7 stories mid-rise. 5

[mronlinetutor]

This is a 7 stories mid-rise building. Steel moment frame for girders. Beams are simply supported on both ends. Beam end released. Stairs momently framed. Lift momently framed. Parking is actually floor beams that are simply supported on both end and beam end released.

This building is far from being built. It is still in the conceptual stage where I am acting as a conceptual designer, preliminary architect, preliminary engineer, and draftsman. Due to my lack of experience, I have to ask senior engineers to help me to design this building. This building will eventually be given to prominent architects and engineers for a redesign.

I am using Midas Gen 2014 and Can-S16-01 Canadian Code for design. I have girders, columns, and bracing that do not pass the code check by Midas Gen 2014. I know how to do the code check but I don't know how to do the optimal design. Enclosed is some information on my project and my questions are: "How to get all the steel members to pass the code check. For the girders, columns, and bracings, Midas gen cannot find a replacement section from the code to satisfy the code check. In columns and bracings, Midas Gen 2014 set the tensile strength to Fy=0 because I defined them as solid sections. I later use a very large column from the American code and Midas Gen 2014 gives them a tensile strength of Fy=50ksi, but the column and bracing's area does not have any larger area sections that can replace. I guess I can try them as a built-up member.

I have enclosed the Midas Gen 2014.mgb file and the related Docx files.

Please comment on them.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

 

[RPMG]

Fy is not the tensile stress. It is the yield stress for flexural, tensile, and compression checks. I believe it is 44 ksi in Canada for all sections.

I hope that helps with your design checks, but you have bigger issues here with your reliance on computers and "optimal" mindset. Try over estimating the axial and moment requirements for one girder and one column, and then size them using the manual, by hand. And then make everything similar.

 

[dik]

I'm currently using CSA S16-14 for steel code and G40.21-350W is common (50 ksi) although 44 is also common for angles, channels and plate. I'm not sure what the jurisdiction requirement for S16 is, but I've been using the S16-14 for a few years. For a preliminary design, I'd use a quick portal approach if rigid framed and just tributary areas for braced construction. The site doesn't seem to allow me to upload an excel file for some reason. Not even zipped...

Dik

 

[JLNJ]

What is your lateral force resisting system?

 

[human909]

If you want better answers more pictures and diagrams might help.

Like RPMG said you really shouldn't be relying on the computer to optimise the design. It can be a handy tool often once you get the concept right but you seem to be using it far too early in the design.

Also as JLNJ said have a look at your lateral restraints. If you have an unstable or barely stable structure then basic member size optimisation runs often won't fix instability issues.

 

[dik]

try again... these are *.xlsm files. It worked... treating the archive as a directory.

Dik

 

[TLHS]

dik,

300W plate is still the standard, but it's gotten to the point where you can reasonably specify 350W channel and angle (and you may be getting it even if you specify lower grade steel)

https://www.cisc-icca.ca/new-cisc-handbook-features-350-mpa-channels-and-angles/

Not that I'm usually loading that kind of section to a stress where it would matter.

 

[mronlinetutor]

Enclosed is a word file containing the image of the building. The building is 7 stories plus roof and a total of 144' high. Each story is 18' high. The building uses a moment frame system where the ends of the girders are moment welded into each other. But I don't think that is enough to resist the lateral movement. Should I introduce a concrete core for the lift at the center of the building to resist the torsional vibration of the building? Should I introduce shear walls in the X and Y directions to resist the lateral load? Should the building better off using concrete instead of steel? Currently, the building has a vertical Howe and Pratt Trusses as bracings on four faces of the building.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

 

[mronlinetutor]

Here is more information. Enclosed are two images of the building. The top image is a side elevation view showing the vertical Howe and Pratt trusses. Below is a top view of the building showing the layout of the beams and girders.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

 

[human909]

So what exactly is the question here?

 

[BadgerPE]

I think you would be better served to sit down with your senior engineers and ask them your questions. It seems like you are trying to wear a lot of hats without having enough experience to make some of these relatively basic, but highly important preliminary decisions. They will have a better idea of how they want this building framed and it will save you the trouble of redesigning down the road. Also, don't fully rely on a design program to layout the building for you without having a solid understanding of load path - especially your lateral.

Out of curiosity, what type of building is this that it has 18' floors all the way up?

 

[dik]

TLHS; "300W plate is still the standard"

Please re-read my posting, "although 44 (AKA 300) is also common for angles, channels and plate." I do work for several fabricators and either 350 or 300 can readily be obtained. If nothing is specified, I default to 300 except for rolled sections.

