This information is based on SABS 0100-1: 2000 and is intended to serve as a guide only for the professional engineer responsible for the structural design of the project.

Polyform PolySlab systems comprise interlocking polystyrene blocks and ribs which form a permanent shutter into which reinforcing and concrete are placed.

DESIGN GRAPHS

The graphs are based on the ultimate moments provided by the relative reinforcement indicated at the bottom of the ribs. The nominal dead loads are factored by 1.2 and the imposed loads by 1.6. A nominal load of 0.66 KPa for 30mm floor screed has been allowed, in addition to the self weight. As no plaster is required for the ceilings, additional load must be allowed where suspended ceilings are specified.

The graphs are for simply supported spans with uniformly distributed nominal imposed loads.  Localised concentrated loads (see Table 4 SABS 0160 - 1989) or line loads from partitions can be distributed as per SABS 0100 clause 6.2.2.2. The effects of these on shear have to be checked. The thicker lines shown on the graphs allow for the deflection limitations described in SABS 0100-1: 2000 Clause 4.3.6 for span/depth ratio of approximately 20. The thinner line can be used at the Engineers discretion where deflections are not crucial.  Where slab supports partitions, the deflection must be limited as in clause 3.2.3.2.1.2

Allow for minimum reinforcement over continuous supports specified in clause 4.5.6.2.1 . Additional
reinforcing to the mesh may be required.

The graphs allow for 15mm cover to the bottom reinforcement, 60mm structural concrete topping and 30mm screed which provides for 0.5 hours fire resistance [Table 45 e)]and mild exposure conditions for 25MPa concrete. Alternatively a 90mm structural concrete topping, without screed, can be used.

VERTICAL SHEAR

The point at which shear exceeds the permissible value of `vc’ in the code, assuming all bars are taken through to the supports, is indicated by grey ellipse on the graphs.   In the case where only one bar is taken through to the support and the other bar is curtailed the critical shear point on the graph is indicated by a boxed "1". Where this point is not shown on the graph, the Engineer should check shear manually if bars are to be curtailed.  Where `v’ exceeds `vc’ shear reinforcement will be required [clause 4.5.4].

The punching shear for concentrated load specified by SABS 0160 -1989 and spread according to Clause 4.4.5.2.3 of SABS 0100 - 2000 must be checked.

REINFORCING IN TOPPING

Minimum reinforcing in a 60mm thick topping, according to Clause 4.5.6.2.2 is weld mesh Ref. 156 (99mm²/m) or equivalent in reinforcing bars.

TEMPORARY SUPPORT LINES FOR POLYSTYRENE FORMWORK

Temporary support spacings should allow for a nominal construction line load of 2 KN/m over a 300 mm width transverse to ribs [taken from composite beams in SA Steel Construction Handbook] in addition to the appropriate dead load. The maximum spacing of supports is determined by the strength of the polystyrene blocks and acceptable self weight deflections[calculation spread sheet available]. A factor of safety of 2.5 is recommended.  Normally blocks are specified of 16 Kg/cum polystyrene [ultimate flexural strength = 160 KPa] up to 170 mm thick & `X’ grade[ ultimate flexural strength = 80 KPa] above.

DRAWINGS

Besides the reinforced concrete details, the drawings or separate overlays should indicate the marked Polyform products and the temporary supports. Polyform product order sheets are provided, to be completed by the Engineer.  The order will be processed by the Polyform Agent.

CONSTRUCTION PROCEDURES

The relevant Polyform Erection forms ERS + erection drawing PE for Polyslabs, ERT for Poly T Slabs and ERST for stairs  must form part of the documents issued. The Contractor's attention must be drawn to provisions required for windy conditions.