No abstract

The interventricular septum, which flattens and inverts in conditions such as pulmonary hypertension, is considered by many to be an unstressed membrane, in that its position is assumed to be determined solely by the transseptal pressure gradient. A two-dimensional finite element model was developed to investigate whether compression and bending moments (behavior incompatible with a membrane) exist in the septum during diastole under abnormal loading, i.e., pulmonary artery (PA) constriction. Hemodynamic and echocardiographic data were obtained in six open-chest anesthetized dogs. For both control and PA constriction, the measured left ventricular and right ventricular pressures were applied to a residually stressed mesh. Adjustments were made to the stiffness and end-bending moments until the deformed and loaded residually stressed mesh matched the observed configuration of the septum. During PA constriction, end-bending moments were required to obtain satisfactory matches but not during control. Furthermore, substantial circumferential compressive stresses developed during PA constriction. Such stresses might impede septal blood flow and provoke the unexplained ischemia observed in some conditions characterized by abnormal septal motion.

Modelling load bearing in diarthrodial joints is challenging, due to the complexity of the materials, the boundary and interface conditions and the geometry. The articulating surfaces are covered with cartilage layers that are filled with a fluid that plays a major role in load bearing [Mow, V.C., Holmes, M.H., Lai, W.M. (1984) "Survey article: fluid transport and mechanical properties of articular cartilage: a review", Journal of Biomechanics 17(5), 377-394]. Researchers have tended to approximate joint geometry using axisymmetry [Donzelli, P.S., Spilker, R.L., Ateshian, G.A., Mow, V.C. (1999) "Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure", Journal of Biomechanics 32, 1037-1047], often with a rounded upper articulating surface, creating a form of Hertz problem [Donzelli, P.S., Spilker, R.L., Ateshian, G.A., Mow, V.C. (1999) "Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure", Journal of Biomechanics 32, 1037-1047]. However, diarthrodial joints (shoulder, hip and knee) are equipped with peripheral structures (glenoid labrum, acetabular labrum and meniscus, respectively) that tend to deepen the joint contact and thus cause initial contact to be established at the periphery of the joint rather than "centrally". The surface geometries are purposefully incongruent, and the incongruency has a significant effect on the stresses, pressures and pressure gradients inside the tissue. The models show the importance of the peripheral structures and the incongruency from a load-bearing perspective. Joint shapes must provide a compromise between demands for load-bearing, lubrication and the supply of nutrients to the chondrocytes of the cartilage and cells of the peripheral structures. Retention and repair of the functionality of these peripheral structures should be a prime consideration in any surgical treatment of an injured joint.

During the past half century, the use of prestressing in different structures has increased tremendously. One of the most important techniques of prestressing is post-tensioning. The main problem associated with post-tensioning in different structures is the corrosion of the prestressing steel tendons even with well-protected steel. New materials, fibre reinforced plastics or polymers (FRP), which are more durable than steel, can be used for these tendons/strands and thus overcome the corrosion problem. However, different shortcomings appear when FRP tendons are introduced to post-tensioning prestressing applications. For carbon fibre plastic tendons (CFRP), there is no suitable anchorage system for post-tensioning applications. Some of the anchorages developed by others for use with FRPs are therefore described and assessed. A new anchorage system developed by the authors, which can be used with bonded or unbonded CFRP tendons in post-tensioning applications, is described. The results of direct tension and fatigue tests on CFRPs anchored with the new system are presented.Résumé : Au cours des 50 dernières années, l'utilisation de la précontrainte dans différentes structures s'est accrue remarquablement. Une des principales techniques de précontrainte est la post-tension. Le principal problème relatif à la post-tension dans différents ouvrages est la corrosion des câbles en acier précontraints, même s'il s'agit d'acier bien protégé. De nouveaux matériaux, tels que les plastiques ou polymères renforcés de fibres (PRF), qui s'avèrent plus durables que l'acier, peuvent être utilisés pour ces câbles/torons, et enrayer les problèmes de corrosion. Toutefois, différents défauts apparaissent lorsque les câbles en PRF sont soumis à des applications précontraintes en post-tension. Pour les câbles en plastique renforcé de fibre de carbone (PRFC), il n'existe aucun système d'ancrage adéquat pour les applications de post-tension. Quelques ancrages développés par d'autres auteurs utilisant des PRF sont décrits et évalués. Un nouveau système d'ancrage que nous avons développé, lequel peut être employé avec des câbles en PRFC scellés ou non dans des applications de post-tension est décrit. Les résultats de tests de traction directe et de fatigue sur des PRFC ancré avec le nouveau système sont présentés.

Composite beams with corrugated steel webs represent a new innovative system which has emerged in the past decade for short and medium span bridges. The new system usually combines the usage of corrugated steel plates as webs and reinforced/prestressed concrete slabs as flanges for plate or box girders. Bridges that have been recently built with this hybrid system are outlined in this paper, which focuses on the advantages of using corrugated steel webs as opposed to traditional flat webs. The flexural behaviour and bearing resistance of girders with corrugated steel webs is briefly discussed. The flanges of the new system solely provide the flexural strength of the beam with no contribution from the corrugated web. On the other hand, the corrugated web provides the shear capacity of the system. Thus, the shear behaviour of girders with corrugated webs is explicitly discussed focusing on the different failure and (or) buckling modes that affect the design of the corrugated steel web plates. Design charts for such webs are constructed based on the different interaction equations of failure. The torsion-warping behaviour of composite box girders with corrugated steel webs is also discussed.Key words: bridges, composite beams, corrugated steel webs, global buckling mode, interactive buckling, local buckling.