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SPACEPLATESUnderwater Habitat, Sydney

Structural documentation for the main structure

Date: October 31st 2014

By: Anne Bagger, Anne Bagger ApS

Daniel Sang-Hoon Lee, Royal Danish Academy of Fine Arts, School of Architecture

1. IntroductionThe “SPACEPLATES Underwater Habitat” is an underwater shell structure, designed so that it is a liveablespace.

In the present report, the basis of design for the structure is presented, as well as the structuralcalculations.

The habitat is designed by N55 and Anne Romme, in cooperation with Lloyd Godson and numerous otherpeople in Australia and Denmark, including the authors of this report.

N55, Anne Romme, Daniel Sang- Hoon Lee and Anne Bagger has done their part of the design as a wayof thinking through a purely theoretical possibility to construct an Underwater Habitat. The constructionof an actual, real Underwater Habitat is solely the responsibility of the person who would do so. N55,Anne Romme, Daniel Sang-Hoon Lee and Anne Bagger can not be made legally responsible for any use oftheir design in any way. If Lloyd Goodson should decide to realise the habitat and actually build it, allliability rests with him. Any kind of accident that might occur in relation to the building and potential useof an Underwater Habitat would be the responsibility of Lloyd Goodson.


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2. Codes of practiceThe following codes of practice have been used in the preparation of this report:

DS/EN 1990:2007 Basis of structural designDS/EN 1991-1-1:2007, Eurocode 1: Actions on structures – Part 1-1: General actions – Densities,self-weight, imposed loads for buildingsDS/EN 1993-1-1:2007, Eurocode 3: Design of steel structures – Part 1-1: General structural rulesDS/EN 1993-1-8:2007, Eurocode 3: Design of steel structures – Part 1-8: ConnectionsDNV-RP-C205: 2010, Environmental conditions and environmental loads

In addition to these, the appropriate Danish national annexes have been used.

3. MaterialsSteel:

Alloy AS/NZS 3678 - 250 XLERPLATE® steel

Characteristic yield stress: fy = 280 MPa

Characteristic ultimate stress: fu = 410 MPa

Partial safety factors on yield stress: M0 = 1.1 (resistance of cross section)

M1 = 1.2 (resistance of members to instability)

M2 = 1.35 (resistance of connections)

E-modulus: E = 210 GPa

Poisson’s ratio: = 0.3

G-modulus: G = E/2/(1+ ) = 80.8 GPa

Welds:

Welds are fillet welds, or butt welds with partial or full penetration. There are no intermittent welds.

Bolts:

Bolts are in quality 8.8 with the following strength parameters:

Characteristic yield stress: fy = 640 MPa

Characteristic ultimate stress: fu = 800 MPa

PMMA (acrylic sheets):

Characteristic tensile strength: f = 70 MPa (reduces to 20 MPa at 80 degrees Celsius)

Estimated design value: fd = 50 MPa

E-modulus: E = 3.2 GPa

Poisson’s ratio: = 0.37

G-modulus: G = E/2/(1+ ) = 1.2 GPa


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4. Loads

4.1 Self weightMaterial densities:

Steel: = 7.8 ton/m3 = 77 kN/m3

Concrete: = 2.4 ton/m3 = 24 kN/m3

PMMA: = 1.2 ton/m3 = 12 kN/m3

Salt water: = 1.0 ton/m3 = 10 kN/m3

Marine growth: = 1.4 ton/m3 = 14 kN/m3

The self weight of the steel structure is applied according to the plate thickness. The concrete ballast loadis added as described in Section 4.4.

4.2 Hydrostatic pressureThe hydrostatic pressure increases linearly with the water depth, d, as shown in Figure 1. The load on thehabitat at a given depth, di, is equal to the hydrostatic pressure at that depth (pw = w * di), actingperpendicular to the surface.

Since the hydrostatic pressure is balanced by the internal pressure, the absolute depth of the habitatdoes not affect the load experienced by the structure (see also Section 4.3).

The force resultant of the hydrostatic pressure (buoyancy) is equal to the mass of the water displaced bythe habitat (Archimedes’ principle).


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Figure 1: Hydrostatic pressure

4.3 Internal pressureThe internal pressure balances the water pressure at the free water surface in the entrance tube.

The habitat is loaded by the difference between the hydrostatic pressure and the internal pressure.

