Where is the most stress?

In designing and assembling a masonry building, the engineering work can provide helpful insight which is simple and powerful.  

For example, if we consider the masonry building I'm currently completing, it's insightful to ask: where is the highest stress in the building? Where is the highest compressive force, squeezing together?  Where is the highest tensile force, pulling apart?

The engineering for this building was done by Cheng-Ning Jong, PE.  He has some familiarity with my company's masonry system, since he helped compose, file and prosecute all of our patents.  We've worked together for several years and have a good rapport, a comfortable back-and-forth as we discuss, develop and fully articulate ideas.  

Mr. Jong's most critical role, in my opinion, is the detailing of the reinforcement and the size of the concrete footer from which the stem wall is laid.  A 'footer' is the base of the building, typically located in an excavated trench.  Here's a picture of the footer, with the first few block being arranged for the stem wall:

A stem wall is the bottom section of all the vertical walls buried below the ground, sitting on the footer.  Here is a completed stem wall for a room:

This building has arched masonry roofs, domes, half-domes, flying buttresses, arches meeting at intersections; there is a lot of structural configuration, rebar, weight, stress and so on within the building structure. Here are some architectural drawings, showing some of this detail.  Our architect for this building was Robert Ferry, AIA, RDP.

So if we consider this entire structure, where is the most stress?  Where is the highest compression?  Where is the highest tension?

The highest compression occurs at the bottom of the stem wall, where the stem wall meets the footer, on the outside of the building.  Why?  The entire weight of the building sits on this point.  In addition, the vertical wall acts as a giant lever, translating any thrusting force from the masonry roof and increasing this force by the length of the lever, or wall height to this location. This location, at the corner of the stem wall and the footer, wants to act as a hinge on which the lever of the vertical wall acts.  The highest tension occurs at the bottom of the stem wall, where the stem wall meets the footer, on the inside of the building.  The same lever action of the wall wants to pull up from the hinging on the outside, a mere 8 inches away: the wall thickness.

It's useful to note these areas of high stress.  It makes one pay closer attention to the detailing of rebar, rebar placement, connections, centering, etc., when you are consciously aware that the building you're making will have these high stress locations.  Build accordingly, get it right.

Sestina

As a child I became enthralled with masonry

and entered reverently great halls of stone

and marveled at structures made of block.

How was it made, this wonderful building?

Who were these people so skilled with mortar?

What had become of this lost art?



The cathedrals of Europe showed me this art.

I was lucky to see this bold masonry

and contemplate the skilled slingers of mortar.

How did they figure and know that a stone

could be cut such a way to construct this building?

All this amazement at stacks of block.



As I grew older the wonder of block

seemed to vanish with the lost art.

Daily surrounded by boring new building,

concrete blocks stacked in straight-walled masonry.

Gone from my sight were wonders of stone,

just boring-ass buildings, institutional mortar.



Gone from my mind were wonders of mortar,

gone too was thought of carved block;

when I looked on the ground an occasional stone.

Painting and drawing replaced my lost art.

Carpentry, plumbing, drywall and masonry

all seemed the same dreary task used in building.



As an adult I threw pots, and was soon building

giant architectural vases: assembly without mortar.

A house out of clay was my goal, without masonry,

still far removed from thought of block.

Twisted, turning and long was this art

for I would return to the skill of built stone.



How could it be done, to build wonders with stone?

Using modern methods and materials for building

to reclaim this lost and once lofty art?

To assemble a vaulted roof with mortar?

When all that was left was rectangular block:

a mass-produced world didn’t want good masonry.



I thought of art, casting concrete as stone,

realized masonry was still a key to good building.

Alas I found mortar, and secrets of triangular block.