Replacing a removed masonry wall - seismic

[mikesg]

Dear colleagues,

I received a call from a client who has removed a 25cm (10") unreinforced masonry wall in his apartment. This wall is between two columns, the clear width is 3.60m (11ft 10"), there is an unreinforced door opening 90cm(3ft) wide on one side of the wall, which makes 2.70m(8ft 10") solid masonry panel. This wall goes down to the base and this is 7-th storey out of 11. The wall is made of bricks with vertical openings less than 25% and about 12mm (1/2") diameter which are usually used for masonry bearing walls or masonry shear walls. There are no RC walls and the RC space frame carrying the vertical loads is not designed as a seismic force resisting system.

Our city is in a high seismic zone (ag/g=0.27, IX on MSK scale).
By requirements of our code in order to allow removing/replacing/modifying a masonry wall the entire building has to be ananlyzed, but since preliminary analysis shows great discrepancies in the capacity versus demand, calculations will not give satosfactory results.

The bad deed is done. He has removed a wall that /at least by calculations/ participates in seismic force resistance.
Vertical loads are OK, there is a RC beam containing reinforcment amounts as expected for the imposed loads.

How can this be repaired before the next quake comes? A steel frame? Restoring the wall (concrete was poured afger masonry was made) - how to restore the bond? Other options?


I will be grateful if you share some ideas I can incorporate in the final solution - of course after analysis on my side and calculations accoding to our codes

Thanks!

Mike

 

[concretemasonry]

mike -

If I understand the scope of your problem, you have and older RC structure where someone removed one wall panel of a 11 story building that may have been built according to the codes and standards of the day. Because a wall (not structural) was removed it is now required that the entire structure be evaluated according to the new codes and standards. that creates the problem.

You now have two options:

1.Show the removal of a non-structural partition wall does not destroy the original approvals.

The removal of the partition wall is minor and does not change the structure Show the removal of the wall did not remove or change the building and get it "grandfathered" in as being allowable because the removal did not effect the compliance with the original code. construction and approvals. If you can show this, it would be a good solution.

The problems will be that a 10" wall is thought of as being monumental and important in the eye of the uneducated because of its appearance.

If you look at recent tests of this type of individual wall for shear resistance, it may show that it is significant but may be moot in the terms of a total structure. A lot of testing has been done to show that unreinforced masonry has a very high longitudinal shear resistance if it can be used or harnessed.

2. If the "grandfathered" approach is not acceptable, the other choice is to come up with an acceptable structural replacement in the form of a welded frame or using some diagonal bracing at the upper corners to create a steel frame to replace the supposed "non-bearing" structural wall element that was removed.

The problem will be to be able to recognize the shear resistance capacity of the removed wall panel by calculation or comparison to tests. Unfortunately, the number of tests for "hollow" clay tile laid withe cores running vertically instead of horizontally may be limited. The thinner walls are usually laid vertically for the use of electrical installation and the thicker wall are often laid with the "cores" horizontally because of ease of construction. I do not know what walls may have been tested.

It certainly sounds like a challenge. I owned a architecturally significant home with 10" hollow clay tile block laid horizontally and it is still a magnificent structure after over 100 years.

Good luck on the project. I wish I could provide some detailed sources, but my masonry engineering has been limited to concrete masonry.

Dick

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

 

[msquared48]

I would be very reticent to put in anything of the type other than what was removed due to variations in stiffness. Otherwise you will be affecting other elements of the structure, necessitating a total building upgrade. I am sure you do not want to go there.

Is there any means for a variance considering the ramifications here, especially being in a high seismic zone?

This structure has to be from the 60's or earlier.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[mikesg]

Thank you for your answers,

Our calculations show that this wall works a part of the structure and not a partition wall only /using tables that are a supplementary part of the code/. It contributes about 7~10% of the shear resistance of the affected level. I cannot claim for "precise" calculations, since masonry wall resistance varies greatly and is very sensitive to openings, but I am sure that this wall has been intended to participate in horizontal force resistance and removing a panel from it is not harmless.

The obvious solution is to rebuild the wall and he even has the original bricks still on site. I still cannot persuade him to do this.
The other thing I have checked is a steel frame that will have the same resistance and stiffness -I have calculated the deflection of the wall imposing a horizontal load /replacing the wall with a strut and tie system/ and then have applied the same load on the steel frame to check whether deflections are the same or lower.
I am thinking of an option to make a concrete panel with an opening /he wants an opening/ because it will be stiffer than the steel frame/especially if it is a moment frame/ and will make better bond with the old structure.

Thank you for sharing your opinion, I would be glad if someone who has encountered such an issue described how it was solved.

Mike