The design load case is when the water level is at the very bottom of the habitat, as this yields thelargest difference between the internal pressure and the hydrostatic pressure.

pw(dbottom) = w * dbottom

d = 0 pw = 0

pw(dtop) = w * dtop

pw(dtop)

pw(di)

pw(di) = w * di

dbottom

dtop

di

pw(di)

Pres = w * V

pw(dbottom)d


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Figure 2: Internal pressure

4.4 Ballast loadConcrete is cast into the lower part of the habitat to counteracts the buoyancy, to place the centre ofgravity as low as possible, and to form a floor. In the FE model, the ballast load is modelled so that itcorresponds to concrete with a density 2,4 t/m3. Subsequently in the calculations, the load is scaled up tobalance the buoyancy, which in reality is achieved by adding scrap steel to the concrete. In this way, theappropriate amount of added steel is determined.

The casted concrete is outlined in Figure 2.

4.5 Growth loadThe marine growth is assumed to have a maximum thickness of 150mm, and the ensuing load on thestructure is determined using the density of the growth, minus the density of the water. In one load casewhere the structure is lifted above the water, the full density is applied. Thus, in the water, the growthload is 0.6 kN/m2 distributed over the entire outer surface, and above water the load is 2.1 kN/m2.

4.6 Live loadDue to the small enclosed space and the special access circumstances, the live load is likely to berelatively small. It is assessed to have a maximum value of 1,5 kN/m2 (150 kg/m2). This includespossible extra ballast, added after the initial installation of the habitat.

pw(dbottom)

pw(dbottom)

d = 0 pw = 0

pw(dbottom) = w * dbottom

d


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The live load is considered to act on the entire floor surface, including the removable plate over theentrance tube.

4.7 Wave loadWhen the water moves relative to the habitat, forces act on the habitat and its anchoring. The nature andvalue of these loads depend on the velocity and acceleration of the moving water, which again mainlydepends on the wave height and speed, the water depth, and the size and shape of the habitat. To somedegree, the load also depends on the compliance of the anchoring points, but conservatively this effect isignored.

The loads are determined using three different approaches. The first two approaches are analyticalapproaches, described in the Norwegian recommended practice DNV-RP-C205 [3]. The third approach isa simplified calculation of a wave load on a sea wall, adjusted according to the actual geometry of thehabitat. As shown in the following, the three approaches gives approximately the same wave load value,and thereby act as a mutual approval of the result.

According to the Office of Environment & Heritage in New South Wales, Australia, the largest occurringwave heights in Sydney Harbour is as follows:

From ships: H = 0,62mWind waves: H = 0,71m (at Fort Denison)

In the following, a maximum wave height of 0,71m is assumed, and a corresponding period of 2,3seconds.

Morison’s Formula

Morison’s Formula calculates a drag-contribution and an inertia-contribution to the load, based on thewater speed and acceleration respectively. In the case of the habitat, the inertia-contribution isdominant, which is typical for relatively large objects (when compared to the wave height).

Using Morison’s Formula, the wave load resultant is calculated for a vertical cylinder with a diameter of 3meters, placed so that it sticks 4 meters into the water from the surface. To adjust for the actual habitatgeometry, the resulting load is divided by a factor of 2. The wave height is set to 0,71 meters, and theperiod is set to 3 seconds. This yields a wave length of 14 meters.

This method yields a horizontal load resultant of 23kN on the habitat.

Froude-Krylov force

The Froude-Krylov force is the pressure field generated by undisturbed waves passing the habitat. Theresulting force on the habitat is equal to the Froude-Krylov force plus the diffraction force on the habitatdue to the floating body that disturbs the waves. Based on experiments and full scale measurements, it isgenerally seen as a good approximation to determine the resulting force by multiplying the Froude-Krylovforce by 2,0.

Just like when using Morison’s Fomula, the wave load resultant is calculated for a vertical cylinder with adiameter of 3 meters, placed so that it sticks 4 meters into the water from the surface. To adjust for theactual habitat geometry, the resulting load is divided by a factor of 2. The wave height is set to 0,71meters, and the period is set to 3 seconds. This yields a wave length of 14 meters.


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This method yields a horizontal load resultant of 21kN on the habitat.

Approximate calculation of load on sea wall

The load is calculated as quasi-static, as breaking waves are not assumed to affect the habitat. Thefollowing expression determines the load of a quasi-static wave load on a sea wall, near the watersurface:

P = * g * H

This yields a maximum pressure of 7,0 kN/m2. This load can be reduced, corresponding to the followingfactors:

The habitat is immersed in the water, 2-4 meters below the surface, and is therefore not loadedby the maximum load in the water surface.The habitat is not a plane, vertical wall, but a curved object that the water can pass around.

