CONCRETE MASONRY FENCE DESIGN
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Concrete masonry fences and garden walls are used to fulﬁll a host of functions, including privacy and screening, security and protection, ornamentation, sound insulation, shade and wind protection.
In addition, concrete masonry provides superior durability, design ﬂexibility and economy. The wide range of masonry colors and textures can be used to complement adjacent architectural styles or blend with the natural landscape.
Because fences are subjected to outdoor exposure on both sides, selection of appropriate materials, proper structural design and quality workmanship are critical to maximize their durability and performance.
Masonry fences are generally designed using one of ﬁve methods:
- as cantilevered walls supported by continuous footings;
- as walls spanning between pilasters, that are, in turn, supported by a footing pad or caisson;
- as walls spanning between wall returns that are sufﬁcient to support the wall;
- as curved walls with an arc-to-chord relationship that provides stability; or
- as a combination of the above methods.
This TEK covers cases (a) and (d) above, based on the provisions of the 2003 and 2006 editions of the International Building Code (refs. 1, 2). Although fences up to 6 ft (1,829 mm) high do not require a permit (refs. 1 and 2, Ch.1), this TEK provides guidance on design and construction recommen- dations. Fences designed as walls spanning between pilasters (case b) are covered in TEK 14-15B, Allowable Stress Design of Pier and Panel Highway Sound Barrier Walls (ref. 3). In addition, fences can be constructed by dry-stacking and surface bonding conventional concrete masonry units (see ref. 4), or by utilizing proprietary dry-stack fence systems.
Figure 1—Typical Construction Requirements for a Cantilevered Fence
CANTILEVERED FENCE STRUCTURAL DESIGN
Tables 1, 2 and 3 provide wall thickness and vertical reinforcement requirements for cantilevered walls for three lateral load cases: lateral load, w ≤ 15 psf (0.71 kPa), 15 < w ≤ 20 psf (0.95 kPa), and 20 < w ≤ 25 psf (1.19 kPa), respectively. For each table, footnote A describes the corresponding wind and seismic conditions corresponding to the lateral load, based on Minimum Design Loads for Buildings and Other Structures, ASCE 7 (ref. 5).
Assumptions used to develop Tables 1, 2 and 3 are:
- strength design method
- except as noted, designs comply with both the 2003 and 2006 International Building Code,
- running bond masonry,
- ASTM C 90 (ref. 6) concrete masonry units,
- speciﬁed compressive strength of masonry, f’m = 1,500 psi (10.3 MPa)
- ASTM C 270 (ref. 7) mortar as follows: Type N, S or M portland cement /lime mortar or Type S or M masonry cement mortar (note that neither Type N nor masonry cement mortar is permitted to be used in SDC D),
- ASTM C 476 (ref. 8) grout,
- Grade 60 reinforcing steel, reinforcement is centered in the masonry cell,
- depth from grade to top of footing is 18 in. for 4- and 6-ft (457 mm for 1.2- and 1.8-m) high fences; 24 in. for 8-ft (610 mm for 2.4-m) high fences, and
- reinforcement requirements assume a return corner at each fence end with a length at least equal to the exposed height. Where fence ends do not include a return, increase the design lateral load on the end of the fence (for a length equal to the exposed height) by 5 psf (34.5 kPa).
Table 1—Cantilevered Fences Subject to Lateral Loads up to 15 psf (0.71 kPa)
Table 2—Cantilevered Fences Subject to Lateral Loads up to 20 psf (0.95 kPa)
Table 3—Cantilevered Fences Subject to Lateral Loads up to 25 psf (1.19 kPa)
For cantilevered walls, the footing holds the wall in position and resists overturning and sliding due to lateral loads. Dowels typically extend up from the footing into the wall to transfer stresses and anchor the wall in place. Dowels should be at least equal in size and spacing to the vertical fence reinforcement. The required length of lap is determined according to the design procedure used and type of detail employed. For the design conditions listed here, the No. 4 (M#13) reinforcing bars require a minimum lap length of 15 in. (381 mm), and the No. 5 (M#16) bars require a minimum lap length of 21 in. (533 mm). Refer to TEK 12-6, Splices, Development and Standard Hooks for Concrete Masonry (ref. 9) for detailed information on lap splice requirements.
