This paper gives a simple derivation of the tangent stiffness matrix for a prestressed pinjointed structure: the stiffness is found by differentiating equilibrium expressions at nodes of the structure with respect to the position of the nodes. It uses this derivation to compare the diverse formulations that are applied to understanding the mechanics of prestressed structures by different academ...

The principal causes of cracking in prestressed concrete sleepers are the dynamic loads induced by track irregularities and imperfections in the wheel-rail contact and the in-phase and out-of-phase track resonances. The most affected points are the mid-span and rail-seat sections of the sleepers. Central and rail-seat crack detection require visual inspections, as legislation establishes, and i...

The monitoring of a precast, prestressed girder bridge during fabrication and service provided the opportunity to observe temperature variations and to evaluate the accuracy of calculated strains and cambers. The use of high curing temperatures during fabrication affects the level of prestress because the strand length is fixed during the heating, the coefficients of thermal expansion of steel ...

This paper presents a methodological approach of wide generality for assessing the reliability of reinforced and prestressed concrete structures. As known, the numerical values of the parameters which define the geometrical and mechanical properties of this kind of structures, are affected by several sources of uncertainties. In a realistic approach such properties cannot be considered as deter...

Railway concrete sleepers have been developed and utilized in railway industry for over 50 years. Cyclic loading because of vibration on sleepers due to the train loading and the velocity of train itself and also a small percentage of bad wheels, can eventually lead to a crack network and failure of component. The objective of this study is to investigate the load carrying capacity of the selec...

Phosphoenolpyruvate carboxylase (PEPCase), the key enzyme of Crassulacean acid metabolism, is induced by water stress in leaves of Mesembryanthemum crystallinum. In water-stressed plants or excised leaves, exogenous cytokinin suppresses PEPCase transcript accumulation in the leaves. Cytokinin (6-benzylaminopurine) used in concentrations from 5 to 500 micromolar (a) inhibits the upregulation of ...

According to the different nucleotide occupancies of the F(1)-ATPase beta-subunits and due to the asymmetry imposed through the central gamma-subunit, the beta-subunit adopts different conformations in the crystal structures. Recently, a spontaneous and nucleotide-independent closure of the open beta-subunit upon rotation of the gamma-subunit has been proposed. To address the question whether t...