Engineering on Display

To view the figures and tables associated with this article, please refer to the flipbook above.

The Engineering Design and Innovation (EDI) building is the new gateway to innovation on the expanding west campus at Penn State University Park. With large, column-free spaces, exposed structure, lattice pattern brick, and expansive glass, the 105,000 square feet structure provides an opportunity to witness engineering at every turn. Sprinkled throughout the building are nearly 10,000 square feet of machine shops and manufacturing labs. Topped with five long-span raised roof monitors with clerestory windows for natural light, the fourth level open loft provides students and teachers with a flexible maker space. Isolated from the classroom portion, a three-story high bay housing two 20-ton gantry cranes and a substantial strong wall/reaction floor delivers a unique testing area for experimental research.

Early design iterations for the classroom structure examined multiple solutions for the building framing system, and it appeared initially that a traditional concrete on metal deck with steel beam composite construction would be the least expensive option. However, as the push for sustainability gained momentum and the design and construction teams learned more about CLT and a possible hybrid solution, the decision to use CLT was made.

The project grid consists of a 32-foot spacing in the north-south direction and beam spans of 25-foot, 6 inch, 54 foot, 6 inch, and an additional 12 foot, 8 inch cantilever in the east-west direction. The dimensions were critical in the decision to switch from a traditional composite system to a hybrid system. With a composite floor, two beams would be required within each bay to keep the deck span to approximately 11 feet. However, with five-ply CLT, the deck span could increase to more than 16 feet, allowing one beam to be removed in each bay.

Floor framing design began with verifying allowable span lengths for the CLT panels with respect to strength and vibration. Various CLT manufacturer tables were reviewed to arrive at the final thickness of the CLT panel given the chosen beam spacing and the species of wood the architect preferred. The design team determined that 2 inches of normal weight concrete topping reinforced with 6x6-W1.4xW1.4 W.W.R. above the CLT panels would suffice for acoustic concerns. At the time of the design, limited references were available detailing design for vibration with a CLT hybrid system. The team chose to analyze the CLT by following Chapter 7 of the CLT Handbook and to analyze the non-composite steel beams by following the vibration requirements set forth in AISC Design Guide 11. Due to the long spans, many of the supporting steel beams increased in size and required the additional dead load that the 2 inch topping provided to remain under the recommended acceleration tolerance limit of 0.5%.

The lateral system for the classroom section consisted of steel braced frames and moment frames relying on the CLT panels to act as a diaphragm. Details between the CLT panels and the steel beams were carefully reviewed to ensure that the diaphragm forces were properly transferred into the lateral system. MTC ASSY Kombi screws were used between the underside of the top flange of the steel beams and the underside of the CLT for both CLT panel to steel beam typical connections as well as CLT chord splices. MTC ASSY Ecofast screws and ¾-inch thick sheathing strips were used along the top side of the CLT panels for panel splices. Both size and spacing were based on the shear per linear foot that need to be transferred.

The EDI building, designed under IBC 2015, is Type IIIB unprotected combustible construction with a 2- hour fire rated exterior bearing wall between the existing garage and the new building. As such, the steel beams and bottom of CLT could remain exposed.

Overall, because the steel beams were not composite, they increased in weight, while the total number of pieces used decreased. The combined weight of the CLT with the additional 2 inches of normal weight topping was very similar to that of the composite slab on deck, so column and footing sizes remained comparable to what they would have been with a traditional steel building. There was a learning curve for the entire design team and increased coordination between disciplines. However, the speed of installation of the CLT panels coupled with the reduced embodied carbon, confirmed that this was the correct design choice for the project.

Part of the high bay program required a strong wall and reaction floor that will be used to complete testing on new and innovative structural products and designs. The strong testing walls and floors each have a grid of pipe sleeves that run through the wall and floor allowing for Dywidag tie rods which are used to anchor the testing apparatus to the wall and floor. The force is transmitted to the testing specimen by a hydraulic actuator that is set to deliver a specific force at a given frequency.

The strong wall is 30 feet tall and 2 feet thick between pilasters and buttresses. In plan, it is L-shaped with the long leg approximately 60 feet and the short leg 23 feet, 8 inches. The high bay’s west wall location was set by an adjacent existing parking garage. The space between the west wall and the back side of the strong wall, including testing wall pilasters, had to maintain clearance for a scissor lift to pass between the two. To provide the maximum amount of testing space in front of the strong wall, and maintain the clearance behind it, it was determined that the longer wall would be reinforced with shallower pilasters and allow for testing that required a lower loading capacity. The shorter wall reinforced with longer T- shaped buttresses provides areas for testing at a higher loading capacity.

