Structural glass Design - Faculty of Architecture, TU Delft

New High Tech Lab facility Glass structure in BK-city

Tarik Alboustani - student no.4627709 Argyro Chiou - student no. 4626389 Maria Mourtzouchou - student no. 4621484 TU Delft | Faculty of Architecture and the Built Environment MSc Architecture, Urbanism & Building Sciences - Track Building Technology AR0105 Technoledge Structural Design 2016/2017 Q3 Course teachers: Veer F., Oikonomopoulou F., Louter C.

Table of contents 1. Introduction

page

7

2. Design: Initial concept and evolution

page

8

3. Final design

page

10

4. Sizing and manufacturing

page

16

page page page

16 20 22

5. Assembly sequence

page

24

6. Connections

page

26

7. Safety analysis

page

30

8. Structural calculations

page

32

page page page

32 35 38

9. Conclusions

page

41

References

page

42

4.1 Vertical corrugated components 4.2 Curved parts 4.3 Roof sandwich

8.1 Hand calculations 8.2 Diana results: Vertical corrugated components 8.3 Diana results: Roof sandwich

1. Introduction This research report is part of the course Technoledge Structural Design within the Master of Architecture, Urbanism and Building Sciences, track Building Technology at the Technical University of Delft. The aim of this report is to gain knowledge about the mechanical properties of glass according to the specific design application proposed for a glass structure in front of the entrance of TU Delft Architecture Faculty (BK-city).

At first, an architectural concept is formulated and then it is finalised according to limitations caused by the manufacturing, lamination, transportation processes, assembly sequence, connections, safety factors and structural calculations. This report presents how and why those parameters were set and how they contributed to the final design decision making.

7

2. Design: Initial concept and evolution BK-city is situated in the TU Delft Campus in Julialaan street and it is occupied by the Faculty of Architecture and the Built Environment. It was built back in 1945 but it was renovated in 2009 by Octatube. At that time, glasshouses were added to meet the need for more space and more specifically they were designed by Octatube (overall structure), Fokkema & partners (interior) and MVRDV (Tribune), in collaboration with staff members (modelling studios) and Henk van der Geest (lighting).

The intention of the new proposed design for the glass construction in front of the entrance of the building is to create a simple, clean geometry which complies with the existing architectural values. The free and organic shape of the plan comes in contradiction with the verticality created in the facade which resembles the geometry of the existing building (figure 1). In addition, the three different volumes proposed will create an interesting delusional 8

Figure 1: Sketch - design idea

sense when approaching the building entrance because of the interpolation of glass. Moreover, the smaller volume of the three will be underground and only 0,50m high above ground level so that it can also be used by people to sit on it as illustrated in figure 3.

The type of glass chosen to work with was a combination of corrugated glass pieces and bigger curved pieces. This way, the organic shapes would be created as shown in figure 3. In addition,

Figure 2: corrugated component

from a first research taking account structural and manufacturing aspects, it was decided that the corrugated parts would be constructed in pieces of quarter-half-quarter circle (figure 2) and would be connected on site whereas the curved parts would have a width of maximum 3,2m because of production and lamination limitations. The roof would be a bit bigger than the volumes creating eaves and would also be out of glass pieces supported by glass bins and fins.

Figure 3: 3d visualisation of initial design concept

9

3. Final Design After the initial design idea was formulated, the technical aspects of the construction had to be taken into account which led to smaller or bigger alterations of the initial design. A decision made was to use a composite roof out of glass consisting of three parts: two flat sheets and a corrugated layer inbetween. This way, the beams needed would be much less and what’s more this roof would act like an insulation reducing the high temperatures that will be achieved in the interior in summer time due to the glass construction.

The limitations that arose according to this decision led to the redesigning of the first rough shape. The span of the roof pieces should be no more than 11 meters because of transportation limitations so the plan was drawn again according to this parameter. Moreover, the curves were integrated in parts of actual circles so that the best optimization of the design could be achieved. The new design according to these changes is 10

shown in plan and section in figures 4 and 5 accordingly. Nevertheless, it was made sure that the needed square meters were kept unchanged so that the given programme would still fit. The space division is interpreted in figures 6 and 7. In addition, 3d visualisations of the new design are shown in figures 8 and 9.

