Expansion Joint In Seismic Zone 3 Building

[Waqas Haider]

Assalam o alaikum..

My building is in zone 3 and it has a 2 inch expansion joint in it... So my building is divided into two blocks. Now I m worried when my structure will go under seismic excitation, Whether both blocks of structure will behave exactly same and will have same frequency of vibrations or will both of them can move towards each other causing collision.. Maximum story displacement for my structure is 0.81 inch. and I have assigned it value of R as 8.5. So maximum inelastic response displacement will be 0.7 x 8.5 x 0.81 = 4.82 inch. which is more than expansion joint. Both of blocks are NOT SYMMETRICAL. So both may not be having same stiffness. 

[EngrUzair]

W. Assalam.

 

In principle, in order to avoid pounding effect (collision of the two buildings during an earth quake), you will need to provide an expansion joint that would be a larger than the maximum drift of both the buildings, at the expansion joint location.

 

I have read somewhere (and If I remember correctly), width of such an expansion joint is LESS than the sum of the maximum drifts of the two buildings. I will have to search for the reference, however, to give you exact relation.

 

You may also go through this post http://www.sepakistan.com/topic/1411-expansion-joint/, containing a good discussion as well a couple of nice references on expansion joints.

[UmarMakhzumi]

Please also read:

http://www.sepakistan.com/topic/109-building-drifts-in-etabs/

http://www.sepakistan.com/topic/1341-ubc-seismic-drift-limits/

Uzair is right. I don't remember exactly but I believe the minimum distance between buildings should be equal to square root of sum of squares of max inelastic displacements of individual buildings. Its is UBC 97. You can find it easily.

Thanks.

[WR1]

Dear Engr. Waqas, I dont think 2" expansion joint will be sufficient for a building in seismic zone 3. But other things do matter as well for example; how many stories? etc

 

In ASCE/UBC/Australian codes, seismic separation should be SRSS of inelastic displacements. that is delta = [ (inelastic detla of building 1)² + (inleastic delta of building 2)² ] ^ 0.5

 

Remember that these delta values should be at the same level. For example if a building is 9 story high and adjacent building 3 story high. You have to calculate expansion joint at level 3 of both buildings.

 

Ofcourse you need to check expansion joints at all other stories too (Level 2, Level 1 and basements) if displacement on those levels is more than level 3 (due to high seismic weights or anything).

 

Please also remember that usually in softwares you consider X or -X directions for seismic analysis (and Y / -Y)

 

take the max from X and -X and multiply it with Cd/I (for ASCE) or 0.7R (for UBC) to calculate seismic movement of that building. Do this for the second building and then SRSS will give you final value.

 

HTH

[Waqas Haider]

I have once Done this SRSS in previous office when our new building was to built near an existing building. So we did this under the title SEPERATION OF ADJACENT BUILDINGS from UBC97. Now in my case, my maximum inelastic displacement is 5.3 inch at roof. so SSRS gives me required separation 7.5 inches. Now i m worried it will seem weird to Provide 8" expansion joint because between corridors of upper stories etc, how will i cover it. More over, should i also provide expansion joint in footing? 

[WR1]

No need for expansion joint in footings...But dont consider it final answer..Discuss with others too...

 

Regarding 5.3 inelastic displacement at roof..yes you need 7.5in gap but first ask why 5.3 inch? That means 132.5mm. Improve your framing. Is your building like 120m high? How many stories? And how much is W and base shear in terms of W?

[Waqas Haider]

My building is just two story building in quetta. And I had provided expansion join in footing but this is not working. Footings get over stressed under columns. Increasing size is not working. I ave provided combined footings but still fail. So now i am thinking to eliminate expansion joint from my footings. Can i eliminate it? My main concern is for thermal stresses. When isolated portions from super structure shrink/expand, can footing handle this movement?

[UmarMakhzumi]

There are different recommendations for expansion joints in different books. I have seen no joints up to 200 feet in some text for RCC buildings. Anyways, you can do analysis for thermal differential case and see how much moment gets induced in your foundation.

Visit the link below for information about carrying out thermal analysis.

http://www.sepakistan.com/topic/1367-effect-of-temperature-changes-on-buildings/

Thanks

[Waqar Saleem]

i am told once that no need to provide expansion joint in raft/footing . i provided no expansion joint in raft and provided 2" expansion joint in the building,so parallel columns along the joint were failing the raft in punching.but senior engineer said its ok columns will not punch.

[UmarMakhzumi]

i am told once that no need to provide expansion joint in raft/footing . i provided no expansion joint in raft and provided 2" expansion joint in the building,so parallel columns along the joint were failing the raft in punching.but senior engineer said its ok columns will not punch.

You should always do your due diligence. Most senior engineers in Pakistan have limited knowledge.

Never listen to such people as they breed ignorance.

Thanks.

[WR1]

It would depend. Edge columns usually dont have problem in punching (they carry half load as compared to the interior ones). But again there is lot of moment. So it depends upon loading and span. I dont see much problem in edge columns as far as punching is concerned for usual spans and loading.