مهندسی عمران شریف (Aug 2022)
Seismic Resilience Analysis of High-Rise Diagrid Structures with Various Skeletal Configurations Based on Robustness Criterion
Abstract
Evaluation of the fragility characteristic and its related parameters is an efficient method to assess the seismic performance of structures subjected to earthquake tremors. The probability of exceeding limit state criterions for structural performance associated with a conceptual lemma is usually considered and numerically illustrated as a function of seismic intensity to be used in preparing the fragility curves. By implementing a statistical distribution for preparing the fragility curves, the evaluation process of the vulnerability of structures and its related probable collapse estimation will be available. The concept of resilience is introduced as the ability of structures to reduce the probability of any exceeding performance level over control time. The resilience criterion is an important concept in conjunction with various disaster management processes, in which the structural capability to sustain skeletal stability is determined during strong ground motions. Based on comprehensive researches, there are essential factors that must be considered to establish an effective implementation for the seismic resilience lemma. The aforementioned essential factors are entitled as robustness, resourcefulness, redundancy, and rapidity. In this paper, the conceptualization of the structural resilience was assessed for three studied diagrid structural systems. Moreover, there is a basic studied model comprising a full bundled tube skeleton which has been used for performing all numerical comparisons among the seismic response parameters. The effect of the geometrical configuration of the perimeter diagonal beam-column elements on the seismic resilience lemma was evaluated though numerical explanations due to the released fragility curves. The three studied 24-story diagrid structures were considered with uniform geometric configurations and internal bundled flexural cellules, which form a hybrid resistant skeleton. The uniform diagonal angles for diagrid models were considered 49°, 67°, and 74° respectively. Several nonlinear time history (NTHA) and incremental dynamic analyses (IDA) were performed on the four studied 24-story structural models under near-field ground motions with various directivity effects. The probability of the exceeding performance limit states for the studied structures was calculated based on the FEMA provisions. The assumed performance levels in preparing fragility curves included the immediate occupancy (IO), the life safety (LS), the collapse prevention (CP), and the probabilistic global instability (GI) indices. Also, the robustness of seismic resilience for the studied structures was determined according to the proposed formulation of the damage function as reported by MCEER. The results obtained from conducting nonlinear time history and incremental dynamic analyses indicate that the assumed geometric pattern for the perimeter inclined elements would relatively reduce the maximum inter-story drift and increase the collapse capacity of the diagrid structures. In addition, the definition of large angles for diagonal elements can increase the probability of the seismic performance levels to be higher than the L.S. criterion. The values of the robustness parameter for the studied diagrid structures with skeletal angles of 49°, 67°, 74° and also the studied bundled tube model were obtained as 95.9, 91.7, 88.6, and 85.1, respectively. Moreover, the evaluation of the related seismic resilience for all the studied structures proved that the diagrid systems had a great ability to resist a specific limit of damage. It is demonstrated that implementing triangular patterns in the external framed panels of the seismic-resistant skeleton would decrease the estimated amount for the qualified deterioration effects in structures after a strong earthquake. In this regard, upon increasing the skeletal angles of inclined elements, the effect of diagonal configuration on controlling the occurrence probability of higher performance limit states would be effectively decreased. This research results indicate that the geometric pattern of diagrid elements is able to increase the value of the skeletal hard resilience component and relatively exceed the capability of structural stability against near-field ground motions.
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