Hollow Core Slab Design Tables

[Magdalen Tibor]

Chapter4 of the "PCI Manual for the Design of Hollow Core Slabs", Second Edition is a standard reference that engineers use to calculate horizontal shear transfer elements, i.e. collectors, chords, and drag struts. When considering the connection at the D-BEAM, typically, the hollow core shear strength is less than the grouted beam's shear strength.

For designing the GIRDER-SLAB system in RAM engineers will let RAM select a standard WF shape but ignore the output. The engineer will then size the D-BEAM girders from the D-BEAM girder Design Tool located on our website. Since the D-BEAMs are not normally used in a braced frame this procedure works well. If the D-BEAM girders were located in a braced frame, engineers would again model it as a WF beam to obtain the axial load in the beam due to the lateral load. Then the engineer will check the D-BEAM girder, manually, for the combined axial and bending stresses.

Compared to low rise CMU or light gauge metal bearing walls the GIRDER-SLAB system is not likely to be cost competitive. It will be very schedule and quality competitive. When comparing Girder-Slab to a CMU wall bearing system all structural CMU should be removed from the Girder-Slab design. The use of metal studs for exterior wall backup, interior walls, stairs/elevator shafts etc. (Depending on project specifics) may result in an overall savings to the project. Compared to conventional structural steel and precast hollow core slabs, the GIRDER-SLAB system is cost competitive because the D-BEAM girder allows you to lower the floor to floor height of the building. Compared to cast in place flat plate concrete the GIRDER-SLAB system is very cost competitive. The GIRDER-SLAB system is the only non proprietary, prefabricated, precast and steel system that offers significant savings while offering low floor to floor heights. Experienced steel fabricators can provide budgets and time tables from preliminary plans for your specific project so you can compare speed and cost economies. Every project is different. You must consider geographic location of your project, availability of skilled workers, building size and unique requirements. The GIRDER-SLAB system is widely used in the Northeast, New England, and the Mid-west for high-rise (8 stories and above) or large square footage low rise buildings. The GIRDER-SLAB system lighter building weight can save foundation, column and lateral bracing costs, and our rapid assembly process can meet special schedule demands for occupancy.

The design guide and details are graphic illustrations; the web openings in the D-BEAM girder are not always going to line up with the openings in the hollow core slabs. When the web openings do not line up the rebar is placed on an angle or hooked to find its way into the openings of the hollow core. Note: Design Guide dimension tables show the web opening sizes for various D-BEAM girder sections.

A572 gr 50 or A529 gr 50 flat bar are commonly rolled, you may also substitute rolled plate of equal or greater strength, if required splice welds must develop the full capacity of the cross section.

Our system does not anticipate spliced bars just as any engineer's design would not anticipate spliced wide flanges. When a fabricator deviates from the norm, his procedure is controlled by AISC requirements and all of his deviations must be submitted to the SER for review.

Although cutting lengths may fall at an opening in the web, there should be enough remaining web to transfer the shear to the end plate connection but this must be checked by the EOR. When the EOR specifies the "Tree Column Elevation S16" he can adjust the length of the "tree" so that the connecting D-BEAM girders have at least 2" of solid web for the connections at each end. This should result in most of the project's D- Beams being of identical lengths. When checking these connections the EOR may determine the need for reiniforcement. The fabricator can fill in the missing web with plate or a doubler plate can be used.

The GIRDER-SLAB system utilizes precast concrete slabs and steel components joined compositely by grout and steel reinforcing. Both precast and steel components have been used in seismic areas. The use of standard details allows the GIRDER-SLAB system to adapt to the high seismic environment. (Concrete topping and reinforcing is usually required.)

This is intended to be an end plate shear connection, as shown in AISC Code on end plate shear connections. In order to preclude Fixity, employ one or more of the following; 1. Use only enough bolts to transfer end reaction. 2. Use a relatively thin plate. 3. Limit the amount of welding between the top and bottom flanges and the end plate. 4. Consider using 2 bolts in the web and 2 bolts below the bottom flange, vertically spread about 6" apart.

Yes, we often see D-BEAM girders used in braced frames. This is primarily done to facilitate mechanical systems. We suggest you look at using HSS (tube) sections as a single diagonal. The HSS is designed as both a tension and compression member, and the axial load on the D-BEAM due to frame action is zero.

Shimming the plank as required. Threaded Rods and Plates are also used to clamp the plank prior to grouting. A lightweight gypsum floor underlayment is often applied to the top of the plank to eliminate plank surface irregularities. All camber issues and concerns should be discussed with the plank supplier and erector.

Yes, plank has been used on hundreds of high end properties. A high strength gypsum underlayment topping product is recommended. Thickness can vary depending on plank span length. A 2" concrete topping can be used for structural reasons or when there are large expanses of a brittle floor finish (i.e.: ceramic tile).

Rebar is suggested to be #4 x 2'-0" long spaced at 24" 0/C max, and these reinforced cells require block outs. As for intermediate cells, grout has to be able to flow to create a monolithic system. EOR is the sole determiner of how much reinforcing is required and how often.

It depends upon the diaphragm loads and if they are needed for erection (see Girder-Slab typical details). Consult with your local hollow core supplier for availability of weld plates, alternative details may be suggested that will meet the engineer's requirements.

One method is that the hollow core supplier provides these cut outs in the plant and then provides a core plug to stop the grout from flowing more than required into the cell. Another method is the saw cutting of the top of the hollow core in the field and then removing the cut outs and placing them in the hollow core of the slab.

This is a decision for the EOR and the erector. Each building is different. It involves stability; the amount of permanent bracing which is installed and the use of temporary bracing such as tie beams, cables, and or angles temporarily fastened to the columns and floor slabs. Some engineers and contractors will call for weld plates in the bottom of the plank, and field tack weld to the D-BEAM girder. This technique is used so that in the event of freezing weather erection can continue while the grouting is postponed until weather conditions are more favorable.

Consult with your local plank supplier about his tolerances. Plank should be carefully detailed around steel columns to assure proper bearing and avoid interference. Clip angles are often added to columns for plank bearing. NOTE: Some engineers will stop steel bracing short of the "work point" to simplify plank & grout installation. A Plank detailer familiar with steel and plank projects is recommended.

This is more a question for your precast supplier and we would advise you to check with them. We would suggest however, that no slots parallel to the D-BEAM girder be any closer than 18" to the center line of the D-BEAM girder.

Various hollow core plank suppliers throughout the country will have different options. Generally speaking; for curves with radii of 10ft. or greater, the hollow-core plank can be factory cut in straight lines to approximate the curve. Some additional minor trimming in the field will also be required. For curves with smaller radii less than 10ft. it may be better to provide rectangular plank augmented with cast-in-place infill.

Structurally, yes; after grouting is complete (SEE GIRDER-SLAB DESIGN GUIDE FOR SPECIFICS) the composite action will develop between the precast hollow core slabs and the D-BEAM. Note, if the architect is specifying UL K912 for fire resistance, the precast hollow core suppliers should be sure they can comply, not all suppliers are specifically mentioned in these UL numbers.

All types of finished floors; carpet, tile, hardwood, "engineered" hardwood, can be installed over precast hollow core concrete slabs. Your architect will specify a proper leveling material over the precast hollow core slabs. Located in the sidebar of this page is a helpful publication called "Hollowcore 101 - Finished Floors".

Great question. The GIRDER-SLAB system works with all precast hollow core suppliers. Each supplier has minor but unique differences. A great place to start would be the Pre and Post Installation FAQs located in the sidebar of this page.

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