Carruthers & Wallace Limited

Transcription

1 Anchoring or Fastening To, or Drilling Through, the Structure Lester B. Pearson International Airport Parking Structure 1. General The Parking Garage is a cast-in-place concrete structure prestressed (post-tensioned) with highly stressed high-strength steel cables (tendons) that store large quantities of energy. These Prestressed floors are levels 2 to 8. The penthouse roofs and the level 9 machine room floor are not prestressed. The slab tendons extend both in the north-south and the east-west directions. The beams in both the north-south and east-west directions are also post-tensioned, with a very few exceptions. It is critically important that the slab tendons and their protective sheath not be damaged during any alterations in the garage such as drilling and fastening for electrical conduits, pipes, etc. Extra special care is required in fastening to the slab top or bottom surface as the slab tendons are unbonded and in a plastic sheath. Replacement of damaged tendons or repair to damaged plastic sheath will be very costly. Drilling and fastening shall be carried out only under the fulltime supervision of a responsible person who shall monitor the operation from start to finish to verify that the tendons will not be damaged. Care is also required with respect to the reinforcing bars and similar precautions should be followed as indicated for the tendons. A Quick Reference Guide with respect to precautions to be taken when installing anchors/fasteners or drilling holes is provided in Appendix A. This should be read in conjunction with the following more detailed instructions. Typical structural characteristics that are of importance when contemplating fastening to or drilling through the structure are tabulated in the attached Appendix B General Description of Structure. Some areas of the garage differ significantly from the tabulation in the Appendix B and reference should be made to the structural drawings to determine the design in any particular area. Reinforcement shop drawings were prepared by Harris Rebar/Gilbert Steel. Post-Tensioning shop drawings were prepared by Harris P.T/BBR. Page 1 of 9

2 2. Anchoring or Fastening to Concrete Slab Top or Bottom Surface Slab tendons are unbonded and enclosed in a 16 mm diameter plastic sheath, of draped profile with a specified distance (concrete cover) of 40 mm from the concrete top surface at the high part of the profile and 32 mm from the concrete bottom surface at the low part of the profile. Due to construction tolerance of 10 ± mm, the tendons should be considered as 30 mm below the top surface and 22 mm above the bottom surface in the slab at the high and low portions of the profile respectively when installing anchors/fasteners. It must be recognized that some tendons may be even closer to the surface than these dimensions because specified tolerances are not always met. The reinforcing bars are specified as 40 mm and 32 mm clear from the top and bottom surfaces. Due to construction tolerances, these should be considered as 30 mm and 22 mm respectively when planning the installation of anchors/fasteners. Special Hilti Anchors HDI-P Drop-In Anchors that penetrate only 20 mm (3/4 ) into the concrete may be used for fastening to the top or bottom surface of the floor (and roof) slab. These anchors are sufficiently short in length that they should not reach the tendons or reinforcing bars. These anchors are inserts that are placed in a pre-drilled hole. The insert is internally threaded to receive a 3/8 diameter threaded rod or bolt. The anchor insert has an allowable load capacity of 1.7 kn (380 pounds) in tension and an allowable load capacity of 2.7 kn (600 pounds) in shear (Hilti Technical Manual 2002 edition). These anchor inserts are installed in holes drilled with a carbide-tipped drill bit. Special care is required to ensure that the depth of drilled hole does not exceed 20 mm (3/4 ) depth so as not to damage the slab tendon plastic sheath. Damage to the plastic sheath would allow the corrosion protection coating inside to leak out, and is not acceptable. If these anchors do not have sufficient capacity an anchor with greater penetration into the concrete may be used only if the following measures are taken to ensure that the slab tendons and their plastic sheath are not damaged: a) Use an accurately calibrated pachometer (covermeter) to determine the depth to the steel tendon and reinforcing bar from the surface on which the fastener is to be installed. Select a fastener with a depth of penetration such that there remains at least a 20 mm clearance from the fastener end (i.e. the tip that is embedded in the concrete) to the tendon OR b) X-ray the slab to locate both the north-south and the east-west tendons and bar reinforcement in the area where the fasteners are to be installed. Arrange for the X-ray technician to mark the location of all the tendons and bar reinforcement on the concrete Page 2 of 9

