Proposal
Executive Summary
In June 2012, Massachusetts State College Building Authority completed construction on a new residence hall, nicknamed “Tree House” by students of the Massachusetts College of Art and Design (MassArt). The Tree House embodies the collaborative and didactic spirit by which it was designed. Study lounges and gathering spaces are located throughout the 145,000 square foot area of the building. Visible sustainable design strategies educate students on efficient use of building systems and support the LEED Gold status of the building obtained in April 2015.
Though the footprint is small, the structure of the building is relatively complex due to its height and configuration. At 260 feet tall, a direct load path to the ground is difficult to achieve. Transfer girders are implemented in the design where gravity loads cannot directly reach the foundation through a single column line. Also, lateral forces increase with height. The Tree House utilizes a combination lateral force resisting system consisting of moment frames and braced frames. Lastly, the base of the building does not follow the same shape as the upper floors due to a sewer easement. This easement causes a major column line to recede, and 19 floors of load plus the roof load are cantilevered out nearly a full bay size from the structure. This cantilever affected the design of the foundation system, which consists of concrete grade beams, slab-on-grade, and steel piles.
Considering the complexities discussed above, the structural system of the Tree House demands meticulous analysis. The primary factor for a proper analysis is understanding the load path, especially with regards to the receding column line mentioned previously. Due to the composite deck floor system, vibration serviceability may be another concern. Lastly, at first glance the lateral force resisting system seems inefficient. Further investigation regarding these topics has been performed in notebook submissions throughout the semester.
The results of this investigation have resulted in a proposed redesign in reinforced concrete to improve the efficiency of the structural system. The gravity system will be a flat plate two-way slab, and the lateral system will be reinforced concrete shear walls. In order to further understand the viability of this design alternative, a cost analysis will be performed and compared to the existing structure. In addition, the façade will be analyzed for its moisture, thermal, and structural performance.
Depth Topic
MAE Requirements
The proposed alternative system will be a reinforced concrete flat slab system with reinforced concrete shear walls. The slab will be 10” thick, and the typical column will be 20” x 20”. The shear walls will be placed around the elevator and stair wells. Loads will be determined by ASCE 7-10 and the current Massachusetts State Building Code.
Since concrete is a heavier material, more dead load will be applied to the cantilever system. Also, providing support at the roof level is not viable with concrete since these elements will be in tension. Therefore, support must be provided through heavy concrete beams at the cantilever. In order to reduce the size of these beams, prestressed concrete will be investigated as a design solution at this level. Prestressed concrete offers higher capacity with less material than reinforced concrete, thus improving efficiency. If prestressed concrete is deemed not viable, a thicker transfer slab at this level will also be investigated as an alternative to beams.
Breadth Topics
Construction Breadth
Building Enclosure Breadth
As the central catalyst of the architectural design of the building, the façade is arguably the most important feature of the building. The 5,500 colored metal rainscreen panels give the Tree House its iconic look. Therefore, durability of these elements is critical from an architectural standpoint. From an engineering perspective, these panels also provide protection against damage from weather. Failure of the building enclosure could lead to detrimental costs. This breadth will investigate the moisture, thermal, and structural performance of the critical elements of the building enclosure and seek to improve the durability of the system if possible.
In order to fully compare these two systems, a cost and schedule analysis of the alternative system must be performed and compared to the actual budget and schedule. Indeed, the original design sets a high standard to reach. The total project cost was well under budget, and the project was completed in just two years. This breadth will provide clarification regarding the viability of the proposed design alternative.
The proposed redesign will require modeling of both gravity and lateral elements. This topic was covered in AE 530 Computer Modeling of Building Structures. Additionally, the building enclosure breadth will require comprehension of topics covered in AE 542 Building Enclosure Science and Design.
Proposal