Slab Capacity

NOTE: Slab capacities are based on mesh over joists raised as indicated.
*Loads indicated are the total allowable service load that the slab can carry, Ws, and are determined from the conservative equation:
Ws = (Wf – 1.25 + D) / 1.5 + D
Where: Wf = Factored Total Load D = Minimum Dead Load (weight of slab + joist)

Concentrated Loads

It is important to separate the total uniform loads from other special loads such as wall loads, concentrated loads, line loads, point loads, and partial loads, which should be shown on the drawings and will be added to the design requirements accordingly.

Hambro® can accommodate special loads in several different ways:
  • Increasing slab thickness with the use of Hangerplate™
  • Adding another layer of mesh
  • Adding a joist under the load
  • Using headers to transfer the load to adjacent joists

The method of choice will depend on the type and extent of special loading conditions. We stand ready to assist the professional engineer in his determination of the method to use to accommodate any special loading conditions.

Joist Designation

To designate a joist the project engineer should specify the joist depth, slab thickness, mesh size and the design loads (dead, live and total load together with any concentrated loads where applicable). For maximum efficiency, joists will be designed to specifically meet these loading requirements. Live load deflection will be limited to L/360.

The Total Load includes the uniform live load, the weight of the joist, mesh, concrete, partitions, all mechanical, ceiling, and miscellaneous loads. A slash separates the Total Load and uniform live load which include furnishings and people.

It is important to separate the total uniform loads from other special loads such as wall loads, concentrated loads, line loads, point loads, and partial loads, which should be shown on the drawings and will be added to the design requirements accordingly.

Example of joist identification:

Joist Depth = 16 in.
Live Load = 40 lbs./sq. ft.
Dead Load = 60 lbs./sq. ft.
Total Load = 100 lbs./sq. ft.

Designate joist as H16/410
410 = 100 psf x 4.1 ft. (spacing)

Or simply: H16 with the live, dead and total loads clearly listed on the framing plans.

Selecting a Joist

The following tables are to assist you in selecting the most efficient joist depths for a given concrete thickness and typical spans. It is often best to select typical joist depths based on the typical spans as the cost of some heavier joists will be less than the cost of raising the building height. The tables indicate the most efficient depth based on various loads, spans and slab thicknesses. The minimum joist depth is also provided.

Mechanical Interface

Hambro®'s open web design, no permanent bridging or bracing, and 4' to 6' joist spacing accommodates mechanical distribution within the joist plenum. Large main ducts can be placed between joists while secondary ducts "out of the box" are threaded through joist webs, above the ceiling. Full lengths of pipe, sprinkler lines and electrical systems are all easily run throughout the joists and to where you want them. This virtually eliminates costly and unsightly bulkheads and dropped ceilings. Interface Hambro® with strategically located open web girders, with modified web openings and you no longer have solid web beams blocking the way. Larger joist openings are available. Contact us to assist you with conceptual designs and pricing.

IMPORTANT COORDINATION NOTE: As a material supplier, we are not responsible for the coordination of the structural framing with the mechanical, electrical and plumbing systems. However, as a courtesy, we will assist the Purchaser and/or General Contractor with their coordination of the slab penetrations with the Hambro® Joists. The Hambro® shop drawings will illustrate the bathtubs, showers, toilets, and chases as shown on the architectural and structural drawings. The joists will be located accordingly to avoid the penetrations illustrated.

In addition, we recommend that a copy of our shop drawings be provided to the mechanical, plumbing and other trades for review and coordination during the approval process. If requested, additional prints, sepias or CAD files can be provided for distribution to the other trades.

We will review mechanical or plumbing plans that are provided, as a guide in assisting the Purchaser and/or General Contractor with their coordination. In most cases, the exact locations and sizes of the vertical and horizontal penetrations and mechanical duct locations are not shown on the contract drawings. As a joist supplier we are not experts in, nor can we be responsible for, coordination of the mechanical, electrical or plumbing trades and their impact on the project. Although the penetrations may be illustrated, the Hambro® Shop Drawings are not meant to indicate their exact locations and always require review, coordination, and approval by the Purchaser and the design team.

Mechanical Support

Pipe Hangers and Mechanical Loads:

Hanger loads of up to 50 lbs. can be supported from the slab provided that the hangers are at least 2’ apart. Hangers in the slab shall be placed within a zone 6” to 12” of the joists.

Hanger loads above 50 lbs. and up to 200 lbs. can be hung from the slots in the joist top chord at any location provided that the cumulative mechanical loads do not infringe on the other design loads. The capacity available to support mechanical loads will vary depending on joist span and the design loads specified on the plans.

Hangers can also be supported from the joist bottom chords using threaded rods or bolts placed between the bottom chord angles. Hangers from the bottom chords must be placed immediately adjacent to the panel points (where the web connects to the chord). Do not weld or drill into the Hambro joists. We have not addressed the type of hangers or anchors that will be used. This should be examined by the structural engineer, architect and mechanical engineer. Please make certain that a proper hanger design is used to eliminate any impact vibration in the slab.

