Advanced Materials Research Vols. 163-167

Abstract: Based on reference [1], complex shear wall bending design was researched farther. It was shown that reinforcement partitioned design was belonged to asymmetric reinforcement design method. It might result in the unsafe problem that ‘shear walls were designed as a little eccentric compression member, but failed as a large eccentric compression member’. Then adjusted reinforcement partitioned design method was brought forward. And it was adjusted to symmetric reinforcement design method. Then its unsafe problem was solved. But its uneconomical problem was aggravated. If this uneconomical problem could not be accepted, whole section design method of reference [1] would be suggested.

Abstract: A mathematical model using the beam-shell compound finite strip method is established to study the elastic stability analysis of multi-trough rectangle aqueducts. The impacts of the transverse stiffeners and crossbars for the model are taken into account. The principle of minimum potential energy is used to deduce the eigenvalue equation for elastic stability problems. To verify the accuracy and efficiency of the beam-shell compound finite strip method, the numerical solution of the stability analysis for an actual aqueduct is calculated through the established model and other FEM methods. The result of the stability analysis for an actual aqueduct shows that: the buckling coefficient is reduced as the water level increasing while buckling mode remaining constant; and prestressed load has a great impact on not only the buckling coefficient but also buckling mode.

Abstract: Modified Housner model is presented in the paper for seismic analysis of aqueducts on rigid buttress. Invective mass is attached to walls of aqueducts rigidly instead of springs with low stiffness, which ensures vibrating frequencies can be computed. The coefficient α of invective mass is introduced to adjust the enlargement brought by the rigid attachment. The value of the efficient for aqueducts with different height-width ratio is determined by tentative calculation. Modified Housner model inherits the merit and avoids shortcoming of conventional Housner model. Finally the modified model is verified by an example and the accuracy of the model is proved to meet requirement of practical seismic analysis.

Abstract: For new large space plate-wall structure, the out-of-plane problems of shearwall caused by vertical loads cannot be ignored. The out-of-plane stiffness can be increased by introducing Hollow-shearwall. However, currently rare attention has been focused upon research on the out-of-plane problems of hollow-shearwall. Based on the theory of elastic thin plate，the hollow-shearwall is regarded as an orthotropic plate in this paper. According to the actual situation of the loading on the shearwall, it is the first time that the analytic solution of the hollow-shearwall with different boundary constraints under the combined action of the end moment and vertical pressure has been derived in this paper. The numerical results by the program developed with Mathematical based on the analytic solution are compared with those obtained with ANSYS and it shows that this method is correct and reliable. Under various operating conditions, it is easy to apply this program for the out-of-plane force analysis, which can provide reference for the further research on the out-of-plane capacity and a reliable basis for engineering design.

Abstract: The effects of recycled rubber powder on working abilities, density and compressive strength of high strength concrete (HSC) at room temperature were studied in this paper. The characteristics of rubberized high strength concrete (RHSC) after fire was investigated by surface observation, weight loss and retained strength testing. The sieve number of rubber powder used in test is No.40 (420μm), No.60 (250µm) and No.80 (178µm), and the content of rubber powder filled in RHSC is 1%, 2%, 3% and 4% with respect to cementation material respectively. Test results show that the increase in rubber powder content reduces the concrete strength, while the decrease in compressive strength of RHSC is less than 10% when the content of rubber powder is within 2%. RHSC with small content of rubber (1%) can restrain the spalling failure of concrete under high temperature.

Abstract: The internal relative humidity (RH) and humidity gradients in concrete at early ages have a significant influence upon the properties of concrete, where exists a great discrepancy among the test results under different methods. By comparing and analyzing the traditional measuring methods of the RH in concrete, a new measuring method will be developed in this study, which could measure the internal RH in cement-based materials accurately, conveniently and digitally. The changing laws of the internal RH in concrete at early ages were discussed. The results indicate that the measuring results under the new developed system was more accurate than that by the predrilled hole method, while the external environment does not have any effect on the measured results obtained by using the new measurement system. What’s more, the results achieved by the new developed system approached the real RH in concrete very quickly; the RH near the surface of the specimen decreased quickly, while the RH in the center of the specimen decreased slowly, the moisture contents unevenly distributed through the various height of the specimen. Hence, there exists an obvious humidity gradient in concrete.

