Bam Earthquake Observation 1

[JAE]

It appears that many if not all of the buildings in Bam, Iran, were made up of load-bearing masonry wall structures.

This is perhaps a very poor system to use in a high seismic area but this leads to some questions -

Was Bam considered to be high seismic to begin with?

Does Iran have building codes that deal with seismic in the first place?

Were many of the buildings built a long time ago and thus were not ever brought up to any current level of seismic resistance?

Is this area of Iran in an economically backward condition such that home-building could only be accomplished with masonry load-bearing walls?

I can understand that this was an ancient city (the citadel that was ruined was a tremendous loss I'm sure) and that many structures were simply old wall-type buildings.

It's just that 25,000 people dying? That seems very very high compared to similar events in California and other areas of the globe.

Any observations on this?

 

[dik]

and was the quake triggered by the recent bombing in Iraq?

 

[ERV]

JAE,

The construction in the area is mainly mud bricks (hand made, sun dried). Very primitive constuction, no building codes to speak of. The material is very heavy, thus any type of colapse is catastrophic. This is also a very poor (economically) area.

Yes, this is a high seismic area.

The recent quake in Cambria, California killed two people due to colapse (unreinforced masonry) and the quake was the same (releative) magnitude. Although not all quakes are created equal in respect to ground motion (sliding as opposed to uplifting). A quake with sudden uplift can compress, then create tension on the members or components as it releases. This is particularly devastating to unreinforced masonry or brick type construction because it literally separates the components. On the other hand sliding motion is more dependent on the natural frequency of the structure and brick type construction may fair better (not much).

 

[Qshake]

I follow much of the earthquake news and reports (engineering, of course) from major earhquakes around the world. In doing so, it is pretty obvious how well we have progressed with our system in the US. For that matter, how well any developed country has faired in public safety in extreme events.

In many respects these areas are lacking the fundamental resources necessary to live let alone build a sustainable environment.

The building material has is always the case, a function of what's available. Out in the desert there are no trees, no plentiful stone formations, no raw materials. As such redundant timber framing construction is out of the question. Also out of the question are the materials requiring manufacturing such as concrete and steel.

As we know, the roof makes up the largest percentage of the load in residential construction and it is that load being excited by the earthquake. With little or no positive connection to the walls these deathtraps simply collapse burying the occupants.

There have been several major earthquakes in the middle east in recent years. The death toll is always high and the single most resonating contributor is building with poor materials.

Of course, beyond the engineering aspects of the death toll is the lack of resources to rescue and managing disaster aide. Thus disease becomes problematic as well as tending to the injured and homeless.

It seems that we've done well with our built environment, how about determining what these people can do with what little they have so that they may reduce the death toll. For example, if you must build with mud-brick whats the best way to avoid collapse. The UN or Red Cross or Missonaries could help with that.

 

[JAE]

It would be interesting to know what the primary mode of construction was for all those collapses in Bam; and then determine if there is a simple way to allow the brittle failure to occur without collapse.

I'm thinking about some kind of cable suspension system built into the roof to allow the diaprhragm to fail in shear but still create a cantenary support to let the occupants get out OK...similar to ACI's Chapter 7 Structural integrity stuff.

 

[dik]

I suspect for many of historic structures that the weaker ones have been destroyed over the ages and that those that fail have been weakened by previous quakes, the buildings have been modified, or the new quake is of a much greater intensity.

I haven't seen any of the quake data from the Bam event; but from what I've heard the quake was of unprecedented intensity.

With historic masonry structures, the jointing between the masonry units fails and there can be a significant internal damping, the materials are often lightly stressed (large mass, but a large area that is loaded), and simple but redundant structures. These are likely the main reasons that historic masonry structures are still standing in quake zones. There is still the problem with the stiffness imparting large forces as well as the mass itself.

Not knowing where and when the next seismic event is going to happen, I'm not sure it's possible or practical to 'reinforce the world' to reduce the number of fatalities or the damage. Even in areas, such as California, with the knowledge and financial resources to protect against levels of activity, there are, relatively speaking, a large number of fatalities and huge costs stemming from relatively small earthquakes.

Also, in developed areas, there is an infrastructure in place to assist against disasters that is mobilized with minutes (hours?) and not days... as in some out of the reach areas...

 

[Qshake]

I agree we can't reinforce the world, but for me here is the catch...

We've long since made it over the hump of positively anchoring timber roof beams in masonry pockets or timber floor beams in the same. Once the problem was identified, the solution was pretty easy - provide a positive load path. As a result, many benefits are derived from one action. The roof support is tied into the walls, the walls are less likely to be excited out of phase, and since it generally stays together the occupants are safer than in the older conventional method.

