I first dis­cov­ered the power of ar­chi­tec­ture in Florida, where my sprawl­ing ex­tended fam­ily used to gather for sum­mer beach va­ca­tions. The thirty-or-so of us would pack into three or four rented houses for a week of fam­ily bond­ing over card games, beach hang­outs, and din­ners. Each year a dif­fer­ent one of these houses would be­come The Place to Be.

These gath­er­ings had rep­re­sen­ta­tives from every part of the po­lit­i­cal spec­trum, with ages rang­ing from new­born Baby Liam to “Happy 80th Birth­day!” Grandpa Leo. Throw into this mix a few vague, deep-seated grudges based on who bul­lied whom as chil­dren, and you couldn’t get the group to come to con­sen­sus on any­thing. Yet, be­fore Day Three, some­how every­one would have tac­itly agreed which house to focus on for that year’s fam­ily gath­er­ing.  As a kid, I strug­gled to com­pre­hend what force could have enough power to unify this un­ruly group.

It was the houses them­selves that had this ef­fect. Each year, the group of Zah­n­ers had the same goals: be near the ac­tion, hang out with your fa­vorite cousins, and play lots of cards.  The house that best ac­com­mo­date these goals rapidly be­came The Place.

This sim­ple rev­e­la­tion first opened my eyes to the power of ar­chi­tec­ture. If the lay­outs of houses could hold such ir­re­sistible sway over a group as vig­or­ously stub­born as my ex­tended fam­ily, what other ef­fects did ar­chi­tec­ture have on our lives?

How En­gi­neers Think about Build­ings

I had a struc­tural en­gi­neer­ing pro­fes­sor who liked to say, “En­gi­neer­ing de­sign is not ‘How big is the beam?’ but ‘Should there be a beam?’” That is, while a build­ing’s struc­ture is gov­erned by build­ing codes with thou­sands of pre­scribed rules, the struc­tural en­gi­neer’s main con­cern is not the mere ver­i­fi­ca­tion of these reg­u­la­tions. After all, it is much faster and cheaper for com­put­ers (or in­terns) to plow through this litany of re­quire­ments. What, then, is left for the struc­tural en­gi­neer?

The an­swer lies in the struc­tural en­gi­neer’s most fun­da­men­tal tool: the con­cept of a “load path.” The idea is sim­ple: how does a force, ex­erted some­where on a struc­ture, make it to the ground with­out break­ing any­thing? For ex­am­ple, con­sider the load path for the weight of a Zah­ner cousin (let’s go with Beth) play­ing cards in one of those Florida houses. Beth’s chair is sit­ting on a hard­wood floor.  The boards in the floor dis­trib­ute the weight of her and her chair to the closely spaced wooden beams below. The ends of these beams rest on the base­ment walls, which in turn sit on the house’s con­crete foun­da­tions. The foun­da­tions bear on the soil below, trans­mit­ting the weight of my cousin (and every­thing else in the house) down to the earth it­self. The load path, then, for any force on that floor is:

floor­boards

↓

beams

↓

walls

↓

foun­da­tion

↓

earth.

Now let us con­sider a less ob­vi­ous ex­am­ple: Beth, sit­ting in the same chair, but this time on the sev­enth floor of a medium rise build­ing. This build­ing has yet to be de­signed, so there are many po­ten­tial load paths that could keep Beth up in the air. She could be sit­ting in a much taller ver­sion of the same wooden house with the same sim­ple load path. Al­ter­nately, she could be on a con­crete slab which hangs, like the deck of the Golden Gate Bridge, from huge ca­bles sup­ported by even larger steel tow­ers. Both these op­tions, like an in­fin­ity of oth­ers, are per­fectly valid.

How­ever, each choice of load path has its own con­se­quences. There are en­gi­neer­ing con­se­quences: a seven story build­ing sees a lot of wind, so what hap­pens in a big storm? Will Beth’s perch be­have bet­ter in an earth­quake if it the floor is light­weight wood or heav­ier (but also stur­dier) con­crete? How do you con­nect one giant beam to an­other any­ways? Then there are ar­chi­tec­tural con­cerns: while a seven story tall stone pyra­mid would be an ex­tremely sta­ble base on which to play Spades, the ar­chi­tect’s vi­sion for the ideal lobby may not call for a blank wall of stone. Fi­nally, mon­e­tary cost is al­most al­ways a con­cern to the one foot­ing the bill. How dif­fi­cult (and thus ex­pen­sive) will it be to build? Is there a dif­fer­ent op­tion that would use less ma­te­r­ial?

The struc­tural en­gi­neer’s job is to se­lect load paths out of this jum­ble of pos­si­bil­ity and con­se­quence. Once a load path is de­ter­mined, a com­puter can an­a­lyze it and op­ti­mize every link in the load-path chain; to use my pro­fes­sor’s ter­mi­nol­ogy, once the en­gi­neer has an­swered “should there?” the com­puter han­dles “how big?”.  Thus, the en­gi­neer’s pri­mary chal­lenge is de­vel­op­ing the in­puts: of the in­fi­nite num­ber of ways beams, ca­bles, slabs, columns, and trusses could be or­ga­nized to sup­port Beth, only one load path will best sat­isfy the owner and ar­chi­tect while still main­tain­ing gen­eral com­pli­ance with physics. De­sign, for the struc­tural en­gi­neer, is find­ing that best so­lu­tion.