Figure 4: Plan view of the proposed design

11

Figure 5: Section of the proposed design

12

Figure 6: Space division according to the given programme - floor plan

Figure 7: Space division according to the given programme - underground plan

13

14

Figure 8: 3d visualisation of the proposed design

Figure 9: 3d visualisation of the proposed design

15

4. Sizing and manufacturing 4.1 Vertical corrugated components The panels used for the vertical corrugated parts are 3,0m and 4,0m high for the two different volumes accordingly like shown in figure 10.

They will be manufactured in units of quarter-half-quarter circles as already mentioned. The radius of these circles to obtain the corrugated geometry is 0.25m. The pieces will be connected vertically with each other with structural silicon as shown in figure 11, whereas on top and bottom they will be fixed with metal connection elements and screws.

16

Figure 10: Dimensions of the vertical corrugated component

Figure 11: Dimensions and connection array of the vertical corrugated component

17

The primary production of the curved units is that of simple float glass at first.

Then the flat sheets are chemically strengthened and bended to become corrugated with a process called hotbending (figure 13). This production technique necessitates the making of ceramic or steel mould, by milling or by forging into shape which require much manual labour. However, hot bending allows greater flexibility in shape and curves if the component does not apply for overhead glazing and offers high geometrical accuracy by providing the widest range in curvature intensity (Doulkari K., 2013). Nevertheless, the costs can be relatively high due to the degree of customization and labour compared to the cold bending method. In the end, the corrugated panels are laminated and two layers of glass are used, 15-15mm with double sentry interlayers (figure 12). In this case, the choice of two layers was preferred instead of three layers of for example 10-10-10mm for two main reasons, first because it is cheaper since less individual plates will be manufactured and second because it will accommodate dimensional intolerances.

18

Figure 12: Lamination layers of the vertical corrugated parts

Figure 13: Hot bending process to create corrugated glass using a mould

19

4.2 Curved parts The bigger curved parts of glass inbetween the corrugated ones are also chemically tempered and laminated with the same way as the corrugated parts so that a uniform thickness is achieved which will accommodate the vertical connections (figure 14).

The division of the pieces is again made according to manufacturing limitations which means they can have a maximum width of 3.21 meters. Due to that fact, the perimeter of these parts is divided by 3.21 meters and the remaining width is again divided by two because of aesthetic purposes. These curved parts are interpreted in figure 15 and the division was made as follows: P1 = 6 x (3.21m) + 2 x (1.56m) with height: 4.00m P2 = 6 x (3.21m) + 2 x (0.62m) with height: 4.00m P3 = 6 x (3.21m) + 2 x (1.215m) with height: 3.00m P4 = 6 x (3.21m) + 2 x (1.12m) with height: 3.00m P5 = 6 x (3.21m) + 2 x (0.45m) with height: 0.26m 20

Figure 14: Lamination layers of curved parts

Figure 15: Curved parts on the plan

21

4.3 Roof sandwich The roof is composed of pieces consisting of two glass sheets and a corrugated surface in-between. These pieces are formed so that a triangle is created in the middle which has additional beams to hold the structure. The rest of the roof does not have beams. The maximum dimension of these panels is 11 meters as already mentioned because of transportation limitations and in order to prevent connections on the width.

An additional reason this roof was chosen, which resembles a composite, is because it works also like an insulation, reducing partly the extreme temperatures that would be reached because of the glass construction. The division of the roof pieces and the points of connection between the corrugated parts of the sandwich are shown in figure 16.

22

Figure 16: Positioning of connections of the corrugated roof parts

The glass sheets above and below the corrugated surface are composed of two layers of glass, 10-10mm with sentry interlayer (figure 17). The corrugated intermediate part is one layer of 10mm glass and has the same radius as the vertical corrugated parts, namely 25cm.

It is manufactured with a steel mould because it is a custom made geometry.

It is not just curved like the one used for the facade but it also consists of a straight part which comes in touch with a sentry layer which then comes in touch with the glass sheets (figure 18). The total height of the composite roof is 54cm. The glass beams of the roof are also chemically tempered and laminated.

