Concrete Protection Cover

The protection covers that will be tested are basic, tunnel shaped arch covers. As a simplification, stock drain pipes cut into halves was provided by Multiblokk AS. The specific drain pipe to be used is called IG-Rør Armert Falsrør, Basal.

Figure 4.5.3-35 Material data for drainage pipe supplied by Multiblokk AS

Source: http://www.skjeveland.no/skjaeveland/avlopsror-og-deler/ig-ror-og-deler-basal/ig-ror-armert-falsror-basal, downloaded 3/3-2015

According to the product catalog, see Figure 4.5.3-35 and Chapter 6.4 in the Basal Standard (Basal AS, 2009), the data of the inner diameter of this pipe is 2000 mm (+/- 15 mm), the length is 1500 mm (+ 30 mm, - 10 mm), the thickness is 215 mm (+/- 5%) and the weight is 5700 kg (when cut in half it is 2850 kg). This is enough inner space for cover of a 16”

pipeline, included motion of the pipeline as well as clearance.

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The reinforcement used in the first test at Multiblokk AS’ premises was 8 oval bars of diameter Ø12 mm with a center distance of about 163 mm. For the second test at UiS laboratories, the amount of reinforced used was increased to 12 double bars of diameter Ø12 mm with a center distance of about 100 mm, resulting in a total of 24 bars. The distance between the double reinforcement rings was 153 mm.

Figure 4.5.3-36 Reinforcement data: O = Oval reinforcement, DK = Double reinforcement Source: (Basal AS, 2009)

Multiblokk AS uses a special dry-casting method for their products. This results in ‘zero slump, and the forms can be stripped as soon as the concrete has been consolidated’

(ConcreteNetwork.com). This method enables easier mass production of products, but does, according to Multiblokk AS, suffer somewhat in strength tests compared to regular wet-cast concrete, making them slightly more brittle.

Figure 4.5.3-37 The protection covers provided by Multiblokk AS.

86 4.5.3.2 Concrete material data

The concrete material used by Multiblokk AS is in accordance with the concrete standard NS-EN 206-1:2000. There are some small differences between material data and

requirements between this standard and the Eurocode 2, but the NS-EN 206-1:2000

standard was not available at the time of writing, and thus it was decided to give indicative material data from Eurocode 2 for the same material strength B40.

According to Chapter 6.4 in the Basal Standard (Basal AS, 2009), the minimum durability class of the concrete used in the covers is M40 and maximum water to binder-ratio (v/c+Σkp) = 0,40.

According to Table NA.E.1N in the Eurocode 2 (Norsk Standard, 2004), the expected minimum concrete strength class is B40, based on the durability class of M40.

Further, according to Table 3.1 of the Eurocode 2, some of the strength and deformation characteristics of the concrete are therefore:

Table 4.5.3-1 Material data for B40 concrete from EC2 Table 3.1

Concrete strength

class B40 Explanation

fck (MPa) 40 Characteristic compressive cylinder strength of concrete at 28 days fck,cube (MPa) 50 Characteristic compressive cylinder strength of concrete at 28 days fcm (MPa) 48 Mean value of concrete cylinder compressive strength

fctm (MPa) 3,5 Mean value of axial tensile strength of concrete

See the Eurocode 2 (Norsk Standard, 2004) for more details about the material.

87 4.5.3.3 Dropped objects

The dropped objects used in the test have been made using different methods. For use in the initial test at Multiblokk AS, only the 1400 kg object for the 50 kJ test was made. This object broke during the test. For the tests at the University of Stavanger laboratories, the 1400 kg object from the first test had to be remade, and in addition, the rest of the objects 550 kg, 850 kg and 140 kg were also created. See the full calculations in in Appendix D Impact Calculations.

4.5.3.3.1 1400 kg object

The 1400 kg object was made by filling a reinforced 700 mm outer diameter drain pipe with concrete. The total height of the object was calculated to be 1,51 m using concrete density of 2400 kg/m³.

On the bottom of the object a steel plate was placed in order to achieve even distribution of the forces from the impact. Onto this plate several reinforcement bars that point upwards into the object were welded on, making sure that the plate stuck to the object properly and that the impact energies were absorbed upwards into the object as well as on the impact plate.

A wire to hook into the release mechanism was fastened with a rebar inside the object and cast into place.

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Figure 4.5.3-38 The 50 kJ impact object of approximately 1400 kg and diameter 700 mm.

Figure 4.5.3-39 The impact plate of the 1400 kg object.

89 4.5.3.3.2 550 kg and 850 kg objects

The 550 kg and the 850 kg objects were made using a diameter Ø500 mm steel pipe kindly provided by the Subsea 7 base at Dusavik as walls and formwork of the object cut into the necessary heights. The objects were made by pouring concrete into the steel pipe up to the calculated height. As with the 1400 kg object, impact plates with vertical reinforcement bars are fastened to the bottom of the objects.

The height calculations are as follows, assuming a density of concrete of 2400 kg/m³ and of steel of 7850 kg/m³.

