Academic literature on the topic 'DISSIPATIVE BRACES'

The thesis presents research into the understanding and improvement of heat dissipation from friction brakes. The investigations involved two brake types, considered to be the most thermally loaded and therefore most challenging; axle mounted high speed railway and commercial vehicle disc brakes. All three modes of heat transfer (conduction, convection and radiation) and airflow characteristics have been analysed experimentally and theoretically in order to increase the understanding of heat dissipation. Despite the very practical aspects of this research, a 'generic heat transfer approach' was applied, enabling wider engineering applications of the results. Experimental analyses conducted on a specially developed Spin Rig allowed measurements of cooling and airflow characteristics for different designs. Methodologies have been developed to determine thermal contact resistance, heat transfer coefficients, emissivity and aerodynamic (pumping) losses. Established values and relationships compared very favourably with theoretical work. Analytical, FE and CFD analyses were employed to further investigate design variations and perform sensitivity studies. Inertia dynamometer route simulations provided disc temperatures for validation of the overall work. Recommendations have been made for optimising heat dissipation, by proposing practically acceptable and economically viable design solutions. A proposed ventilated disc design efficiency ratio allows large, high speed ventilated disc designs, to be efficiently and accurately evaluated and compared, providing a valuable disc design optimisation tool. The determination of the methodologies, parameters and functions defining cooling characteristics, enable heat dissipation to be predicted confidently and accurately for brakes and other engineering assemblies at early design stages.

This project focuses on the design and modeling of a two degree-of-freedom dissipative passive haptic display. Haptic displays are man-machine interfaces that transmit forces to the human operator. A dissipative passive haptic display is one that may only remove energy from the system using actuators such as brakes and dampers, thus ensuring the safety of the human operator. These devices may be used to implement virtual constraints such as desired paths and obstacles. Traditional friction brakes have previously been used as dissipative and coupling elements in a two degree-of-freedom parallel manipulator, resulting in undesired effects such as vibration, stiction, and slow response times. Alternatively, the new robot is actuated by rheological brakes, which feature fast response times and smooth application of torque. This approach aims to improve upon the accuracy and feel of the previous design. A commercial magnetorheological (MR) fluid brake was selected and put through an extensive series of tests. The data was used to develop a model that characterizes MR fluid behavior in low speed braking applications. A parallel five bar linkage was designed and built that has separate configurations corresponding to 3-brake and 4-brake operation. The length of each arm was chosen by means of a geometrical optimization that weighs the size and area of the workspace and actuator effects. A simulation was then developed by incorporating the brake model into the equations of motion of the robot. Next, two forms of path following velocity control were devised and tested in simulation. Finally, the accuracy, workload, and smoothness of both controllers and both configurations were examined in preliminary tests with human operators.

In questa tesi si propone il miglioramento sismico di un capannone in calcestruzzo armato prefabbricato a due piani a pilastri isostatici mediante l'inserimento di controventi dissipativi in acciaio con forma speciale (Crescent-Shaped-Braces). PREMESSA In primo luogo si dimostra come la struttura studiata soddisfi già i requisiti del DM 2008, sia allo SLD (spostamenti d’ interpiano) che allo SLV (elementi strutturali verificati). OBIETTIVO Migliorare le caratteristiche prestazionali di un edificio in calcestruzzo armato prefabbricato a due piani, sottoposto ad azione sismica. STRATEGIA Inserimento di dispositivi dissipativi di tipo Crescent Shaped Brace in alcune specchiature del capannone prefabbricato, in entrambe le direzioni. PROGETTAZIONE DELLA STRUTTURA RINFORZATA 1) Identificazione delle caratteristiche (rigidezza e resistenza) dei dispositivi CSB, sulla base di obiettivi scalati al livello superiore (deformabilità allo SLV e resistenza allo SLC) per il sistema «struttura + dispositivi», attraverso lo sviluppo di una procedura specifica per capannoni prefabbricati a 2 piani. 2) Progettazione dei dispositivi CSB (scelta della geometria e della sezione) 3) Verifica delle effettive prestazioni ottenute mediante simulazioni numeriche time-history

