1,636 research outputs found
Mega Floating Concrete Bridges
No full textIntroduction This graduation project has been initiated to research the technical feasibility of floating bridges. The project has been done in co-operation with the FDN engineering company and Delft technical university. A design is made of a continuous pontoon floating bridge, which connects a mainland to an island. Floating bridges can be constructed where conventional bridges are impractical (under the conditions that are described in section 1.4.2). The buoyancy forces support the bridge in the vertical direction and the mooring system in the horizontal direction. The project contains also a survey of the most known floating bridges in the world. Problem definition Which design limitations and structural parameters can ensure stability of the continuous pontoon floating bridge under wind and wave load? Research The objective of this thesis is to understand the response of the continuous pontoon floating bridges under wind-wave load and traffic load that is described in the euro code which enables us to optimize the structural design procedure. That can be accomplished by studying the influence of the pontoon dimensions and the pontoon connector rotational rigidity on the global stability of the bridge. Determination the principles of response reduction and converting the displacement into internal forces are a relevant part of this thesis as well as the mitigating of the local environmental loads to be redistributed along larger parts of the bridge. The scope of the graduation project is very wide. It contains an overview of floating bridges; its hydrodynamic behaviour will be defined and due to the limited period of time will be not analyzed. The hydrostatic behaviour and analysis of continuous pontoon floating bridges will be researched as a multi-body slender structure with flexible connections. Also the conceptual design of the pontoons and the connections and the shape effects were researched. Detailed design calculations for the case study are included in this thesis. Results Environmental loads are the main loading on the floating bridge. Because of the random form of the sea wave forces and the wind force, it is difficult to expect the precise value and direction of loading on the bridge. The environmental loads twist the bridge and excite it in the horizontal and in the vertical direction. When it is possible to construct a sliding pile mooring system to introduce the wind and wave load in the horizontal direction, the floating bridge will have a satisfactory stability. The efficiency of the mooring cable is lower than the sliding pile due to the relatively large compliance range. That is valid also for the vertical displacement; the bridge response will be introduced by the bridge flexural rigidity, the bridge mass, the water spring, the water damping and the pontoon connector stiffness when discrete pontoons are used. The linear theory is applied to determine the sea wave load. The hydro-static and the hydro-dynamic analysis of a multi-body slender structure consisting of rigidly or flexibly connected elements will be made.. The design procedure of the mooring cables of the offshore structure is applied to design the mooring system. Conclusions and recommendations The connection stiffness of the pontoon has a large influence on the bridge response. The ratio connection stiffness over pontoon stiffness is very important for the bridge structural behaviour. When this ratio is smaller than 10-8 the bridge behaves as rigid bodies connected by hinges. When this ratio is larger than 10-3 the bridge behaves as a continuous elastic beam. The largest deflections, moments, and shear forces occur in the ends of the bridge. Additional supports, masses, or dampers at these ends can reduce these moments and forces strongly. Embedment steel crossheads are used to introduce the large mooring line forces without damaging the concrete walls of the pontoons. Further optimization of the pontoon length is recommended. Fatigue of the prestressing steel and the concrete are shown to be critical and need to be further investigated.Design and ConstructionCivil Engineering and Geoscience
An Illustrated Guide for Monitoring and Protecting Bridge Waterways Against Scour - Project TR-515 - Final Report, March 2006
No full textThis report is a well illustrated and practical Guide intended to aid engineers and
engineering technicians in monitoring, maintaining, and protecting bridge
waterways so as to mitigate or prevent scour from adversely affecting the
structural performance of bridge abutments, piers, and approach road
embankments. Described and illustrated here are the scour processes affecting
the stability of these components of bridge waterways. Also described and
illustrated are methods for monitoring waterways, and the various methods for
repairing scour damage and protecting bridge waterways against scour.
The Guide focuses on smaller bridges, especially those in Iowa. Scour processes
at small bridges are complicated by the close proximity of abutments, piers, and
waterway banks, such that scour processes interact in ways difficult to predict
and for which reliable design relationships do not exist. Additionally, blockage
by woody debris or by ice, along with changes in approach channel alignment,
can have greater effects on pier and abutment scour for smaller bridges. These
considerations tend to cause greater reliance on monitoring for smaller bridges.