Dik

 

[r13]

You should mark the failed members, and indicating the loading condition that causing failure - gravity, lateral wind/earthquake..etc.

 

[mronlinetutor]

Thank you for your input. I act as a real estate developer. Since I have a degree in structural engineering, I thought I should have an idea of what my project looks like before I talk to the investors and then to the architect.

Yes, you are right. The vertical Howe and Pratt trusses are only bracings. It does not resist lateral road and torsion. So I have decided to change the project into precast, prestressed concrete. I will introduce an inner concrete core and an outer concrete core. The girders will be prestressed and the beams and floor are ordinary concrete. The inner concrete core and outer concrete core provide resistance to lateral loads and concrete loads.

The building is 18' high per stories with 12' high being the wall and 6' for ceiling to hide the girders and ductworks. I don't know how thick the inner and outer concrete core and the outside wall is going to be. Is 3' thick sufficient for the inner and outer core and the outside walls for 8 stories mid-rise including the roof. The building is 144' high including the roof.

Enclosed is a picture of the concrete core, girders and outside walls.

Please comment on it.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

 

[dik]

18' per storey seems awfully high; 12' seems more reasonable.

Dik

 

[BadgerPE]

Plenty of 144’ tall, 10+ story, steel buildings out there with braced or moment frames. 18’ is a ridiculous floor to floor height and you will likely get laughed at by any investors that work on this type of development. We recently completed a hotel that was 8 stories of steel with braced/ moment frames and was just under 12’ floor to floor.

I suggest you hire a real structural engineer to perform a basic structural layout for your project. Work with that person to develop the most economical layout that maximizes your usable space (read revenue) in the footprint you are allotted. Your most recent “decision” to make this a PC building doesn’t do this, at all, and could cause foundation issues depending on soil types present.

While your education is in structural engineering, it sounds like you have no real practical experience in it and it shows. Therefore, it would be wise money spent to hire somebody that makes you look good in front of your clients/potential investors. We are not here for that.

 

[spieng89]

I second BadgerPE, in that it'd be best for you to hire a structural engineer to advise you on the development. Even looking at your floor beam layout, it's not economical from a construction standpoint as your girders and filler beams are flip flopping throughout the floor plan. I think this level of design may be pushing your knowledge of structural engineering a bit too far. There is no harm in paying someone to do a job they have been trained to do.

 

[mronlinetutor]

I am going to hire a structural engineer to do the design. But the accounting book must be balanced. I am not going to put money up in advance. I am not going to get any money before the presale so I have to do the design myself.

I have a degree in structural engineering and I have experience in large scale engineering projects. I worked on the Millenium Line which is a post-tensioned guideway train line. I have experience in precast and prestressed concrete. I worked in a concrete plant. I also have experience in large residential projects, steel frames. I also have experience in large hospitals.

I have used Autocad since the 2.56 version. Now I use Autocad 2010 and Autocad Lt 2020 to do the drawings. I use Midas Gen 2014 to do the structural design. Midas Gen does the displacement, force, and stress diagrams. It does natural vibration mode shape, response spectrum, and time history analysis. It also does push-over analysis, code checks, and optimal design. Once you give the members an initial size, it will select the members for you. Also, I am well learned in finite element analysis.

You are right, I am going to hire a structural engineer to do the design, meanwhile, I do the conceptual plan. 18' ceiling is too high. I settle for 14' because of the girder is 3' and the ductworks is 2' which means an 8' ceiling. I want a 10' ceiling for esthetic.

The building is 200' by 200'. So is a 40' column spacing good? It is impossible to do a prestressed girder and precast floor at the same time. So the building is going to be in situ concrete.

The building is square and symmetrical. The building has 2 concentric cells, first core, and a second core.

Please comment on it.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

 

[dik]

Explain the circumstances to the consultant and see if he can provide any input 'on spec' with the potential that the project may go ahead. I suspect many professional associations frown on members doing it on spec, but there are likely some consultants that might.

Dik

 

[mronlinetutor]

Will you do it "on spec?" Dik.

The project will proceed after money is collected from the pre-sale. But it takes a long time to sell all the units. There are about 122 units. Each unit is about 1000 sq ft. Some units are bigger and they sell at a much higher price. The goal is to do an estimate on the project and working out how much each unit sells for.


There is no money now.

More input is appreciated. If anyone of you is interested in the project "on spec", I am very happy to give the project to you.

Meanwhile, I have the layout drawn. Enclosed is the layout.

Please comment.


disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.