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Concrete Industrial Slabs. Australian Society for Concrete Pavements. Alan L Wright. Introduction. Design Brief Geotechnical Parameters Design Methods Documentation Clients Expectations. Design Brief. Block Stacking Racking Systems Forklifts Wheel Types pneumatic Solid
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Concrete Industrial Slabs Australian Society for Concrete Pavements Alan L Wright Alan L Wright and Associates
Introduction • Design Brief • Geotechnical Parameters • Design Methods • Documentation • Clients Expectations Alan L Wright and Associates
Design Brief • Block Stacking Racking Systems • Forklifts • Wheel Types • pneumatic • Solid • Polyethurane • V N A (very narrow aisles) Stackers • Floor Tolerances - Australian Standards variations of difference over 3metres - American Ff and Fl numbers - British FM1,FM2 FM3 as well as Superflat ,Category2 & 3 • Performance • If no design brief supplied then ensure you document your criteria Alan L Wright and Associates
Geotechnical Parameters • CBR • Generally a soaked parameter may not be applicable to internal slabs • Modulus of sub grade reaction -Determined by a Benkleman beam test.Essentially a local parameter.Some geotechnical engineers argue that there should be two values one for short term loads and one for permanent loads • Young’s Modulus - Short Term- Applicable for wheel loads and other transient loads - Long term - Applicable to permanent and relatively permanent loads Alan L Wright and Associates
Geotechnical Design • Subgrade Preparation • Granular Subgrade -Advantages - working surface -limits pumping (unlikely in internal slabs) -assists in limiting curling - reduces the effect of expansive soils. - Disadvantages –little reduction in thickness • Sand Layer only advantages is in levelling surface and in slip resistance.Excessive thickness can significantly reduce subgrade strength. • General Earthworks Specification compliance essential.Recommend sign off from the geotechnical engineer as well as proof roll inspect. • Cut off walls or other methods of limiting moisture changes essential for expansive soils. Alan L Wright and Associates
Design Process • Selection of type of slab Reinforced jointed,unreinforced jointed,post tensioned,steel fibre both jointed and jointless. Design Process needs to consider. 1 Local Effects –wheel loads,post loads. 2 Global effects-block stacking and racking systems Alan L Wright and Associates
DESIGN METHODS • Australian References • T48 C & CA Industrial Floors and Pavements • -Design Charts based on the use of FEAR program.(unique to Australia) -Limitations 1 Edge condition modeling 2 Racking systems not modelled well. 3 Not well correlated with other methods • Does reference other software e.g Strand,PCA Mats,Rigid 5. • Austroads Pavement Design Guide Alan L Wright and Associates
UK Design Document TR34 Concrete Industrial Floors Limited to internal slabs although TR66 has recently been published to extent methods to external slabs. Key Features Adopts k modulus of subgrade reaction as parameter.(no indication of long or short term moduli) Local effects adopts a limit state method proposed by Meyerhof and Losberg . Method requires ductility (Re3=0.3 for fibre) or doubly reinforced slabs. Global effects uses Hetenyi .Good approach to joint design,does suggest methods of assessing shrinkage effects. Limited in recommendations for dealing with single or unreinforced slabs. Alan L Wright and Associates
American Methods ACI Manual of Concrete Practice 2004 Design of Slabs on Grade –ACI 360R-92(reapproved 1997) Uses k modulus of subgrade reaction PCA Method based on work of Packard and influence charts of Pickett and Ray.This method is essentially the design approach used in T34 the predecessor of T48. Wire Reinforcement Institute Method based on Winkler Model Corps of Engineers Method based on Westergaard’s formulae. Other methods Post Tensioning Institute,ACI 223 for shrinkage compensating concrete. Supplies advice on shrinkage,warping,curling and temperature stresses. Recommend against the use of membranes Alan L Wright and Associates
JOINTS • Type (must be designed as most design methods assume a certain degree of shear transfer.)Critical to design performance. -saw cut (soft or wet cut)-either dowelled or undowelled.The ACI gives methods of determining if undowelled joints can be used.TR34 gives a far more detailed design approach based on the work of Colley and Humphrey. -Construction Joints –dowelled or keyed.A number of special dowels now available.Actual design design is well covered in TR34 which is based on the work of Yoder and Witczak which in turn references the work of Friberg.The dowel capacities calculated using Fribergs method are considerably lower than TR34 however one must remember that his work dates to 1938. • Spacing (5-7.5m) • Layout Alan L Wright and Associates
Documentation • Drawings • Clear layout of joints including any intrusions and discontinuities e g pits,garden beds etc • General Notes • Include all items that are essential to performance • -Concrete strength both flexural and compressive;cement, water fly ash content as well as slump and shrinkage limits. • - Surface finish and tolerances • - Curing requirements • - Design load assumptions Alan L Wright and Associates
Construction • Concrete Quality Control Obtain a mix design from the supplier Slump Control including no water on site. • Reinforcement Placement Control Correct height and alignment of reinforcement Alignment and spacing of dowels • Placement Methods • Conventional • Laser Screed • Finishing • Surface Treatments Alan L Wright and Associates
CONSTRUCTION • Polythene Engineers are divided as to its necessity.Advantage is that it assists in minimising shrinkage cracking by providing better resistance to slip.Disadvantages include promotes surface crazing and definitely contributes to curling. • Finishing Burnished,Steel trowel,Broomed. • Sawcutting.Either soff cut or wet cut. • Curing Curing Compounds(must comply with AS3799 Moist Curing Alan L Wright and Associates
Clients Expectations • The client expects a level ,crack free,maintenance free slab. • These expectations are unrealistic and often beyond the consultants control. • Concrete cannot be expected to be crack free .The consultant can only minimise cracks.Acceptable size of crack 0.5mm. • The levelness of the slab can only be controlled at finish.It is important that all level control is checked within 14days of placement Alan L Wright and Associates
The performance of joints is controlled by the operation of the user as well as performance of the slab.Educate the client that a proper maintenance regime will be necessary. • Once cracks in excess of 0.5mm form then they need to be repaired. Alan L Wright and Associates
Conclusion • Ensure your brief in clear • Ensure documentation is extensive. • Construction Control Essential • Try to define your clients expectations Alan L Wright and Associates