The Guide is intended to augment and support, as a source of information,
existing procedures for monitoring bridge waterways. It also may prompt some
adjustments of existing forms and reports used for bridge monitoring. In accord
with increasing emphasis on effective management of public facilities like
bridges, the Guide ventures to include an example report format for quantitative
risk assessment applied to bridge waterways. Quantitative risk assessment is
useful when many bridges have to be evaluated for scour risk and damage, and
priorities need to be determined for repair and protection work. Such risk
assessment aids comparison of bridges at risk.
It is expected that bridge inspectors will implement the Guide as a concise,
handy reference available back at the office. The Guide also likely may be
implemented as an educational primer for new inspectors who have yet to
become acquainted with waterway scour. Additionally, the Guide may be
implemented as a part of process to check whether existing bridge-inspection
forms or reports adequately encompass bridge-waterway scour
Concrete overlay of movable steel orthotropic bridges: The repair method for movable steel bridges
No full textIn 1997 cracks were found in the relatively new movable part of the Van Brienenoord bridge, a repair method for steel orthotropic bridges has searched for ever since. For fixed bridges a solution was found: the steel deck plate is overlayed with a concrete layer with a thickness varying between 50mm and 120mm and on top of the repair layer a new wearing surface is created. The concrete layer is either connected by studs or by an epoxy layer. Movable bridges have a thin wearing surface. Due to weight restrictions, it is not possible to apply a relatively thick concrete layer on top of the steel deck plate. So, different solutions have been researched and the best option seems to be to overlay the steel deck plate with a thin heavily reinforced concrete layer. This method has already been analysed under static loads, but also the fatigue resistance should be guaranteed. This master thesis project aims at designing a 20mm concrete layer in order to increase the lifespan of an orthotropic steel deck of a movable bridge by replacing the wearing surface of this deck by this concrete layer. The main topic dealt with is to determine the fatigue life of the repaired structure. It is assumed that the governing position in the structure is the connection between the trough web and the steel deck plate above the crossbeam. At this position the largest hogging moment exists. Three different alternatives are defined to come up with the most effective solution, all with the same composition, dimensions and material properties except the type of reinforcement. The repair method consists of a 17mm thick high strength fibreless concrete layer, on top of an epoxy layer sprinkled in with calcinated bauxite. The different types of reinforcement are: epoxy coated and sprinkled in with sand Carbon Fibre Reinforced Polymer (CFRP), stainless steel and epoxy coated “ordinary” steel reinforcement, all with a bar diameter of 6mm. The centre to centre distance of the rebars is 12mm and the concrete cover on the rebars is 6mm thick. The stresses occurring due to the fatigue loading based on the Eurocode (load model 3) are calculated and the fatigue lifetime of each material is defined. Since uncertainties exist about the fatigue behaviour of the interaction between materials, an experimental research has been started. Test specimens were created and dynamically loaded by a hogging moment in a four point bending test. In the experimental research it became clear that the steel reinforced alternatives fail by reinforcing bar failure, whereas the CFRP alternative fails by debonding of the rebars. Besides these failure modes, concrete cracks occurred in the anchorage zone of the reinforcement. These cracks have been further researched, because they might become critical in practice. It is concluded that the concrete is only governing in case of relatively high moments.Design and ConstructionCivil Engineering and Geoscience
The structural reliability of bridges subject to time-dependent deterioration
No full textPaper presented at the 11th International Conference on Civil, Structural and Environmental Engineering Computing, Malta, 18-21 September 2007The reliability of the structural performance of any given structure is affected by both in-service loading and material deterioration due to environmental attack. They must be evaluated at any given time in order to compute lifetime probability of failure. This paper presents an innovative methodology to derive the structure lifetime load effect due to existing traffic using a statistical tool known as Predictive Likelihood. Loss of resistance due to corrosion originated by chloride ingression is also taken into account. Finally the lifetime probability of failure is evaluated via the application of a time-discretization strategyNot applicableConference detailshttp://www.civil-comp.com/conf/cc07.htmConference website at http://www.civil-comp.com/conf/cc07.htm. Record must include a full reference to the published paper and a DOI weblink to the final published version - http://dx.doi.org/10.4203/ccp.86.189. DG
