LAMELLA DOME ASSIGNMENT 2
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Rubeena MAR11005 Advanced Structural Structural System
Content Space frame Lamella roof Lamella dome Features Advantages Wooden lamella dome Steel lamella dome Astrodome • •
SPACE FRAMES Space frames are classified as Based on structure single-, double- or multilayered structures, Based on shape flat, resulting in grid structures, curved in one or two directions, forming barrel vaults and dome structures. • •
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Fig 1. Space frame Ref: http://www.geometrica.com/sites/default/files/images/Sys.Module.png
SPACE FRAMES Grid structures can be further categorized lattice space grids • •
in which the members may run in two, three or four principal directions. Double-layer lattice grids: the top and bottom grids are identical, with the top layer positioned directly over the bottom layer.
Double-layer space grids: formed from pyramidal units with triangular or square bases resulting in either identical parallel top and bottom grids offset horizontally to each other, or parallel top and bottom grids each with a different configuration interconnected at the node points by inclined web members to form a regular stable structure.
Fig 2. double layer grids
SPACE FRAMES Structural performance. •
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Single-layer grids : flexural moments, - 15 m span double- and triple-layer grids : axial tensile or compressive forces – 100 m span and economical
Skeletal space frames curved in one direction forming single- or doublelayer barrel vaults also provide elegant structures capable of covering large clear spans.
Fig 3. L‟Agora Space frame
Ref: https://www.slideshare.net/flemingprakash/miscellaneous-structures
SPACE FRAMES Single-layer vaults : spans of up to 40m, Double-layer barrel vaults: clear spans in excess of 120m. Single-layer steel domes : tubular members with spans in excess of 50m Double-layer dome : clear spans slightly greater than 200m. Skeletal steel dome structures based orientation and position of the principal members. ribbed domes, Schwedler domes, three-way grid domes and parallel lamella domes. • • • •
Fig 4. Bracing of single layer barrel vault
LAMELLA ROOF A lamella roof, also known as the "Zollinger roof" , is a vaulted roof made up of simple, single prefabricated standard segments as a way to span large spaces. Lamella dome is made of intersecting arches hinged together at their midpoints to form an interlocking network in a diamond pattern The individual pieces are joined together with bolts and/or plates to form a rhomboid pattern. Wooden sheathing covers the structure on the outside. The lamella roof was patented in 1910 and became popular between the World Wars, especially in Germany when metal for construction was in short supply. Some of these structures are now almost 100 years old and many of them remain in very good condition. Sometimes very similar roofs were built with steel In the 1950s, this concept was adapted to the construction of large dome structures by architect Gustel Kiewitt in the U.S.
LAMELLA ROOF These roofs are inexpensive, very easy to build and elegant. Local wood can be used. The standard wooden segments are short and can therefore easily be mass produced. There is no extensive scaffolding.
need for an temporary
Fig 4. Hale County Animal Shelter (Auburn University's Rural Studio Project)
Fig 4. Models built for the exhibit: "Weniger ist Zukunft" Berlin Galerie Mutter Fourage
LAMELLA DOME They are generated with concentric rings, where each subsequent ring is rotated by a half module. This reduces the length of the ring tubes as the geometry proceeds towards the apex. When the tubes of the rings become too small (usually half the length of the first), they "consolidate" to the next ring, joining the two divisions into one.
Fig 5. Bracing of single layer barrel vault
The separation between rings in Lamella domes can be varied so they are equilateral triangles forming each ring. Because the tubes of each ring are equal, the manufacturing time is fast and assembly is easy. Domes such as the Cancun Hyatt and the Mustafa Centre use Lamella geometry. Only few of the ribs running from the rim to the crown of the dome as meridional spherical sector dividers. All other ribs running as intra- sector parallel lines, curvilinear or straight thus forming a diamond grid
ADVANTAGES OF LAMELLA DOME Eliminating the crowding effect of meridional ribs at the crown of the dome
Dispensing with the necessity of introducing a compression ring around the crown Having all panel loads at rib intersections almost equal in magnitude Requiring only short, light struts for all rib segments Uniform stress distribution
LAMELLA DOME
Fig 6. Cancun Hyatt
Fig 7. Mustafa Center in Singapore
FEATURES Pin jointed framed domes Not framed with rotational symmetry All are subject to unsymmetrical loadings. Analysis methods model testing techniques, (accurate pierced membrane analogies space truss solutions. The largest lamella dome to date is approximately 240 ft. in diameter. •
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Formed from a number of „lozenge‟-shaped lamella units which are interconnected together to form a diamond or rhombus arrangement.
Fig 8. Various lamella dome frames
DOMES
Ref: http://www.thecivilbuilders.com/2013/01/space-
WOODEN LAMELLA DOMES
Fig 9. Gymnasium, St. Joseph, Missouri.
Fig 10. Church, Ft. Lauderdale, Florida.
Non-structural roof deck Secondary bracing by sub purlin for the dome framing. Both installations are supported on columns pinned radially and fixed tangentially at the outer ring.
STEEL LAMELLA DOMES In the Houston dome, temperature variations displaced the sunward columns by as much as 2 inches radially at their tops in an effective length of 6 ft. 0 in. 37 temporary erection towers were used for scaffolding, and the longer Lamella units were required to be in excess of 120 ft in length in order to span between scaffold towers. Fig 11. Sports stadium, Houston, Texas.
Special cranes with boom length up to 275 ft. were used to lift units up to the 210 ft clear center height. The weight of the roof structure including the outer (tension) ring was slightly less than 16 lbs/sq.ft.
EXAMPLES 1. Astrodome 2. Silver Dome Ballroom
Fig 12. Astrodome Ref: https://sites.google.com/site/theastrodomeamarvelofcivil/structural-engineering-design
Fig 13. Silver Dome Ballroom Ref: http://silverdomeballroom.net/about/ABOUT
ASTRODOME Roof design : diagonal trusses and horizontal supports with 12 pieces and fit together at the site. Each truss support of the roof is 5‟6” deep for more support. The effects of gravity caused a great outward force of the roof segments that had to be contained with a 376 ton tension ring that spanned the circumference of the dome, much like the ring of a barrel.
The ring rested on 72 columns that were located at every five degrees from the center and employ a “knuckled” column design to disallow shear forces but support central forces. The outer walls of the stadium are also constructed of trusses to bear the load of the crowd and the roof (Macauley, 2000). There were challenges in finding the loads because of the asymmetry of parts of the stadium, large mechanical equipment, and temperature considerations. A wind tunnel test and model testing for structural stability was performed
ASTRODOME
Fig 14. A detail of a segment of the lamella roof.
ASTRODOME Challenges faced: the deflections of the dome once the construction supports were removed.
Fig 15. The forces of the dome were transferred to the support columns.
If all went according to plan, the pins and welds held and the tension ring was strong enough, the deflection should only be 1.88”. The final measurement was within .25” of the prediction
CONCLUSION Steel Lamella domes are inexpensive compared to wooden. Lamella domes are beautiful and a favorite for architectural applications. No Lamella truss dome structure has ever featured the rounded, band-shell style ends found on the Silver Dome, making it a one-of-a-kind building. Buckling is one of the most important problems for dome structures.
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