Visualizing Structure

Structures and Design

An important component of my design ability comes from my understanding of structures. Not just understanding engineering but understanding how science and math can be used as a tool to inform design. This understanding first solidified in graduate school over a decade ago and this is how I remember it.

Frank Lloyd Wright's falling water, compliments of Google image search for cantilever. When I look at this cantilevered porch I can see the forces of sheer, bending, torsion and deflection and how they've been hidden away inside the structural parapet/railing. I also see how it informed his design and was carried through to other areas of the house to give the structure and architecture continuity.

Phil Gallegos of UCD (University of Colorado in Denver) taught a very practical class and one of my favorites -- structures. After years of engineering math, physics and chemistry, it all finally came together. A practical application of the knowledge learned to date.

Structures is a very math oriented technical class keeping many with interest in architecture from pursuing the study. This 'fear of math' was very apparent the first day of structures class at UCD, but Phil Gallegos saved the day in the last 5 minutes of class when he pulled out a crusty piece of yellow bed foam in the shape of a beam with black lines on it and bent it -- changing my life forever!

Remembering back, it may not have been beam shaped or with markings other than water stains, but when he bent the CFB (Crusty Foam Beam) and talked about the top being in compression and the bottom in tension, I immediately had a visual for the internal loads developed as a beam sustains transverse loading.

Diagram of simple cantilever

What the CFB did in an instant inside my head was to create a mind's eye visual image of Tension and Compression--two forces that drive structures.

And from here everything else we learned made sense. It was easy then to visualize a cantilevered beam as half of a simple loaded beam turned upside down. As long as I abided by the basic principals and concepts like equal and opposite forces, component reactions and outermost fibers, I could always rationalize my way through any structural problem to locate the critical stress and strain happening within.

Diagram of point loaded beam

We moved on to other forces like shear, bending moment, deflection, and torsion and then on to more advanced topics like catenary arches, trusses and balanced sections for systems with two or more different materials. It did get quite complicated but I loved it and if I ever had a problem I just referred back to the CFB. Sometimes visualizing it on end, upside down, being tugged in multiple directions or being twisted, the CFB continued to provide me with the correct answers through visualization.

Overturning due to lateral loads and no hold downs illustrated.

Many of the lessons of structures are simple but not so obvious. Take Lateral loads for instance. Why would a house with all it's mass ever need to be held down. I did see the wizard of Oz but some quick airfoil calculations make it more than apparent that even with 100 mph winds not enough uplift is generated for a house to fly!

But they can tip over, and Phil showed us how! By looking at the centroid of any object (it's center of mass), the lever arm acting on this centroid and the force being applied, it's easy to see why you need hold downs on a building even if it's heavy; because a rigid box with a lateral load has an overturning moment.

I enjoyed structures so much I brought in other designs to analyze; designs I knew we wouldn't get to in a year of structures but that I wanted to know about. Phil was always willing to share his knowledge of more advanced topics with me, staying late to discuss hypothetical structural situations after class.

Left-a cantilever chair. The advantage here is the longer length of the structural member allowing for more controlled deflection. In this case suspension to make the ride softer.


How structures changed my design

It is here, in these conversations, where my thinking of spaces and structure morphed into one thought process. When I realized that the components of a building not only needed to inform each other, I also realized that I needed to design in more dimensions. To design not just in plan and section, but in mechanical, structural, environmental and building code, and that details needed to be developed, building materials selected, construction process refined during the entire process of design. That consideration for all these elements needed to happen concurrently and that good design meant iterating the design to reflect these findings.

A classic ship illustrating Corbu's point

So it was at this point in my education, half way through my design studios and in my second semester of structures when engineering and architecture became one. Since then I have developed a distinct and identifiable style for my architecture focused on the integration of math and art.

Corbu (Le Corbusier)

A refinery. Beautiful considering zero design was applied to it's aesthetics.

Examples of math, art and design.

Corbu talked of the beauty of ships. Due to stresses, manufacturing, and economy the designs are honest to their materiality, yet have simple repeating elements and variations to the elements based on needs and conditions.

One of my favorite types of structures are cranes, because it's so easy to see the structure respond to the different forces and to trace the loads. Ever since the CFB (crusty foam beam) I've been able to not just look at a crane and understand deflection, overturning moment, bending and sheer but by tracing a fictitious loading condition in my head I'm able to take a very good forensic look at how failure may occur based on my imaginary loading.

Left-A large crane where you can almost see the tension in the cables and the compression in the trusses. The trusses get bigger in the middle to respond to buckling and have small removable pins at connections that transfer all the loads with sheer. And, if it picks up a large load now, the leg in the back will want to life up so all the forces going down are on the front two legs.

How I use this knowledge over a decade later.

For years now, because of two semesters of Structures, two good books and one dedicated and knowledgeable Phil Gallegos, I've done the preliminary engineering on all my projects. I'll diagram the loading, figure my volumes and weights, trace the loads, solve beam reactions, calculate footing areas, point loads, size beams and check them for deflection, horizontal shear and bearing. And the I will go through and adjust my design accordingly.

Right-diagrams for a simply loaded beam. a)Loading diagram b)Shear diagram c)Moment diagram d)slope diagram e)deflection f)Phil never tough me what this one is!!

For as long as I can remember, I've been using Wendell Reed of Reed and Associates for my engineering. Even though I'm not an engineer and don't know the latest engineering codities (code + oddities), the fundamentals Phil left me with have allowed me to save thousands on engineering by doing this preliminary work. With these savings, I allocate more time to iterating and improving the design.

The Challenge When the CFB and the engineer don't see eye to eye!

But I do have a question for Phil Gallegos of University of Colorado and PE.

Left- On the structure being framed, there is debate between Wendell and I over the stresses driving the sizing of the steel poles which are perpendicular to the roof.

In the picture of the building being constructed, Wendell and I have had numerous discussions on which forces drive the design of the angled steel poles (photo of building under construction) Wendell insists that the steel pipe supports are driven by bending moment because the poles do not point towards the center of the earth (straight down). I contest that because there are metal hangers/connectors at the ridge end of the rafters and because this ridge is attached to a shear box, that they can't drop on this end but in fact they're hinged. If they're hinged, then they want to rotate and by having the steel posts perpendicular to the roof they are in pure compression and will fail by buckling, having no bending moment.

Another example of what I consider to be a hinged roof. The rafters are firmly attached with nails and plywood to an existing structure. The attachment at the house can't move up, down or out- if it weren't for the poles, it would rotate. So putting poles perpendicular to this rotation puts them in pure compression.