Wind Loads on Architectural Attachment
Wind Loads on Architectural Attachments
By: Leana Lu | Ryan Ocampo | Shannon Stever | Civil Engineering Students | Florida International University
Here at Eastern Engineering Group, we offer structural engineering internships every semester, and we love to be around students. We have had the pleasure of meeting brilliant minds through our student initiatives, and we are proud to share their work on our platforms. In this case, we will be sharing a research project regarding wind loads on architectural attachments. Leana Lu, Ryan Ocampo, and Shannon Stever are civil engineering students at Florida International University. All three of them are truly wonderful and we hope you enjoy their research paper as much as we did. To see the full document, please refer to the PDF at the end of this article.
To gain a better understanding of how wind loads affect architectural attachments, we selected structures in the community of South Florida as real-world applications of architectural attachments. We chose to study and investigate the Royal Caribbean Cruise Terminal at the Port of Miami; and the Student Academic Success Center at Florida International University’s (FIU) Modesto A. Maidique Campus. We consider these structures as excellent examples to conduct research based on their various architectural attachments. These include glass doors, guard rails, columns, canopies, and curtain walls. To learn more, we contacted some of the engineers who played a major role in the engineering design and development of these structures. In the following two sections, we will share the findings and differences on these structures.
The first case study for this research is the Royal Caribbean Cruise Terminal at the Port of Miami. This structure is an excellent example of a curtain wall system that includes unique inclined walls. This with the intention to imitate and resemble the shape of a giant glass crown. We had the opportunity to learn more about the specific design and testing of the Cruise Terminal by speaking with the project engineer from Eastern Engineering Group.
Eastern Engineering Group is a civil and structural engineering consulting firm in Doral, Florida that provides high-quality structural engineering and specialty engineering services of a variety of structural components. The project engineer at Eastern Engineering Group served as the project lead for the curtain wall window system in this project. She played a major role in the determination of the structural integrity and durability of the aluminum mullions on the West inclined curtain wall and the front side of the structure.
The design and construction of The Royal Caribbean Cruise Terminal were precast concrete elements that envelope the building as a skeleton.
The structure mainly consists of a curtain wall system attached to the exterior of the structure. The composition of the curtain wall at the Cruise Terminal is double-insulating laminated glass panes. Aluminum mullions support the structure and silicone joints connect them to the structure. The connection of the mullions is every 16 feet in a horizontal direction. And every 4 feet 6 inches in the vertical direction.
The curtain wall system does not provide any support to the structure or mitigation of wind loads to the overall structure. Thus, it primarily accommodates the architectural intent and vision of resembling a giant glass crown. The curtain wall system carries its own weight and transfers gravity and lateral wind loads exerted upon the structure. These loads are transferred to the mullions, which are then transferred to the structure.
The design of the curtain wall system was in accordance with the Florida Building Code and ASCE 7. They used Two different safety factors based on the components, where the design of the skeleton used a Load and Resistance Factor Design (LRFD) safety factor of 1.0 and the curtain wall used an Allowable Stress Design (ASD) safety factor of 0.6. A safety factor of 2 was also used in the design of the reaction forces because doubling the forces and stresses would also double the strength of the curtain walls and improve the safety and durability of the
overall structure. The design of the curtain wall withstands severe wind effects for up to 700 years with 175 mph winds and stronger.
The curtain wall design was selected from a Florida Approval Notice of Acceptance (NOA). An NOA is a certificate issued and approved by the Miami-Dade County Regulatory and Economic Resources Product Control Section. An NOA certifies the structural integrity and extreme weather impact resistance of specific engineering products designed in accordance with rigorous rules and regulations (K-Line Impact). However, the inclined curtain wall system on the West side of the structure did not use an NOA. Therefore, they required a wind tunnel test of this side of the structure to verify that the design meets the Florida Building Code standards, and the design can perform successfully under hurricane wind forces.
Wind Tunnel Study
The wind tunnel study was performed by RWDI Consulting Engineers. It was conducted using a 1:300 scaled model of the structure in a 12-foot by 7-foot boundary layer wind tunnel. The wind tunnel test procedures followed the requirements established in Section 31.2 of the ASCE 7-10 Standard. The model of the structure was analyzed under the exposure C category where open terrain was considered. This in accordance with the design wind load standard for High-Velocity Hurricane Zones established by the Florida Building Code and ASCE 7.
The Miami design wind speed was used at the ultimate design wind speed in this study. Which is a 3-second gust wind speed of 175 mph at a height of 33-feet in an open-terrain environment. The model was instrumented with pressure taps and tested with a scaled model of the existing surroundings within a 1,200-ft radius. The model tested did not include any additional structures or objects, including docked cruise ships or shipping containers.
They modeled horizontal and inclined wind components for this terminal. They exposed each side of the structure to negative wind pressures ranging from -50 to -180 lb/ft 2. And positive pressures ranging from +50 to +110 lb/ft 2. They also applied Internal and external pressures in the wind tunnel study to determine the net pressure applicable for the design of the structure. The terminal façades received an internal pressure of ± 20 lb/ft 2. The roofs and soffits received an internal pressure of ± 11 lb/ft 2. To evaluate the amount of wind loading the aluminum mullions could withstand, these members went through a specific analysis process.
