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| Lattice Girder Floors |
| Technical Data |
Download PDF FactsheetMilbank Lattice girder floor units are used as permanent precast concrete formwork to Insitu concrete slabs. This type of composite floor is equally suited to use in almost every building type, - masonry, steel or concrete structures and particularly those with progressive collapse considerations.
These floor slabs comprise a 50 to 70mm thick precast concrete soffit slab, containing individually designed main and transverse reinforcement cast on steel moulds giving a good soffit finish ready for direct decoration after normal preparatory treatments.
Lattice girders are cast into the slab to provide a mechanical fixing between the precast unit and the Insitu concrete. These girders provide rigidity to the unit during transportation and their placement onto the prepared bearings.
The Lattices girder comprises 1 No. (8–16mm dia.) high tensile steel top bar, inclined diagonal bars of 4.5 to 7mm hard drawn wire and typically 2No. 5mm bottom bars.
For more information scroll down or click Links;
• Design
• Manufacture
• Dimensions
• Layout Drawings
• Handling and Stacking
• Temporary Supports
• Insitu Concrete Toppings
• Finishes
| Design |
The floor units are designed in accordance with EC2 and the British National Application Document / BS 8110.
Design considerations will determine the amount of reinforcement in the precast unit and the height and size and spacing of the Lattices.
Milbank Lattice Girder Slabs will generally require temporary propping until the structural concrete topping has matured.
However propping can be reduced or eliminated by increasing the stiffness of the slabs by increasing the diameter of the reinforcement to the top of the lattices and/or reducing the spacing of the lattices.
Unpropped spans of up to 5m can be achieved depending upon the design loads and the overall depth of the slab.
Milbank Floors will Design the precast concrete units and provide Bending Schedules for any Reinforcement or Structural mesh fabric required within the Insitu concrete topping. The Main Contractor is required to provide and place this additional reinforcement / mesh fabric, together with the Insitu concrete topping.
Normally the minimum cover to the reinforcement will
be 20mm; however the cover to the reinforcement can be adjusted to meet
the specific Durability and Fire Resistance requirements for individual
contracts.
Milbank Lattice Girder Slabs can provide a solution where Design for Progressive
Collapse must be considered.
| Manufacture |
Milbank
Lattice Girder Slabs are manufactured within an enclosed factory environment,
“wet cast” on steel moulds giving a superior soffit finish
and dimensional tolerance.
All materials used conform to the requirements of the relevant British Standards.
Water Reducing admixtures are used to achieve the correct workability.
Units are bespoke -cast to meet the requirements of each project, including reduced widths, curved sections, services and if required cast in fixings.
| Dimensions |
Milbank Lattice Girder Slabs are manufactured to comply with the cross sectional tolerances set out in BS8110. Length Tolerances: ± 20mm
Units are manufactured in 50mm to 70mm depths. The Standard nominal Width is 2400mm. Non standard width and shaped units are readily accommodated
Floor layout drawings are based upon normal tolerances, and adjustment to the joint widths or side bearings on flank walls may be required to complete the floor area.
| Layout Drawings |
Milbank
will provide layout drawings for the floor units prior to manufacture.
The drawings show the structure supporting, the precast floor units, position
of service entries etc, typical sections, the loads for which the floors
are designed and the location of props to be provided by the Main Contractor.
| Handling & Stacking |
Milbank
Lattice Girder Slabs are delivered to site, ready to be offloaded and
directly hoisted into position on the supporting structure indicated on
Milbank Floors’ approved layout drawings.
The Slabs can be lifted by the lattices using multiple hooks or by using a lifting frame for longer panels.
When it is not possible to lift the units directly into position, they must be stacked on timber bearers on a firm level surface. The slabs should not be stacked more than 6 units high.
| Temporary Supports |
Milbank Lattice Girder Slabs are designed to span onto the supporting structure and as with any formwork system will require intermediate propping with continuous head trees until the Insitu concrete topping has matured.
The position of the props will be shown on Milbank Floors’ layout drawings, and these props must be in place before positioning the precast concrete slabs.
| Insitu Concrete Topping |
To complete the floor, the Main Contractor is to provide mesh fabric and additional reinforcement over the top of the panels.
Prior to placing the Insitu concrete, the tops of the slabs should be cleared of any loose debris.
When placing the Insitu concrete by pump or by crane and skip, care should be taken to avoid discharging large quantities in any one area.
| Finishes |
Milbank Lattice Girder Floors are manufactured on steel beds giving a “Type A” soffit finish; chamfers are provided to the bottom edges of the units forming a “Birds mouth” feature where slabs abut one another.
Textured paint finishes may be applied after appropriate preparation in accordance with the manufacturer’s instructions.
The Insitu concrete topping can be left with a tamped finish to receive the specified finish, or alternatively power floated as the finished floor.