Data of diameter Ø500 mm steel pipe from Dusavik Base:

𝑂𝑢𝑡𝑒𝑟⁡𝑟𝑎𝑑𝑖𝑢𝑠 =500𝑚𝑚

2 = 250𝑚𝑚 𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑⁡𝑤𝑎𝑙𝑙⁡𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 = 19𝑚𝑚 𝐼𝑛𝑛𝑒𝑟⁡𝑟𝑎𝑑𝑖𝑢𝑠 = 250𝑚𝑚 − 19𝑚𝑚 = 231𝑚𝑚

Needed height for object mass 550 kg:

𝑚𝑎𝑠𝑠⁡𝑜𝑓⁡𝑠𝑡𝑒𝑒𝑙⁡𝑝𝑟.⁡⁡𝑚𝑒𝑡𝑒𝑟 = (𝜋 ∗ 250𝑚𝑚²− 𝜋 ∗ 231𝑚𝑚²) ∗ 7850𝑘𝑔

The needed pipe and object height of the 550 kg object are therefore approximately 880 mm. The same calculations for the 850 kg object, which can be viewed in the appendices, yielded a necessary object height of 1350 mm.

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Figure 4.5.3-40 The reinforcement inside the objects.

Figure 4.5.3-41 The 30 kJ and 20 kJ impact objects of approximately 850 kg and 550 kg and diameter 500 mm.

91 4.5.3.3.3 140 kg object

The object of 140 kg was made in a slightly different manner due to the impossible height needed when pouring concrete into the Ø100 mm steel pipe that was found on Subsea 7’s Dusavik base alone. It was decided to use a protruding diameter of Ø100 mm as the impact area, and expand the diameter to Ø300 mm above it to limit the needed object height. The Ø300 mm part of the object was made using a ventilation duct of the same size as

formwork. It is assumed that the weight added by the ventilation pipe can be neglected.

The Ø100 mm pipe found at the Dusavik base will be inserted about 200 mm into the Ø300 mm object, leaving about 150 mm to protrude from the wider part. The protruding part of the pipe will also be filled with concrete to limit the chance of buckling of the pipe walls. An impact plate of diameter Ø100 mm was added to the bottom of the protruding pipe. The necessary object height of the Ø300 mm part is calculated from:

Data of Ø100 mm steel pipe from Dusavik Base:

𝑂𝑢𝑡𝑒𝑟⁡𝑟𝑎𝑑𝑖𝑢𝑠 =100𝑚𝑚

2 = 50𝑚𝑚 𝑊𝑎𝑙𝑙⁡𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 = 10𝑚𝑚

𝐼𝑛𝑛𝑒𝑟⁡𝑟𝑎𝑑𝑖𝑢𝑠 = 50𝑚𝑚 − 10𝑚𝑚 = 40𝑚𝑚 Needed height for object mass 140 kg:

𝑚𝑎𝑠𝑠⁡𝑜𝑓⁡𝑠𝑡𝑒𝑒𝑙⁡𝑝𝑟.⁡⁡𝑚𝑒𝑡𝑒𝑟 = (𝜋 ∗ 50𝑚𝑚²− 𝜋 ∗ 40𝑚𝑚²) ∗ 7850𝑘𝑔

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The concrete column part of diameter Ø300 mm of the 140 kg object will need to be 780 mm high.

Figure 4.5.3-42 The reinforcement inside the 5 kJ object.

Figure 4.5.3-43 The 5 kJ impact object of approximately 140 kg and impact diameter 100mm.

93 4.5.3.4 Deflection measuring devices

The deflection measuring devices used in the first test at Multiblokk AS’ premises were tested as a proof of concept before the full scale test at the laboratories of the University of Stavanger. Due to the potential of crushing of whatever equipment that was placed beneath the cover, a decision to use cheap and replaceable equipment was made.

Four different methods of measuring were used:

 A telescope magnet that could easily be retracted, but would stop once it was no longer pushed back. The telescope staff was placed in an upright position beneath the cover to measure the maximum deflection of the cover, and also the amount of deflection retraction caused by the tension in the reinforcing bars.

 A metal rod with a sharp tip being pushed down by the cover deflection into oasis foam used for gardening was placed in an upright position beneath the cover. Like the telescope staff, this method will also yield the maximum deflection as well as the deflection retraction by the reinforcement.

 A simple ruler was placed in front of the cover and the deflection could easily be recorded from this. The maximum and end deflection was also filmed by a front facing camera.

 The depth between the water surface and the top of the cover was measured using a ruler when the cover was submerged in the basin.

For the first test at Multiblokk premises, the telescope magnet, metal rod into oasis foam and the ruler was used successfully. The magnet method was used for the 5 kJ and 20 kJ impacts, but was destroyed while lifting the cover out of the basin. After that, the deflection was measured using the depth between water surface and top of the cover. This would essentially give the same approximate result as measured from underneath, because the measuring itself was difficult under water and underneath the midpoint of the cover. A camera was also set up in front of the cover underneath the water, but the sand and silt from the sand bags whirled up into the water and severely limited the sight under water, rendering the recordings useless.

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Figure 4.5.3-44 Deflection measuring devices used during the test.