Footings over 24 in. (610 mm) wide require transverse reinforcement (see footnotes to Table 4). For all footings, the hook should be at the bottom of the footing (3 in. (76 mm) clearance to the subgrade) in order to develop the strength of the bar at the top of the footing.
The footing designs listed in Table 4 conform with Building Code Requirements for Reinforced Concrete, ACI 318 (ref. 10). Note that concrete for footings placed in soils containing high sulfates are subject to additional requirements (refs. 1, 2).
Table 4—Footing Sizes for Cantilevered Fences
Serpentine or “folded plate” wall designs add interesting and pleasing shapes to enhance the landscape. The returns or bends in these walls also provide additional lateral stability, allowing the walls to be built higher than if they were straight.
Serpentine and folded plate walls are designed using empirical design guidelines that historically have proven successful over many years of experience. The guidelines presented here are based on unreinforced concrete masonry for lateral loads up to 20 psf (0.95 kPa). See Table 2, footnote A for corresponding wind speeds and seismic design parameters.
Design guidelines are shown in Figure 2, and include:
- wall radius should not exceed twice the height,
- wall height should not exceed twice the width (or the depth of curvature, see Figure 2),
- wall height should not exceed ﬁfteen times the wall thickness, and
- the free end(s) of the serpentine wall should have additional support such as a pilaster or a short-radius return.
A wooden template, cut to the speciﬁed radius, is helpful for periodically checking the curves for smoothness and uniformity. Refer to TEK 5-10A, Concrete Masonry Radial Wall Details (ref. 11) for detailed information on constructing curved walls using concrete masonry units.
Figure 2—Serpentine Garden Walls
All materials (units, mortar, grout and reinforcement) should comply with applicable ASTM standards. Additional material requirements are listed under the section Cantilevered Fence Structural Design, above.
To control shrinkage cracking, it is recommended that horizontal reinforcement be utilized and that control joints be placed in accordance with local practice. In some cases, when sufﬁcient horizontal reinforcement is incorporated, control joints may not be necessary. Horizontal reinforcement may be either joint reinforcement or bond beams. See TEK 10-1A, Crack Control in Concrete Masonry Walls, and TEK 10-2B, Control Joints for Concrete Masonry Walls – Empirical Method (refs. 12, 13) for detailed guidance.
In addition, horizontal reinforcement in the top course (or courses if joint reinforcement is used) is recommended to help tie the wall together. For fences, it is not structurally necessary to provide load transfer across control joints, although this can be accomplished by using methods described in TEK 10-2B if deemed necessary to help maintain the fence alignment.
Copings provide protection from water penetration and can also enhance the fence’s appearance. Various materials such as concrete brick, cast stone, brick and natural stone are suitable copings for concrete masonry fences. Copings should project at least ½ in. (13 mm) beyond the wall face on both sides to provide a drip edge, which will help keep dripping water off the face of the fence. In cases where aesthetics are a primary concern, the use of integral water repellents in the masonry units and mortar can also help minimize the potential formation of efﬂ orescence.
- 2003 International Building Code. International Code Council, 2003.
- 2006 International Building Code. International Code Council, 2006.
- Allowable Stress Design of Pier and Panel Highway Sound Barrier Walls, NCMA TEK 14-15B. National Concrete Masonry Association, 2004.
- Design and Construction of Dry-Stack Masonry Walls, TEK 14-22. National Concrete Masonry Association, 2003.
- Minimum Design Loads for Buildings and Other Structures, ASCE 7-02 and ASCE 7-05. American Society of Civil Engineers, 2002 and 2005.
- Standard Speciﬁcation for Loadbearing Concrete Masonry Units, ASTM C 90-01a and C 90-03. ASTM International, Inc., 2001 and 2003.
- Standard Speciﬁcation for Mortar for Unit Masonry, ASTM C 270-01a and C 270-04. ASTM International, Inc., 2001 and 2004.
