What procedure do I use to calculate the diaphragm shear transfer with the composite GIRDER-SLAB® system?
Chapter 4 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.
Can the GIRDER-SLAB® system be designed for point loads or non-uniform loading?
Since all section properties are available, the EOR is able to calculate stresses for all loading conditions.
Does Girder-Slab Technologies provide assistance to the SER?
Yes. Please call for further information. Additionally, all standard details are provided on our website.
I am a structural engineer who uses RAM software. How do I design your D-BEAM® girders using this software?
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-BEAM®s 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.
Our structural engineering firm designs multi story residential projects throughout the country. Can you give me a brief summary of how competitive the GIRDER-SLAB® system will be compared to other alternatives?
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.
Without using the "tree" column, detail S16, how far can the D-BEAM® girder span?
Some Engineers have found that with camber and the heavier D-BEAM® girder, a span up to 25' with no tree columns can be achieved. The EOR is the sole determinant of the D-BEAM® girder span.
I noticed your "tree" column, detail S16, is welded to the column flange. Can we design a bolted connection?
Yes, but consider that the bolts may interfere with the precast slabs.
How high of a building can be constructed using the GIRDER-SLAB® system?
As high as any other steel building. The D-BEAM® girder and the hollowcore plank carry the gravity loads. The height of the building is a function of lateral resisting system.
I have been on your website and looked through your design guide, I cannot understand how the D-BEAM® girders get manufactured in such a way that the openings in the web line up with the openings in the hollow core slabs?
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.
The D-BEAM® girder top flange is specified in your Design Guide as a flat bar (Grade 50). I would like to substitute flame cut plate, is this ok and what weld would be required when the plates butt together?
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.
Can I splice the top flange flat bar?
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.
When the D-BEAM® girder is cut to length we may be cutting through the web opening, how does that affect fabrication?
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.
Can the GIRDER-SLAB® system be used as a diaphragm in a high seismic area?
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.)
I am an engineer and want to specify an end plate connection to the D-BEAM® girder. I do not want to develop "fixity". What do you suggest?
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;

  • Use only enough bolts to transfer end reaction.
  • Use a relatively thin plate.
  • Limit the amount of welding between the top and bottom flanges and the end plate.
  • Consider using 2 bolts in the web and 2 bolts below the bottom flange, vertically spread about 6" apart.
We are designing our third Girder-Slab job and this has never come up before. Can we use the D-BEAM® girders in braced frames?
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.
How is differential camber removed from the plank?
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.
Can Plank be used on ownership property and luxury apartments?
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).
Is a topping needed for the UL fire rating (Design number K912) as shown on the 3 details? Or is there a separate fire rating for the no topping system?
A concrete topping is not required for the 2 hour unrestrained rating. A 1-1/8" concrete topping is required for the 3 hour restrained rating.
A hollow core manufacturer) is asking if every cell in their plank needs to be broken out to place grout.
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.
Are weld plates needed in plank?
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.
Your design-guide says "Open the top of the slab core for inspection and reinforcing installation". Can you please describe the various methods for doing this and show some details?
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.
How many floors of steel and plank can be erected before we must grout?
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.
Our job has weld plates specified. Should we weld or grout first?
If you have a choice, grout first then weld.
I am concerned about plank clearances and bearing around steel columns. Has this ever been a problem?
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.
What size mechanical holes or openings can I core in the hollow core slabs?
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.
I notice in your Design Guide you say that plank spans of 28'-0 are very efficient. The design tables from my local precast hollow core supplier say that 8" plank can span around 33'. Why are you suggesting 28' and they are saying 33'?
Please discuss vibration, deflection, and differential camber ramifications with your local hollow core supplier.
I am a structural engineer with previous experience using hollow-core planks on both masonry and steel structures. Typically the geometry of the building is rectangular with maybe a few skewed ends. How are curved and round areas best handled with Girder-Slab and hollow-core plank?
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.
We are steel fabricators bidding our first Girder-Slab project. A subcontractor is quoting us on the grouting work so we can offer a complete bid of; all the structural steel, the D-BEAM® girders (which we intend to fabricate in our shop), hollow core precast slabs, all erected and grouted. Are there any “scope issues” we should watch out for with the grouting?
We encourage steel fabricators to bid this “entire” scope. Our system is often an alternative to cast in place flat plate concrete. When builders compare the two, having an entire package price is beneficial.

A certain amount of wood form work, bent plate, angles or light gauge pour stop is always required around columns, block outs or edges prior to grouting. Who is including this: you, your subcontractor or the builder? Filler material or mesh will be required for small openings; larger openings may require a temporary plywood form.

As you know the D-BEAM® girder and hollowcore plank must be grouted together to develop the “composite action”. Be sure to discuss this and agree with the hollow core supplier how their plank will be prepared (opened) for reinforcing and grout. The FAQ’s on our website (these pages) discuss various methods. Additionally ask about “weep holes” in the plank. Are they required? You should also check to see what plank embeds are needed, curtain wall framing, wall panels etc. are these all shown? Will some have to be done in the field?

If your project is located in New England (or other Northern climates) you can minimize the cost/delays of “Winter Conditions”. If you anticipate erecting in the winter months ask the precaster to supply some weld plates for the bottom of the precast. Install the temporary and permanent bracing then weld the plank to the D- Beam®. This may be sufficient to stabilize the building and allow you to continue erecting. On a mild day you can go back and do the grouting. Each building is different so be sure to consult with the structural engineer.

For more information on this subject please read the article "Let's be Plank" from the September 2007 issue of Modern Steel Construction. You can find this article under the
Published Articles
section of our website.
Can any precast hollow core supplier be used on a Girder-Slab project?
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.
I am an Architect considering your system of structural steel and hollow core slabs for a student housing project. Some of the rooms must accommodate showers for handicapped students. I want to avoid the cost of a 2" concrete topping, I prefer to specify a 1/2 or 3/4" light weight leveling material. Please describe how this can be done.
The use of a light weight material on top of the plank, ½” to ¾” will make it suitable for most all flooring applications; tile, carpet, parquet, etc. After the leveling coat is applied, the door sill is applied, and the shower base goes down. The difference in elevation from the top of the shower (tub) base to the sill can be 2” +/-. A Sloping mud bed is applied for the tile base, so the tile can remain ½” +/- below top of shower tub. We believe the ½” is code acceptable for Handicapped areas.
I have questions about the correct way to install various finished floor material over precast hollow core plank. Where can I get information?
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".
I am an architect and have little experience using precast hollowcore slabs. Can you give me some idea what I have to watch out for?
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.