P Delta Analysis Etabs

[Jasmine Lemaitre]

dearuzair i had chekd ur attachment regarding p-delta analysis parameters.to some extent it is informative but in that it is not mentioned that for p-delta what load combinations we shud take. instead it is referred to chek download ETABS VERSION 7 MANUAL but in that manual too i was unable to find the required load combos n scale factors.that was for ur kind info.

Most of us must be knowing that etabs works on the structural analysis method of FINITE ELEMENT METHOD. This method is taught at Masters level under a separate subject under above mentioned name bt wat abt those engineers who r practising after bachelors n even better exerienced at design. But they definitely hvnt complete idea as to how etabs performs the analytical process. Can some1 refer any precise n brief material to understnd the FEM?

UBC-97 and ASCE 7-05 or later require that the base shearcalculated using modal response spectrum dynamic analysisshould exceed or match a certain percentage of the staticbase shear calculated using Equivalent Lateral Forceprocedure (static analysis). The requirements of ASCE 7-05are implemented in this example. For completeness, relevantsteps on how to set up the spectrum cases in ETABS arepresented.

The seismic parameters are project specific dependent onseismicity of the region, the underlying soil class and typeof building structure. Eccentricity in seismic loading willnot be considered for the static cases since the base shearobtained from EQX and EQY cases would only be used for baseshear scaling and not for design, i.e. seismic design willonly use the forces from dynamic analysis.

Define the P-delta parameters based on project specificcriteria or standard practice. Usually, the factors of thegravity load component of the governing seismic loadcombination is used. For example, if the load combinationincludes1.2 DEAD + 1.0 LIVE + 1.0 EARTHQUAKE, anddeem that the gravity component of this combination wouldproduce the highest P-delta effect, you would input:

Set up the modal case which must include vibration in bothx- and y-direction. There should be sufficient number ofmodes to achieve at such that at least 90% total massparticipation (ASCE 7-05 Section 12.9.1). In this example,Ritz method is used with 16 modes analyzed.

The response spectra is to be multipliedg/R*I(ASCE 7-05 Section 12.9.2), hence an initial scale should beentered for each response spectrum case. Note that bydefining an initial scale as a factor ofg, the results obtained from the response spectrum analysiswould be a force value, e.g. in kN unit.

For complex or irregular structures which do not have clearly defined orthogonaldirections, it may be unclear as to how the orientationof response-spectrum analysis should be applied.In the paper entitled Orthogonal Effects in RSA , Dr. Wilson explains that combined directional effectsmay be accounted for more effectively by using analternative method in which the SRSS combination of two100-percent spectra analyses is applied in any direction,or along either orthogonal axis.

Scale values of 1.0 are applied for eachcase. This can be adjusted later in the load combination ofSPECXY after the analysis has beencompleted. If a higher scale factor is necessary to satisfycode requirements, this can be applied in the combinationwithout having to rerun the dynamic analysis. This can savehours or even days of computer analysis time in case of ahuge model!

Notice how we used the combined effect SPECXY instead ofSPECX or SPECY individually. This reduces the total numberof seismic combinations we would need to define in ETABS.ASCE 7-05 also requires us to include the vertical componentof the earthquake force in the combination (not shown inthis simple example).

The above diagram shows the original unscaled dynamic storyshear (red lines) and the scaled up dynamic story shear(green lines). In this example, it can be seen that theshear force distribution for each corresponding story islower in the dynamic analysis procedure as compared with thestatic analysis procedure. This is generally the case,therefore most structural designers prefer to apply dynamicseismic analysis which could result to more economicaldesign.

In today's world, domains like mechanical engineering, civil engineering, structural engineering, and naval architecture go hand-in-hand with computational tools. Software tools and applications are indispensable in every form of engineering because they simplify several processes, help us carry out accurate calculations, and run simulations that would otherwise be too expensive to try out in the real world.

The field of structural engineering is a subdivision of civil engineering where engineers focus on the stability, strength, and rigidity of structures. Structural engineers should understand when to use which material to build a structure, what geometry it should have, and other such factors. There are some specialized software packages to assist these engineers in their work, one of which is ETABS.

