Strengthening to seismic action of reinforced columns with rectangular cross-section

The first part of this research work regards the assessment of the mathematical modelling of reinforced concrete columns confined with carbon fibre (CFRP) sheets under axial loading. The purpose was to evaluate existing analytical models, contribute to possible improvements and choose the best model(s) to be part of a new model for the prediction of the behaviour of confined columns under bending and compression. For circular columns, a wide group of authors have proposed several models specific for FRP-confined concrete. The analysis of some of the existing models was carried out by comparing these with several tested columns. Although several models predict fairly the peak load only few can properly estimate the load-strain and dilation behaviour of the columns. Square columns confined with CFRP show a more complex interpretation of their behaviour. Accordingly, the analysis of two experimental programs was carried out to propose new modelling equations for the whole behaviour of columns. The modelling results show that the analytical curves are in general agreement with the presented experimental curves for a wide range of dimensions. An analysis similar to the one done for circular columns was this turn carried out for square columns. Few models can fairly estimate the whole behaviour of the columns and with less accuracy at all levels when compared with circular columns. The second part of this study includes seven experimental tests carried out on reinforced concrete rectangular columns with rounded corners, different damage condition and with confinement and longitudinal strengthening systems. It was concluded that the use of CFRP confinement is viable and of effective performance enhancement alone and combined with other techniques, maintaining a good ductile behaviour for established threshold displacements. As regards the use of external longitudinal strengthening combined with CFRP confinement, this system is effective for the performance enhancement and viable in terms of execution. The load capacity was increased significantly, preserving also in this case a good ductile behaviour for threshold displacements. As to the numerical nonlinear modelling of the tested columns, the results show a variation of the peak load of 1% to 10% compared with tests results. The good results are partly due to the inclusion of the concrete constitutive model by Mander et al. modified by Faustino, Chastre & Paula taking into account the confinement effect. Despite the reasonable approximation to tests results, the modelling results showed higher unloading, which leads to an overestimate dissipated energy and residualdisplacement.

Embedded Through-Section shear strengthening technique using steel and CFRP bars in RC beams of different percentage of existing stirrups

The Embedded Through-Section (ETS) technique is a promising technique for the shear strengthening of existing (RC) elements. According to this technique, holes are drilled through the beam section, and bars of steel or FRP material are introduced into these holes and bonded to the concrete with adhesive materials. An experimental program was carried out with RC T-cross section beams strengthened in shear using the ETS steel bars and ETS CFRP rods. The research is focused on the evaluation of the ETS efficiency on beams with different percentage of existing internal transverse reinforcement (ρsw=0.0%, ρsw=0.1% and ρsw=0.17%). The effectiveness of different ETS strengthening configurations was also investigated. The good bond between the strengthening ETS bars and the surrounding concrete allowed the yield initiation of the ETS steel bars and the attainment of high tensile strains in the ETS CFPR rods, leading to significant increase of shear capacity, whose level was strongly influenced by the inclination of the ETS bars and the percentage of internal transverse reinforcement.

A model to simulate the moment-rotation and crack width of FRC members reinforced with longitudinal bars

The present work describes a model for the determination of the moment–rotation relationship of a cross section of fiber reinforced concrete (FRC) elements that also include longitudinal bars for the flexural reinforcement (R/FRC). Since a stress–crack width relationship (σ–w)(σ–w) is used to model the post-cracking behavior of a FRC, the σ–w directly obtained from tensile tests, or derived from inverse analysis applied to the results obtained in three-point notched beam bending tests, can be adopted in this approach. For a more realistic assessment of the crack opening, a bond stress versus slip relationship is assumed to simulate the bond between longitudinal bars and surrounding FRC. To simulate the compression behavior of the FRC, a shear friction model is adopted based on the physical interpretation of the post-peak compression softening behavior registered in experimental tests. By allowing the formation of a compressive FRC wedge delimited by shear band zones, the concept of concrete crushing failure mode in beams failing in bending is reinterpreted. By using the moment–rotation relationship, an algorithm was developed to determine the force–deflection response of statically determinate R/FRC elements. The model is described in detail and its good predictive performance is demonstrated by using available experimental data. Parametric studies were executed to evidence the influence of relevant parameters of the model on the serviceability and ultimate design conditions of R/FRC elements failing in bending.

