The project is in seismic design category d and has irregularities which require use of a modal response spectrum analysis for seismic loading. Response spectrum analysis by using etabs software youtube. Apr 17, 2020 the first step in a modal response spectrum analysis is the determination of the 3d modal shapes and natural frequencies of vibration eigenmodes and eigenvalues. Modal parameters are identified by a process of curve fitting that is used to estimate the poles natural frequencies and damping ratios. 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. Created by ondrej, last modified by jessica napier on apr 04, 2014 responsespectrum analysis rsa is a lineardynamic statistical analysis method which measures the contribution from each natural mode of vibration to indicate the likely maximum seismic response of an essentially elastic structure.
Response spectrum analysis massachusetts institute of. In a response spectrum analysis, workbench mechanical permits description of supports zero displacement boundary conditions in the modal environment. These structures are always loaded by natural loads that cannot easily be controlled and measured, for instance, wave load offshore structures, the. Modal analysis calculates the natural frequencies of the system alone. The standard response spectrum for medium soil type and that can be given. Modal transient response analysis is another method for computing the transient response of a structure. Response spectrum analysis is a giant idealization. Introduction to structural dynamics and earthquake engineering module 9 response spectrum modal analysis prof. I have previously contacted bentley about how to set up the model to use the direct analysis method with the.
Today, this task can be performed very reliably and efficiently by many computer programs dedicated to seismic response analysis for the purposes of earthquakeresistant design. Response spectrum analysis for irregular multistor ey structure in seismic zone v 8 the variation of the time period in different mode is shown in figure 3. 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. Evaluation of modal combination methods for seismic. The objective of this project was to reevaluate the current regulatory guidance for combining modal responses in response spectrum analysis, evaluate recent technical developments, and recommend revisions to the regulatory guidance. The first stage in the response spectrum procedure is to estimate the peak values of these modal responses. Responsespectrum analysis provides insight into dynamic behavior by measuring pseudospectral acceleration, velocity, or. The use of mathcad provides details of the analysis that are not easily extracted from the commercial software. New analysis methods can be implemented with ease to take the advantage of the visualization, measurement and analysis framework. Structural dynamics testing and analysis solutions dewesoft. Run a seismic analysis robot structural analysis products.
Sep 10, 20 the response spectrum method of analysis is developed using the following steps. Confused about direct analysis method and modal response. Nov 18, 2016 some fea software call the input for modal analysis an eigl card for fea basics. Asce 716 response spectrum analysis in rfem dlubal software. Modal response spectrum analysis earthquake resistance eurocode. However, the mass participation of subgrade levels may be subtracted from the total mass. Effective and affordable modal analysis and modal testing solution for ods, mimo, and oma testing methods. Mechanical vibrations overview of experimental modal analysis. Watchits and limitations in applying response spectrum analysis in seismic design and assessment. When a vibration load applied to the structure matches the natural frequency, it can be dangerous leading to the destruction of the system. With intuitive controls and powerful features, it is the ultimate tool modal analysis applications. Channel provide you knowledge about all competitive exam including computer proficiency test and current affairs too.
Openmodal is built using established libraries such as numpy, pandas, pyqtgraph, scipy and others. Multi modal response spectrum analysis implemented in. Post processing of modal analysis sol 103 response at each modal frequency is calculated the modal response is dependent on participation factor in direction of excitation spectrum input value at modal damping stressforces based on mode shape each modal response is combined using absolute summation rss summation. 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. Modal analysis and modal testing ods, mimo, oma dewesoft. Since the exact time history of the load is not known, it is difficult to perform a timedependent analysis. This is generally true for relatively short regular structures.
However, none of the above literature explains appropriate software method for seismic analysis. Display these loads graphically, in a table, and using the calculation notes. The eigrl card is just a way to enter the parameters for the modal analysis, which are in general. Evaluation of modal combination methods for seismic response. The standard response spectra for type of soil considered is applied to building for the analysis in etabs 20 software. It is apparent that all response spectrum curves represent the properties of the earthquake at a specific site and are not a function of the properties of the structural system. Gsa masterclass on response spectrum analysis oasys. The response spectrum method of analysis is developed using the following steps. All the data, from measurement and analysis, is kept in pandas dataframes, which can be read and modified freely. Responsespectrum analysis rsa is a lineardynamic statistical analysis method which measures the contribution from each natural mode of vibration to indicate the likely maximum seismic response of an essentially elastic structure. The damping is included in the acceleration data when the transient acceleration time history is converted to a response spectrum using a q value in the conversion. The final results of the multimodal response spectrum analysis taking into account the zpa method result from the results of the first two eigenvalues here modally superimposed with the srss rule and the results of the zpa. Ansys apdl commands objects after response spectrum analysis. From a set of frf measurements made at defined points on a structure, we can begin to build up a picture of its response.
Openmodal accelerating the implementation of your ideas. The chapter discusses the development of an elastic response spectrum and then explains the determination of the displacements in each mode. The definition of the response spectrum, how it represents different features of the earthquake ground motion, and how it is represented in design codes. Edm modal is a complete modal testing and modal analysis suite for experimental modal analysis ema.
Responsespectrum analysis technical knowledge base. Examples of such events are earthquakes and shocks. It was developed based upon the sophisticated technologies of modern modal analysis theory and technique. 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. 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.
