In the face of building code revisions tied to tighter seismic design requirements, plus traditionally conservative treatment of reinforced concrete masonry
In the face of building code revisions tied to tighter seismic design requirements, plus traditionally conservative treatment of reinforced concrete masonry walls, Drexel University is undertaking a multi-year investigation whose findings stand to support long-term competitiveness of block in multi-story construction. Research and testing dovetail with the Philadelphia school’s efforts to develop for architecture and engineering students a concrete masonry building design program modeled after the National Concrete Canoe Competition. That annual event involves undergraduate engineering students from across the country in hands-on concrete practice.
Beginning later this year, Drexel Department of Civil, Architectural, and Environmental Engineering faculty and student investigators will conduct a series of lab demonstrations with scale model building and wall specimens to show how provisions in the widely adopted International Building Code (IBC) lead to overdesign of concrete masonry walls in some markets. Those provisions have what Drexel faculty notes is the potential to mandate grouting and reinforcement levels typical of earthquake-prone Western states in the often low-seismic areas of the Eastern U.S.
Current research and testing stem from a National Concrete Masonry Association Education and Research Foundation-funded plant upgrade in the Drexel Structural Testing Lab. Located on the edge of downtown Philadelphia, the facility took delivery in mid-2006 of a semi-automated, three-at-time machine molding concrete block at ? scale to conventional units (2.5- _ 2.5- _ 5.125-in. versus 8- _ 8- _ 16-in.). The machine replaces an early-1980s model the school mothballed in 2002 due to low output and high maintenance. That led to the school’s discontinuation of an annual Masonry Design Competition in which students built scaled structures with miniature block.
The ability to produce one-third scale ASTM C90 concrete masonry units allows students to build multi-story assemblies and many smaller sample structures and specimens, says Michael F. Iannelli, who as sales manager for Philadelphia-based Fizzano Bros. Concrete Products assisted Drexel in obtaining the NCMA Foundation grant and for more than two decades helped champion the school’s concrete masonry program. Scale model unit production and specimen testing take away the stumbling block of using full-size concrete masonry, which can be cumbersome and cost prohibitive given the space and budget constraints of most university labs.
Drexel’s block production and testing example can be replicated in other universities with strong engineering programs, he contends. The scale model production also opens up testing beyond structural aspects to grouting, rebar, lightweight aggregate, and fly ash mixes.
When engineering faculty see what can be done with the machine, they will be convinced of the need to have one at their schools. The impetus for teaching and research on block and masonry construction is there, Iannelli adds.
On the research side, Drexel will focus on overall building performance versus past programs’ pier, wall and other component testing. Using scale model methods and the miniature concrete masonry units, the two-level Structural Testing Lab will accommodate the equivalent of a seven-story building. Faculty and students envision quasi-static and dynamic (shake-table) testing of reduced-scale building systems to assess seismic performance.
The capability to perform reduced-scale experiments has led to numerous research opportunities and resulted in the awarding of several Ph.D. and M.S. degrees, says Assistant Professor Frank Moon, who left Georgia Tech University in Atlanta two years ago, joining Drexel’s long-time masonry education and research proponent, Professor Ahmad Hamid.
Prior to arriving in Philadelphia, Dr. Moon oversaw a full-scale masonry building test that demonstrated how design assumptions in current model code provisions can underestimate block walls’ actual strength by a factor of two. In the NCMA Foundation proposal for the miniature block machinery, he and Dr. Hamid cited that finding, adding: Lack of masonry research has slowed advances in code provisions, which are derived from university research. Slow advances have fueled the misconception that masonry is a material of the past and thus well understood. In fact, while masonry is perhaps the oldest building material, it is also one of the most complicated and least understood from a behavior standpoint. These complications, coupled with the lack of research community attention, have resulted in grossly conservative design provisions that unduly penalize masonry buildings, particularly in seismic regions.
In addition to research prospects, they also note how the use of small-scale masonry units has had an important impact on undergraduate students. The availability of reduced-scale units from Drexel’s original machine facilitated the development of the hands-on Masonry Design Competition, involving construction, testing and analysis of small-scale masonry walls. The competition ran for eight years, with Delaware Valley Masonry Institute and Pennsylvania Concrete Masonry Association as sponsors.
After a five-year hiatus attributable to the lack of small-scale block-making capabilities, Drexel reinstituted the competition last spring. Similar undertakings, such as American Society of Civil Engineers’ National Concrete Canoe Competition, Precast/Prestressed Concrete Institute’s Big Beam Competition, and American Institute of Steel Construction’s Student Steel Bridge Competition, have become increasingly popular at universities. Drexel faculty recognize competitions’ appeal, and see Masonry Design augmenting traditional structural engineering coursework.
The Masonry Design Competition is founded on the three requisite scientific method components: hypothesis, observation, and validation. Students design and participate in construction of their 13-scale concrete masonry walls. They then hypothesize mathematical models to predict walls’ behavior. The models range from simplified code-type approaches to more refined simulations using commercial finite element software. Once the predictions have been finalized, walls are tested to failure by applying in-plane shear forces. Students observe and document walls’ response and failure modes. Following the test, they compare the response data obtained with the predictions of their mathematical models in order to validate or update various modeling assumptions. Competition judging evaluates structural efficiency (strength per weight), prediction accuracy, and aesthetic quality.
Throughout the 1990s, the competition proved to be an effective way of introducing materials, design, construction, testing, and modeling of load-bearing masonry walls, explains Dr. Moon. The framework and hands-on approach provides a unique opportunity for students used to traditional lectures, and motivates learning and fosters excitement about masonry and structural engineering in general. In an effort to broaden participation, he adds, Drexel is planning an expansion of the competition to include other Philadelphia-area universities this spring. Ideally, the competition could be expanded to state and national levels within the next five years. That effort should be boosted by NCMA Foundation Student Design Competition grants (see box, page 12).
The National Concrete Masonry Association Education and Research Foundation has begun awarding grants to universities launching masonry and hardscape design competitions for architecture and engineering students. A template for grant applications is posted at www.ncma.org/foundation/competition/announcement.htm
The first grants were issued last year to Drexel University Department of Civil, Architectural, and Environmental Engineering (separate from the block machinery grant) and University of Arizona School of Architecture. At their meeting later this month, during the NCMA annual convention in Orlando, Foundation trustees will review recent grant applications from Florida Atlantic University School of Architecture; Mississippi State University; University of Idaho Department of Architecture and Interior Design; University of Cincinnati; and, Washington State University.
The grants are intended to help architecture and engineering students become familiar with concrete masonry and hardscape design. Additional information can be obtained from NCMA Manager of Education and Certification J. David Rozsa, 703/713-1900, [email protected].