The area of the habitat, projected on the wave direction, is 7 m2. All this information leads to anapproximated force resultant of a magnitude very similar to the result of the two previous methods.

Conclusion

The wave load has a horizontal force resultant of 20-25kN. The application of the load is described morein detail in Section 6.1.


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4.8 Load combinationsSince hydrostatic pressure and internal pressure will always affect the structure simultaneously, togetherwith self weight, ballast load, and growth load, these loads are applied in the same load combination(LC1).

LC2 is the same as LC1, where live load is added. The live load is multiplied by a safety factor of 1.5.

LC3 is the wave load, acting together with LC1 and a reduced live load.

LC4 is self-weight and ballast multiplied by a load factor of 1.5, to simulate the situation during hoistingabove water. The load factor covers possible dynamic effects. The growth load is multiplied by 3.5 to takeinto account that the growth layer will be water filled when the habitat is hoisted above water.

The load combinations are summed up in the following. SW is self-weight, B is ballast load, GL is growthload, HP is hydrostatic pressure, IP is internal pressure, LL is live load and WL is wave load.

“+” denotes “combined with”.

LC1 = 1.0*SW “+” 1.0*B “+” 1.0*GL “+” 1.0*HP “+” 1.0*IP

LC2 = 1.0*SW “+” 1.0*B “+ ”1.0*GL “+” 1.0*HP “+” 1.0*IP “+” 1.5*LL

LC3 = 1.0*SW “+” 1.0*B “+” 1.0*GL “+” 1.0*HP “+” 1.0*IP “+” 0.75*LL “+” 1.5*WL

LC4 = 1.5*SW “+” 1.5*B “+” 3.5*GL


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5. Geometry and static systemThe structure consists of 6mm steel plates welded together. The swords for the hanging points (seeFigure 6) are 10mm in thickness, and the pins that connect the chains to the structure’s hanging pointshave a diameter of 20mm.

Figure 3: 3D view of the habitat (left) and the cast concrete ballast (right).

Figure 4: Side views of the habitat.

Hanging points(3 in total)

Legs(3 sets in total)

Concrete ballast, cast intolower part of the habitat.

Entrance tube

Windows ofacrylic plates

(PMMA)

2.86 m 2.98 m

2.96 m

0.70 m


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Figure 5: Top view of the habitat.

5.1 Structural principleThe basic structural principle of the habitat is that of a plate shell structure [1]. A plate shell structure isa shell structure with a facetted geometry, where the tessellation is organized so that the plate elements(the facets) carry the load on the structure. This way, no additional structure is needed, other than theplates and the connections between their edges. The geometry of a plate shell structure is characterizedby the number of plates meeting in each vertex on the surface: three plates meet in all vertices, andstructurally this has the consequence that the vertices are not active in the overall load transfer of shellforces.

The most dominant loads on the habitat (hydrostatic pressure, internal pressure, and ballast load) aredistributed loads, acting symmetrically around the vertical centre axis of the structure. This makes thecircular shape well suited for the load. In addition to this, these dominant loads are almost in internalequilibrium, meaning that only a small part of the load ends up in the supports.

As a consequence, bending moments will primarily come from local plate bending of the planar elements(the facets), and stress concentrations will primarily occur around the support points.

In the lower part of the habitat, where concrete ballast is cast into the structure, shear studs are weldedonto the inner surface of the facets, creating a structural coherence between steel wall and concrete.

5.2 Support conditionsDuring the submergence in Sydney harbour, the structure will be hanging from chains connected to apontoon in the water surface and to the hanging points on the habitat. The legs ensure that in case of anaccident where the anchoring fails, where the habitat could fall to the bottom of the sea, the entrance willnot be covered.

In other applications, the habitat may be standing directly on the seabed instead of hanging from thewater surface. However, since this is not the case here, this report does not cover design and calculationsof the legs.

The anchoring points are constructed as steel “swords”, welded to the inner surface of the structure, andpenetrating the structure through a sealed hole in a facet, as shown in Figure 6. This distributes the pointload from each chain into the structure’s surface. The swords are embedded in the cast concrete, andstructural cooperation between steel and concrete is ensured by shear studs welded onto the internalsurface of the steel.