Wind Tunnel Study – Results
The wind tunnel study found that the wind pressures are not the same on each side of the building. The results indicated that the West inclined curtain wall is the most vulnerable side of the structure. This side receives the most loads of each load component, as compared to the vertically framed curtain walls. Since the design considered an open terrain environment, the structure was more susceptible to higher wind loads. The wind tunnel study also determined that the curtain wall system needed additional mullion reinforcement due to high wind pressures exerted upon the structure.
The design and testing of the curtain wall system and mullion reinforcement led by Eastern Engineering Group increased the strength and durability of the overall Royal Caribbean Cruise Terminal. The design and analysis performed by Eastern Engineering Group assisted the architect and Engineer of Record in further designing the remaining curtain walls for the structure.
Student Academic Success Center
There are many types of buildings that incorporate a multitude of architectural attachments to their structural design. One building that should be highlighted due to the incorporation of structural and architectural components is the Student Academic Success Center (SASC), as shown in Figure 15 (PDF), located on the Modesto A. Maidique Campus at Florida International University (FIU) in Miami, Florida. In order to determine specific details about this building, Scott Martin, who is the Principal at Walter P. Moore, was able to provide details regarding the structure. They hired Walter P. Moore for the structural engineering aspects of this project.
Important design details about this project were that a wind tunnel study was not performed. The reason for this is because the building was not big enough. Any findings discovered in a wind tunnel study would not result in significant cost reductions. The structure was also designed to have a service life of 50 to 75 years since there were no specifications made by the owner in terms of serviceability. Wind loading on the structure was a huge factor that had to be considered on multiple elements.
The SASC was an educational facility with high occupancy spaces. Hence, they chose building Risk Category III to pilot the wind load parameters. Engineers designed the building to sustain wind speeds up to 170 mph specified in the Florida Building Code. They utilized fluid dynamics to analyze the wind effects on the building. This determined how the building would respond to extreme wind speeds. This process developed wind velocity profiles that helped conclude that the drag coefficients and wind pressures were at their greatest at the top of the building.
The project was originally designed to have metal panels for walls. However, they chose precast concrete elements instead. With precast elements, construction was faster, but they had to change parameters regarding architecture. Due to these changes, the columns and beams utilized had to be stiffer to hold the precast concrete walls. This would influence the design parameters for architectural and structural components.
To highlight the different architectural attachments, some elements that can be noticed within this structure are the curtain walls, roof, railings, guard rails, columns, and canopy. The engineer specified that the architectural attachments did not provide any type of mitigation or support for the structure. They used these solely for aesthetics. It was also noted that the railings and guardrails supported less wind load as per code. Nevertheless, the roof and curtain wall system was designed with a 50-year wind speed event.
Specifically, the curtain wall system was a glass and aluminum system, and the design is part of the structure, from the floor to the roof system. In this glass system, cladding was used and required a specific contractor in order to be installed. Cladding is the process of placing one material over another to create this second layer, or what is also considered as a “skin”. The vertical mullions are clipped to the roof and floor. While the attachments of the horizontal girts are to the columns. Mullions added resistance for the curtain wall against wind effects. While the horizontal components, called girts, collected the winds. Ultimately, both components acted as one system.
When discussing wind effects,
an interesting feature about the Student Academic Success Center on campus is the overhang. The overhang and the wall near the overhang both received a negative pressure of -173.9 lb/ft 2 of wind loading that flows over the top of the building. While a positive pressure of +149.3 lb/ft 2 flowed under the overhang. These positive wind pressures directly affect the curtain wall and girts as they absorb loads that then transfer to the columns. Another interesting architectural attachment on this building is the side panels that absorb most of the wind loading on the building. While the design of the canopies located at the top of the grass steps was able to withstand wind effects.
Conversely, the structural components mitigated the wind loading. They needed the design of the skeleton of the structure in order to analyze the loads that each component would sustain. When designing, they used ASCE 7 and the Florida Building Code to determine the wind loads. There were structural components with a design that specifically combats uplift and shear loads. These components included the precast shear walls located on the north end of the building that takes most of the wind loads and transfers them to the structure. While the design of the precast soffits was against uplift.
To read the student’s conclusions on this topic, please refer to the PDF we have attached below. On behalf of Eastern Engineering Group, we want to thank Leana Lu, Ryan Ocampo, and Shannon Stever for letting us share their research. Their paper is much more detailed and extensive, and we would like to encourage you to read it. It is very insightful, and it shows how hard they worked. This is just one of the endless examples where we learn from the students we build relationships with. Ask us about our internship program and other student initiatives we host!
**Note that the marketing team at Eastern Engineering Group changed some of the wording for SEO purposes. Please refer to the PDF attached to this document to see the original research paper.**
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