COMPARISON OF SOME VARIANTS OF THE FINITE STRIP METHOD FOR ANALYSIS OF COMPLEX SHELL STRUCTURES

The subject of this paper is to explore and evaluate the semi-analytical, analytical and numerical versions of the finite strip method (FSM) for static, dynamic and stability analyses of complex thin-walled structures. Many of bridge superstructures, some roof and floor structures, reservoirs, channels, tunnels, subways, layered shells and plates etc. can be analysed by this method. In both semi-analytical and analytical variants beam eigenvalue vibration or stability functions, orthogonal polynomials, products of these functions are used as longitudinal functions of the unknowns. In the numerical FSM spline longitudinal displacement functions are implemented. In the semi-analytical and numerical FSM conventional transverse shape functions for displacements are used. In the analytical FSM the accurate function of the strip normal displacement and the plane stress function are applied. These three basic variants of the FSM are compared in quality and quantity in view to the following: basic ideas, modelling, unknowns, DOF, a kind and order of the strips, longitudinal and transverse displacement and stress functions, compatibility requirements, boundary conditions, ways for obtaining of the strip stiffness and load matrices, a kind and size of the structure stiffness matrix and its band width, mesh density, necessary number of terms in length, accuracy and convergence of the stresses and displacements, approaches for refining results, input and output data, computer resources used, application area, closeness to other methods, options for future development. Numerical example is presented. Advantages and shortcomings are pointed. Conclusions are given

Response Spectra Evaluation Including Pounding Effect

Most of the existing seismic resistant design codes are based on the response spectrum theory. The influence of inelastic deformations can be evaluated by considering inelastic type of resisting force and then the inelastic spectrum is considerably different from the elastic one. Also, the influence of stiffness degradation and strength deterioration can be accounted for by including more precise models from material point of view. In some recent papers the corresponding changes in response spectra due to the P- Ä effect are discussed. The experience accumulated from the recent earthquakes indicates that structural pounding may considerably influence the response of structures and should be taken into account in design procedures. The most convenient way to do that is to predict the influence of the pounding on the response spectra for accelerations, velocities and displacements. Generally speaking the contact problems such as pounding are characterized by large extent of nonlinearity and slow convergence of the computational procedures. Thus obtaining spectra where the contact problem is accounted for seems very attractive from engineering point of view because could easy be implemented into the design procedures. However it is worth nothing that there is not rigorous mathematical proof that the original system can be decomposed into single equations related to single degree of freedom systems. It is the porpose of the paper to study the influence of the pounding on the response spectra and to evaluate the amplification due to the impact. For this purpose two adjacent SDOF systems are considered that are able to interact during the vibration process. This problem is solved versus the elastic stiffness ratio, which appears to be very important for such assemblage. The contact between masses is numerically simulated using opening gap elements as links. Comparisons between calculated response spectra and linear response spectra are made in order to derive analytical relationships to simply obtain the contribution of pounding. The results are graphically illustrated in response spectra format and the influence of the stiffness ratio is clarified

Computer-Aided Static Analysis of Complex Prismatic Orthotropic Shell Structures by the Analytical Finite Strip Method

The paper describes a development of the analytical finite strip method (FSM) in displacements for linear elastic static analysis of simply supported at their transverse ends complex orthotropic prismatic shell structures with arbitrary open or closed deformable contour of the cross-section under general external loads. A number of bridge top structures, some roof structures and others are related to the studied class. By longitudinal sections the prismatic thin-walled structure is discretized to a limited number of plane straight strips which are connected continuously at their longitudinal ends to linear joints. As basic unknowns are assumed the three displacements of points from the joint lines and the rotation to these lines. In longitudinal direction of the strips the unknown quantities and external loads are presented by single Fourier series. In transverse direction of each strips the unknown values are expressed by hyperbolic functions presenting an exact solution of the corresponding differential equations of the plane straight strip. The basic equations and relations for the membrane state, for the bending state and for the total state of the finite strip are obtained. The rigidity matrix of the strip in the local and global co-ordinate systems is derived. The basic relations of the structure are given and the general stages of the analytical FSM are traced. For long structures FSM is more efficient than the classic finite element method (FEM), since the problem dimension is reduced by one and the number of unknowns decreases. In comparison with the semi-analytical FSM, the analytical FSM leads to a practically precise solution, especially for wider strips, and provides compatibility of the displacements and internal forces along the longitudinal linear joints

