Special truss moment frame (STMF) is a relatively new type of steel framing system used for buildings in seismic areas. One of the major advantages of the STMF system is that the truss girders can be economically extended over longer spans. In addition, the open-webs can easily accommodate mechanical and electrical ductwork. Research work carried out on STMFs with light angle sections as truss members during the 1990s led to the formulation of design code provisions. However, they did not adequately reflect the current practice in design and detailing where much heavier sections are needed for buildings in high seismic areas. In this project, component specimens consisted of double-channel and double-HSS built-up sections were tested under cyclic bending tests in order to study their viability. The specimens represented the chord members as well as the vertical web member in the special segment (a structural fuse used to dissipate earthquake energy) of prototype STMFs. Special detailing of the member-to-gusset plate connection was also developed through these component tests. Moreover, a short buckling restrained brace (BRB) was tested in order to understand its seismic application in STMFs. The findings from component tests were later used in full-scale STMF subassemblage tests at Multi-Axial Subassemblage Testing Laboratory, an NSF NEES facility. The first two specimens were made of double-channel sections and the third specimen was made of double-HSS sections. In the last specimen, the truss girder was made of double-channel sections with two short BRBs oriented in chevron pattern in the special segment of the truss. The test results proved that by using the detailing proposed in this research, STMFs’ seismic performance and safety can be enhanced. Moreover, BRBs can be incorporated into STMF system to enhance its damage control capability.

Steel staggered truss framing (STF) system was first developed in the 1960s to achieve a more efficient structural framing system to resist wind loads and at the same time to provide versatility of floor layout with large open areas. The result was an efficient steel framing system for mid- to high-rise buildings that was simple to fabricate and erect, with low floor-to-floor heights and large column-free spaces. Because of the design flexibility, construction efficiency, and overall cost efficiencies, many STF buildings have been constructed in low-seismicity regions. However, STFs’ seismic performance is highly unknown and necessitates urgent research. In this project, limitations of the conventional STF for use in seismically active areas were extensively investigated through computer simulations. Subsequently, an alternative structural layout was investigated in which the conventional diaphragms composed of precast concrete hollow-core slabs are replaced by horizontal steel trusses as in-plane diaphragm to transmit the large diaphragm shears in the lower stories. In addition, diagonal braces were added in the non-truss frames to alleviate the large forces in columns. The preferred yield mechanism of the STF system is to have plastic hinges form only within Vierendeel panels located at the center of the truss similar to that in the special segments of STMFs. A single Vierendeel panel in the middle of a truss leads to extremely high rotational demands in the chord members even at small roof drift ratios. In order to increase the overall drift capacity of the structure, the Vierendeel panels were expanded over three panels. This reduced the rotational demand at the ends of the chord members in the truss and allowed the structure to reach larger drifts without strength degradation. The addition of diagonal braces alters the seismic load transfer path from a staggered pattern via floor diaphragms to a more direct path from upper truss to the non-truss at lower level. This, in turn, relives the high force dem...

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