Fachadas y Techos Instituto de la Paz, Washintogn, D.C

7/28/2019 Fachadas y Techos Instituto de la Paz, Washintogn, D.C

1/6

232 Steel Construction 5 (2012), No. 4

Reports

DOI: 10.1002/stco.201210028

Roos and aades o United States Institute o Peace, Washington D. C.

Free-orm steel-glass grid-shell symbolizing a white dove o peace in fight

Thorsten HelbigMatthias Oppe

The Institute of Peaces new facility, a modern conference and aninteractive educational center dedicated to the theme of peace-making, faces the National Mall in Washington, DC and is withinsight of the Lincoln, World War II, Korean, and Vietnam Veteransmemorials. The building is organized around two atria, one part fac-

ing the Potomac River, the other the Mall and the Lincoln Memorial.The north atrium serves as the centerpiece for the spaces devotedto the organizations work and research, and the south-facingatrium is focused on public programs and conferences. The roof ofthe building features a series of undulating, wing-like elementsconstructed of steel frame and white translucent glass forming an

image resembling the wings of a dove. The glass appears opaqueand white during the day and glows gently from within at night.The two roofs and four curtain wall faades have been designed,fabricated and installed by seele, being responsible for the reali-zation. Optimisation of conceptual design, structural and detaileddesign for the free forms of the self-supporting shell structures

and the vertical facades was conducted by Knippers Helbig,

Advanced Engineering.

1 Introduction

Located at the intersection o 23rd Street and ConstitutionAvenue, the United States Institute o Peace Headquarters,designed by Moshe Sadie and Associates, occupies the lastprominent site on the National Mall acing the LincolnMemorial. Given its extraordinary location, adjacent to

many other memorials, the building is by denition a struc-ture that symbolically represents peace on the capitals sky-line (Figure 1).

The atria are rooed by a series o undulating sphericaland toroidal elements constructed o steel rames. Cladded

with white translucent glass, the image o the wings o adove evokes. The dove-like design is made up o variousgeometrical segments. Aluminium glazing bars on top osteel sections, concealed toggles and a continuous siliconejoint orm an aesthetically sophisticated roo glazing solu-tion. White membranes spanning across aluminium ramessuspended below the roo glazing lter the incoming day-light and scatter it evenly across the interior below. Duringthe day, the roo suraces appear white, at night they radi-ate like luminous objects (Figure 2).

The two roos are supported by our glazed curtainwall aades. These have to satisy a high blast-proo spec-

ication. The transoms o the two large vertical aades areconnected to the building at the sides by adjusted tensionsprings. Thereore the orces transerred to the aades inthe case o dierential deormations between the mainbuilding structure and the aades are minimised. Further-more the dimensions o cross-section or vertical mullionsand horizontal transoms can be reduced, since the buck-ling length is signicantly smaller.

The roo overhang on the north side could not be car-ried on the aade because the latter is directly above the

Fig. 1. United States Institute o Peace and National Mall Fig. 2. US Institute o Peace South roo and CW1


2/6

Reports

233Steel Construction 5 (2012), No. 4

entrance to the underground car park, supported on along-span reinorced concrete beam. Additional loadswould have overstressed the beam. Thereore, there is asliding joint between the inward-curving curtain wall andthe roo construction, to guarantee that no loads are trans-erred rom the roo to the aade. Those moving connec-tions were a challenging part o the design, since severalexpansion joint details to other materials had to be createdin order to allow or the movement o the aade structure.

