chapter 3 - Dome collapses

Question 1

What gives domes their impressive stability

Answer 1

1. curved and continuous shape.

Question 2

To prevent masonry arches from opening-up and collapsing, they need massive outside buttresses. What is the form-resistant that means domes do not require such buttresses, and why are domes exceptionally strong

Answer 2

do not require much buttresses due to parallels, which is the ideal horizontal circles of its surface. it keeps the staves together.

they are strong due to the interaction of the meridians and the parallels.

Question 3

To what is a dome’s extreme rigidity sensitive to

Answer 3

they are sensitive to soil differential settlements and earthquakes. this is due to the weak material in tension, so to counteract, there needs to be more buttressed around the base.

Question 4

what four factors acting together can be used to explain the collapse of two Binishells in Australia

Answer 4

1. the air pressure of the balloon ( can cause flattening or expanding)
2. the tension in the spiral springs ( used to keep in place the reinforcing bar and wet concrete)
3. the weight of the distribution of the concrete.
   4.the variable air temp while concrete is setting

Question 5

One of the two Binishell collapsed, following on-site repairs to overcome a circular crack.

What had the engineer overlooked when approving the change to the original design details,

and what was the failure mechanism that occurred 10 years after the dome’s erection

Answer 5

1. repair the crack by adding additional meridional steel bars and pouring concrete over the crack. they overlooked the dead load that will be added from the concrete as it did not blend with the hardened shell
2. the extra stress this added to the dome cause it to slowly flatten, after 10 years the dome inverted and collapsed.

Question 6

On 21 January 1978, and after seven years in use, there was the sudden catastrophic collapse of the C. W. Post dome under mounds of snow and ice. What did Nicholas W. Koziakin conclude was the root causes for the collapse of this reticulated dome

Answer 6

1.it was concluded that the dome had been under designed with a simple structural theory.

2. theory used assumptions of uniform dead loads and live loads. so that the snow and ice added too much stress and was over the allowable limit. as the snow was blown from the east.

Question 7

Based on the more realistic theoretical modelling by Weildlinger Associates what non-uniform distribution and value of snow load was bound to, and did, collapse the dome

Answer 7

the snow load was 1/4 th of the load required by the code, but concentracted over a sector 1/3 of its surface was bound to collapse the dome.

Question 8

What clever, but incorrect assumption is used to apply membrane theory to reticulated domes, and why is it incorrect

Answer 8

1. the elementary membrane theory.
2. is that dome behave as if they are continuous and with a thickness obtained by spreading uniformly the weight of their framework over the surface of the dome.
3. the dome thickness varies between 1/6 and 1/3 inches. so the dome does not have the same structural properties at every point.

Question 9

What dangerous phenomenon is ignored by using membrane theory in the design of shallow reticulated domes

Answer 9

snap-through - instability in buckling as a whole, which causes the dome to invert.

Question 10

Which member type in the C. W. Post dome was the weak link in the reticulated frame’s design

Answer 10

the compressed diagonals

Question 11

What is the moral of the story of the C.W. Post dome collapse

Answer 11

1. each new design must analyse the results of the latest theories and experimental investigations
2. that the elementary structural knowledge should not be trusted whenever one moves beyond the limits of traditional structures.

Question 12

Why do you believe almost all of our structures stand

Answer 12

1. the advance computers that allow solutions to complex problems in structures
2. this leads to new and safe structures.
3. so more confident for why all structures stand

Question 13

Following the solution by A. A. Beale and M. A. Soare to the mystery of the failure of the Bucharest Dome what two conditions at the joints do we now know must be satisfied for a light reticulated dome to be self-supporting

Answer 13

1. rigis connections at the nodes of a reticulated dome are essential to maintain unchanged geometry of the dome and to prevent bending deformation at the joints