Concrete behavior usually degrades due to freeze-thaw cycles, fire, or both. Existing studies on the degradation behavior of concrete due to exposure to high temperatures were primarily focused on unfrozen concrete. In this paper, the degradation behavior of damaged concrete, after different freeze-thaw cycles (25, 35, 45, and 55 cycles), exposure temperatures (20°C, 300°C, 400°C, and 500°C), and cooling methods (water-cooled and air-cooled), was tested with seventy-five prism specimens. The degradation behavior of the damaged concrete, such as surface characteristics, weight loss, compressive strength, peak strains, and elastic modulus, was studied and analyzed. Results show that (i) the surface color of the concrete does not change significantly throughout the test. As the number of freeze-thaw cycles and temperatures increase, the weight loss of the concrete specimens increases gradually. (ii) After freeze-thaw cycles, the relative strengths and elastic modulus of the concrete specimens significantly degrade compared with those of the unfrozen ones at same temperatures. (c) At elevated number of freeze-thaw cycles and exposure temperatures, the peak strain of the concrete increases gradually. (d) Cooling methods have different effects on the degradation of concrete under different number of freeze-thaw cycles. Finally, a uniaxial compression constitutive model for concrete after freeze-thaw cycles and then exposure to high temperatures was established and a good agreement was observed with test results.

Ancient pagodas are prone to damage or even collapse under seismic loading due to material aging and structural characteristics. To enhance the seismic performance of ancient pagodas, a seismic-strengthening design method for retrofitting ancient pagodas with embedded glass fiber reinforced polymer (GFRP) bars is proposed. The limit values of the story drift angle of ancient pagodas are statistically analyzed to determine the story drift angles at the elastic and elastic-plastic limit points. The corresponding solutions are proposed in view of the primary problems in the seismic reinforcement design of the ancient pagoda, such as the calculation of seismic shear force, the distribution of seismic shear force, and the calculation of shear bearing capacity. The seismic fortification target for the ancient pagoda is proposed with consideration of the special requirements of cultural heritage protection. The two-stage design method is further proposed to achieve the seismic fortification target. Taking the 1/8-scale model of the Xiaoyan Pagoda with cracks as an example, the design method proposed in the paper is used to carry out the reinforcement design with embedded GFRP bars. The proposed design method can provide a theoretical basis and technical reference for the seismic reinforcement of the ancient pagoda.