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Lintels for Masonry Walls
Masonry lintel design is a critical part of an efficient structural masonry solution. The design of masonry lintels can add significant structural capacity to a wall that contractors and owners will welcome for crack prevention. In the past, we have made assumptions to simplify the analysis of masonry lintels that has been a detriment to its engineering and architectural design. This article will take a closer look at masonry vs. steel lintel options, with tables to compare equivalent sizes. We will also discuss the impact of arching action, and how to increase the capacity and efficiency of masonry lintels.
Steel vs. Masonry Lintels
In recent years, there has been a renewed interest in using reinforced masonry lintels instead of steel lintels.
There are several reasons to consider masonry lintels:
A) Previously it was thought the only way to reduce shoring was to specify a steel lintel. This is no longer true due to:
1) New and innovative methods for shoring to build in-place masonry lintels.
2) Availability of pre-fabricated masonry lintels.
3) Precast concrete lintels that allows better integration with masonry.
B) Steel lintels are not performing as well over time due to:
1) Differential movement from dissimilar materials creating serviceability issues and potential cracking.
2) Steel lintels are often detailed to slide at one end, however in some cases the bearing is rusting and binding, preventing the steel from sliding which results in issues at the bearing.
3) Large bearing plates are being specified which result in aesthetic and constructibility issues.
4) Challenging interface details of vertical masonry reinforcement, steel bearing, and control joint.
C) Steel lintels require additional and costly reinforcement. The required U bar in Figure 2 is difficult and expensive to place, but is essential to prevent cracking. The vertical jamb reinforcement must be shifted away from the opening, which requires the jamb to be designed for more tributary width, resulting in a larger jamb. This condition also requires additional grout under the steel bearing.
D) Masonry lintels create an integral joint with vertical jamb reinforcement. This leads to a more robust design with many design benefits, schedule reduction, and proves to be less expensive.
E) Fixed ends can be considered with masonry lintels with top and bottom reinforcement. Negative moment can then develop that is resisted by top bars, resulting in less positive bending moment and more efficient distribution of loads through the wall. Steel lintels cannot be detailed with fixed ends with bottom flanges bearing on a plate and top flanges unrestrained. Instead, steel lintels are considered simply spanning with pinned ends, resulting in higher positive moment than fixed masonry lintels.
F) Perhaps the most compelling reason to use masonry or specialty precast lintels is due to the ability to use arching action, which allows the design load to be much smaller. Arching action, discussed later in this article, requires the lintel to be built integrally with the jamb with no control joints (CJ) at the openings. Steel lintels often require CJs at the end of the lintel due to differential movement, which prevents arching action and therefore requires much more load for the design.
Drawings, Charts, and additional content is available in PDF in ‘read more’.
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