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Figure 6: The three swords that connect the hanging points to the structure are highlighted.

In this report, the buoyancy of the pontoon is not investigated and proven, as this falls under theresponsibility of the team in Australia.

5.3 Basic geometric valuesThe following volume-values are approximate. They will be used for calculation of the necessary ballast,to generate loads to the FE model, and to check the model.

Volumes:

Total volume, including entrance tube: 12.626 m3

Total volume, not including entrance tube: 12.286 m3

Volume of ballast: 3.46 m3

Volume of steel (outer skin): 0.18 m3

Volume of acrylic: 0.095 m3

Areas:

Floor area (not including tube area): 6.36 m2

Floor area (including tube area): 6.74 m2

Surface area, structure (one side): 26.8 m2

Weight values:

Ballast (only concrete, no steel): 83 kN

Steel plates (outer skin): 13.9 kN


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6. Finite element modelIn this chapter, it is described how the habitat is modelled in the finite element analysis software“Autodesk Robot Structural Analysis Professional 2014” (in short “Robot”).

The analysis in Robot is a geometrically linear calculation – the structure is loaded mostly in tension andplate bending, so instability will not occur. Also, the deflections are relatively small.

6.1 Application of loadsThe weight of the concrete ballast is modelled as a distributed load on the steel plates in the lower part ofthe habitat. The stiffness that the concrete brings to the structure is modelled as rigid links to the steelplate members, meaning that the plates behave as if infinitely stiff perpendicular to their own surfaceplane.

As explained in Section 4.7, the wave load has a resultant of 20-25kN. To model this load, a staticpressure load has been applied on 7 facets at and around a fixing point. The value of the pressure ischosen so that the force resultant matches the deduced wave load resultant. Also, to include thestructure’s response to the asymmetrical aspect of wave loads, a suction load has been applied to thesides of the structure, in a way so that the side loads level each other out, and thereby only loads thestructure internally. This suction’s load per area has a value of 2/3 times the pressure load.

Generally, for all load types, distributed load on the panels is applied with a constant value over eachpanel. The value is determined relative to the position of each plate’s centre.

6.2 Post-processing of the FE resultsFor each load, the maximum stress is noted, together with the maximum deflection and the sum of thereaction forces in the three main directions.

The reaction forces are compared to the expected value, for verification of the model.

The maximum stresses and deflections are then superposed, according to each of the load combinations.To simplify the analysis, maximum stresses and deflections are added together, regardless of whetherthey occur in the same position.


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7. Results of FE analysis

7.1 Self-weight when the habitat is immersed into waterThis load includes hydrostatic pressure, internal air pressure, self weight of steel, and concrete ballastload.

Figure 7: Loads on model from self weight in the water. Left: Outside view. Right: Section through thecentre of the habitat, showing also the loads on the inner surface.

The applied loads are illustrated in Figure 7. The resulting Von Mises stresses are shown in Figure 8, andthe deformed structure in Figure 9. Stresses around the top plate will look a little different in the finalversion, as a 25mm acrylic plate will replace the centre of the steel plate.

Max. stress Max. deflectionSum of reaction forces

Fx Fy Fz(MPa) (mm) (kN) (kN) (kN)114 3 0.0 -3.1 4.8


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Figure 8: Von Mises stresses in the steel.

Figure 9: Deformed plot. Maximum deflection 3mm.(The colours depict the Von Mises stresses, see also Figure 8.)


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Check of reaction forces:

The summed reaction forces are used to verify the model in the following. The forces are extractedseparately for hydrostatic pressure, internal air pressure, self weight of steel, and the concrete ballastload.

There is a total buoyancy in the model of 132 kN (or 13,4 tons – found by determining the vertical forceresultant for the hydrostatic pressure load), corresponding to a total volume of 13,4 m3. The actualvolume is 12,6m3 (including the entrance tube) so the model overestimates the buoyancy with about 6%.

There is a total concrete weight of 114 kN (11,6 tons), and a steel weight of 13,6 kN (1,4 tons) in themodel.

The internal pressure yields a sum of reaction forces of zero, as expected.

The above values result in a total buoyancy of 5 kN, acting upwards. However, since there areuncertainties connected to the determination of the weight, this value will in reality be different. Theexact value must be determined and adjusted during the production of the habitat. The optimum will be aresulting buoyancy of 5 kN acting downwards.

