Ram Structural System 2

[gyroman10]

After strong recomendations, our firm finally bought bentley Ram structural System. I have used, staad, etabs, midas gen at various firms, and this is my first time with RAM SS, and i am surprised to learn RAM SS is incapable of assigning a two-way load distribution type floor deck to a simple multistory building model, modeled in RAM modeler. therefore load is not distributed to all four beam but is distributed through One-way, in direction selected when assigning the Deck to the floor slab. Is this correct? or am i missing something ? ?

 

[prsconsultant]

Yes. There is no two way deck modeling option in RAM. But you can achieve this by modeling some additional dummy beams and assigning decks oriented at 45 deg and 135 deg.

 

[gyroman10]

well then i model the slab assign it a deck of specified thickness and manually workout two beam loads and apply it to the beams ? would this be correct ?

 

[Taro]

RAM's capabilities are very limited in comparison to Etabs, et al. RAM is a very user-friendly program, but the list of things RAM cannot do is quite long. It is not a true finite-element solver. With a few exceptions, you are limited to simply supported, statically determinate structures. I use RAM for simple buildings but prefer more "powerful" programs for complex situations.

 

[TimmyH76]

RISA all the way!!

 

[gyroman10]

yeah but can RISA calculate center of rigidity ? this is very handy tool in locating shearwalls or bracings in the building.?
(just a question)

 

[Lion06]

RAM is worthwhile just for the 180 Load combinations it generates for wind seismic and everything else. Additionally, as pointed out, it gives very refined frame analyses. Will RISA consider the torsional effects of the center of rigidity not being in line with the center of mass?

 

[prsconsultant]

Call RAM tech support and they have a document showing how to simulate a 2 way slab action by adding some diagonal dummy beams and changing the deck orientation.

 

[abusementpark]

The great thing about Ram Structural System is that it will reduce the live load automatically based on the trib area it calculates and member classification. I guess, this is why it stays away from two-way action and keeps everything determinate.

 

[gyroman10]

prsconsultant

apparently Bentley dont have such document. Can you guide me a litle bit on how i can model two way loading using dummy beams

 

[prsconsultant]

gyroman10:

I could not find the documentation RAM had sent me few years ago. But, you can look at the attached sketch which basically shows how to simulate 2 way action. In a typical bay, model the column strips as beams. Divide the typical bay in to 4 quadrants using 3 dummy beams. Full span dummy beam would be along the shorter of the two spans. Model the flat slab with deck oriented at 45 deg and 135 deg as shown in the attached.

RAM in their documentation had claimed that by doing this way the column loads & moments would be quite accurate.

Let me know how this works for you. I will keep looking for that document and will post it if & when I find it.

 

[gyroman10]

prsconsultant

thankyou so much this helped a lot, now i dont have to calculate loads manualy. However i distribute load on beams via Traingular method of distribution, but strip method is also fine i presume.

Thanks again

 

[gyroman10]

By the way there is no dummy beam option in RAM. or is there ?

 

[abusementpark]

I think he means "other" beam.

 

[prsconsultant]

What I mean by dummy beam is that you define a beam with a small section (say 1"x1") with other material.

 

[gyroman10]

prsconsultant
i have tried your way, it may be good for column design but surely is not good for beams. do you use RAM SS to design complete concrete structures ? columns beams and footing ? if so then how do to you model two load onto the beams

 

[prsconsultant]

gyroman10

We use RAM SS for complete concrete design when we have a wide joist module one way system. When we have 2-way slab system, we export the RAM SS model data to RAM CONCEPT and design it there. All columns and foundations are designed in RAM SS / RAM Foundation.

Just curious what kind of problem did you see with beam forces? What did you compare the RAM beam forces to? If properly modeled I would have expected comparable results.

 

[gyroman10]

When suggeted method used, the beams are only transfered half the load they should be transfered to, and remaining load goes to the columns in form of point load, the beams are therefore designed for half the load. and columns recieve half the moment they should be recieving. I wrestled with RAM SS for one long week. Now i am calculating floor loads in form of line loads and applying it to the beams. even though there is a large room of improvement in RAM SS i still tend to like, or may be i have no other option ! this is the only software my company has. Also RAM does not design a beam for Torsion that was too a bit surprising.

 

[gyroman10]

what is the difference between gravity beam and lateral beam ?

 

[prsconsultant]

As the name says, gravity beams carry dead and live loads only. The frame beams are part of the buildings lateral system & carry gravity loads plus additional loads due to wind / seismic.