MASONRY DESIGN AT UNIVERSITY OF NEBRASKA
During the first lecture of the new semester for the Masonry Design course at University of Nebraska- Lincoln’s (UNL) Durham School of Architectural Engineering and Construction, students saw images of a beloved historical masonry building in Old Market, Omaha, which was severely damaged by an explosion, followed by several hours of fire. In the aftermath, while the interior framing of the structure (made mostly of timber) was damaged almost entirely, the masonry walls continued to stand tall. Later, the local engineer who assessed the building declared it salvageable, thanks to the resilient masonry wall system.
The Case for Resilience
Students then viewed pictures of other completely damaged buildings, this time from the small town of Pilger NE. These buildings were completely damaged from dual tornadoes on June 16, 2014, sparing only loadbearing masonry bell tower [2, 3]. A family of EF-4 tornados dropped from a parent supercell moving over northeast Nebraska during a multi-day tornadic event. The supercell near Pilger was the most dramatic of the tornado season. St John’s Lutheran Church, one of the only easily recognizable buildings in Pilger, was constructed of brick in 1949 for $30,000. Summary statement of this first lecture was:
Masonry is strong and resilient. A masonry building envelope is capable of doing much more than providing a pretty brick façade. It can provide a strong and resilient structural system, be the envelope that protects against most environmental factors and be a source of desirable aesthetics at the same time. Further, masonry is more commonly used than our engineering education makes it seem, as very few universities require a masonry engineering course in the curriculum compared to many concrete and steel related courses. In short: Masonry Matters, Pay Attention!
Throughout the following 16 weeks, students paid attention and learned how to design masonry structures.
Preparing Graduates for the Built Environment
Having spent more than 16 years conducting research in the field of masonry structures, including assessment of existing / historical masonry structures with the use of nondestructive testing and advanced finite element analyses and material research for rehabilitation of existing / historical structures, I convinced my UNL colleagues to approve Masonry Design as a required graduate-level course in the Architectural Engineering (AE) Program.
The case for adding the course was simple. Masonry structures are resilient and strong, so they last a long time, which makes them perhaps the most sustainable buildings. However, they are typically complex to analyze and design. That, combined with the fact that most engineers graduate without ever taking a masonry design class, makes existing masonry structures a cause of fear and perhaps unjust conservatism. In the case of existing structures, practicing engineers are often ill-prepared as to how to approach them. For instance, because they may not understand the system and the material well, even for minor cracking, they may suggest replacement of the whole structure instead of repair or rehabilitation. In the case of new construction, unfortunately, their lack of familiarity and confidence means masonry is not often the first choice. When it is used, designs are often too conservative or not even feasible for construction (for example, always requiring type M mortar regardless of design criteria and specifying too many reinforcement bars unnecessarily causing congestion). I aspire to educate the engineers to understand masonry so that they can efficiently utilize it in design, analyze and rehabilitate masonry systems. I teach them to use correct methods instead of wrong/harmful methods.
I convinced my UNL colleagues to approve Masonry Design as a required graduate level course in the Architectural Engineering (AE) Program.
UNL offers a 5-year Master of Architectural Engineering Program (MAE) accredited with a set curriculum. Masonry Design is offered each spring to MAE students, Master of Science (thesis-based) and PhD students of AE or Civil Engineering as well as Civil Engineering seniors as a technical elective.
As course content was being developed, I attended The Masonry Society’s University Professors Masonry Workshop to gain knowledge and inspiration from the international group of experienced professors, practicing architects and engineers and industry leaders who present seminars and hands-on learning events. UNL’s course covers topics such as masonry terminology and material specifications, lateral load distribution into the lateral force resisting elements (i.e. masonry shear walls), design of nonloadbearing masonry panels and curtain walls, loadbearing walls, beamcolumns, shear walls and lintels/beams.
History of masonry structures and empirical design are covered through special lectures and reading assignments. A Revit workshop is provided by Todd Shackelford, BIM (Building Information Modeling) manager, Alvine Engineering, to help students realize their class projects in professional looking plans and 3D renderings. Students are assigned to read and summarize a recent technical article in the field of masonry structures to learn how to stay in touch with developments in the masonry world. Requirements and suggestions of TMS 402/602-13 Masonry Code Requirements and Specification for Masonry Structures are followed .
For their term project, students design the entire structural system of a building using only masonry structural elements. Students are given a list of design criteria, an approximate building lot and a programming list. They learn masonry terminology and importance of modularity in architectural design of masonry buildings. As the project progresses through stages of schematic design and design development, they go deeper into the structural design of walls, lintels and if applicable, columns. While building type changes every year (dormitory, church, warehouse, fire station), constant is the main requirement of using masonry systems for the main gravity and lateral load resisting systems. Nebraska projects also always include requirements for resiliency against tornados, typically in the form of a community tornado shelter.
