Vibraciona platforma i model višespratne zgrade za dinamičko ispitivanje

In the paper we present the development of vibration-platform (biaxial mechanical shaker) for vibration testing of spatial structure. Presented are details of platform operation and harmonic displacement generation. Also, design and construction of model of multi-storey building with dynamic properties adequate for testing on vibration platform. Details of member dimensions and node connections are explained to achieved target dynamic properties for testing on vibration platform. Modal analysis of the building model carried out using FEM software for structural analysis SAP 2000.U radu je dat prikaz konstruisane vibro-platforme (dvoosnog mehaničkog pobuđivača vibracija za dinamička ispitivanja modela konstrukcija i elemenata. Prikazani su detalji funkcionisanja vibro-platforme i način generisanja harmonijskih pomeranja. Takođe, prikazano je projektovanje i konstruisanje modela višespratne zgrade sa dinamičkim karakteristikama adekvatnim za ispitivanje na vibro-platformi. Geometrijske karakteristike elemenata kao i način ostvarivanja veza u čvorovima prikazane su u svrhu postizanja odgovarajućih dinamičkih karakteristika modela konstrukcije. Numerička modalna analiza modela višespratne zgrade sprovedena je primenom programa za analizu konstrukcija konačnim elementima SAP2000

Development of a tool for measuring the effect of surface roughness on steel structural response

Driven by the industry's needs to address energy dissipation issues in mechanical connections, the set goals of the global scientific community, and previous research efforts to interpret how the condition of contact surfaces between two bodies in contact can be significant, a unique experimental setup has been devised to study the impact of the state of contact interaction between two bodies on the system's response. The purpose of the designed experimental setup is to correlate the roughness of contact surfaces with the deformation of a specially designed experimental sample. The roughness of contact surfaces represents the most dominant influencing factor in the contact interaction of two bodies. In terms of scale, the study, measurement, and analysis of surface roughness fall under the micro and nano scales. On the other hand, the change in deformation of the experimental sample as a result of the change in roughness falls under the macro scale. Based on all the aforementioned, the fundamental idea of the designed experimental setup can be seen. Considering that it is not possible to enter into contact interaction and explicitly analyse the influence of roughness on the response of a mechanical connection, the idea in overall research is to consider the macro behaviour of a specially prepared experimental sample depending on the level of roughness of the contact interaction surfaces at the micro level. The aim of this paper is to present details and challenges in the construction of an instrument necessary for such precise examinations, named “Precision Press with Arcs”

EXPERIMENTAL AND NUMERICAL IDENTIFICATION OF STRUCTURAL MODES FOR ENGINEERING EDUCATION

Abstract. Development of simple classroom demonstration device and software for visualization of structural normal modes is presented. Device is made of parts of old speaker, controlled with personal computer, where the harmonic motion of solenoid is used as an excitation for beam and plate models. Simple code for finite element free vibration analysis of plates is written in Wolfram Mathematica. Good agreement of results and attractive visual patterns of normal modes attracted attention of students. Results are confirmed using modern modal testing methods. Presented approach is complementary to standard teaching of structural dynamics. Key words: engineering education, normal modes, Chladni plate, modal testing, finite element metho

Experimental determination and study of structural damping and dry friction

The challenge that will be posed to researchers for an even longer period is the development of a predictable model for describing mechanical connections, their variable stiffness and dissipative contact interaction processes. The main challenge to this goal lies in the lack of understanding of how friction behaves on a small scale. Coulomb friction, a large heuristic model is not predictable and has actually been proven to be untrue in many modes. Expecting a universal law of friction for all types of materials and therefore contact interactions is not very realistic. Instead, the goal of the international research community is to develop a predictable model for a limited range of cases. So far, the metal-metal contact is most often tested, respectively the contact interaction behaviour of aluminium and steel elements of different quality. We also know that in the application those two metals are most often found in making mechanical connections. The aim of this paper is to make a brief overview of some of the previous tests and approaches to the study of contact interaction in mechanical connections and the role of friction in energy dissipation

Penalty method for 1d problem of two rods with basic concepts of contact mechanics of frictionless contact

Problems involving contact are of great importance in industry related to mechanical and civil engineering, but also in biomechanics and other applications. The contact interaction between surfaces in a bolted splice connection joint or area through which tire interacts with the road is not known a priori, leading to a nonlinear boundary value problem. Due to the rapid improvement of modern computer technology, today one can apply the tools of computational mechanics to analyze contact problems with limited accuracy, depending on design requirements. However, even now most of the standard finite element software is not fully capable of solving contact problems, including friction, using robust algorithms. The aim of this paper is to present some basic concepts of Contact Mechanics. To illustrate the difficulties arising in computational contact mechanics, Newton-Raphson scheme was used to solve simple 1D contact problem using penalty method

Numerical and experimental analysis of structural damping for bolted splice connection joint