Estudo numérico sobre o reforço de pilares de betão armado com cantoneiras e presilhas metálicas: análise paramétrica e modelo de cálculo

Dissertação de mestrado integrado em Engenharia Civil

Traffic forecasts under uncertainty and capacity constraints

Traffic forecasts provide essential input for the appraisal of transport investment projects. However, according to recent empirical evidence, long-term predictions are subject to high levels of uncertainty. This paper quantifies uncertainty in traffic forecasts for the tolled motorway network in Spain. Uncertainty is quantified in the form of a confidence interval for the traffic forecast that includes both model uncertainty and input uncertainty. We apply a stochastic simulation process based on bootstrapping techniques. Furthermore, the paper proposes a new methodology to account for capacity constraints in long-term traffic forecasts. Specifically, we suggest a dynamic model in which the speed of adjustment is related to the ratio between the actual traffic flow and the maximum capacity of the motorway. This methodology is applied to a specific public policy that consists of suppressing the toll on a certain motorway section before the concession expires.

Field/Laboratory Testing of Damaged Prestressed Concrete Girder Bridges, HR-397, 1999

Due to frequent accidental damage to prestressed concrete (P/C) bridges caused by impact from overheight vehicles, a project was initiated to evaluate the strength and load distribution characteristics of damaged P/C bridges. A comprehensive literature review was conducted. It was concluded that only a few references pertain to the assessment and repair of damaged P/C beams. No reference was found that involves testing of a damaged bridge(s) as well as the damaged beams following their removal. Structural testing of two bridges was conducted in the field. The first bridge tested, damaged by accidental impact, was the westbound (WB) I-680 bridge in Beebeetown, Iowa. This bridge had significant damage to the first and second beams consisting of extensive loss of section and the exposure of numerous strands. The second bridge, the adjacent eastbound (EB) structure, was used as a baseline of the behavior of an undamaged bridge. Load testing concluded that a redistribution of load away from the damaged beams of the WB bridge was occurring. Subsequent to these tests, the damaged beams in the WB bridge were replaced and the bridge retested. The repaired WB bridge behaved, for the most part, like the undamaged EB bridge indicating that the beam replacement restored the original live load distribution patterns. A large-scale bridge model constructed for a previous project was tested to study the changes in behavior due to incrementally applied damage consisting initially of only concrete removal and then concrete removal and strand damage. A total of 180 tests were conducted with the general conclusion that for exterior beam damage, the bridge load distribution characteristics were relatively unchanged until significant portions of the bottom flange were removed along with several strands. A large amount of the total applied moment to the exterior beam was redistributed to the interior beam of the model. Four isolated P/C beams were tested, two removed from the Beebeetown bridge and two from the aforementioned bridge model. For the Beebeetown beams, the first beam, Beam 1W, was tested in an "as removed" condition to obtain the baseline characteristics of a damaged beam. The second beam, Beam 2W, was retrofit with carbon fiber reinforced polymer (CFRP) longitudinal plates and transverse stirrups to strengthen the section. The strengthened Beam was 12% stronger than Beam 1W. Beams 1 and 2 from the bridge model were also tested. Beam 1 was not damaged and served as the baseline behavior of a "new" beam while Beam 2 was damaged and repaired again using CFRP plates. Prior to debonding of the plates from the beam, the behavior of both Beams 1 and 2 was similar. The retrofit beam attained a capacity greater than a theoretically undamaged beam prior to plate debonding. Analytical models were created for the undamaged and damaged center spans of the WB bridge; stiffened plate and refined grillage models were used. Both models were accurate at predicting the deflections in the tested bridge and should be similarly accurate in modeling other P/C bridges. The moment fractions per beam were computed using both models for the undamaged and damaged bridges. The damaged model indicates a significant decrease in moment in the damaged beams and a redistribution of load to the adjacent curb and rail as well as to the undamaged beam lines.

