Advanced Materials Research Vols. 163-167

Abstract: Experiments have been finished for the bending resistance of 4 corroded RC beams with different corrosion degree and sustained load. From test results, the main conclusions are summarized as follows: when the anchoring situation is good, the local steel corrosion has no remarkable effect on the flexural capacity on normal section; even if the crack width reached 1.8mm along bars, the failure type has no change, still the flexural bending failure on normal section; the remained flexural capacity can be calculated based on the formula of uncorroded beam, if only considering the decrease of effective area and mechanical property for corroded steel bar; the degradation of local bond behavior has no clear influence on the bending resistance of RC members.

Abstract: Coupon tests were conducted to investigate the mechanical characteristics of basalt FRP (BFRP) sheet, basalt-carbon hybrid FRP sheets and the corresponding epoxy rein under the effect of freeze-thaw cycling. FRP sheets and epoxy rein coupons were subjected to up to 200 and 250 freeze-thaw cycles respectively. Test parameters included the number of freeze-thaw cycles and the types of FRP composites. Test results show that (1) BFRP sheet perform better than CFRP or GFRP sheets under high freeze-thaw cycles; (2) exposed hybrid FRP sheets not only show very little loss in mechanical properties, but also contribute to the stability of test data; (3) mechanical properties of rein epoxy decrease significantly with increasing freeze-thaw cycles.

Abstract: Based on chloride diffusion and random field theory, an analytical model of PC structures in erosive environment with chloride corrosion subjoining cyclic freeze-thaw was formulated. Models presenting the influence of chloride and cyclic freeze-thaw to failure probability are used to track the structural failure. It is found that cyclic freeze-thaw could be the driving force to damage of concrete in rigidity and mechanics. The computing results show that reliability index increases with the cover thickness, and cyclic freeze-thaw increases with decrease reliability. It is important to reliability calculation whether considering cyclic freeze-thaw.

Abstract: An experimental device which provided uniaxial sustaining tension stress to concrete was especially designed with pressed spring. The accelerated, steady state chloride migration experimental method was used to test the permeability of concrete under tension resulting from designed device. Concrete with two mixture proportions was tested to get chloride diffusion coefficient under different tension stress. Mathematics models were built to show the change of chloride diffusivity coefficient of concrete under tension.

Abstract: Several experiments were carried out to investigate the effects of water to binder ratio(w/b) and mineral admixtures on water sorptivity and permeability of new-old concrete composite system in this paper in order to further understand the transport properties and thus degradation mechanism of new-old concrete repair system. Results indicate that a reasonable choice of w/b of new concrete is of great importance for obtaining new-old concrete composite with a low water sorptivity. Addition of ultrafine powder such as silica fume as one of component of repairing materials will benefit for effectively reducing water sorptivity and permeability of new-old concrete repair system in practice. The linear correlative coefficient between capillary sorption coefficient, coulomb electricity and porosity of new-old concrete composite sample is bad and lower compared with those of corresponding new concrete samples. The total porosity of new-old concrete composite sample is not an exclusive factor determined its water sorptivity and permeability. The pore structure of new-old concrete composite sample, especially interfacial transition zone between new and old concrete plays more important role on transport properties of sample.

Abstract: The reasonable selection of a location for underground structures has a great influence on the stability of surrounding rock masses, especially when the construction is built in the alpine and gorge regions. In general, the higher and steeper the mountains are, the more significant the effect is. In this paper, numerical analysis was carried out to study the stress distribution characters in the mountain with different slope angles of 30 °, 45 ° and 60 °. The results show that, the initial vertical component of stress field can not be directly determined by the buried depth when the slope angle is greater than 30 °. Meanwhile, numerical results indicate that is unfavorable for the structural stability when the underground caverns are constructed in the stress concentration areas of mountains with high slope angle. Moreover, some conclusions and recommendations were proposed for the design of underground constructions.

Abstract: The coming national specification for steel highway bridge will adopt the design method of probability limit state based on the structure reliability theory. Then the statistical parameters of loads and resistance play a key role in this method. Based on the extensive survey and investigation on site, the parameters of resistance are calculated in the study. In the work, three aspects of resistance’s uncertainty which are the uncertainty of materials properties, geometric parameters of members and calculation model are analyzed respectively. Then, the statistical parameters of five typical members of two commonly used steels—Q235q and Q345qD—in steel highway bridges are calculated. The recommended statistical parameters of resistance of steel highway bridge can be a reference for the new specification.

Abstract: The existing long-span bridges deteriorate with time due to fatigue, overloading, corrosion and environmental effects. To date, condition evaluation of the existing long-span bridges is important to carrying out the activities related to maintenance, rehabilitation and replacement of bridges. In this paper, a methodology was developed to evaluate the condition of the existing long-span bridges. The analytic hierarchy process was combined with the fuzzy synthesis. A procedure is given for condition rating of the existing long-span bridges as well. A bridge as the example is evaluated by this method and the results show that the damage of the bridge is marginal, which is same as the conclusion obtained from the traditional methods.

Abstract: Damage evolution equations of asphalt mixture specimen beams were analyzed using the fracture toughness index and the ultimate tension strain index, respectively. The fracture toughness of the asphalt mixture was calculated by FEM. Damage evolution equations controlled apart by the stress and the strain were given. Their coefficients were back-calculated using partial fatigue tests data. The fully coupled stress-damage method and the fully coupled strain-damage method were used. The life prediction precision of each equation was verified by residual fatigue tests data. The results show that FEM is effective to calculate the fracture toughness of the asphalt mixture. Two damage evolution equations have better life prediction abilities comparing with the S-N equation used usually.

Abstract: For the safety of salt rock underground gas storage cavern, uncertainties of material parameters and their influence to structure must be considered. In this paper, random field method is used for failure probability analysis of gas storage cavern. Random field model of material parameters is introduced firstly, local average method is used in discretization of random field, then Monte-Carlo stochastic finite element method is used in failure probability calculation. Conclusions can be drawn as follow: Failure probability in middle part of the cavern is higher than that of upside and underside, and failure probability decreases when operation pressure increasing. Middle part of cavern in release process is the most dangerous. Failure probability of cavern computed by random field model and random variable model based on response surface method are campared. It is obviously that failure prabability computed by random field is lower than that of by RSM. As variation coefficient and fluctuation range increasing, failure probability of salt rock cavern will increase.