Handling and transport

Hollow core slabs are extremely strong when supported in their intended manner; however, if they are not handed and stored properly, they can be damaged. It is imperative that the supervisor of the field crew understands the proper procedures as described herein to avoid damage and accidents due to mishandling.
Handling, loading and storage arrangements on delivery should be such that the hollow core slabs are not subjected to forces and stresses that have not been catered for in the design. The units should have semi-soft (e.g. wood) bearers placed at the slab ends. Where they are stacked one above the other, the bearers should align over each other.
When stacking units on the ground on site, the guidelines will be similar to the above. The ground should be firm and the bearers horizontal, such that no differential settlement may take place and cause spurious forces and stresses in the components. During handling, provisions shall be taken to ensure safe manipulation, for example safety chains under the slab.

Assembling

The erection of the hollow core floor slabs should be done according to the instructions of the design engineer. If needed, METRIC can send personnel to supervise the construction methods. METRIC will supply written statements of the principles of site erection, methods of making structural joints and materials specification on request.
The nominal bearing length of simply supported hollow core floor units is given in the table.


Supporting material

Slab thickness

Support length a

 

 

Max length

Minimum effective length

Concrete or metal

≤ 250 mm

70 mm 100 mm

50 mm 80 mm

Bricks 

≤ 250 mm

100 mm 120 mm

80 mm 100 mm

Openings

Holes in hollow core floors are made as indicated in the figure. The dimensions are limited to the values given in the table. Small holes may be formed at the center of the longitudinal voids. The maximum size is limited to the width of the void. Holes are normally made in the fresh concrete during the production process. The edges of the openings are rough.

Openings in Hollow Core Slab


l/b

 HCS 180 - 300

Corner (1) 
Front     (2) 
Edges (3)

600 / 400 
600 / 400 
1000 / 400

Center    (4)  
    round holes
     square openings

Core minus 20 mm 
1000 / 400

 

Locating Openings


Openings are a critical component to the design and layout of  hollowcore plank. It is extremely important to give METRIC all required opening sizes  and locations as early as possible  in the design process. It is also recommended that the locations of penetrations are properly coordinated early enough so that the precast can be properly designed. However, it is possible that some openings may need to be moved or re-sized for structural reasons.
The best place to locate large openings is near the bearing point. This location has the least design impact to the floor system. Large openings near the bearing may require solid concrete areas that are done either in the plant prior to shipping or in the field after installation. Large openings near the mid-span of the plank will require more prestressing and will impact camber. 
Small core drilled openings can be placed anywhere provided they are located in the hollow void of the plank and are small enough that they do not cut any prestressing strand.  Any core drilled openings that cut through the strand must be accounted for in the design of the plank and carefully monitored in the field.  Any core drilled opening that cuts prestressing strand that was not accounted for in design  needs the immediate review of METRIC’s engineer. For multiple cores concentrated in one area, it is recommended that these are aligned and bunched together in order to reduce the amount of coring perpendicular to the spans.

Important Considerations for Opening

 

Effect of Openings

Openings may be provided in hollow core systems by saw cutting after a deck is installed and grouted, by shoring and saw cutting, by forming or sawing the openings in the plant or by installing short slabs with steel headers. In laying out openings for a project, the least structural effect will be obtained by orienting the longest dimension of an opening parallel to a span, or by coring small holes to cut the fewest prestressing strands, or when several openings must be provided, aligning the openings parallel to the span to again cut the least number of prestressing strands.
Penetrations can affect the following design aspects: thickness; amount of prestressing; fire ratings; camber; composite topping; solid cores; redistribution of loading; steel headers;and layout of plank. 

Field Cutting

1. For ease of field cutting openings try to go through hollowcores.
2. Do NOT strike or cut any prestressing strands without permission from METRIC and the Architect/Engineer.
3. There will be some spalling at the exit point of the tool through the deck.

field core drilling

Figure 3 : (L) When field cutting openings up to 1” diameter a power drill or a star drill can be used. (R) When field cutting openings 1” to 6” diameter a core drill or a cutoff saw can be used.

Hanging other Constructions from Hollow Core Slab

Figure 4 : Example of utility placement in Hollow core slab.

 

 

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