BDCS Notes - Floor Construction

SUPERSTRUCTURE

FLOOR CONSTRUCTION

STRUCTURAL FRAME

• Spans and tables for long-span concrete construction are based on mild reinforcing steel.
• For spans exceeding 40 ft., consider post-tensioning.
• When building concrete frames, consider embedded items such as conduits and penetrations for ducts and pipes when coordinating a structural system.
• Concrete may have less flexibility for locating large duct openings close to beam lines or small penetrations immediately adjacent to columns.

TYPES OF CONCRETE FLOOR CONSTRUCTION

• Flat Plate:
• Simple flat plate with four columns makes a typical bay.
• Columns are typically spaced 20’-25’ apart, on center.
• Flat Slab:
• Drop panel placed near transfer between column and slab.
• Typical dimensions for drop panel are 1/16 of span for each direction.
• The majority of columns designed under this loading system are square in cross-section, but can be circularly shaped as well (as an optional design).
• Typical spacing of columns is 25’-30’ apart, on center.
• Banded Slab:
• Transfers are extended, in a beam-like way, through parallel columns.
• Typical spacing of columns is 25’-30’ apart, on center.
• Joist Slab:
• Extended transfers/girders are laterally braced by joists running perpendicular to the transfers/girders.
• Typical spacing of columns is 30’-40’, apart, on center.
• Skip Joist:
• Extended transfers/girders are laterally braced by joists, thicker, and more widely spaced, running perpendicular to the transfers/girders.
• Typical spacing of columns is 30’-40’, apart, on center.
• Waffle Slab:
• A continuation of perpendicular joists meshing into one another in 3’-4’ inch intervals.
• Gaps filled with concrete near the column transfer.
• Typical spacing of columns is 30’-40’, apart, on center.
• One-Way Slab:
• Columns and beams are precast in concrete and erected to support the flooring.
• Beams in columns can span a maximum of 60’, typically.
• Spacing between beams (or bay spacing) is 18’-27’, typically.
• Two-Way Slab:
• Beams run through the top of columns two ways, perpendicular and parallel.
• In both directions, typical spacing between beams is 30’-40’ apart, on center.

