Blast loading and seismic excitations are widely recognized as the most detrimental occurrences that a building structure may encounter throughout its lifespan. Therefore, this study investigated the ...retrofitting capacity of external devices (ENTA damper systems) for reinforced concrete (RC) frames in term of enhancing their resistance under the combined effects of blast and seismic loads. This study presents the establishment of finite element (FE) models for retrofitted RC frames with ENTA damper systems through the utilization of the dynamic analysis software LS-DYNA. The investigation involved the validation for blast performance of RC column in order to identify the most effective method for modeling blasts. Additionally, the study aimed to validate the performance of RC frame models through effects of ENTA damper systems under seismic loading. Subsequently, a performance evaluation of RC frame structures was carried out to examine the impact of the ENTA damper systems when subjected to blast loading. The findings of the study indicate that the use of external ENTA damper systems effectively enhanced the rigidity and structural integrity of RC frames, while maintaining their ability to resist deformation. Finally, the damage assessment of blast and seismic performance is investigated based on various parameters such as ductility, drift and energy-based damage limits.
•Finding the suitable model blasts based on the blast performance of RC column.•Validating performance of the RC frame models under seismic loading.•Investigating the blast performance of RC frame and retrofitted RC frame.•Considering the damage performance of RC frames under blast and seismic loadings.
Field investigation revealed that soil liquefaction occurred in seasonal freezing regions, which was frequently associated with earthquakes. Most previous studies focused on the effects of ...freeze-thaw cycles on the cyclic response of seasonal freezing soil, little attention has been given to the influence of pre-seismic history on soil liquefaction resistance. Therefore, a series of element tests were conducted on sand to explore the combined impact of freeze-thaw cycles and pre-seismic history. The test results showed that both the frost heaving ratio and thaw settlement coefficient initially increased and then stabilized after the 4th freeze-thaw cycle. The sand’s liquefaction resistance was found to improve with a small pre-seismic history (upre≤0.2), but gradually decreased with upre≥0.4. Notably, the sand exhibited the highest strength at approximately 1.3 times that of the original sample, while showing the weakest resistance at only 0.33 times that of the original. Furthermore, when sand underwent both freeze-thaw cycles and pre-seismic history, only 15% of samples showed increased resistance. These findings suggest that the influence of freeze-thaw cycles on sand liquefaction was more pronounced than the impact of pre-seismic history.
•Impact of pre-seismic load on cyclic behavior of seasonal soil is studied.•Combined effects of freeze-thaw cycles and seismic history are considered.•Dominant factor affecting liquefaction resistance in seasonal soil is revealed.•A threshold line is proposed to assess the liquefaction resistance.
This work investigates the effect of earthquakes on the stability of a collective pile subjected to seismic loads in the soil layer. Plaxis 3D 2020 finite element software modeled pile behavior in ...dry soils with sloping layers. The results showed a remarkable fluctuation between the earthquakes, where the three earthquakes (Halabja, El Centro, and Kobe) and the acceleration peak in the Kobe earthquake had a time of about 11 seconds. Different settlement results were shown, as different values were recorded for the three types of earthquakes. Settlement ratios were increased by increasing the seismic intensity; hence the maximum settlement was observed with the model under the effect of the Kobe earthquake (0.58 g), where subsidence values at the three tremors differed between the pile distribution pattern. The highest drop recorded by the results was 60 mm in a distribution pattern 2×3. In general, increasing the size of the cap leads to an additional drop due to the weight of the cap.
Under the combined action of environmental and seismic loadings, offshore wind turbines supported by tetrapod piled jacket (TPJ) foundations may experience tilting and rotational failures, and even ...the shutdown. However, there is still a notable gap in the research on the dynamic response of the TPJ system in this condition, especially in the multilayered clay deposits. This study conducts advanced three-dimensional finite element simulation to investigate the seismic response of TPJ systems in soft-over-stiff clay deposit under the combined influence of wind and wave loadings. The results indicate that with a minor strength ratio between two layers, especially for strength ratios < 0.28, the peak values of the pile bending moment envelopes increases obviously, which is located near the soil layer interface. Near the soil layer interface, a sudden expansion in the soil plastic strain can be observed at this location. When the top layer thickness is substantial, surpassing 0.75 times the pile length, the restraining effect of the bottom stiff layer on the pile results in the peak value of the acceleration response envelopes and a significant reduction in bending moment near the pile end.
The safety and reliability of wind turbines subjected to multiple loads has recently attracted great attention. To investigate how soil-structure interaction (SSI) affects the seismic performance of ...operating wind turbines, a wind tunnel-shaking table test platform has been built which can realize applying wind load and seismic load simultaneously. A 1:100-scaled wind turbine model with two different kinds of foundations (soil-structure interactive foundation and rigid foundation) has been tested under four seismic excitations (El-Centro and Taft, input in two directions) when it keeps operating in wind excitations. Nacelle displacement with the soil-structure interactive foundation was significantly larger than that of the rigid foundation, reaching 3–5 times at a peak ground acceleration (PGA) of 0.8 g. The maximum nacelle displacement of the scaled model with soil-structure interactive foundation always occurs in the direction of incoming wind, unlike the rigid one occurring in the direction of seismic input direction. The rigid foundation model presents a strong whipping effect with an acceleration amplification factor of the tower top (APF = 3). In contrast, the model with soil-structure interactive foundation shows mild whipping effect due to smaller foundation stiffness (APF of the tower top = 1.5). The study demonstrates SSI could weaken dynamic responses, reducing bending moments but inducing excessive nacelle displacement, risking structural damage. This study underscores the importance of SSI in evaluating the safety and reliability of wind turbines subjected to the wind and seismic loads and provides experimental results for future designs.
