Response spectrum analysis massachusetts institute of. Modal combination rules in response spectrum analysis. At the point in time where iyiti is maximum, the response is defined as yi. The opinions and conclusions stated are those of the author and may or may not be those of the laboratory. The results from the x, y, and zdirection analyses are tabulated below. The purpose of the experimental modal analysis is to determine the resonance frequencies, mode shapes and mode damping for the structure. The maximum responses for each mode are calculated independently. Pdf multi modal response spectrum analysis implemented in. Mar 26, 2020 this chapter analyzes an 8story building by using the modal response spectrum mrs procedure provided in section 12.
Included in this series are papers on the following seminal topics. Topic 6 structural dynamics iii analysis of elastic mdof systems. These modal responses are then combined to obtain the models overall response to the applied spectra. The terms and are known as modal participation factors.
It requires to define a design response spectrum,in general, a spectrum of pseudo. Frequency response shock spectrum analysis random vibration ddam analysis most solutions offer both direct and modal solution capabilities direct applies the direct equations of motion to every grid point, providing a more accurate but more costly answer. Introduction the basis of engineering seismology is the need to quantify how a given structure will respond to complex ground motions. A replacement for the srss method in seismic analysis, e. In this we have to calculate the magnitude of forces in all directions and then see the effects on the building. Discrete system with incomplete modal information in practical modal analysis, usually mode shapes and frequencies are available for only the first modes, where. Response spectrum analysis is performed for both the building. Wong1ab 1national institute of standards and technology, usa abstract a fast nonlinear response spectra analysis algorithm based on the theory of modal analysis and. Two point weights of 10 lbf each are attached at midpoint and end point of the beam.
Responsespectrum analysis technical knowledge base. Modal analysis is performed to identify the modes, and the response in that mode can be picked from the response spectrum. Seismic analysis modal spectral analysis it defines the seismic behavior of the structure as the superposition of n. Theory of response spectrum analysis new mexico tech. Nukala june 1999 this is an informal report intended primarily for internal or limited external 7 distribution. Response spectrum analysis rsa is a method widely used for the design of buildings.
In nuclear piping engineering, the response spectrum method of analysis is widely used to analyze piping systems. The modal analysis of the 3d bridge exposes that it has many closelyspaced modes. Alternate modal combination methods in response spectrum analysis. Assign these check sections to the piers, change the pier mode from design to check, and rerun the design.
Nov 19, 2010 shock response spectrum analysis via the finite element method revision c by tom irvine email. Datta department of civil engineering, iit delhi response spectrum method of analysis 0 5 10 15 20 25 30 0. After this identification, more sophisticated analysis methods can be applied based on the results. The matter of combining modal responses is of great interest. Learn about the etabs 3d finite element based building analysis and design program for performing response spectrum analysis to analyze a building subjected. Dynamic analysis of a structure subjected to earthquake excitation using the response spectrum. Summary of the analysis of the existing lateral system. Modal response spectrum analysis earthquake resistance eurocode. Pdf mode shape identification using response spectrum in. Determine the displacement responses of two weights.
Base shear determination using responsespectrum modal analysis of multi degreeoffreedom systems with soilstructure interaction abstract. Seismic analysis of highrise building by response spectrum. Shock response spectrum analysis results result is a single output set containing the combined responses of the spectrum analysis. In the response spectra analysis procedure, each of the models modes is considered to be an independent sdof system. Channel provide you knowledge about all competitive exam including computer proficiency test and current affairs too. Earthquake design and evaluation of concrete hydraulic structures. Concep tually the method is a simplification of modal analysis, i. Modal analysis methods in seismic design for buildings dtic. Base shear determination using responsespectrum modal analysis. However, as we will show in section 3, this formulation provides a basis for response spectrum analysis. Since the response spectrum procedure uses modal methods to define a models response, the value of any physical variable is defined from the amplitudes of the modal responses the generalized coordinates. You may notice that if both modes are normalized to 1. Consideration of torsional irregularity in modal response. Implementation of modal combination rules for response.
