1. Roustness
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2. What is robustness?
Shanghai 2009
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3. History Progressive collapse. Ronan Point in London
Gas explosion in a 18 stories building
In1997 it was introduced in DS. The structure should be designed so it can withstand a locale collapse.
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4. Robustness according to NA and EC 0
A structure is robust if:
– ”The parts of the structure that are decisive for the safety are only slightly sensitive to unintended effect and defects, or
– There is no extensive failure of the structure if a limited part of the structure fails.”
In other words: design the structure so unintended loads don’t course a domino effect of collapses in the building.
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5. Robustness – When?
Robustness requirements – are relevant for all buildings, but:
CC3: For buildings with a high consequence class there is requirements to provide documentation for robustness.
CC2: For building with a medium consequence class, an evaluation of robustness should be provided.
CC1: where as there are no requirements for building with a low consequence class.
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6. Robustness – how?
At least on of the following criteria must be fulfilled according to EC0/NA:
By verifying that the essential parts of the structure i.e. key members, have low sensitivity to unintended effects and defects
By verifying that no extensive failure of the structure occurs if a limited part of the structure fails (loss of a member- Bortfald af element)
By verifying sufficient safety of key members , such that the level of system safety as an equivalent structure for which the robustness is documented by verification of suficient safety in the event of the loss of member.
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7. Loss of a member Design of robustness by ”loss of a element”
Guidelince for buildings up to 15 stories:
The acceptable extent collapse may be taken as 15 % of the floor space of two consecutive storeys but not more than 240 m2 per storey and not more than 360 m2 in total
Assuming the following of the collapse:
Loss of a limited part of a given column and an associated floor area
Loss of a limited part of a given 3 m length wall with an associated floor area
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8. Key elements
Robustness design with increasing safety factor on key elements
Increasing the paterial factor on material strength by 1,2
Every effort should be made to in the design to find another solution and not just include the increased safety factor
Where safety factor are used on key members, it should however be ensured that the resistance of the structure towards unintended effects and defects is actually increased
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9. Key element – Example 1/5
Center building with 2 stories with shops (levels 1 and 2) and 2 stories with parking lots (levels 3 and 4).
Main structure: column/beam made of concrete elements.
Dimensions:
Column module 7.2 x 16.9 m.
length 7.2 m (module dimensions).
Deck span16.9 m (module dimensions). Asses the robustness requirements for the described column / beam construction, assuming CC3.
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10. Key elements – Example 2/5
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11. Key elements – Example 3/5
Failure of deck element. Collapsed area corresponding to deck element 2.4 x 16.9 ≈ 40 m2 in the relevant floor. Acceptable collapsed area. ⇒ No special robustness requirements for the deck.
Collapsed area max. 7.2 x 33.8 ≈ 240 m2 in the relevant floor. Just acceptable collapse volume. ⇒ No special robustness requirements for the beams.
Failure of column Collapse volume max 14.4 x 33.8 ≈ 480 m2 per. Floor of 3 floors. Not acceptable collapse volume ⇒ Columns must be designed as key elements according to EC0 / NA, Annex E (9)
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12. Key element – Example 4/5
Design and calculation of joints between concrete elements:   The column is considered as a key member.
The material coefficient γM is increased to the factor 1.2 in the design of the column
In addition, special measures must be taken to effectively improve the design's resistance. This is done by performing the columns with vertical continuity reinforcement which are casted in corrugated tubes and ensure horizontal retention using the reinforcement in the overlay as shown in the detail below
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13. Key elements – Example 5/5
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14. Horizontal ties between walls and floors - EC2
N:7,5kN/m, min 40kN H:15kN/m, min 80kN
+ Vertical ties
N:15kN/m, min 40kN H:30kN/m, min 80kN
N:15kN/m, min 80kN H:30kN/m, min 160kN
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15. Drawings
Look in Bips A113
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16. Periferitrækforbindelser – eksempel CC2
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17. Interne trækforbindelser - eksempel CC2
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18. Vandrette trækforbindelser – eksempel CC2
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19. Vandrette trækforbindelser
Forskydningsbæreevne af strittere ifølge Spæncom A/S
Gældende for beton C35 med en minimumskantafstand på 50mm.
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20. Vertical ties
In buildings of 5 stories and above vertical reinforcement has to be included. This could be solve by the use of vertical continuity reinforcement which are cast in corrugated tubes or a standard solution as shown below
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