E NGINEERING A W A R D S O F E X C E L L E N C E

$10M OR GREATER, BUT LESS THAN $25M NATIONAL WINNER . The University of Arizona tephen Criswell S

y Large Binocular Telescope Enclosure b Mount Graham, AZ Photo

JUROR COMMENT “A precision structure, with very tight tolerances, designed for unusual loads—movement of the structure due to environmental loads, rotation of the telescope, and thermal loads—not usually significant for structural designs.”

he University of Arizona’s The enclosure structure is co-rotat- Large Binocular Telescope ing—it rotates with the telescope, Structural Engineer and Architect (LBT), located on Mount Gra- although by separate drives. To maintain M3 Engineering & Technology Corpo- ham in southeastern Arizona, accuracy of observation, the telescope ration, Tucson, AZ an optical telescope in structure must be independent from Engineering Software theT equivalent of a 12-story that the building structure. The main rotat- COSMOS/M rotates on a 38’-high circular concrete ing structure is a rectangular prism, 105’ . Tolerances for design by 95’ by 115’ high. The available site, Owner and construction varied from as coarse cleared within Coronado National Forest, LBT Corporation, Tucson, AZ as 1/16” to as fine as nanometers for the was limited by permit. The building foot- Detailer, Fabricator, and Erector optics. print needed to be minimized, resulting Schuff Steel Company, Phoenix, AZ, In addition to the basic loading crite- in urban-type construction. AISC member ria, several operational elements were With an overall building height of 168’ incorporated into the design of the rotat- above grade, the rectangular prism struc- Detailing Software ing enclosure including: bi-parting build- ture has a system of steel beams and col- AutoCAD ing and to allow observation, umns with braced frames to carry loads General Contractor a 55-ton overhead bridge crane, side down to a three-dimensional steel truss Hart Construction Management Ser- and rear ventilation , a roof snow- system supported by four bogie drive vices (HCMS), Safford, AZ melting system, a service , and assemblies. Some fabrication weighed access platforms for shutters, the eleva- as much as eight tons, while the load tor, and a weather station. transmitted to the support bogies was

May 2005 • Modern Steel Construction Photo by John Hill. approximately 2,000 tons. The bogies — Overhead crane: 55-ton capacity has several tight curves, limiting the rotate this mass at up to 2º per second — Seismic: UBC Zone 2B maximum length of a piece to 40’. to maintain alignment with the telescope. Steel framing forms a box with the All bolted connections were speci- Bogie assemblies are mounted on a cir- observing level at the bottom, two fixed fied as slip critical due to the dynamic cular steel track 38’ above grade. walls on the sides that carry the overhead nature of loads on the structure. Stress Displacement control of the struc- crane runway, and a fixed wall behind reversals are common during operations. ture for operating wind load cases was the telescope that houses the elevator. Due to the geometry of the structure, the accomplished by optimal use of diago- The two sidewalls and a back wall incor- sidewalls that support the crane rails nal stiffening of the structure. Survival porate horizontal rolling ventilation doors. will move laterally when the shutters are wind load displacements are controlled Two 33’-wide moveable shutters, one for opened and closed. Also, lateral deflec- by latch mechanisms designed to tie the each of the telescope’s 8.4 m primary tions due to wind will affect the operation moving parts of the structure together to mirrors, are “L” shaped. The vertical 93’- of the crane as the crane rail supports accomplish lateral stiffening and reduce high leg of each shutter forms the wall in move in and out. displacements to acceptable levels. front of the telescope and the 100’-long In order to control the deflections The rotating enclosure structure con- horizontal leg forms the roof of the box. within operational limits for seals sists of eight levels, including a bogie Open configuration lattice and crane operation, an exterior struc- level, a mechanical equipment , an and bracing with thicknesses less than tural skeleton was provided to both observation level, a visitors’ gallery level, 3/4” were used to minimize the thermal reduce the deflections due to shutter an elevator equipment room, a crane mass of the structure and to increase movement and wind loads. The unique access level, a meteorological level, and thermal response to air temperature configuration of the LBT enclosure com- a snow-melting roof. The design criteria changes. bined with the environmentally decreed were as follows: The fourth level is an tight site provided interesting challenges — Wind speed with telescope opera- interstitial space of the 16’-deep two-way to the structural steel design and erec- tional: 45 mph (shutters open) trusses consisting of steel wide-flange tion. Steel provided the flexibility and — Wind speed with shutters open: 90 chords diagonals and verticals. The light weight required for the unique func- mph (telescope not in operation) interstitial space houses the mechanical tions of the structure.  — Wind speed survival: 125 mph (shut- and electrical support systems for the ters closed) telescope. — Base elevation: 10,720’ above sea The LBT enclosure structural design level incorporated details to facilitate erection — Snow load: 90 psf on Mount Graham at 10,720’ elevation. — Ice load: 60 psf The access road up to Mount Graham