3 surface. Fasteners shall not be located closer than 100 mm to a tendon or bar (to allow for inaccuracies in the x-ray). 3. Anchoring or Fastening to Vertical Edge of Slab Anchors or fastenings must not be installed in the vertical edges of slabs (such as in stair wells, at lightwell, at ramps, and around the perimeter of the floors, etc.) unless the slab is x-rayed to determine the slab tendon and its end anchor location. Anchors or fasteners should be located at least 100 mm away from tendon anchorage hardware. Anchors or fastenings must not be installed in the grout-filled slab tendon stressing pockets that are visible in the slab edges, or within 150 mm of these grout pockets. 4. Anchoring or Fastening to Beams Beam tendons are bonded within a 100 ± mm diameter grout-filled metal duct which is specified to be a minimum of 60 mm from the concrete bottom surface. Due to construction tolerances some tendons must be expected to be 40 mm or closer to the bottom surface of the beam. Beam tendons should be 100 ± mm minimum from the side face of the beam. Top and bottom reinforcement is specified to be 40 mm clear from the side faces of beams (30± mm after allowance for tolerances). Edge beams (such as north-south and east-west beams adjacent to the expansion joints and at the perimeter of the structure) have horizontal reinforcement distributed along the vertical faces (i.e. skin reinforcement). Since the beam side faces are sloped, and the stirrups are vertical, the distance to the side face horizontal skin reinforcement is greater near the top of the beam than near the bottom. The tendon duct and reinforcing bars should be located by pachometer (covermeter) to determine if the fastener or anchor can be installed without conflict with the tendon duct, beam stirrups or horizontal skin reinforcement. For anchors or fasteners to be installed directly above the beam, the restrictions as outlined for anchoring to concrete slab apply (paragraph 2). Page 3 of 9

4 5. Drilling Through Concrete Members a. Floor Slab With special care it is possible to drill holes up to about 200 mm diameter through the floor slab. Any holes must be clear of all beams and must not be in close proximity (minimum 3 diameters centre-to-centre) to each other. Before drilling any holes through the slab, the slab shall be x-rayed to locate the posttensioning tendons in both directions (north-south and east-west) and reinforcing steel in both directions and the location of the desired hole adjusted so as not to damage either a tendon or a bar. Drilling shall not be done closer than 100 mm to a tendon or bar reinforcement (to allow for inaccuracies in the x-ray in determining the plan location of the tendon and bar). b. Beams and Columns Drilling either vertical or horizontal holes through any concrete beam or column is not permissible without express approval of GTAA and review by a structural engineer licensed to practise in Ontario and experienced in post-tensioned structures. 6. Sawcutting Sawcutting into the slab or beam is prohibited. Page 4 of 9

5 APPENDIX A QUICK REFERENCE GUIDE Page 5 of 9

6 QUICK REFERENCE GUIDE FOR ANCHORS & FASTENERS (To be read in conjunction with the more detailed description at the front of this document) ELEMENT LOCATION PROCEDURE COMMENT Concrete Slab Top Surface and Bottom Surface Hilti HDI-P Drop-In Anchors that penetrate 20 mm (3/4 ) into the concrete. Take special care not to drill deeper than 20 mm. Vertical Edge X-ray to ensure fastener is clear of slab tendon and concealed tendon anchors. Do not install in exposed stressing pocket grout plugs or within 100 mm Beams Top Surface Same restrictions as for top surface of slab Bottom Surface and Side Face Use Hilti HDI-P Drop-In Anchors that penetrate 20 mm (3/4 ) into the concrete. If these have insufficient load capacity, longer fasteners can be used if pachometer (covermeter) investigation is carried out. If these have insufficient load capacity, use x-ray or covermeter as per Paragraph 2 Anchoring or Fastening to Concrete Slab Top or Bottom Surface of text. Refer to Paragraph 3 Anchoring or Fastening to Vertical Edge of Slab of text. Refer to Paragraph 4 Anchoring or Fastening to Beams of text. QUICK REFERENCE GUIDE FOR DRILLING THROUGH CONCRETE MEMBERS (To be read in conjunction with the more detailed description at the front of this document) ELEMENT LOCATION PROCEDURE COMMENT Concrete Slab Not over beam X-ray the slab and locate tendons and rebar in both directions and have x-ray technician mark out the locations in spray paint on the concrete. Refer to Paragraph 5 Drilling Through Concrete Members of text. Do not drill closer than 100 mm to a tendon or rebar. Do not drill more than 200 mm diameter holes unless analyzed by a structural engineer. Beams and Columns Do not space holes closer than 3 diameters on centres. Not permissible to drill holes vertically or horizontally through beams or columns without express approval of GTAA and review and check by structural engineer. Page 6 of 9

