I was going to use the missing mass correction command to boost the mass participation. Pdf response spectrum analysis for irregular multi. I was able to get the modal frequencies and the mass participation factors but i dont know how to convert this to frf. It is often wise to check your software results with a small regular structural model where results are predictable with hand calculations. Need help working from home with your bentley software. The mass participation factors table only gives results for the first six modes even if there are more than six modes.
Meanwhile many codes, such as asce 7, define the minimum no. Cases turbine side generator side amp from permissible remarks amp from permissible remarks ampstaad amp staad 1 vertical vibrations y 0. The eigrl card is just a way to enter the parameters for the modal analysis, which are in general. Why does sap2000 divide the responses of structures into 12. Example of how to use the mass participation factor in. The frequencies and modal mass participation ratios obtained from staad pro and etabs are. The mass participation factors table only gives results for the first six. Structural enterprise the most popular structural applications in a single a costeffective license. Pdf advanced analysis of a structure using staad pro. Structural engineering, analysis, and design software. Seismic analysis and design of multistoried rc building. 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.
Learn more about risa3d here or request a live walkthrough with one of our engineers. 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. Why does sap2000 divide the responses of structures into. Structural engineering forum of india structural engineers.
I have applied response spectra in x and z direction i. 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. Similarly, missing mass correction was applied in software. 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. Nov 18, 2016 some fea software call the input for modal analysis an eigl card for fea basics. Returns the modal participation factors for missing mass mode for specified load case. Analysis and design of footbridges for the dubai metro. Ive attached the model as well for to know where are the erros. Modal mass from staadpro ram staad opentower forum. Modes with relatively high effective masses can be readily excited by base excitation. 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.
The design response spectrum curve suggested by the is. Modal participation factors are required to perform dynamic analysis and response spectrum analysis in. In reference to the mode shapes that we find in the. Is it possible to get it to display more than six factors. Is there a way to get the mode participation factor please notice, i am not talking about mass participation factors but mode participation factor. Please notice, i am not talking about mass participation factors but mode participation factor. Naturally, the same goes for dynamic analyses with centers of mass shifted. After that, you shall learn how you can analyze the structure and check the seismic mode shapes for all modes.
The mode participation factor can be obtained by adding the command. The frequencies and modal mass participation ratios obtained from staad pro and etabs are tabulated in table 2. Sep 06, 2012 till now we are not considering the mass participation factor for targeting the modes. One common rule of thumb is that a mode should be included if it contributes more than 2% of the total mass. 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. Scale factor concept while defining response spectrum seismic analysis. 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. Modal effective mass ratio participation ratios by degrees of freedom on the basis of participation ratio of each mode being set at 100%. Mass participation factor and its role in modal anlysis. Thus, openstaad allows users to link inhouse or thirdparty applications with staad.
User provides the value for z2xir as factors for input spectrum program calculates time periods for first six modes. Are those mode shapes normalized with mass, i mean, are they normalized so that the generalized mass matrix is the identity. Vertical distribution for base shear determined by. The complete etabs professional for structural engineers udemy.
As the modal mass participating factor is more than 75% in the higher mode, the considered structure is stiff for earthquake excitation. How to calculate mode shapes and frequencies in staad pro v8i using eigen extraction method. In several studies llately i am having a hard time getting to the 0. Staad tower connect seismic analysis the video shows how to create a definition for seismic loading. Pro advanced adds faster, more advanced and complex analysis. 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 4. How many modes should we consider in modal analysis of 7 storey. Also gives the value of modal mass participation, design results of beam and column with shear wall. Another is that a cumulative mass participation factor of 0. Test results including base shear and story drift are presented and get effective lateral load resisting system. Whilst the software provides enablement, its success is highly dependent upon the management and control of the corresponding infrastructure, data and users that drive its. Specifically, for those examples which use the change command see tr. Dynamic seismic analysis of rcc building as per is.
Aug 19, 20 how to calculate mode shapes and frequencies in staad pro v8i using eigen extraction method. Design procedure of tabletop foundations for vibrating. Results must be scaled to within 85% of v as described in section 12. The sum of the effective modal masses in a certain direction j for all eigenmodes equals the total mass of the structure.
