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70 3.1 Fundamentals of Reinforcement

3.1 fundamentals of ReinfoRcement Compressive strength is the capacity of a material to withstand axially directed pushing forces. The concrete that makes up the framework of an ARXX structure is recognized as having tremendous compressive strength. However, non-reinforced concrete is relatively weak in tension. Tension results when a specimen of material is loaded in such a way that it bends. Steel has immense strength characteristics in tension. Steel-reinforced concrete provides the solution of correcting the weak tension in the concrete by introducing steel reinforcement bars into the concrete wall, marrying materials with both compressive and tension strength characteristics. The critical purpose for steel reinforcement in concrete is to provide tensile strength to the concrete wall. This can be broken down into two similar but different functions: control of cracks, due to stress caused by temperature or shrinkage; and control of deflection of the wall, due to loads imposed on the concrete caused by backfill, wind, etc.

Placement of reinforcements must be in accordance with the local standards, regulations, or code. in the united states, the Placement and design of reinforcing steel must be in conformance with aci 318, or aci 332, or the latest international residential code (irc). in canada, the Placement of reinforcing steel must conform to csa a23.1; design requirements must be in accordance with csa a23.3 and the national building code of canada (nbcc).

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71 3.2 Reinforcement Design and Specifications

3.2 ReinfoRcement design and specifications

ARXX forms are the basis for a reinforced concrete wall. Reinforced concrete can be used for any type of building, including multi-story and tall wall applications for residential, institutional, commercial, and industrial structures. The design and specifications for the reinforcement in an ARXX wall may be developed in a number of ways. Whichever method is followed, the contractor must adhere to reinforced concrete design principles, in accordance with American Concrete Institute ACI 318 or Canadian Standards Association CSA A23.3, and meet the requirements of the applicable building code. The major building codes (IRC, IBC and NBCC) recognize insulating concrete forms and have developed reinforcing tables that apply to specific applicability limits for residential or light commercial applications, with a limiting wall height of 10’ (3 m) between lateral supports for one wall below grade plus two floors above grade. The same criteria has been used to develop tables by Portland Cement Association (PCA) in PCA 100-2007 Prescriptive Design of Exterior Concrete Walls. ARXX has also developed product specific prescriptive design tables following the same design criteria.

For any project that exceeds the applicability limits, as applied in the building code or the ARXX prescriptive design tables, the walls may be designed in accordance with ACI 318 or CSA A23.2. Please refer to the ARXX Technical Library for additional information.

Typical reinforcement bar sizes used in ARXX walls follow Tables 3.2-1

Table 3.2-1 ReinfoRcing baR DesignaTion anD sizes

the engineer of record on any Project has resPonsibility for the structural design, which includes the reinforcement. reference should always be made to the design or structural drawings.

in areas where the Project design meets the aPPlicability limits in the building code and/or the PrescriPtive design tables, stamPed engineered drawings may not be required. in this case, the reinforcement design must follow one of these PrescriPtive methods.

comPlete reinforcement requirements, including sPacing and lintel design, should be reviewed before Placing blocks.

arXX walls must be reinforced with deformed steel with a minimum yield strength of either 40 ksi (275 mPa) or 60 ksi (413 mPa) dePending on the structural design and comPliance with aci 318 or csa a23.3.

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AmericAn - ASTm STAndArd cAnAdiAn - rSic STAndArd

Bar Designation Diameter (in) Bar Designation Diameter (mm)

#3 0.375

#4 0.500 10M 11.3

#5 0.625 15M 16.0

#6 0.750 20M 19.5

#7 0.875

#8 1.000 25M 25.2

72 3.3 Splices in Reinforcing Steel

3.3 splices in ReinfoRcing steel

3.3.1 lap splices

A lap splice is when two pieces of rebar overlap to form a continuous line. Lap splices help with the proper transfer of loads within the structure. There are two types of lap splices used: contact and non-contact lap splices.

Contact lap splices occur where the overlapped sections of the rebar are wired together to secure them against displacement, particularly when concrete is being placed. It is necessary to provide an appropriate overlap length for the splice to satisfy reinforcement regulations per ACI 318.

