@165thspc Michael, I’m not sure what to elaborate on but I’ll have a try.
Warning: Pretty dull non-modelling post follows.
In my neck of the woods, bricklaying is divided into three general types: residential, commercial and industrial. Industrial is the refractory guys, which is a whole different ball game.
I suspect the vast majority of the brick you’re seeing is residential and in general these are veneer walls that contribute to the appearance and weatherproofing of the structure and one other important element. By definition, they provide no structural support. It is possible to tie a veneer wall into a building in such a way that it adds structural support but then it is referred to as a face wall. Most of the veneer style of masonry work grew from municipal responses to the “Great fire of (insert your favorite big city here)”. I like London. The city Fathers would then decree that all new structures would have a masonry (brick or stone) facing to prevent the spread of fires and a veneer wall provided the easiest solution. Fire codes have changed over the decades/centuries but most urban centers have rules governing the flammability of exterior surfaces. In the time honoured tradition of turning necessities into virtues, brick facings became “stylish” and attractive and veneers are found on all sorts of structures whether required by code or not. The drawback to veneers is the requirement for a supporting back-up, a perimeter beam or a shelf angle. Single wythe structural walls only need a footing.
In the commercial brick world and before cinder block became common, many structures were built of single wythe fired clay brick as curtain walls, sheer walls, load bearing, interior sound dampening, fire or support walls. If you think on it, a cinder (concrete) block is nothing more than a really big brick. There’s no practical reason that block walls can’t be built with regular modular brick and for many years they were. Block walls ubiquity came about because a relatively small crew can put up a lot of square feet very quickly i.e. it’s cheaper. Brick is added to block walls (picture a school or a library) to protect the relatively fragile block from the elements and provide additional sheer and load support. These building are expected to endure and it’s worth the extra expense to the owner. Compare the weight of a pallet of brick to a pallet of block and you’ll get a feel for the durability and strength of each component. You’ll also recognize that a wood or metal stud wall behind the brick doesn’t have much of a chance of stopping a masonry wall if something causes a collapse. The brick wall has to support itself and anything resting on it. In this instance the studs, insulation, drywall etc are the veneer. If you look at a typical modern warehouse, it’s framed with steel with block running between the vertical members to counter shear and has an interior lining to suite the tenant. In older construction the vertical steel would have been replaced with brick columns, buttresses or arches as called out by the designer and the horizontal steel replaced by a masonry bond beam. Remember that as these structures go up all the wall elements are installed at the same time, each course including all of the elements and becomes a single monolithic structural wall. My grandparents stone farmhouse in the UK had a brick extension added long before I was born. A sort of mini barn with a lightly buttressed single wythe wall running up about 5m (roughly 16 1/2 ft) to the rafters and a heavy slate roof - plenty of load. These were not uncommon.
Modern multi-wythe walls are typically double wythe cavity walls with weep holes in the bottom course to allow the inevitable water to drain and not penetrate the structure. Sometimes they’re built a bit thicker to allow for utility chases or have a local thickening for beam pockets and what have you.Old multi-wythe walls, which could be ridiculously thick, kept the cold and rain out but referring to them as multi-wythe is a bit of a misnomer. Typically the outer and inner face would be laid in the traditional “line, level and plum” but everything between them would be a dogs breakfast of chipped and broken brick with a bit of mortar to hold it all together. Something to consider adding to a diorama.
Your observation on precision is quite correct. I was a second year apprentice the first time I laid a course of brick, put my level to it and went to tap the brick into alignment with the butt of my trowel, only to be surprised that every brick touched the level exactly as desired. Several thousand bricks later I could do that consistently as can any qualified journeyman (being a bit more accurate; you do run into the occasional bricklayer who really shouldn’t be allowed to own a trowel). No inspector or QC/QA will except a bowed or bellied walls for the reason you point out - it would buckle and collapse when heavily loaded. In that regard, double wythe or greater walls are much more forgiving of “rushed” craftsmanship.
As for dynamic loading, you’d be surprised at how much a brick wall can move and retain it’s integrity. This is mostly down to the mortar. Traditional mortar (pre-cement) was a mix of sand, slaked lime and water and was effectively self healing - those walls survived tremendous abuse. Cement mortars aren’t as forgiving but can tolerate remarkable load movement without failure. In locations with notable seismic activity (eg. California) specific mortars will be identified in the building code ( I believe a Type S, but don’t quote me on it) that are designed to accommodate significant movements. If it helps, you can imagine a brick wall as a concrete wall with really big aggregate. The mortar transfers the applied load to all of the brick in the wall and on to the foundation. Considering that the minimum acceptable compressive strength of a brick is about 3.5N/mm2 (a bit more than 73,000 lbs/square foot), brick walls have a lot of inherent strength.
I’ve rambled on far too long about a non-modelling subject and hopefully elaborated successfully. What it really boils down to is that a single wythe wall is fully capable of being a useful structural component in spite of appearances to the contrary and by definition all single wythe walls are structural except for the veneer wall. Welcome to the exciting world of bricklaying.