Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.0

Inquiry

Innovative Structural System/Efficient Use of Materials Intent: Develop and employ a structural system that reduces the environmental impacts associated with structural material manufacturing and transportation. Requirement: Design a structural system that reduces the quantity of raw materials manufactured and employed for the project\'s structure by 20% when compared to the same building tower that would be conventionally-framed. AND Demonstrate that the innovative structural system out-performs the typical system by both increasing the building\'s structural resistance to lateral forces and its load path redundancy thereby enhancing occupant comfort and safety. AND Fine tune the tower configuration so that, because of its unique sculpting, it has the same or lower energy use as compared to the same tower that is conventionally-framed. Design Approach: Early in the design process, determine what the most appropriate structural system for the building will be, depending on building type and location (e.g. steel, concrete, wood framing). Based on the structural system selected, develop a baseline of materials that will be required to construct the determined structure of the building. Then develop and evaluate innovative ways in which the structure of the building can be constructed, using smaller quantities of materials without reducing the desired floor area or programmed spaces as they are represented in the baseline. The innovative structural system must increase the efficiency and performance of the building materials employed by not only requiring fewer materials, but also by increasing the structural redundancy of the project or reducing the conditioned volume. Documentation: Provide a narrative and drawings that describe both the baseline and the high performance structural system. AND Provide calculations that indicate the amount of material savings resulting from the employment of the high performance structural system. AND Provide calculation that indicate that the energy cost is the same or lower. Project Actions: Early in the planning phases of the project, it was determined that a steel structural system would be the most appropriate type of structural system for the Hearst Headquarters project. Programmed as a 43-story commercial high-rise office building in Midtown Manhattan, the only economically feasible structural systems to consider were steel and concrete. Ultimately, steel was selected because it would allow for the flexibility of an open floor plan that is now a necessity in modern office design. Typically, column and beam "moment frame" structural systems are employed for commercial high-rise office buildings in this area. However, the proposed structural solution is a drastic departure from the traditional approach of the beams and column frame system. The structural elements at the perimeter of the tower are placed at an angle with respect to the vertical axis, forming a sub-assemblage of triangulated structures interconnected together. This concept is repeated on all four sides of the tower creating an inherently highly efficient, strong, redundant structural system. The efficiency of the system is due to the fact that all forces are primarily transferred by axial forces in the members. Therefore, demand on the structural steel material is reduced to a minimum. As a result, the proposed Diagrid structural system reduces the steel material required for the project by 2500 tons in comparison with a conventional moment frame system. Figure One: Moment Frame and Diagrid Comparison Redundancy With the proposed triangulated Diagrid structural system, any load at any point in the structure has multiple load paths to transfer the load to the foundation. If for any reason in an unforeseen extreme event one or more of the structural elements were not functioning, the load would be transferred to the foundation via the other back-up load paths. Emulating the natural redundant behavior of the diagrid in a conventional moment frame approach would further increase the material resource difference between the two systems to about 3000 to 3500 tons of structural steel. Reduction in Energy Use The Diagrid system creates a "bird\'s mouth" geometry at the corners of the building. By comparison with a straight fa