Leaderboard

There are major flaws in your structural system. There is no load path for transferring lateral loads from top to foundation. They way you have modeled it, you are relying on moment connections, which, I think is not practical, and also not applicable for open web joists. Why have you selected open web joist for 15 ft span. You can use hot rolled section You have not modelled bracing required to prevent local buckling of compression flanges of your flexural members. You can ensure buckling restraint by running beams in longer directions of the shed as well; Span between the beams will depend upon required unbraced length. You will also need to put cross bracing in the plane of roof deck, as well in the plane of column grid-lines (in both direction) , at-least in one bay, to improve global stability of the system. You will need to check, among others, if the model is using correct values of unbraced length, moment gradient factor (Cb) and effective length factor. If you want to use open-web joist, then you need to ensure that Etabs knows that it is built up section. I suggest you to select compact section for you flexural members, and ensure that slenderness ratio of elements of column-section are low enough to ensure inelastic behavior. You should be using 2D model.

at the outset, i want to suggest that you DONT actually need to send .ebk file which you did in zip. .$et file is enough for anyone to review and check. The facility is in seismic zone 4 Make LL factor in p-delta = 1.0 (im leaving the question for you to research..why) You have made the base fixed, take care in the design of baseplates. (Bi-axial moments....how would you design it)? Coming back to your main question, When i ran the model, all of the members passed including the columns. (LOL). Is there something I am not getting? Check in your model, the effective length factors for columns and beams. They might need to be adjusted. I would assert that you should have made a simple 2d model of this and should have studied it properly before starting the 3d model. Its never too late, if you haven't done one yet. You can do it now. In 2 model, check how much are the reactions, column axial forces and drifts to have a FAIR idea about the structure you are dealing with. For drift, search in this forum. I have made a lengthy topic about building drifts. Just do the struggle to search it. I am surprised to see no WIND load on the structure as it would be more critical for uplift of foundations and drift (If seismic is not governing). Is that the reason? 0.25inch thick shell to model the slab? I would recommend to make it as thin as possible (to the point just near where ETABS does not start giving errors...try 5mm may be). This is to exclude any out-of-plane effects of the shell.

software are the tools that provide assistance to make things more accurate . i am using these softwares bt i am intrested to know what are the limitations of these?

ETABS is great tool for dealing with RCC frame and steel frame structures according to the established building codes. You cannot perform nonlinear analysis in ETABS; it has limited ability e.g. for pushover . You can model masonry but it is not the best tool for masonry because you can only remain in elastic region, and you do not have control on element type. Likewise, it is not suitable for water tanks as well, especially underground water tanks. You cannot perform soil-structure interaction, which is the on of the reason that its is not suitable for underground water tanks. In finite element analysis, forces and displacements are computed at nodes and then distributed inside the element. So every FEM software does the same.