Anholonomic frames in constrained dynamics

We demonstrate the usefulness of anholonomic frames in the contexts of nonholonomic and vakonomic systems. We take a consistently differential-geometric approach. As an application, we investigate the conditions under which the dynamics of the two systems will be consistent. A few illustrative examples confirm the results.     

Uniform antiplane shear stress inside an anisotropic elastic inclusion of arbitrary shape with perfect or imperfect interface bonding

We consider an anisotropic elastic inclusion of arbitrary shape embedded inside an infinite dissimilar anisotropic elastic medium (matrix) subjected to a uniform antiplane shear loading at infinity. In contrast to the corresponding results from linear isotropic elasticity, we show that for certain anisotropic materials, despite the limitation of perfect bonding between the inclusion and its surrounding matrix, it is possible to design an arbitrarily shaped (not necessarily elliptic) inclusion so that the interior stress distribution is uniform provided the shear stress in the matrix (of dissimilar anisotropic material) is also uniform. Further, in the case when the bonding between the inclusion and the matrix is assumed to be imperfect, we show that for the stress distribution inside the inclusion to be uniform, the inclusion must be elliptical.     

减小门式刚架中柱平面外计算长度的方法

门式刚架的中柱设计中,常因为平面外计算长度较大,所选实腹式截面无法满足平面外稳定验算,从而导致用钢量增加.文中针对设有吊车梁的门式刚架中柱,对3种设计方案进行比较,证明利用吊车梁设置隅撑,为中柱提供可靠侧向支承点,从而减小其平面外计算长度,该方法最经济实用.     

Mental space travel: Damage to posterior parietal cortex prevents egocentric navigation and reexperiencing of remote spatial memories.

The ability to navigate in a familiar environment depends on both an intact mental representation of allocentric spatial information and the integrity of systems supporting complementary egocentric representations. Although the hippocampus has been implicated in learning new allocentric spatial information, converging evidence suggests that the posterior parietal cortex (PPC) might support egocentric representations. To date, however, few studies have examined long-standing egocentric representations of environments learned long ago. Here we tested 7 patients with focal lesions in PPC and 12 normal controls in remote spatial memory tasks, including 2 tasks reportedly reliant on allocentric representations (distance and proximity judgments) and 2 tasks reportedly reliant on egocentric representations (landmark sequencing and route navigation; see Rosenbaum, Ziegler, Winocur, Grady, & Moscovitch, 2004). Patients were unimpaired in distance and proximity judgments. In contrast, they all failed in route navigation, and left-lesioned patients also showed marginally impaired performance in landmark sequencing. Patients' subjective experience associated with navigation was impoverished and disembodied compared with that of the controls. These results suggest that PPC is crucial for accessing remote spatial memories within an egocentric reference frame that enables both navigation and reexperiencing. Additionally, PPC was found to be necessary to implement specific aspects of allocentric navigation with high demands on spontaneous retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

钢框架高等分析研究综述

为了加深对高等分析的理解,介绍了钢框架现行计算长度设计方法的缺点和高等分析与设计的特点,详细讨论了影响钢框架稳定性和极限承载力的主要因素,如几何非线性、材料非线性、几何缺陷、残余应力、局部屈曲、弯扭屈曲等,以及分析时各种因素的考虑方法．同时介绍了国内外在钢框架高等分析方面的研究现状、不足以及可能的发展趋势,为钢框架结构整体分析与设计方法的研究提供一些理论参考．     

Sources of elastic deformations in steel frame and framed-tube structures: Part 2: Detailed subassemblage models

