Bulletin of Earthquake Engineering最新文献

Unreinforced masonry structures are a significant percentage of the global building stock and are often vulnerable to seismic events due to their inherent structural weaknesses and limited deformation capacity. Although seismic codes promote regularity in structural design, achieving this in unreinforced masonry buildings is often a challenging task. Despite extensive research using shake table tests, quasi-static testing of unreinforced masonry buildings remains limited, particularly in the presence of plan irregularity and rigid diaphragm. The present study addresses this research gap by investigating the seismic response of a half-scale, two-story, unreinforced masonry building with plan irregularity through cyclic quasi-static testing. The experimental campaign presented here shows the findings from two tests, including dynamic identification. The first test indicated torsional amplification and rocking-induced wall detachment during the pre-peak response. These results prompted modifications to the experimental setup, including the addition of extra weight to prevent overall rocking and the repairing of the boundary interface to re-establish structural integrity for subsequent testing. The initial results highlight the influence of plan irregularity within the pre-peak behaviour and provide a basis for further exploration in the seismic assessment of irregular, unreinforced masonry buildings.

Due to architectural and open-ground space constraints, buildings with transfer structures are often constructed in areas with minimal earthquake activity. Since the current building code standards of different countries lack explicit design guidelines, it is critical to identify the critical factors influencing their ability to respond to severe shaking. By (i) adding a transfer storey up to the first, third, and fifth storeys, (ii) altering the dimensions of the transfer storey, and (ii) raising the buildings’ heights, respectively, a parametric study is carried out on 2D RC moment frame buildings. Additionally, their responses are compared to those of a conventional building. The number of transfer storeys and their dimensions have a significant impact on the stiffness ratio (K_SR) of buildings. Their performances are evaluated using nonlinear static and nonlinear dynamic time history analysis. As a building’s height and dimensions of transfer storey increase, its lateral stiffness and strength decrease, but they increase with the number of transfer storeys. Increasing the number of transfer storeys and their dimensions also reduces the inelastic drift, which is mobilized by about 1.5% to 2%. However, it shifts the damage to the beams and columns above them and only ensures damage-free transfer storeys when the K_SR is ≥ 27. More focus is then needed on the columns just above the transfer storey. Buildings with transfer structures often feature structural walls to reduce the possibility of damage to structural elements. Although these walls lessen damage to the transfer structure and the conventional frame, probabilistic analyses (using developed fragility curves) show that these buildings are still quite vulnerable to catastrophic damage and collapse under earthquakes. In areas with high earthquake risk, buildings using transfer structures should not be utilised.

Until now, many probabilistic seismic hazard analyses (PSHA) have been conducted for Turkey. However, except in a limited number of cases, characteristic fault source modeling was not used. Since the North and East Anatolian Faults (NAF and EAF) show some evidence of characteristic rupture behavior, the first objective of this research is to develop a sound hybrid characteristic recurrence model for the NAF and EAF. The so-called hybrid model involves a composite characteristic model (i.e., an exponential part for the smaller and a characteristic part for larger magnitudes) developed for each segment combined with a characteristic recurrence proposed for multi-segment ruptures. Two different hybrid earthquake recurrence models are developed with time-independent (or Poissonian) and time-dependent (or renewal) characteristics. The North Anatolian Fault has been known for its capacity to generate multi-segment ruptures, evidenced in the twentieth century by the 1939 Erzincan and the 1999 Kocaeli earthquakes. The EAF, on the other hand, had not produced any multi-segment rupture in the recent past. The occurrence of the February 6, 2023, Kahramanmaraş-Pazarcık earthquake (Mw 7.8, rupture length of 350 km) shed new light on the earthquake hazard-related analyses of this fault zone. In the present study which also allows for multi-segment ruptures on both faults, the effects of characteristic modeling, as well as those of seismic gaps along the NAF and EAF on seismic hazard are assessed, including a pre- and post-2023 modeling comparison for the EAF. The model also allows for a comparison of the results with the fully exponential model of the NAF and EAF, which, generally, produced higher seismic hazard compared to the Poissonian hybrid model. As shown by the occurrence of the 2023 Kahramanmaraş earthquake, slip deficits on some fault segments can increase the seismic hazard dramatically. A renewal seismic hazard model would be more suitable to handle such cases. In any case, the 2023 Kahramanmaraş earthquake has also shown that modeling for the really (even inconceivably) big one is never an overestimation, especially for the major plate-boundary faults.