Figure 17: Lamination layers of sandwich roof panel

Figure 18: Detail of sandwich roof panel

23

5. Assembly sequence The assembly sequence is interpreted in figure 19. The first step is to fix the steel U-profile to the ground so that afterwards the vertical corrugated components as well as the curved parts can be placed and secured in it. Due to the fact that there are many pieces to be connected, tolerances are important to be kept in high precision, so that everything fits well. Right after, the vertical corrugated pieces as well as the curved pieces are put in that steel U-profile. These are connected vertically with each other with structural silicone.

Afterwards, the beams are placed in the spots where the roof sandwich panels are connected and in the end the roof panels are put on top creating an eave of 0.50 meters. As already explained, the roof is composed of different layers.

The corrugated pieces of the sandwich are connected again like the vertical ones with structural silicone and then the glass layers on top and bottom are 24

connected with the corrugated layer with glue, namely UV-curing acrylate.

The side of the sandwich panels is also covered with curved glass pieces which are glued. As soon as the sandwich panels are ready, they are placed on top of the vertical glass pieces and are connected to those both with glue as well as metal connections and screws.

Figure 19: Assembly sequence of the glass structure

25

6. Connections Connections needed to be considered so that the structure would be structurally safe. The horizontal joints are in cases of corrugated glass facades the most important type of joints because they have to serve continuity of the surface from the top to the bottom. This is essential because they must prevent the tensile stresses occurring from the wind on the glass to open the joint and lose continuity of the surface (Doulkari K., 2013).

In all applications until now a linear clamping steel profile was chosen to solve this problem. For that reason, but also because of assembly feasibility, such a connection is being proposed for this project as well. Besides, it is logical that the clamp is preferred instead of drilled connections as the latter ones would create stress concentrations in this geometry.

Furthermore, robustness and post failure behaviour is determined mostly from the horizontal joints. If a panel breaks at the bottom 26

of the faรงade then the linear joint has to be continuous and able to transfer the dead load of the top panel to the panel at the sides. This is called creating an alternative load path until the panel that broke is replaced (Doulkari K., 2013).

The connection to the ground is shown in figures 20 and 21. As illustrated, a layer of silicone is used which gives to the structure a small degree of movement when subjected to bending stresses.

These stresses cause the maximum deformation around the middle vertical edge. The joint has to be flexible enough to transfer shear stresses coming from this action.

Figure 20: 3D detail of the corrugated component to the ground

Figure 21: Connection detail of the corrugated component to the ground

27

As far as the vertical connections are concerned, the critical point was at the roof. For the connection to the roof another connection needed to be designed which not only would have the appropriate geometry to connect the curved parts at any angle but also would be aesthetically pleasant to fit to the pure glass construction. Research on connections was conducted and six different connections were designed as illustrated in figure 22 in order to choose the most appropriate one. In the end, the one inside the red rectangle was chosen (figure 22).

A detailed interpretation of the chosen connection is shown in figures 23 and 24. A detail worth mentioning is that between the metal connection and the roof panel another metal piece is used, that is pre-glued on the bottom layer of the sandwich. Consequently, the roof and the wall partitions are independent from each other in order to allow easy replacement should an incident of breakage occur. This way, only the broken compartment will be taken out.

28

Figure 22: Proposed connections for attachment to the roof

Figure 23: Roof to vertical corrugated component connection

Figure 24: Detail of the chosen connection

29

7. Safety analysis One important factor in order to ensure the safety of the glass construction is the determination of the worst risk scenarios which are applicable in the short or long run. The calculations of these scenarios were made by multiplying the consequence with the probability according to the given values shown in table 1.

The possible scenarios taken account are the following:

into

1) a human could bump against the construction 2) a human on a bicycle could bump against the construction 3) a car could crash into the construction 4) vandalism - objects could be thrown against the construction by someone.

The results are interpreted in table 2.

30

The RD value should always be below 70 in terms of safety, a parameter which applies to all four cases considered for this design. This means that no extra measures need to be taken. Besides, the choice made that all glass parts are laminated ensures that the structure will not fail in case of damage.

Table 1: Risk analysis table - RD values

Parameters

WS

BS

ES

RD1

human impact

10

6

1

60

bicycle impact

10

6

1

60

car impact

1

0.5

40

20

vandalism impact

3

1

7

21

Table 2: RD values according to risk scenarios

31

8. Structural calculations 8.1 Hand calculations The volume used for all calculations was estimated to be approximately 0,07m3.

