Jointless Post Tensioned Slab on Grade. The Future for Industrial Concrete Flooring?

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1 Jointless Post Tensioned Slab on Grade The Future for Industrial Concrete Flooring?

2 Floor Slab Function (ref N.I.M. Williamson, Concrete floors for warehousing and distribution facilities: fit for purpose?. ICE 1996) To distribute, without deformation or cracking, the loads applied to it to the weaker sub-grade below, and to provide a suitable wearing surface upon which the operations in the facility may be carried out efficiently and safely.

3 Concrete The Shop Floor for Industry... the floor is the most important part of the building. All activities occur on or near the floor and the remainder of the structure is simply a means of protecting the floor and workforce from the environment. B.C. Crisp B.E., M.I.P.E.N.Z., M.I.E. (Aust).

4 The demands on floors have increased over the last few years and in any event floors have not performed too well. The C&CA in Australia reports there are more complaints about floor slabs than all other concrete put together. It would seem we need to do the job better.

5 The floor is becoming increasingly important as we use higher racking and faster forklifts. We want our floors to be flatter and last longer. We can no longer accept opening cracks, failed joints or potholes.

6 A USA study of 200 Large Industrial floors showed joints as the biggest cause for concern. This all adds up to the need to ensure that the floor is designed properly. Its not satisfactory just to use the same design as before.

7 What defines a Good Floor? Optimum Joint Detailing - Most floors fail at the joints

8 Flatness - Forklifts travel faster on flatter floors - improved productivity Hardness - resistance to abrasive wear Low Maintenance Costs and Few Repairs

9 Main Elements Of A Concrete Floor Levelling sand Slip Membrane Slab t 1 = Subbase t 2 = Imported Fill (if used) t 3 >t 1 +t 2 Subgrade

10 Uneven Ground Causes Restraint

11 Restrained shrinkage causes multi directional cracking of the floor, curling and rapid disintegration of structural integrity

12 A unreinforced floor is really a number of smaller floors joined together = JOINTS

13 Formed Construction Joints Sawed Contraction Joints

14 What Has Changed in the last 30 Years? Fast Moving Consumer Goods

15 Bigger Warehouses & Higher Racking

16 Efficient Distribution

17 Higher Stacking

18 Faster Forklifts

19 24 Hour Operations

20 Lets get the good stuff out FAST

21 Impact Point Aggregat e looses cont act and slab fault s when joint opens Joints open due to Drying Shrinkage and Curling Sawed Cont ract ion Joint Sect ion

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23 A facility managers worst problem FAILED JOINTS!!!!!

24 Industrial Concrete Floors Following are examples of jointed floors that were easy to construct and would NEVER BE A PROBLEM

25 Rocking Slabs

26 Curled Edges

27 Joints cut too late

28 Joints too far apart

29 Inadequate Sub - base

30 Overloading

31 Curling of Joints

32 Why we need to reduce Joints

33 Damaged Wheels = $$$$$$$$$

34 Load Tippage

35 Forklift Maintenance

36 Floor Repairs

37 joints unfilled 6-12mm wide joints unfilled over 12mm wide cracks over 6mm wide joints where slabs rock joints repaired but failed joints where filler became brittle cracks with spalled edges joints filler too soft to support cracks with islands joints opening 2-5mm joints with one side higher surface worn away joints with a metal screed key 54% 47% 45% 44% 44% 42% 39% 34% 32% 28% 27% 23% 16% Results from the survey of over 200 USA Distribution facilities Joints are a big problem.

38 Joint Requirements Increasing Loads have increased Wheels have got smaller Wheels are harder Modern floors need to eliminate JOINTS

39 Jointless Floors the way to go Traditional 2000m 2, 860m saw cut joints PT JOINTLESS 2000m 2, NO saw cut joints

40 Hidden Cost wheel replacement operator fatigue and moral increased housekeeping load tipping and breakage reduced building value

41 OUR INDUSTRY MISSION... To provide the owner with a world class surface facility offering long life and low maintenance....this is not possible using unreinforced jointed concrete

42 Our Team was approached by BMW South Africa to design, supply and construct a 9,000m 2 Jointless Surface Bed for their new parts Distribution Facility.