06/07/10
au,ti, ke - AL 23/07/201
La politica della legalità : il ruolo del giurista nell'età contemporanea
No full textAs the author of this book shows as he tests his theses, impartiality and justice require specific and scrupulous forms of civil engagement which render obsolete the traditional call for neutrality. At the same time, citizens must be made to understand how formal features of law that usually evoke their hostility actually guarantee their rights. The legal professional must learn to be a "relativist", obliged - through his choices - to establish priorities among distinct and often irreconcilable value domains
Vibration based performance assessment of concrete-concrete composite bridges
No full textIncludes bibliographical references (leaves 142-148).Concrete composites consisting of precast pre-stressed standardized beams and a cast in-situ deck slab have been used for the construction of short to medium span bridges for the past four decades in South Africa and worldwide. The pre-cast beams and cast in-situ slab are commonly connected using shear connectors. Failure of these connectors would compromise the composite action of the structure, thus reducing the load carrying capacity and hence its efficiency. This study seeks to assess the integrity of such shear connectors using dynamic testing and Finite Element (FE) analysis. The main objective of the work is to assess the practicality of vibration-based techniques to detect damaged shear connectors using experimental and analytical modal data. A scaled bridge model was constructed and 10 mm bolts connected the beams and slab to simulate shear connectors in the prototype bridge. Different damage scenarios were introduced by loosening some of the connectors and vibration testing was done to detect the artificial damage. An FE model of the system was also developed. The shear connectors were modelled as non-linear spring elements capable of simulating the composite action between the slab and beams. Damage of shear connectors was simulated by reducing the spring stiffness. The updating of the FE model was done manually by adjusting appropriate spring stiffnesses. The experimental and analytical results show that the natural frequencies are sensitive to this damage. The frequencies dropped from undamaged to severe damaged structure. Very little information was deduced from the damping ratios, modal assurance criteria (MAC) and coordinate modal assurance criteria (COMAC) values. The experimental and analytical first bending, torsion and transverse modes were sensitive to the damaged shear connectors. 65% of damaged connectors were located using these modes. Using experimental modal data, the mode curvatures and flexibility changes were able to locate the damaged region when more than 35% of shear connectors were loosened. However, using numerical data, the mode curvatures and flexibility changes were able to localize the damaged region for 6% damage introduced. 75% of the loosened connectors were identified. The stiffness change technique could only identify less than 10% of damaged shear connectors using experimental modal data. The same technique was applied on analytical data and over 75% of damaged shear connectors were located. The FE modelling of shear connectors used in this work was applied on an existing bridge. Van der Kloof bridge (South Africa) was constructed using precast pre-stressed beams and a cast in-situ slab. Extended beam web stirrups were used as shear connectors. The main aim was to develop a robust FE model for this bridge that could be used in future to investigate the condition of shear connectors. Using 6-0 non-linear spring elements to model the shear connectors, a maximum difference of 0.98% was observed between the measured and theoretical frequencies after manual updating. This is quite a small difference. This model could therefore be used as a true representative of the physical structure for future investigations
Cercando di dimenticare Savigny
No full textIl presente scritto è un contributo alla discussione del libro di Aurelio Gentili, Il
diritto come discorso del 2013. Del predetto volume si approvano senza riserve
a) la critica alla concezione del vecchio positivismo, secondo il quale il giurista
non farebbe altro che esplorare un misterioso oggetto denominato “realtà
giuridica”, e b) l’interesse per le tecniche argomentative quali strumenti di
controllo interno dei discorsi. Sul piano propositivo, l’autore della recensione
ammette che la conoscenza dei significati normativi letterali, quando la si