This paper presents the finite element modeling of bolted joints for structural dynamic analysis to achieve a reasonable accuracy in simulation results. Non-linear effects in splice connected joints involve normal compressive loads holding components together combined with dynamic lateral loads inducing some amount of shear slip in contact interaction between elements of splice connection joint. The complexities of the slip process are responsible for the nonlinear nature of the interfaces, both in terms of stiffness and dissipation. Exploring the physics of joints directly is not readily done because key interactions takes place at the interface of surfaces, where instrumentation cannot be placed without changing the problem. Consequences of the specific conditions of joint connections are increased dynamic problems related to vibrations and dissipative processes in structure connection joints. Structural joints are the main reason for the significant level of energy dissipation and source of structural damping. The aim of this paper is to present some problems regarding research of structural damping and the importance of study Contact Mechanics to better understand the problem of structural damping

Further Development of the Short Psychopathy Rating Scale

In the present work we describe the further development of the Short Psychopathy Rating Scale (SPRS), a 9 item inventory for measuring three psychopathy traits: Deceitfulness, Emotional coldness and Recklessness. We administered this inventory on a sample of 210 students (76% females, Mage=21.21; SD=2.10) who rated their parents on psychopathic traits. Analyses were conducted on 373 participants (54% females, Mage=51.47; SD=5.91). We calculated Cronbach's α coefficient as a reliability estimate, tested the latent structure of the construct using Confirmatory Factor Analysis (CFA) and explored the validity of the SPRS scales by examining their relations with Triarchic Psychopathy Measure. Psychopathy scales showed acceptable reliabilities, having in mind that all scales consisted of 3 items (αs in range from .60 to .68). CFA showed good fit for the SPRS model: χ²(24)=85.57; p<.01; NFI=.88; CFI=.91; RMSEA=.078. Predictable sex differences were found - males had significantly higher scores on all three psychopathy traits. Finally, the validity of the SPRS scales was determined by establishing relations with psychopathy traits of Triarchic Psychopathy Measure: Meanness, Boldness and Disinhibition. Deceitfulness showed unique relations with Boldness, Emotional coldness with Meanness, and Recklessness with Disinhibition, as expected. In sum, SPRS measures showed acceptable reliabilities, adequate factor structure and excellent convergent and divergent validity. However, there is still room for improvement, especially in elevating scale reliabilities

Experimental and numerical study of structural damping in a beam with bolted splice connection

The objective of this research is to develop a numerical model of one widely used bolted beam splice connection that dissipates energy through structural damping. The reference experimental setup is carefully designed to obtain the highly nonlinear dynamic response due to the suddenly released load. The fact that the monolithic beam with welded connection has a linear response is utilized for the initial calibration of the numerical and experimental models. Then, the numerical model of bolted beam splice connection is verified and adopted through an iterative process. The influences of time and spatial integration, bolt load application, element type, contact formulation, bulk viscosity, and mass scaling are discussed. A special attention is given to the load application and load release functions. After the verification, the Abaqus/Explicit numerical model is validated through the comparison with experimental data, where an appropriate friction coefficient is adopted. It is demonstrated that the nonlinear structural damping occurs due to the complex micro slip behavior at the contact interface

Razvoj dvoosnog pobuđivača harmonijskih vibracija

U radu se daje kratak prikaz razvoja uređaja za harmonijsku pobudu modela građevinskih konstrukcija. Uređaj je razvijen u namjeri približavanja eksperimentalne dinamičke analize konstrukcija studentima i inženjerima građevinarstva.Osnovni pogonski mehanizam uređaja su elektromotori čije se rotaciono kretanje prevodi u translatorno. Ovo omogućava da se modelima mogu zadati harmonijski poremećaji koji i jesu među najčešćim u eksperimentalnoj analizi konstrukcija.U skladu sa skromnim materijalnim sredstvima, cilj je postavljen tako da uređaj bude izvodiv a istovremeno i primjenljiv za određene tipove eksperimenata, u čemu se i uspjelo

Vibraciona platforma i model višespratne zgrade za dinamičko ispitivanje

In the paper we present the development of vibration-platform (biaxial mechanical shaker) for vibration testing of spatial structure. Presented are details of platform operation and harmonic displacement generation. Also, design and construction of model of multi-storey building with dynamic properties adequate for testing on vibration platform. Details of member dimensions and node connections are explained to achieved target dynamic properties for testing on vibration platform. Modal analysis of the building model carried out using FEM software for structural analysis SAP 2000.U radu je dat prikaz konstruisane vibro-platforme (dvoosnog mehaničkog pobuđivača vibracija za dinamička ispitivanja modela konstrukcija i elemenata. Prikazani su detalji funkcionisanja vibro-platforme i način generisanja harmonijskih pomeranja. Takođe, prikazano je projektovanje i konstruisanje modela višespratne zgrade sa dinamičkim karakteristikama adekvatnim za ispitivanje na vibro-platformi. Geometrijske karakteristike elemenata kao i način ostvarivanja veza u čvorovima prikazane su u svrhu postizanja odgovarajućih dinamičkih karakteristika modela konstrukcije. Numerička modalna analiza modela višespratne zgrade sprovedena je primenom programa za analizu konstrukcija konačnim elementima SAP2000