Atta Civil Engineering

Dramatic Cantilever

Singh Center for Nanotechnology Wins National Architecture and Engineering Award (Chicago, IL) – The Krishna P. Singh Center for Nanotechnology, a 78,000-sq.-ft research and teaching laboratory on the Philadelphia campus of the University of Pennsylvania, has earned national recognition in the 2014 Innovative Design in Engineering and Architecture with Structural Steel awards program (IDEAS2). The center’s most dramatic and complex structural design feature is the forum, a 4,000-sq.-ft assembly space that cantilevers 68 ft over the courtyard and includes multi-purpose functions such as lectures, receptions and meetings. Strength and vibration were core design parameters, and the vibration of the floor under dynamic human loading is the controlling criteria of the structure. The vibration of the floor beams and the overall rhythmic vibration of the room are controlled by the stiffness of the steel trusses and lateral restraint of the braced frame. The cantilever is constructed of two inverted trusses with hang columns to capture the horizontal floor diaphragm. The south-facing curtain wall façade of the center’s galleria has a sloping roof that slices through the curtain wall plane stepping it in two directions. A horizontal truss diaphragm is employed at the sloping roof plane to resist the horizontal wind loads on the curtain wall. The north side of the horizontal truss is supported by steel columns on the foundation wall. The south side of the horizontal truss is more structurally dynamic and is supported by cantilevered beams with hanging columns that suspend the north edge of the truss from above. The hangers and columns are all architecturally exposed structural steel (AESS). In order to match the construction tolerances of the AESS, slip connections are provided where the hangers meet the upper roof steel. The lower roof between the hangers and the columns is constructed with AESS tolerances. The monumental stair is unusual because it is a 55-ft-long free-span stair stringer supported by a 24-in.-deep, 20-ft cantilever. Though deflection and strength were considerations, similar to the forum, vibration parameters controlled the design. Five 24-in.-deep steel wide-flange members frame the 10-ft wide stair. The laboratories require very strict vibration tolerances for maximum equipment performance. The lower level transmission electron microscope (TEM) rooms require a completely isolated six-sided box construction. The clean room bay and chase have 52-ft free-span beams that create a column-free space for maximum flexibility, and the general labs contain 34-ft free-span beams to allow for a column-free space. This design resulted in an actual vibration criterion that exceeded the anticipated design criteria. The building’s project team members include: Owner: University of Pennsylvania, Philadelphia Architect: WEISS/MANFREDI, New York (entered project in the competition) Structural Engineer: Severud Associates, New York General Contractor: Gilbane, Inc., Philadelphia Steel Fabricator: Lynchburg Steel & Specialty Company, Monroe, Va. (AISC Member/AISC Certified Fabricator)...

Inovatie fatala

Cosmarul turistilor – Terminalul 2E din aeroportul Charles de Gaulle In 2003 era inaugurat cel mai nou terminal al unuia din cele mai aglomerate aeroporturi din Europe, Charles de Gaulle din Paris, avand un design indraznet si spatii larg deschise. Proiectat de arhitectul francez Paul Andreu, acest terminal era considerat „un triumf elegant al unui design inovator dar si practic” Insa acest triumf a durat pana pe 23 mai 2004, cand o portiune a terminalului s-a prabusit, omorand patru persoane! La ora 06:57 AM, o parte din bolta acoperisului cu deschiderea de 30m si inaltimea de 20m a cedat omorand patru persoane si ranind alte trei. Terminalul laudat pentru aspectul sau futuristic si considerat bijuteria acestui aeroport, s-a prabusit la doar unsprezece luni de la inaugurarea sa. Scena a fost descrisa ca cea a unui cataclism, la fel ca in cazul unui cutremur. Dilema era cum de o structura atat de apreciata pentru solutiile structurale inovative aplicate a putut ceda dupa o perioada atat de scurta. Inainte de colaps Inaugurarea terminalului fusese amanata cu o saptamana din cauza ca nu primisera avizul favorabil din partea inspectiei din cauza ca un candelabru cazuse din tavan chiar in timpul efectuarii inspectiei. Cu cateva minute inainte de tragedie, cativa pasageri au auzit sunete puternice si au observat cum incepea sa cada praf din acoperis. Cauza prabusirii Acoperisul terminalului era alcatuit din trei straturi: un strat exterior din sticla, stratul din mijloc format dintr-o structura metalica si stratul interior alcatuit din blocuri de beton care sustineau structura metalica. Aceasta structura mixta a fost motivul care a condus la prabusirea boltei. In urma unei analize ulterioare s-a observat ca structura metalica era prea adanc incastrata in structura de beton, ceea ce a cauzat perforarea acesteia din urma. Acest detaliu a dus la slabirea rezistentei structurii in ansablul ei si implicit la pierderea stabilitatii. In mai multe rapoarte s-a constatat ca acele blocuri de beton au fost slab armate in timpul prefabricarii lor, iar unele armaturi au fost pozitionate gresit. In plus, grinzile orizontale care sustineau bolta, au fost slabite de trecerile pentru ventilatie. Totusi, unul din cei mai importanti factori care a dus la prabusire a fost diferenta mare de temperatura din timpul zilei (25 grade) si cea din timpul noptii care scadea pana la 4 grade. Astfel, ciclul rapid de dilatare/contractie a structurii metalice a dus la smulgerea acesteia din beton. O dovada a acestei cauze a fost si ora la care terminalul s-a prabusit. Astfel, acest mixt intre metal si beton s-a dovedit o formula fatala in acest caz. Dovada vie o reprezinta terminalul 2F, care are acelasi desing, doar ca structura a fost integral metalica si rezista fara nicio problema. Motivele economice au dus la schimbarea...