The glass properties used are shown in table 3. The total load for the facade and the roof is calculated using the values shown in table 4.

The structural performance of the laminated glass was calculated by using the effective thickness t* with the following formula:

The results are interpreted in table 5.

32

Glass properties

Value

Unti

Density

2520

kg/m3

Young’s modulus

70

GPa

Compressive strength

200

MPa

Annealed

20

MPa

Annealed (long term loads)

6

MPa

Heat strengthened

40

MPa

Fully tempered

80

MPa

Tensile strength

Glass type

Table 3: Glass properties

Load type

Reference number (kN/m2)

Total (kN/m2)

Live loads (multiplied by a factor of 1,5)

980

1,47

Wind load for facade ( pressure+suction)

1

1

Wind load for roof (suction only)

-0,4

-0,4

Snow load

0,8

0,8

Maintenance load (point load)

1

0

Maintenance load (distributed load)

0,4

0

Dead load (multiplied by a factor of 1,2)

-

1,71

Total (facade)

5,74

Total (roof)

4,34

Table 4: Calculations of load types

Thickness - 1st layer (mm)

Thickness - 2nd layer (mm)

effective thickness t* (mm)

Laminated glass (facade)

10

10

10

Laminated glass (roof)

15

15

15

Table 5: Effective thickness t* for laminated glass

33

The Critical Buckling force is calculated as follows: Fcritical = Î 2EI(nL)2 Fcritical = ((3.14*3.14*70,000*12,61,891)/ (((0.5*4,000)*(0.5*4,000)))/1,000)/4 Fcritical = 544 KN The maximum force on the 11 meter length coulmn is: 4.3 kN/m2 * 10.53 = 22.6 kN < 544 The result is acceptable and the column can work under buckling.

Where, Fcritical = maximum vertical load on column E = 70,000 N/mm2 I = 12617891 mm4 (unsupported length of column) L = 4,000 mm (unsupported length of column) n= 0.5 if both ends are fixed

34

8.2 Diana results: Vertical corrugated component After testing three possible curvatures for the vertical components, in terms of the lowest deflection due to section shape, we concluded that the quarterhalf-quarter circle option was the best.

It presented a reduced deflection in the half-circle part compared to the elliptical and half-circle section (figure 25), so it was the shape of choice for the design.

In terms of construction, the component consists of a 15mm Low iron Tempered Safety Glass, two intermediate layers of sentry glass with a total thickness of 2.5 mm, followed by another layer of 15 Low Iron TSG. Since it is under compression, the real thickness of 32.5 mm was considered for the Diana model calculations along with the maximum height of 4 meters.

Figure 25: Deflection of corrugated components with different dimensions

35

In order to test the load-bearing capacity of the constructionâ&#x20AC;&#x2122;s facade, the loads (SLS) - corresponding to a single vertical component - transferred from the biggest horizontal beam unit, that of 11 meters span, were used. It can be seen in figure 26 that the maximum deformations for the vertical corrugated component on the Y axis are 0.00244 mm. The result can be considered acceptable since the deformation ratio is lower than the limit of 1/200 of the componentâ&#x20AC;&#x2122;s height.

36

Figure 26: Deflection of vertical corrugated component, maximum on Y axis = -0.00244mm

As shown in figure 27, most of the vertical unit is under cÎżmpression stresses with a maximum of 0.76 N/mm2.

In addition, the maximum occuring tensile stresses are 0.0587 MPa (figure 28). Since the maximum glass strength for compression is 200 MPa, while the maximum tensile strength reaches 20 MPa (for annealed), these results are more than acceptable.

Figure 27: Principle stresses S3 of vertical corrugated component

Figure 28: Principle stresses S1 of vertical corrugated component

37

8.3 Diana results: Roof sandwich In the beginning, due to Diana software difficulties, the roof panel was initially tested only as a corrugated beam and not as a sandwich panel beam, for the maximum span of 11 meters.

The maximum allowable deformation of a glass beam, considering a feasible solution, is 1 mm for every 100 mm. In correspondence, the maximum deformation acceptable for the 11-meter span would be 11 cm.

Additionally, the maximum allowable deformation-serviceability is 1 mm for every 200 mm which would translate in 5.5 cm for the 11 m span.

The deflection, however, as shown in figure 29, can still be acceptable in this corrugation-only case, even though it could be considered a less strong beam than a corrugated sandwich panel.

