Damage Avoidance Design Steel Beam-Column Moment Connection Using High-Force-To-Volume Dissipators

Existing welded steel moment frames are designed to tolerate substantial yielding and plastic rotation under earthquake loads. This sacrificial design approach can lead to permanent, and often irreparable damage when interstory drifts exceed 2%. The experimental seismic performance of a 50% full-scale damage avoidance designed structural steel beam-column connection is presented. The beamcolumn joint region consists of a top flange-hung beam connected to the column by an angle bracket. High-force-to-volume (HF2V) devices are attached from the column to the beam to provide joint rigidity and energy dissipation as the joint opens and closes. The HF2V devices are connected either below the beam flange or concealed above the beam’s lower flange. Reversed cyclic lateral load tests are conducted with drift amplitudes up to 4%. No damage is observed in the principal beam and column structural elements. The need for stiff device connections to achieve optimal device performance is demonstrated, and potential design solutions presented. Stable hysteresis and repeatable energy dissipation for a large number of cycles up to the 4% drift level is observed. It is concluded that superior and repeatable energy dissipation without damage can be achieved for every dynamic motion cycle, in contrast to conventional sacrificially designed welded moment frame connections. UCRR http://ir.canterbury.ac.nz/handle/10092/3580 CE Database subject headings: Steel structures; Damage; Energy dissipation; Beam columns; Connections; Frames. Introduction repairs and enabling businesses to continue without causing further financial loss to the owner or tenants. Occupant safety and use of steel frame buildings following major earthquakes is often limited by damage to the structural frame system. Most of this damage is restricted to the plastic hinge zones at beam ends or the panel zone within steel beam-column joints. As evidenced by the extensive damage to steel structures following the 1994 Northridge earthquake, repair costs and downtime can be substantial to owners and users of such structures, creating a significant long-term social and economic impact. Presently, steel connections are designed using sacrificial Compact high-force-to-volume (HF2V) energy dissipating devices using a bulged shaft in a prestressed lead cylinder have been developed and experimentally characterized (Rodgers et al. 2007). These devices are capable of fitting within standard structural connections. They are also inexpensive to manufacture, potentially making them economically feasible for widespread use in large buildings. The use of supplementary HF2V devices fitted directly into beam-column connections provides a damage avoidance design (DAD) structural connection. The devices use lead yielding at beam ends to dissipate dynamic response energy. Plastic hinges form at the ends of beams, causing permanent damage and the possibility of failure under extreme interstory drifts due to flange buckling or weld fracture. The associated damage can be difficult, time consuming, and expensive to repair. It is thus desirable to have damage-free connections, eliminating expensive because of its unique rheological properties, low recrystallization temperature to give consistent force levels on successive cycles, and the ability for lead to creep over time, giving the device the ability to allow residual compression forces to dissipate through creep effects. With these devices, the same or a greater amount of energy can be dissipated on successive cycles and without causing permanent damage, unlike conventional steel connections or Graduate Assistant Researcher, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77840. 2Ph.D. Candidate, Dept. of Mechanical Engineering, Univ. of Canterbury, Christchurch 8140, New Zealand (corresponding author). Professor, Dept. of Mechanical Engineering, Univ. of Canterbury, Christchurch 8140, New Zealand. Zachry Professor, Design and Construction Integration, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77840. Associate Professor, Dept. of Civil Engineering, Univ. of Canterbury, Christchurch 8140, New Zealand. sacrificial dissipators (Solberg et al. 2008). Previous research has also investigated the concept of damagefree steel structures. The inclusion of posttensioned steel tendons provides self-centering ability to the joint (Christopoulos et al. 2002; Ricles et al. 2001; Pekcan et al. 2000), with energy dissipation typically provided by either friction, viscous, or yielding steel devices (Christopoulos et al. 2008; Garlock et al. 2005). The systems that utilize posttensioned tendons have the advantage of joint self-centering. However, these systems also have the limitation that they are dilating frame systems, which must be accommodated by gap opening or tearing of the flooring system during earthquake response cycles, as discussed in Garlock et al. (2007). This paper presents the results of an experimental investigation on the seismic performance of DAD structural steel beamcolumn connections using these HF2V devices. Instead of