In every development of a new or improved mechanical product, structural dynamics testing on product prototypes is used to assess its real dynamic behavior. Using experimental dynamic modal analysis in assessing structural. However, invariable lateral force distributions are still adopted in the mpa. Nonstructural components, high rise buildings, dynamic modal analysis. Effective and affordable modal analysis and modal testing solution for ods, mimo, and oma testing methods.
With this in mind, some design recommendations and areas of future work are proposed in the conclusion. The modal pushover analysis is shown to have a superior accuracy in evaluation of seismic demands for higher buildings, especially for story drift ratios and column shears. Evaluation of equivalent static wind loads on buildings. Civil engineering southwest jiaotong university, 2011 submitted to the department of civil and environmental engineering in partial fulfillment of the requirements for the degree of master of engineering in civil and environmental engineering at the. Topic 6 structural dynamics iii analysis of elastic mdof systems equations of motion for mdof systems uncoupling of equations through use of natural mode shapes solution of uncoupled equations recombination of computed response modal response spectrum analysis by example use of reduced number of modes. Verification of simple modal analysis in staad ram. Modal analysis is the study of the dynamic properties of structures under vibrational excitation. Modal pushover analysis for highrise buildings by ming zheng b. Dynamic analysis of buildings for earthquakeresistant. This is essentially a vertically orientated, stainless steel tube with intermediate supports over the lower section and a large unsupported cantilever at the top.
The modal analysis of the buildings with moment resisting frames without infill has been carried out using staad pro software by using beam and plate elements to model beams, columns and slabs. Examples would include measuring the vibration of a cars body when it is attached to a shaker, or the noise pattern in a room when excited by a loudspeaker modern day experimental modal analysis systems are composed of 1 sensors such as transducers typically accelerometers, load cells, or non contact. This field of measuring and analysing is called modal analysis. Introduction exact solution of the free vibration problems is where coefficients can be determined from the initial conditions. Modal analysis of a 4 story shear building problem description input file output file analysis results in this example we compute the eigenvalues, natural periods of vibaration, and modal shapes for a 4 story shear building. Nov 18, 2016 i wanted to know how to identify the local and the global modes from a modal analysis obtained over a range of frequencies. Dec 03, 2017 introduction what is structure, modal and analysis. We use modal analysis to help design all types of structures including automotive struc. The modal pushover analysis mpa procedure, presently restricted to one horizontal component of ground motion, is extended to three. With our solution, you are able to excite the structure with an impact hammer or modal vibration shaker and easily measure the response. Operational modal analysis of super tall buildings by a bayesian.
A schematic description of a machine containing rotating components. Since only the fundamental mode is considered and the inelastic theorem is imperfect for the conventional pushover analysis, a modified modal pushover analysis mpa is proposed by researchers. The pushover analysis poa procedure is difficult to apply to highrise buildings, as it cannot account for the contributions of higher modes. Theoretical foundations of structural dynamics in the section, the theoretical foundations of structural dynamics and modal analysis are presented under the assumption of linear behavior. Analysis of ambient vibration records enables the dynamic structural behaviour identification trough. Frequency domain decomposition fdd and enhanced frequency domain decomposition efdd concepts are presented and ap. Today, modal analysis has become a widespread means of finding the modes of vibration of a machine or structure figure 3. In various forms, modal analysis has been widely used in the earthquakeresistant design of special structures such as very tall buildings, offshore drilling platforms, dams, and nuclear power plants. This article presents the evolution of experimental modal analysis in the civil engineering field, from inputoutput to outputonly modal identification techniques. The modal superposition method is a general procedure for linear analysis of the dynamic response of structures.
Modal analysis is the study of the dynamic properties of systems in the frequency domain. To overcome this limitation, a modal pushover analysis mpa procedure was proposed by chopra et al. And the responses by considering both fixed base and. Goel, california polytechnic state university, san luis obispo and anil k. Topic 6 structural dynamics iii analysis of elastic mdof. The dynamic characteristics of a structure can be obtained by traditional experimental modal analysis. The study of modal analysis is an excellent means of attaining a solid understanding of structural dynamics. Operational modal analysis another way of doing modal testing. The modal procedures, modal pushover analysis 5, method of modal combinations 6, are able to consider the effects of higher vibration modes in different manners, keeping a fixed distribution. Evaluated is the accuracy of the modal pushover analysis in estimating the seismic demands for six sac buildings. In operation, all machines, vehicles and buildings are subjected to dynamic forces which cause vibrations. Industrial applications of modal analysis modal analysis has become a standard approach in todays structural dynamics studies. The plan dimensions of the two rectangular buildings are 40 m x 80 m for building 1 and 60 m x 120 m for building 2.
Assessment of modal pushover analysis for midrise concrete. A comprehensive modal analysis of an arbitrary multistory shear building having rigid beams and lumped masses at floor levels is obtained. I am currently working on a project where i wish to use staad pro v8i ss4 to perform a modal analysis to determine the natural frequency of a turbine exhaust extension. The modal test is an indispensable tool to determine natural frequencies and mode shapes of any structure. Dynamic analysis of buildings for earthquakeresistant design article pdf available in canadian journal of civil engineering 302. Pdf modal analysis of civil engineering structures researchgate. Operational modal analysis another way of doing modal. Modal analysis is a powerful tool to identify the dynamic characteristics of structures. Goel the nonlinear static procedure nsp or pushover analysis in fema273 fema, 1997 has become a standard procedure in.
