The Benefits of Angle Masonry
Pro Angle Masonry Charleston structures rely on a variety of techniques and methods. Accurate layout and measurement are critical to success, as is selecting the correct mortar mix and trowel size for the project.When designing a sloped piece of brick masonry, one must consider the special right triangle it makes with its two sides. This article will explore important aspects of this geometry and its relationship with masonry.
The large L angles used in construction are much different than the angle irons that most home projects use. They are sized to support heavy loads and can be found supporting beams in buildings, certain columns on building foundations, and even providing vertical support on structures such as cell phones and broadcast towers. In the case of masonry structures, the long L angles offer great strength and help keep brick or block walls from crushing in windy conditions.
Typically, the shelf angle is located near or in the center of the wythe above doors and windows to provide the additional load-bearing capacity needed. It also accommodates movement within the wythe and between the structure and cladding. In addition to these structural functions, the shelf angle can act as a point where the water exits the wall assembly and supports flashing. This seminar will review design and construction considerations when detailing a shelf angle, including movement control, moisture management, thermal performance, constructability with interfacing components, and strategies for optimizing shelf angle location.
An engineer designs lintels and shelf angles to meet the strength requirements of the steel design code. Based on a non-cracked section analysis, they are sized to resist deflection between points of support no greater than the allowable amount. The sizing of the angle can be affected by its placement in the wythe and the type of grout used to fill it.
For grouted masonry, the nominal flexural tensile strength varies with the direction of span, mortar type and bond pattern, and the percentage of the grouted wythe. The code conservatively assumes that stack bond masonry that is grouted has no flexural strength. For ungrouted masonry bending out-of-plane, the modulus of rupture is determined through shear-dominated performance.
Both welded and mechanical splices that are incorporated into masonry elements that are designed by the strength design method must be classified as either Type 1 or Type 2 by ASTM A 706 (ref. 12). Type 1 splices are only required to develop 125 percent of the nominal yield strength of the reinforcement being spliced. In contrast, Type 2 splices must be capable of producing the full little flexural tensile strength.
Masonry has long been regarded as a durable material capable of withstanding harsh climates. However, costly masonry problems due to moisture penetration continue to plague buildings. These issues are often caused by inappropriate design, poor artistry quality, and a need for more understanding of masonry expansion and contraction properties. In addition, climate change is expected to lead to warmer, wetter conditions that will pose new challenges for masonry.
One way to reduce these problems is to incorporate a vapor barrier between the cladding and the structure. Using a vapor barrier helps protect the concrete masonry units from water infiltration and limits moisture migration through the wall system. However, this approach is not the only way to mitigate moisture penetration into a concrete masonry wall. Other methods include incorporating barrier protection at the masonry surface, post-applied breathable coatings, and internal moisture management strategies.
Another method is to integrate a steel shelf angle into the wall construction. This shelf angle helps to provide vertical support for the cladding and acts as a movement joint. The seminar reviews various design and construction considerations when detailing a shelf angle, including movement control, moisture management, and thermal performance. It also covers techniques to optimize shelf angle location and constructability with interfacing components and strategies for accommodating construction tolerances.
Brick is a porous material, and it expands when exposed to moisture. For this reason, it is important to detail a gap between the brick veneer and the shelf angle to allow for expansion. This gap will help to prevent the brick from pushing up against the shelf angle and causing it to crack.
The insertion of the shelf angle can also reduce the effects of thermal bridging in a masonry wall. The seminar will review a system of folded angle systems that can be engineered to the engineer’s specifications for each project. It can include the type of load, cavity size, and fixing position. In addition, a special Armatherm FRR structural thermal break material can be integrated into the wall assembly at the shelf angle to reduce the thermal transmittance through this connection further.
As the popularity of masonry veneer increases in building construction, designers are becoming more innovative with their designs. One example is the use of “shelf angles,” which transfer the load of a masonry wall onto major elements of the building’s concrete frame and provide a space to allow for masonry and definite structure movement. These are a key component of the design of most modern brick and stone veneer structures and are usually located in large openings such as ribbon windows.
The shelf angle is a critical detail in this type of wall, and its proper installation is vital to the entire project’s success. However, many of these structural elements are installed, which can lead to serious failures in the building envelope. In addition, using steel shelf angles in concrete framed buildings can lead to energy code compliance issues because they create linear thermal bridges between the masonry veneer and the concrete or steel structure.
Masonry Support Systems utilize Austenitic stainless steel to eliminate these thermal bridging issues. This material is also corrosion-resistant, so it will not need to be replaced during the lifespan of the building. In addition, the insulating foam is adhered to the outside of the stainless steel angle, which further reduces thermal conductivity. This combination of a thermal break and a sealed, watertight barrier greatly improves the performance of the building’s exterior cladding system.
While the failure of this particular building was largely due to the architectural design, a review of the construction documents revealed some deficiencies in the detailing for the shelf angles. In this case, the architectural drawings did not show a gap under the shelf angle, and the masons did not include a space for expansion. In addition, the last course of brick was lipped and did not align with the underside of the angle. This misalignment resulted in the cracking shown in the photo below.
The shelf angle and anchor design details are very complex, but it is important to get these right to ensure a long-lasting and successful wall. In addition to sizing them correctly, it is also critical to attach the angle to the concrete or masonry structure through anchor bolts properly. These details are often overlooked or misunderstood by installers, leading to problems that can be costly to repair.
In addition to the structural benefits, angle masonry is a highly attractive building material. It can be made with various surface treatments and coatings matched to most architectural styles. It is available in multiple colors, including earth tones and some fluorescents. In a natural setting, concrete masonry walls interact with changing sunlight to present a color palette of its own. It can be enhanced by using electric lighting to accentuate the wall’s colors and textures.
The beauty of brick masonry can be enhanced by using special units, such as angle masonry blocks that have one side treated for a textured finish and the other for a smooth face. These units can be used instead of conventional lipped blocks and in conjunction with various unit sizes to create banding, such as a 4-in. (102-mm) high band in a wall of 8-in. (203-mm) units.
Another way to enhance the aesthetics of masonry is to choose the mortar color and texture carefully. A mortar that contrasts with the masonry accentuates its appearance, especially any imperfections, while a mortar that complements the masonry blends in and becomes less noticeable. Also, the profile of any flashings or drip edges should be a consideration, as they can cast shadows and affect aesthetics.
Throughout history, architects have sought to balance the aesthetics of a structure with its engineering requirements. For example, Vitruvius considered firmitas (strength), Utilitas (Functionality), and Venustas (beauty) to be the three main elements of architecture. While he did not specifically address design principles for the latter, his philosophy has guided aesthetics in modern architecture.
While code-required construction tolerances govern structural performance, they do not address the effects of geometry or composition on the overall appearance of a building. However, several guidelines are available to help the designer define aesthetic requirements. These include sample panels, mock-ups, and a variety of industry publications.
For example, a failure to properly design the lipped-brick shelf angles in a structural arch can result in unacceptably long shadows at the corners of the turn. These shadows may give the building an erroneous appearance of unacceptably poor materials or artistry. In some cases, the cause of the problem can be traced to architectural drawings that do not adequately describe the details of lipped brick shelf angles.