La risposta sismica degli edifici CLT è analizzata con lo scopo di valutare la correlazione tra la capacità dissipativa, rappresentata dal fattore di comportamento q, e la metodologia di costruzione, ovvero le proprietà geometriche dell'edificio ed il comportamento delle connessioni adottate. Questo studio presenta un modello numerico in grado di simulare la risposta dinamica di una parete a tre piani costituita da pannelli portanti a strati incrociati, nella quale sono state utilizzate connessioni innovative, rappresentate da staffe ad alta capacità dissipativa caratterizzate da una particolare forma ad "X": queste staffe sono resistenti a forze di trazione e a forze di taglio e sono state concepite per realizzare tutti i giunti sismici dell'edificio, con un tipo di collegamento unico in grado di massimizzare la capacità sismica di tutta la struttura, assicurando alta duttilità e comportamento allo schiacciamento trascurabile. Questa nuova connessione è stata studiata ed ottimizzata attraverso modellazione numerica; poi, il suo comportamento è stato convalidato attraverso test sperimentali. La connessione di tipo X-bracket, quando viene utilizzata per collegare pannelli CLT alle fondazioni, ai diaframmi, ai solai o anche reciprocamente, consente di raggiungere elevata dissipazione e duttilità anche quando vengono adottate grandi pareti in CLT senza giunzioni verticali. A tal proposito, è stata eseguita un'analisi dinamica incrementale su due diverse configurazioni della parete progettata, differenti per quantità di connessioni e per la presenza o meno di giunzioni verticali, allo scopo di valutare il valore del fattore di comportamento q, in funzione delle scelte progettuali e delle proprietà geometriche dell'edificio.

L'elaborato di tesi tratta lo studio di un collegamento trave-pilastro di tipo semirigido dissipativo. L’idea progettuale alla base di tale studio è quella di posizionare nel nodo trave-pilastro di un telaio in acciaio una coppia di dispositivi metallici che durante il sisma si snervino prima dei pilastri. In tal caso infatti si concentrerebbe parte della dissipazione energetica in tali dispositivi ritardando la formazione delle cerniere plastiche alla base dei pilastri e preservando quindi questi ultimi dalla plasticizzazione. Lo studio è stato effettuato considerando come dispositivi metallici i Crescent Shaped Braces (CSB), dispositivi isteretici che, grazie alla loro configurazione geometrica, sono caratterizzati da un legame costituivo elastico-incrudente trilineare. A partire proprio da tale legame costitutivo (noto una volta ipotizzate le dimensioni e la sezione dei CSB) e dalla configurazione geometrica del nodo trave-pilastro, si è studiato il comportamento del collegamento fino alla determinazione del legame Momento-Rotazione: per ogni rotazione della trave rispetto al pilastro si ha infatti una reazione dei CSB che generano sulla trave un momento contrario alla rotazione stessa. Si è poi passati ad un particolare caso di studio, andando ad analizzare il beneficio in ambito sismico derivante dall’inserimento dei Crescent Shaped Brace nei nodi trave-pilastro di un telaio monopiano a singola campata in acciaio. Per verificare tale beneficio si sono eseguite delle analisi non lineari (statiche e dinamiche) su telai con e senza CSB e se ne sono confrontati i risultati.