Non-contact lap splices occur where the overlapped rebar does not touch, but the distance between the lap sections meets specified code approvals. For non-contact lap splices, spliced bars must be overlapped and are permitted to be separated by up to 1/5 of the bar lap length to a maximum of 6” (150 mm). Regardless of the method chosen to create the lap splice, there is a minimum length of material that must be overlapped, which is determined using a formula of lap splice length equals 40 times the bar diameter. For example:

›› 10M (#4) - 40 x 0.5” = 20” (40 x 11 = 440 mm)›› 15M (#5) - 40 x 0.625” = 25” (40 x 16 = 640 mm)

It is recommended that all reinforcement be placed using non-contact lap splicing.

figuRe 3.3.1-1 non-conTacT lap lengTh

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73 3.3 Splices in Reinforcing Steel

3.3.2 coRneR lap splices

Where lap splices are required in a corner form, pre-bent standard corner bars are an efficient method to achieve corner non-contact splices. This method meets the requirements and can be efficiently dropped into the corner forms as the walls are constructed. The length of the splice should be determined in accordance with the formula of 40 times the bar diameter for each leg plus the 90° bend.

For corner splices for all ARXX forms, the most efficient method for a #4 (10M) bar is to bend a straight bar with minimum length 49” (1245 mm) at 90° in the middle. For a #5 (15M) bar, bend a straight bar with minimum length of 59”(1500 mm) at 90° in the middle.

figuRe 3.3.2-1 coRneR lap JoinT

when making sPlices, it is essential that that the flow of concrete will not be comPromised. care should be taken to ensure that the Placement of the laP sPlice will not create a void beneath the sPlice or cause the concrete to get hung-uP.

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74 3.4 Installation of Reinforcement

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3.4 installation of ReinfoRcement

3.4.1 pRepaRation

Once the first or second course of blocks have been placed, all the lengths for the horizontal rebar in each wall should be determined and can be pre-cut and bent before the next block courses are placed. It is recommended to have the right tools available to efficiently and safely cut and bend the reinforcing bars.

Distribute the cut-to-size rebar near the base of each wall for installation.

Prepare any dowels, lintel or brick ledge stirrups, etc. prior to block placement.

steel reinforcing bars are tyPically suPPlied in 20’ (6.1 m) lengths.

confirm and/or coordinate with the local building dePartment if insPection/aPProval is required on the walls Prior to Placing concrete.

use safety equiPment and Precautions when cutting rebar. Protect workers from the ends of eXPosed rebar on the job site.

3.4.2 HoRizontal ReinfoRcement placement

3.4.2.1 ARXX Prime and ARXX Edge FormsThe webs for the ARXX Prime and ARXX Edge forms are designed to accept and hold rebar in place during the placement of concrete. It is recommended to place the horizontal reinforcement bars into the notches of the web inside the form. For example, for the first course, place the rebar in the notch closest to the EPS panel, then on the next course, stagger the rebar position so that it is placed in the next notch toward the center of the wall. As the blocks are placed in the following courses, it is recommended to repeat this placement pattern. By staggering the horizontal reinforcement bars in this manner, the vertical reinforcement bars can easily slide down from the top, so that they weave themselves through the horizontal rebar, thus ensuring that the vertical rebar is held in position relative to the surface of the wall. In this way the rebar can be placed either at the center of the wall or on either side of the wall to maximize the strength benefits of reinforced concrete.

3.4.2.2 ARXX Steel FormsFor ARXX Steel forms, it is recommended to secure horizontal rebar to the steel web by tie-wire or zip-ties. Stagger the placement of the horizontal rebar as detailed in Figures 3.4.3-1 and 3.4.3-2 to allow the vertical rebar to weave between the horizontal bars.

tyPically, for all walls, a horizontal bar is required in the first block course and the toP block course, Plus under and over oPenings. refer to engineering tables.

75 3.4 Installation of Reinforcement

3.4.3 VeRtical ReinfoRcement placement

3.4.3.1 ARXX Prime and ARXX Edge FormsFor ARXX Prime and ARXX Edge forms, it is recommended to place vertical reinforcement after the wall is erected. Prior to placing concrete, cut the vertical reinforcement bars to length and place them into the form cavity, so that it weaves through the horizontal rebar courses, which should be staggered in the webs. Following these steps ensures that the vertical reinforcing is held away from the face of the form and the required concrete cover will be maintained.

