Concrete Frame with Brick Infills: Shear Wall

[sybie99]

Good Day,

Has anyone used a concrete beam and column frame structure, infilled with brickwork, as a lateral bracing structure in a building?

It is common to have a concrete column and beam frame work to form stair and hoist shafts and to then infill it with brickwork. To what extent can one use/design the structure to act compositely and together resist lateral forces?

In my case I have beams at 3m vertical centres to 18m building height. All infill brickwork is tied to columns with hoop iron ties every 3rd course. Usually a small gap is left between beam soffit and top brickwork, infilled with a soft joint.]

Would it be okay to have this gap filled with mortar to allow effective transfer of compressive forces? Concrete columns can be designed to resist all tensile forces.

I would like to hear from anyone who has used this system before, as I would think that the infill brick must increase stiffness of this frame, but to what extent?

 

[bookowski]

Don't know too much about these but we did some work in Haiti after their quake and it's common there so I did a bit of reading. Do a google search of concrete moment frame with masonry infill and you will find loads of papers and info on it - it's a well researched/documented system. It is common outside the US and unintentionally maybe even a common system when there is poor detailing of the masonry infill to maintain a separation.

My recollection is that you are trying to combine a very flexible/ductile system (frame) to brittle/stiff (infill wall) one. So initially the infill attracts all the force and forms diagonal compression struts with the frame acting only as a confining ring. It is possible that this compression strut shears your column off at the base. Alternately the infill becomes damaged quickly and loses most stiffness and the frame takes over. I don't think it's a desirable system for seismic unless you are in a situation where it's a local practice and you're stuck with it (again I have limited knowledge). All of the above is for seismic - for wind it's probably a lot more predictable of as system.

Try googleing 'confined masonry building' and you will get a lot of info as well.

http://nisee.berkeley.edu/turkey/Fturkch3.pdf

 

[concretemasonry]

syrbie99 -

That type of construction is very common internationally and there are many sources from different countries detailing the action and construction to achieve the desired results. The term "confined masonry" will provide many hundred papers on the subject. The key to the success is to use mortar between the mortar and the concrete or even casting a combination beam/floor slab to partially replace the plain beam. Since a masonry wall is a composite of masonry units (clay brick, concrete brick, hollow clay block, concrete block, etc.), general specifications suggest to use the lowest strength possible to carry the loads and maintain integrity of the wall because other properties are more important than compressive strength indicators that are commonly mis-used.

One thing you will find in the various papers is that the construction techniques are very important - 1. concrete before masonry, 2. concrete columns during building a story broken into two stages or 3. concrete beams poured with a slab after the columns and masonry panels are completed. Normally, the wall panels are unreinforced. because of the sizes. Most of the applications are from 1 story to 6 story cellular type structures.

Also keep in mind the papers are not from the U.S., but representative international construction and results through the years using many of the U.S. and European materials.

The important factor is that the term "confined masonry" indicates that the masonry is confined, so a soft joint has been shown to be counter productive and negative.

Dick


Engineer and international traveler interested in construction techniques, problems and proper design.

 

[sybie99]

I will not intend to use it to resist seismic loading, only normal wind forces or notional horizontal forces.

It seems there are two systems, namely rc frame with masonry infill and rc frame with confined masonry.

Each has different construction methods and performs differently. In my case I would prefer to have the rc frame built first and then the infill masonry. If anyone knows of a good piece of literature on the subject and how to design and detail I would appreciate you sharing.

I am inclined to detail the bricks to have no gap to columns on the sides or top, to create a rigid structure. I will then calculate compressive stresses at base of wall in masonry due to lateral load to be less than allowable compressive stress. On the tension side I will design the column to resist all tensile forces.