Calculation of the critical crack size for cold form rectangular hollow section tube (CRHS) under bending load at -40º C temperature

To predict the capacity of the structure or the point which is followed by instability, calculation of the critical crack size is important. Structures usually contain several cracks but not necessarily all of these cracks lead to failure or reach the critical size. So, defining the harmful cracks or the crack size which is the most leading one to failure provides criteria for structure’s capacity at elevated temperature. The scope of this thesis was to calculate fracture parameters like stress intensity factor, the J integral and plastic and ultimate capacity of the structure to estimate critical crack size for this specific structure. Several three dimensional (3D) simulations using finite element method by Ansys program and boundary element method by Frank 3D program were carried out to calculate fracture parameters and results with the aid of laboratory tests (loaddisplacement curve, the J resistance curve and yield or ultimate stress) leaded to extract critical size of the crack. Two types of the fracture which is usually affected by temperature, Elastic and Elasti-Plastic fractures were simulated by performing several linear elastic and nonlinear elastic analyses. Geometry details of the weldment; flank angle and toe radius were also studied independently to estimate the location of crack initiation and simulate stress field in early stages of crack extension in structure. In this work also overview of the structure’s capacity in room temperature (20 ºC) was studied. Comparison of the results in different temperature (20 ºC and -40 ºC) provides a threshold of the structure’s behavior within the defined range.

The Plastic Capacity of Boiler Supporting Headers

The goal of this thesis was to make a dimensioning tool to determine the plastic capacity of the boiler supporting header. The capacity of the header is traditionally determined by using FE-method during the project phase. By using the dimensioning tool the goal is to ensure the capacity already in the proposal phase. The study began by analyzing the headers of the ongoing projects by using FE-method. For the analytical solution a plain header was analyzed without the effects of branches or lug. The calibration of parameters in the analytical solution was made using these results. In the analytical solution the plastic capacity of the plastic hinges in the header was defined. The stresses caused by the internal pressure as well as the normal and shear forces caused by the external loading reduced the plastic moment. The final capacity was determined by using the principle of virtual work. The weakening effect of the branches was taken into account by using pressure areas. Also the capacity of the punching shear was defined. The results from the FE-analyses and the analytical solution correlate with each other. The results from the analytical solution are conservative but give correct enough results when considering the accuracy of the used method.

Feasibility of industrial implementation of laser cutting into paper making machine