Ex­am­ple

Rem Kool­haus and Joshua Prince-Ra­mus’s Seat­tle Cen­tral Li­brary has evoked a tremen­dous pub­lic re­ac­tion since open­ing in down­town Seat­tle in 2004. Some hate it (it looks noth­ing like a tra­di­tional li­brary: way too mod­ern) and oth­ers love it (it’s very mod­ern: it looks noth­ing like a tra­di­tional li­brary!), but no one doubts that it makes a pow­er­ful im­pres­sion. What role did the struc­tural en­gi­neer play in the cre­ation of this Seat­tle land­mark?

With the Seat­tle Cen­tral Li­brary, the de­sign team sought to pro­vide Seat­tle with a build­ing that, like the best of those Florida houses, would draw peo­ple in and pro­vide them with a fo­cused place for in­ter­act­ing with each other. The cen­ter­piece of this strat­egy of com­mu­nity in­volve­ment is “The Liv­ing Room.” The Liv­ing Room is the first place you come to when you enter the li­brary from 5th Av­enue. The ar­chi­tects en­vi­sioned the Liv­ing Room, like the com­mon rooms of those Florida houses, as the cen­ter of the ac­tion.  Un­like the com­mon rooms of those Florida houses, this Liv­ing Room cov­ers nearly an en­tire city block, with seven floors packed with books and peo­ple above.

How­ever, when you first enter the Liv­ing Room, you are obliv­i­ous to all this weight. In fact, all you see is open space and nat­ural light from the glass walls and cen­tral atrium, with only four or five thin columns scat­tered around the edge of the build­ing. How was the de­sign team able to achieve this sense of open­ness and light given the phys­i­cal mass and weight of the floors above?

The an­swer lies in cre­ative load paths. Let’s move Beth’s card game to one of the study ta­bles hid­den within the stacks of the “book spi­ral” sec­tion of level seven. As be­fore, the weight of her chair goes from floor to beam. How­ever, at this point the load path di­verges: in­stead of sim­ply mov­ing down walls to the foun­da­tions, the force in the beams trans­fers to gi­gan­tic four-story trusses ring­ing the out­side of floors six, seven, eight, and nine. These trusses gather up all of the load from these four floors and con­cen­trate it into one or two points on each side. Slen­der steel columns, sloped to match the fa­cade, sup­port these few points, car­ry­ing the con­cen­trated load down through the atrium and past sev­eral other floors to the foun­da­tions be­neath the Liv­ing Room. By sup­port­ing the whole mid­dle sec­tion of the li­brary on those few steel columns, the en­gi­neers man­aged to es­sen­tially sneak all of the weight of the shelves above down through the Liv­ing Room with­out hurt­ing the ar­chi­tect’s vi­sion of open­ness and light.

De­vel­op­ing this un­usual load path was an it­er­a­tive process in­volv­ing many rounds of col­lab­o­ra­tion be­tween ar­chi­tects and en­gi­neers. The ar­chi­tects knew what they wanted: an airy cen­tral space with the stacks hid­den above. En­gi­neers are prob­lem solvers: they knew there was a way to turn the ar­chi­tects’ vi­sion into a build­able re­al­ity. As the de­sign evolved, the en­gi­neers helped in­form the ar­chi­tects on the many trade-offs pre­sented by dif­fer­ent load paths. For ex­am­ple, the four-story trusses that en­cir­cle the mid­dle floors only work if the edges of those floors all match up. These trusses help re­duce the num­ber of columns going through the Liv­ing Room so, since a min­i­mally ob­structed view from the Liv­ing Room was one of the ar­chi­tects’ first pri­or­i­ties, they chose to align the mid­dle floors. As the de­sign pro­gressed from rough con­cepts to its final, ready-for-con­struc­tion state, the ar­chi­tects and en­gi­neers made hun­dreds of these types of de­ci­sions.

This is a gross over­sim­pli­fi­ca­tion: I didn’t even begin to de­scribe all that thought given to what hap­pens when an earth­quake hits and all of those books start shak­ing. If you’re ever in Seat­tle, swing by down­town and I’ll give you a full hour-plus tour of how care­ful en­gi­neer­ing helps achieve the ar­chi­tects’ goals for the li­brary, some­times by hid­ing the struc­ture and other times by putting it on cen­ter stage. Until then, con­sider this the the­sis of this essay: ar­chi­tec­ture has power, the re­al­iza­tion of am­bi­tious ar­chi­tec­ture often re­quires tal­ented en­gi­neer­ing, and thus the role of the struc­tural en­gi­neer is to fa­cil­i­tate the cre­ation of pow­er­ful spaces.