Cette thèse regroupe une série de travaux ayant tous trait à des systèmes hamiltoniens non linéaires spatialement étendus présentant une bifurcation nœud-col. Elle est constituée de deux parties. Nous étudions dans une première partie la transition à la dissipation de systèmes unidimensionnels soumis à un forçage local et régis par des équations de type sine-Gordon ou Schrödinger non linéaire (ESNL). Nous en calculons analytiquement les solutions stationnaires et caractérisons le comportement dynamique au voisinage de celles-ci près de la bifurcation. Lorsque la relation de dispersion des systèmes possède une fréquence de coupure, le comportement dynamique est caractéristique de systèmes hamiltoniens. A contrario, lorsque la relation de dispersion ne possède pas de fréquence de coupure, la dynamique du système se couple avec l'émission d'ondes sonores qui joue le rôle d'un amortissement effectif. Elle devient alors typique de systèmes dissipatifs. En outre, les modes propres temporels du système subissent une délocalisation spatiale. La seconde partie de la thèse concerne l'étude de deux types d'écoulements bidimensionnels de fluides parfaits barotropes autour d'un obstacle : un écoulement décrit par l'ESNL et un écoulement à surface libre dans l'approximation eau peu profonde, où sont pris en compte les effets dispersifs dus aux effets de tension de surface. Lorsque la longueur caractérisant la dispersion des ondes sonores tend vers zéro, ces deux écoulements se réduisent à l'écoulement autour d'un disque d'un fluide eulérien compressible, auquel se superpose une couche limite que nous calculons analytiquement. Par des méthodes de suivi de branches fondés sur des développements pseudo-spectraux, nous calculons le diagramme de bifurcation complet des deux écoulements. En étudiant la dynamique des deux systèmes au-delà de la bifurcation, nous mettons en évidence une émission d'excitations (dans le cas de l'ESNL) dont la nature dépend du rapport de la longueur de cohérence sur la taille de l'obstacle. Dans le cadre de l'écoulement en eau peu profonde, cette émission est remplacée par une singularité à temps fini de démouillage.

Elastoplastic energy dissipators are used in earthquake-resistant design in order to dissipate a substantial part of the seismic energy acting on a building. They are elements that are not part of the load-bearing structure and, therefore, are easily replaceable in case of damage. Their behaviour is usually stable and their degree of degradation difficult to appreciate visually. To assess their degree of degradation, damage indices are used which estimate their remaining dissipative capacity through the combination of a number of variables such as, for example, the number of cycles sustained and their amplitude, the energy dissipated, accumulated deformation and maximum deformation. In the first part of this doctoral thesis, the current state-of-the-art in terms of existing damage models is reviewed. The second part of this thesis brings together a wide experimental foundation based on data obtained in previous research works complemented with new tests carried out within the present thesis. In its third part, the validity of various fatigue models is assessed through the experimental foundation brought together in the second part of this thesis. In its fourth and final part, the validity of some of the best-known hysteretic models has been analyzed in order to reproduce the experimental response of the dissipators tested. Notable as the most important contribution of this thesis is the attainment of two models of mixed fatigue and dimensionless variables, which demonstrate excellent validity considering, in the same fatigue curve, dissipators of different types and geometry based on low carbon steel and uniform plastification in uniaxial states of stress<br>Els dissipadors d’energia elastoplàstics s’utilitzen en el disseny sísmic per dissipar una part substancial de l’energia sísmica introduïda en una construcció. Són uns elements que no formen part de l’estructura portant i, per tant, fàcilment reemplaçables en cas de quedar danyats. El seu comportament sol ser estable i el seu grau de degradació difícilment apreciable de forma visual. Per avaluar el seu grau de degradació es recorre als índex de dany, que estimen la capacitat dissipativa romanent a partir de la combinació de variables diverses com són, per exemple, el nombre de cicles suportats i la seva amplitud, l’energia dissipada, la deformació acumulada i deformació màxima. A la primera part d’aquesta tesi doctoral es revisa l’estat de l’art relatiu a models de dany existents. La segona part d’aquesta tesi recull una àmplia base experimental basada en dades obtingudes en treballs previs de recerca, complementats amb nous assajos realitzats a la present tesi. En una tercera part es valora la bondat de diversos models de fatiga mitjançant la base experimental recollida a la segona part. En la seva quarta i última part s’ha analitzat la bondat d’alguns dels models histerètics més coneguts per a reproduir la resposta experimental dels dissipadors assajats. La conclusió més important que s’extreu de la tesi és l’obtenció de dos models de fatiga mixtes i variables adimensionals, els quals demostren una excel·lent bondat considerant, en una mateixa corba de fatiga, dissipadors de diferent tipologia i geometria, basats en acers de baix contingut en carboni i plastificació uniforme en estat uniaxial de tensions<br>Programa de Doctorat en Tecnologia