Also, the model shows a resulting horizontal reaction of 3.1kN. This value comes from the hydrostaticload case. The value is supposed to be zero. The reason for this error has not been located, but since theconsequences are negligible in terms of stresses and deflections, the error is ignored.

7.2 Live loadThis load is an equally distributed load of 1,5 kN/m2 on the entire floor, including the top of the entrancetube.

Figure 10: Live load. (The load symbol is difficult to see in the plot. It is applied to the surface at the top ofthe entrance tube.)

The applied loads are illustrated in Figure 10. The resulting Von Mises stresses are shown in Figure 11.


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Fx Fy Fz(MPa) (mm) (kN) (kN) (kN)

10 0 0.0 0.0 -10.1

The largest Von Mises stress is 10 MPa, and occurs at the fixing points. The deflections are negligible.

Figure 11: Von Mises stresses in the steel.

Check of reaction forces:

The force resultants in the horizontal directions are zero. In the vertical direction there is a reaction forceresultant of 10.1 kN. This corresponds to a floor area of 6.7 m2 and a load of 1,5 kN/m2 so it is ok.


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7.3 Wave loadA pressure load of 3,0 kN/m2 is applied to 7 facets around a fixing point, as shown in Figure 12. Also asuction of 2,0 kN/m2 is applied to the sides of the structure. The sum of the vertical reaction force is thencompared to the actual wave load, and the load case is scaled up accordingly.

Figure 12: Wave load. Left: Outside view, where only the pressure load on the front is visible.Right: Section through the center of the habitat, where the suction in the sides is visible.



15 0 -8.6 0.0 0.7

The summed up horizontal reaction force is 8.6 kN. As explained in Section 4.7, the wave load is 20-25kN. Therefore, the results from the present calculation are scaled up with a factor 3 in the calculations.Hence, the largest Von Mises stress is 3 x 15 MPa = 45 MPa.

The deflections are negligible.

Stresses are shown in Figure 13 and Figure 14.


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Figure 13: Von Mises stresses from wave load. To be scaled by a factor 3.

Figure 14: Zoomed image of maxium stress location. To be scaled by a factor 3.


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7.4 Growth loadThe results of the growth load analysis are only showed in tabular form. The load is a vertical distributedface load of 0.6 kN/m2 under water (where the buoyancy counteracts the load), and 2.1 kN/m2 abovewater. The load is acting on the outer surface of the habitat.

Growth load under water:



10 0 0.0 0.0 10

Growth load above water:



35 0 0.0 0.0 35

7.5 Self-weight when the habitat is above waterThis load includes the self weight of steel and the concrete ballast load, so it is a part of the load analysedin Section 7.1.

The results are shown in tabular form below.


Fx Fy Fz(MPa) (mm) (kN) (kN) (kN)129 0 0.0 0.0 -127

According to this analysis, the weight of the structure plus ballast is 127 kN, or 13 tons. The actualweight will be determined more into detail at a later point, when it is fine tuned to match the buoyancy.


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7.6 Load combinations

In the following, stresses and deflections are checked for the 4 load combinations listed in Section 4.8.

The allowed maximum stress is

fyd = 280MPa / 1,1 = 255MPa

Load combination 1: 1.0 * SW “+” 1.0 * B “+” 1.0 * GL “+” 1.0 * HP “+” 1.0 * IPMaximum stress: 1.0 * 114MPa + 1.0 * 10MPa = 124MPaMaximum deflection: 1.0 * 3mm + 1.0 * 0mm = 3mm

Load combination 2: 1.0 * SW “+” 1.0 * B “+” 1.0 * GL “+” 1.0 * HP “+” 1.0 * IP “+” 1.5 * LLMaximum stress: 124MPa + 1.5 * 10MPa = 139MPaMaximum deflection: 3mm + 1.0 * 0mm = 3mm

Load combination 3: 1.0 * SW “+” 1.0 * B “+” 1.0 * GL “+” 1.0 * HP “+” 1.0 * IP“+” 0.75 * LL “+” 1.5 * WL

Maximum stress: 124MPa + 0.75 * 10MPa + 1.5 * 45 = 199MPaMaximum deflection: 3mm + 0.75 * 0mm + 1.5 * 0mm = 3mm

Load combination 4: 1.5 * SW “+” 1.5 * B “+” 3.5 * GLMaximum stress: 1.5 * 129MPa + 3.5 * 10MPa = 229MPaMaximum deflection: ~0mm

Both stresses and deflections are within acceptable limits.