High Line 23

Excellence In Structural Engineering Award – Award Winner High Line 23 Structural engineer : DeSimone Consulting Engineers Substructure: Concrete Superstructure: AESS steel with plate steel cross bracing South and North Elevation: glass, steel and aluminum curtain wall East Elevation: stamped stainless steel panels The project contains 12 floors and 45,000 sf of high-end residential space, featuring generous ceiling heights and expansive column-free zones. Above the fourth floor, the structure projects outward, creating an undulating facade that cantilevers over the high line. As well, the building’s south facade features a structural diagonal that serves to ‘hang’ the cantilevered floors from above from the interior...

Excellence In Structural Engineering Award

Raymond & Susan Brochstein Pavilion Structural engineer : Haynes Whaley Associate, Walter P. Moore A square in plan, the pavilion is supported by a steel frame around its perimeter, which holds floor-to-ceiling panes of high-performance glass. The column-free interior is interrupted only by a core that houses restrooms, storage, and the mechanical room a level below. Designers addressed lateral torsional buckling concerns for the stacked steel bar grid and analyzed various required cambers to meet the exacting requirements of a flat and level finished trellis structure with a leading edge of only ľ in. This delicate steel grid is held 17 ft in the air by slender 4˝-in. square billet columns with concealed fixed bases. The architect required submission of a sample of the column to verify the hot rolled billet would have acceptably square, unrounded corners. To ensure the aesthetic integrity of the trellis versus constructability, designers closely coordinated all details during the design phase. Splices in the structural steel members were coordinated with the architectural grid to create manageable lengths and were detailed with mortised joints and decorative head steel bolts. The steel fabricator and erector met the architecturally exposed structural steel tolerances, which were required to align and attach the prefabricated aluminum trellis frames to the top of the steel grid, without any need for fieldmodifying the shop-fabricated steel. The finished trellis forms an open shaded area for exterior seating surrounding the pavilion. Four 77 ft by 15 ft clear glass curtain walls form a square and enclose the pavilion. The exterior steel columns supporting the structural steel roof were limited to the smallest structural steel wide-flange shape of W4×13. These exposed columns are spaced at 7 ft all around the perimeter and are integrated as part of the glass wall support system. Each vertical mullion is placed in front of and attached to a W4 column. Each horizontal mullion is in front of and attached to a horizontal ST2×43/4 spanning between the W4 columns. This allows the sizes of the aluminum mullions to be minimized and enables the architect’s desire for an unencumbered visual connection between exterior and interior. Likewise, the view from interior spaces to the exterior is unencumbered, since the structure has no interior columns other than those concealed within the 14 ft by 49 ft service core. This required spans of 42 ft to the W4 exterior columns, created with W18 beams that are partially exposed by the perforated metal ceiling. The beams are spaced at 7 ft on center and coordinated with the perimeter curtain wall, shrouded skylights, sprinklers, and the perforated metal panel ceiling which partially exposes them. The building was detailed with AutoCAD and analyzed with Risa3D. Jurors noted the link between form and function. “A great...

Outstanding Project

Excellence In Structural Engineering Awards – Outstanding Project Fishers Island Residence – Fishers Island, NY Structural engineer : Skidmore, Owings, and Merrill, LLP In an effort to create this uninterrupted connection, the architect used high-performance, insulated floor-to-ceiling glazing on all four external walls of the house. To minimize visual interruption in the glazing, the structural engineer designed slender 2.75-in. square, solid steel columns supporting W10 primary beams that span 29 ft and W4, L3x3 and L5x5 secondary steel beams. The wide-flange steel roof framing supports a 1.5-in. wide, rib metal roof deck. Steel framing was essential for maintaining uninterrupted windows and allowing shallow roof spans. The design of the Fishers Island Residence is a response to the unique island setting and the personal interests of the client and primary resident. “A very simple design that lends itself very well to its surroundings,” commented Brad Lange, pre-construction manager, The Weitz Company, Des Moines, Iowa, and a judge in the competition. “They did a nice job of using exposed structural steel to add an artistic flair.” The structural elements were carefully coordinated with the architectural expression, which greatly understates their relationship: the structural steel elements are the architecture. The exposed structural steel columns were engineered to be as small as structurally possible and designed to maintain a consistent, clean aesthetic throughout the house. The aesthetic treatment of structural steel is prominently displayed by the 50 steel “trees” every 11-ft, 6-in. around the house. Each tree consists of a solid 3.25 by 3.25 in. steel cantilevered column, rigidly fixed at the base. A steel casting at the top of the column is connected with a single, concealed, high-strength bolt. The casting spreads into four diagonal cast “branch arms” at the top of each column that cantilever out approximately 8 ft from the columns. A trellis of solid aluminum rods is supported at the tips of each branch arm. A secondary system of trellis framing spans above the aluminum rods, cantilevering an additional 3 ft beyond the edge of the branch arms. The secondary system is supported by individual, high-strength rods attached to an innovative concealed “tongue plate” connection detail. The concealed tongue plate and rod connection allows the trellis to float above the branch arms with almost no visible means of support. An adjustable and fully concealed steel puck-like connection at the base of each support rod permits adjustment of the trellis-to-branch arm connections. The trellis, steel trees, and branch arms are visually dramatic but also are essential to making the residence habitable. The canopies and trellis shield the full-height glass walls from direct overhead sunlight, dramatically reducing glare and light levels within the house. The steel trees also play an important role in the psychological...