Advanced Materials Research Vols. 368-373

Abstract: For the long-term monitoring of structure, the deformation trend changes periodically and is hard to extract. A small amount of recent data can be selected to avoid such problem. The study refers to the idea of grey system theory and provides an improved way of deformation prediction in time series analysis with a small amount of data. By cumulating the original data, the trend item is made clear and the rule of data becomes obvious. The prediction results show that the way provided by this article gives a more accurate prediction in the short term. When the prediction results have a large deviation with actual deformation, it can be believed that the trend has changed and the monitored structure may be affected.

Abstract: In order to solve the problem that the domestic and overseas research on the mud-jack materials were used for treating voids caused voids again, based on Yantai-Weihai highway testing section as backing project, the cement, organic and sand mud-jack materials were improved by using the shrinkage-compensating principle. The rechecking results of core drilling indicated that the treating effect of recommended self-compensation mud-jack materials were good.

Abstract: Recently, bridge deterioration with time and ever increasing traffic loads raise concerns about safety and durability of aging bridges. Based on the studies about damage assessment on the level of materials and components，the author made a comparative analysis on the damage mechanism and applicable conditions，and put forward the amended formulas for calculating the flexural and shears capacity，This paper combined with results of previous studies, based on the structural damage assessment research, reinforced concrete beam structure correction formula is given in the event of cracks and shear cracks.The assessment formula for shear capacity was established as well，and in which various impact factors of shear strength was considered comprehensively.

Abstract: Today’s construction quality signifies a lot to the tomorrow’s rate of return on investment for the project. The quality control over construction process shall be implemented following the principle of “well planning beforehand, tight control during the process and timely inspection after completion, and emphasis to be laid on the control of key positions”. To ensure to achieve the goals of building the project into a high quality project at national level in China, quality plan and detailed rules for implementation of supervision should be developed. Quality control over working process during the construction is very important too.

Abstract: The engineering geological condition of the mine goaf and the exploitation method are proposed with an engineering example. With the study on surface failure mechanism, the structural stability of key layer and the deformation control function of damaged buildings, the simulation model is built. The surface movement is analyzed with FLAC3D. Moreover, the building stability and impacts of mine goaf are evaluated. Finally, the disposal measures of mine goaf and the protection methods of buildings are given. By comparing the simulation results with the practical observation data on surface movement, the condition and method produced are efficient and precise.

Abstract: Damage identification for a cantilever beam with a breathing crack was presented based on instantaneous frequency(IF). One time-varying stiffness model was introduced by considering the breathing effect of the crack in vibration. A simplified single-degree-of-freedom(SDOF) time-varying dynamic differential equation was built. Relationships between the structural instantaneous frequencies (IFs) and damage location and degree were analyzed. IFs of the free vibration displacements were estimated by using phase difference and Teager energy operator (TEO).Moreover the influence of noise on IFs estimation was discussed. Damage indices were built by IFs and the damage degree was identified. Structural IFs are two-dimension function of damage location and degree and the intra-wave phenomenon of IFs verified the non-linearity of damaged structure. The damage indices based on IFs are more reliable than traditional frequency on identifying damage degree and have some anti-noise properties.

Abstract: The shear resistant with SWR (steel wire rope) external prestressing is a kind of new type of reinforcement technique. The advantages of the method are ideal reinforcement effect, durability, and convenient construction. So the method has been paid attention by more and more scientists and technical workers. Through the experiment of 1 basic beam and 3 strengthened beams which are in different dead load levels, the influence of damage degree of original beams and the dead load level of strengthened beams are analyzed. The reduction coefficient values of shear capacity under different dead load level are researched. The research is shown that: with the dead load level increasing, the improve degree of shear capacity of strengthened concrete beams is smaller. The mathematical model is established, which is about dead load level and reduction coefficient of shear capacity of strengthened concrete beams. The result is to take 0.75 as the reduction coefficient of shear capacity. The value is reasonable in calculating the shear bearing capacity of strengthened beams under dead load.

Abstract: Aluminizing has been verified to be an effective way to improve the corrosion resistance of steel due to the formation of continuous Al₂O₃ layer, but traditional aluminizing processing carried out at high temperature can not be used to prepare aluminide layer on the surface of oil casing steel. In this paper, an aluminide coating was prepared on oil casing steel N80 by a low-temperature pack cementation only at 803 K for 2 hours by adding zinc in the pack powder and pre-treatment of N80 substrate by surface mechanical attrition. The phase compostion, microstructure, element distribution and properties of as-aluminized oil casing steel N80 were characterized by means of XRD, SEM, EDS, micro-hardness test and electrochemical corrosion measurements. The results indicate that aluminide coating mainly consists of FeAl3, Fe2Al5 and FeAl. The continuous aluminide coating with an average thickness around 50 μm could be successfully formed on the surface of oil casing steel N80 which shows a good coherence with as-packed substrate. After preparation of aluminide coating, oil casing steel N80 shows a higher microhardness in the range of aluminizing coating than that of the virgin material because of the formation of iron aluminide. The exception noted is that the proposed low-temperature aluminizing processing does not have any damaging impact on the mechanical properties of steel substrates. Moreover, it is concluded that oil casing steel N80 with aluminizing coating shows a better corrosion resistance than that of original N80 by analyzing of electrochemical test results.

Abstract: The properties of recycled coarsee aggregates from repeatedly recycling waste concrete were determined. In this study, five series of concrete mixtures using coarse and fine natural aggregates were prepared, which have the same objective slump value from 35mm to 50mm and different compressive strengths ranging from 25MPa to 60 MPa. These five concretes were crushed, sieved, washed with water, hot treatmented at 300°C before they were used as recycled aggregates. After that, recycled aggregate concrete (RAC) was produced with an objectively compressive strength of 30MPa, in which the recycled coarse aggregate was used as 30%, 70% and 90% replacements of natural coarse aggregate and recycled fine aggregate as 10%, 20%, and 30% replacements of natural fine aggregate. After that, these recycled concretes were used as second recycled aggregates to produce RAC with the same objectively compressive strength of 30MPa. The physical properties of coarse aggregates including apparent density, water absorption, attached mortar content and crushing value were tested and their mineral characteristics were analyzed. The results showed that the quality of recycled coarse aggregates from twicely recycling waste concrete reached the requirements from structural concrete.

Abstract: This paper proposed a method to calculate the nature frequencies of generally supported plate with hole. The boundary of plate is considered as the combination of rotational springs and translational springs. The generally characteristic equations of generally supported plate with damage can be derived using Rayleigh-Ritz method. The nature frequencies of damaged plate can be obtained by solving the generally characteristic equations. The calculated results by proposed method were compared with that of FEM (finite element method) and analytical solutions. The compared results demonstrated that the proposed method is accurate and effective. Numerical examples are presented to analyze the effect of damage on the plate under different kinds of elastic restraint. The results suggest that: the effect of damage is little to the first order nature frequency and is relative large to the third order nature frequency when the rotational restraints are weak; the effect on the first order nature frequency rises but the effect on the third order nature frequency fall as the rotational restraints increase.