43 OUR INDUSTRY MISSION BMW had identified Joint Failure in many of their existing floors as a problem for their handling operations and consequently wanted a Jointless Floor.

44 OUR INDUSTRY MISSION Criteria that had to be met : No Joints No Cracking CAT 2 Floor Tolerances No Curling Wire Guidance

45 OUR INDUSTRY MISSION Could not use unreinforced concrete option as this would exhibit saw cut joints, construction joints, shrinakge opening of joints, curling of joints and would need to be in excess of 200mm thick.

46 WHY WE CHOSE PT : No Joints No Curling It was the greenest option using the least concrete It is an engineered solution It is a robust, durable system proven worldwide It had best capital cost and life cycle values

47 PT GROUND SLABS Francois Le Roux Nyeleti Consulting

48 What are Post-Tensioned industrial slabs? Slabs on ground reinforced with Post-Tensioned tendons consisting of steel cables Jacks tension cables at slab edges Permanent 2-way compression placed on slab

49 Two Main Functions of the PT Counteract initial shrinkage cracking Pre-Compress concrete to counter cracking due to: Ongoing Shrinkage Flexural Tensile Stresses due to external loads Temperature gradients in slab

50 BASICS Bonded Flat Slab system used Tendons comprise of bare steel cables (Strands) inside galvanised steel duct 12.9 and 15.7 dia. strand Tendons un-profiled in one layer Placed centrally in slab Equal or close to equal tendons in both directions

51 Advantages of post tensioning Eliminate JOINTS PT Compression force counter shrinkage forces that cause cracking Eliminate need for joints Extensive joint-free areas ~ 2500 sq.m Savings on joint cost, repair costs & downtime for facility

52 Advantages of post tensioning Increased Strength and load capacity Thinner slabs achieve same strength ~ 20 to 30% saving on slab thickness Overcomes poor ground conditions easier Less sub-grade preparation required i.e. It usually requires less supporting layer-works Therefore, savings on capital cost usually achieved

53 Advantages of post tensioning Increased robustness If cracked by overload, crack held closed by permanent compression force in slab Rapid deterioration & breakup avoided Ongoing repairs minimised

54 Typical applications Distribution Centres & Warehouses

55 Typical applications Refrigerated stores

56 Typical applications Bulk solid storage

57 Typical applications Heavy equipment maintenance facilities

58 Typical applications Freight forwarding centres

59 Typical applications Container-handling facilities

60 Typical applications Base Slabs for Water Retaining Structures

61 applications Typical applications Raft Slabs

62 Materials

63 High Tensile Strand 15.7 or 12.9mm dia, 7 wire cable Modulus c. 195 kn/mm² Approx 3 tonne coils

64 Duct (Void Former) Galvanised metal 70 or 90mm wide x 20mm high. 3 Strand also available Joints Tape Sealed

65 ANCHORAGES Grout Tube Anchor Block Ducting Steel Strand (Cable) Anchor Casting Corrosion-protective Grout LIVE END (For Stressing/Tensioning)

66 ANCHORAGES Corrosion-protective Grout Grout Tube Ducting Steel Strand (Cable) Bulbed Strand Ends DEAD END Protruding cables cast into concrete to anchor cables at the one end to allow tensioning at the other

67 Analysis and Design

68 Analysis stage Analysis & Design of PT ground slabs is carried out in a rigorous manner based on engineering principles Finite Element modelling of slab & subgrade

69 Analysis stage ALL Service loads considered Racking, vehicles, materials, containers Edge & internal load cases Environmental influences considered Temperature Subgrade movements Creep & shrinkage Base Friction etc.

