Freeze-thaw cycles in seasonally frozen soil affect the boundary conditions of aqueducts with pile foundations, consequently impacting their seismic performance. To explore the damage characteristics and seismic behaviour of aqueduct bent frames in such regions, a custom testing apparatus with an integrated cooling system was developed. Two 1/15 scale models of reinforced concrete aqueduct bent frames with pile foundations were constructed and subjected to pseudo-static testing under both unfrozen and frozen soil conditions. The findings revealed that ground soil freezing has minimal impact on the ultimate bearing capacity and energy dissipation of the bent frame-pile-soil system, but significantly enhances its initial stiffness. Additionally, the frozen soil layer exerts a stronger embedding effect on the pile cap, ensuring the stability of the pile foundation during earthquakes. However, under large seismic loads, aqueduct bent frames experience greater damage and residual deformation in frozen soil compared to unfrozen soil conditions. Therefore, the presence of a seasonally frozen soil layer somewhat compromises the seismic performance of aqueduct bent frames. Subsequently, a finite element model considering pile-soil interaction (PSI) and frozen soil hydro-thermal effects was developed for aqueduct bent frames and validated against experimental results. This provides an effective method for predicting their seismic behaviors in seasonally frozen soil regions. Furthermore, based on the seismic damage characteristics of aqueduct bent frame with pile foundations observed in pseudo-static tests, a novel selfadaptive aqueduct bent frame system was designed to mitigate the adverse effects of seasonally frozen soil layer on seismic performance. This system is rooted in the principle of balancing resistance with adaptability, rather than solely depending on resistance. The seismic performance of this innovative system was then discussed, providing valuable insights for future seismic design of reinforced concrete aqueduct bent frames with pile foundations in seasonally frozen soil regions.

Integral abutment bridges (IABs) have been widely applied in bridge engineering because of their excellent seismic performance, long service life, and low maintenance cost. The superstructure and substructure of an IAB are integrally connected to reduce the possibility of collapse or girders falling during an earthquake. The soil behind the abutment can provide a damping effect to reduce the deformation of the structure under a seismic load. Girders have not been considered in some of the existing published experimental tests on integral abutment-reinforced-concrete (RC) pile (IAP)-soil systems, which may not accurately represent real conditions. A pseudo-static low-cycle test on a girder-integral abutment-RC pile (GIAP)-soil system was conducted for an IAB in China. The experiment's results for the GIAP specimen were compared with those of the IAP specimen, including the failure mode, hysteretic curve, energy dissipation capacity, skeleton curve, stiffness degradation, and displacement ductility. The test results indicate that the failure modes of both specimens were different. For the IAP specimen, the pile cracked at a displacement of +2 mm, while the abutment did not crack during the test. For the GIAP specimen, the pile cracked at a displacement of -8 mm, and the abutment cracked at a displacement of 50 mm. The failure mode of the specimen changed from severe damage to the pile top under a small displacement to damage to both the abutment and pile top under a large displacement. Compared with the IAP specimen, the initial stiffness under positive horizontal displacement (39.2%), residual force accumulation (22.6%), residual deformation (12.6%), range of the elastoplastic stage in the skeleton curve, and stiffness degradation of the GIAP specimen were smaller; however, the initial stiffness under negative horizontal displacement (112.6%), displacement ductility coefficient (67.2%), average equivalent viscous damping ratio (30.8%), yield load (20.4%), ultimate load (7.8%), and range of the elastic stage in the skeleton curve of the GIAP specimen were larger. In summary, the seismic performance of the GIAP-soil system was better than that of the IAP-soil system. Therefore, to accurately reflect the seismic performance of GIAP-soil systems in IABs, it is suggested to consider the influence of the girder.

Rammed earth building has garnered attention from researchers due to its low energy consumption and excellent thermal performance. However, addressing the issue of low seismic performance in rammed earth buildings still lacks effective solutions. This study investigated the influence of embedded steel wire mesh and bamboo reinforcement mesh on the in-plane seismic performance of rammed earth walls through pseudo-static tests. Four half-scale models of rammed earth walls were constructed, each with dimensions of 1900 mm in length, 1200 mm in width, and 250 mm in height. The experimental results were compared in terms of failure mode, hysteresis response, lateral bearing capacity, displacement, ductility, stiffness degradation, damage index, and energy dissipation capability. The peak ground acceleration (PGA) for each specimen was calculated using the N2 method to assess their seismic performance. The results indicated that both steel wire mesh and bamboo reinforcement mesh can significantly enhance the seismic performance of rammed earth walls. Finally, based on the hysteresis curves of the specimens and the strain test results of the steel wire mesh or bamboo reinforcement mesh, this study proposed a hysteretic model and lateral bearing capacity calculation formula for rammed earth walls.

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.

This paper presents the design and commissioning of a novel pseudo-static test apparatus for underground structures that accounts for soil-structure interaction by simulating the soil with suitably designed springs. The developed apparatus was employed to conduct 1:10 large scale tests on a two-story three-span prefabricated subway station structure. Two comparative cyclic load tests were conducted: one involved the developed springs-structure system; and one involved the structure alone (no springs). The test results demonstrated important differences in the damage location, damage degree, bearing capacity, and deformation capacity of the prefabricated subway station structure under the two loading conditions (i.e., with and without springs). The presence of springs (i.e., soil-structure interaction) enhanced the lateral collapse resistance of the underground structure and affected the inter-story displacement ratio (IDR) between the upper and lower layers of the two-story prefabricated subway station structure. However, it did not affect the deformation coordination of the walls and columns of each layer. A finite element model of the prototype station was also established to conduct dynamic time history analysis simulating the soil-structure interaction. The results from the dynamic analysis validated the effectiveness of the pseudo-static test method employing the spring-structure system. The excellent agreement between the calculated dynamic responses and the responses obtained from the pseudo static tests confirmed the ability of the developed apparatus to conduct seismic tests on complex large-scale underground structures such as prefabricated subway stations. Thus, this test methodology might be utilized to attain valuable insights into the seismic performance of prefabricated subway stations at a relatively low cost and effort.