It is practical to envelope response spectra such that a smooth curve represents the peak response for each realization of. Prashanth2 1 assistant professor, department of civil engineering birla institute of technology and science. Modal response spectrum analysis, equivalent lateral force analysis, torsional irregularity. Responsespectrum analysis provides insight into dynamic behavior by measuring pseudospectral acceleration, velocity, or displacement as a function of structural period for a given time history and level of damping. Most building codes require a response spectrum analysis to evaluate the behavior of structures that are sensitive to multiplemode excitations e. Biot stated a buildinghas a certain number of so called normal modes of vibration, and to each of them corresponds a certain frequency. Johnson department of earth and environmental science, new mexico tech 1. Dynamic response in nx nastran stress analysis experts. Mass participation of second vertical mode is driving. Rerun the design and verify that the actual flexural reinforcing provided is adequate. Response spectrum modal analysis of buildings using spreadsheets.
Mrsa is popular as the method provides a more realistic assessment of structural demand under the. Response spectrum analysis of structures subjected to seismic. Seismic applications of nonlinear response spectra based on. As a result, when modal response spectrum analysis is used, a threedimensional model is required for all structures, including those with diaphragms that can be designated as flexible. The twelfth east asiapacific conference on structural engineering and construction seismic applications of nonlinear response spectra based on the theory of modal analysis k.
The highly irregular structure is analyzed using three techniques. Response spectrum is a plot of the peak or steadystate response displacement, velocity or acceleration of a series of oscillators of varying natural frequency, that are forced into motion. In the right window select display show mode shape 1mode shape 2 does not exist if we try to ask one. Response spectra can also be used in assessing the response of linear systems with multiple modes of oscillation multidegree of freedom systems, although they are only accurate for low levels of damping. Implementation of modal combination rules for response spectrum analysis using gemini phani k. The first stage in the response spectrum procedure is to estimate the peak values of these modal responses. Pdf response spectrum analysis for irregular multistorey. Lateral loads are far too high for mounting structure to survive. Seismic analyses may be performed using time history analysis methods in lieu of response spectrum analysis. Modal response spectrum analysis for existing special reinforced shear walls29 table 7.
Sep 15, 2020 this is the tenth in a series of short papers on the early history of seminal concepts in earthquake engineering and structural dynamics. Responsespectrum analysis faq technical knowledge base. Moreover, some commercial computer programs with modal response spectrum analysis capability may not perform such an analysis in accordance with the relevant requirements. Jan 05, 2021 modal analysis and its results clause 4. Since the response spectrum procedure uses modal methods to define a models response, the value of any physical variable is defined from the amplitudes of the modal responses the generalized coordinates, q the first stage in the response spectrum procedure is to estimate the peak values of these modal responses. If we look at the calculated response spectrum we can see that the. Construction of design response spectrum the chilean way.
For each mode, a response is read from a design spectrum based on the modal frequency and a given damping ratio. Seismic performance of rc building using spectrum response. Complications may occur with the response spectrum method for large systems. The diaphragms were modeled as semirigid although the diaphragm could have been classified as rigid in accordance with section 12. Modal response spectrum analysis example 1 modal response spectrum analysis in sap. The basic concept of modified response spectrum analysis mrsa nonlinear structure detailed 3d nonlinear response history analysis nlrha. The maximum modal response associated with period tn is given by. Response spectrum method of analysis mechanical engineering. During response spectrum analysis, loading is applied to the entire structure, though subgrade modes will have much higher frequencies, providing minimal contribution to modal response. Following procedure is generally used for the spectrum analysis. The modal superposition method of time history analysis is used for seismic analysis of u. Rational design spectra for structural reliability assessment using. Nov 07, 2012 response spectrum modal analysis of buildings using spreadsheets 1. May 15, 2017 for each mode, a response is read from the design spectrum, based on the modal frequency and the modal mass, and they are then combined to provide an estimate of the total response of the structure.
1251 1325 703 733 699 717 1787 615 1624 823 1648 245 499 259 822 1531 1219 751 975 704 1615 1263 1092 293 88 876 1046 1442 695 554 500 913