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Pre-stressed Predalle





Safe load tables in single span condition
Table above has been based on standard width of 2.50 meters in simple supported condition. An allowance of 2.0 Kn/sq.m. has been taken for finishes in addition to self weight of slab.


Safe load tables in multiple span condition
Safe superimposed loading for continuous panels in double and/or multiple spans can be improved by the addition of reinforcement over supports placed on chairs. Detailed information can be requested from manufacturer for individual project conditions.


Prestressing Cables
Low relaxation 3x3 wire strand diameter 6.5mm cross-sectional area 21.20
Characteristic strength fpu = 1760 N/ stressed at fpi = 1350 N/


Fire construction
Cover to all reinforcement/cables must be minimum 25 mm for a fire construction of 1 hour.


Concrete grades
Preslab shall be in C35 (35 N/mm2) concrete at release for an ultimate strength of C40 concrete (40 N/mm2).
In-situ topping shall be in minimum C25 (25 N/mm2) concrete.


Preslab reinforcement
Reinforcement in the form of mesh must be placed in preslab to cater for lifting points/hook arrangement; typically A98 for a maximum lifting span of 3.50 meters.


Top surface Preslab
The top surface of preslab is to be finished rough and/or brushed to provide a good key between preslab and in-situ topping.


Provide a minimum seating of 75 mm on mortar bedding.


Handling and Storage
Preslabs should be lifted by multiple hooks, which should be self-balancing, at maximum 500 mm from corners. Slab units should be stacked on bearers on firm level ground. Stacks should be not more than 10 units high and each layer separated by bearers at not more than two meters intervals.


Erection/Sequence of operations
Pre-stressed wide slabs should be lifted from transport directly onto prepared supports. Never walk on unsupported slabs. Once the slabs are in position, any loose reinforcement required by the design, including trimming of holes, continuity reinforcement, top reinforcement over supports etc., is placed. Site in-situ concrete is spread and compacted in position. Temporary supports are removed between 7-14 days after the in-situ concrete is poured to ensure that the in-situ topping has achieved the design strength of C25 concrete.


Continuity ties
Compliance to be achieved by providing longitudinal and transverse ties to ensure compliance with stability requirements of code; recommendations can be requested from manufacturer for individual project conditions.


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