Bearing Systems

Metal Stud Framing

Masonry Construction

Wood Framing

ICF Construction

Structural Steel

Fire Ratings

Hambro® brings you one of the finest fire rated structural floor systems in the world. There are many accepted methods to achieve satisfactory fire protection with the Hambro floor system. Extensive fire testing has been performed by Underwriters Laboratories (UL) resulting in many milestones and again proving the superior performance of the Hambro® system. The full scale fire tests are performed while the system is loaded to its full design capacity and the results are as follows:

Gypsum Board Membrane

Gypsum “drywall” ceiling membranes (Type C) installed directly under Hambro® joists are generally used in residential construction. They are economical; aesthetically pleasing and can safely accommodate integrated sub-systems, recessed light fixtures and ventilating units without impairing their fire rating capabilities. UL Design No. G-524 has been the most popular Hambro® rating for residential applications due to its enormous flexibility. For each 100 square feet of ceiling area, it allows unprotected ceiling penetrations up to 256 square inches for 1 hour (See UL item 10Q), 196 square inches for 1.5 hours (see UL item 10F) and 100 square inches for 2 hours (see UL item 10K).

This design permits unshielded, non-metallic electrical wiring for up to 2 hours; and for 1 hour, as an alternate to the unprotected duct outlet, 2 & 4 inch PVC pipe is permitted per 100 square feet of ceiling area to run throughout the Hambro® plenum, penetrate the ½ “ ceiling and run down through non-rated partition wall (see UL item 10E).

You can also substitute unprotected duct outlet with unprotected recessed light fixtures, up to 4 standard 6 ½ “ diameter high hats per 100 square feet for a one hour rating (see UL item 10H). Always consult the latest listing published before detailing.

Gypsum Board Membrane UL Designs: G-524 , G-525

Suspended or Lay-in Ceiling

Accessible ceiling panels commonly referred to as "lay-in” ceiling tiles are generally used in office, commercial and institutional construction. These removable fire rated panels allow access to the ceiling plenum for alterations to mechanical or electrical equipment. Any penetrations to the assembly need to be protected as per the UL design.

Suspended or Lay-in Ceiling UL Designs: G-003, G-201, G-213, G-222, G-227, G-228, G-229, G-236, G-243
Sprayed-on Fireproofing

Insulating the Hambro® joists by sprayed on fireproofing is another accepted method of fire protection. This option is typically selected when there would be so many protected openings that spray becomes a cost effective alternative or spray can also provide flexibility to future tenants who want the option to use a non-rated ceiling of their choice.

Sprayed-on Fireproofing UL Designs: G-702, G-802

Through-Penetration Firestop Systems for the G-500 Series Design

Through-penetration firestop systems are intended to restore the hourly rating of fire-resistive assemblies that have been breached due to penetration by electrical, plumbing or mechanical items.

Through-Penetration Firestop Systems : F-E-1001, F-E-1002, F-E-1003, F-E-2001, F-E-2002, F-E-2003, F-E-2004, F-E-3001, F-E-3002, F-E-3003, F-E-3004, F-E-5001, F-E-7001, F-E-7002, F-E-8001, F-E-8002, F-E-8003

The above links are to the UL Designs that incorporate Hambro® joists. Always check your UL Directory for the latest updating of these listings and applicable building codes before detailing ceiling construction.

Specification on Hambro D500



The supplier shall:

(a) Furnish all labor, materials, equipment and services necessary for, and incidental to, the fabrication of the Hambro Composite Floor System in accordance with these specifications and applicable drawings. Hambro Steel joists and Rollbar shall be manufactured and marketed by Hambro or their authorized representatives.

(b) Fully coordinate the Hambro Composite Floor System with the other structural, mechanical, electrical and architectural components of the buildings.


All fabrication shall be in strict accordance with the Hambro Shop Standard Practice, using steel conforming to Canadian Standards Association CAN/CSA G40.21-04 or similar ASTM Standards, or their engineering equivalent capacities.


Flexural design shall be by the Limit States Design method and as described in the Hambro literature. The slab shall be designed in accordance with CAN/CSA A23.304 “Design of Concrete Structures for Buildings”, the top chord shall be designed in accordance with CAN3-S136-M94 “Cold-Formed Steel Structural Members”, the bottom chord and webs shall be designed in accordance with CAN/CSA S16.01 - “Steel Structures for Buildings (Limit States Design)”.


(a) All welding materials and methods used for fabrication shall be in accordance with the requirements of the Canadian Welding Bureau.

(b) All field welders shall be certified, qualified operators in accordance with the requirements of CWB for the materials and methods being used, except that Hambro joist repairs or modifications that may be required may be done by factory approved personnel.


(a) Submit detailed erection drawings to the Architect, Engineer or the General Contractor for approval showing material lists, mark numbers, types, locations, and spacing of all joists and accessories. Show method of attachment of the joist to supporting members. Contract drawing notes relative to the Hambro system shall be considered a part of this specification as though fully set forth herein.

(b) Shop drawings prepared only from approved erection drawings shall be used for fabrication and erection.

(c) Figured dimensions only shall be used, scaling drawings shall not be permitted.


Care shall be exercised at all times to avoid damage to Hambro joists through careless handling during unloading, storing and erecting.