Modern Steel Construction • May 2005 E NGINEERING A W A R D S O F E X C E L L E N C E

$10M OR GREATER, BUT LESS THAN $25M MERIT AWARD

St. Martin’s Episcopal Church Houston

Photo by Christof Spieler.

Structural Engineer Matrix Structural Engineers, Houston Engineering Software RISA-3D RAM Steel Owner St. Martin’s Episcopal Church, Houston Architect Jackson & Ryan Architects, Houston Erector Photo

Steel Masters, Inc., Houston, SEAA by Mark Scheyer member General Contractor Tellepsen Corporation, Houston .

or the new sanctuary of St. Mar- Each steel frame, 80’ wide at the base Between the frames are tall stained tin’s Episcopal Church, the design and 87’ tall at the peak, carries the wind glass . To meet deflection team worked hard to capture loads for a 16’ strip of the façade. The requirements, these had to be braced to the form and details of a Gothic main columns are W27×146. Below 32’, the W27 columns. A steel frame around cathedral. Beneath the struc- the main columns are connected with the —fabricated to exact dimen- ture,F however, the buttresses and pointed moment connections and angle braces sions so the windows would fit in with- are anything but traditional. to the beams and columns of the aisle. out blocking—is attached to steel tubes Gothic was the owners’ Above 47’, the columns are joined to the welded to the sides of the columns. Sev- request. The design team’s job was to gabled roof truss, which is made up of a eral different distributions of wind were make it work with a $20 million budget wide-flange top chord and double angle evaluated to make sure the columns and a tight schedule. Work on design diagonals. Under wind loads, the main would not twist excessively under this development started in December 2000 columns bend in an “S” shape due to the load. and the building had to be completed fixity from the aisle frames and the roof The towers posed their own problems. exactly four years later. The challenge truss. No base fixity was counted The steel structure extends to 108’, and was to replicate, in modern materials, the on for strength calculations. With allow- above this are 80’-tall pre-engineered forms of an architecture based on load- ance made for some fixity, lateral deflec- steeples. Four W14×176 columns form bearing masonry. tion under 110 mph winds is less than the corners of the tower. Above 47’, the Several structural systems were con- 1/300th of the height. columns are connected with double sidered for this unconventional building. As soon as the steel frames were angle X-braces and ring beams. Below A hybrid system of steel and concrete erected, it was obvious that these were that, the opening for the was considered. But the final choice the “bones” of a Gothic church. The and a large stained glass window elimi- was what had been sketched in the first diagonal braces of the aisle frames form nate both east-west X-braces in the design team meeting: a series of steel the arches of the aisle , and the tower. A series of girts, sloping beams, frames forming the nave, spaced at beams above form a classic triforium, and diagonal braces concealed in the 16’ on center to match the architectural used here for air conditioning ducts. tower buttresses transfer the wind loads module, and two X-braced steel struc- The underside of the roof truss forms the sideways and down to the ground. tures forming the towers. shape of the vaulted ceiling. Because the tower brick extends 128’

