For real systems there is often mass participating in the forcing function such as the mass of ground in an earthquake and mass participating in inertia effects the mass of the structure itself, m eq. Version 18 brings many new essential features to an all new interface, delivering increased easeofuse, improved workflows and maximized efficiency. Is there a way to get the mode participation factor please notice, i am not talking about mass participation factors but mode participation factor. The design response spectrum curve suggested by the is. Dynamic seismic analysis of rcc building as per is. Response spectrum analysis in staad part 2 explanation video.
Pro cannot calculate this, i would appreciate it if you can help me to convert the modal frequencies and the mass participation factors to frf. In this lecture, modal analysis case eigen or ritz vectors is discussed. Mode participation in staad ruchirak12 structural op 15 jun 15 17. Staad tower connect tutorial civil engineering community. Pdf response spectrum analysis for irregular multistorey. I presented the results that you can obtain using that software. Under the hood, it is the same capable product our customers love. Mode participation factor of each mode pk mass participation factor for. Slight variation in frequencies and modal participation factors was observed as each software. Go into define load cases modal cases define modal case change the number of mode shapes you want to consider.
Because the default number of mode shapes entered in sap2000 are 12. Over time, mass has built up an unparalleled wealth of experience within the specification, development and delivery of functional, reliable and usable software solutions. The base shear based on elf and t ta cu should be calculated to check if the computed from modal analysis is less than 85% of the elf base shear. I have applied response spectra in x and z direction i. How to calculate mode shapes and frequencies in staad pro v8i using eigen extraction method. Eigenvalue analyses to derive mode shapes and mass participation factors assisted the design of large number of footbridges in a timely and efficient manner the red and green lines of the dubai metro light rail scheme are being constructed as a designbuild contract by a consortium of international contractors. Specifically, for those examples which use the change command see tr. Mass participation ratios are important in determining the adequacy of the calculated modes to solve dynamic problems with base motion. And the software will limit it to that many number of modal r. I was going to use the missing mass correction command to boost the mass participation. Now in case of an earthquake, acceleration is fed into the building from the ground and the building starts shaking. The sum of the effective modal masses in a certain direction j for all eigenmodes equals the total mass of the structure.
Dynamic analysis of rc multistoreyed building a comparative. Mass participation factors in percent mode x y z summx summy summz 1 0. Analysis and design of footbridges for the dubai metro. Learn more about risa3d here or request a live walkthrough with one of our engineers. Is it possible to get it to display more than six factors. Test results including base shear and story drift are presented and get effective lateral load resisting system. Modal participation factors are required to perform dynamic analysis and response. Mass participation factor the amount of system mass participating in that particular mode. Confidently design steel, concrete, timber, aluminum, and coldformed steel structures anywhere in the world using over 90 included international design codes. The effective modal mass is a quantity related to the modal participation factor. Apr 25, 2016 the mass participation factor for the ith mode is calculated using the following formula. Staad tower connect seismic analysis the video shows how to create a definition for seismic loading. May 11, 20 priestley et al 1996, among other authors, confirm that a sum of all empf known as cumulative effective mass participation factor, cempf of 80% to 90% in any given response direction can be considered sufficient to capture the dominant dynamic response of the structure. Meanwhile many codes, such as asce 7, define the minimum no.
The frequency in first mode of vibration is found between 0. Modal mass participation for the concrete deck bridge. Need help working from home with your bentley software. Understanding the mass participation factor engineer jau. Structural engineering forum of india structural engineers. The set nl command is used in a multiple analysis run if you want to add more primary load cases after one analysis has been performed. Modal effective mass ratio participation ratios by degrees of freedom on the basis of participation ratio of each mode being set at 100%. How do i calculate the natural frequency of the floor. Dynamically loaded, the point mass is allowed to bounce happily up and down on the spring in one direction, hence the whole of the mass in theory is participating in the bouncing in that direction. So according to the time priod of the structure in different modes it staad reads corresponding acceleration from the graph you have entered into it and then simply gives u the base shear as acc. The effective modal mass for mode i, with respect to excitation in direction j, is defined from the participation factor and the modal mass as. Are those mode shapes normalized with mass, i mean, are they normalized so that the generalized mass matrix is the identity.
This is called modal mass participation factor which shows how much a particular mode is contributing to the overall deformation of the system. The design lateral shear force is at each floor in. Design procedure of tabletop foundations for vibrating. This forum also aims in aiding professionals from allied fields such as architecture, construction, sociology, planning, conservation and disaster mitigation to interact with. Cases turbine side generator side amp from permissible remarks amp from permissible remarks ampstaad amp staad 1 vertical vibrations y 0. I have a doubt that now the mass participation which has to be considered 90% will be checked for x, y, z or only for plan directions.
Returns the modal participation factors for missing mass mode for specified load case. Most codes require that at least 90% mass participation factor in each of the lateral directions be obtained for the modeshape extraction used for dynamic analysis. The complete etabs professional for structural engineers udemy. Modal mass coefficient and modal participation factor in sap2000. The frequencies and modal mass participation ratios obtained from staad pro and etabs are tabulated in table 2.
Dynamic analysis of multistory building using response. The modal participation factor i for mode i is mo ii li i 26 the modal participation vector is thus. Structure designed using staad and etabs software,international. Straus r7software dynamics analysis linkedin slideshare. The square root in this case of the point mass is the participation factor, since the whole of the mass is participating in the mode. Nov 18, 2016 some fea software call the input for modal analysis an eigl card for fea basics. Modes with relatively high effective masses can be readily excited by base excitation.