Abstract: Applying to high performance concrete mix design, overall calculation method can fully quantify the various components of concrete. While the application of overall calculation is very wide, its applicability has weaken with the increase of fly ash. In particular, overall calculation is not applied to high volume fly ash concrete. The reason is simplely considered fly ash cement as a simple alternative to cement when designing of concrete mix, and then following the water-cement ratio strength formula to design concrete mix, neglecting the differences of contribution to concrete strength between fly ash and cement. To solve these problems, this paper considers the fly ash as a separate component of concrete, and re-establishes two variables strength formula based on water-cement ratio and fly ash dosage. On the basis of the generally applicable volume model of concrete, overall calculation is re-derived, then used to directly design high performance concrete mix ratio. Improved overall calculation method is more widely ,more scientific and more reasonable, and will have a far-reaching influence on the application of high volume fly ash high performance concrete.

Abstract: Physical filling effects of limestone powders, which are stated by compactness change of mixtures of limestone powders and cement, play an important role in the pore structure and strength of cement stone. The compactness of mixture of limestone powders and cement has been analyzed by the method of wet packing density, tested the void structure of cement stone by mercury intrusion porosimetry(MIP) and strength of cement stone. Effects of limestone powders with specific areas of individually 416m² /kg, 841m² /kg, 1243m² /kg on compactness of cement, compressive strength of concrete as mineral admixture, and pore structure of cement stone were studied when its cement is substituted for the mass proportion of 5, 10, 15% with it. The results show that the compactness of powder mixtures and compressive strength of concrete are biggest, and the improvement of pore structure of cement stone is the best when limestone powder is 10%; the compactness of powder mixtures and compressive strength of concrete are bigger, and the improvement of pore structure of cement stone is better when limestone powder is finer. That is to say, the proportion of limestone powder is the best substitution at 10%; physical filling effects of limestone powder are better when limestone powder is finer from particle sizes. It is important guiding meaning for the application of limestone powder in cement materials.

Abstract: To study the seismic performance of RC shear wall, and to develop its fine nonlinear analysis method, systemic studies on nonlinear static analysis and it’s realization method are carried out. Beginning with rotating-angle softened-truss model for coupled shear and flexural responses, analytical model of solid wall is presented based on the comparative study on four types of constitutive law of concrete for confined concrete of boundary zone. Good agreements between analytical and experimental results of load-displacement relation are found, which indicates that the proposed analytical method can reflect the global mechanical behavior of shear wall well. Studies on coupling beam and global perforated wall modeling are implemented, then modeling approach and nonlinear static analysis method for perforated wall are proposed. Comparing analytical load-displacement curve to experimental, initial stiffness and first turning point agree well and analytical ultimate capacity is close to experimental, which is shown that the load-displacement curve can actually exhibit the general load-displacement trend of perforated wall.

Abstract: Based on the bending experiment for two-span continuous beams of retard-bonded prestress concrete, the analysis of the stress increment of prestressed tendons is made in the loading process. The theory that the working performance of retard-bonded prestressed concrete members is as same as unbonded prestressed concrete members during the retarding period is demonstrated. It is feasible to use the formulas for the reference (Technical specification for concrete structures prestressed with unbonded tendons) to calculate σ_puthe ultimate stress and Δσ_p the Stress increment of the retard-bonded prestressed tendons and the recommended formulas are advised to use. It is also demonstrated that retard-bonded prestressed concrete members have the same working performance as bonded prestressed concrete members after the retarding period. The conclusion of this paper can provide the reference date for the design of retard-bonded prestressed concrete continuous beam.