70 Analysis stage Stress ratios for repeated loads Vehicles ~ unlimited Racking ~ daily-weekly cycle (full bay) Containers ~ daily cycle (full stack) Materials ~ weekly cycle

71 Design stage Final design expectations Thickness ~ 70 to 80% of equivalent RC slab Pre-Stress ~ 1-2 Mpa (long-term)

72 Construction

73 Construction Key to success is attention to detail

74 Installation stage Key items Subgrade preparation is key i.e. Compaction & levels Isolate Columns etc 100% sand/poly cover Dowel sleeving

75 Installation stage External Slabs Prior to pour

76 Concrete Placement Key items : Proper planning Correct equipment Adequate Manpower

77 Post-Concreting Key items : Early formwork stripping for stressing vital Unlock blocking and joint systems Initial stress to control initial shrinkage cracking - 9Mpa concrete strength required Final stress - 25Mpa concrete strength required

78 Stressing Hydraulic Pump and Stressing jack to tension strands/cables Certificate of Calibration essential for each Jack & Gauge

79 Grouting

80 Post-Grouting

81 Post-concreting stage The finished Product (Coca Cola Melbourne)

82 CONCLUSION Sophisticated design process followed which, models all significant forces & actions on & in slab It is a properly ENGINEERED slab Joint free areas ~ 2500 sq.m Greatly reduces joint const n costs Greatly reduces joint maint costs & downtime Potential savings in capital cost

83 CONCLUSION Durable & robust Proven & reliable technology SSL have designed and installed in excess of 1,4mill SQ-m of PT SOG between 1994 and 2009 SSL have completed approx. 500,000 Sq-m of external heavy duty PT SOG Adopted widely for major facilities

84 BONDED POST TENSIONED SOLUTION AT BMW Case study

85 Client: Consultant: Contractor: TEAM BMW SA Nyeleti Consulting (NC) Concrete laser flooring (CLF) PT Supplier and design assistance: Structural Systems Africa (SSA)

86 BACKGROUND Clients requirements Rehabilitated facility floor Full production during rehabilitation CAT 2 regularity suitable for VNA Phased construction Lower life cycle cost

87 BACKGROUND Analysis Approach Load transfer testing Floor visual survey

88 BACKGROUND Load transfer testing LWD testing done 143 tests Poor transfer 72%

89 BACKGROUND Visual survey High percentage floor defects Shattered slabs, cracking, joint failure etc. Poor surface regularity

90 Vertical floor level (m) BACKGROUND Long Section of Row K-J mm level difference Row K-J Row K-J Distance (m)

91 Height in m from datum BACKGROUND Transverse regularity of aisle BB Meters from datum line Joint 1 Between J1 and J2 Max limit Min Limit Joint 2 Joint 4 Betwee J4 and J5 J 5

92 OPTIONS OFFERED Conventional Rehabilitation Bonded post tension slab (150mm thick) on slip membrane Continuously reinforced slab (175mm thick) on slip membrane 200mm SFRC on slip membrane

93 Other Problems 1. Building constraints a. Saw tooth roof with 4.5m height beams at low end b. Cable trays at 4.5m height c. CANNOT OPEN A BOOM PUMP d. Columns at 10m grid (MOVEMENT RESTRICTIONS) e. 4 Phases with 8 weeks wait period between pours

94 WHY PT Eliminating all control joints Max floor 150mm thick Jointless pour up to 5000m2 No transverse joints Eliminate slab curl

95 WAREHOUSE LAYOUT

96 Warehouse layout 4446m² 2556m²

97 POST TENSIONING LAYOUT

98 POST TENSIONING LAYOUT 1. Edge reinforcement

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103 POST TENSIONING LAYOUT

104 POST TENSIONING LAYOUT 1.Movement joints a.movement was estimated as 0.5mm / m to free edge. b.main movement joint estimated as 18mm c.measured on site as 12mm to date (after 60days)

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107 Tensioning direction

108 Tensioning direction

109 Construction sequence 1. Installation of a. Polyterm Sub base b. Formwork and slip sheets c. PT system d. Concrete and finishing

110 CONSTRUCTION SEQUENCE 1. INSTALLATION OF LEVELLING COURSE

111 CONSTRUCTION SEQUENCE 2. INSTALLATION OF SLIP SHEETS/FORM WORK

112 3. POUR OF CONCRETE CONSTRUCTION SEQUENCE

113 CONSTRUCTION SEQUENCE

114 CONSTRUCTION SEQUENCE 4. Post Tensioning

115 CONSTRUCTION SEQUENCE Post tensioning Initial tensioning at 9MPa Final at 25MPa

116 CONSTRUCTION SEQUENCE WHAT IF THINGS GO WRONG?

117 Construction sequence Finish product.

118 End