Laser cutting implementation possibilities into paper making machine was studied as the main objective of the work. Laser cutting technology application was considered as a replacement tool for conventional cutting methods used in paper making machines for longitudinal cutting such as edge trimming at different paper making process and tambour roll slitting. Laser cutting of paper was tested in 70’s for the first time. Since then, laser cutting and processing has been applied for paper materials with different level of success in industry. Laser cutting can be employed for longitudinal cutting of paper web in machine direction. The most common conventional cutting methods include water jet cutting and rotating slitting blades applied in paper making machines. Cutting with CO2 laser fulfils basic requirements for cutting quality, applicability to material and cutting speeds in all locations where longitudinal cutting is needed. Literature review provided description of advantages, disadvantages and challenges of laser technology when it was applied for cutting of paper material with particular attention to cutting of moving paper web. Based on studied laser cutting capabilities and problem definition of conventional cutting technologies, preliminary selection of the most promising application area was carried out. Laser cutting (trimming) of paper web edges in wet end was estimated to be the most promising area where it can be implemented. This assumption was made on the basis of rate of web breaks occurrence. It was found that up to 64 % of total number of web breaks occurred in wet end, particularly in location of so called open draws where paper web was transferred unsupported by wire or felt. Distribution of web breaks in machine cross direction revealed that defects of paper web edge was the main reason of tearing initiation and consequent web break. The assumption was made that laser cutting was capable of improvement of laser cut edge tensile strength due to high cutting quality and sealing effect of the edge after laser cutting. Studies of laser ablation of cellulose supported this claim. Linear energy needed for cutting was calculated with regard to paper web properties in intended laser cutting location. Calculated linear cutting energy was verified with series of laser cutting. Practically obtained laser energy needed for cutting deviated from calculated values. This could be explained by difference in heat transfer via radiation in laser cutting and different absorption characteristics of dry and moist paper material. Laser cut samples (both dry and moist (dry matter content about 25-40%)) were tested for strength properties. It was shown that tensile strength and strain break of laser cut samples are similar to corresponding values of non-laser cut samples. Chosen method, however, did not address tensile strength of laser cut edge in particular. Thus, the assumption of improving strength properties with laser cutting was not fully proved. Laser cutting effect on possible pollution of mill broke (recycling of trimmed edge) was carried out. Laser cut samples (both dry and moist) were tested on the content of dirt particles. The tests revealed that accumulation of dust particles on the surface of moist samples can take place. This has to be taken into account to prevent contamination of pulp suspension when trim waste is recycled. Material loss due to evaporation during laser cutting and amount of solid residues after cutting were evaluated. Edge trimming with laser would result in 0.25 kg/h of solid residues and 2.5 kg/h of lost material due to evaporation. Schemes of laser cutting implementation and needed laser equipment were discussed. Generally, laser cutting system would require two laser sources (one laser source for each cutting zone), set of beam transfer and focusing optics and cutting heads. In order to increase reliability of system, it was suggested that each laser source would have double capacity. That would allow to perform cutting employing one laser source working at full capacity for both cutting zones. Laser technology is in required level at the moment and do not require additional development. Moreover, capacity of speed increase is high due to availability high power laser sources what can support the tendency of speed increase of paper making machines. Laser cutting system would require special roll to maintain cutting. The scheme of such roll was proposed as well as roll integration into paper making machine. Laser cutting can be done in location of central roll in press section, before so-called open draw where many web breaks occur, where it has potential to improve runability of a paper making machine. Economic performance of laser cutting was done as comparison of laser cutting system and water jet cutting working in the same conditions. It was revealed that laser cutting would still be about two times more expensive compared to water jet cutting. This is mainly due to high investment cost of laser equipment and poor energy efficiency of CO2 lasers. Another factor is that laser cutting causes material loss due to evaporation whereas water jet cutting almost does not cause material loss. Despite difficulties of laser cutting implementation in paper making machine, its implementation can be beneficial. The crucial role in that is possibility to improve cut edge strength properties and consequently reduce number of web breaks. Capacity of laser cutting to maintain cutting speeds which exceed current speeds of paper making machines what is another argument to consider laser cutting technology in design of new high speed paper making machines.

Improve the production capacity: A case study of Eurofins Viljavuuspalvelu Oy

In any manufacturing system, there are many factors that are affecting and limiting the capacity of the entire system. This thesis addressed a study on how to improve the production capacity in a Finnish company (Viljavuuspalvelu Oy) through different methods like bottleneck analysis, Overall Equipment Effectiveness (OEE), and Just in Time production. Four analyzing methods have been studied in order to detect the bottleneck machine in Viljavuuspalvelu Oy. The results shows that the bottleneck machine in the industrial area that constraint the production is the grinding machine while the bottleneck machine in the laboratory section is the photometry machine. In addition, the Overall Equipment Effectiveness (OEE) of the entire system of the studied case was calculated and it has been found that the OEE of the Viljavuuspalvelu Oy is 35.75%. Moreover, two methods on how to increase the OEE were studied and it was shown that either the total output of the company should be 1254 samples/shift in order to have an OEE around 85% which is considered as a world class or the Ideal run rate should be 1.45 pieces/minute. In addition, some realistic methods are applied based on the finding in this thesis to increase the OEE factor in the company and in one realistic method the % OEE has increase to 62.59%. Finally, an explanation on how to implement the Just in Time production in Viljavuuspalvelu Oy has been studied.