This method requires a previously calculated number of undamped free vibration frequencies and the corresponding mode shapes. Modal analysis computes the frequency shape of modes and displays a magnitude of displacement that has no meaning for the displacement of a real structure because there is no load applied to the structure in a modal analysis to obtain displacement magnitudes of real structures, you have to apply a load and see the response. Set up a response spectrum analysis robot structural. These peak responses are then combined to estimate a total response. An additional seismic analysis type, the response spectrum method assigns a response of each vibration mode on seismic excitation to calculate the internal forces distribution and. Aug 31, 2018 channel provide you knowledge about all competitive exam including computer proficiency test and current affairs too. If the address matches an existing account you will receive an email with instructions to reset your password. Modal is the simplest analysis and the only thing it does is telling you what are the resonance frequencies of your geometry. 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. My question is why we dont apply u2 and u3 in the same load case. This method uses the mode shapes of the structure to reduce the size, uncouple the equations of motion when no damping or only modal damping is used, and make the numerical integration more efficient when the equations of motion are. Mar 04, 2014 module 9 response spectrum modal analysis 1. Eigenvector modal analysis finds the natural vibration modes of the structure, which can be used for understanding the behavior of the structure, and also as the basis for modal superposition in responsespectrum and modal timehistory load cases. Pdf response spectrum analysis for irregular multistorey.
I have previously contacted bentley about how to set up the model to use the direct analysis method with the response spectrum analysis. Tall buildings, and those with structural irregularities have other modes that contribute significantly to the seismic response of a building torsion or whipping. Modal analysis is performed to identify the modes, and the response in that mode can be picked from the response spectrum. Jan 05, 2017 the project is in seismic design category d and has irregularities which require use of a modal response spectrum analysis for seismic loading. After an estimation is made of the linear viscous damping properties of the structure, a specific response spectrum curve is selected. In a multi modal response spectrum analysis, it is important to determine a sufficient number of eigenvalues of the structure and to consider their dynamic responses. Oct 29, 2018 the standard response spectra for type of soil considered is applied to building for the analysis in etabs 20 software. Earthquake loads are defined in the form of curves called acceleration response spectra which is the. The shear forces, moments, and support forces resulting from these equivalent loads are shown in figure 05. Dynamic analysis of multistory building using response. How peak modal results are obtained from modal analysis and the response spectrum, and how these modal results are combined using statistical combination rules e.
Response spectrum analysis provides insight into dynamic behavior by measuring pseudospectral acceleration. Jul 30, 2018 response spectrum analysis rsa is a lineardynamic statistical analysis method which measures the contribution from each natural mode of vibration to indicate the likely maximum seismic response of an essentially elastic structure. A linear static analysis assumes the response of the building is first mode dominant inverted triangle. Using the acceleration response spectrum, an equivalent static load is derived which will provide the same maximum response as that obtained in each. Lets assume the excitation angle 0 and building principle direction is u1 so i will apply response spectrum function per ibc 2006 in u1 direction by a scale factor. Zpa method in response spectrum analysis dlubal software. For models with diagonal mass and diagonal damping matrices the superposition of the modal reaction forces can provide a reasonable approximation of a nodal reaction force in modebased analyses other than response spectrum analysis. What are the load combinations for a response spectrum. Response spectrum method of analysis with simplified. Features bridge analysis, design and rating csibridge.
Multi modal response spectrum analysis implemented in opensees. In singlepoint response spectrum analysis, an excitation input of response spectrum displacement, or velocity, or acceleration can be added as an object in a response spectrum environment. In a response spectrum analysis, the damping is included in the acceleration spectrum data, so the modal analysis must be undamped or you would be double counting the damping. Create a new seismic analysis using equivalent lateral force load cases. Skyciv releases frequency and response spectrum analysis. The first step in a modal response spectrum analysis is the determination of the 3d modal shapes and natural frequencies of vibration eigenmodes and eigenvalues. It isnt related to a loading at this stage, only to the geometry. Modal response spectrum analysis earthquake resistance. Response spectrum analysis gives users the ability to perform seismic analysis based on the building properties. Select seismic, and then select the code according to which you want to run the calculations.
Modal analysis is the study of the dynamic properties of systems in the frequency domain. In response spectrum analysis the model response can be better represented by requesting section stresses and. Some fea software call the input for modal analysis an eigl card for fea basics. In most cases, an mrs analysis is carried out using commercial finite element analysis software.
Structural testing part 2, modal analysis and simulation. Edm modal is a complete modal testing and modal analysis suite for experimental modal analysis ema developed based upon the sophisticated technologies of modern modal analysis theory and technique. Then it calculates mode participation factors, mode coefficients,etc, which are used to scale those gloads into realistic loads. Pdf response spectrum analysis for irregular multi. Responsespectrum analysis faq technical knowledge base. The operational modal analysis is used for large civil engineering structures, operating machinery or other structures, making use of their output response only. With our solution, you are able to excite the structure with an impact hammer or modal vibration shaker and easily measure the response. Response spectrum analysis is a method to estimate the structural response to short, nondeterministic, transient dynamic events. Dynamic frequency analysis, or modal analysis, is needed to determine the natural frequencies or resonant frequencies of a structure in order to predict its maximum response. It takes every modal frequency within the range your response spectrum is defined, and finds the gloading at that frequency.
The objective of this project was to reevaluate the current regulatory guidance for combining modal responses in response spectrum analysis, evaluate recent technical developments, and recommend revisions to the regulatory. The modal test is an indispensable tool to determine natural frequencies and mode shapes of any structure. You need to set up a modal analysis before you can set up a seismic analysis. Response spectrum analysis, mode shapes, modal mass participation factors, natural frequency, eigenvalues, eigenvectors. Regulations such as en 19981 1 and other international standards require to activate 90 % of the structural mass. Useful elearning website will also be shown to give idea about topic clearly.
1549 1522 1260 1521 1574 737 688 1649 230 1627 580 1507 1412 1049 1342 1398 127 1649 166 207 104 743 434 780 1189 600 882 627 884 413 386 1561 552 519 110 811 401 945 63 1446 387 684 933 550 811