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
LEED ID credits are granted for projects that provide significant improvements over industry standard operations. A previous project demonstrated that it had reduced structural steel use by 35% to achieve an ID credit. This is not to imply that a 20% reduction is not significant. The relative significance of the saving 20% of steel as compared to conventional building systems should be more fully developed. Additionally, was use of other materials increased as a result? What is the net effect of the change? One area of concern is the term \'increased load path redundancy\'. While this may represent an innovative structural solution, this strategy does not necessarily represent an environmental achievement. Increased redundancy should not form part of the basis of reduced material use claims by inflating the baseline steel calculation. The energy savings presented is less than 1/2 of 1%. This does not represent a significant environmental savings. The most challenging part of this ID credit will be clearly and convincingly documenting the validity of the baseline to which the project is compared. To achieve the credit proposed, it will be necessary to provide a convincing and thorough analysis of this condition by a knowledgeable professional, such as s structural engineer. However, the format proposed for the ID credit is a reasonable approach to an ID credit in this category.