Load Path? Lateral Forces? So many numbers...
Behind every great work of architecture lies mountains of calculations and left-brained feasibility concerns. Pursuing both degrees in architectural design and engineering have exposed me to the amazing feats that common materials and methods can achieve when effectively applied.
Architecture is more than just napkin sketches. Architectural Engineering is actually just a lot of math.
The basis of nearly all principles and applications of architectural engineering is statics. In essence, for most buildings, the sum of forces in every direction ought to equal zero. If they do not, a building will move. Unless it is specifically designed to do so, a moving building is not a welcome sight.
Enter the structural engineer! A structural designer's goal is to work with an architect, their client, and their fellow architectural consultants to create a reasonable, economic support system that allows the owner's final vision as designed by the architect to stand proudly and safely.
An engineer makes use of a vast array of tools from building codes like the IBC, material-specific design manuals such as the AISC Steel Construction Manual or The Masonry Society 402, to comprehensive structural analysis software like RISA Floor and RISA 3D among many others. The overall process is an iterative, semi-empirical dash between various references, programs, and fellow engineers that results in a verifiably safe building with regard to gravity's ever-present pull.
Regardless of the chosen material or system, the loads remain the same.
Much like how Batman and the Joker will forever be adversaries despite their mutual dependence on each other for purpose, an engineer would have no meaning in the world of architecture without the very gravity, wind, and seismic loads that they work to combat. Long story short, if humans need even the most basic of shelters above their heads, something must adequately support that shelter and someone must be able to validate the support's adequacy.
In the world of architectural engineering, nearly every single (U.S. based) project starts from only a handful of sources, namely the ASCE 7-16 and IBC 2018 as of late. The American Society of Civil Engineers (ASCE) has produced the Minimum Design Loads and Associated Criteria for Buildings and Other Structures for decades in an effort to consolidate all of the sources for building loads and forces that must be accounted for in structural design. Simlarly, the International Building Code provides some design parameters and values for structural purposes as required for specific building types or materials.
Tools of the Trade: A Reminder to Thank Your Local Code Official or Standards Author
Once the design loads for a given building have been determined using the aforementioned sources, the number crunching can really begin. Based on what the desired structural system is for a building project, one or multiple design manuals or codes can be utilized.
In reality, the true unsung heroes of structural engineering are the authors of these comprehensive sources as well as the genius engineers and mathematicians that develop the countless equations, tables, and volumes' worth of information for a given material based on decades of empirical data and industry standard practices.
After Finding the Numbers, What Do We Do With Them?
Finally, once the particular design loads and material-specific methods are determined for a building project, the fundamental application can begin. Above are two examples of the many possible load cases for a simply-supported beam. The equations to the right of the diagrams are commonly used to determine the most important load-related criteria for the average member in a structural system:
Shear: an in-plane stress that causes the material layers to separate
Moment: a force applied at a distance from a supported point
Deflection: the amount of flexural bending that occurs under loading
The design manuals for the most commonly used building materials provide equations or tabulated values of manufactured or constructible members/systems that can then be compared to the highest values of shear, moment, and deflection. On a member-by-member basis, the most basic of rules states that a member's capacity should never be exceeded by the demand that a given load generates.
Basic Load Cases are simply the categories of loads, both gravity and lateral in nature, that apply to a given building project. Gravity loads most often consist of the weight of the building materials and the intended occupants while lateral loads are most often generated by wind and seismic activity. A building's structural system must be designed to safely carry loads generated by all load cases simultaneously in a safe and efficient manner so that they can ultimately be dissipated into the building's foundation.
The following projects provide examples of the structural design process for a building project: