Truss Element

The problem must be simplified considerably to permit solution in the context of this book. Suppose an equilateral triangle is subjected to some loads in the vertical direction as in Figure 7-22. A load P of 100 lb (445 N) is applied to the top joint, and that load can go in either the downward or upward direction (in the diagram, not in space ). This truss must take its reversible load with, say, a factor of safety of two against whatever event would cause it to fail. What material, size, and weight of truss element would you select to satisfy the design requirements that include building the structure for the lowest cost ... 

In order to evaluate one of the issues that is very pertinent to this material selection, the cost to get the truss elements up into space must be known. In 1985, a Shuttle flight cost 90 million. If the Shuttle is capable of carrying a payload of 60,000 lb (27,000 kg), then for every... 

In the truss model, each truss element represented a chemical bond or a nonbonded interaction. The stretching potential of each bond corresponds with the stretching of the corresponding truss element. Atoms in a lattice have been viewed as masses that are held in place with atomic forces that is similar to elastic springs. Therefore, bending of Truss elements is not needed to simulate the chemical bonds, and it is assumed that each truss joint is pinned, not fixed. Fig. 9.7 shown the atomistic-based continuum modeling and RVE of the chemical, truss and continuum models. 

The bearing massive walls and the tambour walls have been modelled by the SOLID 3D finite element with eight nodes. The steel vertical and horizontal strengthening elements were modelled by 3D-FRAME, i.e., 3D-TRUSS elements. All the vaults and the domes have been modelled by SHELL elements. 

According to the DDM, the consistent FE response sensitivities are computed at each time step, after convergence is achieved for response computation. Response sensitivity calculation algorithms impact the various hierarchical layers of FE response calculation, namely (1) the structure level, (2) the element level, (3) the integration point (section for frame/truss elements) level, and (4) the material level. Details on the derivation of the DDM sensitivity equation at the structure level and at the element level for classical displacement-based finite elements, specific software implementation issues, and properties of the DDM in terms of efficiency and accuracy can be found elsewhere (Kleiber et al. 1997, Conte 2001, Conte et al. 2003, Gu Conte 2003). In this study, some newly developed algorithms and recent extensions are presented which cover relevant gaps between state-of-the-art FE response-only analysis and response sensitivity computation using the DDM. 

Once all the above improvements are put into the effect and the diastole is satisfactorily evaluated, it would be recommended to incorporate the active features of the fibers in the model so as to enable the simulation of the systolic phase. This can be done by introducing initial strains in the truss elements and so reproducing the active contraction of the fibers. The time of introduction of the initial strains can vary from element to element and follow the activation sequence of the electrophysiological excitation. 

In this paper the main parameters affecting a finite element simulation of the LV cardiac cycle have been reviewed. As a result, a step-by-step procedure towards developing a more comprehensive model is proposed based on the combination of 3-D brick and truss elements. Though the task of performing a realistic simulation of the cardiac cycle still seems enormously difficult, it is hoped that the gradual sophistication of the model will enable its materialization. 

ANS Indeed, in the same way that we can put 5 layers of truss elements, one can put 5 layers of whatever you wish. But this is not the point. The number 2 is not a magic number. It is only a matter of means. If we get a bigger computer, we can have 6 layers or more. 

The simplified strut approach based on the representation of infiU walls with truss elements can also be used for the analysis of structures where the infill walls have openings. A relatively small opening will not have a significant effect on the behavior of an infilled fi ame, and for this reason stmt-based models can still be used with minor modifications. Al-Chaar (2002) has recommended that the cross-sectional area of the diagonal stmts be multiplied by a reduction factor, Ri, which accounts for the existence of openings and is given by ... 

The nonlinear force-based fiber element is also used to model the columns of the DBF. The beams and braces of the DBF are modeled using linear elastic truss elements. The gravity frames are idealized using the concept of a lean-on column, where an elastic beam-column element with geometric stiffness is used to model the lean-on column. The section properties of the lean-on column are obtained by taking the sum of the section properties of each gravity column within the tributary area (i.e., one quarter of the floor plan) of the MRF and the DBF. The MR dampers are modeled using the MNS MR damper model implemented into OpenSees by Chae et al. (2010). The MR damper is assumed to be located between the top of the brace and the adjacent beam-colunm joint, as shown in Fig. 8. The results reported in this paper are for MR dampers that are passive cOTitroUed with a constant current input of 2.5 A. Studies with the MR dampers in semi-active control mode are presented in Chae (2011). 

The resulting values are given in Table 1.1. The values show that the inequality in (1.40) is satisfied except for in the case of Poisson s ratio (v). As truss elements have no transverse strain, effectively the value used for Poisson s ratio is zero. Therefore the fact that the effective averaged value is below the value for the matrix is acceptable. 

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