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The Joys of Keeping The Roof Up

It’s a fairly common scenario. Fresh off the plane and ready to get started on a project. On the way out to the project site you start to get a funny feeling in your stomach. No, it’s not that. You haven’t eaten anything other than airline food so far although Continentals ‘snack packs’ could certainly present a risk. What is making you nervous is the fact that none of the buildings here are built out of wood. Not a stud in sight. All you see is…. Confined Masonry.

Turns out, a good chunk of the world does not build with small dimension wood lumber. We in the United States do so mostly because our construction methods and industry developed around our most readily available resource. Wood framing is an extremely versatile system but it does have its drawbacks. One primary drawback is that you need a large supply of softwood.

 The way people build and what they build with is closely tied to where they live. Locally available materials, climactic conditions and cultural preferences all determine how and with what people build. For a good part of the world, that way is confined masonry. We often get questions about confined masonry, starting with : ‘what is it?’ So, in the interest of sparing people that sinking feeling, here is a quick primer on confined masonry. Sorry, nothing we can do about any other sinking stomach feelings.
 

In reinforced concrete frame construction in the US, a concrete frame is erected using formwork and staging and then the resultant frame is in filled with some material. In masonry construction is the US, open celled masonry units are used and then those cells are infilled with reinforcing steel and concrete at specified intervals.  In confined masonry, it goes the other way. The wall is built using some masonry material, like brick, and gaps are left where the columns are supposed to go. Steel reinforcing bars are inserted and the two open sides of the gap are sealed up with plywood or some other form material. Concrete is poured into the void in order to make a reinforced frame. The resultant reinforced frame, if done correctly, provides vertical and lateral stability far beyond what an un reinforced masonry building could provide.  Below is a sequence for the construction of a simple building. This is actualy the first stage of a prototypical house we designed for an Agros village. The yellow shading represents the concrete. 

Stage one: The foundation and slab has been poured with rebar poking up so that the column reinforcing can be tied into the foundation.
Stack the masonry, leaving gaps for the columns.

Stage Two: Place reinforcing in the gaps for the columns.  Place form work on each side of the gaps and form the first ring beam. Pour the concrete so that it fills all the voids, binding with the reinforcing and the masonry.

Stage Three: Stack masonry for next level.

Stage four: Reinforce, form and pour columns.

Stage five: Form and pour top ring beam.

Stage six: Build the roof structure being sure to tie the roofing into the ring beam.

 

The second question that often comes up, both from designers and from the occupants and builders, is: ‘Why go through all this trouble? It is more expensive and takes more time.” For a quick answer, look to Haiti and Chile. Earthquakes are a fact of life in much of the world and the consequences of poorly built structures are all too familiar. So what if you aren’t building in an earthquake zone? Well, are you building in a high wind zone? How about a possible landslide area?
 
The fact is, as a designer, you cannot abdicate the responsibility for life safety. You have to be the advocate for adequate structural design. In developing countries (and some developed ones) you can’t count on the building inspector to make sure it is being built right. Many times there isn’t a building inspector or if there is, a significant portion of his income comes from being paid to look the other way. Often projects we work on are in areas with no building department, no code and builders who are encouraged to make buildings cheaper by reducing the amount of steel and cement.
 
 
So, what do you do? You do it right. Yeah, its more expensive. Yeah, you could probably build two houses for the cost of the one you just built if you just cut down on the cement. But you won’t lie awake at night when the earthquake hits (and it will) wondering if the family living in the house you built, or the kids in class at the school you worked on are standing safely in a doorframe or buried in the rubble. That said, sometimes it isn't your call. When you don't have final control over how it is built the best you can do is advocate for good building practices. Be loud.
 
If you plan on using confined masonry and would like to find out more about it, we encourage you to look at some of the resources listed below. And as with all the information contained here, please use it responsibly. Know when to call in the experts. Engineers aren’t really all that scary.

 

First: A document put together by Richal Smith. We have had the pleasure of working with Richal in the past and I don't know of anyone who understands confined masonry better than him. Richal is a retired engineer in Seattle who devotes much of his time to working for Engineering Ministries International and Agros International. You might have seen him as he flew past your car on his bike. 
http://docs.google.com/Doc?docid=0AfNWXwrNk0BAZDN3cGg4ZF8wZ2h0OHp4OHo&hl=en
 
 
Second: A great description of the system from the City University of London
http://www.staff.city.ac.uk/earthquakes/MasonryBrick/ConfinedBrickMasonry.htm
 
 
Third: A report from UNIVERSIDAD NACIONAL DE INGENIERIA in Lima Peru
http://iisee.kenken.go.jp/net/saito/web_edes_b/construction_of_masonry_English.pdf
 
 
There are a bunch more but that should hold everyone but the engineers...

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