FLOOR STRUCTURE ASSEMBLIES

• Wood Joist
• Hierarchy of assembly is placing of the wood joist, with the subflooring nailed into the top transverse side of the joist, followed by the ceiling being set in underneath.
• Typical depth is 7-13 inches.
• Nominal joists typically used are 2X6, 8, 10, and 12.
• Dead load typically supported is 5-8 PSF.
• A suitable live load ranges from 30-40 PSF.
• A span range for wood joists has a maximum of 18’.
• The main mechanism for failure is deflection.
• Wood I-Joists / Wood Trusses
• Wood I-Joist / Truss is placed, and in a similar fashion as the wood joist, the subflooring is nailed atop the members and the ceiling set in underneath.
• Typical depth is 13-21 inches.
• Nominal joists are 12, 14, 16, 18, and 20 inches.
• Dead load typically supported is 6-12 PSF.
• A suitable live load ranges from 30-40 PSF.
• A span range for wood I-joists is 12’-30’.
• The main mechanism for failure is deflection.
• Wood Beam and Plank
• Wood beam is placed, and plank is nailed on top transverse side of beam.
• Typical depth is 10-22 inches.
• Nominal joists are 2, 3, and 4 inches.
• Dead load typically supported is 6-16 PSF.
• A suitable live load ranges from 30-40 PSF.
• A span range for wood beams is 10’-22’.
• Glue-Laminated Beam and Plank
• Glulam is placed, and plank is nailed on top transverse side of beam.
• Typical depth is 8-22 inches.
• Nominal joists are 2, 3, and 4 inches.
• Dead load typically supported is 6-20 PSF.
• A suitable live load ranges from 30-40 PSF.
• A span range for glulams is 8’-34’.
• Steel Joist with Subflooring
• Steel joist is framed with wood nailer placed on top of joist. Subflooring is attached atop the nailer, and ceiling set in below.
• Typical depth is 9-31 inches.
• Nominal joists are 8-30 inches.
• Dead load typically supported is 8-20 PSF.
• A suitable live load ranges from 30-40 PSF.
• A span range for steel joists is 16’-40’.
• The main mechanism for failure is deflection.
• Steel Joist with Concrete Slab
• Steel joist is framed with steel decking placed on top of joist. A concrete slab is attached atop the nailer, and ceiling set in below.
• Typical depth is 11-75 inches.
• Nominal joists are 8-72 inches.
• Dead load typically supported is 30-110 PSF.
• A suitable live load ranges from 30-100 PSF.
• A span range for steel joists is 16’-60’.
• The main mechanism for failure is deflection.
• Lightweight Steel Frame
• A structural steel frame has the subflooring attached atop it, and ceiling set in below.
• Typical depth is 7-12 inches.
• Nominal sizes can vary.
• Dead load typically supported is 6-20 PSF.
• A suitable live load ranges from 30-60 PSF.
• A span range for a steel frame is 10’-22’.
• Structural Steel Frame
• A steel beam is either welded or bolted in place, with steel decking placed atop it, followed by a concrete slab atop that. Ceiling is set in beneath.
• Typical depth is 9-15 inches.
• Nominal beams vary in sizes (check AISI).
• Dead load typically supported is 35-60 PSF.
• A suitable live load ranges from 30-100 PSF.
• A span range for a steel frame is 16’-35’.
• The main mechanism for failure is deflection.
• Structural Steel Frame (with Precast Concrete)
• A steel beam is either welded or bolted in place, with steel decking placed atop it, followed by a concrete slab atop that. Ceiling is set in beneath.
• Typical depth is 8-16 inches.
• Precast structural concrete is 16-48 inches wide, 4-12 inches deep.
• Dead load typically supported is 40-75 PSF.
• A suitable live load ranges from 60-150 PSF.
• A span range for a steel frame is a little less than 35’. Max of 50’.
• The main mechanisms for failure are deflection and creep.
• Precast Concrete
• Concrete girder/beam is set in place. Precast concrete is set in panels above the girder/beams, following by a concrete topping over that.
• Typical depth is 6-12 inches.
• Precast structural concrete is 16-48 inches wide, 4-12 inches deep.
• Dead load typically supported is 40-75 PSF.
• A suitable live load ranges from 60-150 PSF.
• A span range for precast concrete is a little less than 35’. Max of 60’.
• The main mechanisms for failure are deflection and creep.
• One Way Concrete Slab
• Concrete girder/beams (with rebar and running parallel) are set in place.
• Typical depth is 4-10 inches.
• Dead load typically supported is 50-120 PSF.
• A suitable live load ranges from 40-150 PSF.
• A span range for one-way is 10’-20’. More is allowed with post-tensioning.
• The main mechanisms for failure are deflection and creep.
• Two Way Concrete Slab
• Concrete girder/beam (with rebar and running perpendicular) and slab are set in place.
• Typical depth is 4-10 inches.
• Dead load typically supported is 50-120 PSF.
• A suitable live load ranges from 40-250 PSF.
• A span range for one-way is 10’-30’. More is allowed with post-tensioning.
• One Way Ribbed Concrete Slab
• Concrete ribs (with rebar and with ribs running parallel) and slab are set in place.
• Typical depth is 8-22 inches.
• Typical pan forms are 20-30 inches wide, 6-20 inches deep.
• Dead load typically supported is 40-90 PSF.
• A suitable live load ranges from 40-150 PSF.
• A span range for one-way is 15’-50’. More is allowed with post-tensioning.
• The main mechanism for failure is creep.
• Two Way Ribbed Concrete Slab
• Concrete ribs (with rebar and with ribs running perpendicular) and slab are set in place.
• Typical depth is 8-22 inches.
• Typical dome forms are 19X19 or 30X30, 6-20 inches deep.
• Dead load typically supported is 75-105 PSF.
• A suitable live load ranges from 60-200 PSF.
• A span range for two-way is 25’-60’. More is allowed with post-tensioning.
• The main mechanism for failure is creep.
• Concrete Flat Slab
• Column is placed, topped with capital and drop panel. Concrete flat slab abuts into drop panel with rebar running through both
• Typical depth is 6-16 inches.
• Minimum slab thickness (without drop panel) is 5 inches. With drop panel, thickness is 4 inches.
• Dead load typically supported is 75-170 PSF.
• A suitable live load ranges from 60-250 PSF.
• A span range for a concrete flat slab is 20’-40’. A max of 70’ is allowed with post-tensioning.
• The main mechanism for failure is creep.
• Precast Double Tee
• Double tee and topping above, both of which are preset, are set in place together.
• Typical depth is 8-18 inches.
• Typically 48, 60, 72, 96 and 120 inches wide, 6-16 inches deep.
• Dead load typically supported is 50-80 PSF.
• A suitable live load ranges from 40-150 PSF.
• A span range for a double tee is 20’-50’
• The main mechanism for failure is creep.
• Precast Tee
• Single tee and topping above, both of which are preset, are set in place together.
• Typical depth is 18-38 inches.
• Typically 16-36 inches deep.
• Dead load typically supported is 50-90 PSF.
• A suitable live load ranges from 40-150 PSF.
• A span range for a precast tee is 25’-65’. A max of 70’ is allowed with post-tensioning.
• The main mechanism for failure is creep.
• Composite
• Steel beam is welded/bolted in place. A welded shear connection holds the composite metal decking atop the top flange, and a concrete slab is placed on top of that.
• Typical depth is 4-6 inches.
• Nominal beams vary in sizes (check AISI).
• Dead load typically supported is 35-70 PSF.
• A suitable live load ranges from 60-200 PSF.
• A span range for composite framing is up to 35’.
• The main mechanism for failure is deflection.
• Concrete Flat Plate
• Columns effectively sandwich a concrete flat plate running in between in cross section.
• Typical depth is 5-14 inches.
• Dead load typically supported is 60-175 PSF.
• A suitable live load ranges from 60-200 PSF.
• A span range for a concrete flat plate is 18’- 35’.
• The main mechanism for failure is creep.