I realize that is a simplistic look at it, but it seems that the overall problem is not what to do, but how to get those who are ignorant toward seismic mitigation educated to help one another. The next thing is to make sure someone is providing a level of assurance by noting that the appropriate measures have been made and were done right.

My last gripe is this, we've educated a lot of international engineers, who for the most part never seem to dispense of the information. It seems that many are still here or have gone to other locations but have clearly not used that education to help the less privilaged.

 

[ishvaaag]

Certainly lack of effective connection is always some kind of built-in risk. And this not only in earthquake regards, but ordinary ruin. The problem we see in the earthquake's death tolls is anywhere else as social (national e international) dysfunction causing much physical and mental pain. The world is far from perfected even for human exploit, and our inability, lack or will or whatever is visible in that the knowledge (and many times the means) are present but a will and a social structure conductive to the actualization of this benefitial reality is not. On the other hand some have pointed to the facts of that we have to work more time to live than hunter gatherers, and as well that humans once they have had (historically) the chance have elected to reproduce at bigger rates instead than ensure the more fruitful and happy lives for the as many then living. This may make sense as a species to ensure by sheer number its continuation, and this oblivious to the pains suffered by important numbers.

 

[dik]

BBC Link...

http://news.bbc.co.uk/1/hi/world/middle_east/3363125.stm

 

[JAE]

I doubt that the "quake-proof" house illustrated at the bottom of the article is all that quake-proof. In fact, with a concrete roof, I would have a hard time feeling safe within during a quake.

 

[dik]

I wouldn't be there either... <G>

 

[ERV]

Hmmm,

Hollow masonry on stone rubble, supporting a reinforced concrete roof (at least it has a rigid diaphragm). Anything to tie the structure together? Sounds like another disaster! Contrary to seismic engineering and building safety.

I suppose maybe it is safer, they are only single story, maybe only half as many people will die in each structure.

 

[AlohaBob]

The principles of mechanics still apply to unreinforced masonry. It's just that with higher lateral loads, the look of a properly designed wall would likely be thicker and normal practice in these parts would deem excessive.

I'm sure structural engineers could prevent these catastrophic death tolls. I'm sure it's a matter of a problem with a country's leadership in providing for their people's needs. Building safety just isn't a priority. I suspect a great number of the people who are killed are illiterate. They haven't a clue about the future. They are likely trapped in efforts and concerns just to meet their daily needs. The dangerous housing meets these peoples immediate needs expediciously.

 

[Qshake]

Alohabob, I agree about the leadership point you bring up. It takes more than simply putting engineering into something up front. It takes diligent adherence to proper construction techniques and maintenance.

I would like to point out though that masonry is about as far from the ideal homogenous and isotropic material we can get to.

 

[AlohaBob]

Thank You Dik for the link to story and pictures on Bam Iran.

There's a prototype dimensions to the buildings. Something like a modular pattern. There's a lack of pilasters evident in photos. The walls look too thin for what I would expect to see for high seismic and unreinforced masonry.

The quake proof house and it's rationale appear dangerous. Where did this come from and why if it were untested or uncritiqued is it proposed safe? Under the circumstances, wouldn't the journalists exercise prudence in what they publish and at least verify a building design with a trusted professional?

 

[anka]

There is reinforcement in the walls of the prototype building. The proper method is putting reinforcement through the holes in the hollow bricks, and than filling the holes with concrete, thus creating reinforced columns.

 

[AlohaBob]

With such tremendous loss of life, and so many structures just typically reduced to rubble, there's a serious flaw in design concepts used here.

Greater loss of life is associated with lack of ductility. Ductility in turn is associated with lighter structures. The evidence says things just crumbled. Perhaps ductility can't be achieved with the bricks being used.

If the basic bricks are too susceptible maybe straw or a fiber material in the adobe mix would improve the characteristic way they fail. Was something like this used?

If plain mud brick must be the preferred method, I think of the pyramids. They have a wide base and stand the test of time. Then again, there aren't any pyramids in Iran.

Maybe in the debris, there's evidence that points in a direction of what can work. I hope past mistakes aren't repeated. These trajedies seem all too common there.

 

[AlohaBob]

There's a bunch more photos from BAM on NPR National Public Radio website. They were posted last weekend.

These photos provide a much better basis for a discussion of structural issues here.

 

[Qshake]

I have seen some additional photos on the Bam earthquake and was surprised to see some more contemporary steel structures. Of course, there was damage to those structures but overall they didn't fail catastophically. I was amazed though since I understood most of the city to be mud-brick construction.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[cyrusf]

25,000 people died because they didnt know what to do if there was an earthquake becuase their goverment never educated them.