ATSM C90 Modification Benefit Areas of the Country with Adoption of 2015 International Building Code
Rick Roach, President, Barnes & Cone, Syracuse, New York
Figure 1 12 x 8 x 16 2-Web, Figure 2 12 x 8 x 16 1-Web, Figure 3 8 x 8 x 16 3-Web (2 core), Figure 4. 8 x 8 x 16 3 –Web (2 core) showing full thermal bridging.
CMU Innovations Possible with ASTM C90 Modifications
In the last decade, competition from wood and metal systems has challenged masonry to reinvent itself to compete more strategically. Effort has been made to strengthen masonry’s position within the competitive structure and enclosure market. This commentary is not a detailed explanation of the complex technical issues; it is a basic overview of changes that benefit many areas of the country with the adoption of the 2015 International Building Code. These modifications are a positive example of what the masonry industry can accomplish as we work together.
People who are paid a lot of money to study markets have determined that while there is a great appreciation for masonry’s aesthetics, durability and fire resistance; masonry units are heavy and slow to install. As a result, they believe this makes cost of a masonry structure too high. When we remind them that structural single wythe masonry walls are one of the fastest systems to build in the construction market, they counter with masonry walls are weak in energy performance. We paid attention. We listened.
Industry Research to Address Perceptions
Approximately ten years ago, the National Concrete Masonry Association Education and Research Foundation began several research programs to address these perceptions. The Foundation focused on determining if ASTM C90 requirement for full webs on a concrete block was valid. Additionally, the Foundation zeroed in on more accurately determining the design strength of a masonry wall when the prescriptive table was used – the Unit Strength Method.
The Foundation’s goal in challenging the full web requirement of ASTM C90 was focused on improving the energy performance of block walls.
For 70 years, ASTM C90 Standard Specification for Loadbearing Concrete Masonry Units required full webs, or a solid grouted assembly, for structural loadbearing block. It was believed that full webs were required to transfer stresses from one faceshell to the other. This severely limited a block producer’s ability to create new shapes that could both speed up construction by reducing the weight of a block for the masons and improve energy performance by limiting thermal bridging.
Foundation research demonstrated that three full-height webs were not necessary to transfer stresses between faceshells.
A new minimum web area was established that would ensure transfer of stresses between faceshells and also allow the web area of a block to be significantly reduced. Foundation research was so convincing that within one year of submitting the change to ASTM, the new web requirements were adopted. A full review of the new web requirements can be found in NCMA TEK 02-5B New Concrete Masonry Configurations under ASTM C90.
Both configurations in Figures 1 & 2 exceed the new ASTM C90 web requirements.
Mason Productivity and Speed of Construction
What do ASTM C90 web modifications do for mason productivity and speed of construction? When I started my career in 1976, the 12" wide block produced in our plant weighed 59 lb 12 oz. Today, our 12" normal weight 2-web block weighs 35 lb. The 12" 2-web lightweight block weighs just 27 lb. Masons can lay more block per day with less fatigue. It is safer for masons, increases the speed at which block walls can be built, and reduces costs. There is nothing proprietary about these block, every block producer can manufacture them.
What do ASTM C90 web modifications do for energy performance? The web change is a game changer. The three renderings in figures 7 – 9 show the inside web area of a block wall with one face removed. Three-web (2 core) Figure 7, 2-web (1 core) Figure 8, and 1-web Figure 9. As the web area is reduced, so is the thermal bridging. Energy performance improves. Another benefit is that the minimized web area means grout flows through the cores faster and the speed of construction improves.
The modification to ASTM C90 web requirements is an enormous benefit to pre-insulated concrete masonry systems. Figure 5.
Pre-insulated block can comply with ASTM C90 and have less than one full web. Insulation inserts fill the void of the partial web and cover mortar joints. Energy code compliance with single wythe construction is practical in all climate zones.
The second phase of the NCMA Foundation research focused on demonstrating that the Unit Strength Table in the code was overly conservative. It was common knowledge that the Unit Strength Table assigned strengths for masonry walls that were much lower than actual tests showed. The Foundation research program tested hundreds of prisms and showed definitively that the strengths of masonry walls listed in the codes were too low.
Figture 5 New modified web pre-insulated CMU, Structural masonry wall being constructed using new modified web pre-insulated CMU»
The Foundation’s goal in challenging the full web requirement of ASTM C90 was focused on improving the energy performance of block walls
Unit Strength was recalibrated with a 33% increase in the strength of masonry. While every structure has its own unique conditions, this 33% increase, coupled with other newly introduced design efficiencies, potentially reduces the reinforcement in concrete masonry walls by 50%.Masons can build walls faster using significantly less labor and material. This also provides significant improvement for masonry insulation systems like injected foam. There is potentially less grout and reinforcement in the wall, which means potentially fewer locations with no foam insulation.
Figure 7. Three-web CMU with faceshell removed, Figure 8 Two-web CMU with faceshell removed, Figure 9. Single-web CMU with faceshell removed
The Foundation Research Program tested hundreds of prisms and showed definitively that the strengths of masonry walls listed in the codes were too low
Direct Design v3
Version 3.0 of the Direct Design software is scheduled to be released in January 2018. This is a Foundation program focused on making state-of-the-art structural masonry design easier and faster for engineers. Version 3.0 includes recent enhancements to the 2015 IBC and now accommodates reduced web, pre-insulated concrete masonry systems. The software is fast, prints fully detailed wall elevations and displays the full text of every calculation so the user can verify every step.
BIM-M Compatible. Later in 2018, Direct Design software will be able to interact with Revit, the modeling software used by the majority of architects and engineers. Buildings will be drawn in Revit, and then exported into Direct Design. After the structural masonry design is completed, the file will be integrated back into the Revit model of the building. This is all part of the Building Information Modeling for Masonry (BIM-M) Initiative that NCMA Foundation and our masonry allies began in 2012. Architects, engineers, contractors and owners are using BIM-M tools every day for masonry modeling and analysis. Free downloads are available by going to bimformasonry.org
Modifications to ASTM C90 finally give block producers the full flexibility to take advantage of 21st century material science. We collaborate with allies, the mason contractors, and use the 2015 IBC to show architects and engineers how they can be more competitive using masonry. These modifications can facilitate a creative period in the masonry industry that can fuel the resurgence of masonry in areas where wood and metal systems are making inroads. The recent masonry advancements in the codes, Direct Design and BIM-M demonstrates what can be accomplished with the Masonry industry all working together.
Rick Roach is president of Barnes & Cone, block producer in Syracuse NY where he has worked since 1976. He began serving on National Concrete Masonry Association (NCMA) committees in 1979; he served as Chairman of the Board of NCMA in 2001 and was Chairman of the Board of NCMA’s Education and Research Foundation in 2016. Rick and his wife Randi live in a structural masonry, passive solar earth sheltered home, they built in 1983 in Syracuse, NY. Their home is heated with a Russian Fireplace, and cooled using thermal mass.