Structures 101 is designed for architecture students; it is a collection of structural concepts, rules of thumb and precedents collected in response to student questions. Do I need columns? Where do I need columns? How big should my column be? While these are apt questions, they can detract from a larger conversation about, and indeed the seamless integration of, structural systems with an architectural concept. My hope is that this growing (and by no means exhaustive) collection of rules and images can enable simple decision making and an increase in structural fluency. 

I have endeavored to keep things simple, and to that end, I have not provided exhaustive text on concepts. References are included wherever possible for your further  investigation. I would highlight that any "rules" presented here are more so guidelines, than actual rules. These guidelines may suggest approximate column and beam sizes sufficient for an architectural plan or section, but sizes could easily be shifted to become slimmer or heavier based on the desired architectural expression. Ultimately, a civil or structural engineer will consult on your project if it were to be built (barring some exceptions) and would complete a set of calculations and/or computational studies to size your structural members and optimize your structural system. 

The collection is divided into a few common structural topics for clarity: Gravity Systems, Lateral Systems, Structural Hierarchy, Materials. However, it should be noted that a fluency in all topics is recommended to enable a structural dialogue. As an architect works in plan and section, so to does an engineer work in gravity and lateral systems.

Lastly, I would like to emphasize the importance of building a structural intuition, which can not be done within the confines of this webpage. Build models and observe the built environment. Physical models, built with the same inherent structural system as your proposed architecture, are the best method for understanding if your structural system is working. Is the model difficult to build? Does it sway? Where does it deflect or collapse under loading? A physical model will answer questions on constructability, stability, connections, and more. Further, question the buildings around you. How is a balcony supported? Where are the shear walls in my house? How big is that office tower column? Learn from your built environment. You're in it.
GRAVITY SYSTEMS
Grids
Grids are a fundamental element of the architectural plan. They provide a means for referencing  plan regions and registering various drawings to each other, promoting an understanding of the proposed architecture. Notably, the structural grid is connected to or informs the architectural grid. Structural columns are positioned at gridline intersections. Structural walls are positioned along gridlines. Structural beams or floor systems need to span from column to column, or wall to wall. Sometimes the structural floor cantilevers out from a wall.  A regular grid suggests a constant structural floor depth, while an irregular grid with varying span lengths results in varied structural floor depths. Rectangular grids imply one-way systems; square grids imply two-way systems. A project can have multiple grids. While an architect should not feel confined by the grid, it does provide a natural means for establishing a spatial rhythm and internal layout.