Nonlinear dynamic analyses are required to account for the structural performance of mid- to high-rise buildings and complex structures. Generally, time history analyses are carried out considering several ground motions for a certain seismic action. These analyses are often very time-consuming, mainly because of the high resolution of the ground motion signal. Therefore, performing these calculations based on lower resolution accelerograms can be very useful, especially when dealing with large sets of buildings (e.g., seismic vulnerability studies on an urban scale). In this paper, two methods for signal reduction are tested against each other: i) an open-source Fourier-based resampling implementation; and, ii) a simple reduction algorithm that preserves both the highest and lowest peaks of the signal. The experiments compare the two methods at several levels of resolution reduction and for three different accelerograms. The influence of amplitude scaling on important earthquake demand parameters (EDPs), namely, the peak floor displacements and accelerations have been studied for three reinforced concrete case study buildings modelled in OpenSees: low- (5-storey), mid- (8-storey) and high-rise (11-storey). The results allow establishing a set of criteria to choose the appropriate reduction method and level. This depends on the balance desired of computation time versus calculation accuracy. Real accelerograms without baseline corrections have been for the tests. The simple reduction algorithm method appears to capture better the accelerograms by avoiding excessive interpolation. This results in peaks and areas closer to the original signal. However, it presents greater variability in energy preservation, introducing large abrupt changes in acceleration. These large fluctuations have led to inducing significantly larger displacements in OpenSees, causing greater structural damage. The Fourier method led to better and consistent results than the reduction algorithm proposed. Resolution 50 provided a reduction in time of up to 30% and an error margin of the engineering demand parameters of around +/- 15%.

In earthquake-resistant design, the characteristics of ground motion and soil conditions play a crucial role. Soil liquefaction, a critical issue in earthquake engineering, leads to significant ground deformations, including lateral spreading, settlements, and shear strain accumulation. While extensive research has focused on single-fault rupture, the impact of multiple-fault ruptures on liquefiable soils remains underexplored. This study examines the dynamic behavior of liquefiable soils subjected to single and multiple-fault ruptures through two-dimensional nonlinear fully coupled effective stress analyses within the Open Source Earthquake Engineering System (OpenSees) framework. The seismic response of saturated sandy soils with varying relative densities is simulated by the Pressure Dependent Multi Yield Material 02 (PDMY02) model. Three seismic records (Antakya record from the 2023 Kahramanmara & scedil; earthquake, Sakarya record from the 1999 Kocaeli earthquake, and Izmit aftershock record from the 1999 Kocaeli earthquake) were analyzed to assess settlements, lateral spreading, and excess pore water pressure. The results demonstrate that multiple-fault ruptures induce more complex and severe soil responses than single ruptures. These findings enhance the understanding of soil behavior under seismic loading, emphasizing the necessity of considering multiple-fault ruptures in liquefaction analysis for improved earthquake resilience.

Rocking shallow foundations interrupt the seismic transmission path from the base of the structure and possess advantages, such as effective seismic isolation, self-resetting capabilities post-earthquake, and low costs. A numerical model of the rocking shallow foundation was developed in OpenSees (version: Opensees 3.5.0) based on field test data using numerical simulation. The effect of different parameters (column height, foundation sizes, top mass, and soil softness and stiffness) on the seismic response characteristics of rocking shallow foundations is investigated, and the seismic response characteristics of rocking shallow foundations are analyzed under the action of sinusoidal waves of different frequencies and various seismic wave types. The results of the study show that, as the height of the column increases, the bending moment decreases and settlement decreases; as the size of the foundation increases, the bending moment increases and settlement increases; as the mass of the top increases, the bending moment increases and settlement increases; and as the soil becomes softer, the bending moment decreases, and settlement increases. Inputting a sine wave that matches the structure's natural oscillation frequency may induce resonance. This phenomenon can significantly amplify the structure's vibrations; thus, it is essential to avoid external excitation frequencies that coincide with the foundation's natural oscillation frequency. Under seismic loading, the rocking shallow foundation can mitigate the bending moment in the superstructure. When the displacement ratio remains within -0.5 to 0.5 percent, the foundation settlement is minimal. However, when the absolute displacement ratio exceeds 0.5 percent, the soil exhibits plastic deformation characteristics, resulting in increased foundation settlement. This study is an important contribution to the improvement of seismic performance of buildings and an important reference for improving seismic design standards and practices for buildings in earthquake-prone areas. In the future, the seismic response characteristics of rocking shallow foundations under bidirectional seismic action will be investigated.

