Notes

Single-wythe Brick Panel Fence Failures

I have noticed many brick fence s throughout the west and southwest. Most are in wonderful condition, but some require repair or reconstruction. Are you able to clarify the variation in performance and the way best to design them?



Answer

Within the 1970s, Acme Brick Company developed a design for constructing thin brick fences with a single layer of clay brick in panels suspended between strengthened brick posts on drilled piers. Panels are reinforced with joint reinforcing, which is designed to hold wind masses and the much lower stresses from gravity loads on the brick. Typical panels span between posts which might be 10 to 12 feet on center.


A whole bunch of miles of these fences have been built in Texas, as well as in other parts of the nation. Lots of these fences show no signs of distress after 20 or extra years of wind and weather exposure. Properly designed, we anticipate them to final fifty years or more. However there are also numerous fences that have deteriorated in ten years or much less, and must be replaced. That deterioration has occurred as a result of those that constructed the fences both did not perceive the design or didn't use the proper materials and workmanship.



Figure 1. Perspective view of post and panel fence system.

The Panel and Publish System



Determine 1 shows a perspective view of the major components of the fence system.

Determine 2. Element sections of typical posts displaying reinforcing.


Posts are constructed with two faces of clay brick tied together with wire reinforcing (Figure 2). The design requires 3/16-inch diameter wire that's either hooked on the ends or welded as ladder wire to interact the brick faces. A core of grout is formed and poured between the brick faces to create a composite post that carries wind masses in bending to a drilled concrete pier. Pockets are formed roughly three inches deep on every facet of the posts to obtain the bolstered brick panels.


Panels are remoted from the posts with compressible foam to stop arduous contact between them that would cause crushing or spalling with differential motion. Panels are usually laid in place on non permanent varieties and stay three inches clear of the ground or mud slabs beneath. Wire reinforcing in the mattress joints is designed to resist out-of-aircraft bending from wind hundreds. Vertical bending stresses from the burden of the brick are usually about one % of the wind load stresses, so they aren't vital to the design.



Requirements for Power and Durability

Strength necessities are straightforward:


- Piers must be drilled deep enough to resist overturning hundreds from wind on the panels and posts in the soils encountered at the positioning. NCMA TEK 14-15A provides some guidance for pier design to resist wind masses, but soil types differ broadly and should require deeper piers. - Posts should be sufficiently bolstered and grouted to carry overturning wind loads to the drilled concrete piers below. - Pier reinforcing want not be greater than a single bar in the middle, since shear hundreds are low and shear reinforcing shouldn't be obligatory. - Panels could be both prefabricated or laid up onsite, but will need to have reinforcing designed for the wind hundreds. - Panel reinforcing should have sufficient cowl to forestall corrosion. The masonry code and specification (TMS402/602) requires 5/8-inch cover. This could also be tough or not possible to realize with 2-5/8-inch brick and ladder wire. Consider a single wire on the centerline for these bricks. - Reinforcing wire have to be hot-dip galvanized or stainless steel to prevent corrosion. - Steps should be taken to guarantee adequate bond between brick and mortar and between mortar and reinforcing. Oil must be removed from stainless steel wire.


Determine 3. Fence breaking other than corrosion of joint reinforcing. Fence was less than 2 years old at time of photograph in 2005, Austin, TX.



When Things Go Improper

There have been various failures of fence panels (Figure 3). These are seen as cracks creating between mortar and brick. As cracks progress, mortar spalls off and rusted reinforcing appears close to the surface. This will consequence from one or more of the following causes:


- Poor bond between brick and mortar. - Insufficient cowl on wire reinforcing. - Wire reinforcing might not be sizzling-dip galvanized after fabrication.


Poor mortar bond can outcome from using mortar with too excessive an air content material. For that cause, portland-lime Kind S mortar is recommended, however good results may be achieved with prime quality masonry cements as properly. Workmanship plays the most crucial position in reaching mortar bond, including well timed placement of brick after stringing mortar, proper moisture content material and workability of mortar, and pre-wetting of sure brick which have high preliminary rates of absorption. There can also be a potential for failure if mortar is over-sanded. When bond is poor, a crack can develop between brick and mortar that enables a path for water to reach the wire reinforcing and cause corrosion.


One approach to guarantee that the bricklayer will achieve good mortar bond is to design the panels without shelf angles supporting the bottom course. If the panels are constructed on short-term forms, which are removed after 1 to three days, any brick that are not properly bonded will fall off the underside of the panel when the kinds are eliminated. This is an early quality check for the bricklayer’s workmanship. But many fence builders insist on laying the brick on steel angle lintels at the underside of the panels. These lintels keep any poorly bonded brick from falling off, and it might take a number of years before normal deterioration of the mortar and corrosion of the joint reinforcing turn out to be evident.



The Structural Engineer’s Function

Single-wythe panel fences are engineered constructions. However as a result of they are typically 6 toes high or much less, they might not be regulated by native building codes. We recommend that every municipality require a professional structural engineer to design and supervise building of brick panel fences. Design is relatively easy and repetitive, so design time for every venture is very low. There's a design and building guide on the Acme Brick website. The creator has additionally prepared a spreadsheet that can be utilized to design joint reinforcing within the panels for various brick thicknesses and wind hundreds.


Area supervision want not be continuous, provided the engineer develops confidence that the masonry contractor understands the construction strategies and is willing to observe them explicitly. Additionally it is recommended that quality masonry fence contractors be chosen and completely skilled in this very specialised type of structural brick masonry.

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