The blue coloured area in this diagram indicates the maximum deflection which reaches 8 mm in the Z direction.

38

Figure 29: Deflection of the roof corrugation layer without upper and bottom glass panes

After overcoming the difficulties mentioned, a digital sandwich panel beam model was possible.

Running the simulation showed even less deformation in total than the corrugation-only model did. The Diana diagram (figure 30) indicates that the upper layer suffers the maximum deflection as it is exposed to the wind and live loads. The loads are applied also at the bottom layer since it is glued along side the beam length. In result, the maximum displacement reaches 1.2mm for the whole panel as one piece (the corrugation glued to the flat glass surfaces) and the sandwich panel layers act as fixed beam altogether. The equivalent thickness considered in the digital model is 12.59 mm for the upper and lower glass layers whereas in reality the thickness is 22 mm (10mm Low Iron glass TSG + sentry glass folie + 10 mm Low Iron glass annealed).

Figure 30: Deflection of the glass sandwich panel

39

The principal stresses in the beam were found to be equally distributed on the model (figures 31 & 32) indicating that the sandwich as a whole is subjected to tension. This is probably due to the different parts working together to resist deformation.

Figure 31: Principle stresses S1 of the glass sandwich panel

40

Figure 32: Principle stresses S3 of the glass sandwich panel

9. Conclusions The project designed offers a very interesting transition zone before entering the Architecture Faculty building. The corrugated along with the curved glass provide different kinds of views, with different qualities, making passing through an overall unique experience. The heights are kept low in order not to be too intrusive compared to the facultyâ&#x20AC;&#x2122;s facade. The corrugated glass offers less transparency than flat one would, but besides this being in many occasions a desirable effect, the kind of transparency it does provide, is the one to give enough information to the viewer in order to provoke curiosity for the inside.

Structurally speaking, corrugation is used for its enhanced capacity to bear loads. In the few examples already built or designed, huge facades are created to cover great openings and the corrugation is used in order to bear self-loads rather than extra ones. In this project, the glass facade

has not extensive self-load but it is attempted to carry a significant roof load. The corrugated panels proved to respond greatly to this task in the digital simulations, making it possible to even use annealed glass for the vertical components.

The roof was an even more of a challenge, since the shape can be considered irregular and the notion of beams and columns was not an appealing one. Finally corrugation was used for this part as well , in the form of sandwich panels constituted of flat sheet-corrugation-flat sheet glued together pieces. This set-up proved capable of providing beam-like panels that could cover a span up to 11 meters that indicated a great behavior in terms of deflections and stresses in the Diana simulations. The middle corrugated part could also use annealed glass under these circumstances.

the roof and facade panels that would be discrete while enabling disassembly for damage control, was designed.

In general, the experimentation described in this report, reaches the conclusion that corrugation can exhibit significantly increased strength compared to a similar flat glass panel of the same size, giving the benefit of reducing the glass thickness and increasing the strength of the structure.

In addition, a glass sandwich panel can be a very interesting alternative to roof and probably floor beams, behaving very well structurally while providing a worth mentioning aesthetical result.

On top of that, a connection between 41

References Doulkari K.; ‘The transparent facade of the future - Design strategies for maximizing transparency with selfsupporting glass facade systems’ MSc Architecture, Urbanism and Building Sciences Master Thesis, Building Technology, Delft University of Technology, 2013 Oikonomopoulou F., Veer F., Nijsse R. & Baardolf K.; ‘A completely transparent, adhesively bonded soda-lime glass block masonry system’ in: Journal of Facade Design and Engineering, Vol. 2, No. 3-4, 2014 (201-221) O’Callaghan J. BEng (Hons) MIStructE, Marchewka M., MEng O’Callaghan E.; ‘Thinking Big Structural Glass’, www.gpd.fi, Performance Days, 2009

42

CEng MRes with Glass

‘The Glas-Sandwich-Aluminiumprofile The Glass-Sandwich-wooden boards’, www.facadeworld.com, retrieved in 2016 Bristogianni T.; ‘Glass Structures Theme: Design of an all-transparent cast glass column’, Building Engineering, Department Design & Construction, Faculty of Civil Engineering and Geosciences, Bachelor of Science Project , release date: March 2016