›› Refer to Reinforcement Figures 3.4.3-1, 3.4.3-2 and 3.4.2-3

due to the sPecially designed configuration of the web and the secured Positioning of the reinforcing bar, it is seldom necessary to tie the vertical reinforcement.

3.4.3.2 ARXX Steel FormsFor ARXX Steel forms, it is recommended that vertical rebar be secured prior to concrete placement. This can be achieved by: tying the rebar together with wire, tying the rebar to the steel webs with either tie-wire or plastic zip-ties, or tying the vertical rebar to the top horizontal rebar with tie-wire or plastic zip-ties.

When required by local code, the bottom of the vertical rebar can be secured in place by installing 1½” (38 mm) diameter by 1½” (38 mm) high PVC rings. Prior to placing the first course of ARXX Steel blocks, the PVC rings are placed over the footing or slab vertical dowels to align them with the vertical rebar spacing required in the wall. If required, the PVC rings can be glued to the footing or slab to maintain proper alignment. When the vertical rebar is placed in the wall, the bar should be aligned to fit inside the ring.

figuRe 3.4.3-1 6” foRm ReinfoRcing

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76 3.4 Installation of Reinforcement

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figuRe 3.4.3-2 8” foRm ReinfoRcing

figuRe 3.4.3-3 10” foRm ReinfoRcing

77 3.4 Installation of Reinforcement

3.4.4 cold Joint in a continuous Wall

If continuing with ARXX walls for subsequent construction after the first concrete pour is completed, the connection of the lower and upper walls will be a 'cold joint‘. A cold joint is a structural detail that provides strength for wall sections that are joined together. There are five main installation requirements for cold joint applications:

1. Reinforcement bars must create a non-contact lap splice between the two wall segments. This can be done by either extending the lower wall rebar the required length (40 x bar diameter) or by inserting separate vertical dowels.

2. Cold joint dowels must be spaced a maximum of 24” (610 mm) apart and embedded in the concrete a minimum of 16” (406 mm). Refer to Design/Engineering Figure 3.4.4-1.

3. It is recommended that the concrete on the lower wall should be stopped within the form 5” to 8” (125 mm to 200 mm) from the top of the form, exposing the top of the web or connector. When the wall is continued, the next form can be tied to the exposed web or connector.

4. It is recommended that the concrete is left unfinished to provide a better bonding surface between successive lifts.

5. If required to meet the vertical rebar spacing of 24” o.c. (610 mm), dowels may be cut and placed in the fresh concrete of the first placement. It is recommended that these dowels are embedded the required depth and that they provide the required lap splice length for the subsequent concrete placement.

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78 3.4 Installation of Reinforcement

figuRe 3.4.4-1 colD JoinT ReinfoRcemenT

all cold joints require a non-contact laP sPlice reinforcement at 24”o.c. (610 mm)

at the toP of a finished wall, the vertical rebar requires a minimum of 1½” (38 mm) concrete coverage.

cold joints are not allowed in walls below grade.

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79 3.5 Reinforcement Placement Around Openings

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3.5 ReinfoRcement placement aRound openings In order to support superimposed loads created by roofs, floors, snow, etc., the concrete above an opening (the lintel) must be reinforced properly. Penetrations through walls increase the load intensity in the area immediately surrounding the opening. To account for the increased stresses in the wall, additional reinforcement is required vertically and horizontally around the openings, which will distribute the loads.

›› Refer to Section 6.2 – Reinforcement at Openings for typical placement of reinforcement around openings.

figuRe 3.5-1 ReinfoRcemenT layouT

if the aPPlicable design limits in the building code or the PrescriPtive design tables listings cannot Provide an aPPlicable reinforcement layout, then it is recommended to retain a local design Professional to PrePare the design in accordance with recognized standards.

lintels may be designed in accordance with the Pca 100 PrescriPtive method for insulating concrete forms, irc code, the nbcc code or the arXX PrescriPtive design requirements.