Issue 76

A.Abdulridha et alii, Fracture and Structural Integrity, 76 (2026) 129-153; DOI: 10.3221/IGF-ESIS.76.09

T HE INFLUENCE OF THE BRACING ON THE SEISMIC RESPONSE

T

he results from a number of steel braced frame positions on the building base shear at various points in time are summarized in Tab. 7. The braced periods are approximately 62–67% smaller compared to brace frames at all the three elevations, and damper-only with smaller reductions of 12–24%, shows that Eigen period is mostly governed by stiffness and damping merely influences energy dissipation rather than Eigen properties. Hybrid bracing dampers for all three stories and records provide the least base shear compared with bracing only, with average base shear reductions ranged from 18% to 33%, which verifies the idea that the combination of stiffness and frictional energy dissipation in the form of stiffness and friction has a great potential for force mitigation and the lateral rigidity should not be compromised. THREE Hybrid bracing dampers outperform traditional solutions in • Displacement demands (Fig. 8). The record sensitivity is acute: Kobe dominates base-shear demands in all strong-motion realizations for hybrid systems, which experience the highest relative gain under this input, suggesting that velocity/strong content further improves damper performance and confirming that single-period metrics cannot serve as design surrogate. The device requirements are fairly large: the peak axial forces are of the order of 2.4 MN (five stories) and 1.6 MN (15 stories). Therefore, slip load, bolt torque, and connection detail shall be sized such that the hysteresis can be repeatedly, without stiffening too much the brace or locking the slip in presence of strong motions. In the term of controlling drifts and forces, friction dampers hybrid bracing system can be regarded as the best choice for medium and high- rise steel frames. However, the design should be checked by some hazard-consistent ground motions and additional site-specific analyses are recommended to evaluate the damper force capacity, higher-mode participation and residual drift to conduct a sensitivity analysis of the design to variation in earthquake intensity and spectral contents. As with the “Without” case, the fundamental period is shortened by the steel bracing approximately by 62% at 5 stories, 67% at 10 stories and 67% at 15 stories, while the damper-only decrement is negligible at about 12%, 23%, and 24%, respectively. This indicate that stiffness is dominant in period control, and damping only reduce periods slightly as a result of similar mechanisms of equate stiffness and energy dissipation. Under El Centro, figure demonstrates that braced frames with supplemental dampers (hybrid) decrease base shear by 25%, 18%, and 20% at 5, 10, and 15 stories, respectively, which confirms that additional energy dissipation would further reduce force demands beyond what stiffness could solely do. The hybrid decreases shear when compared to bracing by about 28% at 5 stories, 12% at 10 stories, and 1%–2% at 15 stories for Loma Prieta, revealing a decreasing incremental damping benefit with height and more severe higher-mode effects under this record. For Kobe, the hybrid reduces shear relative to bracing by approximately 33% at 5 stories, 34% at 10 stories, and 22% at 15 stories, indicating greater damping effectiveness for a record consisting of larger velocity and long-period contents which causes extensive inelastic energy dissipation in the devices. Hybrid bracing combined with friction dampers leads to the best overall response, it exhibits a significant period shortening similar to bracing, and, beam-shear reductions comparable to the curve of damper-only systems, what could be the ideal stiffness–damping combination for every height and record. The numerical technique accurately determines lateral displacement, maximum drift, and base shear. It corresponds to Zhang et al. (2025) [4].

Maximum axial load of damper P (kN)

Base shear Vmax (kN) El Centro Loma Prieta

Number of stories

Steel brace Position

Period sec 3.423 1.299 3.02 1.972 10.0 3.245 7.739 4.406 16.827 5.616 12.722 7.191

Frequency cycle/sec

Building code

Kobe

SB5-W SB5-B SB5-D SB5-BD SB10-W SB10-B SB10-D SB10-BD SB15-W SB15-B SB15-D SB15-BD

Without Steel brace Steel damper Without Steel brace Steel damper Without Steel brace Steel damper

0.292 0.77 0.331 0.507 0.308 0.129 0.227 0.059 0.178 0.079 0.139 0.1

- -

5559.2

8188.9

13248.1

10500.8 13770.2 19914.0

5

1508.7 2423.1

3487.0 3996.7 4177.7 5371.5 2280.1 3418.8 2648.7 3797.8 1800.9 2106.9

5077.3 5911.7 6892.4 5200.6 6025.4 4654.8 8264.8 3926.9 4607.6

8314.9 8884.1 10877.0 6519.8 7106.4 7283.2 14243.9 4738.3 5643.6

Steel brace and damper

- -

10532.5 12490.8

10

846.5 1272.5

Steel brace and damper

- -

15

827.9 1614.1

Steel brace and damper

Table 7: Seismic performance of 5-, 10-, and 15-story steel frames with and without hybrid bracing and friction dampers.

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