Along with STAAD Pro and ProtaStructure, ETABS is one of the most powerful software tools for structural analysis. 3D modeling, visualization, and automatic code-based learning are some of the unique features of this software. ETABS also supports several analytical models like response spectrum analysis, time-history analysis, and line direct integration time-history analysis.

The first part of the course covers an introduction to ETABS usage. You get to learn about the various components on the ETABS screen and how to use the grids for modeling (similar to any other computer-aided design or CAD software).

Then, you learn how to define the various parameters that structural engineers use for modeling and analysis (for example: how to load samples in certain structures like beams or slabs, how to give supports, etc.). Assigning of parameters and creating the model is the primary step, and incorrectly doing this could spoil all the analysis that follows.

The last part of this module covers the drawing aspects of various ETABS elements. By the end of this, you should have the fundamental knowledge of how to build a model, including answers to questions like, "Why should meshing be done?", "How to draw beams and how to draw slabs?" "How to give labels?" and so on.

In the next module, you get hands-on experience in building a 3D model. Using the ETABS grids and the other CAD tools available, you can design a structure in the software, thereby getting a good idea of the theory and its application.

The procedure followed for the linear static analysis is per the IS 1893 (Part 1): 2016 standard. In this module, you have to define the various parameters associated with the linear static earthquake analysis, like the time period, zone factor, and the range of impact.

For dynamic analysis, the same standard, IS 1893 (Part 1): 2016, is followed. Here, you need to calculate the natural time period or frequency of the building or the structure of interest with the help of modal averages.

Using these values, you then calculate the peak response time of the structure using a spectrum acceleration curve. In the end, you need to analyze the results, check for errors and warnings, and frame a conclusion.

A structure usually handles various forms of forces and loads, one of which is the force of moving wind. Unlike earthquakes, which are relatively rare occurrences, a structure's interaction with wind is a daily phenomenon.

The main factor that distinguishes different regions in India is the average wind speed. Based on this number, as well as building parameters like the height and area, you should calculate the force field of the wind on the structure. You will learn how to perform this calculation using the ETABS software.

P-Delta analysis is a type of secondary analysis that captures the softening effect of compressive forces and the stiffening effect of tensile loads, especially in the lateral directions (i.e., not gravitational forces).

If an axial force, P, displaces a part of the structure by a small amount, delta, the total moment, P multiplied by delta (hence the name), must be taken into consideration for all structural analysis calculations.

Since this structure is essentially a collection of built-up parts, the structural analysis is not the same as that of a regular structure. You learn how to define different parameters and tweak the calculations for wind and earthquake analysis.

From a simple two-bedroom house to the Burj Khalifa, every structure ever built needed the assistance and guidance of structural engineers. If you are interested in structural engineering, knowing an overview of ETABS and other such structural analysis packages can vastly enhance your job prospects.

Abstract: Analysis and design of the structure are the most critical steps in the pre-construction steps involved. Nowadays, as technology is well developed, there is plenty of software available to carry over the analysis and design of any structures in a short period. In every software, the building model with all storey will be modelled, and loads are applied to the modelled structure on respective members, and their responses will be studied for the whole structure. But in reality, the building will be constructed in sequence as a step-by-step process, i.e., storey after storey with their respective loads, which may produce different responses. This analysis with sequential loading at each step is called Construction Sequence Analysis (CSA). In the present project work, the ten-storey setback building with a built-up area of 25m x 30m placed on the slope of 10, assumed to be situated in Darjeeling, is modelled in ETABS software. The loads, namely gravity and lateral loads are applied to the developed model. Then the model is analyzed for different loads and their combinations as prescribed by IS codes. The combinations that produce high response are selected and dead load in those combinations are replaced with three modes: CSA without P-Delta effect, CSA with P-Delta effect, and CSA with P-Delta and Time-dependent effects combined. Thus the model is analyzed with these three additional combinations along with selected conventional load combinations. The various comparisons such as storey displacement, and storey drift between these four combinations of analysis were studied, and results were discussed. The building design is also done based on the analysis performed.

3a8082e126