This paper investigates the dynamic response of a model pile-soil-bridge system subjected to seismic loading using a finite element model (FEM) developed in OpenSees. The numerical model is validated against shake table test data from a companion experimental study, which tested a piles-bridge model fabricated from organic glass. The bridge model comprised four piers, each supported by two-by-two pile groups, with edge piers featuring 60 x 60 mm rubber pads between the pier and deck. Two earthquake ground motions, El Centro and Tianjin, were applied at three intensity levels. The calculated and measured responses show good agreement. The validated FEM reveals that the El Centro earthquake typically induces higher acceleration and moment responses in structural elements compared to the Tianjin earthquake, while the Tianjin earthquake results in greater displacement responses. These findings highlight the impact of earthquake wave characteristics, such as predominant period, on the bridge system's response. Furthermore, the bending moments at the pier top for edge piers remain relatively consistent across different earthquake motions and intensity levels, indicating the role of rubber pads in mitigating seismic forces in the piers.

Kathmandu, located in a high seismic zone, predominantly features irregular structures among its building stock. These structures are particularly susceptible to severe damage during seismic events, primarily due to torsional effects. Traditional seismic designs rely particularly on fixed -base conditions that underestimate forces and displacement primarily on soft soil conditions leading to irrational design practices. This study aims to quantify the seismic performance of buildings on various base conditions through fully nonlinear Soil -structure Interaction (SSI). The soil nonlinear behaviour was modelled using the Pressure-Independ-Multi-Yield (PIMY) material with an octahedral shear stress -strain backbone curve. Three distinct soil types were considered, and structures with irregular plan configurations were modelled using finite elements in both Opensees and STKO platforms. Structural performance was analyzed through nonlinear dynamic analysis, and outputs were evaluated based on seismic parameters. Comparing nonlinear SSI with linear SSI and fixed -base conditions revealed a significant increase in structural response, expressed in terms of displacement, drift ratio, and base shear. The magnitude of diaphragm rotation was found to be influenced by a combination of building torsional irregularity and SSI effects. It is suggested that the conventional practice of using the torsional irregularity ratio as a measure of torsional irregularity be revised and enhanced to better account for these influences. It has been quantified that torsional irregularity has a relatively lesser impact on displacements, drifts, and base shear compared to SSI. In all cases, fixed -base conditions consistently exhibited the minimum response. The study explored that linear SSI and fixed -base conditions tend to underestimate structural responses, while nonlinear SSI coupled with dynamic analysis provides a more accurate representation of realistic structural behaviour for seismic design particularly in soft soil cases.

The pounding between two structures may cause severe damage, as demonstrated during historical seismic events. In particular, the effects of the continuity between the foundations below two structures have been investigated a few times in the past literature. Two different configurations (continue and non -continue foundations) have been investigated herein by considering several low-rise buildings. In order to consider the effects of Soil Structure Interaction (SSI) between the structures, the foundation, and the soil, a deformable soil below the foundations was considered. 3D Numerical simulations have been performed with Opensees by considering the SSI non -linear mechanisms of the complex system: soil-foundation-structure. A parametric study on the dynamic characteristics (fundamental periods) of the two structures was performed in order to assess the mutual effects of the soil and the considered low-rise buildings. It was demonstrated the role of continued foundations, whether for existing or new buildings, on reducing the pounding risk between structures. In particular, the collision between the two foundations may significantly increase the response of the building, depending on its flexibility. Also, the level of stress in the soil depends on the pounding forces causing significant increases in the structural deformations.