Recent studies have placed growing emphasis on the significant role of mainshock-aftershock (MS-AS) sequences in seismic structural fragility and risk analyses. An important step involved is the probabilistic characterization of aftershock ground-motion intensity measures (IMs) (e.g., 5%-damped spectral acceleration). This study presents a versatile framework to construct the damping-dependent conditional joint distribution of aftershock multi-component IMs based on novel generalized intensity measure correlation models (GIMCMs). A step-by-step procedure with mathematical expressions is provided to facilitate the implementation of this framework. As a key feature, the GIMCMs quantify damping-dependent correlations between MS-AS pairs of ten representative IMs in both horizontal and vertical directions for the first time, based upon a substantial database and machine learning. The MS-AS correlations are found to be generally stronger when IM pairs correspond to larger damping ratio, or more similar ground-motion frequency ranges (e.g., same-IM pairs), or identical (horizontal or vertical) directions. The presented framework is applied to two examples for modeling aftershock IMs conditioned on a vector of recorded mainshock IM values and a specified mainshock IM value from seismic-hazard disaggregation, respectively. When utilizing recorded mainshock IM values as conditioning information, the framework can significantly improve IM prediction with a reduction in the mean absolute error by over 20% relative to the conventional unconditional approach. This study could be useful for seismic risk assessment of damping-specific structures and geotechnical systems subjected to MS-AS multi-component ground-motion sequences.

For the low-strength shear wall where cross-sectional enlargement is constrained, the partial concrete replacement method at wall ends with conventional high-strength concrete offers a cost-effective strengthening solution. To evaluate the seismic performance of strengthened walls in comparison with both low-strength and design-strength reference specimens, cyclic lateral loading tests were conducted on 12 concrete walls with an aspect ratio of 2.4. Meanwhile, the effects of concrete replacement length on the seismic performance of the strengthened walls under different axial loads were analyzed. The results s indicate all specimens exhibited flexural failure and all strengthened specimens demonstrated excellent interfacial bond performance. The strengthened specimens exhibited significant enhancements in both load-bearing capacity (increased by 13 ~ 22%) and seismic performance compared to the low-strength specimens. Compared to the design-strength specimens, the strengthened specimens demonstrated a 2 ~ 12% increase in load-bearing capacity, while the improvement in seismic performance was found to be dependent on the replacement length under different axial loads. Additionally, the calculation model and formula of flexural capacity for strengthened specimens were proposed. The study demonstrates the strengthened wall can achieve seismic performance comparable to the design-strength wall, provided that the replacement length of the strengthened wall exceeds its calculated compression zone height at peak load. Beyond this critical length, increasing the replacement length further has negligible effects on seismic performance of the strengthened wall.

Offshore wind energy is increasingly recognised as a vital source of renewable energy worldwide, with offshore wind farms currently being operated and developed in regions of moderate to high seismic activity. However, there is still limited data on how large-scale offshore wind turbines perform during earthquakes, highlighting the need for further research. This study focuses on the assessment of the seismic performance of large-scale jacket-supported offshore turbines, which have received less attention compared to monopile-supported turbines, and can offer a more attractive solution in seismic regions. Using a risk-based approach, this study investigates the seismic acceleration demands at the rotor-nacelle assembly (RNA) level for a four-legged, X-braced reference steel jacket structure supporting a 10-MW turbine, acting as a representative example of existing and future large-scale jacket-supported offshore wind turbines. The structure is assumed to be located in a reference site in a highly seismically active region, where the hazard is driven by different source types. Particular focus is given to the associated hazard-consistent ground-motion selection methodology considering combined horizontal and vertical ground-motion excitation at different seismic intensity levels that is required for the proper evaluation of the structural system response. 300 nonlinear response history analyses are conducted where the performance is evaluated against a representative range of RNA acceleration limits for which conditional fragility curves are developed. Moreover, to aid in further damage and loss assessments of such structures, a demand curve showing the annual rate of exceeding different demand values is reported. In addition, the contribution of higher-mode response including vertical system excitation is discussed. Finally, in order to relate the acceleration demands to potential structural damage levels, buckling strength evaluations for the support tower are presented and discussed.

