Masonry supports, or shelf angles, provide a horizontal movement joint within masonry walls. This seminar will discuss design and construction considerations, including movement control, moisture management, thermal performance, optimizing shelf angle location strategies, and accommodating structural tolerances. Check out https://masonrycharleston.com/ for more information.
Simple, effective angle bracket system designed to suit varying cavity widths. Suitable for either concrete framed structures with site-drilled expansion bolts or steel framed structures with coated setscrews.
Brick masonry walls attached to a concrete frame tend to shrink and expand at different rates due to temperature changes, moisture expansion, elastic deformation, and settlement. These differential movements are provided in a masonry wall assembly through horizontal and vertical expansion joints, shelf angles, and adjustable veneer anchors.
Relieving angles (also known as masonry support or corbels) transfer the weight of the masonry to the main building structure and allow space beneath the masonry for building movements to occur. They are installed at intervals along the wall elevation, typically at each floor level. The frequency and number of relieving angles in a wall system depend on several factors, including the height of the building, the size, and location of windows, the type of lintel or header, masonry anchorage, and the code requirements for structural movement tolerances.
While the purpose of relieving angles is clear, properly installing these metal elements can be difficult to accomplish during construction. That is due to the long lead time for galvanized or stainless steel relieving angles and a tight schedule for installing brickwork. In addition, a lack of communication and coordination between the contractor and structural engineer during the design phase can result in a mismatch between the masonry loads and the structure’s load capacity.
A common deficiency of relieving angle installation is using a sealant (typically mortar) under the underside of the relief angle. It can restrict water drainage from the masonry wall and prohibit it from meeting energy codes. In addition, the lipped bricks are often installed directly above the underside of the angle, requiring that they be cut to fit. This detail usually leaves a gap under the arch that is not sealed and may leak and deteriorate over time.
An alternative to a sealant is a flexible membrane such as Armatherm FRR or other structural thermal break material. It significantly reduces the linear transmittance of the thermal bridge and allows for the removal of the rigid metal flashing used for waterproofing.
Shelf angles are steel angle irons installed in masonry veneer buildings to support brick above a masonry opening. New construction requires them to reduce the likelihood of collapse and damage due to excessive vertical movement. They are typically installed on each floor and support the brick above that story. Like lintels, shelf angles must be engineered and properly sized to ensure they meet the strength requirements for their design. Lintels and shelf angles should also be stiff to minimize masonry cracks caused by excessive deflection.
Many multifamily building projects require steel shelf angles to achieve high energy efficiency levels and comply with state energy codes. However, these structural elements form significant thermal bridges that can reduce the wall’s R-value by up to 50%, creating costly energy losses. To limit upfront material and long-term maintenance costs, SWA recommends that these elements be limited in frequency and, where possible, offset to further reduce the thermal bridging impact.
SWA’s field review of this project found that the last course of brick under the shelf angle was cut to “fit” the pitch instead of being sized to a proper mortar joint. It resulted in excessive expansion and spalling of the bricks at the toe of the shelf angle and inadequate drainage of the area.
Another problem observed was improper shimming of the shelf angle. It allowed water to infiltrate and corrode the steel angle, which could not support the brick above. This condition is commonly referred to as “lipped brick” and can be caused by poor installation, inadequate mortar joints, condensation, or improper protection of the steel angle.
SWA’s engineering services review of this project included 3D thermal modeling to understand the impact of various design solutions for addressing masonry thermal bridging caused by shelf angles. Specifically, modeling focused on the influence of a stand-off shelf in an angle connector geometry, thermal properties, spacing of the connectors, and insulation thickness on the performance of the thermal break. This information will help SWA develop a more effective solution to address masonry thermal bridging in future projects.
Masonry support systems are horizontal ledges that transfer the load of brick or stone veneer buildings onto the main structure. They are typically located at the perimeter of a building and all openings, including doors, windows, and vents. The masonry supports are also designed to allow for differential movement between the brickwork and concrete frame by providing a space or gap at the supporting level that allows for movement.
Brick masonry is known to expand, while concrete tends to shrink. Provision for movement between the two materials is achieved by a system of vertical and horizontal expansion joints, shelf angles, adjustable veneer anchors, and concrete and steel reinforcement. Inadequate or improper mounting may lead to corrosion of embedded steel elements such as lintels, anchors, and ties, which can subsequently cause deflection cracks in the masonry veneer or structural distress in the concrete frame structure.
Typical failures of masonry support systems occur when the bracket angle is either fixed too tight or not tight enough. It can be due to a need for more detailing and specification of the required bolt size or better installation practices. It is common for builders to fix the masonry support as they go along rather than at an early stage in construction, and this can result in the bracket being skewed or incorrectly fitted.
The most common masonry support systems consist of continuous thin-angle supports, welded brackets, or individual bracket angle supports. The welded system is the most economical to design and supply. It consists of various sizes of stainless angle brackets, depending on the loading being fixed back to the structural frame at system centers. These are then loaded into the stands and adjusted. The system can be improved on-site by the use of shimming. However, this should only be used up to the maximum thickness of the outside diameter of the fixing bolt or 16mm, whichever is less.
AnconOptima masonry support systems include:
- Laser-cut brackets.
- Two-step angles with pre-marked fixing zones.
- Locking wedges to ensure the correct contact.
The system is compatible with Ancon Thermal Breaks, which minimize heat loss through cold bridging and improve the U value of the wall assembly. The standard methods referenced, AnconOptima 10, 12, and 14, can support uncategorized masonry loads up to 10kN, 12kN, and 14kN per meter, respectively.
Masonry has several types of joints, and each performs a different function. Concave joints are the most common and provide excellent resistance to water penetration, whereas rodded or V-shaped mortar joints offer less protection. Struck or raked joints tend to degrade more rapidly, while beaded or extruded joint profiles produce an old-fashioned and formal look but may not be as durable as other types of joints.
Different joint styles also produce varying degrees of masonry weathering. A concave joint, which extends past the surface of the brick, typically sheds more moisture than any other type of joint and provides the best overall masonry weathering performance. On the other hand, the beaded or v-shaped joint does not extend far enough from the face of the brick to properly shed rain, resulting in a wall that collects water and can lead to structural and aesthetic problems.
Movement joints separate the masonry wall into segments, which minimizes cracking that occurs as dissimilar materials expand or shrink. In angled masonry walls, movement joints are usually provided in horizontal directions (as opposed to vertical) and must be spaced at least 0.375 inches apart. Considering their differing expansion tendencies, the spacing between the movement joints should be adjusted to allow for anticipated dimensional changes in the concrete frame and the brick veneer.
In addition to movement joints, a minimum of two expansion joints should be provided for angled masonry walls laid in running bond. These expansion joints are required to prevent the corners of the masonry units from contacting each other, which can cause shear and differential movement between the brick and concrete frame, resulting in random wall cracking.
All expansion and head joints should be finished using a tool rather than by hand raking, as this produces a more compact, clean, and resilient finish. The joints should be sprayed with water or a diluted masonry sealant before application of the adhesive to improve adhesion and minimize the potential for deterioration.