Identification of stiffness properties of composite tubes from dynamic tests

The identification of the stiffness properties of typical laminated composite tubes from dynamic tests is presented. Unknown coefficients are identified by a technique of model updating. The fomulation is based on the minimization of the eigensolution residuals (sensitivity method). Errors of generalized masses are considered. The technique allows for the simultaneous identification of several properties from a single test. Stiffness properties of extension, bending/twisting and transverse shear are identified. Important points of the model updating of tubes in dynamics are addressed: potential energy evaluation, placement of sensors and the problem of multiple eigenvalues. Results obtained by numerical simulation show the efficiency of the proposed method.     

Passively confined tests of axial dynamic compressive strength of concrete

Passively confined dynamic impact experiments on plain concrete specimens were performed employing steel and aluminum jackets with a 76.2-mm-diameter split-Hopkinson pressure bar system. The specific requirements of the specimens for jacketed tests were achieved with metallicmold casting. The confining pressures were determined from foil strain gages mounted on the outer wall surface of the jackets. Permanent deformation and residual static strength were measured and studied in the characterization of the behavior of plain concrete specimens under dynamic multiaxial loads.     

Free vibration analysis of third-order shear deformable composite beams using dynamic stiffness method

The dynamic stiffness method is introduced to investigate the free vibration of laminated composite beams based on a third-order shear deformation theory which accounts for parabolic distribution of the transverse shear strain through the thickness of the beam. The exact dynamic stiffness matrix is found directly from the analytical solutions of the basic governing differential equations of motion. The Poisson effect, shear deformation, rotary inertia, in-plane deformation are considered in the analysis. Application of the derived dynamic stiffness matrix to several particular laminated beams is discussed. The influences of Poisson effect, material anisotropy, slenderness and end condition on the natural frequencies of the beams are investigated. The numerical results are compared with the existing solutions in literature whenever possible to demonstrate and validate the present method.     

Axisymmetric dynamic problem for a nonuniform shallow spherical shell with finite shear stiffness

Samarskoe Institute of Architectural Engineering. Translated from Prikladnaya Mekhanika, Vol. 30, No. 9, pp. 50–57, September, 1994.     

Residual stiffness assessment of structurally failed reinforced concrete structure by dynamic testing and finite element model updating

When an under-reinforced concrete beam structure has been loaded to the point where reinforcing steel on the tension side has yielded, it is deemed to have structurally failed and the full load capacity and stiffness can no longer be developed. When unloaded from the point of failure, the residual stiffness of the structure is difficult to estimate. There is a need to establish the serviceability of the structure and ultimately establish the levels of further loading that can be sustained before total collapse. In this paper we present a method for assessing residual stiffness of such a “failed” reinforced concrete structure, through the application of dynamic testing and finite element (FE) model updating. In an experimental study, failed zones in a beam structure were simulated in a FE model. Through a procedure of sensitivity-based updating using the measured modal properties, the stiffness distribution along the failed beam structure was identified.     

带剪刀撑木框架墙体抗剪性能试验研究

彩图制作了5组10片木框架剪力墙分别进行单向和反复荷载试验,研究了剪刀撑及不同覆面板对剪力墙的抗剪强度、弹性抗侧刚度、极限位移、耗能的影响。试验数据说明:增加剪刀撑的墙体最大墙骨柱上拔量仅为未加剪刀撑的对照墙体墙的22.7%,剪刀撑对于抑制墙骨柱上拔的现象有显著作用,能控制墙体面板钉连接破坏先于墙骨柱连接破坏;而且剪刀撑还能增大墙体刚度,约束墙体位移。此外,试验各项参数表明:采用国产胶合板作为覆面板的墙体的抗剪性能良好,说明国产胶合板可以替代OSB板应用于剪力墙制作;而采用国产花旗龙板作为面板的墙体抗剪强度远远低于GB50005-2003《木结构设计规范》中采用木基结构板材的剪力墙抗剪强度设计值(fvd为4.7kN/m)的指标要求,建议在实践中仅作为强度储备。     

Rheological model of concrete in the dynamic field

Summary The definition of the rheological model of concrete, or uncracked reinforced concrete, in the field of dynamic stresses sufficiently far from breaking, is here attempted; an aim towards which we had already recently directed a series of investigations to clarify the different aspects of experimental behaviour.Even with gaps in detail, the model found seems to correctely interpret the dissipativemechanism of our material, and it is — contrary to current viscous schematizations — of a prevalently plasto-elastic characteristic, with dampers of asolid-friction type.This work concludes dealing with the experimental determination of the parameters of the model and with particular approximate solutions of motion.

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Sommario Viene qui tentata la definizione del modello reologico del calcestruzzo, o cemento armato non parzializzato, in campo di sforzi dinamici sufficientemente lontani dalla rottura; fine al quale avevamo di recente già indirizzato una serie di indagini, volte a chiarire i diversi aspetti del comportamento sperimentale.Pur con lacune di dettaglio, il modello trovato sembra correttamente interpretare ilmeccanismo dissipativo del nostro materiale, ed è — contrariamente a correnti schematizzazioni viscose — a caratteristica prevalentemente elastoplastica, con smorzatori di tiposolid-friction.Il lavoro si conclude trattando della determinazione sperimentale dei parametri del modello e di particolari soluzioni approssimate del moto.

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The first results of this work were presented at 2° Convegno Nazionale Gruppo di Studio C.N.R. sulle Costruzioni Antisismiche — Camogli (Genova), Nov. 1966 [1].     

Lattice Boltzmann simulations of turbulent shear flow between parallel porous walls

The effects of two parallel porous walls are investigated, consisting of the Darcy number and the porosity of a porous medium, on the behavior of turbulent shear flows as well as skin-friction drag. The turbulent channel flow with a porous surface is directly simulated by the lattice Boltzmann method （LBM）. The Darcy-Brinkman- Forcheimer （DBF） acting force term is added in the lattice Boltzmann equation to simu- late the turbulent flow bounded by porous walls. It is found that there are two opposite trends （enhancement or reduction） for the porous medium to modify the intensities of the velocity fluctuations and the Reynolds stresses in the near wall region. The parametric study shows that flow modification depends on the Darcy number and the porosity of the porous medium. The results show that, with respect to the conventional impermeable wall, the degree of turbulence modification does not depend on any simple set of param- eters obviously. Moreover, the drag in porous wall-bounded turbulent flow decreases if the Darcy number is smaller than the order of O（10-4） and the porosity of porous walls is up to 0.4.     

一个改进的混凝土非线性双剪切强度准则

通过对混凝土、岩石等材料强度理论的分析研究,基于普遍形式强度理论及双剪切强度理论,考虑混凝土在多轴荷载作用下材料强度性质在π平面和拉伸压缩子午线上不同的变化规律,将混凝土的强度准则定义为两个较大主剪切应力平方和的函数;并考虑其对应剪切应力作用面上的正应力和静水压力的影响,推导了一个考虑中间主应力效应和复杂极限面情况的非线性双剪切强度准则;通过实验数据获得了相关参数。结果表明该强度准则可以较好地描述混凝土材料的破坏特性。     

Transverse shear stiffness of a chevron folded core used in sandwich construction

Using Kelsey et al. (1958) unit load method, upper and lower bounds for the effective transverse shear moduli of a chevron folded core used in sandwich construction are analytically derived and compared to finite element computations. We found that these bounds are generally loose and that in some cases chevron folded cores are 40% stiffer than honeycomb-like cores.