- Standard Speciﬁcation for Grout for Masonry, ASTM C 476-01 and C 476-02. ASTM International, Inc., 2001 and 2002.
- Splices, Development and Standard Hooks for Concrete Masonry, TEK 12-6. National Concrete Masonry Association, 2007.
- Building Code Requirements for Structural Concrete, ACI 318-02 and ACI 318-05. Detroit, MI: American Concrete Institute, 2002 and 2005.
- Concrete Masonry Radial Wall Details, TEK 5-10A. National Concrete Masonry Association, 2006.
- Crack Control in Concrete Masonry Walls, TEK 10-1A. National Concrete Masonry Association, 2005.
- Control Joints for Concrete Masonry Walls – Empirical Method, TEK 10-2B. National Concrete Masonry Association, 2005.
NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication.
5 Fun Outdoor Rebar Projects to Try This Summer
Steel rebar is used for giving extra strength to concrete and other building materials, but it’s far more versatile than you might imagine. It’s easy enough to bend, shape, and cut it with just a few power tools. If you’re looking to get creative and decorate your yard without spending a ton at the local hardware store for pre-made outdoor accessories, try some of these fun rebar projects yourself. You’ll build useful skills you can use if you ever decide to pour your own concrete slabs reinforced with rebar.
5 Rebar Projects to Try This Summer
1. Rebar Deck Railing
If you’re not sure of the best way to cut rebar and can’t weld yet, start out with an attractive deck railing that combines the steel rods and pre-cut lumber. Build a top rail and vertical support pieces from the wood, then run horizontal lengths of rebar through holes drilled in the supports to create balustrades. You can also stick with vertical pieces too by drilling down through the top bar.
2. Durable Woven Fencing
Have you ever admired the flowing lines of fencing made from green willow or bamboo? You can weave with rebar tool, if you’ve got some bending tools and plenty of elbow grease. Hammer rebar into the ground at two foot intervals to serve as posts, then run longer lengths of the metal horizontally along the fence line. Start with the horizontal rod positioned behind the first post, then alternate to the front of the next rod, and so on to create a wavy look. You can also try using sheet metal, wicker cane, or other materials as the bending fence material to contrast against the vertical rebar pieces.
3. Decorative Garden Trellises and Arches
Give your favorite plants some supports that last for decades, even out in the wind and rain. The simplest design consists of three lengths of rebar tied together at the top to create a triangle shape. To get more creative, bend the rebar into U-shapes or even wavy lines for a more artistic look. 20 foot lengths of metal can be bent into large U-shapes and set up a few feet apart to create a full-sized arch way. It’s perfect for framing the entrance to your garden, especially if you plant vining flowers like morning glories to grow over the frame and cover it.
4. Lovely Reclaimed Patio Table
Ready to get welding? With a welder and some cutting equipment, you can turn a salvaged slab of barn wood into a patio table your neighbors will envy. Build a simple frame for the table top by cutting and connecting four lengths of rebar that fit exactly around your wood. Attach a second set of rods, about half an inch smaller than the first on all sides, underneath the edge of the wood to create a lip it rests on. Add four legs at the corners and you’re ready for a barbecue or backyard party.
5. Sturdy Support for Planters and Bird Baths
Elevate your humble pots and planters by building a pedestal base that can support their weight with tough rebar. Bend curving shapes from the steel to mimic the lines found in nature, then attach a joined ring at the top that lets the planter nestle down at least half way to prevent tipping. You can also support concrete or resin bird bath tops this way. Consider painting the exposed metal to add a burst of color, or coat the bars in linseed oil to prevent rusting while allowing a natural patina to develop.
All five of these projects give you a chance to express your creativity with rebar art. Start out simple, then add more flourishes and twists as you gain confidence with the techniques and tools you’re using. Visit our blog for more tips and tricks regarding construction, rebar, and household projects.
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How to Install Rebar in Vinyl Posts
Read More: Vinyl Fence System Overview
The drawing illustrates the proper installation of in-ground vinyl posts. Two pieces of 1/2" rebar are placed in opposite corners of the post and can be held in place during installation by special rebar clips.