•A joint wind tunnel and shaking table test system is developed for testing scaled wind turbine in operation.•Various soil-structure interactions, wind loads, seismic loads and operation loads are considered in the tests.•Dynamic characteristics and displacement, acceleration and bending moment are measured and analysed.•Compared to rigid foundation, soil-structure interaction leads to greater displacement but less acceleration and bending moment.
This paper presents results of an experimental program in which basalt and carbon fiber-reinforced polymer (FRP) sheets are used as confining jackets to enhance the seismic performance of square ...reinforced concrete (RC) columns with inadequate transverse reinforcement. Crack patterns, failure modes, lateral hysteresis loops, displacement ductility, energy dissipation capacity and stiffness degradations of one unretrofitted column and five retrofitted columns are presented and discussed. The effects of the amount and type of FRP sheets on the seismic behavior of the retrofitted columns are also examined. Experimental results indicate that the unretrofitted column has poor ductility with brittle shear failure, while the FRP jackets are useful in enhancing the seismic resistance of the retrofitted columns and result in more stable hysteresis loops with improved energy dissipation capacity and lower stiffness degradations. The columns retrofitted with BFRP sheets have equivalent or even superior seismic performance compared to counterparts that are retrofitted with the same number of layers of carbon FRP (CFRP) sheets, and the material costs of the former are only 20% that of the latter. It has been demonstrated that the BFRP composites have promising potential for use as an alternative to conventional FRPs for seismic retrofit of square RC columns.
•Study on hybrid connections of precast concrete.•Steel bars yielding of PC beams were not achieved in the critical section.•The performance of PC2 significantly improved due to stiffening of the ...steel angles.•RC and PC2 specimens failed in flexural and PC1 failed at the steel plate yielding.•Concrete crushed did not occur in the PC specimens.
In general, precast concrete structure has insufficient ductility to resist seismic load. Detailed understanding on the behaviour of precast concrete connections are limited and current researches are focused addressing this. In this study, two precast and two monolithic concrete joints for exterior beam-to-column connection were tested under cyclic loading. The installation of precast specimens was prepared using dry type method while the monolithic joints were casted in-situ. The evaluation of seismic performance of the joints was conducted by applying hysteretic reverse cyclic loading until failure. Information regarding the strength, ductility and stiffness properties of the connection were recorded and analysed. Based on the test results and damage condition, the initial design of the joint was improved. Consequently, a new joint was constructed and tested, which exhibited a better performance. Precast concrete connections showed stable load–displacement cycles and dissipated a higher energy. The structural drift obtained was up to 9.0%. Pinching and deterioration were attained at a drift ratio of 4.5%. Also, there was improvement in the tested precast joints based on deflection, plastic hinges, crack pattern and shear deformation. Thus, the precast joints had a satisfactory resistance to seismic loads.
Earthquake-induced vibrations of wind turbines may compromise structural serviceability and safety. Most previous studies adopted passive control devices to mitigate the seismic responses of wind ...turbines. However, their control effectiveness is heavily dependent on the mass ratio between control devices and wind turbines, and they were typically housed at the tower top or within the nacelle. The restricted space within the hollow tower and the nacelle imposes considerable challenges for the implementation of such devices, rendering the application of large-scale control devices unfeasible for structural vibration control of wind turbines. To this end, this paper integrates a negative stiffness element within a conventional tuned mass damper (TMD), termed KDamper, to mitigate vibrations of wind turbine towers under seismic loads. Specifically, the widely used NREL 5 MW wind turbine is selected as a prototype structure and its tower is modelled as a multiple-degree-of-freedom system. Then KDamper is incorporated into the developed model and its parameters are optimized based on the H2 criterion. Subsequently, the control effectiveness of KDamper is investigated and compared with TMD in the frequency domain, and the control performances in terms of the effectiveness and robustness of KDamper are further examined under a series of earthquake records. Results show that KDamper has superior control effectiveness and robustness than TMD, indicating it has considerable potential for application in improving wind turbine performances against earthquake hazards.
•KDamper is proposed to control seismic responses of wind turbines.•KDampers with different negative stiffness and connecting configurations are optimized.•Control performances of KDampers are examined under a series of earthquake records.
The Open Ground Story (OGS) building is a functional need of all urban areas so cannot be eliminated. According to studies from previous earthquakes, when there is severe earthquake shaking, ...Reinforced Concrete (RC) frame buildings with open ground levels function badly. In this work, four models of G+14 RC frame buildings with and without a shear wall, coupled sheal wall, and diagonal strut were modeled and analyzed using ETABS-2018 software's static and dynamic response spectrum method. Model 1 open ground story RC building without strut and the shear wall was compared to the other three models that included a shear wall, coupled shear wall, and diagonal strut. As a result of the findings, it has been determined that shear wall, coupled shear wall, and diagonal strut not only increased the stiffness but also reduced displacement. A model with a combination of shear wall and coupled shear wall showed a minimum base shear and overturning moment than all other models.
The Open Ground Story (OGS) building is a functional need of all urban areas so cannot be eliminated. According to studies from previous earthquakes, when there is severe earthquake shaking, ...Reinforced Concrete (RC) frame buildings with open ground levels function badly. In this work, four models of G+14 RC frame buildings with and without a shear wall, coupled sheal wall, and diagonal strut were modeled and analyzed using ETABS-2018 software's static and dynamic response spectrum method. Model 1 open ground story RC building without strut and the shear wall was compared to the other three models that included a shear wall, coupled shear wall, and diagonal strut. As a result of the findings, it has been determined that shear wall, coupled shear wall, and diagonal strut not only increased the stiffness but also reduced displacement. A model with a combination of shear wall and coupled shear wall showed a minimum base shear and overturning moment than all other models.
