Howard Roark

Codes: ACI 318, ASCE 7-10, UBC -97 Units: SI Drawing and Detailing: AutoCad and Revit Structural Analysis software: ETABS 2015, SAFE 15. (SP Column and Tekla Tedds for quick checks) Detailing Manual: ACI Reinforcement Detailing Manual (Reinforced Concrete), Zalim Steel Manual (Steel Structures) Foundation Design: Reinforced Concrete Foundations - Brain J.Bell Personal Favorite: Tall Building Structures; Analysis and Design by Bryan Stafford

In a dual system, you'll design your shear walls to cater for lateral loads and moment resisting frame will take care of gravity loads. Mostly in dual systems, it is considered a good practice to make your moment resisting frame system strong enough to withstand at least 25% of total base shear. So here's what you can do; when designing walls against lateral loads, (EQ and Wind), assign moment releases to beams. This will mean that all lateral forces are being taken up by shear walls only. As for your Moment resisting frame design, delete shear walls and in your Static Earthquake load cases (ELF), assign 0.25 scale factor instead of 1. This will ensure that your moment resisting frames are being designed to account for 25% base shear as well, along with gravity loadings. (You can call this emergency backup) Perform above procedure and you are good to go I hope this helps.

This is not possible in this case. I can't provide shear walls along extreme short sides. Previously, I wanted to perform Pushover analysis but that's not an option anymore. Since Pushover analysis takes into account only the fundamental mode, assuming it to be predominant response and does not consider higher modes, my analysis based upon Pushover won't provide a reliable estimate of deformation demands. (It is recommended to have modal mass participation around 70% for 1st mode) to effectively estimate deformation demands. Now, I am thinking of performing Time history analysis. It will be great if you can recommend me some valuable research papers, books or lecture series on this topic.

PSCE ( Pakistan Society of Civil Engineers) is another great option. It was introduced recently and response of society members has been good. There's a lecture every month and speakers are mostly from industry having vast experience. Engr. Rizwan Mirza (one of the best structural engineer in Pakistan) is a part of BOD and is very keen on introducing productive learning environment for civil engineers. https://psce.org.pk/

Since rectangular shape is most susceptible to torsional stresses, for given plan of building, 1st mode as torsional mode now makes sense to me. To counter this, I added shear walls at extreme end of shorter side of building, and my fundamental mode switched from torsional to translational mode (as expected). But later on, had to shift the the position of shear walls in Y-direction (Lx= X axis, Ly= Y-axis), due to architectural reasons and that's when torsional irregularity kicked back in. If there is any other better alternative, kindly do suggest. I am all ears. Eccentricity between centre of mass and centre of rigidity is well within limits of ASCE-07.

Hi there, I am currently working on a 20+ story building (For educational purpose only) having dual resisting system (Moment resisting frames and concrete shear walls located in center). I intend to perform Non-Linear Static Pushover Analysis to capture non-linear response of the structure and to study Demand/Capacity ratios for in-elastic response of structure. However, when I performed Response Spectrum analysis, I got 1st mode of vibration as "Torsional mode", which doesn't make sense to me. Story-drifts are restricted as per code's limitations. Also Torsional irregularity checks are also okay (Considering eccentricity between center of mass and center of rigidity). Base shear for both, Equivalent Lateral Force Procedure and Response spectrum analysis also matches (approximately equal). Since, Pushover analysis is applicable to structures whose response is dominated by its first mode of vibration (Which isn't the case here), although my first mode appears to be in rotation, my gut feeling says its translational. I am attaching Modal participating ratios, any sort of help is appreciated.

Hi there, I am interested in performing "Performance Based Design" for a 20 story building. I'll be performing "Non-Linear Static Pushover Analysis" for my model. Until now, I have decided to go with "Displacement Co-efficient method". I will be using ETABS 2017 for performing Pushover Analysis. While assigning plastic hinges, I have an option of using ASCE 41-17 (Seismic Evaluation and Retrofit of Existing buildings". I would like to know what would be a better estimate for relative distances for plastic hinges in case of beams, columns. Any input concerning assignment of hinges to beams, columns and shear walls is highly appreciated. Normally it's taken 0.05 and 0.95 or 0.1 and 0.9. What's your opinion on this? Secondly, it would be great if someone can recommend me a book or some good source to understand how to characterize building using performance levels. Any sort of help is appreciated. I have recently graduated and joined a structural design firm, so kindly guide me, considering me a beginner.

JazakAllah "Simple Structure" for explaining in detail. Your explanation of difference between Major load bearing walls and Minor load bearing wall did the trick for me. It would be great if you can share the source of these images, where you have highlighted how using certain formulas, load can easily be approximated on slab sides.

Hi there, I have recently joined a design firm and was assigned a task of designing wall footing. My senior told me to use "Tributary Area Method" for this specific task. He gave me a list of formulas for various cases such as load transfer from slab to exterior short, exterior long, interior short, interior long beams etc. For rectangular slab sections, these formulas are quite easy to implement, but in cases, where slab isn't rectangular anymore, I don't know how to distribute load in order to get approximate the results. I have attached a pic below, in which I have to design wall footing for bath and kitchen as well. Kindly help me in understanding how this method works.

I am working on modelling of "Nicholson's Obelisk" (located in Taxila city) in SAP2000 for identification of its dynamic characteristics and mode shapes as well. This is how structure looks like. This structure is made up of Granite stones only. I haven't modeled a "Solid model" before, I have been trying to model this structure for past few days but have been unable to model it. Problems I am facing are following: 1- In SAP2000 which section property should I use for modelling this structure? Should I consider a wall section or slab section? 2- Should I opt for some other software instead of SAP2000? 3- How can I model the tapering of the structure in software? After getting fed up using SAP2000 for modelling, I tried ETABS for modelling base of the structure but the structure didn't read any object and this is the error displayed But when I modeled the base in SAP2000, this was what I got I have to submit this model by Monday and it's last deadline, so any sort of help regarding modelling of this structure would be highly appreciated. Let me know if you have want more information concerning this structure. Thanks.