L’expérience vécue à domicile par les conjointes de partenaires atteints de la démence de type Alzheimer au moment des soins d’hygiène

Suite à une recension des écrits sur les soins d’hygiène des personnes atteintes de démence de type Alzheimer (DTA), force est de constater la rareté, voire l’absence de recherches sur la question des soins d’hygiène (SH) dispensés à domicile par les conjointes. Pourtant, la conjointe à domicile est confrontée aux mêmes difficultés que les intervenants des établissements de santé et doit ainsi faire face aux comportements, parfois difficiles de la personne atteinte. Dans la pratique, les infirmières questionnent peu les difficultés rencontrées par les aidantes au moment des soins d’hygiène, ce qui permet difficilement de prendre conscience de leurs sentiments d’isolement et de détresse et de les réduire, le cas échéant. Pour pallier cette lacune, la présente recherche vise à comprendre l’expérience que vivent des conjointes d’hommes atteints de DTA lorsqu’elles leur dispensent des SH à domicile. Un second objectif vise à identifier les dimensions qui sont associées à cette expérience. Une approche de recherche qualitative est utilisée. Les participantes ont été recrutées par l’entremise des Sociétés Alzheimer de Laval et des Laurentides. La stratégie de collecte des données a impliqué la réalisation de deux entrevues individuelles, face à face, de même que l’administration d’un court questionnaire portant sur les aspects sociodémographiques. La démarche retenue pour l’analyse de l’ensemble de données est inspirée de l’approche proposée par Miles et Huberman (2003). Les résultats permettent d’abord de mettre en évidence des profils de conjointes qui, tout en étant variables, présentent certaines similarités. Eu égard aux SH, toutes ont à consacrer des efforts soutenus, quotidiens et intenses. Elles doivent faire montre de patience et compter sur des capacités personnelles les amenant à ressentir des sentiments positifs malgré les situations difficiles. Les résultats montrent par ailleurs que la dispensation des SH provoque aussi des sentiments négatifs associés au fardeau que ces soins impliquent. Les conjointes mettent toutefois en œuvre une variété de stratégies d’adaptation au stress telles la résolution de problème, la recherche de soutien social et le recadrage. Cinq ensembles de dimensions personnelles et contextuelles sont associés à l’expérience des aidantes : 1) En ce qui a trait aux caractéristiques personnelles des conjointes, l’avancement en âge et l’état de santé physique ou psychologique influencent négativement l’expérience lors des SH. Par contre, les ressources personnelles intrinsèques (acceptation de la réalité, capacité de trouver un sens à l’évènement, habileté à improviser et sens de l’humour) sont utilisées de manière naturelle ou acquise; 2) Les caractéristiques personnelles du conjoint (année du diagnostic, pertes d’autonomie et troubles de comportement) affectent négativement l’expérience vécue; 3) La relation conjugale présente un intérêt important puisqu’il apparaît qu’une relation conjugale pré-diagnostic positive semble favoriser des sentiments positifs chez la conjointe en ce qui a trait aux SH; 4) Les dimensions familiales ont un impact favorable, étant donné le soutien psychologique reçu de la famille; 5) Les dimensions macro-environnementales, incluant l’aide reçue du réseau informel plus large de même que du réseau formel, ainsi que les divers aménagements matériels de l’environnement physique du couple, ressortent enfin comme ayant un impact positif. Au terme de l’analyse des résultats, l’auteure est en mesure de proposer une synthèse de l’expérience des conjointes. La discussion aborde quatre enjeux qui se dégagent des résultats observés : impacts des difficultés rencontrées lors des SH dans la décision d’hébergement, réticence des aidantes à faire appel aux ressources du réseau formel pour obtenir de l’aide eu égard aux SH, importance des ressources personnelles des aidantes et potentiel de l’approche relationnelle humaine (human caring) pour faire face aux défis que pose la dispensation des SH.

Effects of food structure and ingredient interactions on antioxidant capacity

Foods are complex biological materials, and the lipids within the food are susceptible to lipid oxidation, which is retarded by antioxidants. The precise structure and composition of the food may affect the antioxidant activity quite strongly in some cases. Solubility of the antioxidant in the phases present is one of the main parameters that affects the variation in antioxidant activity with phase composition of food. Polar antioxidants are more effective in oils, whereas non-polar antioxidants are more effective in oil-in-water emulsions. Antioxidant activity has been reported in a range of different media, including oils, emulsions, liposomes, microemulsions, fish and meat muscles, and the antioxidant activity may vary from one medium to another. Synergy between antioxidants may also vary from one medium to another. Interactions with metals and with proteins affect antioxidant activity and these interactions are also dependent on the phases present.