ritiene rilevante, comporta a livello collettivo (ma assai meno al livello dei
singoli) un giudizio partecipante. Tali significati, del resto, lungi dall’essere
entità fisse, sono sempre in movimento. Ciò stabilito e con questi limiti,
occorre ammettere che non c’è solo un ordo ordinans imposto dai giuristi sui
confusi materiali estratti dalle fonti, ma si può scorgere, e si deve ritrovare,
anche un ordo ordinatus, frutto tanto dell’attività legislativa quanto delle precedenti interpretazioni, che il singolo interprete non può far a meno di
riconoscere. Insomma: tra i due ordini, fra le attività dei giuristi e i prodotti di
tali attività, si stabilisce un rapporto dialettico.This article is a contribution to the discussion regarding Aurelio Gentili’s 2013
book Il diritto come discorso. From the said volume, the author fully approves:
a) the criticism of the old positivism’s conception that a lawyer does nothing
but explore the misterious object that is “legal reality”, and b) the interest in
argumentative techniques as instruments for internal control of discourses. The
author of this article proposes admitting that the knowledge of literal normative
meanings, when believed to be relevant, requires at the level of the collective
(much less so at the individual level) a judgment, which demonstrates
participation. These meanings are, moreover, far from being fixed entities,
always changing. Within these limits, it should be admitted that there is not
only an ordo ordinans, made by the jurists, using the confused materials
extracted from the sources, but that we may also observe, and must rediscover,
an ordo ordinatus, which results from both legislative activity and previous
interpretations – that an individual interpreter cannot but recognize. In short, a
dialectic relationship between the two orders, between the activity of lawyers
and the products of these activities, is thus established
Exact two-dimensionalization of low-magnetic-Reynolds-number flows subject to a strong magnetic field
No full textWe investigate the behavior of flows, including turbulent flows, driven by a horizontal body-force and subject to a vertical magnetic field, with the following question in mind: for very strong applied magnetic field, is the flow mostly two-dimensional, with remaining weak three-dimensional fluctuations, or does it become exactly 2D, with no dependence along the vertical? We restrict attention to low-magnetic-Reynolds number (Rm) flow. Because liquid metals have low magnetic Prandtl number, such low- flows can have a kinetic Reynolds number as large as one million and therefore be strongly turbulent. We first focus on the quasi-static approximation, i.e. the asymptotic limit of vanishing magnetic Reynolds number Rm << 1: we prove that the flow becomes exactly 2D asymptotically in time, regardless of the initial condition and provided the interaction parameter N is larger than a threshold value. We call this property absolute two-dimensionalization: the attractor of the system is necessarily a (possibly turbulent) 2D flow. We then consider the full-magnetohydrodynamic equations and we prove that, for low enough Rm and large enough N, the flow becomes exactly two-dimensional in the long-time limit provided the initial vertically-dependent perturbations are infinitesimal. We call this phenomenon linear two-dimensionalization: the (possibly turbulent) 2D flow is an attractor of the dynamics, but it is not necessarily the only attractor of the system. Some 3D attractors may also exist and be attained for strong enough initial 3D perturbations. These results shed some light on the existence of a dissipative anomaly for magnetohydrodynamic flows subject to a strong external magnetic field
Letter from Lee C.R. Baker, Reference Assistant to Michi Weglyn, September 25, 1974
No full textThis letter refers to a thesis written by Warren Page Rucker in 1970 entitled, "United States--Peruvian Policy Toward Peruvian-Japanese Persons During World War II." Baker explains that Weglyn can purchase a copy of the thesis if she so desires.Collection of notes, articles, correspondence, photographs, and term papers collected by Yukio Mochizuki, a student at CSU Dominguez Hills, while researching Japanese American incarceration and Japanese Peruvian internment during World War II
Flow instabilities and reversals in non-uniformly thermocapillary driven melt pool
No full textWith transient LES and DNS simulations, we investigate flow in melt pools driven by thermocapillary forces. The developing pool is at first axisymmetric as are the boundary conditions, but flow instabilities arise that lead to 3D oscillatory flow patterns. At higher laser powers a sign-change in the surface tension temperature coefficient occurs, resulting in a flow reversal in the pool and thus two counter-rotating vortices, which exhibit similar though more complex flow instabilities
- …