碩士<br>國立臺灣大學<br>土木工程學研究所<br>100<br>Self-Centering Energy Dissipative Brace is a kind of brace which uses tendons to constrain compression elements of the brace and provide self-centering properties under tension and compression force (restore to zero residual deformation). Traditional self-centering energy dissipative brace’s deformation capacity relies on the elastic deformation capacity of the tendons used inside the brace, and results in limitation of the braces’ deformability. Traditional SCED brace has a maximum strain of 1.3% when the tendons reach 1.9% strain and the frame reaches 2% inter-story drift. Tendons required to have large elastic strain mainly uses composite material. However, tendons having over 2% elastic strain material properties are rare and seldom used or researched. This research develops a new kind of SCED brace by adding a second core element and another group of tension elements which doubles the deformation capacity compared to traditional SCED brace while using tension elements comprised of the same material properties (or largely reduce the elastic strain demand of the tendon elements to 1% under the same brace deformation when compared to traditional SCED brace). This research designed four specimens to validate the double core SCED brace which uses different materials for its tendons. Four specimens’ tendon uses D16 steel strand, D22 glass fiber, D29 glass fiber and D13 carbon fiber respectively. The results show that the mechanism of double core SCED brace is consistent with prediction. The test results and prediction of tendon strain is close which is 0.8%, 1.05%, 0.9% and 1.09% for specimen 1 to 4 respectively while the brace has a 1.2% strain corresponding to 2% inter-story drift. The result shows that double core SCED brace can significantly reduce the demand for tendon elastic strain. Except specimen 1 due to loss of pre-tension force has poor behavior in self-centering, specimen 2 to 4 have good behavior in self-centering with no pre-tension loss. This research also uses the finite element software ABAQUS to analyze double core SCED brace behavior and compare with the testing results which is proved similar. The parametric study of double core SCED brace we choose different pre-tension force, different friction force, and different tendons to observe the difference in brace behavior. Results indicate that the lager the friction force is the larger the energy dissipation there will be, yet in order to have full self-centering behavior, the pre-tension force should be larger than friction force. However the larger the pre-tension force is the smaller the deformation capacity there is left. Unlike pre-tension force and friction force, the difference of tendons only effect the post-stiffness of the response and limits the deformation capacity due to its limitation in elastic strain.

Earthquake-prone regions of the world are usually characterized by a high number of Reinforced Concrete (RC) buildings designed before seismic building codes were enforced. As a result, the amount of existing RC buildings requiring seismic assessment and likely retrofitting is large. The use of innovative techniques for the seismic amelioration of existing RC buildings has been attracting the attention of both academic and technical communities since the second half of the previous century. Among these techniques there is the employment of passive energy dissipating devices that are mounted in series to metallic braces installed within the existing RC frames. Such energy dissipating devices can be 1) fluid-viscous, 2) viscoelastic, 3) elasto-plastic, 4) frictional or 5) based on shape-memory alloys. The large number of devices available on the market is not accompanied yet, at least within the Italian Building Code, by a mature and detailed description of the design procedure, so that the practicing engineer who would like to adopt this technique is often referred to scientific publications. With the aim to contribute to fill this gap, an energy-based methodology is proposed and applied and compared with some of the most innovative design procedures available in the scientific literature to date. The validity of each procedure is appraised on the basis of non-linear static and non-linear dynamic analysis results.