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A superior seismic strengthening technology should be not only secure and reliable, but also economical and feasible for the widespread structures. In China, the gravity pier with low longitudinal steel ratio has been widely used in railway bridges, and most of them have insufficient seismic performance due to limited technological level in the early days. In this study, a novel preventive seismic strengthening technology with steel grid by planting and welding measures was presented for gravity railway bridge pier with flexural failure modes. Five 1/8-scale piers, including two different reference piers and three strengthening piers, were fabricated and tested through quasi-static test. It was shown that the piers exhibit uplifting and swaying behaviors due to highly-centralized crack at pier-footing region under lateral loading. The strengthening using steel gird led to a reduction up to 50% in residual displacement approximately, which was effective to prevent collapse of piers. The strengthening piers exhibited an enhanced the load-carrying capacity and cumulative dissipated energy by 120% to 150%, compared to the pier without strengthening. Moreover, the initial stiffness and cracking load of strengthening piers also were improved where the maximum increment was 1.5 times. The effect of strengthening thickness on strengthening efficiency was more significant than that of strengthening height. Therefore, it could be concluded that the seismic strengthening technology, by steel grid with reasonable arrangement at the pier bottom region, are suitable for gravity railway bridge pier with low longitudinal steel ratio in seismic zones.

Ground seasonal freezing and thawing in cold regions can alter boundary conditions of bridge pile foundations and influence their seismic behaviors. This article describes a test apparatus with a custom-designed cooling system for investigating the seismic behavior of pile foundations in seasonally frozen ground. Two 1/8-scale models of a reinforced concrete bridge pier with pile foundations were fabricated for conducting quasi-static tests under unfrozen and frozen conditions. Test observations and data were used to analyze failure characteristics of pile foundation subjected to cyclic lateral loading under the two conditions and reveal the frozen soil effects. It was found that ground freezing greatly enhanced the loading carrying capacity while partly weakened the deformation capacity of the pile-soil system. It is not easy to fail if upper layer soil was frozen, and the frozen soil layer shifted the pile failure zone upward compared with the unfrozen condition. The strength degradation was obvious in the pile-soil system under frozen condition due to the fracture of the steel bar. Furthermore, the pile foundation in frozen soils exhibited more stable and reliable energy dissipation than the pile foundation in unfrozen soils under large seismic load, which was attributed to the severe damage of the pile foundation in frozen soils. A simplified force–displacement model was proposed for the pile-soil system under unfrozen and frozen conditions based on the testing results. These results can provide references for seismic design of reinforced concrete pile foundations in cold regions.

A double-spring model for rocking isolation of tall piers with pile foundations, restoring force curve and the spring stiffness are proposed. Rocking isolation for bridges with tall piers are analyzed by using nonlinear time-history method, and the results are compared with those obtained by using concentrated rotational springs which are more simplified. The results show that the vibration period is not fixed after rocking and uplift of the pier, the anti-overturning moment is very close to the peak moment at the bottom of piers with the effect of rocking isolation is stable, and less affected by input ground motions. Displacement-time curve of the top of the pier and the moment at the pier bottom, obtained by using double-spring model is close to those obtained by using concentrated rotational-springs model, which are more simplified.

During an earthquake, the nonlinearity of the bridge structure mainly occurs at the supports, bridge piers and restrainers. When entering nonlinear stage, members of the bridge structure affect the elasto-plastic seismic response of the whole structure to a certain extent; for multi-span continuous bridges, longitudinal restrainers can be installed on the movable piers to optimise the distribution of seismic force and enable the movable piers to bear a certain amount of seismic effect. In order to evaluate the effect of nonlinearity of restrainer and supports on the elasto-plastic seismic response of continuous girder bridge, analytical models of continuous girder bridge structure considering the nonlinearity of movable supports, restrainers and bridge piers were built and the nonlinear time history analysis was conducted to evaluate the effect of nonlinearity of restraining devices and supports on the elasto-plastic seismic response of continuous girder bridge. Relevant structural measures and recommendation were made to reduce the seismic response of the fixed piers of the continuous girder bridge.

An extra-dosed cable-stayed bridge is taking as the practical engineering background to make the finite element nonlinear analysis of a section of reinforced concrete of the main tower by large software Ansys in this paper. Concrete cracking and crushing were considered, obtained the ultimate load of test model can bear as well as the stress-strain relationship of its steel and concrete, and draw a diagram of concrete crack distribution, when the value of concrete of the model to withstand the horizontal splitting stress, the bottom and top of the concrete of the saddle appeared signs of crack at the same time. The maximum compressive stress uniform distribution in the bottom area of the saddle and did not meet the design value of compressive strength, tensile stress first reached the limits of state.