Abstract:Because the conventional method of natural vibration analysis fails to make full use of the inherent symmetry of the structure, the calculation cost increases significantly when the degree of freedom of the structure increases. Based on group theory, an efficient method for analyzing the dynamic characteristics of symmetrical prestressed structures is presented in this paper. Firstly, the generalized characteristic equation of the prestressed structure is established by combining the uniform mass matrix and tangential stiffness matrix, and the influence of the initial prestress on the structure is considered to solve the natural vibration frequency and mode of the structure. Then, a symmetric coordinate system is established to decompose the stiffness matrix and mass matrix into a series of partitioned diagonalized matrices. Because each submatrix is independent of each other, the difficulty of solving the generalized eigenvalue problem is significantly reduced, and the natural frequency and corresponding mode of the structure can be efficiently solved. Numerical examples illustrate the basic calculation process and significant advantages of the proposed method. Compared with the results of finite element method and conventional method, the symmetry method based on group theory is accurate and efficient.

Abstract:In this paper, an ultra-high performance cement-based material RPC-Reactive Powder Concrete (RPC-reactive Powder Concrete) was developed to anchor multiple bundles of CFRP-Carbon Fiber Reinforced plastics (CFRP-Carbon Fiber Reinforced) Polymer) bond anchorage system of prestressed tendons. A set of CFRP strain-anchor assembly GA12-9 with 9 CFRP bars of 12.6mm diameter as prestressed tendons was fabricated, and its mechanical properties were studied by tensile test. In the experiment, the non-uniform stress characteristics of the multiple beams were observed, and finally the adhesive failure of the multiple beams occurred. It is proved that the unique non-uniformity of the group anchor specimens will reduce its bearing capacity, and the bearing capacity reduction coefficient is determined. At the same time, the prediction formulas for bond strength and critical anchoring length of single and multiple CFRP bars are determined, which are in good agreement with the test results. It has been proved that nine ribbed CFRP bars with tensile strength of about 2300MPa are used as prestressed bars, RPC with strength of 130MPa is used as bonding medium, the net distance between reinforcement is set to double the diameter of reinforcement, and the anchorage length needs 25 times the diameter of reinforcement to provide effective anchorage.

Abstract:The whole load test of 3 external prestressed concrete two-span continuous beams was carried out. The test results show that the continuous beam is in the elastic stage before the concrete cracks in the tension area under self-loading, and the measured values of the side support, the reaction force of the middle support, the bending moment of the middle span section and the middle support section are close to the calculated values using the elastic theory. The measured values of the side support reaction and the moment of the mid-span section start to deviate to the direction larger than the calculated value of the elastic theory. The measured values of the reaction force of the middle support and the bending moment of the section of the middle support deviate to the direction less than the calculated value of the elastic theory. When the tensile non-prestressed tendons in the beam yield, the deviations between the measured reaction force of the side support and the middle support and the measured bending moment of the middle span section and the middle support section and the calculated values of the elastic theory increase further, and the deviations reach the maximum when the test beam is damaged. The bending moment redistribution values of the three test beams are 12.8%, 16.9% and 14.6%, respectively. The measured values are also compared with the calculated values of bending moment redistribution in 4 different design codes. The results show that the bending moment redistribution values calculated by ACI 318-95 and GB 50010-2010 are both smaller than the measured values. The predicted values of the Canadian A23.3-M84 code are the closest to the test values, except for a beam numbered B5; The British BS8110 specification is not safe. In practical design, the bending moment redistribution of external prestressed concrete continuous beams can be calculated according to the Chinese standard formula, but the ultimate stress of external prestressed tendons must be reasonably determined.

Abstract:The chord-supported dome is composed of a single lattice shell and its lower cable rod. In order to accurately and reliably guide the actual construction of the chord-supported dome structure and ensure the smooth progress of the construction, the forward construction simulation calculation method of the chord-supported dome structure is proposed according to the principle of determining the difference between the stress-free length of each element in the initial state and the zero state. The experimental research on the tensioning of a single diagonal cable by cable is carried out using a scale model with a span of 8m Although the number of tensioning times is more, the tensioning control is more convenient and the construction simulation theory can be well verified. The experimental results show that in the process of tensioning, the theoretical calculated value of tensioning control is in good agreement with the measured value, which indicates that the proposed forward construction simulation calculation method can simulate the construction of the actual structure conveniently and accurately.