Hollow Core Building Brochure
Hollow Core Building Brochure
Hollow Core Building Brochure
Introduction 2
Design Criteria for Development of the Span-Load Charts 2
Related Publications 3
Manufacturing Tolerances 4
8" Bare Hollow Core Span-Load Chart 5
8" Topped Hollow Core Span-Load Chart 6
12" Bare Hollow Core Span-Load Chart 7
12" Topped Hollow Core Span-Load Chart 8
12½" Bare Hollow Core Span-Load Chart 9
8" Hollow Core Residual Camber 10
12" Hollow Core Residual Camber 11
ICCES Evaluation Report 12
General Notes 14
Blockouts 15
Allowable Ripped Slab Widths 16
Dimensions for Detailing 17
Dimensions for Safe Drilling 18
The Hollow Core slab has a variety of uses, including floors and roofs for buildings and parking garages, decks for
piers and short-span bridges, lids for storm water detention vaults, and lagging for retaining walls. Cast-in-place,
composite concrete topping may be added to provide a smooth, level floor surface that serves as a horizontal
diaphragm when properly reinforced. For untopped and non-composite topping applications, the horizontal diaphragm
is provided by shear friction reinforcement in the grouted shear keys and in the end closure pours. See ICC Evaluation
Service Report No. ESR-2152.
The following Span-Load Charts show the 8” and 12” sizes with and without a minimum 2½” thick composite topping.
The 12½” size with topping is not shown as it is usually used in untopped applications. It is designed with a thicker top
flange to provide the greater durability and increased “punch-through” capacity normally supplied by the topping.
ALLOWABLE STRESSES – The extreme fiber stress under full service load is limited to 0.45f ’c for compression and
12 f c′ for tension in accordance with ACI 318-05 for Class U or Class T prestressed concrete flexural members.
FLEXURAL STRENGTH – The nominal flexural strength, φMn, exceeds the required factored moment, M u = 1.2Md +
1.6Ml , in accordance with ACI 318-05, Sections 9.2.1 & 18.2.1. The strength reduction factor, φ, is calculated per
Section 9.3.2.7. The stress in the pretensioned reinforcement at nominal strength (f ps) is calculated in accordance with
Sections 12.9 & 18.7.2, and all superimposed load is considered as live load. Where flexural strength governs the
design, superimposed loads comprised of dead and live load combinations will increase the capacity over the values
given in the Span-Load Charts.
SHEAR – The nominal shear strength, φVn, exceeds the required factored shear, Vu = 1.2Vd + 1.6Vl , in accordance
with ACI 318-05, Sections 9.2.1 and 11.1.1. Web shear strength (Vcw) is calculated in accordance with CTA Technical
Bulletin 85B1. This method determines the applied shear which causes a principal tension of 4 f c′ at the centroid of
the pretensioned member, as allowed in ACI 318-05, Section 11.4.3.2. Flexure shear strength (Vci) is calculated as set
forth in CTA Technical Bulletin 78B1. This method uses a modified version of Equation (11-10) of ACI 318-05, based
on full-scale testing of Hollow Core slabs.
Filling a predetermined number of voids with cast-in-place concrete will result in higher web shear capacity in the
transfer zone at the ends of the slabs. Contours in the Span-Load Charts indicate the number of voids filled with 3,000
psi concrete (typically to 2’ from the face of support) to achieve the given capacity. The capacity of the filled voids is
discussed in CTA Technical Bulletin 85B1.
All values in the Span-Load Charts are based on Hollow Core slabs without shear reinforcement. It is not possible to
provide shear reinforcement in extruded Hollow Core slabs.
The weight of the cast-in-place topping has already been included in determining the allowable superimposed load on
composite slabs. Do not deduct the weight of the topping from the values derived from the Span-Load Charts.
The natural camber of the Hollow Core slabs, combined with the wet weight of the cast-in-place topping, will normally
require a variable thickness of topping to provide a flat finished floor. Residual Camber Contour charts are provided to
estimate the amount of residual camber or sag after placement of the topping. The weight of the variable thickness in
addition to the 2½” minimum has been considered in the development of the Span-Load Charts.
FIRE RESISTANCE RATING – The fire resistance rating of Hollow Core slabs is given in ICC Evaluation Service
Report No. ESR-2152.
DEFLECTIONS – Total deflection is defined as the upward camber of the slab due to the eccentricity of the
pretensioning less the downward deflection due to applied loads, including the long-term effects of prestress loss,
creep and shrinkage. Allowable loads from the Span-Load Charts limit the theoretical total deflection to l /180. In
addition, the deflection due to prestress and dead load, including long-term effects, is limited to l /240. Instantaneous
deflections due to live loads are limited to l /360. The load combinations considered in the deflection analysis are 50%
dead and live load, or 100% live load.