The spring semester 2016 project was the redesign for St John’s Lutheran Church in Pilger, which collapsed in the dual tornadoes of 2014. As the church was being rebuilt, 60 mph winds collapsed the new church under construction. Students were given the assignment to design a strong and resilient loadbearing masonry structure to withstand strength level design winds per ASCE 7-10  for the entire structure and tornado level winds on the walls of a community tornado shelter per FEMA Specification P-361 .
Students first designed the 9,600 sf building architecturally. The program includes a large sanctuary, social hall, bell tower and a tornado shelter with a 300-person capacity. Architectural layout students designed five distinct areas: social hall, classroom and office area, atrium and gathering area, sanctuary and bell tower. Students were asked to design the sanctuary roof with a masonry vault as an option, in addition to a more traditional roof. Three particularly unique challenges to this project were:
- Design of a tornado shelter
- Design of a bell tower
- Design of a masonry vault
Revit was used for drawings and 3D renders. After the group established the architectural layout, students worked individually on structural designs. Figures 1 and 2 show two different approaches to the masonry vaulted sanctuary. Figure 3 shows three exterior views designed by different students, even though the initial architectural design was the same. Decisions were mainly guided by their structural design. Students gained insight on the architecture-structural engineering interactions that happen when designing masonry buildings.
Since 2014, this term project has been an annual competition sponsored by the Nebraska Concrete Masonry Association (NCMA). NCMA provides a $500 scholarship to the winning team or individual. A jury of engineers, faculty members, doctorate students and NCMA members evaluate projects and determine the winner. Jon Bergren was this year’s winner, gathering top points in the categories of material selections and details, load calculations, structural design of the masonry system, any above and beyond items such as economy and presentation skills.
NCMA President Tyler Jensen congratulates Jon Bergren (left) for his winning design and scholarship. Bergren determined that the enclosure of the shelter area with tornado level 250 mph wind speeds, needed #9 bars spaced 4′ oc.
Bergren’s structural system is composed of loadbearing masonry shear walls and wood roof framing and, in the sanctuary, a masonry vault covered by a truss. Masonry shear walls are two-wythe drainage walls formed of 4” clay brick veneer and 8” reinforced concrete masonry units (CMU) with an air gap, 2” of rigid foam insulation and vapor barrier (Figure 4) Bergren calculated the lateral forces applied to the structure by both wind and seismic requirements and found that, given the location, wind load values govern. Lateral forces are distributed through the shear walls assuming a rigid diaphragm. Each wall section is designed for both in-plane and out-of-plane bending and axial force as well as in-plane and out-of-plane shear. Five masonry lintels are designed to support different wall openings ranging from 4′ to 10′. Students considered CMU control joints and clay brick expansion joints. For the tornado shelter, 250 mph wind speed and a 2-hr fire rating were considered per FEMA P-361 requirements. With increased wind pressures, tornado shelter walls need to be stronger, especially for out-of-plane bending resulting in heavier vertical reinforcement. In Bergren’s design, shelter exterior walls could have #4 bars every 4′ for design wind speeds, but require #9 bars 4′ on center (oc) for tornado-level wind pressures.
Dennis Young, PE, structural engineering consultant from Omaha, participated as a jury member, stated that this experience was very positive as it gave him a chance to meet the students at a critical time in their education and, hopefully, provide positive and constructive comments on their work. He acknowledged that the presentation must be tough for students as each had 15 minutes to cover various details of their design, assumptions, calculations while differentiating their design and presentation from the others. He also acknowledged the various project challenges and commented that students did a good job executing.
Ece Erdogmus PhD, PE, is associate professor and program coordinator, Durham School of Architectural Engineering and Construction, University of Nebraska-Lincoln. She is an active member of The Masonry Society (TMS), serving on the 402/602 Code and Existing Masonry Committees. She has attended and presented papers in every North American Masonry Conference since 2003. Erdogmus received her Bachelor of Architecture from Middle East Technical University in Turkey and her Master and PhD in Architectural Engineering from Pennsylvania State University. email@example.com | 402.554.2035
Nebraska Concrete Masonry Association has supported Erdogmus’ masonry-related teaching, research and service activities, including with a subscription to SMART|dynamics of masonry, travel support for masonry-related conferences, financial aid to students for Masonry Code purchase, financial sponsorship for the competition detailed above and providing volunteer masons and materials for masonry research projects. For this strong and continued support, Erdogmus extends her deepest gratitude to the group, specifically to Tyler Jensen, Larry Reimnitz and Terri Holtzen.