masonry infill panels designed not to take any seismic inplane forces

[Oversee]

I am conducting a reference design of masonry infill panels inside a concrete frame which has been designed to seismic design category B. Masonry infill panels must be detailed in such a way that it will not perform as a shear wall under ground seismic movement. This might be achieved by isolating the masonry panel from the primary frame (UBC 97 method) but this will weaken its out-of-plane strength and the wall may fail as a result of internal wind pressure. I reckon a few concrete wind posts are needed together with horizontal tie bars to ensure its out-of-plane integrity. I am not familiar with American codes. Are there any codes/standards or good practice guides for this calculations/detailings. Another question is: is there any restriction on masonry infill panel deflection for seismic design?

I wish to thank you all in advance.

 

[mmillerpe]

If the concrete wall is designed to span vertically, and a connection is made at the top of wall that would allow for both vertical deflection of the frame above as well as allow for differential in plane horizontal movement you would not need the concrete wind post or horizontal tie bars. The vertical joint between the frame and masonry infill would need to be sized to accomodate the anticipated movement of the frame.

 

[concretemasonry]

Keep in mind that clay brick has a long term expansion and concrete has a long term shrinkage and creep, especially when loaded. This concept is the basis for the soft joint in brick veneer exteriors. On a 7 story concrete frame building about 20 years old, I saw an expansion of the continuous brick veneer of 3" is comparison to the frame shortening at upper story windows that were no longer operable.

It may be built according to current ideal assumptions, but will change over time to where the in-fill panels begin to take up and redistribute loads.

Many studies on the subject and behavior have be made internationally because this type of construction is common in multi-story apartments and commercial buildings. The lack of real original construction information on older buildings is highly variable. I do not know of any specific studies, but most of the work I heard about was from Central and South America where the constuction was common to produce old buildings today where the long term effects can be observed. It is avery complex combination of variable material properties and loading.

Dick

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

 

[Oversee]

Thanks for your valuable and prompt responses!

Wind post and horizontal bars will be required for this case. Wind post alone is not going to keep all blocks work together under crowd load and/or internal pressure as arching action is not going to come into being without a solid contact with the main frame.

I had ordered appropriate American codes for masonry infill panel design, i.e. TMS402/ACI530/ASCE5. Infill panels and wind posts will be designed separately. I will think about the issues arising from masonry creep and concrete shrinkage, i.e. gaps between two media will be decided after considering all these factors.

 

[DaveAtkins]

You don't need wind columns. As mentioned above, just design a slip connection at the top of the wall.

DaveAtkins

 

[Oversee]

Thanks Dave
But the wall is going to be 4.4 meter tall and over 8 meter long (this means I need movement joint to cope with temperature change). I have not got the American masonry code yet but I really doubt it can stand in one-way and also in a decent thickness.
My friend in the US said that typically two criteria would be required for my case:
1) Infill panel height <4m
2) Height/thickness<30
Shall I place a beam when the height exceeds 4m? Or satisfying the second criterion only is going to be sufficient.

 

[JLNJ]

Do you need isolation of the side of the panel as well as the slip plane at the top? Masonry tight to the columns must transmit a good share of the shear, even with the top free.

 

[Oversee]

Hi JLNJ
That is why I wish to place a wind post by the column (but with a gap) and this post, together with tie bars, will give an encastre boundary to the panel (its top is only restrained in horizontal direction).

 

[concretemasonry]

If you are concerned with the long term volume change, the in-fill material is important.

American codes are weak on the subject and may not address it because it is used quite rarely compared to other locations.

Clay brick are a problem because the long term effects of the material are different from the concrete in the frame. If concrete block are commonly used, the isolation situation is minimized because the CMUs have properties similar to the concrete frame. The block are usually cured when laid while the concrete frame will shrink as it cures. The construction process becomes a factor. On larger structures, the frame is usually in place long before (weeks) the infill is placed. For the more common smaller project the process is different and floor-by-floor construction is common.

On smaller structures (residential and 2-3 story apartments, the panel dimension are smaller and the masonry is used in interior walls the studies of performance have been very positive when the panels are not isolated. In a seismic event the panels work with the frame and translates the structure into a "bee-hive" or honeycomb structure with great rigidity. There may be some minor cracks that can be repaired easily, but with maximum wall spacing of 4 meters and poured in place concrete floor slabs, the life safety is not a problem and repairs are minimal.

In some countries, 20 story apartments in large complexes are built with interchangeable designs (6" loadbearing concrete masonry of different specified strengths or a frame of 6" thick by ??? inch columns with 6" CMU infill) on a single site of buildings.

Bottom line - The effects of the infill material (and its long term shrinkage/expansion) on the frame and then most importantly, the panel dimensions, since that represents the greatest area of the frame/panel combination, depending on the construction process.

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

 

[Oversee]

In the UK, vertical movement joints are the usual provisions to prevent the detrimental effect of masonry contraction. Spacing between movement joints varies according to the materials used:

Clay masonry: <15m (more frequent spacing of movement is required if different types of clay units are used. Or cladding is used.)
Calcium silicate masonry: 7.5m~9m
Concrete masonry: 6m~9m

Compressible joint is also required for external walls but required difference between spacing is greater than those required for contraction joints.

 

[csd72]

I would suggest you look to see if there is any eurocode guidance on this.

 

[DaveAtkins]

Your wall is only 14.4 feet tall (4.4 meters). You should have no problem getting it to span vertically for internal pressure. You may have to grout some cores, or use some reinforcing, but I don't see the problem.

DaveAtkins

 

[JLNJ]

It seems like a lot of the answers posted have to do with shrinkage or expansion of the infill material. This is not the question as I see it.

I see the meat of the question as how one details the panels so that they do NOT contribute to the lateral force resisting system.

I have a similar multi-story problem in hand in that the owner wants solid walls for hygiene reasons (food facility - no gaps or hollow areas) but wants to wait until the last minute to decide where the walls will be. Many of the walls need to be designed as removable (for future equipment openings) and/or don't extend all the way to the foundation. We agreed on a concrete frame rather than shear walls but we still need to detail a system whose walls either don't contribute, or if they do works with these "accidental" shear walls in place. It is turning out to be a real challenge - even in SDC B.

 

[csd72]

JLNJ,

Why dont you use a sacrificial drywall that can be replaced after an earthquake?

 

[JLNJ]

Owner doesn't want any voids. Studs and drywall are not really suitable for a food processing facility.