other options

[brillito]

Hi, I have a 2 story building design in steel (moment frame) but with the increase of the steel cost the building is not giving the right numbers. What other options can I consider. Shear walls, combining concrete with steel???. The building’s architecture allows to have the first level in concrete and then to continue in steel also the sreal wall option is arch. acceptable.

 

[civilperson]

Diagonal braces are the most cost effective if the architect will allow them. Round threaded rods in an X alignment,(tension only), are the cheapest of the diagonal brace types.

 

[gyroman10]

How about a concrete flat slab structure ? i think its the most economical up to 6 stories.

 

[msquared48]

Currently we are involved in a multi-family residential project over a PT slab where the upper residential units are being redesigned from light gage steel studs with shear walls to wood frame with shear walls, all due to $$$ difference in materials. No surprise with the steel costs...

Mike McCann
MMC Engineering

 

[brillito]

thanks everyone
One thing I want to be sure about. does the braces go from joint to joint, because if this is rigth then the will cut the open area (architectural openings) where wall are to be built. more details in attached drawing.

 

[hokie66]

Yes, braces go from joint to joint, unless the members receiving the braces are designed to take the brace forces, in which case you are back to a moment frame of sorts. Also, if the braces are tension only as civilperson suggested, you will need one with the opposite slope, but not necessarily in the same bay.

 

[jike]

This is often the challenge of our work: selecting a bracing system that is economical and fits with the architectural requirements. Moment frames are not always the best solution. Search for walls that you can hide bracing in. The next best solution is to find a wall where you can work around the openings.

 

[gyroman10]

Typically braces go from joint to joint, but not necessarily, it depends on your analysis and assumptions too. For example K-type Bracing.

 

[csd72]

You may want to politely suggest small modifications to the architecture that will make considerable cost savings. Some things like exit doors can be relocated to allow for mbracing/better spacing of beams/columns/better alignment of members.

It is usually best to discuss these with the architect first so you dont tread on their toes.

 

[Lexatus]

The Moment Resistant Frame Solution isn’t the best you can have due to its deformability (deformability check could coerce you to increase sections dimensions) and for huge detailing. But has a good ductility.

So you can choose a Braced Frame solution. If you go for CBF (Concentric Braced Frames) you will have small drift but less ductility if compared to MRF. And braces can occupy space needed by windows. But watch out, because you have:

- X-brace;
- K-brace,
- Chevron-brace (V-shape);
- Upside-down chevron-brace
- Single diagonal brace;

so, pick one of these that fits well for your architecture.

But I would suggest you to go for EBF, Eccentric Braced Frames. You will occupy less space and the “links” will provide you global rigidity and ductility (benefits from both MRF and CBF). I will go for it: EBF shear-type link (short eccentricity).

 

[msquared48]

CSD:

Some Architects stick their foot in their mouth so much, I never realized that they had toes!



Mike McCann
MMC Engineering