This paper examines the accuracy of a set of equations for computing Displacement Participation Factors (DPFs) for beam-column subassemblages of steel moment resisting frame buildings. These factors allow the analyst to determine how the entire subassemblage or individual components of a subassemblage contribute to a given structural displacement. Additionally, the component’s contribution to displacement may be evaluated in terms of sources of axial, flexural, or shear deformation.When applied to a set of 12 isolated subassemblages, it was shown in Part 1 of the paper that deformations in the beam-column joint are very significant, and that flexural deformation in the joint, which is often ignored, should be considered in all analyses. The total displacement predicted through the use of the DPFs correlates extremely well with the results of detailed three dimensional finite element analyses of the same subassemblages. However, it was also shown that there is considerable uncertainty in the bending moments and moments of inertia that are used to compute joint flexural deformations.The objective of this paper, which is the second part of a two-part paper, is to further investigate the accuracy of the DPF expressions developed in Part 1. This is done by computing DPFs from the results of detailed three dimensional finite element analysis, and comparing these to those computed through the use of the simple expressions.The results of the analysis show that the joint flexural deformations are accurately predicted by the simple DPF expressions, but that this accuracy arises from compensating “errors” in the simplified analysis. It is also shown that the use of beam flange continuity plates has a marginal effect on computed displacements. The paper ends with recommendations for using the simplified expressions for computing subassemblage deformations, and for including such deformations in structural analysis of steel frame and tube structures.     

Hedratecture and Expandable Platform

This paper is directed only to the basic aspects of hedratecture. The word hedratecture is derived from the Greek “to build with hedrons.” It is used to describe the art and science of constructing with framed elements that are hedron‐shaped, usually in the form of the five convex polyhedrons. Hedratecture encompasses two major elements: the expandable platform and structures thereon. The platform when set on a surface by computer has the capability to incorporate within itself a whole variety of integrated lesser structures that provide dwelling units and a modular internal transportation system. The platform can be placed in a designated area as a hedron city or expanded in a linear dimension and in that mode it becomes a trestle or a bridge. The basic elements provide an endless variety of shapes with uses that vary from a small helicopter pad to a small city on earth. When placed on the Moon or Mars it can provide a telerobotically placed base.     

Numerical and experimental analysis of pure aluminium shear panels with welded stiffeners

In the field of passive seismic protection of framed buildings shear panels can be effectively applied as hysteretic devices. Recently, a wide experimental and numerical study has been undertaken at the University of Naples in order to investigate the behaviour of aluminium alloy stiffened shear panels. Test results show that the proposed system is characterised by a large energy dissipation capacity and therefore is suitable to be used for seismic protection of new and existing framed buildings. To simulate the hysteretic behaviour of the systems, according to the experimental tests, a refined FEM model has been set up. The comparison between experimental and numerical results shows that the adopted model is reliable enough to well interpret a number of important behavioural phenomena in terms of the main global features of the system.     

Influence of connection design parameters on the seismic performance of braced frames

Special concentrically braced frames (SCBFs) are commonly used lateral-load resisting systems in seismic design. In SCBFs, the braces are connected to the beams and columns by gusset plate connections, and inelastic deformation is developed through tensile yielding and inelastic post-buckling deformation of the brace. Recent experimental research has indicated that the seismic performance of SCBFs can be improved by designing the SCBF gusset plate connections with direct consideration of the seismic deformation demands and by permitting yielding in the gusset plate at select performance levels.Experimental research provides important information needed to improve SCBF behavior, but the high cost of experiments limits this benefit. To extend and better understand the experimental work, a companion analytical study was conducted. In an earlier paper, the inelastic finite element model and analysis procedure were developed and verified through detailed comparison to experimental results. In this paper, the model and analytical procedure extend the experimental results. A parametric study was conducted to examine the influence of the gusset plate and framing elements on the seismic performance of SCBFs and to calibrate and develop improved design models. The impact of the frame details, including the beam-to-column connections, the brace angles, and their inelastic deformation demands, was also explored. The results suggest that proper detailing of the connections can result in a large improvement in the frame performance.     

Earthquake-induced net section fracture in brace connections — experiments and simulations

Results from six tests, finite element simulations and a synthesis of previous test programs on slotted end bracing connections are presented. The main objective of the research is to examine the deformation capacity of these connections, with the ultimate objective of minimizing the requirement for net section reinforcement that is often inconvenient from the perspective of fabrication. The experiments and simulations feature commonly used pipe specimens and end details. The main parameters investigated include the gusset plate thickness, the slot length and introduction of a wrap-around weld that eliminates the reduced section at the edge of the gusset plate. The results indicate that even without reinforcement, the connections offer adequate to excellent deformation capacity if they are provided with the wrap-around weld or if the net section strength is larger than the gross yield strength. This may be achieved in situations where shear lag in the connection is minimal, and where the area reduction due to the slot is small relative to the gross area. Design considerations are presented along with limitations of the study.