Identify the shell type shown here.

1. As a way of checking your understanding of shell structures to this point, you might try to answer the following 4 questions. Permission Pending for use of this image Identify the shell type shown here. (Click the mouse to turn the page)

2. Permission pending for use of this image Despite its apparent free-form design, Jack Christiansen’s Rivergate Convention Center in New Orleans (demolished) is a modification of the multiple-bay barrel vault. Its fundamentally disciplined, and engineering-oriented form places it within the German School. Click mouse for answer Permission pending for use of this image Click here to go back!

3. Permission pending for use of this image Explain the function of the up-turned edge surrounding the Rivergate Convention Center. (click for answer) The up-turned edge functions as a stiffening beam. The edge of the half-barrel cantilevered at the sides of the building would be very flexible, if it were not provided with additional stiffening. The barrels at the front in this view , since they are not provided with diaphragms, also need stiffening at their open end.

4. Identify the similarities and differences between the following two buildings, and the design traditions to which these differences may be attributed. Permission pending for use of this image St. Louis Air Terminal: Minoru Yamasaki, Architect Anton Tedesko, Engineer

5. Permission pending for use of this image Click here to go back! Bacardi Bottling Plant, Carretera Mexico; Felix Candela, Engineer

6. Permission pending for use of this image Click here to go back! Similarities: These two structures superficially present great similarities--the basic conception of a main longitudinal vault with intersecting vaults creating three groin-vaulted bays is the same, as are the fundamental symmetries of the plan. The use of the space between cross-vaults to add skylights to the main vault is strikingly similar. In fact, according to Billington, the Yamasaki/Tedesko vault was the inspiration for the Candela structure. Differences: Candela uses a hypar vault rather than a uniform parabolic cross-section, as evidenced in the change in crown height along the length of the main vault. This subtle difference allows him to dispense with the heavy stiffening ribs along the groins. This provides a striking illustration of the differences between the German school, as exemplified by Tedesko, and the Spanish school, as exemplified by Candela. Click mouse for answer.

7. What is wrong with this shell? Click here for a view of the Kresge Auditorium, Cambridge MA, by Eero Saarinen Go to the next page for the answer. The problems that beset the Kresge Auditorium will be discussed in much greater detail in Module 3.

8. This is a simple model of the Kresge Auditorium shell—it consists of a ‘spherical triangle,’ that is a triangle cut from a sphere—it is actually exactly 1/8 of a sphere. The edges were provided with shallow stiffening beams. The stiffening beams at the edges proved to be inadequate—on removing the formwork and shoring, the edges underwent large permanent deflections. They had to be jacked back up, and the window mullions were strengthened to provide additional support to the edges.

9. Conclusions of Module 2 End of Section Use the navigation bar to return to Table of Contents • A thin shell is a concrete structure that is shaped in such a way that it resists loads primarily by the development of membrane tension and compression, rather than bending through the thickness. • A thin shell structure is dependent on the shape in which it is formed—where the ideal shape is disturbed or restraints are introduced, bending stresses are introduced. • Reinforced concrete, concrete provided with widely spaced steel reinforcement to resist tension, and ferrocement, concrete placed over a mesh of closely spaced steel reinforcement are the materials used to construct thin-shell concrete structures. The steel is necessary to resist membrane tension and the tensile stresses due to bending. • The principal types of thin shell structures are barrel vaults, domes, hyperbolic paraboloids, and folded plates. Within the constraints of these shapes a wide variety of forms are possible • The form and long span carrying capacity of the shell has been exploited to great advantage by both architects and engineers during the mid-twentieth century.