Given the horizontal low cycle reciprocating motion of the integral abutment bridge pile foundation under cyclic loading of temperature, the traditional reinforced concrete (RC) pile cannot be applied to accommodate the large longitudinal deformation appropriately because of its significant lateral stiffness and its weak cracking resistance; the surface area of the H-shaped steel (HS) pile is small, it cannot provide enough friction in deep soft soil areas, and due to its high cost and easy buckling during pile driving, it is not suitable for domestic popularization. This paper proposes a new concept of composite stepped pile consisting of HS and rectangular RC piles, the RC pile in the lower provide sufficient friction, reduce the length of the pile to save materials, and the stability is also good; the HS pile in the upper has good horizontal compliance, which can meet the horizontal deformation requirements of the integral abutment bridge. Pseudo-static tests of model piles were carried out of one HS pile and two HS-RC stepped piles with different stiffness ratios of 0.25 and 0.5. The test results show that the cracking displacements of HS-RC (0.25) and HS-RC (0.5) stepped piles are 10 similar to 15 mm and 5-8 mm, respectively, and the corresponding cracking loads are 4.66-5.99 kN and 3.22-4.52 kN, indicating the stepped pile with a smaller stiffness ratio has a stronger crack resistance; The HS-RC stepped pile has larger plastic deformation capacity, and its initial stiffness of pile-soil system is smaller, 0.48 times and 0.57 times that of RC piles, respectively, and can be applied to integral abutment bridges. Based on these tests, a finite element (FE) model using OpenSees software was validated and used for a detailed numerical simulation analysis considering the pile-soil interaction of HS-RC stepped piles. Simulating the low-cycle reciprocating motion of full-scale stepped piles under the control of displacement loads, the effects of stiffness and length ratios on the load-bearing performance of stepped piles were studied and analyzed. The FE simulation found that the stepped pile's crack resistance can be improved by reducing the stiffness of the HS pile's upper section. Still, the stepped pile's horizontal load-bearing capacity (deformation) is very low if the stiffness is unreasonably small. Furthermore, increasing the upper HS pile length cannot significantly change the horizontal load-bearing capacity of the stepped pile because the deeper pile below the inflection point will not significantly take part in the bending deformation. According to the simulation, the theoretical optimum ratio is 0.33. With the practical construction and soil property variance, it is recommended that the length ratio of the stepped pile be around 0.33 to 0.5.

In recent decades, research on renewable energy has been boosted by the emerging awareness of energy security and climate change and their consequences, such as the global cost of adapting to the climate impacts. Both onshore and offshore wind turbine farms have been considered as one of the main alternatives to fossil fuels. Their development currently involves seismic-prone areas, such as the Californian coastline and East Asia, where the risk of soil liquefaction is significant. Onshore wind turbines (OWTs) typically are founded on shallow rafts. Their operation can be affected strongly by the simultaneous presence of intense earthquakes and wind thrust, which may cause remarkable permanent tilting and loss of serviceability. In these conditions, accurate evaluation of the seismic performance of these structures requires the development of well-validated numerical tools capable of capturing the cyclic soil behavior and the build-up and contextual dissipation of seismic-induced pore-water pressures. In this paper, a numerical model developed in OpenSees, calibrated against the results of dynamic centrifuge tests, was used to evaluate the influence of some ground motion intensity Measures of the seismic behavior of OWTs included the amplitude, frequency content, strong-motion duration, and Arias intensity (energy content) of the earthquake, together with the effect of a coseismal wind thrust, which is not well explored in the literature. The seismic performance of an OWT was assessed in terms of peak and permanent settlement and tilting, the latter of which was compared with the threshold of 0.5 degrees typically adopted in practice.

The dynamic behaviour of saturated coarse-grained soils has recently received wide attention because of its impact on the seismic performance of geotechnical and structural systems. This is due to the peculiarities of their cyclic response (e.g., liquefaction, ratcheting and volumetric-deviatoric coupling). Consequently, the seismic risk mitigation of the built environment requires efficient predictive models applicable in design and assessment. To this end, several constitutive models have been developed for a realistic description of the cyclic soil behaviour. From this perspective, this paper describes the implementation and testing of the bounding surface plasticity model developed by Papadimitriou and Bouckovalas (2002) in OpenSees as a means for advanced assessment of soil-structure systems. The implemented model includes essential features of the cyclic soil response. Moreover, a modified fabric tensor evolution equation is introduced for improving the response and numerical stability in boundary value problems, at the cost of an extra model constant. The workflow concerning the integration of the model into OpenSees is presented, followed by instructions about its use in boundary value problems. A comprehensive verification of the model response is discussed. The numerical simulations demonstrated the robustness of the implemented code in capturing soil behaviour from small to large strain levels.