(a) Hambro joists:
1- All composite joists shall be fabricated in accordance with Section 2.1 and 2.2 of these Specifications.
2- Top chord member shall act as a continuous shear connector of cold rolled steel, minimum 13 gauge with Fy = 350 MPa (50 ksi) minimum.
3- Bottom chord member shall consist of either hot rolled angles with Fy = 380 MPa (55 ksi) minimum or cold rolled angles of equal capacities of steel.
4- Web members shall consist of minimum 13 mm (1/2”) diameter hot rolled bars of Fy = 350 MPa (50 ksi) minimum.
5- All composite joists shall be shop painted with a rust inhibitive primer. According to CISC/CPMA Standard 1-73a one coat paint.

(b) Rollbar shall be designed specifically to support 10 mm (3/8”) to 15 mm (5/8”) plywood forms, a 2 kPa (40 psf) construction load and slab weight until the slab has cured sufficiently (concrete cylinder strength of 3.5 MPa (500 psi)), and act as temporary bridging and spacers for Hambro composite joists.

(c) Standard bearing shoes shall be angle shape 100 x 50 x 6 x 120 (4” x 2” x 1/4” x 4 3/4”) wide, unless otherwise noted.

(d) Slab reinforcement shall be minimum 152 x 152 MW13.3 x MW13.3 ( 6 x 6 - 8/8) welded wire fabric, with Fy = 400 MPa (60 ksi) minimum unless otherwise required by structural engineer.

(e) Forms shall be 1 220 mm (4’-0”) or 1 500 mm (4’-11”) plywood sheets, and may be 10 mm (3/8”) to 15 mm (5/8”) thick.

(f) Concrete
1- Minimum ultimate compressive strength f’c = 20 MPa (3 000 psi) at 28 days for Hambro design.
2- Standard density i.e. 2 450 kg/m3 (145 pounds / ft3).
3- Maximum size coarse aggregate: 19 mm (3/4”).


(a) Fabrication shall be in accordance with the Hambro Shop Standard Practice.
(b) The joist top chord shall be fabricated to allow for 40 mm (1 1/2”) embedment into the concrete slab.
(c) Provide Hambro joist bottom chord ceiling extensions unless otherwise noted.
(d) After installation, permissible Hambro joist sweep shall be 25 mm (1”) in 6 m (20’-0”).
(e) Hambro joists shall be fabricated with an appropriate camber to suit span and slab thickness. The camber shall be designed according to the non-composite dead load.


Joist shall be manufactured in a fabricator’s facility having a continuous quality control program. Theinspection shall include checking of size, span, assembly and weld.



(a) Installation shall be in accordance with the latest Installation Manual for the Hambro Composite Floor System, approved erection drawings and any amendments which may be issued by the manufacturer.

(b) All joists shall be erected in such a manner so that they are vertical, level and plumb and at the proper elevation. Any shimming that may be required shall be done with metal.

(c) Special conditions requiring top and/or bottom bracing shall be shown on erection drawings prepared by supplier.

(d) Welded Wire Fabric - Lapping shall be in accordance with the provisions of CAN/CSA A23.3-04 and Hambro construction drawings.

(e) End anchorage - Joist shoes shall be properly welded, anchored or embedded as per engineer’s or architect’s drawings.

(f) Concreting Practice

1- Do not pour concrete in excess of the slab thickness stated on the erection drawings.
2- Do not drop large bucket loads in concentrated areas over Hambro joists. Lightly vibrate concrete
3- Construction joints made parallel to the joists should be made midway between the joists but never closer than 150 mm (6”) to the top chord. Construction joints made perpendicular to the joists should be located over the supporting wall or beam.
4- It is recommended that the following publications be followed:
(a) CAN/CSA A23.3-04 “Design of Concrete Structures for Buildings”.
(b) CAN/CSA A23.2-04 “Methods of Test for Concrete”.
(c) CAN/CSA A23.1-04 “Concrete Materials and Methods of Concrete Construction”.

(g) Stripping - Under normal conditions form work may be stripped at such time as the concrete has reached a cylinder strength of 3.5 MPa (500 psi).

(h) Construction Loads
1- Bundles of plywood or roll bars should not be placed on joist system but rather on supporting walls or beams.
2- During construction, the minimum non-composite joist capacity for a 70 mm (2 3/4”) slab and joist spacing of 1 251 mm (4’-1 1/4”) on center, shall be 3.5 kN/m (240 plf). Joists spaced at greater than 1 251 mm (4’-1 1/4”) on center shall have their non composite capacity adequately increased to carry the additional load. Construction loads may be applied when the concrete has reached a cylinder strength of 7 MPa (1000 psi).

(i) Minimum joist bearing shall be as follows:
1- Steel support: 65 mm (2 1/2”) for 75 mm (3”) shoe 90 mm (3 1/2”) for 100 mm (4”) shoe.
2- Masonry, concrete, wood and metal stud support: 90 mm (3 1/2”). Bearing surface of supporting units to comply with applied shoe end reaction, based on minimum supplied bearing area of 107 cm2 (16.6 in2).

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