2 Construction2.1 General

The building is organized around two atria anning outrom a corner entrance one acing the Potomac River, theother the Mall and the Lincoln Memorial. The atria arerooed (South Roo and North Roo) by undulatingspherical and toroidal wing-like elements constructed osteel rames and white translucent glass evoking at the im-age o the wings o a dove. Furthermore our vertical a-ades are located between the concrete building parts. The

North Roo consists o 675 m2 surace area covering theatrium between the concrete building parts A and B witha maximum span o 16.50 m. Vertically the atrium is closedby a aade structure (CW-2) which is located underneaththe North Roo both structures are decoupled vertically.The South Roo has a total surace area o 1100 m2, coversthe atrium and spans 24 m between the concrete buildingparts B and C (cp. Figure 3).

nally the conceptual design solution was optimized bymodication o the quadrangular grid, eliminating diago-nal elements as oreseen within the initial design and im-plementation o adjusted horizontal spring connectorsbetween vertical aades and adjacent parts o concretestructure.

Grid optimisationAlthough both the South and North Roo appear to be reeorm, the shapes are a combination o toroidal and spher-ical cut-outs (cp. Figure 4).

Fig. 3. Overview Roo and aades

Fig. 4. Geometry o South Roo

Due to the regular geometry o the shape, it was possibleto come up with a quadrangular grid consisting o planarquads. The grid o the south (cp. Figure 5) and north roowhere designed in such a way that they have as many iden-tical structural members and glass panels as possible.

Since panel sizes are small, at cladding elements

could be used producing less o a aceting eect, keepingthe architectural vision o a smoothly shaped building en-velope. Furthermore seele took advantage o the repetitiono structural members and cladding panel geometries.

Fig. 5. South Roo and CW1 with horizontal tied arch

Portions o the roo also cascade o the edges. Alongthe south elevation acing the National Mall, one wingo the roo extends 12 m away rom the building. The rontpart o the roo is supported by the vertical aade (CW-1)which is horizontally supported by a tied arch. Three10.5 m long steel props an out rom this horizontal tiedarch along the aade and meet the roo near the middle othe cantilever, leaving the tip o the roo untouched.

The our glazed curtain wall aades have to satisy ahigh blast-proo specication.

2.2 Design process

GeneralThe initial design was improved by carrying out intenseinvestigations on several alternative design concepts. Fi-

Elimination of diagonalsIn order to stien the quadrangular grid and avoid bendingeects, additional diagonal elements creating sti trianglesprovide the most efcient structural solution.


3/6

Reports


The visual impact o those elements was investigatedwithin a mock-up. As shown in Figure 6 it was not possibleto completely hide the diagonal bracing by covering thestructure with white translucent glass and using an addi-tional white translucent membrane on the inside.

Thereore a bolted connection detail providing suf-cient bending resistance along weak axis and causing novisual impact was developed. The solution was to weldtogether multiple-cranked steel sections or the transversebeams o the grid-shell structures beorehand and bolt theintermediate beams via end plates during erection (cp. Fig-ure 7).

2.3 Details

The quadrangular grid o the roos consists o 200 100 mmsteel hollow sections. Since the steel structure is abricated

in Pilsen, Czech Republic, the actual material used is cate-gorized as European structural steel S355. Results o struc-tural design show that it is necessary to increase thecross-section dimensions (up to solid proles), adjust the

Fig. 6. Visual MockUp

Fig. 7. Connection o transverse (welded) and intermediate(bolted) beams

Implementation of spring connectors

The basic concept o a clear and reduced structure hasbeen pursued during the complete design process. Theteam opted or a statically efcient solution implementinga mix o adjusted sliding and spring connectors betweentransverse elements o the two large vertical aades andadjacent parts o concrete structure (Figure 8).

By providing horizontal supports to the vertical mul-lions the buckling behaviour has been increased signi-cantly (cp. Figure 9). Allowing or supports with a certaindegree o exibility constrained orces transerred to theaade in case o dierential movements caused by e. g.thermal eects have been minimized.

The dimensions o cross-section or vertical mullionsand horizontal transoms have thereore been reduced inorder to achieve a transparent aade structure (cp. Fig-ure 2).

