2. Content
1st hour:
• Use and functions of UCF’s
• Distribution of forces
2nd hour:
• Design-rules (CUR77)
• Case: guidelines for preliminary design
Extra:
• Steel fibre reinforced UCF’s
• Projects
• Innovations
3. 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!
13. Functions of UCF’s
1. Water retaining layer
2. Horizontal force equilibrium (strut)
3. Vertical force equilibrium (up burst / heave)
Often a combination of the above!
15. Distribution of forces
4 mechanisms:
• Boundary-disturbance à “Randstoringseffect”
• Arching à “Boogwerking”
• Membrane-effect à “Membraanwerking”
• Re-distribution of forces à “Krachtenherverdeling”
21. 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 wall
5) 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)
22. Design rules (CUR77)
CUR77 provides
guidelines for design
of unreinforced UCF’s
with respect to:
• Schematisation
• Modelling
• Dimensioning
• Detailing
Revision in 2014!
Demand is to comply with Eurocodes (0, 2 & 7)!
23. • Longitudinal (“lange richting”):
à no boundary-disturbance
à normal forces absent
à membrane-effect is big!
• Cross-sectional (“korte richting”):
à boundary-disturbance is critical
à normal forces present (strut-function)
à limited membrane-effect
Assumption:
Schematisation #1
“lange” richting
“korte” richting
onderwaterbetonvloer
damwand
palen
Ly
Lx
Ly =< Lx
CUR77:2001+2014
24. à hgem = average height (minimum 800mm?)
à tolerances on floor thickness
à calculate stresses with:
hmin = hgem - √(tolonder
2+ tolboven
2)
Schematisation #2
Guidelines:
tolonder à 250 mm for peat/clay
à 150 mm for sand/gravel
tolboven à 75 mm for hob-dobber
à higher for slopes?
26. Longitudinal:
à
Serviceability Limit State (SLS)
à dry building pit
à 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£
27. Ultimate Limit State (ULS)
à structural safety
à 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
, ,
1
8
s d s d xM q L= × ×
28. New in revised CUR77 (v2014):
1. Revised according to Eurocode 2 (NEN-EN1992)
2. No design rules for SLS in cross sectional direction
3. Optimization of arch-height (z) in ULS
4. Check on shear forces near retaining wall
5. Safety check for case of UCF slipping at retaining wall
6. 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-value
à according to CUR236 : Anchor-piles
8. Calculation method for optimization with membrane force
9. Guidelines for use of 2D calculation models
Latest developments published in
Cement 2013/3 and Cement 2014/?
29. Not in CUR77…
Hydration of concrete produces heat à temp. in UCF to 30-45oC
Cooling after heating à shrinkage
Strength of concrete at 50% à sensitive for cracking
Thermal shrinkage of concrete:
à In relatively big building pits the risk of water-conducting
cracks to occur is high even before pumping out the water !
31. 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 necessary…
à Do not check SLS in cross-sectional direction!
à Only check SLS longitudinal direction, punching shear, and
equilibrium in arch
32. 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
33. 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.
34. Case: guidelines for preliminary design of UCF
5. Determine normal forces in UCF (with D-Sheet Piling):
à suggested modelling:
35. Case: guidelines for preliminary design of UCF
6. Check safety in arching-mechanism (ULS cross-sectional direction)
36. Steel fibre reinforced UCF
Potsdammer Platz Berlijn
(1997)
In the Netherlands:
• Heinoseweg Zwolle
(1998)
• Betuweroute
(1999-2002)
• multiple others…
2014:
• Mauritshuis (The Hague)
• Groninger Forum
37. Staalvezelversterkt OWB
“After-crack-behaviour”
à Tensional strength ≈
à Early tensional strength
à Tensional strength after crack
à Re-distribution of forces
à Moment capacity
Effect on force distribution
tension:
bending:
à prevents big shrinkage-cracks
à limited crack-depth
38. Moment capacity for UCF with steelfibres
à 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
momentcapaciteitMRd[kNm/m']
kromming κ [mrad] *10-6
M-N-κ diagram
SVB (UGT)
C25/30 (UGT)
fctd,pl
εUGT = 0,1%:
MRd = 380 [kNm/m']
Egescheurd = 4.664 [MPa]
45. Link to video (dutch) with animations
made by diving company C.O.W.:
https://vimeo.com/24826624
Lecture CiTG
46. Innovations…
Traditional building method:
- Unreinforced UCF with
temporary function
- Reinforced concrete floor
has permanent function
Integrated floordesign:
- Steelfibre reinforced UCF
- For the permament
function the UCF is
collaborating with a
(traditional) reinforced
concrete floor
Permanent UCF:
- Steelfibre reinforced UCF
has a temporary and a
permament function