Associated building elements that may be affected by deflections should be placed with adequate tolerances. It is not
practical to deflect the formwork to produce desired cambers. Suggested methods for calculating cambers and
deflections are described in the 6th Edition of the PCI Design Handbook, Section 4.8.4. Contact CTC’s Marketing
Department with any questions about deflections.
ROUGH OPENINGS – The values in the Span-Load Charts apply to Hollow Core slabs without openings. Rough
openings through the voided area of a Hollow Core slab normally have little effect on its load-carrying capacity.
However, large openings that cut webs and strands can have a significant impact on the load-carrying capacity of the
slab. Contact CTC’s Marketing Department with questions on the capacity of slabs with openings.
CTA Technical Bulletin 73B6, “Shear Diaphragm Capacity of Precast Floor Systems”
CTA Technical Bulletin 74B6, “Composite Systems Without Roughness”
CTA Technical Bulletin 75B10/11, “Flexural Bond Performance”
CTA Technical Bulletin 76B3, “Non-Destructive Testing of Concrete”
CTA Technical Bulletin 76B4, “Composite Systems Without Ties”
CTA Technical Bulletin 78B1, “Shear Strength of Hollow Core Members”
CTA Technical Bulletin 79B4, “Shear Strength of Continuous Hollow Core Systems”
CTA Technical Bulletin 80B3, “Shear Diaphragm Capacity of Untopped Hollow Core Floor Systems”
CTA Technical Bulletin 82B2, “Grouting Precast Floor Systems”
CTA Technical Bulletin 85B1, “Web Shear Strength of Prestressed Concrete Members”
525
450
ACI 318-05 ALLOWABLE SUPERIMPOSED LOAD (psf)
8"
425
400
325
300
275
250
225
200
175
7 Strands
150
125 6
100 5
75 4
50
25
0
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
NOTES:
1. The values given in this chart are in compliance with ACI 318-05.
2. The values given in this chart are based on hollow core slabs without shear reinforcement. See SHEAR for
discussion.
3. Refer to DEFLECTIONS for discussion of deflection criteria.
4. This Span-Load Chart is intended as an aid to preliminary sizing only, and must be interpreted using sound
engineering judgment.
500
See Note 5
212"
475
450
ACI 318-05 ALLOWABLE SUPERIMPOSED LOAD (psf)
425
8"
400
325
300
275
250
225
200 6 7 Strands
175 5
150
125 4
100
75
50
25
0
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
NOTES:
1. The values given in this chart are in compliance with ACI 318-05.
2. The values given in this chart are based on hollow core slabs without shear reinforcement. See SHEAR for
discussion.
3. Refer to DEFLECTIONS for discussion of deflection criteria.
4. This Span-Load Chart is intended as an aid to preliminary sizing only, and must be interpreted using sound
engineering judgment.
5. Interface shear governs the design of composite topped hollow core slabs above this line.
1050
900
ACI 318-05 ALLOWABLE SUPERIMPOSED LOAD (psf)
850
12"
800
750
3'-117 8"
700 (4'-0" Nominal Width)
650
600
(2) Void Fills required for 2'-0"
550 at each end of each slab.
500
450
400 11 Strands
350 10
300
9
250
8
200 7
150
5 6
100
4
50
0
16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
NOTES:
1. The values given in this chart are in compliance with ACI 318-05.
2. The values given in this chart are based on hollow core slabs without shear reinforcement. See SHEAR for
discussion.
3. Refer to DEFLECTIONS for discussion of deflection criteria.
4. This Span-Load Chart is intended as an aid to preliminary sizing only, and must be interpreted using sound
engineering judgment.
1000
212"
950
900
ACI 318-05 ALLOWABLE SUPERIMPOSED LOAD (psf)
12"
850
800
750
3'-117 8"
700 (4'-0" Nominal Width)
550
500
450
400
See Note 5
350
300 9
8
250 11 Strands
7
200
6
10
150 5
100 4
50
0
16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54
NOTES:
1. The values given in this chart are in compliance with ACI 318-05.
2. The values given in this chart are based on hollow core slabs without shear reinforcement. See SHEAR for
discussion.
3. Refer to DEFLECTIONS for discussion of deflection criteria.
4. This Span-Load Chart is intended as an aid to preliminary sizing only, and must be interpreted using sound
engineering judgment.
5. Interface shear governs the design of composite topped hollow core slabs above this line.
1200
1150 (3) Void Fills required for 2'-0"
at each end of each slab.
1100
1050
ACI 318-05 ALLOWABLE SUPERIMPOSED LOAD (psf)
1000
1212"
950
900
850
3'-117 8"
800 (4'-0" Nominal Width)
750
700
650 (2) Void Fills required for 2'-0"
600 at each end of each slab.
