Hyaluronic Acid Inhibits Polycation Induced Cellular Responses

Positively charged macromolecules cause a variety of pathological events through their electrostatic interaction with anionic sites present on the membrane of target cells. In the present study we have investigated the effect of hyaluronic acid, a negatively charged molecule, on rat paw oedema induced by poly-L-lysine as well as on histamine release from rat mast cells and nitric oxide formation from rabbit aorta, both induced by this polycation. The results indicate that hyaluronic acid is able to suppress these poly-L-lysine induced effects with a mechanism which possibly depends on its negative charges which may balance the effects of positively charged polycations

Out-of-plane behavior of one-way spanning unreinforced masonry walls

An analytical model is developed to describe the out-of-plane response of one-way spanning unreinforced masonry (URM) walls by investigating the effects of various parameters. Horizontal crack height, masonry compressive strength, and diaphragm support stiffness properties are assumed as variables, and sensitivity analyses are performed to study the influence of these parameters on the cracked wall characteristic behavior. The parametric studies show that crack height significantly influences wall stability by affecting both the instability displacement and the wall lateral resistance. The reduction in cracked wall lateral resistance and in the instability displacement caused by finite masonry compressive strength is shown to be significantly amplified by the applied overburden. A study using the typical configuration of flexible diaphragms and URM walls indicates that the wall top support flexibility does not significantly influence cracked wall out-of-plane response. An existing simplified wall behavioral model is improved, and a procedure is proposed for calculation of the wall out-of-plane response envelope.Hossein Derakhshan; Michael C. Griffith; and Jason M. Ingha

Experimental evaluation of the in-plane stiffness of timber diaphragms

The seismic response of unreinforced masonry (URM) buildings, in both their as-built or retrofitted configuration, is strongly dependent on the characteristics of wooden floors and, in particular, on their in-plane stiffness and on the quality of wall-to-floor connections. As part of the development of alternative performance-based retrofit strategies for URM buildings, experimental research has been carried out by the authors at the University of Canterbury, in order to distinguish the different elements contributing to the whole diaphragm's stiffness. The results have been compared to the ones predicted through the use of international guidelines in order to highlight shortcomings and qualities and to propose a simplified formulation for the evaluation of the stiffness properties

In-plane stiffness of wooden floor

Paper 49The seismic response of existing un-reinforced masonry (URM) buildings is strongly dependent on the characteristics of wooden floors and in particular on their in-plane stiffness and on the quality of the connections between the floors and the URM elements. It is generally well-recognized that adequate in plane-stiffness and proper connections improves the three-dimensional response of the whole system and provides better distribution and transfer of forces to the lateral load resisting walls. Extensive damage observed during past earthquakes on URM buildings of different type have however highlighted serious shortcomings of typical retrofit interventions adopted in the past with the intention to stiffen the diaphragm. Recent numerical investigations have also confirmed that stiffening the diaphragm is not necessarily going to lead to an improved response, sometimes actually having detrimental effects on the response. The evaluation of the in-plane stiffness of timber floors in their as-built and retrofitted configuration is still an open question and delicate issue, with design guidelines and previous research results providing incomplete, when not controversial, suggestions to the practitioner engineers involved in the assessment and/or retrofit of these types of structures. In this contribution, a summary of the state-of-the-art related to the role of the inplane stiffness of timber floors in the seismic response of un-reinforced masonry buildings is presented and critical discussed based on the limited available experimental and numerical evidences. A framework for a performance-based assessment and retrofit strategy, capable of accounting for the effects of flexible diaphragm on the response prior and after the retrofit intervention, is then proposed. By controlling the in-plane stiffness of the diaphragm, adopting a specific strengthening (or weakening) intervention, the displacements, accelerations and internal forces demand can be maintained within targeted levels, in order to protect undesired local mechanisms and aim for a more appropriate hierarchy of strength within the whole system