The short wall was designed for 250 kips at the top and mid-height of the wall, while the long wall was designed for 150 kips at the top and mid-height of the wall, apart from the free end which had a reduced load of 110 kips. The reaction floor is 2 feet thick and has a clear span of 8 feet, 10 inches between 14-inch-thick walls below the testing floor. The wall and floor thickness were limited based on a request to keep the Dywidag rod length reasonable for the users of the facility. So, in addition to the vertical and horizontal reinforcement on each face, the walls and floor required #5 single leg stirrups at 6 inches on center in both directions. Post-tensioned tendons were also installed vertically within the wall to help limit cracking and improve overall performance.

For several reasons, the design team specified that the strong wall be poured monolithically with no joints. During the design team’s research, including discussions with other teams that had built strong walls, it was discovered that the difficulty of leveling the concrete and the preparation of the construction joint were common issues that this team chose to avoid. The alignment of formwork between separate pours was also a concern that would be alleviated by a single pour. The wall was specified to limit surface irregularities to 1/16”, so eliminating any variables that could allow misalignment was critical.

The wall contains over 250 tons of reinforcing steel and 450 post tension cables, resulting in a level of congestion a standard concrete mix could not feasibly overcome. To meet this challenge, the concrete supplier designed a self-consolidating concrete mix that met all the specified requirements. Typically, full liquid hydrostatic head must be considered for self-consolidating concrete when designing the formwork. With a formwork height of 30 feet, the pressure on the forms at the base of the wall would be considerable. To ensure the proposed upgraded formwork would work, the concrete subcontractor performed mix specific studies to determine cure rates while keeping pressures below the allowable pressure of the upgraded formwork system. Additional mix considerations included a shrinkage reducing admixture and smaller aggregate due to the reinforcing congestion.

While the high bay is a 3-story open space, the original design included a shared basement wall between the high bay and the classroom side, as well as shared framing between the high bay roof and the fourth level CLT floor. After discussions with the vibration consultant, consideration was given to mitigate vibrations created by both testing performed in the high bay and overhead crane use from impacting the classrooms and offices. This resulted in unique isolation details along the first floor and a full -height expansion joint above grade. The addition of the expansion joint lead to the need for a separate lateral system for the high bay, comprised of CMU shear walls, steel braced frames and moment frames.

Most of the brick facade on the project consists of standard brick laid in running bond with punched windows. However, one section required a different approach. On the lower floors, the main corridor pops out beyond the main wall with glazing on three sides to provide a bright lounge space. At the fourth floor, the space is similar, but the facade aligns with the remainder of the wall. To maintain the exterior aesthetic, the architect wanted to provide brick at the end of the corridor but still allow natural light. Therefore, the architect required perforated, or lattice, brick construction.

There are two approaches to lattice wall design. The first is to provide custom units to receive either vertical or horizontal reinforcing. The second is to determine the stresses in the overlapping mortar bed segments. In this case, the team chose to use the second option and sized the brick as required to satisfy the stress requirements. Since the protection of the reinforcement would have been difficult, along with the inevitability of water collecting on the tops of brick below the opening, corrosion of the bars likely would have caused issues in the future. The lattice wall has 4-inch openings at 8 inches on center horizontally and every other course vertically. Using an allowable flexural tensile stress of 53 psi and spanning the wall horizontally, it was determined that the brick needed to be 5 5/8 inches wide to satisfy the stress requirements.

Having significantly reduced the embodied carbon on the project by using CLT, the design team set their sights on lowering the carbon in the concrete. Since the addition of low carbon concrete was introduced late in the project, the requirements were considered an alternate to be vetted by the Construction Manager. Due to cure times of concrete with high supplemental cementitious materials (SCM), only certain elements of the building were included for the alternate mixes. These included elements that could take longer to reach strength without affecting the schedule, such as the footings, interior and exterior foundation walls, and the interior topping.

The concrete supplier used a combination of slag and E5 Liquid Fly Ash to replace the portland cement. The footing and interior wall mixes were able to receive the highest replacement of portland cement (48%), while the exterior walls and interior topping mixes were only marginally better due to w/c ratio and placement concerns. However, all the concrete mixes beat the National Ready Mixed Concrete Association regional benchmarks, which are typically less than 20% SCM, helping the project reach its sustainability goal.

From the CLT to the strong wall, many of the EDI’s challenges were novel to both the design and construction teams. Thanks to extensive coordination and collaboration, discussions with other engineers and builders and open communication, the project was completed successfully. With this project, along with the rest of the expanded west campus, it is an exciting time for Penn State Engineering. ■