This paper proposes a carbon fiber reinforced polymer (CFRP) retrofitting scheme for improving the seismic performance of atrium-style metro stations (AMS). Past experimental studies have confirmed that the weakest of the AMS during strong earthquakes is located at the upper-story beam ends. However, there is thus far no candidate for a reference approach to retrofitting and strengthening the AMS. This study addresses this gap by applying CFRP retrofitting to both ends of the upper-story beam. The main objective is to assess the effectiveness of the proposed retrofitting scheme. First, a three-dimensional finite element model is developed to simulate dynamic soil-AMS interaction. The validity of the numerical method is assessed via a comparison with measured data from reduced-scale model tests. Second, a numerical model of the AMS retrofitted with CFRP is built using validated methods. Finally, dynamic time-history analyses of the AMS with and without CFRP retrofitting are conducted, and their dynamic responses, including inter-story drift, dynamic strain, and tensile damage, in conjunction with the lateral displacement of the surrounding ground, are compared. Comparison of the results for the non-retrofitted and retrofitted structures shows that CFRP retrofitting significantly reduces both the principal strains and tensile damage factors at the upper-story beam ends while slightly increasing those values at the mid-span of the beam; additionally, it does not change the structural lateral deformation. Therefore, it can be concluded that CFRP retrofitting could effectively improve the seismic performance of the AMS without changing its lateral stiffness.

With the widespread application of deep excavation projects, deformation control of diaphragm walls and management of surrounding soil displacement have become major challenges in the engineering field. To address these issues, this study proposes a prefabricated multi-limb composite concrete-filled steel tube (CFST) internal support system. The mechanical performance and deformation characteristics of the fixed ends of the system were systematically analyzed through axial compression tests and numerical simulations.First, based on the CFST stress-strain model, the constitutive model was modified to account for the effects of stiffening ribs, and a stress-strain relationship model for mold bag concrete was introduced. The simulation results demonstrate that the modified model can accurately predict the stress behavior of the fixed ends. Next, to characterize the overall mechanical response of the structure, a load-displacement relationship model was established. This model, which is closely related to the CFST strength grade, effectively captures changes in the structural performance.The results indicate that during loading, the CFST internal support system exhibits good stiffness and load-bearing capacity. With an increase in the concrete strength grade, the yield load increases by 12 %, and the ultimate strain decreases by 27.76 %, significantly enhancing the mechanical performance of the structure. This study not only deepens the understanding of the design principles for CFST internal support systems but also introduces new theoretical frameworks and calculation methods, providing strong support for engineering design with broad application prospects.

On 1 January, 2024, a moment-magnitude 7.6 earthquake hit Ishikawa Prefecture, located on the main island of Japan facing the Japan Sea. Tsunami followed the strong shaking, and the maximum inundation height was 5.1 m in Shika Town. Strong shaking in Wajima City resulted in widespread damage to buildings and a fire that burnt the Wajima Morning Market. As of 16 February, 241 casualties had been reported, and 42% of them were due to building collapses. In response to all the described damage, a joint field investigation was conducted by Japan and New Zealand. This paper provides an outline of the earthquake and the damage observed in the affected area.

Underground structures with large openings (USLO), especially those that allow natural light and fresh air, have emerged as alternatives to mitigate the weaknesses of traditional underground frame-box structures. For the USLO, two ends of the upper-story beam are generally recognised as weakest regions during strong earthquakes; however, insufficient attention has been paid to improving their seismic safety. This study performed a detailed numerical comparison of the conventional USLO and beam-end horizontal haunch retrofitting USLO under different seismic intensities, and evaluated the effectiveness of the proposed retrofitting scheme. The finite element numerical modelling approach was validated against shaking table test results, where the numerical results were in good agreement with measured data. Based on the validated numerical methods, the two ends of the upper-story beam in the conventional USLO were strengthened with horizontal haunches. Both soil-structure systems were excited by equal earthquake loads. Various seismic responses were compared between the conventional and retrofitted USLO, including structural strain, tensile damage, and story drift. Numerical simulation results indicate that beam-end horizontal haunch retrofitting significantly reduces the tensile strain and maximum damage degree at the ends of the upper-story beam, as well as the upper-story drift, without changing the lower-story drift. Therefore, beam-end horizontal haunch retrofitting is a potentially effective measure for improving the seismic performance of the USLO.

Seismic retrofitting of existing bridges has been in practice for years to meet the stringent seismic requirements set forward by revised design codes. For retrofitting, however, bridge piers are often prioritized while less attention is given to the bridge foundations, which are equally prone to damage under seismic loadings. The current work presents a series of experimental studies in assessing the performance of 2 x 2 pile groups reinforced with micropiles in terms of head-level stiffness and damping under low-to-high levels of static and dynamic loadings, encompassing the influence of loading-induced soil nonlinearity. Practical micropiles inclinations of 0 degrees, 5 degrees, and 10 degrees with respect to the vertical are studied. Experimental results reveal that the head-level stiffnesses of pile groups reinforced with micropiles, contrary to the general expectations, become smaller than the pile group without micropiles at higher levels of applied loading. To elucidate the governing mechanism for such experimentally obtained results, three-dimensional nonlinear finite-element analyses were carried out. Results from the numerical analyses support the experimental results, suggesting that the presence of micropiles may not always increase the head-level stiffness of soil-foundation systems, particularly at higher levels of applied loading where the soil nonlinearity generated at the vicinity of piles and micropiles governs the overall head-level stiffnesses.

