Precast Design & Engineering Handbook

Architectural

Designed structural elements intended to provide design flexibility and durability.

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Beams & Columns

Foundational pieces that can enhance building strength and aesthetic.

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Double Tees

Pretopped and standard beams used for applications requiring long, clear spans.

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Hollowcore

Precast concrete slabs used for roofing and flooring.

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Wall Panels

Quick to install panels for interior or exterior walls allowing for design customization.

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Some of the data in the handbook is based on industry norms or specific conditions. Below are those unstated conditions that have been applied throughout the handbook.

LOAD TABLES

Load tables are provided for Spancrete hollowcore plank, beams and double tees. The load tables present the superimposed live load capacity of the various members at various spans. The basis of the load capacities is ACI 318-05 which is the reference document for the 2006 International Building Code (IBC). The material properties used are 6000 psi concrete in the precast element and either 250 ksi or 270 ksi prestressing strands.

For the beams and double tees, the capacities are somewhat independent of the available fire rating. However, for the Spancrete hollowcore plank, the fire endurance provided will have an effect on load capacity.

For the Spancrete hollowcore plank and the double tees, specific prestressing strand patterns are provided for the corresponding load capacities. Cambers are also identified for these strand patterns. Beam load charts simply provide the range of load capacities available for a given cross-section.

For any of the load tables, if the user’s case is at the extreme upper end of the table, it may be more economical to consider the next deeper section as the addition of concrete may be more than offset by a reduction in prestressing strand required.

FIRE RATINGS

To properly use the Spancrete hollowcore plank load tables, the required fire endurance should be known. This will be established from the building code occupancy and limitations requirements. The fire ratings that can be provided are based on the prescriptive provisions of the 2006 IBC. Three criteria must be considered in determining the available fire resistance. The first is heat transmission. Sufficient concrete thickness must be provided to limit the temperature rise on the top of the slab. The second criterion is structural endpoint. That is, at the elevated temperatures in a fire, sufficient strength must remain in the slab to prevent collapse at the endurance time. This criterion is satisfied by using the correct amount of concrete cover under the prestressing strands to limit the temperature to which the strands will be exposed. Finally, the span must be defined as either restrained or unrestrained. For a given concrete cover over the prestressing strands, a longer fire endurance will be achieved in a restrained condition. A restrained span is one where expansion due to elevated temperatures is prevented. Conversely, in the unrestrained condition, expansion is not limited. ASTM E119 provides guidance on restrained and unrestrained assemblies. Generally, interior bays are considered restrained and end bays are considered unrestrained.

TOPPING

Where indicated in Spancrete hollowcore plank or double tee load tables, a 2 inch thick, 4000 psi bonded structural concrete topping has been included as part of the structural element for calculation of load capacity. The topping thickness is measured at midspan of the piece. An adjustment of planned topping thickness should be made for the anticipated camber. Please reference the Span Notes discussing ‘Topping’ under the “Research” heading for further information.

LOAD DISTRIBUTION

When non-uniform loads such as bearing wall or post loads are applied, special considerations are necessary for using the load tables. In Spancrete hollowcore plank, such loads may be distributed over several slabs. Please see the appropriate design information in the Research Notes under the “Research” heading. For double tees, such distribution of loads is a special design consideration and our engineering department should be consulted for more information.

ACOUSTICAL PROPERTIES

Spancrete hollowcore slabs were tested for Sound Transmission Class (STC) and Impact Insulation Class (IIC). The following values are provided:

Additional information on acoustic properties can be found in the PCI Design Handbook.

R-VALUES FOR SPANCRETE WALL PANELS

Spancrete insulated wall panel construction provides insulating values that effectively reduce heating and cooling losses through walls, resulting in increased energy savings and greater cost efficiency over the life of the building.

Spancrete Wall Panels can be manufactured in a variety of sizes and finishes. The structural withes are typically 6”, 8” or 10” (10cm, 20cm or 25cm) thick with the insulation being 2”, 3” or 4” (5cm, 7.5cm or 10cm) thick.

Wall Panels used in freezer/cooler applications are available with insulation thicknesses up to 4” (10cm).

¹Extruded Polystyrene: Values shown are averaged aged values tested at mean 75 deg F per ASTM C578.

²Poly-isocyanurate: Long Term Thermal Resistance (LTTR) is the 15 year time-weighted average R-value per ASTM C1289.