Advanced Materials Research Vols. 243-249

Abstract: Nondestructive testing (NDT) is a technique to determine the integrity of a material, component or structure. The commonly NDT methods used for the concrete are dynamic modulus of elasticity and ultrasonic pulse velocity. The dynamic modulus of elasticity of concrete is related to the structural stiffness and deformation process of concrete structures, and is highly sensitive to the cracking. The velocity of ultrasonic pulses travelling in a solid material depends on the density and elastic properties of that material. Non-destructive testing namely, dynamic modulus of elasticity and ultrasonic pulse velocity was measured for high strength concrete incorporating cementitious composites. Results of dynamic modulus of elasticity and ultrasonic pulse velocity are reported and their relationships with compressive strength are presented. It has been found that NDT is reasonably good and reliable tool to measure the property of concrete which also gives the fair indication of the compressive strength development.

Abstract: The maximum and residual deformations of structures subjected to strong ground motions are the most importance indexes, particularly under the performance-based design framework, thus understanding the influencing factors is of great importance to seismic design. In this study, single degree of freedom (SDOF) systems with varying structural properties are analyzed using a series of strong ground motions from FEM/SAC project. The influences of three structural parameters, i.e., yield force, second stiffness after yielding, and stiffness degradation, on the maximum and residual deformations are investigated based on the statistics of the analysis results. The analysis results suggest the follows: (1) larger yield forces lead to smaller residual and maximum deformations for short period structures, and they lead to smaller residual deformations but no necessarily smaller maximum deformation for intermediate and long period structures; (2) larger second stiffness lead to smaller residual and maximum deformations for short period structures, and they lead to smaller residual deformations but no necessarily smaller maximum deformation for intermediate and long period structures; (3) smaller stiffness degradation index leads to smaller maximum deformations but larger residual deformations.

Abstract: In order to master the indoor thermal environment of the traditional dwelling houses in dry hot and dry cold climate zones in winter, the east Gansu province is taken for example to study. Indoor and outdoor air temperature, relative humidity, solar radiation intensity and wind speed were obtained by using field-tested methods for the traditional dwelling houses in this region in winter, and the clothing form and activity of people were surveyed by way of questionnaire. And then, the influence of house orientation, indoor heat sources and insulation on the indoor thermal environment is analyzed, the WCI (wind chill index) is used to evaluate the indoor and outdoor thermal environment at last. The results show that: the indoor temperature can raise about 8.3 °C when the house orientation is better and Chinese kang as the heating heat source. The good practice on local structure is worthy of following for other houses, such as adobe posted solid brick wall, double windows, wooden sash windows and so on. However, people still feel very cool or cold about the indoor temperature for much of the day, and even people feel very cold for 5% of the day. At the end of thesis, some methods about the indoor thermal environment improvement are proposed.

Abstract: Based on the principle of precise integration method, for DOF and MDOF system, it is supposed that external loads are in linear regular within small discrete time. In further, a identification method of dynamic loads are proposed. And two real ice loads are used to study the new method. The results of numerical examples indicate that the precise integration method, with better steady and capability of resisting noise, are applicable for both steady or random loads. Otherwise, it can save more time for calculation and can be applied in real engineering.

Abstract: In order to analyse seismic behaviors of the haunched beam-shaped transfer floor, carried out the pseudo static testing, which were subjected to vertical loads and horizontal cyclic loads, respectively on two specimens, including the framed short-leg shear wall haunched beam-shaped transfer plane framework and the same dimension unhaunched beam-shaped transfer frame. The test shows that: 1) Haunched beam-shaped transfer structure can apparently improve the shear-bearing-capacity of the abutment section and reduce the beam dimension effectively, and it is easier to implement the aseismatic design principles, including “strong column and weak beam, strong shearing and weak bend”; 2) if the design is reasonable, haunched beam-shaped transfer structure can get better seismic behavior.

Abstract: Assembly-box concrete hollow floor is a new kind of cellular voided floor structure, in which a lot of prefabricated box-shaped interior forms are placed regularly on the formwork before the floor concrete is cast. The new type of box-shaped filler is termed assembly-box and could behave as load-bearing elements. Such floor system has many advantages, such as low self-weight, good mechanical behavior, equally flexural stiffness in two directions and high voided rate. The characteristic of this floor structure is the combination of precast assembly-box and cast-in orthogonal grids of ribs. For the purpose of understanding the behavior of this floor, a test has been carried out with three scale specimens under vertical loading. All experimental values provide essentially the same result that a typical flexural failure occurred under ultimate load and the structural system of assembly-box hollow could behave like an overall cast-in hollow floor. A part of the top plate in assembly-box could be viewed as the flange of rib beam during the process of structural design.

Abstract: The theory of geometrical nonlinear analysis is introduced. The sag effect is considered by the multiple-straight truss elements. The unstress length which is modeled the tension force of cable is figured out. Three kind of positions where the new elements are activated on are offered: tangent to old elements, parallel to old elements and original model coordinate, the method of parallel to old elements is used in the construction stages analysis and the method of original model coordinate is used in the construction control analysis. The purpose of construction control analysis for pretensioned structure in this paper is that the architectural configuration should be satisfied after construction control analysis is finished. The procedure of construction control analysis for pretensioned structure is summarized. The computational accuracy and the effectiveness are proven by the example of the cantilever beam with cables.

Abstract: In performance-based seismic design method, it is very important to have a good command of the nonlinear performance of a structural system, including in the collapse stage. In this paper, a nonlinear finite-element analysis on reinforced concrete moment frames is carried out. After studying the forces and deformations behavior in beam-column elements, the element stiffness matrix of distributed plasticity beam-column element is deduced using the Cotes scheme with 5 integration points. During the occurrence and development of plastic hinges, sections at some integration points will experience loading, unloading and reverse loading and the stiffness of these sections will experience various status. A quadrilinear form moment-curvature relationships with curvature- softening behavior and the hysteretic modes are used in the nonlinear static analysis program. The numerical analysis is carried out and the numerical results validate the load-displacement relationships and the yield mechanism of experiment frames.

Abstract: Dynamic flexural buckling equations in large deflection for an elastic column with the effects of axial inertia and rotary inertia are derived via the principle of minimum acceleration for continua at finite deformation. The maximum lower limit formula for critical dynamic buckling load is obtained by eigenvalue analysis for rudimental buckling equation. It is found that the expression is same as the static Euler limit.

Abstract: Mechanical properties experiments of air-entraining concrete after suffered to 0, 100, 200, 300 and 400 freezing-thawing cycles were performed. The experiment method, contents and result of strength and deformation of air-entraining after freezing-thawing cycle under biaxial compression were also introduced. The relationship between the strain corresponding to peak stress and cycle of freezing-thawing as well as the relationship between compressive strength and cycle of freezing-thawing were analyzed. The failure criterion of air-entraining concrete under biaxial compression was established.