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Auto meshing doesn't ensure adequate connectivity between member to member and is therefore recommended for horizontal area elements enclosed by line elements only (floors), where there is no structural connection between floor and any element in between the panel. In case of vertical elements, connectivity between vertical and horizontal elements is of due importance and is better to be achieved through manual meshing. In case of auto meshing as you indicated, change in size of auto mesh could solve the problem as its possible that connections inadequate (nodes not coinciding) on 1m element size can be adequate for 1.2m size (nodes start coinciding) and so on. For p-delta,a possibility exists that due to any meshing error some connection is modelled with inadequate lateral stiffness i.e when program try to impose lateral deflection due to seismic loads,modes start yielding frequency below shift. If you are interested in studying the problem,then easy approach is to check each mode shape and investigate the member that is going in unrealistically large displacement. Solving this member's connectivity inadequacy will solve your problem.

Where did you get this formula? See second link below for how to establish relationship b/w plastic moment and elastic moment and how to find max load. 1) Page 269- https://books.google.ca/books?id=df7R9rT3nmUC&pg=PA269&lpg=PA269&dq=plastic+moment+capacity+of+fixed+end+beam&source=bl&ots=G_6gbccs2A&sig=4Sk9vDgG9Zid2bT3ubiYz195Bys&hl=en&sa=X&ei=0t-dVbaJHML1-AGTs6iYBQ&ved=0CCIQ6AEwAg#v=onepage&q=plastic%20moment%20capacity%20of%20fixed%20end%20beam&f=false 2) http://www.steel-insdag.org/TeachingMaterial/chapter35.pdf

As you know that we allow the yielding in the flexural members. In shearwall, we also allow flexural yielding but do not allow shear yielding. We also do not want the brittle failure we always like to have ductile yielding. In case of shearwall we want the flexural yielding at certain locations. We can not allow the yielding at unwanted locations. When earthquake pushes a shearwall (structure) in one direction the in shearwall there will be Tension on one side (one corner) and Compression on the other side (other corner). This can be reversed. We do not want the shearwall to fail in brittle form and specially at corners. So code required that concrete to be confined by the horizontal reinforcement. In this case the fc' of that corners increased significantly and there will be no yielding at these locations. We need the shearwall to be yielded so we provide minimum flexural reinforcement in the NON BOUNDARY ZONE ELEMENTS. So that the shearwall can yield at the middle locations in case of earthquake. The remaining reinforcement ( Total Flexural Reinforcement - minimum reinforcement) is provided in the BOUNDARY ZONE ELEMENTS. For this actually we need to check the strain limits obtained by Non Linear Time History Analysis but code also provides a method to calculate boundary zone lengths. So thats the reason for confined zones. The length of Boundary zone also depends u[on Thanks Muneeb

Hello Everyone,

General Basement Wall Design. take a unit strip, if your basement wall has a slab on top, you can treat it as a propped cantilever with Ko (Coefficient of Static earth pressure: as wall cant move to Ka state for failure).. If cantilever, design for lateral loading with Ka(Coefficient of active earth pressure). Significant Vertical Load If you have significant vertical load design it as a beam column and use ACI wall provision for min/ max reinforcement.