Fig. 8. Adjusted sliding and spring connectors within CW1

Fig. 9. Buckling behaviour o vertical mullions within CW1


4/6

Reports


structural system or use higher-strength grain-rened con-struction steel S460 in some local areas. Where required,special requirements regarding through-thickness direction(so-called) Z-quality were implemented.

The steel ramework holds about 1500 triple-layeredinsulated glass panels, the majority o which measure1.20 1.20 m, except or custom-sized pieces along theedges. Each panel is ritted on the exterior and covered bya white translucent membrane along the interior side (cp.Figure 10) that gives it a white glow when illuminated rominside at night.

3.3 Numerical simulation

SoftwareThe 3D-sotware SOFISTIK (by SOFISTIK AG, [6]) hasbeen used to design the entire structure.

Architecturally, the roos and aades are autonomouselements. However, it is logical to analyze roos and a-ades within global models (cp. Figure 11) in order to con-sider eects relevant or design and structural behavior.There is signicant structural and constructional interde-pendence, since the curtain walls provide vertical supportsor the roo structures, the roos also have signicant areaso clerestory which are envisioned to be o constructionsimilar to the vertical aades.

Fig. 10. Installation o white translucent membrane panels

3 Structural design3.1 Guidelines and design criteria

Structural design is based on wind loads obtained by

wind-tunnel tests and provided within a structural windload study report by RWDI [1] and [2]. All other loads con-sidered within the design have been applied in accordanceto ASCE 705 Minimum Design Loads or Buildings andOther Structures [3]. Bomb blast protection is not relevantor the design o the steel structure. Furthermore it wasassumed that the resulting vertical deections o the con-crete structure (bearing structure o the roo) do not havea signicant impact on the design o the steel structure, andseismic action does not govern design o the steel structure.

3.2 Materials and geometry

The undertaken analysis and design o all steel members isbased on requirements given in the AISC Specicationor Structural Steel Buildings [4] and Manual o Steel Con-struction Load and Resistance Factor Design; Third Edi-tion; 2001 [5]. All constructed steel members are made oASTM Designation A500 Gr. C. The analysis and designhas been undertaken or steel in that designation. How-ever it must be taken into consideration that the actualmaterial used is categorized as European structural steelS355, since the steel structure is abricated in Pilsen, CzechRepublic. The yield strength o S355 is slightly higher thanthe one provided by A500 Gr. C. The same applies to all

bolts used within the structure, being grade 8.8 accordingto Eurocode and A325M. This advantage o slightly highermaterial strength was not taken into account as structuraldesign was carried out according to American Standards.

All load combinations have been analyzed using secondorder theory, i. e. taking non-linear geometrical eects intoaccount.

Global structural designBecause the roos would span multiple structures and beexposed to winds blowing o the Potomac, structural anal-ysis was a critical element o the complex design. Investi-gations have been made considering eigenvalues o theroo structure. The rst Eigenrequencies are similar to2.31 Hz (South Roo) and 1.70 Hz (North Roo) respec-tively and thereore not critical or any wind-induced vibra-

tion eects.The deormation o the South Roo and adjacent ver-tical aades and clerestory structures within rst Eigenre-quency is presented within Figure 12.

Fig. 11. Numerical models o roos and adjacent aades


5/6

Reports


The quadrangular grid o the roos consists o200 100 mm steel hollow section with thicknesses be-tween 6 and 12.5 mm. Vertical mullions within CW-1 aremade up o 250 100 mm sections with variable materialthicknesses between 6 and 12 mm, while 100 100 8 mmsquare tubes are used or the horizontal transoms.

All members have been designed to satisy the designcriteria given in the corresponding American Standards[6], [7]. The utilization ratio or structural steel elementswithin South Roo, CW-1 and adjacent clerestories undergoverning load combination is presented within Figure 13.

4. Fabrication and installation4.1 Fabrication

The multiple-cranked steel sections or the transversebeams o the grid-shell structures have been welded to-gether prior to transport and bolted to the intermediate

beams via end plates during erection (cp. Figure 14). Theidea was to build up the system using preassembled pieceso roughly 36 m2 each in surace area. Where possibleon-site welding was avoided.