May 28, 2018 dynamics check modal participating mass ratios engineering for all. Analysis and design of turbo generator machine foundation. In a previous post understanding the mass participation factor i have talked about the modal analysis in solidworks and how to make the most of it. Mass participation normalized you can list mass participation ratios in the global x, y, and z directions normalized with respect to the total mass after running a frequency study. Seismic analysisdesign of multistoried rc buildings using. Naturally, the same goes for dynamic analyses with centers of mass shifted. Multiply spectral accelerations by modal participation factor and. For a given floor, the software will generate as many of these plots or modeshapes as required, together with the corresponding natural frequency and modal mass.
The frequencies and modal mass participation ratios obtained from staad pro and etabs are. Modal analysis, or the modesuperposition method, is a linear dynamicresponse procedure which evaluates and. Why does sap2000 divide the responses of structures into 12. Pro advanced adds faster, more advanced and complex analysis. Also gives the value of modal mass participation, design results of beam and column with shear wall. The sum of the mass participation factors can be used as a guide to determine that there is a. As the modal mass participating factor is more than 75% in the higher mode, the considered structure is stiff for earthquake excitation. Im doing a spectrum analysis on a structure that is highly irregular so it is very difficult to get the 90% mass participation that the code requires. How can i differentiate between staad pro, strap, etabs.
The mass participation factors table only gives results for the first six modes even if there are more than six modes. Mass participation factor for the mode for a direction. Pdf response spectrum analysis for irregular multi. To understand this physically, we must first understand that our structures, not unlike the rest of the universe, are very lazy and tend to take the path involving least work. Pdf advanced analysis of a structure using staad pro. The mass participation factors table only gives results for the first six. Frf frequency response function structural engineering. Till now we are not considering the mass participation factor for targeting the modes. Mk 90% one shouldnt consider modes having frequencies 33 hz in case one has considered modes up to 33hz, but still hasnt obtained. The mass participation factor for the ith mode is calculated using the following formula. Scale factor concept while defining response spectrum seismic analysis. Mass participation factor and its role in modal anlysis. In reference to the mode shapes that we find in the.
Another is that a cumulative mass participation factor of 0. Practical dynamic analysis and design for engineers and. Dynamics check modal participating mass ratios engineering for all. It was found that the considered building is stiff for earthquake excitation as modal mass participation factor.
But if the first six modes only contribute 60% mass participation, and above 12 th mode also if for mode the mass participation factor is higher should we check with compressor harmonics upto that or not. Hi indeed the mass participation factors for linear displacements along u,v,w only, no rotation yet are awailable in 4. Modal mass from staadpro ram staad opentower forum. Example of how to use the mass participation factor in. Sep 06, 2012 till now we are not considering the mass participation factor for targeting the modes. Priestley et al 1996, among other authors, confirm that a sum of all empf known as cumulative effective mass participation factor, cempf of 80% to 90% in any given response direction can be considered sufficient to capture the dominant dynamic response of the structure. How can i differentiate between staad pro, strap, etabs and. Please notice, i am not talking about mass participation factors but mode participation factor. Then confidence is gained to use the software on a large complex structural models. Modal participation factors are required to perform dynamic analysis and response spectrum analysis in. Pro v8idynamic response spectrum seismic analysisvideo training chapter1 what is earthquake types of seismic waves classification seismotonics of india earth quake zone general effects of earthquakes types of damage and reason effects of earthquakes site selection building construction materials horizontal and vertical shaking of. In several studies llately i am having a hard time getting to the 0. Response spectrum analysis civil engineering downloads. Seismic analysis and design of multistoried rc building.
Analysis and design of footbridges for the dubai metro light. The effective modal mass provides a method for judging the significance of a vibration mode. The displacements of joints, axial forces, time period and mass participating factors were studied. A mode with a large effective mass is usually a significant contributor to the systems response. Mode participation in staad computers and structures. The complete etabs professional for structural engineers 4. Dynamics check modal participating mass ratios youtube. Seismic base shear in rs is done based on the mass participation factor.
It is often wise to check your software results with a small regular structural model where results are predictable with hand calculations. Two distinct finite element models were created using staad pro finite element fe modeling and the analysis. By plotting the mass participation you can see just how important each mode is. Imposible to approach 90% i am having some difficulties when i try to reach 90% of mass at least in 1 direction, to do a seismic a analysis of the structure. Structural engineering forum of india, sefi is a forum that enables and supports interaction among structural engineers and addresses the issues that concern them. That is the higher the cumulative participation factor, the higher the cumulative mass participation. Eigenfrequency analysis comsol multiphysics modeling software. How many modes should we consider in modal analysis of 7 storey. Im running the seismic model and pops up the errors, for 105 modes the mass participation factor is equal 28.
In practice, it is generally sufficient to consider only the first 30 modes, i. Vertical distribution for base shear determined by. Similarly, missing mass correction was applied in software. What is the difference between mass participation factor. Oct 06, 2011 the universally accepted level of mass participation for a linear dynamic study is 0. The mode participation factor can be obtained by adding the command.
Structural engineering, analysis, and design software. I was able to get the modal frequencies and the mass participation factors but i dont know how to convert this to frf. Why does sap2000 divide the responses of structures into. Results must be scaled to within 85% of v as described in section 12.
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