Optimisation Step 6. - Building Design

Type 1 Frame Entire Structure Saved

- [kg] [kg] [%]

Last step 755 30130 53.3

Optimised Frames 999 24975 61.3

Saved since last step -246 5160 17.1

Total Saving 615 39540 61.3

Table 4.17: Wood Frame Results - Step. 5 Distance - The overall number of frames is reduced, increasing the weight of the single frames

4.4.7.3 Conclusion Step 5.

Increasing the distance between the rows of frames proved to be more material efficient, as few but larger cross sectioned frames resulted in optimisations for the total structure for both wood and steel. The initial drawings (Figure 4.30) of the main hall of the art gallery reveals a short distance between the frames.

This optimisation step suggests longer distances between the frames in order to save material for the entire structure. Compromising with the initial design idea will always be a question of concern between the architect and the engi-neer. Using a parametric program allows for verification and discussion through instant analysis.

Having short distances between the frames as the architects suggest might inter-fere with the openings between the rooms and the openings towards the atriums.

Furthermore the number of rows of frames needs to be compatible with the grid lines⁶ of the structure ensuring that the frames will not block door openings or similar.

4.4 Modelling and Optimisation in Karamba 50

4.4.8.1 Steel Structure Optimisation

The best initial design for the steel structure with changing roof heights can be seen in Figure 4.31. The weight of the entire building would be approximately 50805 kg which is an optimisation of aproximately 65725 kg of the initial simple solution. The initial design is not as material efficient and is thus only resulting in an optimisation of 56.4% compared to the simple initial design solution.

Figure 4.31: Initial design solution from the architects with specifications The solution seen in Figure 4.31 is thus not as good as the previous optimisation steps. The large frame to the far left is weak when exposed to wind and it was thus modified in order to meet the needs of the architects with different heights, but also in order to reduce the amount of material.

In the modified solution, the outer left frame was brought to the same height as the outer right frame (6.7 m) as can be seen in Figure 3.4, but it still had a span of 12 meters. This solution revealed more material efficient results and can be seen in Figure 4.32.

Figure 4.32: Modified solution close to the design from the architects with specifica-tions

The comparison of the initial design by the architechts and the modified solution can be seen in Table 4.18. By making a slight change to the roof height of the outer frames, subjected to the wind load, 32% material is saved.

It can thus be concluded that a more robust structure with smaller heights at the points of application (particularly for wind) is material saving as smaller cross sections can be used to take up the load. A further improvement point would be to minimise the cross sections of the three internal frames not directly subjected to wind. The optimisation would likely depend on the snow loads.

Type 1 Frame Entire Structure Saved

- [kg] [kg] [%]

Initial Design 2030 50,805 56.4

Modified Design 1385 34,605 70.3

Saved since initial design 650 16,202 31.9 Table 4.18: Steel Frame - The Architects initial design and modified design

In order to check this solution against the common solution used in the last five steps with five similar frames, the similar frames are adjusted in length in order to span exactly 55.5 meters in total thus 11.1 meters each. The comparison frames can be seen in Figure 4.33.

Figure 4.33: Comparative solution with specifications

The comparison of this optimised structure at 55.5 meters of width and the modified design of the architects, (Figure 4.32) can be seen in Table 4.19. This solution saves another 35.3% material due to the lower roof heights.

Type 1 Frame Entire Structure Saved

- [kg] [kg] [%]

Modified Initial Design 1385 34,605 70.3

Design Suggestion (11.1m) 1197 29,915 74.3

Saved 188 4690 13.6

Saved since initial design 1690 86,615 74.3 Table 4.19: Steel Frame Results - Step. 6 Final Optimisation

Thus it can be concluded that the smaller frames are material saving as less material is used for the roof beams and the structure is more stable, better able to sustain wind pressure and avoid the build up of large snowbanks. Compro-mising the height of the structure is changing the expression of the building and would be a point of discussion with the architects.

4.4 Modelling and Optimisation in Karamba 52

4.4.8.2 Wooden Structure Optimisation

The architects’ initial design of the structure with changing roof heights for wood, can be seen in Figure 4.34. The weight of the entire building would be approximately 39285 kg, equivalent to a 39% material saving since the initial simple design.

Figure 4.34: Wood solution close to the architects’ design with specifications The same problem occurs for the wooden structure as for the steel structure, thus the outer frames are too weak when exposed to wind pressure. The outer left frame is thus given the same height as the outer right frame of 6.7 meters.

This modified solution provides a better result material-wise. The result can be seen in Figure 4.35 and Table 4.20.

Figure 4.35: Modified wood solution close to the architects’ design with specifications

Type 1 Frame Entire Structure Saved

- [kg] [kg] [%]

Initial Design 1570 39,290 39.1

Modified Design 1056 26,410 59.1

Saved since initial design 515 38,100 32.8 Table 4.20: Wooden Frame - The architects’ initial design and modified design For the wooden structure it can also be concluded that the more robust structure of the outer frames leads to less material consumption as smaller cross sections are able to take up the loads.

In order to compare this modified solution, the last optimised frames must be modified to only span 55.5 meters instead of 60 meters. Each frame spans 11.1 meter and the solution can be seen below.

Figure 4.36: Comparison to the wood solution with specifications

The solution with lower heights is compared to the modified initial design solu-tion by the architects in Table 4.21 and can be seen Figure 4.36.

Type 1 Frame Entire Structure Saved

- [kg] [kg] [%]

Modified Initial Design 1055 26,410 59.1

Design Suggestion (11.1m) 805 20,070 68.9

Saved 195 4905 19.6

Saved since initial design 810 44,445 68.9 Table 4.21: Steel Frame Results - Step. 6 Final Optimisation

The proposed solutions for the wooden structure is not as slender as the ar-chitectural idea. This is both due to the fact that only 5 rows of frames are carrying the entire load of the roof structure giving a larger beam cross section.

The cross sections are thin but deep in order to take up the load, thus seen from the front they seem larger. An alternate and more slender solution is proposed below in Figure 4.37.

Figure 4.37: A more slender version of the frame structure with specifications This solution weighs 28080 kg in total which is an increase of approximaterly 40% compared to the modified solution. See Appendix Q for further detail.

4.4.8.3 Conclusion Step 6

Even though the best solution material-wise would have been with only 2-3 rows of frames carrying the entire structure, both visual and practical means

4.4 Modelling and Optimisation in Karamba 54

need to be taken into account. For practical reasons the connections and wooden beams might be hard to design for large structures and visually the architectural vision needs to be maintained throughout the design optimisation. This would be through discussing options with the architects throughout the process.