Subject: Things to do when we have post-tensioning cables passing through precast panels
If we have both post-tensioning slabs in the location of precast, we have to provide a block-out hole in the precast to pass the tendons through the precast.
What we care to take when detailing precast panel.
We have to provide an opening in the panel for PT cables to pass through. Do not place any precast hardware closer than 100 mm from the hole/block-out.
Cause * During lifting * During Transportation * During Erection * After erection & slab pouring Problem * where the cracking of panel further affected the waterproofing by damaging the internal stud walls of the building. * Reinforcement getting Weak * If any interior work will damage due to the weather proof issue. Remedies * Get concentrate those location & intimate to reinforce team for additional reinforcement * Insist to follow the Guidelines from the engineering team * Insist Factory to concern the reinforcement for the specific openings * Insist Factory & Erection Crew to Follow the standards & guide line when the lifting from the store, during transport & installation the panel * During transportation take care all panels sitting on ‘A’ frame to be vertically supported on 2 points & if any additional support should only be for lateral purposes. Insist to follow the transportation guidelines * The Grouting must be taken care on time for the panel with openings Coordinators to advise if any special cases if needed.
The important things to be considered in lift shop drawings for precast is listed below:
Core Setout.
Door Opening.
Recess at the bottom of lift door.
Landing Call Buttons penetrations.
Controller Box Penetrations.
Service Penetrations and internal platform box.
Lifting Eye Placements & capacity.
1. CORE SETOUT:
Lift Core Panels Setout in Concrete plan and structural plan should match with lift core details.
If any thickness of panels change keep inside dimensions unchanged, because inside dimensions are dictated by lift manufacturer’s drawings. Panels thickness change must affect only the outside dimensions of lift core.
Propping method – Lift Cores are generally erected first. Higher level slab may not have been poured when lift core goes up. Hence propping of lift core need to have some special attention.
2. DOOR OPENING:
The door opening width and height of lift in lift drawing should match with architect and structural drawings.
Make sure that the height of lift door opening in lift drawing are measured from FFL or SSL.
Minimum Header height should maintained Discuss with interested parities if there any doubt.
Always consider the RL’s difference between FFL and SSL while the opening height are finalized. FFL and SSL are usually different
3.RECESS AT THE BOTTOM OF LIFT DOOR:
The recess at the bottom of lift door (as per door sill detail) is provided for door frame installation. Make sure we take this into consideration
The door sill details are not same for all projects we need to confirm the depth and width of recess at the bottom of lift door before start the detailing.
If the door sill height recess is wrongly provided (i.e. Measured from SSL instead of FFL) then there will be a problem in installation of lift door frame.
The provided recess depth should start from the end of clear opening of lift door.
Make sure that the Door sill details provided in lift drawings are measured from FFL or SSL.
4. LANDING CALL BUTTONS PENETRATIONS:
Penetrations for landing call buttons, fire switch and other electrical purpose are to be placed as per lift manufacturer’s drawings.
First confirm the view direction of lift drawing (viewed from landing i.e. Outside) and precast Setout. It will clear the location of the lift call buttons and other penetrations.
Ensure the height of penetrations provided in lift drawings are measured from FFL or SSL.
There will be penetrations of different diameter according to its purpose i.e. call buttons, electrical, fire switch etc. so concentrate more on size and location of penetration while detailing.
Penetration locations and size may vary according to the respective floor entrances so refer the details from correct floor entrance which is given in lift drawings.
5.CONTROLLER BOX PENETRATIONS:
Controller box may need a recess or in some cases could be a penetration.
Ensure the location of the control box from the panel edge, we need to maintain the sufficient gap from the edge of the panel.
Ensure the sufficient cover from reinforcement with the penetrations
6. SERVICE PENETRATIONS AND INTERNAL PLATFORM BOX:
Ensure the Hatch opening / exhaust opening need to be accessible for the whole lift for installation & service.
In some case there will be an internal recess requirement to allow for attaching temporary platforms inside the lift for servicing the lift. Make sure these recesses are same RL and opposite.
7. LIFTING EYE PLACEMENTS & CAPACITY.:
For the whole lift is closed by 2 types of lids One by cast-insitu lid and another by precast lid. If we have the precast lid, we need to consider the following things
Connection between the vertical precast & lid
Slope for the water drain
Finish of the face of the lid
Lifting Eye & Hooks for the Lift car & accessories fixing
Ensure the Capacity & size of the Hooks from the lift design.
