BEAM ON TOP OF A WALL 2

[Ashikunde]

Hi friends, I'm new here but I'm glad to be here,

i was just asking how do you design a reinforced concrete beam on top of a wall ( or supported by a wall ) throughout it's length and it's supporting a concrete slab? what do i check? thanks friends.

 

[ishvaaag]

As an inclusion in the structure. If you include walls, beams, columns, slabs, long term settlement in your modeling (even if as a continuum, which always has some shortcomings since not corresponding to the actual behavior in many cases) you will see the included beam deform and get elements for design.

Tie-Beams like these were a big betterment of wood inclusions, since fitting to the rest of the building was much better, and so the likelihood of the overall structure losing the wanted geometry that ensures some known (or purportedly known) load path was diminished. In that role, included beams didn't need much reinforcement, say from 2 to 4 #3 or #4, you can see it in the masonry codes of the seventies' even.

Then, going upwards in height, we started to get cases of masonry walls unloading (sometimes through concrete creep, or just inability to sustain the loads) in the lower beams included in the floors. A pathology appeared with diagonal cracks from the bottom corners of masonry panels ... secondary equilibrium was attained with the included beams working as ties, but too late, you had the cracks already in façades. So corrective measures were introduced, first cut the number of stories that may unload on some façade beam. Usually this is done every 3 stories a horizontal joint (of course not forgetting to include as much fittings as needed to ensure stability of whatever built, say, under earthquake or wind). Second, calculate your included beam for the potential effects -imbued deformation- such unloading scheme may produce. One can go over conservative here but normally if the number of stories that may unload (load) the included beam is small, not much reinforcement results even if you count all the stories between joints loading in the lower beam. In the process, ensure that the limits of deflection for RC members as per the code are respected, long term included.

 

[ishvaaag]

Not to forget that if the beam is just part of the lateral force resisting system, even if not loaded vertically, it will be taking loads as a chord in diaphragm action. These are as well usually limited and the design is as per the chord forces.

 

[Ashikunde]

thanks ishvaaag for the post
but i want to know the procedure if im designing manually for example
1. i calculate the load on the beam
2. how do i decide on the size of the beam do i look at the openings only or what?
3. do i calculate bending moment considering the openings or how
4. calculate for shear and design

if you help me with this procedure i will be thankful assuming the building is a two storey building. ok i have to design a beam of 8m resting entirely on the wall with 2.4m opening in the middle part how do i do it, it simply carries 6 timber trusses each with a reaction of 10KN.

 

[Ashikunde]

or let me rephrase it in this way how do i design a reinforced concrete beam supporting slabs in a masonry building because there are no columns just the wall or the blockwork,

 

[ishvaaag]

Well, forfeiting bad effects of foundations, you will be designing your beam supported on the walls, certainly. Since your central span may turn out to be significant, you will need to examine the question of support and masonry stresses to the light of the pertinent masonry code. Normally, if the support in the masonry walls causes no special concern, one could select a depth for the beam starting from the span plus a depth and simply supported condition on a table for no need of checks for deflection in the reinforced concrete code, and simply then calculate the beam at the span as simply supported for the loads coming from the slab, live loads, and whatever at the window may cause. If the reinforcement is not much, most would elect to specify a constant section reinforcement for the whole front, not just the span.

If the fixity allows for it, maybe considering the beam fixed will be both more accurate and economical, and you may select the minimum depth according to the fixity conditions for the span.

Design of flexural and shear reinforcement is just to follow the reinforced concrete code, usually no particulars arise.

That just the outline, try to examine examples in masonry design manuals.

Models following my other entry if carefully built may produce better results and some appraisal of the effects of the deformation at the foundations, plus better assessment of the solicitations in the included beams and maybe the masonry panels.

 

[ztengguy]

If its continually supported, wouldnt you just check for bearing, and then check the wall? If it has any out of plane bending, then check that. Check your openings as a lintel design, fixed end moments.

 

[ron9876]

If you mean a concrete beam that is placed on top of load bearing masonry then I agree with ztengguy. Not much going on.

 

[ztengguy]

Yea, wasnt sure either. Can you do some sketches, so we are not missing something?