In general abrication o the structure was very chal-lenging, since various elements within the connection areabetween roos, aades and clerestories respectively had tobe made out o plates with large thicknesses or solid pro-les (cp. Figure 15) with special requirements to the weldseam sizes. Furthermore where required S355 had to bereplaced by grain rened construction steel S460 in orderto provide a sufcient structural resistance.

4.2 Installation

Ground was broken on the project in March 2008 and rooinstallation began in June 2009. Since the roo is going upin vast atrium spaces, a complex scaold system had to bedesigned not only to ll the void between the buildings, butalso to be precisely tiered to match up with the roo curva-tures. The ve-story, 1800 m2 horizontal scaolding is ullyloaded down to slab-on-grade at the parking level belowthe main oor.

Reshoring was added in the garages to support thescaold above. Ater several months o design, the scaold

took nearly six weeks to assemble.To build the roo, sections o the shell were preassem-bled on the ground using mostly bolted connections tominimize welding on site. Each piece was then picked up

Fig. 12. South Roo and aades within rst eigenrequency

Fig. 13. Utilization ratio South Roo, CW1 and clerestories

Fig. 14. Bolted connection o transverse and intermediatebeams

Fig. 15. Kicker element as used within North Roo


6/6

Reports


and positioned with a tower crane. The bow-tie arch waspicked up and lited into place as a single element (Fig-ure 17).

Once the entire shell was set, the scaold is designedto allow workers to stand in each rame and receive each90 kg glass panel as it is individually picked and positionedby the tower crane. The entire project was completed Oc-tober 2010.

Fig. 16. South Roo and scafolding during installation process

Fig. 17. Mounting o bowtie arch in CW1

Involved within project

Client:United States Institute o Peace, Washington D. C. (USA)Architect:Moshe Sadie and Associates, Somerville, Massachusetts(USA)Conceptual Design:Buro Happold, New York City, NY (USA)Design, Fabrication & Installation:seele GmbH, Gersthoen (Germany)/seele Inc., New YorkCity, NY (USA), Seele Pilsen, Pilsen (Czech Republic)Optimization o Conceptual Design, Structural Design andDetailed Design:Knippers Helbig, Stuttgart (Germany)/New York (USA)

Reerences

[1] Structural Wind Load Study United States Institute oPeace, Washington, D. C. by RWDI (Issue: May 9, 2007).

[2] Cladding Wind Load Study United States Institute oPeace Washington, D. C., by RWDI (Issue: October 13, 2006).

[3] Minimum Design Loads or Buildings and Other Struc -tures ASCE/SEI 705.

[4] AISC Specication or Structural Steel Buildings.[5] Manual o Steel Construction Load and Resistance Factor

Design; Third Edition; 2001.[6] Sostik ase General Static Analysis o Finite Element

Structures, SOFISTIK AG, Oberschleiheim 2007.[7] International Code Council: International Building Code

2006.[8] Knippers, J., Helbig, T.: Digital Process Chain rom Design to

Execution, Detail Design & Construction, Manuacturingand Design Synergies in the Building Process, ISBN 978-3-920034-33-1, 2010.

Credits:

seele.com: Figure 6, 8, 1417Knippers Helbig: Figure 3, 4, 7, 913Timothy Hursley: Figure 1, 2, 5

Keywords: aade; roo; steel-glass structure; outstanding con-struction; structural design; detailed design; reeorm

Authors:Dipl.-Ing. Thorsten Helbig, Dr.-Ing. Matthias Oppe, Knippers Helbig GmbH,

Tbinger Strae 1216, 70178 Stuttgart,

[email protected]

Fachadas y Techos Instituto de la Paz, Washintogn, D.C

Documents

Transcript of Fachadas y Techos Instituto de la Paz, Washintogn, D.C