Existing studies have proved that the incorporation of polypropylene fiber can effectively improve the impact resistance of concrete. In this paper, the split Hopkinson pressure bar and digital pulse shaping technology are used to further study the dynamic compression performance and constitutive relationship of concrete in the cold regions under the deteriorating effect of freeze-thaw cycle, and obtain the dynamic increase factor. Studies have shown that polypropylene fiber-reinforced high-strength concrete has a strain rate enhancement effect. The number of freeze-thaw cycle times at low strain rates has an obvious effect on concrete deterioration, and the effect is weaker at higher strain rates. By comparing three typical dynamic strength growth factor models with the test results, after revising the model, the dynamic increase factor equations under different freeze-thaw circulation times were fitted. This research provides a basis for the design of durability and robustness of building structures in cold regions.

Taking a concrete-filled steel tube (CFST) arch bridge with a clear span of 400 m as an example, the in-depth analysis of its natural vibration characteristics is carried out by establishing a finite element model. Then, the three-dimensional El Centro recorded wave after amplitude modulation is taken as the excitation wave; the structural response under three kinds of single dimension and four kinds of multidimensional combined excitation and 0∼90° transformation X(longitudinal) + Y(transverse) orthogonal combined excitation is evaluated. The results show that the structure of long-span top-supported arch bridge extends in the longitudinal and vertical dimensions at the same time, and the mode shape density and mass distribution have multidirection and multiangle coupling. With the increase of excitation dimensions, the value and relative ratio of chord axial force increase. The maximum axial force ratio of X + Y to X and Y is 2.1, the maximum axial force ratio of X + Y + Z (longitudinal) to X + Y, X + Z, and Y + Z is 1.4, 1.8, and 1.8; the displacement in X and Y direction under combined excitation is independent and the displacement in Z direction is its coupling term, but the displacement under X + Y + Z combined excitation is only 10% larger than that under X + Z and Y + Z combined excitation. Under the combined excitation of X + Y with a changing angle of 0°∼90°, the axial force variation of the chord at different positions and on the same section of the arch rib has spatial characteristics. The variation range of upper and lower rod axial force varies from 0.63 to 1.35 and from 0.81 to 1.51, respectively, the change trend of displacement in the X and Y directions is relatively consistent, the change of displacement in the Z direction is asynchronous, and the displacement of vault section increases by one time. The seismic response of this bridge type under multidimensional and multiangle excitation shows obvious superposition.

The effects of processing parameters on deformation behavior of a new near β titanium alloy were investigated by using compression tests. The experiments were carried out in the Gleeble-3800 thermal and mechanical simulator in the temperature range of 770-970°C and strain rate range of 10-3-10s-1, and height direction reduction of 70%. The results show that the flow stress of Ti-7333 titanium alloy increases obviously with the strain and reaches a peak, then decreases to a steady value. The steady and peak stress significantly decreases with the increase of deformation temperature and decrease of strain rate. The flow stress model of Ti-7333 titanium alloy during high temperature deformation was established by using the regression method. The average relative difference between the calculated and experimental flow stress is 6.33%. The flow stress model can efficiently predict the deformation behavior of Ti-7333 titanium alloy during high temperature deformation.

To analyze the causes of failure of cubic concrete test specimens under quasistatic axial compression, microtests and finite element numerical simulation of C40 cubic concrete test specimens were conducted without the freeze-thaw cycle and with 50 freeze-thaw cycles. Based on the analysis of the microstructure of concrete, the variation law of the full curve of stress and strain was analyzed by the uniaxial compression test and the splitting tensile test of concrete. The results show that freeze-thaw damage is mainly caused by the cyclic reciprocating stress of the micropore structure inside the concrete. The peak stress of concrete uniaxial compression and splitting tensile strength gradually decrease with the number of freeze-thaw cycles; the full stress-strain curve tends to shift downward and to the right. Finite element analysis shows that under the quasistatic uniaxial compression loading condition, the stress and strain fields in the test specimens are symmetrically distributed but nonuniform. The plastic deformation of the concrete weakens the nonuniformity of the stress distribution and is closer to the experimental failure morphology.