Post-tensioned Concrete Design PT Installation Guidance Lee Maartensz Construction Manager - Structural Systems UK Ltd PT Installation Bonded Flat Slabs Installation 1
Flat Slabs Beam and Slab Installation 2
Multistrand Transfer Slabs and Beams Bonded Several strands per anchor Ducts lateral inflexibility Grouted Higher ultimate strength P/A = 1.6MPa Nominal loose rebar Faster, but needs grouting Cheaper Easier to cut holes/demolish Unbonded Mono-strands with individual anchors Lower ultimate strength Greased and plastic coated Flexible P/A = 1.0MPa Bottom Mesh Slower More expensive Full loss if cut Installation 3
Live End Anchorage Valid ETA Certificate Compact Flat Duct 2-4 strands Plan location set out as per approved dwg +/- 20mm Temporary mandrel, void former and nut bolts the anchorage/trumpet to edge form Antiburst spiral Design co-ordination with fixings / balconies etc Grout Tube Ducting Anchor Block Anchor Casting Strands BBR Cona VT CMF Anchorage Components Live End Pan Access Pan Access overcomes access restrictions, e.g. core walls, balconies etc Concrete in-filled after stressing, prior to grouting Installation 4
Duct 43mm, 70mm or 90mm wide Galvanised Joined using PVC tape Easily damaged, care required during handling, concreting etc High Tensile Strand 7 wire strand 12.9mm or 15.7mm diameter GUTS of 186 or 279kN Produced to BS5896:2012 Approx 3 tonne coils CARES approved suppliers Installation 5
Strand Installation QA & Records Strand pushed into ducts from live or dead end using a strand pusher 1m protrusion for dead end, plus 600mm at live end for stressing required Anchorages Dead End 1m of each strand protruding from duct Onion formed using jack and press Grout tube inserted into duct, and remaining void sealed using denso mastic Corrosion-protective Grout Grout Tube Ducting Exposed Strand Note: Antiburst spiral not shown Onion Ends Installation 6
Profiling & Securing Duct tied to profile chairs at 1m centres +/- 5mm vertical tolerance Chairs stapled to formply, or tied to bottom mat if soffits are to be exposed Concrete Considerations & Actions Pre-pour Inspection Placement Techniques Pour watch Match cured cubes from last delivery QA and Records Installation 7
Stressing Confirmation of concrete strength via match cured cubes by Contractor - Initial stress 9Mpa - Final stress 25Mpa - Extensions measured, recorded and submitted for approval, prior to cut and seal Stressing Equipment Valid certificate of calibration for each jack & gauge (6 monthly) Pressure required derived from calibration certificate Load applied to corresponding pressure on site Internal jaws to be regularly checked for signs of wear/damage Installation 8
Grouting Plant & Testing Equipment Grouting Procedures Air testing of ducts / repairing blockages Vent Identification Assembly of required testing and safety equipment Suitability and Inspection Testing, prior to and during production grouting to monitor: Flow / Consistency Air / Structure and Grout Temperature Bleed / Volume Change Strength / Density Experienced and trained operatives Grout Venting Installation 9
Quality Assurance CARES Accreditation BS EN ISO 9001 Quality controlled design and drafting practices Detailed method statements & work instructions Structured training of operatives Quality control & traceability Internal & external audits QA Records for Every Pour Inspection and Test Plan Component Installation Record (Strand, anchors, blocks, wedges) Design Compliance Report (Pre-pour inspection) Stressing Handover Sheet (Confirmation by Contractor of concrete transfer strengths) Site Extension Records Extension Check off (Permission to Cut and Seal) Permission to Strike Formwork Suitability / Inspection Testing of Grout Grout Record Dwgs Installation 10
Potential Site Issues Concrete quality / strength / compaction problems, leading to failures at live / dead ends Incorrect stressing of strands leading to under / overextension Broken strands Failure of components (blocks / anchors / wedges) Tendon blockages Site co-ordination / sequencing Design Issues Safety Experienced and trained operatives Calibrated and serviced equipment Exclusion zones during strand pushing Safety barriers and signage during stressing operations Strict adherence to methodology and work instructions Manual handling PT equipment is heavy! Installation 11
Future Alterations / Demolition Bonded post tensioned slabs offer tremendous scope for future alterations, but design guidance from the PT specialist should always be sought prior to works being undertaken Strands are bonded to the structure via grout in the duct minimising risk and impact should tendons be cut or damaged Many penetrations can be located between typical tendons without additional strengthening or reinforcement requirements. SSL penetration assessment procedure issued with design criteria and O&M manual should be consulted for any future works. Demolition fairly practical with a bonded system, less so with unbonded Built in Flexibility for Future Alterations Allowance for future knock out penetrations adjacent all face of all columns Coordination for future services etc Installation 12
Informing Follow on Trades Locating Tendons Desktop study / dwg overlay As-built drawings Staples / painted soffits Ferroscan Drill pilot holes in accordance with SSL penetration assessment procedure. If no tendon is struck it is safe to drill. Installation 13
Forming Epoxy Anchorages for New Penos Set out pocket 700 x 300mm over tendons to be cut Carefully expose the tendon, remove duct and grout Backfill pocket with flowable epoxy to create dead end anchorage Tendon may now be cut to create new peno New Escalator Penetration Installation 14
FRP Strengthening Additional reinforcement options FRP plate and wrap Thank you for your attention Any Questions? Installation 15