May 2005 • Modern Steel Construction up and steps back often, shelf angles spaced 8’ to 15’ vertically provide for brick support. A system of tubes wraps around the towers at every shelf angle, following the shape of every buttress, pier, and wall. These are supported on outriggers off the main tower columns or on buttress beams, and are designed to take both the vertical brick load and the horizontal wind loads. The remainder of the structural sys- tem is fairly conventional; roofs are metal on steel joists and are con- crete slab on metal deck on wide-flange beams. The roofs of the aisle and nave are framed with sloping steel bar joists spaced 5’-4” on center. Deep, long-span metal deck was considered early on to eliminate the bar joists, but discussions with the construction team revealed that joists would be useful for supporting the plaster ceiling, lights, and maintenance catwalks. Point loads were specified on the construction documents and the joists were designed to allow these loads to be placed at any point along the joist. The general contractor and key sub- contractors, including the steel fabrica- tor and erector, were brought in early in the design process. Matrix structural engineers worked directly with the steel detailer to answer questions rather than go through a formal RFI process, and shop drawings were submitted in mul- tiple packages to allow fabrication to begin as detailing continued. The result: The building was completed on sched- ule and in time to install the pipe organ before the first service, Easter 2004.  . by Christof Spieler Photo

Modern Steel Construction • May 2005 E NGINEERING A W A R D S O F E X C E L L E N C E

$10M OR GREATER, BUT LESS THAN $25M MERIT AWARD

Photo courtesy KL&A, Inc. Robert Hoag Rawlings Public Library Pueblo, CO . P hoto by Timothy Hursley Antoine Predock Architect Antoine Predock . Graphic courtesy

ueblo’s new Robert Hoag Raw- to allow free movement due to rotations Structural Engineer and Detailer lings Public Library serves as a at the ends of the trusses and thermal KL&A, Inc., Golden, CO, meeting place, a gallery for art movement. NISD member and permanent displays, and The library’s most prominent structural a location for special events. steel feature is a wedge-shaped trellis. It Engineering Software PThe 109,000 sq. ft structure uses bold forms a point starting at the north side of AutoCAD architectural forms and the juxtaposition the building that descends at 4˚ for 368’, RISA-3D of architectural finishes—with conven- ending in a 45’-long cantilever that is only RAM Structural System tional composite steel framing in most 2’-9” deep at its spring point. The trellis Detailing Software areas—to create interest and drama on is made of built-up, wedge-shaped tube SDS/2 a budget. sections connected by channel sections The first structural challenge was an and diagonal flat plate braces. At the Owner overhead structure spanning approxi- north side of the building, the deep end Pueblo City-County Library District, mately 98’ and connecting two sides of of the wedge contains a gallery that can- Pueblo, CO the library on opposite sides of a street. tilevers 16’ beyond the face of the build- Architects This “” included two levels of ing. This was accomplished with a steel Antoine Predock Architect PC, library stacks and administration spaces, moment frame that allowed side windows Albuquerque, NM (design) as well as mechanical equipment behind in the gallery. Anderson Mason Dale Architects, tall, sloping parapets on the roof. The The main stair in the can- Denver, CO (executive) plan geometry of the skyway was trap- tilevers 20’ from the slab edge support. ezoidal in shape, with a glass-clad tri- However, the landing at the end of the Fabricator angular hole through the middle, allow- cantilever—typically a stiff element that Zimkor LLC, Littleton, CO, ing light in and a view of traffic passing resolves the forces between the struc- AISC member below. Four one-story tall trusses are tural stair runs—is 22’ long. An HSS General Contractor located at the third level, with the 16×16 member was used to connect the H.W. Houston Construction Co., second floor level suspended below. stair runs. A splice was required in this Pueblo, CO Directed spherical bearings were used HSS member to make the stair compo-

May 2005 • Modern Steel Construction nents portable and constructible, but the architectural finishes did not allow for any plates or other protruding elements. A completely field bolted splice was devised that fit entirely within the shape of the HSS to meet these challenges. The 54’-tall atrium glass wall was achieved with minimal structural support by providing horizontal tube-steel girts at the floor levels, with slender sag rods supporting the girts from above. Perhaps as important as the building’s structural elements was the project deliv- ery approach, driven by the needs of the owner and contractor to meet a tight schedule. Structural engineering firm KL&A employed its own in- steel detailing staff, using the 3D steel-detail- ing/modeling package SDS/2. Detailers were able to start work on the 3D model during the construction documents phase, which in turn resulted in the issue of complete shop drawings shortly after the final issue of structural construction documents, and before the final architec- tural package was released. 

Modern Steel Construction • May 2005