GENERALIZATION OF THE METHOD OF FULL APPROXIMATION AND ITS APPLICATIONS

This paper presents a generalized form of the method of full approximation. By using the concept of asymptotic linearization and making the coordinate transformations including the nonlinear functionals of dependent variables, the original nonlinear problems are linearized and their higher-order solutions are given in terms of the first-term asymptotic solutions and corresponding transformations. The analysis of a model equation and some problems of weakly nonlinear oscillations and waves with the generalized method shows that it is effective and straightforward.

MODIFICATON AND RESEARCH ON BENDING RIGIDITY FORMULA OF REINFORCED CONCRETE BEAM

Beam stiffness degrades with its age in service and its service performance is weakened.According to the fundamental characteristics of the reinforced concrete,the influence of stiffness degradation caused by different kinds of damage is obtained.Among them,the crack is the most direct and obvious factor.Furthermore,according to the analysis of bending rigidity formula presented in current standard,an influence parameter of crack development on the stiffness degradation,i.e.,nonuniformity coefficient of tensile steel strain φ,is extracted.Average crack distance and crack depth are taken as crack statistic parameters.Based on analysis and modeling with ANSYS,the modified bending rigidity formula related to crack is obtained.

EFFECTIVE WIDTH AND DISTRIBUTION COEFFICIENTS OF MOMENT IN RC CONTINUOUS SLABS

Using effective width of load and distribution coefficient of moment is a kind of simplified method in the design of continuous reinforced concrete slabs, which is widely used in engineering design. In this paper, through the analysis of load-bearing states of continuous slabs restricted by the main beams under concentrated loads, the effective width of load and distribution coefficients of moment of a continuous slab are obtained with the principle of equivalent loads. On the basis of the data of a 5-span continuous reinforced concrete slab, the formula of effective width is deduced and the distribution coefficients of moment for the mid-span and supports are given.

APPLICATIONS OF STOCHASTIC FEM BASED ON THE LOCAL AVERAGE OF RANDOM FIELD IN RANDOM EIGENVALUE PROBLEMS

This paper applies stochastic finite element method based on the local average of random field to analyze random eigenvalue problems. The local average of homogeneous random vector field is briefly introduced. The formulae for the means and covariances of random eigenvalues and eignevectors of stochastic structures are derived by using second order perturbation method. The numerical results are given to show better convergence with respect to element number in the present method than that in Nakagiri's method.

Load Transferring Mechanism on Transition Section of Composite Bucket Foundation for Offshore Wind Turbines

The composite bucket foundation (CBF) is a new kind of foundation which has been applied in the offshore wind industry. A reasonable connection pattern between the tower and the CBF top cover is crucial for load transmissions from the superstructure. Therefore, it is essential to choose an optimum structure type for the transition section. The line type and the arc transition section models were established by ABAQUS, and the internal forces of cross section were extracted along the height direction. Specifically, the force transfer mechanism for different types of the transition sections was investigated comparatively with monotonic as well as composite loadings. The results show that the curved transition structure exhibits the better mechanical characteristics under the monotonic and composite loadings, and the reason can be illustrated that its specific arc-shape structure can effectively convert the tremendous bending moment from the turbine tower into the limited tensile and compressive stresses downwards, without the occurrence of force concentration. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Flexural Capacity Formula of Diaphragm-Through Joints of Concrete-Filled Square Steel Tubular Columns

Finite element analysis and parametric studies were performed to investigate the flexural capacity of the panel zone of diaphragm-through joints between concrete-filled square steel tubular columns and H-shaped steel beams. Through the comparisons of failure modes, load–displacement curves, and bearing capacity, it was found that the flexural capacity of the panel zone of diaphragm-through joints was determined by the tensile action and influence of the web of H-shaped steel beams, and the axial load should be taken into account. The steel tube and the diaphragm were the major parts of the joint that resisted the bending moment. The contribution of in-filled concrete had little influence on the flexural capacity of the panel zone of the joint and could be neglected. According to the results of these numerical studies, a formula that considered the influence of the web of H-shaped steel beams and the axial load was developed based on the yield lines in the diaphragm and the steel tube. The results of the proposed formula were in good agreement with the numerical data of this investigation. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Influences of Installment Tensioning Technology on Bearing Capacity of Rectangular Prestressed Concrete Beam

To obtain the relationship between use of installment tensioning technology and the bearing capacity of prestressed concrete beams, tensile and cyclic loading tests are conducted on five rectangular prestressed concreted specimens. Two types of prestressed tensioning methods are adopted in the tests, one uses installment tensioning technology to tension beams on days 4, 12, and 8, 12, respectively, and the other adopts the conventional method to tension the beam on day 28 only. The age of concrete, number of times tensioned, and the prestress value of early tensioning are considered in tests. Results show that use of installment tensioning technology has no effect on the bending failure pattern of prestressed concrete beams, but it reduces prestress loss and increases crack and yield loads. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

High spatial resolution sensing by using stepped pump light and its experimental validation

The spatial resolution of conventional distributed fiber optic sensors is 1 m at best, which is inadequate to locate the damage precisely. We adopt an improved sensing technique based on the Brillouin optical time-domain analysis （BOTDA）. The stepped pump light is input to stimulate the phonon so that the spatial resolution can be increased to centimeter order and the strain accuracy of 25 micro-strains is obtained. The feasibility of this sensing technique is demonstrated through strain measurement of three concrete box-girders in bending. Experimental results show that the improved BOTDA measurement can provide a comprehensive description on the strain distribution of steel rebar or concrete. Compared with the conventional strain gauges, the improved BOTDA measurement is more stable. By virtue of higher spatial resolution and better measurement accuracy, it has become possible to perform crack detection and localization for concrete structures.