Seismic performance assessment of a RC frame building was conducted for original and strengthened states to investigate the effectiveness of strengthening technique of infill walls by carbon fiber reinforced polymer (CFRP). Structural model representing CFRP strengthened infill wall was based on the previous experimental work of the author. In the first part of this paper, the experimental work was explained briefly, details of strengthening technique and proposed structural model were given. In the second part, nonlinear time history analyses of a RC frame building were performed for original and strengthened states. Maximum interstory drift ratios obtained from nonlinear time history analysis were used to derive cumulative density functions and a comparison was made in terms of probability of exceedance curves of original and strengthened buildings. It was concluded that strengthening of selected infill walls by CFRP as proposed in this study clearly improved seismic behavior of the structure and that improvement was quantified with cumulative density functions.

The evaluation of repairability for column specimens is a critical component in assessing seismic toughness and can guide post-earthquake repairs. Under the effect of vertical variable axial force, the residual deformation limit specified in FEMA P-58 may be overly high. Existing studies generally suffer from limitations such as insufficient sample numbers, large errors, and incomplete evaluation processes. In this study, the change mode of axial compression ratio at the top of the central column was analyzed, and systematically evaluated the influence of vertical variable axial force and structural parameters on the bearing capacity and residual deformation of columns. The bearing capacity prediction model and residual deformation prediction model of column specimens considering multi-factor changes were established respectively. Based on damage index, the residual deformation limit of the repair interval of column specimens was divided, and the repairability probability model of column specimens was established. Finally, a complete set of columns repairability evaluation procedures was established. The results indicated that the residual deformation limit within the repair interval of column specimens was significantly lower than that proposed by FEMAP-58 and previous research when vertical variable axial force was applied. Specifically, when the change frequency was 3, the residual deformation limits for the “no repair required” and “can be repaired” intervals were less than half of those proposed by FEMAP-58, with the latter decreasing to 0.14% as the amplitude increases. Additionally, the interval limits provided by FEMAP-58 remained applicable when the change frequency of vertical variable axial force was 2 and the amplitude was small; but these limits decreased significantly with increasing amplitude. Ultimately, a comprehensive column reparability assessment system was established, providing critical decision-making basis for the functional recovery of subway station columns after earthquakes.

Performance-based seismic design of post-installed fasteners is an open question since the current state-of-the-art fastener seismic qualification methods (EOTA TR 049 and ACI 355) do not provide fastener capacity information that may be used for performance-based design. The published fastener seismic capacities are not related to actual earthquakes in seismic design scenarios. The seismic qualification and assessment framework of fasteners is conceptually incorrect since its first publication in ACI 355.2–00. This framework was adopted in EOTA documents and referred in EN 1992–4:2018 and EN 1998–1–1:2024 too. To promote the development of performance-based seismic design and a related appropriate fastener qualification framework, a holistic approach is proposed that can provide transparency and opportunities for future improvements. The approach hypothesizes that seismic design scenarios of connections with post-installed fasteners may be characterised by one single simplified parameter. An energy based term, the accumulated damage potential (ADP) has been adopted for this purpose, which has been proposed in the literature for the estimation of fastener displacements in crack cycling tests. The ADP seems to be able to reflect the response of structural members at the location of connections under any earthquake action in any type of building, considering any type of non-structural component and any type of post-installed fastener. Major future work is anticipated in multiple fields to develop the new framework. This paper explores the specifics of such a development, provides a comprehensive assessment of the current status quo, and based on a gap analysis sets the direction for future research. Currently, there are no simplified methods available for designers to determine the ADP in design. Fastener capacity information is very limited in the current assessment documents and does not allow designers to perceive the real seismic capacity of fasteners or their sensitivity to different crack widths. This paper provides an outlook for future developments in seismic design and qualification, which are suitable to account for the fastener response in the relevant range of ADP and the relevant range of maximum crack widths considered in actual seismic design scenarios.