It is essential that this be done on every post on 7' and 8' high vinyl fences to add structural integrity to the vinyl fence. On shorter heights, only end, gate and corner posts should be set this way. Gate posts would require filling the post to the bottom of the top rail hole so the hardware will adhere better to the post. Mount the gates first before filling the gate post. There are steel inserts available by special order to substitute for filling posts with concrete. It is much cheaper to use concrete.
Make sure the rail ends are taped or plugged shut so concrete does not travel horizontally through the rail. It can add weight to the section and make it sag.
Rebar Separator Clips are designed for use in end and gate posts or any other post that needs extra support. All end and gate posts must be filled with concrete and 2 pieces of 1/2" rebar for maximum strength and performance. The Rebar Separator Clip will assure that the rebar inside the post is positioned in opposing corners of the post and is held in a vertical position.
Rebar length should extend from the bottom of the hole to:
End Posts - 1/2 way up the height of post
Gate Posts - 12" down from the top of the post
Rebar Installation Steps:
Step 1 - Attach Rebar Separator Clip to each piece of 1/2" wide rebar, approximately 12" up from the bottom.
Step 2 - Attach Rebar Separator Clip to each piece of rebar, approximately 6" down from the top.
Step 3 - Lower rebar down into post.
Step 4 - Install gate hardware (if applicable).
Step 5 - Fill post with concrete mix to completely cover rebar.
Fence Installation: Piles
Step 1: Pour Concrete For Fence Piles
Step 1: Pour Concrete
Pile Construction Tolerances
Pour concrete meeting or exceeding the minimum strength requirements specified in the approved construction design into the fence pile holes.
During the pour of each fence pile, ensure that the concrete form is braced to maintain the correct elevation and horizontal location. Double check with laser and hand levels to maintain tolerance; minor adjustments will have to be made during the pour.
- Horizontal Tolerance: ±1.0 in. (25 mm)
- Vertical Tolerance: -1.0 in. (25 mm)
Finish concrete using a hand trowel or other equipment to create a flat surface for post placement. For mixing and placing concrete in cold weather check out AB Fence Tech Sheet #2006.
Step 2: Set Rebar
Step 2: Correct Rebar Placement
Step 2: Set Rebar with Spacing Jig
Step 2: Set Rebar with Spacing
Jigs on Piles
Immediately following the concrete pour, relocate the center of the AB Fence post using the AB Fence Pile Layout Jig, shown in Figure 1, and make an impression in the wet concrete to mark it.
Place the vertical steel reinforcement bars (rebar) using the Post Block Template with Piles Steel Placement shown in Figure 2; or for greater accuracy use the optional Rebar Alignment Jig shown in Figure 3. Pay close attention to make sure that the center of the template is at the center of the AB Fence post and square to the adjacent AB Fence post. This can be done using offsets and string lines.
The rebar must be placed to ± 0.5 in. (13 mm) of the design’s horizontal location. When placing rebar, a tolerance of ± 0.5 in. (13 mm) must be maintained to allow for proper interlock between post and panel sections.
The rebar must extend into the pile to the depth specified in the approved construction design, but maintain a 3 in. (75 mm) clear cover at the bottom of the pile.
The rebar should extend out of the top of the pile to a length equal to or greater than the minimum lap splice requirements set by the approved construction design or a minimum of 24 in. (610 mm).
Step 3: Set Fence Posts
Post and Rebar Placement
Before setting any AB Fence Post Blocks, allow the concrete to harden approximately four hours, or until hard enough to resist more than surface scratching when scraped with rebar.
Note: The AB Fence uses two different types of concrete during construction. The piles and AB Fence Post Blocks use concrete with gravel and sand size aggregate. This type of concrete is generally available from concrete plants and used in most types of construction. However, the bond beams require what is referred to as a fine mix concrete grout. This mixture of concrete uses only sand as the aggregate, which makes it ideal for filling the smaller cores of the AB Fence Panel Block.
Fence horizontal rebar
.how to tie rebar
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