Shake table testing of a miniature steel building with ductile‐anchor, uplifting‐column base connections for improved seismic performance

Abstract

Summary Previous research has demonstrated that uplifting‐column or rocking building systems may exhibit improved seismic performance, including reductions in total base shear and decreased residual drift, when compared with systems rigidly connected to the foundation. These beneficial effects may be due to lengthened periods, activation of rocking modes, and energy dissipation of base fuse elements. In the current work, several configurations of a miniature steel building with different combinations of base connection and traditional superstructure fuse strength and stiffness were subjected to identical earthquake motions to evaluate differences in demands and performance. The uplifting base connections incorporate highly ductile concrete anchors with long stretch lengths, allowing robust connection performance and easy replacement of damaged connection elements following the seismic event, an advantage over previously tested systems. Testing and dynamic numerical analysis indicates that ductile anchor uplifting systems may reduce total base shear by over 20%, as well as reducing residual structural drift by more than 80%.

Anchor‐yield exposed column bases for minimizing residual deformations in seismic‐resistant steel moment frames

“…11a, the exceedance functions (i.e., one minus cumulative distribution function) for residual SDRs are nearly identical for the ideally fixed and flexible base case regardless of the ground motion characteristics and the seismic intensity of interest. Interestingly, the 2-story steel MRF with dissipative bases is generally less likely to experience residual SDRs both at DBE and MCE seismic intensities, than its fixed base counterpart, which is consistent with prior observations from shake table testing [20].…”

“…Referring to the annual rate corresponding to the probability of exceedance of 2% in 50 years (2475 years return period), the residual SDR is about 0.6% in all cases for the SD ground motion set, which is deemed acceptable 70 . When the ground motion set depicts LD characteristics, then the two‐story steel MRF with dissipative bases is less likely to experience residual story drifts for the 2475‐year seismic event, which is consistent with shake table experiments on idealized structures with dissipative bases 20 …”

“…Interestingly, the two-story steel MRF with dissipative bases is generally less likely to experience residual SDRs both at DBE and MCE seismic intensities, than its fixed base counterpart, which is consistent with prior observations from shake table testing. 20 Similarly, Figure 11B depicts the exceedance functions for the column axial shortening of the examined two-story steel MRFs designed with ideally fixed and flexible bases. Results for the steel MRF with dissipative bases are not presented, because axial shortening in this case is zero regardless of the seismic intensity.…”

“…70 When the ground motion set depicts LD characteristics, then the two-story steel MRF with dissipative bases is less likely to experience residual story drifts for the 2475-year seismic event, which is consistent with shake table experiments on idealized structures with dissipative bases. 20 For the same annual rate of exceedance (ie, 2475-year return period), the developed axial shortening hazard curves suggest that the column axial shortening is 15 mm (fixed base) and 7 mm (flexible base) when duration is a key ground motion characteristic. Recent studies 6 found that depending on the level of the imposed compressive axial load and column cross-section local slenderness, a 10-15 mm axial shortening may be challenging from a reparability standpoint and may cause appreciable downtime in the aftermath of earthquakes.…”

“…However, first story drift concentration is likely to occur in steel MRFs in this case [17]. Other studies have explored the weak-base/strong-column concept [18][19][20] as a potential alternative in steel MRF seismic design. The strategy rests on the idea that dissipation should be primarily located at the base and withdrawn from the column, potentially avoiding the shortening of the member.…”