550
500
450
11 Strands
400
350 10
300 9
250
8
200
7
150
5 6
100
4
50
0
16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62
NOTES:
1. The values given in this chart are in compliance with ACI 318-05.
2. The values given in this chart are based on hollow core slabs without shear reinforcement. See SHEAR for
discussion.
3. Refer to DEFLECTIONS for discussion of deflection criteria.
4. This Span-Load Chart is intended as an aid to preliminary sizing only, and must be interpreted using sound
engineering judgment.
+¼"
NUMBER OF STRANDS
3
16 18 20 22 24 26 28 30 32 34 36 38 40
Residual Camber
(Add'l Topping)
Figure 1
C
L
Positive Residual Camber Sym.
(N.T.S.)
212" Topping
Residual Camber
(Add'l Topping)
Figure 2
Negative Residual Camber
NOTES: (N.T.S.)
1. Residual Camber is defined as the camber remaining in the hollow core slabs just after the topping slab
has been placed. The contours shown above reflect the upward deflection due to prestress force,
downward deflection due to the hollow core slab self-weight and downward deflection due to the plastic
(wet) topping weight.
+¾"
10
9
+½"
NUMBER OF STRANDS
8
0 -1¼"
-½"
-¾"
4
16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54
Residual Camber
(Add'l Topping)
Figure 1 C
L
Positive Residual Camber Sym.
(N.T.S.)
212" Topping
Residual Camber
(Add'l Topping)
Figure 2
Negative Residual Camber
NOTES: (N.T.S.)
1. Residual Camber is defined as the camber remaining in the hollow core slabs just after the topping slab
has been placed. The contours shown above reflect the upward deflection due to prestress force,
downward deflection due to the hollow core slab self-weight and downward deflection due to the plastic
(wet) topping weight.
VOID DAMS - Void dams are provided by CTC to restrict the flow of C.I.P. concrete into the slab voids. Typically,
the dam is placed six inches from the ends of the slab at voids without pour slots. The dam is placed two feet from
the ends of the slab at voids with pour slots. This distance can be modified as required for embedment of
reinforcement or to increase the slab end shear strength. To facilitate the placement and consolidation of the
concrete fill, CTC recommends and provides blockouts in the top of the voids at locations where endfill length
exceeds 1'-6".
BEARING - The recommended design bearing dimension is three inches with a field installation minimum of two
inches. CTC recommends and furnishes a 3/8" x 1/4" neoprene end bearing strip to provide uniform bearing during
erection. Final bearing is provided when C.I.P. concrete fills the remaining space.
GROUT KEYS - The longitudinal keys between adjacent slabs must be filled with grout to fully develop the
concentrated load distribution and shear friction capacity of the Hollow Core slab system. CTC recommends a mix
consisting of one (1) part cement to three (3) parts paving or builder's sand by weight, with a maximum water
content of five (5) gallons per sack of cement.
RESISTANCE TO LATERAL LOADS - Lateral loads may be transmitted through Hollow Core slabs to resisting
elements, such as frames or shear walls, by diaphragm action. When concrete topping is to be installed over the
slabs, the diaphragm is normally designed to be in the topping. In this case, shear transfer takes place by shear
friction, based on WWF mesh or other reinforcement in the topping. For untopped systems, diaphragm action is
developed by means of shear friction reinforcement at the ends of the slabs, as described in ICCES Report ESR-
2152 and CTA Technical Bulletin 80B3. It is important to detail this reinforcement such that it is effectively anchored
into the lateral force resisting system, such as by reinforcement hooked into shear walls.
VOID DRAIN HOLES - Void drain holes will be installed in Hollow Core slabs. Cap top holes prior to soil backfill or
topping pour to prevent material from washing into void and plugging drains. Drain holes must be cleaned out after
end closure concrete pours are complete. The contractor may patch holes, if necessary, once the structure is
weather proofed.
CONSTRUCTION LOADS - Once erected, the Hollow Core slabs form a safe platform for workers and normal
construction tools. Avoid staging other construction materials on the slabs that have not had the joints grouted and
the grout reach design strength. At no time should these materials exceed 1,000 pounds on a single slab or 1,500
pounds on any two adjacent slabs without prior written approval.
PENETRATIONS - CTC recommends that all penetrations less than 6" in diameter for mechanical, plumbing,
electrical, etc. be field installed by the trades involved. Prior consultation with the Architect/Engineer and CTC is
advisable to insure that the structural capacity of the system is not compromised. CTC recommends that openings
larger than 6" be made at time of slab fabrication. Detailing of these openings on the design drawings will aid in the
shop drawing/calculation submittal process. Refer to page 15 for design considerations when large openings are
used.
8" ULTRASPAN
8" ULTRASPAN
12" ULTRASPAN
12½" ULTRASPAN
8" ULTRASPAN