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. With our solution, you are able to excite the structure with an impact hammer or modal vibration shaker and easily measure the response. 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. Dynamic analysis of buildings for earthquakeresistant design article pdf available in canadian journal of civil engineering 302. 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. 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. Analysis of ambient vibration records enables the dynamic structural behaviour identification trough. Every structure vibrates with high amplitude of vibration at its resonant frequency. This application note emphasizes experimental modal techniques, specifically the method known as frequency response function testing. Modern day experimental modal analysis systems are composed of 1 sensors such as transducers. Currently dynamic modal analysis is widely used to global understand. Their freevibrational responses under gravity are analyzed during the first excursion of uplift following to the first mode vibration in contact phase. 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. Pdf modal analysis for oor s in lightweight buildings.
Nonstructural components, high rise buildings, dynamic modal analysis. Evaluated is the accuracy of the modal pushover analysis in estimating the seismic demands for six sac buildings. At any point in time, the displacements of a twocoordinate system are r1t,r 2t. Dynamic analysis of buildings for earthquakeresistant. Ida edskar modal analysis, dynamic properties and horizontal stabilisation of timber buildings. This field of measuring and analysing is called modal analysis. The modal pushover analysis mpa procedure, presently restricted to one horizontal component of ground motion, is extended to three. 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. The method is not practical for large systems since two unknown coefficients must be introduced for each mode shape. So, basically, modal analysis is the study of the natural characteristics of structures. It is less usual for civil engineers to use this method to.
Pdf dynamic analysis of buildings for earthquakeresistant. 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. This is essentially a vertically orientated, stainless steel tube with intermediate supports over the lower section and a large unsupported cantilever at the top. 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. A modal pushover analysis procedure for estimating seismic demands for buildings. And the responses by considering both fixed base and. This article presents the evolution of experimental modal analysis in the civil engineering field, from inputoutput to outputonly modal identification techniques. Goel the nonlinear static procedure nsp or pushover analysis in fema273 fema, 1997 has become a standard procedure in. Operational modal analysis often called outputonly or ambient modal analysis is described in this article. With this in mind, some design recommendations and areas of future work are proposed in the conclusion.
This chapter will focus on the operational modal analysis oma, i. Angular frequencies radsec, frequencies hz, periods, modal stiffness, modal damping. The modal superposition method is a general procedure for linear analysis of the dynamic response of structures. Effective and affordable modal analysis and modal testing solution for ods, mimo, and oma testing methods. Modal pushover analysis for highrise buildings by ming zheng b. 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. Modal analysis is the study of the dynamic properties of structures under vibrational excitation.
Pdf a modal pushover analysis procedure for estimating. In every development of a new or improved mechanical product, structural dynamics testing on product prototypes is used to assess its real dynamic behavior. Other areas are treated in a general sense to introduce their elementary concepts and relationships to one another. Dec 03, 2017 introduction what is structure, modal and analysis. Modal analysis is a powerful tool to identify the dynamic characteristics of structures. Chopra, university of california, berkeley this paper comprehensively evaluates the modal pushover analysis mpa procedure against the exact nonlinear response history analysis. Today, modal analysis has become a widespread means of finding the modes of vibration of a machine or structure figure 3. Angular frequencies radsec, frequencies hz, periods, modal stiffness, modal damping, modal damping ratio and standard normalized. Understanding both the natural frequency and mode shape helps to design my structural system for noise and vibration applications. 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. Verification of simple modal analysis in staad ram staad. A schematic description of a machine containing rotating components.
A comprehensive modal analysis of an arbitrary multistory shear building having rigid beams and lumped masses at floor levels is obtained. Modal analysis is the study of the dynamic properties of systems in the frequency domain. Analytical modal analysis modal analysis is the process of characterizing the dynamic response of a system in terms of its modes of vibration. 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. In operation, all machines, vehicles and buildings are subjected to dynamic forces which cause vibrations. 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. It is less usual for civil engineers to use this method to characterize the dynamic. Industrial applications of modal analysis modal analysis has become a standard approach in todays structural dynamics studies. Modal analysis and modal testing ods, mimo, oma dewesoft. 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. Modal testing is performed on a plate structure with welldefined modes, resonance frequencies and damping values. These results are compared with those obtained by nonlinear response history analysis and three force distributions in fema273. Structural testing consists of a comprehensive introduction to the theoretical background to modal analysis and struc tural dynamics. 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.
To overcome this limitation, a modal pushover analysis mpa procedure was proposed by chopra et al. Abstract this thesis presents two novel nonlinear modal analysis methods, aimed at the identification of representative engineering structures. 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. Topic 6 structural dynamics iii analysis of elastic mdof. 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. Pdf the effects of building parameters on the modal. The study of modal analysis is an excellent means of attaining a solid understanding of structural dynamics. Pushover analysis is a nonlinear static analysis tool widely used in practice to predict and evaluate seismic performance of structures.
Operational modal analysis another way of doing modal testing. Using experimental dynamic modal analysis in assessing structural. Operational modal analysis of super tall buildings by a bayesian. Evaluation of equivalent static wind loads on buildings. Structural testing part 1, mechanical mobility measurements. The overall objective is to detect, localize, identify and quantify the. The basics about structural building dynamics dynamic analysis 4. Modal analysis of dynamic behavior of buildings allowed to uplift at. I wanted to know how to identify the local and the global modes from a modal analysis obtained over a range of frequencies.
We use modal analysis to help design all types of structures including automotive struc. 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. Frequency domain decomposition fdd and enhanced frequency domain decomposition efdd concepts are presented and ap. Pdf modal analysis of civil engineering structures researchgate. 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. 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.
Modal analysis is an efficient tool for describing, under standing, and modeling structural behaviour. 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. Introduction the nonlinear static procedure nsp or pushover analysis in fema273 fema, 1997 has become a standard procedure in current structural. In this paper, an improved mpa procedure is presented to. I have done modal analysis of a structure with on boundary conditions, thus i get first 6 rigid body modes which have zero frequencies. Pdf modal pushover analysis of sac buildings semantic scholar. 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. Operational modal analysis another way of doing modal. 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. Modal analysis is defined as the study of the dynamic characteristics of a mechanical structure.
Verification of simple modal analysis in staad ram. Pdf modal pushover analysis of sac buildings semantic. However, invariable lateral force distributions are still adopted in the mpa. Modal analysis method an overview sciencedirect topics. Goel, california polytechnic state university, san luis obispo and anil k. 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. Assessment of modal pushover analysis for midrise concrete. Chapter 5 commentary structural analysis procedures. Quantification of uncertainties and model updating master. The dynamic characteristics of a structure can be obtained by traditional experimental modal analysis.
The pushover analysis poa procedure is difficult to apply to highrise buildings, as it cannot account for the contributions of higher modes. 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. The modal test is an indispensable tool to determine natural frequencies and mode shapes of any structure. Introduction exact solution of the free vibration problems is where coefficients can be determined from the initial conditions. Analytical modal analysis depends on the generation of the equations of motion of a system through a finite element model. Now starting from the 7th mode, the frequency rises.
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