The focus of this report is on the nine-story portion of the Murrah Building, which incurred significant damage and partial collapse as a result of the April 19, 1995, bombing. The blast was equivalent to the detonation of approximately 4,000 pounds of TNT.
The purposes of the MAT investigation were to review damage caused by the blast, determine the failure mechanism for the building, and review engineering strategies for reducing such damage to new and existing buildings in the future. Specifically, mechanisms for multi-hazard mitigation, including mitigation of wind and earthquakes effects, were considered.
Using information developed by the federal government, it is possible to identify types of structural systems that would provide significant increases in toughness to structures subjected to catastrophic loading from events such as major earthquakes and blasts.
One of these systems is compartmentalized construction, in which a large percentage of the building has structural walls that are reinforced to provide structural integrity in case the building is damaged. However, the small and inflexible spaces created by this type of construction are not well-suited to office buildings.
Two additional types of detailing, used in areas of high seismicity, are Special Moment Frame construction and Dual Systems with Special Moment Frames (also referred to as Dual Systems).
Special Moment Frames and Dual Systems are frequently used in areas of high seismic activity.
In this type of construction, ductile detailing such as closed-hoop reinforcement to confine columns, continuous bars for continuity, and beam-to-column connections to transfer forces through the joints provide toughness to resist blast and earthquake forces.
Structural members reinforced as Special Moment Frames can provide better resistance to progressive collapse than can Ordinary Moment Frames such as those used in the Murrah Building. Special Moment Frames and Dual Systems can provide very large open spaces. They are suitable for construction of office buildings.
Compartmentalized construction, Special Moment Frames, and Dual Systems provide the mass and toughness necessary to reduce the effects of extreme overloads on buildings. Consequently, it is recommended that these structural systems be considered where a significant risk of seismic and/or blast damage exists.
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