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7.7 Anchoring pointIn the Robot analysis, the detail at the anchoring point was not modelled in a way that was fullyphysically correct. The structure was supported by pinned connections along the edges of the anchoringholes in the swords. In reality, there is a pin through the hole, and the load is transferred in the contactbetween pin and hole edge. The consequences for the calculations are of a local nature. Only the holeedge and the plate in a small area around it will have another stress distribution than what wasdetermined in the Robot model.

To accommodate for this, the bearing resistance of the hole is determined using a calculation method forbearing resistance, given in Eurocode 3 (EN1993-1-8:2009, Table 3.4).

= = = 101

Here, the pin diameter d is 20mm, and the plate thickness t is 10mm.

To accommodate for a smaller pin size than the hole diameter, the value above is multiplied by 0.8, inaccordance with EC3. Hence, the bearing resistance is 81kN.

The maximum load in the connection is when the habitat is lifted above water, covered in water filledmarine growth. In accordance to load combination 4, and the summed reaction forces given in theprevious sections, the largest load in one of the three connections is:

N = 1,5 + 3.5 = 75kN

Hence, the bearing capacity of the anchoring point is just sufficient.

7.8 LegsThe legs of the habitat, as indicated in Figure 3, are not a part of the present investigation, as they havenot been designed at the issue date of this report.

It should be noted that local reinforcement of the structure might be needed at the attachments of thelegs, like shown in Figure 15

Figure 15: Reinforcement in the area near the connection between structure and leg.

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7.9 Acrylic platesThe acrylic plates are calculated as circular plates, using linear plate theory. Since the plates are close tocircular in shape, and since the deflections do not exceed the plate thickness, this is found to be asuitable approximation.

Figure 16: Acrylic plate windows in the habitat.For each plate, an equivalent diameter, d, is estimated. The load on the plate, p, is determined using thedistance from the middle of the plate to the bottom of the habitat (H), as this is the lowest possible levelof the free water surface, and hence gives the largest pressure on the plates (see Sections 4.2 and 4.3).The plate stiffness according to Kirchhoff–Love plate theory, D, is calculated, as well as the maximumbending moment, m, the maximum stress, , and the maximum deflection, u. The expressions are givenhere [2]:

=)

= )

=

=

Here, E is the E-modulus, is Poisson’s Ratio, and t is the plate thickness.

Since the acrylic plates are placed on the inner surface of the structure, and the load is acting outwards,the plate deflection will be zero at the hole edge. Conservatively the equivalent plate diameter relates tothe actual size of the plate.

Thickness 25 mm

Thickness 15 mm


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The results of the calculations are summed up here, sorted after descending plate size:

Plate diameter D (mm) 700 585 551 508 446 385Plate thickness T (mm) 25 15 15 15 15 15Location height on structure H (m) 2.95 1,27 1,60 1,91 2,17 2,40Load P (kN/m2) 29.0 12,5 15,7 18,8 21,3 23,6Bending stiffness D (103 Nmm) 4991 1078 1078 1078 1078 1078Max bending moment M (N) 752 226 253 256 225 185Max stress (N/mm2) 7.2 6,0 6,7 6,8 6,0 4,9Max deflection u (mm) 5.3 5,1 5,1 4,4 3,0 1,8Relative deflection d/u (-) 133 114 108 116 151 212

Conservatively, the stresses are compared to the design strength of the acrylic divided by 3, to take timedependency of the strength into account (long term load). The design strength of the acrylic for this longterm load is thereby assumed to be

fd = 50MPa / 3 = 17MPa

As it appears from the table, all stresses are smaller than this value. The relative deflection is less thand/100 for all plates, which is satisfactory.

8. ConclusionIt has been shown that the strength and stiffness of the habitat and its connection points are sufficient.

The pontoon and the chains that connect the habitat to the pontoon are not covered by this report.Neither are the legs for placing the structure on the seabed.

9. References[1] A. Bagger, Plate shell structures of glass – Studies leading to guidelines for structural

design, Ph.D. thesis, Technical University of Denmark, 2010

[2] Teknisk Ståbi, 21st edition, Nyt Teknisk Forlag, 2011 (Danish collection of formulae and materialparameters for civil engineering).

[3] DNV-RP-C205, Environmental Conditions and Environmental Loads, Recommended practice, DetNorske Veritas, 2010

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