7 APPENDIX B GENERAL DESCRIPTION OF STRUCTURE Page 7 of 9

8 GENERAL DESCRIPTION OF STRUCTURE FLOOR SLAB IN TYPICAL BAYS, LEVELS 2 TO 8 INCLUSIVE Floor Slab Thickness Floor Slab Thickness at Detection Loops Tendons (Cables) in Slab Tendons in Floor Slab in North-South Direction Profile of North-South Tendons in Slab Tendons in Floor Slab in East-West Direction Tendon Anchors Profile of East-West Tendons in Slab Reinforcing Bars in Slab in North-South Direction Reinforcing Bars in Slab in East-West Direction 150 mm 200 ± mm in most locations; 150 at south ramp floors 3 to 6 and some miscellaneous other locations 12.5 mm (1/2 ) diameter 7-wire high strength low relaxation steel (1862 MPa ultimate tensile strength) in high density blue coloured extruded polyethylene sheath 1.5 mm thick (overall diameter of steel strand plus sheath is 16 mm) Monostrand System (zero void), with plastic twist-on gasketed cap filled with corrosion inhibiting material. At jacking ends, stressing pocket is grouted. Groups of 2, and in some cases groups of 3, tendons side-byside at approximately 1,000 mm centres between groups (actual spacing may vary significantly), unbonded as described above. Draped in the vertical plane: 40 mm below the top of the slab where tendon crosses over an east-west spanning beam and 32 mm above the bottom of the slab at mid-span between beams. Parabolic curvatures between these points. In plan view tendons are generally straight, but due to placing tolerances they vary considerably from a straight line. At floor penetrations such as drains the tendons are curved in plan to be clear of the drain. Caution: Due to placing tolerances actual cover to tendon may be less in some locations. Single tendons at approximately 750 mm centres, unbonded in plastic sheaths. Anchorage hardware at the end of each tendon is approximately 130 mm (horizontal) x 60 mm (vertical), generally located at midthickness of the slab. Straight in vertical plane (not draped) at mid-depth of the 150 mm thick slab (i.e. 67 mm below top of slab and 67 mm above bottom of slab, except where tendon crosses north-south beams it is 40 mm below top of slab. Actual distances may be less due to construction tolerances. Continuous top and bottom straight bars. 40 mm cover to top bars, 32 mm cover to bottom bars. Actual cover may be less due to construction tolerances. Continuous bars on top of draped north-south tendon where concave upward, of underside of tendon where concave downward. Cover means the clear distance from the nearest concrete surface to the tendon or reinforcing bar. Page 8 of 9

9 TYPICAL BEAMS LEVELS 2 TO 8 INCLUSIVE Beam Depth from Top of Slab to Bottom of Beam Beam Tendons Profile of Tendons in East-West Beams Profile of Tendons in North-South Beams Reinforcing Bars in Beams Generally 900 mm. In some locations 1000, 1145 and 1185 mm deep. Bonded 16 mm (5/8 ) diameter 7-wire high strength low relaxation steel (1862 MPa ultimate tensile strength). Tendons are grouted in steel duct of approximately 90 mm diameter. Draped to be near top of beam near supports and near bottom of beam at mid-span between supports. Generally 60 mm from bottom of beam to duct. Straight in 5.2 m span beams. Vertical location in beam varies from beam to beam. Draped to parabolic shape in 10.4 m span girders; draped to harped shape in 15.6 m span girders. Longitudinal top and bottom bars and vertical stirrups. Stirrup legs are generally vertical (not sloped to match sloped sides of beams). In addition, edge beams (such as north-south and east-west beams adjacent to the expansion joints and at the exterior perimeter of the structure) have horizontal reinforcement distributed along the vertical faces (i.e. skin reinforcement) 40 mm clear from the side faces of beams. Page 9 of 9