DETERMINATION OF THE DYNAMIC STRESS INTENSITY FACTOR USING ADVANCED ENERGY RELEASE EVALUATION

In this study a simple effective procedure practically based upon the FEM for determination of the dynamic stress intensity factor (DSIF) depending on the input frequency and using an advanced strain energy release evaluation by the simultaneous release of a set of fictitious nodal spring links near the crack tip is developed and applied. The DSIF is expressed in terms of the released energy per unit crack length. The formulations of the linear fracture mechanics are accepted. This technique is theoretically based upon the eigenvalue problem for assessment of the spring stiffnesses and on the modal decomposition of the crack shape. The inertial effects are included into the released energy. A linear elastic material, time-dependent loading of sine type and steady state response of the structure are assumed. The procedure allows the opening, sliding and mixed modes of the structure fracture to be studied. This rational and powerful technique requires a mesh refinement near the crack tip. A numerical test example of a square notched steel plate under tension is given. Opening mode of fracture is studied only. The DSIF is calculated using a coarse mesh and a single node release for the released energy computation as well a fine mesh and simultaneous release of four links for more accurate values. The results are analyzed. Comparisons with the known exact results from a static loading are presented. Conclusions are derived. The values of the DSIF are significantly larger than the values of the corresponding static SIF. Significant peaks of the DSIF are observed near the natural frequences. This approach is general, practicable, reliable and versatile

Conformational effects on the Circular Dichroism of Human Carbonic Anhydrase II: a multilevel computational study

Circular Dichroism (CD) spectroscopy is a powerful method for investigating conformational changes in proteins and therefore has numerous applications in structural and molecular biology. Here a computational investigation of the CD spectrum of the Human Carbonic Anhydrase II (HCAII), with main focus on the near-UV CD spectra of the wild-type enzyme and it seven tryptophan mutant forms, is presented and compared to experimental studies. Multilevel computational methods (Molecular Dynamics, Semiempirical Quantum Mechanics, Time-Dependent Density Functional Theory) were applied in order to gain insight into the mechanisms of interaction between the aromatic chromophores within the protein environment and understand how the conformational flexibility of the protein influences these mechanisms. The analysis suggests that combining CD semi empirical calculations, crystal structures and molecular dynamics (MD) could help in achieving a better agreement between the computed and experimental protein spectra and provide some unique insight into the dynamic nature of the mechanisms of chromophore interactions

Ribonucleoprotein Particles Containing Non-Coding Y RNAs, Ro60, La and Nucleolin Are Not Required for Y RNA Function in DNA Replication

BACKGROUND: Ro ribonucleoprotein particles (Ro RNPs) consist of a non-coding Y RNA bound by Ro60, La and possibly other proteins. The physiological function of Ro RNPs is controversial as divergent functions have been reported for its different constituents. We have recently shown that Y RNAs are essential for the initiation of mammalian chromosomal DNA replication, whereas Ro RNPs are implicated in RNA stability and RNA quality control. Therefore, we investigate here the functional consequences of RNP formation between Ro60, La and nucleolin proteins with hY RNAs for human chromosomal DNA replication. METHODOLOGY/PRINCIPAL FINDINGS: We first immunoprecipitated Ro60, La and nucleolin together with associated hY RNAs from HeLa cytosolic cell extract, and analysed the protein and RNA compositions of these precipitated RNPs by Western blotting and quantitative RT-PCR. We found that Y RNAs exist in several RNP complexes. One RNP comprises Ro60, La and hY RNA, and a different RNP comprises nucleolin and hY RNA. In addition about 50% of the Y RNAs in the extract are present outside of these two RNPs. Next, we immunodepleted these RNP complexes from the cytosolic extract and tested the ability of the depleted extracts to reconstitute DNA replication in a human cell-free system. We found that depletion of these RNP complexes from the cytosolic extract does not inhibit DNA replication in vitro. Finally, we tested if an excess of recombinant pure Ro or La protein inhibits Y RNA-dependent DNA replication in this cell-free system. We found that Ro60 and La proteins do not inhibit DNA replication in vitro. CONCLUSIONS/SIGNIFICANCE: We conclude that RNPs containing hY RNAs and Ro60, La or nucleolin are not required for the function of hY RNAs in chromosomal DNA replication in a human cell-free system, which can be mediated by Y RNAs outside of these RNPs. These data suggest that Y RNAs can support different cellular functions depending on associated proteins