A series of numerical simulations were completed to investigate the behavior of intact, fire -damaged, and Carbon Fiber -Reinforced Polymers (CFRP) retrofitted reinforced concrete (RC) bridge columns of varying sizes subjected to vehicle collisions. Three-dimensional finite element models of isolated RC columns and their foundation systems surrounded by soil volumes were developed using LS-DYNA. A comprehensive parametric study was carried out to investigate the effects of nine demand and design parameters on the performance of bridge columns. Studied parameters included: column diameter, column height, unconfined compressive strength, steel reinforcement ratio, fire duration, CFRP wrap thickness, wrapping configuration, vehicle 's mass, and vehicle 's speed. For each studied scenario, Peak Twenty-five Milli -second Moving Average ( PTMSA ) was employed to estimate the Equivalent Static Force ( ESF ) corresponding to each vehicle collision scenario. Resulting ESF s were then utilized to assess effectiveness of the current ESF approach available in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design ( AASHTO-LRFD ) Bridge Design Specification for analyzing and helping design bridge columns under vehicle collision. Multivariate nonlinear regression analyses were used to derive an empirically based, simplified equation to predict the ESF that corresponds to a vehicle collision. Rather than constant design force, this equation established a correlation between ESF and kinetic energy, column axial capacity, and column height. Results indicated that the proposed equation is reliable and can accurately predict ESF s over a diverse range of collision scenarios that included intact, fire damaged, and CFRP retrofitted columns. To facilitate realistic implementation of the derived equation, an ESF assessment framework was also devised.

This paper presents an experimental and analytical study on a steel slit damper designed as an energy dissipative device for earthquake protection of structures considering soil-structure interaction. The steel slit damper is made of a steel plate with a number of slits cut out of it. The slit damper has an advantage as a seismic energy dissipation device in that the stiffness and the yield force of the damper can be easily controlled by changing the number and size of the vertical strips. Cyclic loading tests of the slit damper are carried out to verify its energy dissipation capability, and an analytical model is developed validated based on the test results. The seismic performance of a case study building is then assessed using nonlinear dynamic analysis with and without soil-structure interaction. The soil-structure system turns out to show larger seismic responses and thus seismic retrofit is required to satisfy a predefined performance limit state. The developed slit dampers are employed as a seismic energy dissipation device for retrofitting the case study structure taking into account the soil-structure interaction. The seismic performance evaluation of the model structure shows that the device works stably and dissipates significant amount of seismic energy during earthquake excitations, and is effective in lowering the seismic response of structures standing on soft soil.

Geotechnical seismic isolation (GSI) is a new category of low-damage resilient design methods that are in direct contact with geomaterials and of which the isolation mechanism primarily involves geotechnics. Various materials have been explored for placing around the foundation system in layer form to facilitate the beneficial effects of dynamic soil-foundation-structure interaction, as one of the GSI mechanisms. To reduce the thickness of the GSI foundation layer and to ensure uniformity of its material properties, the use of a thin and homogeneous layer of high-damping polyurethane (HDPU) was investigated in this study via centrifuge modelling. HDPU sheets were installed in three different configurations at the interface between the structural foundation and surrounding soils for realising GSI. It was found that using HDPU for GSI can provide excellent seismic isolation effects in all three configurations. The average rates of structural demand reduction amongst the eight earthquake events ranged from 35 to 80%. A clear correlation between the period-lengthening ratio and the demand reduction percentage can be observed amongst the three GSI configurations. One of the configurations with HDPU around the periphery of the foundation only is particularly suitable for retrofitting existing structures and does not require making changes to the structural systems or architectural features.

Unpreventable constructional defects are the main issues in the case of steel Moment-Resisting Frames (MRFs) that mostly occur in the rigidities of beam-to-column connections. The present article aims to investigate the effects of different rigidities of structures and to propose Infill Masonry Walls (IMWs) as retrofitting strategy for the steel damaged buildings. A fault or failure to meet a certain consideration of the soil type beneath the building and the current rigidity of connections can cause mistake in determining the performance of building. Therefore, this study comprehensively explores different conditions of soil types, connection rigidities, and implementing IMWs on the 3-, 5-, 7-, and 9-story MRFs. Two nonlinear analyses, namely Nonlinear Dynamic Analysis (NDA) and Incremental Dynamic Analysis (IDA) were performed on 384 steel MRFs having different conditions of defects and the results of the analysis include 3456 performance curves assuming three ground motion subsets recommended by FEMA P695. The results confirm that the proposed retrofitting procedure can effectively improve the performance levels of MRFs, which the connections rigidity of 90 %, 80 %, 70 %, 60 %, and 50 % can reduce the collapse performance level by 2.86 %, 5.35 %, 9.31 %, 16.56 %, and 34.65 %, respectively.

Seismic fragility analysis is an effective method to evaluate the seismic performance of retrofitted wharf systems affected by the uncertainty of soil-cement strength. Nevertheless, fragility analysis usually consumes a large consumption of computational power. In this study, seismic fragility analysis using the artificial neural network (ANN) for the retrofitted wharf, considering the aleatory uncertainty of soil-cement strength and the epistemic uncertainty of the ANN, is carried out; On this basis, the fragility surface for two types of damage limit states considering the uncertainty of soil-cement strength is obtained. It was found that: (1) overall, the soil-cement strengthening strategy is effective for improving the seismic safety of wharf systems, however, the strengthening effect is limited, especially under strong earthquakes, will be further weakened; (2) ANN can effectively predict the maximum seismic response of retrofitted pile-supported wharves, so as to quickly carry out seismic fragility analysis. Examples show that the prediction method has good generalization; and (3) the fragility surface model considers the aleatory uncertainty of soil-cement strength and the epistemic uncertainty of the ANN, which makes the performance-based evaluation of retrofitted pile-supported wharves more comprehensive.