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ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

(OP)
Hello all I am a volunteer construction advisor. All ecuadorean architects and engineers recommend to install 40cm long steel rebar segments on side of columns(see image). My trip to the town closest to the epicenter showed that this practice is a complete failure. Any suggestion is welcomed.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

What used to be attached to them?

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

The leftmost column seems to be CMU[?] and it doesn't have rebar in it [from what I can see]. I don't understand what is meant by this practice of attaching 40cm rebar, like the person on the post above me said, attached to what?

Was there a wall there and it was used as a brace for a moment frame. I don't know if Ecuador is a high seismic zone, but that shouldn't be permitted where you have that such an irregular building that would obviously cause torsion in the building, not to mention that those columns see very slender for a highly seismic zone.

Middle column also doesn't show closely spaced stirrups [as req'd by most codes] it shows 1 from what i can see if i zoom in, at it doesn't to be larger than a #4 bar?

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

I was assuming we were talking about the lengths of rebar coming out perpendicular to the columns that used to be attached to something that's completely disintegrated. Maybe a wall panel, or beams or something.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

(OP)
Hello TLHS is right the lengths of rebar coming out perpendicular to the columns is a common practice in exterior concrete block walls. The empty space on wall is from concrete blocks that came down.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

(OP)
I have read most engineering and technical papers but never found one article to support the use of this building technique by engineers in this country. I can share more pictures that show structural failures that I found in the town. Liquified soil sank several high rise buildings. It is an incredible place to visit and study structures behavior in a violent earthquake as this was. I am trying to develop a pdf file for basic info as to the minimum structural requirements up to three floors. The UN did a video series on this matter for Nepal. They had to do it this way because there is not that many professionals in the remote parts of the country.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

Hello ladrillero,

were the rebars embedded in concrete ties? Maybe the 40cm rule has to do with the anchorage length of a rebar with diameter 8mm to 12mm in concrete (old codes in Eastern Europe specified an anchorage length of 40 times the rebar diameter).

This technique is used sometimes in the Balkans, in Europe (I have to mention that Balkans is a highly seismic region in Europe). Unfortunately, in most cases the use of this technique is erroneous. The only case in which this technique would be considered correct is when the designer has actually considered the effect of infill walls. In the Eurocodes you have specific provisions for masonry infill frames. When you analyze a such building, you have to consider some diagonal struts (i.e. the masonry wall) attached to the nodes of the main frame. You calculate an effective width of the strut, an effective stiffness and then you run the analysis. Nevertheless, there is debate in this field and research is still actively going on. Depending on the position of such infill walls in the structure, they influence the fundamental vibration period of the structure and they may induce considerable torsional effects.

As a conclusion, I would say that this detailing does more harm then good, unless the designer was well aware of the behavior of masonry infill frames.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

(OP)
Hello all thanks for replying. I have seen a shake table test done with a building that have reinforced tie beams and the the walls got destroyed and this was tested only at 6.8mw. In this case the town is at 25m over sea level and is located at the coast line. The soil liquified in several places. That tells me the 1 minute 20 seconds of 7.8mw was to much for certain buildings seating on loose soil. I'm including pictures of 5 floor hotel where I stayed once. I was on 3rd floor. I have read technical manuals and they all recommend tie beams on footings. I agree with it.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

Do the laws of Ecuador require that certain code provisions be met or do the building authorities rely on the engineers to use their own judgment regarding the specifics of seismic design?

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

Hello ladrillero,
I am sorry, I didn't get your comment. I asked you whether the 40cm bars were anchored in a small concrete tie (or call it strip, or belt or something else). I didn't mean to include foundations issues in this discussion.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

It looks to me to be typical Latin-American construction. Concrete column (lightly reinforced) with the bars in question used to anchor cellular ceramic blocks to infill the wall. The masonry is typically poor quality and plastered on both sides to form the finished walls. Very little seismic capacity!

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

Many studies have been performed on "Confined Masonry." The ultimate failure mechanism for "properly" detailed confined masonry buildings is diagonal cracking through the ground floor masonry infill which creates a weak story and amplifies the first floor lateral deflection for long lasting events. This is an overly simplified summation but the resources are plenty and easily found on the web.

Specific to this photo:
1. Columns for seismic (and everything else) should have 4 bars and column ties for the full height.
2. Out of plane buckling on the masonry wall needs to be resisted with reinforcement (ladder type in the joint or bond beam every 4 ft in height). Developing a rebar into "really good mortar" gets us this photo.
3. There is another practice of using a foam core wall with welded wire reinforcing sheets (electromalla) plastered onto the inside and outside faces to create the infill panel. I am not a fan of "really good plaster" either, but this would at least give some diagonal tension capacity to the infill wall.

RE: ECUADOR EARTHQUAKE BUILDING DAMAGE TEC QUESTION

@Teguci,

Some highly seismic places like Mexico banned the use of ladder reinforcement for resisting shear forces in walls. It's kind of tricky the behavior of 'confined masonry'.

I think the code tries to simplify everything but due to some provisions the design tends to be overconservative [adding a vertical confining member [read: column] @ every 3m min. for ex.], especially how it's done, but then again you see cases like this building in ecuador and it makes you wonder why it's not being coded to be more conservative so at least when they half ass the construction they end up with a more proper looking building, at least seismically speaking.



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