Lecture CiTG

Underwater concrete floors

ir. Ruud Arkesteijn

29th of September 2015

Content

1st hour:• Use and functions of UCF’s• Distribution of forces2nd hour:

• Design-rules (CUR77)• Case: guidelines for preliminary designExtra:

• Steel fibre reinforced UCF’s• Projects• Innovations

Use of UCF’s

Conditions for application in building pits:1. sub-surface construction in ‘soft soils’…2. below the groundwater level…3. especially in permeable soils.

Typical Delta/Dutch conditions!

Bouwput en fasering

Bouwput en fasering

Functions of UCF’s

1. Water retaining layer2. Horizontal force equilibrium (strut)3. Vertical force equilibrium (up burst / heave)

Often a combination of the above!

Bouwput en fasering

Distribution of forces

4 mechanisms:• Boundary-disturbance à “Randstoringseffect”

• Arching à “Boogwerking”

• Membrane-effect à “Membraanwerking”

• Re-distribution of forces à “Krachtenherverdeling”

Boundary-disturbance à “Randstoringseffect”

Arching à “Boogwerking”

Membrane-effect à “Membraanwerking”

Arching & membrane-effect

Re-distribution of forces à “Krachtenherverdeling”

Ultimate limit states

1) Bending moments (tension)2) Bending moments in arch (compression)3) Shear failure (near retaining wall)4) Failure or slipping at retaining wall5) Pull-out of retaining wall (geotechnical failure)6) Failure of connection with tension piles (punching shear)7) Pull-out of tension piles (structural or geotechnical failure)

Design rules (CUR77)

CUR77 providesguidelines for designof unreinforced UCF’swith respect to:• Schematisation• Modelling• Dimensioning• Detailing

Revision in 2014!

Demand is to comply with Eurocodes (0, 2 & 7)!

• Longitudinal (“lange richting”):à no boundary-disturbanceà no initial normal forcesà membrane-effect is big!

• Cross-sectional (“korte richting”):à boundary-disturbance is criticalà normal forces present (strut-function)à limited membrane-effect

Focus in CUR77 is on the cross-sectionaldirection. Longitudinal direction is notcritical under the assumption of:

Schematisation #1

“lange” richting

“korte” richting

onderwaterbetonvloer

damwand

palen

Ly

Lx

Ly≤ Lx

CUR77:2001+2014

à hgem = average height (minimum 800mm?)

à tolerances on floor thicknessà calculate stresses with:

hmin = hgem - √(tolonder2+ tolboven

2)

Schematisation #2

Guidelines:tolonder à 250 mm for peat/clay

à 150 mm for sand/gravel

tolboven à 75 mm for hob-dobberà higher for slopes?

Modellingà beam-model of cross-section

Longitudinal:à

Serviceability Limit State (SLS)à dry building pità discrete cracking (minimal compression-zone)

2, ,

1 (without N')8 s rep y r repq L M£× ×

Cross-sectional:à uncracked

or with arching

or with arching + re-dristribution of forces

, ,mod , (with N')s rep el r repM M£

Ultimate Limit State (ULS)à structural safetyà incl. material and load factors

Longitudinal:à no check because of membrane-effect!

Cross sectional:à uncracked

or with arching and infinite re-distribution of forces (local):

, ,mod , (with N' )s d el r d dM M£

2, ,

18s d s d xM q L= × ×

New in revised CUR77 (v2014):1. Revised according to Eurocode 2 (NEN-EN1992)2. No design rules for SLS in cross sectional direction3. Optimization of arch-height (z) in ULS4. Check on shear forces near retaining wall5. Safety check considering slipping of UCF at retaining wall6. Adjustments for disc-shape-connections (micro piles):

- extra safety factor kr for punching shear- increased capacity of concrete compression strength under discs

7. Calculation of axial stiffness piles based on secant-valueà according to CUR236:Anchor-piles

8. Calculation method for optimization with membrane force9. Guidelines for use of 2D calculation models

Latest developments have been publishedin Cement 2013/3 and Cement 2015/5

Not in CUR77…

Hydration of concrete produces heat à temp. in UCF to 30-45oCCooling after heating à shrinkageStrength of concrete at 50% à sensitive for cracking

Thermal shrinkage of concrete:

à In relatively big building pits the risk of water-conductingcracks to occur is high even before pumping out the water !

Verificatie en toepasbaarheid

Case

à Use CUR77:2001 (on Blackboard)à Consider an unreinforced UCF (no addition of steel fibres)

Make a preliminary design for a deep building pit:à Modelling a beam-model is not necessaryà Do not check SLS in cross-sectional direction!à Only check:

SLS longitudinal directionULS punching shearULS equilibrium in arch

Case: guidelines for preliminary design of UCF

1. Choose concrete strength class B25 (nowadays C20/25):à tensional strength fb = 1,15 N/mm2

à compression strength f’b = 18,0 N/mm2

2. Determine Ly using SLS check in longitudinal direction (CUR77).Choose Lx ≤ Ly(for edge piles distance to retaining wall Lx,edge < Lx )

LxLx,edge

Case: guidelines for preliminary design of UCF

3. Determine effective load on piles based on:Lx * Ly * Pwater pressure–weight of UCF (incl. load factors)

4. Check punching shear (CUR77).Adjust hgem or Lx if needed/possible.

Case: guidelines for preliminary design of UCF

5. Determine normal forces in UCF (with D-Sheet Piling):

à suggested modelling:

Case: guidelines for preliminary design of UCF

6. Check safety in arching-mechanism (ULS cross-sectional direction)

Steel fibre reinforced UCF

First use:Potsdammer Platz Berlijn(1997)

In the Netherlands:• Heinoseweg Zwolle

(1998)• Betuweroute

(1999-2002)• multiple others…

2014:• Mauritshuis (The Hague)• Groninger Forum

“After-crack-behaviour”

à Tensional strength ≈à Early tensional strengthà Tensional strength after crackà Re-distribution of forcesà Moment capacity

Effect on force distribution

tension:

bending:

à limits shrinkage-cracks-widths

à limited crack-depth

Moment capacity for UCF with steelfibresà example for UCF with hmin = 700 mm and N’ = 200 kN/m’à 30 kg/m3 of steelfibres

0

100

200

300

400

0,0 2,0 4,0 6,0 8,0 10,0

mom

entc

apac

iteit

MRd

[kN

m/m

']

kromming κ [mrad] *10-6

M-N-κ diagramSVB (UGT)C25/30 (UGT)fctd,pl

εUGT = 0,1%:MRd = 380 [kNm/m']Egescheurd = 4.664 [MPa]

Projects

Groninger Forum

Projects

Groninger Forum

Link to video (dutch) of the process ofpooring the UCF with steel fibres for

project Groninger Forum:https://vimeo.com/89189883

Lecture CiTG

Projects

Mauritshuis (The Hague)

Mauritshuis (The Hague)

Mauritshuis

Link to video (dutch) with animationsmade by diving company C.O.W.:https://vimeo.com/24826624

Lecture CiTG

Innovations…“Traditional building method”:

- Unreinforced UCF withtemporary function

- Reinforced concrete floorhas permanent function

“Integrated floor”:

- Steelfibre reinforced UCF- For the permament

function the UCF iscollaborating with a(traditional) reinforcedconcrete floor

“Permanent UCF”:

- Steelfibre reinforced UCFhas a temporary and apermament function

Lecture CiTG 29th of September 2015