Hi all! Can you please help me to understand the behavior of gravity columns in seismic event?
After reading section 18.14 of ACI, I understood that it is okay for gravity columns to go to yielding under seismic event. If the demands on gravity columns exceeds the capacity during seismic event...
Hi all! Do we design the gravity columns using the load combinations that have seismic component in it? Aren't the gravity columns are designed to resist gravity loads only? Can you please make the concept clear for me?
I saw following load combinations being taken for the design of gravity...
Hi all! I am running into an error message while performing modal analysis using ritz vector. Please see attached image. My model works fine if I switch to eigen vector. Can you please help me understand what is the error here and how can we debug?
Hi all! Can you please help me understand the section 18.14 of ACI (Members not designated as part of the seismic-force-resisting system)?
Section 18.14.2.1 tells you to apply gravity load and design displacement. For the gravity columns, in computer model we will have pinned at the ends. This...
Hi! I am applying a response spectrum along x direction (RSX). The diaphragm should have the chords shown by black arrow but if I checked the sign of resultant forces both are positive. If I was applying ELF it matches the sign convention. I am not understanding why is this happening for the...
Hi all! I am trying to understand the diaphragm behavior for bare steel deck supported by joist (let's say at 6 ft o.c) on perpendicular direction. I think when structure is laterally loaded, deck should be provided with sufficient shear strength to resist the shear stress generated on diaphragm...
Hi all! My structure has precast sandwich wall (insulation in between two concrete walls) for lateral force resisting. How do you guys model this wall appropriately in ETABS? Any suggestions will be greatly appreciated?
Hi all! Lets say I have a beam element (assume similar to reduced beam section) which will be under compression so it has to meet table D1.1 for high ductile member. I am thinking since whole member will be in compression I need to satisfy this requirement at both section cut A and B (see fig)...
Why most of the T-section does not satisfy the width-to-thickness requirement of high ductile members (Table D1.1 of seismic provision)? I am trying to use T-section for the top and bottom chords of special steel truss moment frame and looks like most of the section does not satisfy. What type...
Hi! I am modeling a structure in ETABS. I tried two different model. One with rigid diaphragm and another with semi rigid diaphragm. Floor for my structure is modeled as a bare steel deck. For the case with rigid diaphragm my moment frames are not taking any forces. Can you please help me...
Why is the type of diaphragm influencing the time period of the structure? Time period of structure is related to the mass and stiffness of the lateral force resisting system. Where does the diaphragm action coming into play? I considered two different models: one with rigid diaphragm and...
I am getting higher time period of the structure for my 3D model (T=1.2 secs). From 2D and hand calculation, time period is around 0.14 secs. I also think time period is really high from my 3D model. Is there is a way to check manually how ETABS is calculating time period. This is the second...
Hi all! I am designing a special truss moment frames in SAP2000. I have pinned the ends of all truss members (see attached) and i think it should be like that. When I ran the model it gives warning message saying structure is unstable or ill-conditioned. Am I doing it correctly?
Please recommend...
Hi all! Can you please help me to understand the time period of structure?
I have a structure which has shear walls at all four sides as shown in attached figure and has gravity columns-beams in the central region to support gravity loads. Since the stiffness of the structure is provided only...
Hi all!
Can anyone please help me to understand and eliminate following errors in my model?
1> I am using deck sections in my etabs model. I am having error meassage related to this. It says:
Warning: Check meshing, At Story1 area F2 ( .75?% Reduction)
Why is this happening and how to eliminate...
How do you guys usually do the thermal analysis? Its a pretty big one story steel frame building which has metal roof deck. Do you guys use ETABS/SAP to get the stresses and forces? For metal deck floor what modifiers do you consider?
Hi all! Is it essential to define diaphragm in my model? How does ETABS apply auto seismic load (from ASCE) if diaphragm is not defined? I know it is a simple question to be asked but can you please provide me your insights?
For calculating the base shear of the structure which has shear walls on all four sides, do we exclude the weight of the shear walls parallel to the seismic force applied? For diaphragm forces (ASCE 12.10-1) mentions to include the weight tributary to the diaphragm. I think exuding the parallel...
Hi all! When I checked the information after model (ETABS) running my model, I found that the accuracy has been lost at couple of points. Can you please let me know what might be the reason and how to eliminate this? It is happening at the joint close to joist framing to a shear wall. Two closes...
Hi all! I am receiving warning messages and it is saying structure is unstable or ill-conditioned....I ran it using standard solver to locate the issues. Found out that the problem is with the joints located in the shear walls (see fig). Can you guys please help me what might be the issues with...