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. Pdf response spectrum analysis for irregular multistorey. Response spectrum analysis civil engineering downloads. The mass participation factor for the ith mode is calculated using the following formula. Straus r7software dynamics analysis linkedin slideshare. 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. 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. May 28, 2018 dynamics check modal participating mass ratios engineering for all.
Seismic base shear in rs is done based on the mass participation factor. Structure designed using staad and etabs software,international. By plotting the mass participation you can see just how important each mode is. Mode participation in staad ruchirak12 structural op 15 jun 15 17. Modal mass coefficient and modal participation factor in sap2000. Modal mass participation for the concrete deck bridge. Response spectrum analysis in staad part 2 explanation video. 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.
Practical dynamic analysis and design for engineers and. The sum of the mass participation factors can be used as a guide to determine that there is a. Two distinct finite element models were created using staad pro finite element fe modeling and the analysis. It was found that the considered building is stiff for earthquake excitation as modal mass participation factor. Go into define load cases modal cases define modal case change the number of mode shapes you want to consider. Mk 90% one shouldnt consider modes having frequencies 33 hz in case one has considered modes up to 33hz, but still hasnt obtained. This forum also aims in aiding professionals from allied fields such as architecture, construction, sociology, planning, conservation and disaster mitigation to interact with. The frequency in first mode of vibration is found between 0. Dynamics check modal participating mass ratios engineering for all. Dynamic analysis of rc multistoreyed building a comparative. Understanding the mass participation factor engineer jau.
Dynamic analysis of multistory building using response. 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. The displacements of joints, axial forces, time period and mass participating factors were studied. Dynamics check modal participating mass ratios youtube. Eigenfrequency analysis comsol multiphysics modeling software. Over time, mass has built up an unparalleled wealth of experience within the specification, development and delivery of functional, reliable and usable software solutions. In practice, it is generally sufficient to consider only the first 30 modes, i. Because the default number of mode shapes entered in sap2000 are 12. Seismic analysisdesign of multistoried rc buildings using. Analysis and design of turbo generator machine foundation. How can i differentiate between staad pro, strap, etabs and. Im running the seismic model and pops up the errors, for 105 modes the mass participation factor is equal 28. The modal participation factor i for mode i is mo ii li i 26 the modal participation vector is thus. 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.
Modal analysis, or the modesuperposition method, is a linear dynamicresponse procedure which evaluates and. 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. The effective modal mass provides a method for judging the significance of a vibration mode. I presented the results that you can obtain using that software. Modal participation factors are required to perform dynamic analysis and response. How do i calculate the natural frequency of the floor. Multiply spectral accelerations by modal participation factor and. Till now we are not considering the mass participation factor for targeting the modes.
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. 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. What is the difference between mass participation factor. The effective modal mass is a quantity related to the modal participation factor. In this model, the first fifteen modes were dominant as they contributed for more than 99% mass participation and effect of the remaining mass was considered by applying missing mass correction. Mass participation factor the amount of system mass participating in that particular mode. Under the hood, it is the same capable product our customers love. 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.
Mass participation factors in percent mode x y z summx summy summz 1 0. Analysis and design of footbridges for the dubai metro light. 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. Frf frequency response function structural engineering. This is called modal mass participation factor which shows how much a particular mode is contributing to the overall deformation of the system.
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. Staad tower connect tutorial civil engineering community. A mode with a large effective mass is usually a significant contributor to the systems response. Hi indeed the mass participation factors for linear displacements along u,v,w only, no rotation yet are awailable in 4. Then confidence is gained to use the software on a large complex structural models. Mass participation ratios are important in determining the adequacy of the calculated modes to solve dynamic problems with base motion. The design lateral shear force is at each floor in. Apr 25, 2016 the mass participation factor for the ith mode is calculated using the following formula. Solidworks simulation finding mass participation factor duration. Now in case of an earthquake, acceleration is fed into the building from the ground and the building starts shaking. 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. Mode participation in staad computers and structures. 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. Mass participation factor for the mode for a direction.