Understanding both the natural frequency and mode shape helps to design my structural system for noise and vibration applications. Pdf a modal pushover analysis procedure for estimating. Chopra, university of california, berkeley this paper comprehensively evaluates the modal pushover analysis mpa procedure against the exact nonlinear response history analysis. Structural testing consists of a comprehensive introduction to the theoretical background to modal analysis and struc tural dynamics. Every structure vibrates with high amplitude of vibration at its resonant frequency. The proposed 2005 edition of the national building code of canada specifies dynamic analysis as the preferred method for computing seismic design forces and deflections, while maintaining the equivalent static force method for areas of low seismicity and for buildings with certain height limitations. At any point in time, the displacements of a twocoordinate system are r1t,r 2t.
These results are compared with those obtained by nonlinear response history analysis and three force distributions in fema273. This chapter will focus on the operational modal analysis oma, i. Pdf modal pushover analysis of sac buildings semantic scholar. Modal testing is performed on a plate structure with welldefined modes, resonance frequencies and damping values. Chapter 5 commentary structural analysis procedures. Introduction the nonlinear static procedure nsp or pushover analysis in fema273 fema, 1997 has become a standard procedure in current structural. Pushover analysis is a nonlinear static analysis tool widely used in practice to predict and evaluate seismic performance of structures. A modal pushover analysis procedure for estimating seismic demands for buildings.
Operational modal analysis often called outputonly or ambient modal analysis is described in this article. Pdf modal pushover analysis of sac buildings semantic. Pdf modal analysis for oor s in lightweight buildings. In modal analysis a complex deflection pattern of a vibrating structure is resolved into a set of simple mode shapes with individual frequency and damping parameters. It is less usual for civil engineers to use this method to characterize the dynamic.
Modal analysis of shear buildings a comprehensive modal analysis of an arbitrary multistory shear building having rigid beams and lumped masses at floor levels is obtained. Pdf dynamic analysis of buildings for earthquakeresistant. Modal analysis method an overview sciencedirect topics. Modal analysis and testing of rotating structures load external \ 4 disc drivig \ force anisotropic, driving ocracked element bearings transmission foundation, k n l l bearings f r figure 1. Angular frequencies radsec, frequencies hz, periods, modal stiffness, modal damping, modal damping ratio and standard normalized.
Angular frequencies radsec, frequencies hz, periods, modal stiffness, modal damping. Analytical modal analysis depends on the generation of the equations of motion of a system through a finite element model. Quantification of uncertainties and model updating master. Aug 19, 20 i am currently working on a project where i wish to use staad pro v8i ss4 to perform a modal analysis to determine the natural frequency of a turbine exhaust extension. Examples would include measuring the vibration of a cars body when it is attached to a shaker, or the noise pattern in a room when excited by a loudspeaker. The basics about structural building dynamics dynamic analysis 4. Their freevibrational responses under gravity are analyzed during the first excursion of uplift following to the first mode vibration in contact phase. Ida edskar modal analysis, dynamic properties and horizontal stabilisation of timber buildings.
So, basically, modal analysis is the study of the natural characteristics of structures. I have done modal analysis of a structure with on boundary conditions, thus i get first 6 rigid body modes which have zero frequencies. In this paper, an improved mpa procedure is presented to. Structural testing part 1, mechanical mobility measurements. Now starting from the 7th mode, the frequency rises. Modes of vibration 5 the vector 2 r t r t 2 1 r 22 r 12r 2111 r r t 1 r t 2 q t 1 r 1r 2q t figure 2. This application note emphasizes experimental modal techniques, specifically the method known as frequency response function testing. Modal analysis is an efficient tool for describing, under standing, and modeling structural behaviour. Other areas are treated in a general sense to introduce their elementary concepts and relationships to one another. Modal analysis is defined as the study of the dynamic characteristics of a mechanical structure. The overall objective is to detect, localize, identify and quantify the. Modern day experimental modal analysis systems are composed of 1 sensors such as transducers. Modal analysis and modal testing ods, mimo, oma dewesoft. The method is not practical for large systems since two unknown coefficients must be introduced for each mode shape.
No matter what modal analysis methods we will be using, a very essential question in the analysis is how many vibration modes within a selected frequency range are we dealing with, and, if a particular peak of the frf represents a genuine vibration mode. Verification of simple modal analysis in staad ram staad. Currently dynamic modal analysis is widely used to global understand. Instructional material complementing fema 451, design examples seismic load analysis 9 17 1a, 1b stiffness soft story irregularity vertical structural irregularities irregularity 1a exists if stiffness of any story is less than 70% of the stiffness of the story above or less than 80% of the average stiffness of the three stories above. Modal analysis of dynamic behavior of buildings allowed to uplift at. They have considered shear type, shearbending type and bending type regular highrise buildings and have used the modal analysis through response spectrum procedure and lumped mass story models. Modal pushover analysis mpa has been successfully applied to estimate the seismic demands of regular symmetrical and unsymmetrical plan steel buildings with short to medium periods with a level of accuracy that makes it a strong competitor to nlrha, especially in light of its tremendous saving in computational efforts.
Abstract this thesis presents two novel nonlinear modal analysis methods, aimed at the identification of representative engineering structures. It is less usual for civil engineers to use this method to. I wanted to know how to identify the local and the global modes from a modal analysis obtained over a range of frequencies. Pdf the effects of building parameters on the modal.
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