If you are interested in solving the question I have designed an RC transfer beam for ULS its span is 12.5 meters and it is 1.6 meters deep and 0.75 meters wide. It takes a load right in the middle (x1=6.25 m) of a magnitude 2000 kN @SLS and a distributed load of 78 kN/m @SLS .
During the design the tensile reinforcement found is 7365 mm2 with fy=500 N/mm2 and Fc = 50 N/mm2 .
I want to figure out how much it deflects ? Robot structural analysis does not do that for deep beams btw. I consider this to be a semi-deep beam.
Dear Dren,
There still missing data, slab thickness and end fixation of transfer beam
Anyway, assuming that slab thickness is 150 mm and the beam is simply supported at the ends, the deflection could be calculated as follows:
beam gross inertia for (T) section with effective slab width (12 ts + bo) = 2550mm is 0.37 m4
the cracked inertia of the same beam = 0.087 m4
the effective inertia = 0.091 m4
for Fc = 50 N/mm2 , Ec = 3.3 E+6 ton/m2, then (EI) = 3.0 E+5 ton.m2
own weight of beam = 0.75 x 1.6 x 2.5 = 3.0 t/m
total distributed load = 7.8 + 3 = 10.8 t/m
then the deflection = (5wL^4 / 384EI) + (PL^3 / 48EI) = 0.0386 m
So, the theoretical deflection is 39 mm
To considering the creep effect, the sustained load should be known and the also the amount of compression steel, anyway it is about 1.8 to 2.0 times the short term deflection, hence the total long term deflection is about 2.8 to 3.0 x 39mm = 110 to 120 mm
Practically, you have to consider some other factors such as:
1- Construction stages, the transfer beam will carry all the own weight of the 1st floor, then then next floor load will be carried by a combination of transfer beam and the 1st floor , the load of next floor will be carried by the combination of the transfer beam and 1st & 2nd floors and so on. besides that all walls, finishing and live loads will be carried by a combination of the transfer beam and all the floors. So the actual deflection should be less than the calculated.
2- Practically. the monolithic connection is semi-fixed support not simply supported, hence both actual moment and deflection are less than the calculated.
To get more accurate calculations, you have to use FEM model and consider construction stages, cracked sections and creep effect. you may use SAP200 or ETABS
I hope that answers your question
regards
Dren,
Ahmed's answer is good. You should certainly consider cracking of the beam, and time dependent loading combined with various permutations of Youngs Modulus to allow for creep. A comprehensive analysis would consider deflections due to self weight and other loads immediately after casting - noting that self weight deflection will occur at early age strengths. EC2 has a rigorous methods that involves calculating curvature along the beam, albeit you can avoid the numerical integration aspect by applying 'K' factors.
You can also determine using classical approach of of structural analysis, because the philosophy of deep beam is almost same as the conventional beam, only difference is that the load level is very high (columns load as point load of the number of story transferring the load) and because of that the size of the beam is quite big.
Usually in design office still many peoples check the deflection of transfer beam by hand calculations as well
Please check the following reference.. it might's assist you in your question … Regards…
https://waset.org/publications/10001029/investigation-on-an-innovative-way-to-connect-rc-beam-and-steel-column
- Badges
- Science topic
- Similar topics
- Engineering
- Civil Engineering