What do you use as your default design strength for masonry? Have you checked with local suppliers to see what is commonly available? Masonry strengths can vary widely, but new findings show the design strengths may be higher than what engineers typically assume.
In the April 2019 SE University session, Cathleen Jacinto presented Lintels for Masonry Walls. Cathleen reviewed the behavior and load distribution of lintels and masonry walls with openings and discussed practical design and detailing strategies to achieve high performing lintels. Cathleen also explained the advantages of analyzing masonry walls with finite element software, and shared findings on what engineers can safely assume for the design strength of masonry.
Typically during design, the engineer does not know the exact block strength that will be supplied on site, and to minimize costs we often specify the minimum block strength of 1900 psi, thus giving an f’m of 1500 psi. However, Cathleen shared that these lower strength masonry blocks are not even available from most suppliers, and in most areas of the country, suppliers provide masonry blocks with a minimum block strength of 3750 psi. This allows the engineer to assume an f’m of 2500 psi without any additional costs to the project. Cathleen shared a website that her company, FORSE Consulting, has created to monitor masonry strengths across the country. Click here to access the map and find masonry strengths from suppliers near you. In IBC 2015, which references the MSJC 2013, the masonry strength values have changed as shown in the slide below. The new code allows a minimum block strength of 3250 psi to achieve an f’m of 2500 psi.
Being aware of these higher strength blocks that are being supplied on job sites will allow engineers to lower material costs and create more efficient walls and lintels and reduce steel reinforcement. Be sure to check your local suppliers and take advantage of the higher block strength values that are most likely being supplied on your projects.