4.3 - Temporary propping

From TGN Online
Jump to: navigation, search

Decking is usually designed un-propped, however for longer spans, isolated single span locations (i.e. temporary crane void infills) or large overhangs or cantilevers, temporary propping may be required during construction. Where required, temporary propping must be designed to support the wet weight of the concrete and any construction imposed loads. When contracted to carry out detailing, SMD deck general arrangement drawings will indicate areas where temporary propping is required with a chain-dotted line and the notation 'TP'.


Should a project require tighter control of deck deflection at construction stage, the structural engineer may specify temporary propping to spans within the safe load/span tables to minimise deflections experienced during construction.


Where temporary props are required to spans exceeding 4.0m for R51+, TR50 and TR60+, 5.0m for TR80+, or at any unsupported or large edges (refer to Fig 4.3a), the propping arrangement is to be in position, levelled and adequately braced prior to installation of the deck/edge trim. Consideration should be given to the suitability of fall arrest methods due to the difficulty and logistical issues of installing safety nets in this situation.


4.3a.jpg


Refer SMD Section image 27


Depending on the design criteria (span, storey height and slab depth) in the location to be propped, props normally consist of either a length of timber and/or steel plate supported by adjustable steel props. In locations where the prop load is excessive, a proprietary shoring system may be more appropriate.


The minimum bearing width of the timber and/or plate depends upon the thickness of the slab, these are typically in the range of 75-100mm.


4.3b.jpg


4.3c.jpg


Refer SMD Detail Sheet 176


The timber/steel bearer and sole plates must be continuous and extend the full width of the bay to ensure zero deflection at propped points. Typically the continuous supporting timbers are propped at maximum 1m centres (refer to Figs 4.3b and 4.3c).


Temporary propping should not be removed until the concrete has achieved 75% of its design strength.


The above information is for guidance only, the design and installation of the temporary propping is the responsibility of others (typically the project structural or temporary works engineer) and should be of adequate strength and construction to sustain the dead weight of the concrete plus any construction live loads. For more extensive guidance on Temporary Propping refer to SCI Publication P300, Concrete Society TR75 or contact SMD Technical Team.


SCI P300 REVISED EDITION. Composite slabs and beams using steel decking: Best practice for design and construction


Concrete Society TR75: Composite Concrete Slabs on Steel Decking




Go to NEXT section