Advanced Materials Research Vols. 168-170

Abstract: Freeze-thaw cycle experiments on high performance concrete were carried out while cement was respectively replaced by fly ash for 30%～50%. The test results showed that maximum weight loss rate of concrete was 1.78% and minimum relative dynamic elastic modulus was 94.08% after 300 freeze-thaw cycles for high performance concrete based on low water-cement ratio, efficient air-water-reducing agent and large quantities of industrial waste fly ash. The test data were far less than limits of 5% and 60% in specification. Freeze-thaw resistance performance of high performance concrete with large volume fly ash was excellent according to test results. The high performance concrete with large volume fly ash can meet the requirements of frost resistance performance of concrete in the cold regions. Particularly, it can be fit for the railway concrete engineering.

Abstract: The city of Harbin is famous with its ice art and which attract the attention from the whole world. Ice shell is a kind of new architectural form in China which can be a suitable method for structure by using ice and snow-ice as structural material especially in cold regions. In this paper, an ice shell with span 9m and height 3.5 was completed to investigate the performance of this special structure under human loads and temperature. The results show that the ice shell maintains a bearing capacity under human loads due to the well-known mechanical behavior pf shell. However, the bearing capacity of the shell was largely depend on the variation of temperature. Furthermore, some rational suggests were given during the design and construct the ice shell. Finally, the works of this paper provides some material for the revision of ice code.

Abstract: This study simulated the nanofiltration (NF) process of contamination removing by back-propagation neural network (BPNN), according to the test values of DK membrane pre-treating Imidacloprid pesticide wastewater. The real time nanofiltration (NF) separation model was presented for effective controlling of DK NF separation. The research showed the simulation precision met the application demands, with the correlation coefficient between the simulation and test rejection of COD and salt over 0.99, and absoluteness error below ±4%. In order to test the prediction of this BPNN simulation model, further NF experiments were carried out. Under the same multifactor condition, the predictions for the NF process performances were found to be in good agreement with the experimental results. This BP simulation model for NF process could be used to test the stability and effectively of NF system, and support the membrane technology well.

Abstract: Corrosion is a negative contributor on the structural integrity of rock bolt and leads to degradation of the mechanical properties of steel rock bolt. Exposure to chloride, seawater, salt and saltwater and deicing chemical environments influences rock bolt and weakens it. In order to evaluate the influence of corrosion and the size of the steel on the mechanical properties of rock bolt, an experimental investigation was conducted on rock bolt whose rebar is 8, 12, 16, and 18 mm diameter, and which were artificially corroded for 10, 20, 30, 45, 60, 90, and 120 days. By the simulation corrosion test of loaded and unloaded bolts in Na2SO4 solution, the relation curves of the mechanical performance with the corrosive conditions and the corrosion time are given. The mechanical performance is compared between these two types of bolts. At the same time, the influential trend of the load on the mechanical performance of the corroded bolt is analyzed. The laboratory tests suggest that corrosion duration and rebar size had a significant impact on the strength and ductility degradation of the specimens. after being corroded in Na2SO4 solution, both the ultimate bearing capacity and the maximal tensility of loaded bolt decrease far more than those of unloaded bolt, and the endurance and service life of loaded bolt will also be shortened much more severely. The tensile mechanical properties before and after corrosion indicated progressive variation and drastic drop in their values.

Abstract: Prediction of degree of hydration of concrete is very important on research of crack-resistance capability and durability of the structure. This article studied the relationship between degree of hydration and strength of concrete based on a large number of references, the results show that the compressive strength of concrete is closely related with the degree of hydration, and the correlation function is a function of water-cement ratio and has nothing to do with the temperature. The hydration degree and compressive strength of ordinary concrete is linear correlation, and the prediction model of degree of hydration of concrete was proposed based on BP Artificial Neural Networks.

Abstract: An analytical model is developed for modeling aerodynamic flutter derivatives for long-span Open-Truss Girder Suspension Bridges and their interaction. The approach suggested here is to synthesize the wind derivatives based on proposed functions interpolated from experimental results of previous studies. The model solves the equation of motion and the synthesized aerodynamic forces are solved to find the critical wind velocity of the suspension bridge. The solution procedure and assumptions of the approach are verified using the Golden Gate Bridge flutter analyses, where the experimental aerodynamic coefficients of the bridge are modeled as a function of the wind velocities in the proposed procedure and compared with the analysis based on the interpolated coefficients. The results agree with the results in the literature. The result of the proposed analytical model is close to the values extracted from previous researches.

Abstract: Based on typical hydraulic engineering, difference of performances between full-graded and wet-screened concrete was studied. Results showed that owing to the gradation effect and skeleton effect of coarse aggregate and the size effect of specimen, full-graded concrete was 105%, 75%, 65% and 115% in compressive strength, splitting tensile strength, ultimate tension and compressive elastic modulus respectively, compared with wet-screened concrete. Under the same curing condition, compressive strength of wet-screened standard concrete specimen can represent the actual compressive strength of full-graded concrete.

Abstract: The equation of the middle surface of a simply-supporteded hip-truncated combined parabolical cylinder roof is established by means of the local inclined coordinate system and step function. Then, the formulas of the internal forces and deflection of a simply-supporteded hip-truncated combined parabolical cylinder roof are derived from the theory of shells and variational method. Finally an illustrative example of this roof is presented. This example indicates that the stress and deflection of this roof are much less than those of the hip-truncated four pitch roof of the same dimensions while its rigidity is much larger, so materials will be saved by use of such a proposed roof.

Abstract: Using microwave heating method to establish a set of effective technology about uniaxial compression test of concrete, and obtain the experiment phenomenon of concrete when the temperature is 16 -650 . Experiment results indicate that when concrete is damaged by high temperature, the strength of concrete decreases, the peak strain increases, and the elastic modulus decreases. Based on test data, a unified equation was putted forward to describe the relation between concrete compressive strength, the peak strain, elastic modulus and temperature. While, obtain concrete temperature stress and strain curve, and analysis shows that it gradually becomes compressed with the increase of temperature, peak point falls and moves right obviously.

Abstract: This article established strain characterization of damage factor equation of concrete in elastic stage, and completed the concrete specimens dynamic damage ‘freezing in’ test. A series of concrete under the strain rate had been gotten, and the damage characteristics of concrete under impact load was analysed. The damage evolution process of concrete material was related to both strain size and strain rate size, and the damage evolution and development and strain rate showedf a power function relation. Then the damage evolution equation used to describe concrete materials could be fitted.