχθηκε και αξιοποιήθηκε βάση πειραματικών δεδομένων μελών οπλισμένου σκυροδέματος με περισσότερα από 2800 πειράματα από τη διεθνή βιβλιογραφία. Για τον υπολογισμό της ροπής και της καμπυλότητας στη διαρροή, αναπτύσσονται απλές σχέσεις υπολογισμού, βασιζόμενες σε ανάλυση σε επίπεδο διατομής και καθορίζονται τα κατάλληλα κριτήρια διαρροής. Αναπτύσσονται ακολούθως σχέσεις υπολογισμού της παραμόρφωσης στη διαρροή, και συγκεκριμένα της γωνίας στροφής χορδής του μέλους στη διαρροή, θy, ως άθροισμα τριών όρων: καμπτικής παραμόρφωσης, διατμητικής παραμόρφωσης και παραμόρφωσης λόγω ολίσθησης των ράβδων διαμήκους οπλισμού από την περιοχή αγκύρωσης. Προτείνονται δε δύο εναλλακτικοί τρόποι υπολογισμού της ενεργού δυσκαμψίας, ένας θεωρητικός και ένας καθαρά εμπειρικός. Στη συνέχεια εξετάζεται η παραμόρφωση στην αστοχία και προτείνονται δύο εναλλακτικοί μέθοδοι υπολογισμού της γωνίας στροφής χορδής στην αστοχία, θu. Η 1η βασίζεται στον υπολογισμό της καμπυλότητας στην αστοχία, φu, με εφαρμογή του κατάλληλου προσομοιώματος περίσφιγξης του σκυροδέματος, και στην εφαρμογή της φu σε μήκος πλαστικής άρθρωσης ίσο με Lpl, ενώ η 2η σε καθαρά εμπειρικές εξισώσεις. Εξετάζεται ακολούθως η διατμητική αντοχή σε ανακυκλιζόμενη φόρτιση και προτείνονται προσομοιώματα για αστοχία σε διαγώνιο εφελκυσμό ή αστοχία σε λοξή θλίψη, μετά την καμπτική διαρροή. Στη συνέχεια εξετάζεται η συμπεριφορά μελών οπλισμένου σκυροδέματος υπό διαξονική καταπόνηση. Εξετάζονται επίσης μέλη με χαμηλό λόγο διάτμησης και προτείνονται νέα αντιπροσωπευτικότερα κριτήρια για τον χαρακτηρισμό ενός μέλους ως “κοντό μέλος”, καθώς και νέα μεθοδολογία υπολογισμού της αντοχής των μελών αυτών, με κατάλληλο συνδυασμό του προσομοιώματος των Shohara and Kato, 1981 και των Φαρδής και συνεργάτες 1998. Ακολούθως εξετάζονται μέλη ενισχυμένα με μανδύα σύνθετων υλικών και προτείνονται προσομοιώματα υπολογισμού της γωνίας στροφής χορδής στη διαρροή και την καμπτική αστοχία, καθώς και προσομοίωμα υπολογισμού της διατμητικής αντοχής. Στη συνέχεια εξετάζεται η συμπεριφορά μελών με μάτιση του διαμήκους οπλισμού στην περιοχή πλαστικής άρθρωσης, καθώς και η εφαρμογή μανδύα σύνθετων υλικών για την ενίσχυση της περιοχής αυτής. Τέλος εξετάζεται η συμπεριφορά στη διαρροή και στην αστοχία, μελών ενισχυμένων με μανδύα οπλισμένου σκυροδέματος. Η ανάπτυξη όλων των προτεινόμενων προσομοιωμάτων της διατριβής βασίζεται στην καλύτερη δυνατή συμφωνία με τα πειραματικά αποτελέσματα της βάσης δεδομένων, χωρίς όμως να θυσιάζεται η απλότητα και η ευχρηστία αυτών.
The present Thesis belongs in the general field of seismic assessment, design and redesign of concrete structures with displacement based procedures. Modern methods of this kind are based in controlling and comparing seismic demand with structural elements capacity in terms of displacements rather than forces. This leads in the need of estimating reinforced concrete elements performance under bending and shear, in terms of displacements. The object of the Thesis is development of models for calculating the basic performance characteristics of reinforced concrete elements under bending, in particular: yield moment, deformation at yielding, effective stiffness, deformation at ultimate, shear strength under cyclic loading, maximum strength of members with low shear ratio and behavior under biaxial loading. Members with various types of section and various characteristics are included, as also members retrofitted with FRP jacket or concrete jacket and members with lap-splice of longitudinal reinforcement in plastic hinge region. In order to develop new models and check older ones, a database of more than 2800 experiments from international literature on reinforced concrete elements was created and used here. Simple equations and procedures are suggested for calculating yield moment and corresponding curvature, based on section analysis, by specifying the appropriate yield criteria. Equations for calculating deformation at yielding, in particular chord rotation at yielding, θy as the sum of deformations due to bending, due to shear and due to slippage of longitudinal reinforcement from anchorage zone, are also developed. Calculation of effective stiffness is based on two alternative models, one theoretical and one purely empirical. Deformation at ultimate is then examined where two methods for calculating chord rotation at ultimate are suggested. 1st one is based on ultimate curvature, φu, where an appropriate concrete confinement model is used, and plastic hinge length Lpl, while 2nd one is based on purely empirical equations. Shear strength under cyclic loading is also examined and new models for calculating shear strength for shear tension and shear compression failure after flexural yield are developed. Behavior of reinforced concrete elements under biaxial loading is then examined. Elements with low shear ratio are also covered and new, more representative, criteria to characterize an element as a “short element” are suggested. A procedure based on an appropriate combination of Shohara and Kato 1981 model and Fardis et al. 1998 model is then suggested for calculating maximum strength of such “short elements”. Retrofitted members with FRP jacket are then examined and models for chord rotation at yielding and ultimate, as well as for shear strength are suggested. Behavior of members with lap-splice of longitudinal reinforcement inside plastic hinge region is then examined, including also retrofitting of this region with FRP jacket. Performance at yielding and ultimate of retrofitted members with concrete jacket is also examined. Development of all the suggested models of the Thesis is based on best fit with experimental results of the database, without sacrificing simplicity and applicability of the models.