Advanced Materials Research Vols. 250-253

Abstract: In order to determine the optimal proportion of magnesium phosphate cement mortar, the influences of ratio of magnesium phosphate cement-based binder (MPB) to sand (MPB/S), effects of fly ash on fluidity and strength development of MPB mortar, and the compatibility between MPB and traditional concrete and shrinkage of MPB mortar were investigated in this paper. The optimal proportion in this test was: setting adjusting agent of 12%, P/M ratio of 1:2(in weight), MPB/S ratio of 1:1 and FA/S ratio of 15%. The results showed that the MPB mortar met the higher early strength requirement of rapid-repair materials, with compressive strength beyond 50MPa and flexural strength more than 9.1MPa at 3 hours, and at later ages no reduction of strength happened. There was a good compatibility between MPB and traditional concrete. The shrinkage of MPB mortar at 28 days was less than 2.89 × 10^-4. Therefore MPB is very suitable for rapid repairing of concrete structures.

Abstract: The study proposes the Genetic Operation Tree (GOT), which integrate Genetic Algorithm (GA) and Operation Tree (OT), to build the model for Asphalt Pavement Overlay Cracking. The training data sets of pavement cracks were collected from a 15-year experiment conducted by the Texas Departments of Transportation. Even without a presumed formula structure, the GOT still can self-organize formula and produce a very concise model for predicting the length of pavement cracking.

Abstract: Swelling tests of remolded expansive soil with water immersing are carried out by use of the simple consolidometers. The swelling characteristics of the expansive soil under the different initial conditions are studied. The Dose Response model is used to fit the rules of swelling time interval for expansive soil with water immersing. The quantitative relationship among the swelling and initial overburden pressure, initial water content and initial dry density is attained by use of the three dimensional regression analyses. The important index obtained could be provided to the engineering design, construction and stability evaluation of expansive soil slopes.

Abstract: Creep, as one of the most important properties of concrete, has important influences on concrete structures. In present domestic researches, studies on humidity diffusion in concrete are relative inadequate; and few models can take comprehensive consideration on humidity factors. According to humidity diffusion theory of concrete, this paper studied the distribution of humidity field within concrete at constant humidity condition by using finite element method. Based on the drying creep of the Model B3, this paper analyzes the effects of humidity field on creep of RC beams.

Abstract: For subway tunnels such as Nanjing Metro II excavated by mining method, one of the most important reinforcement methods for preventing surface settlements is the grouting method. There are many soft and weak surrounding rocks and abundant groundwater in the metro section, so grouting has become a major method in reinforcing the fragmented rocks and soil. But bad grouting support caused by fluid loss in soil and rock often allows uncontrollable settlement. In order to analyze the differences in grouting techniques, combined with the actual excavation process and the contrast of different means of settlement control in a complex section of Metro II, this paper adopts the numerical simulation method of FLAC3D to demonstrate that strict management and proper methods can create good and dependable reinforcement of the unstable surrounding materials.

Abstract: Steel braces are widely used in seismic retrofit of buildings. However, their tendency of buckling under compression impairs their efficacy. In this paper, characteristics of a cross bracing with rigid intersection, including its bearing capacity, hysteretic property and fracture ductility are investigated. With the analysis results, performance-based design requirements of a steel cross bracing are proposed based on its width-thickness ratio and effective slenderness ratio.

Abstract: The prediction model of maximal critical velocity of pressurization was established theoretically by analyzed the pressure’s distribution in both sides of smoke bay. Using the computational fluid dynamics software FDS5.0 to build a 3D model of an island platform with platform edge door, Large Eddy Simulation model was used to obtain the critical velocity in different HRR, ceiling screen’s height and arrangement. Results show that the critical velocity rises with the increasing of HRR, and gradually reaching to the maximal critical velocity; in the range from 0 to 2m, it can be regarded that the maximal critical velocity is linear to ceiling screen’s height. The arrangement of ceiling screen has some influence on the critical velocity; setting ceiling screen around the staircase is more effective to restrict smoke.

Abstract: Parameter analysis based on finite element methods was executed to study the in-plane stability capacity of extruded T-section aluminium beam-columns with the tip of the web in bigger compression. The analysis methods considered the effects of material nonlinearity, geometrical nonlinearity, and initial imperfection. The comparisons of calculate results of three kinds of T-sections of weak hardening alloy and strong hardening alloy between GB 50429, proposed formula and numerical methods were executed. And the analytical results show that GB 50429 is safe and suitable, and the modification formula based on GB 50429 is also safe enough and more exact than the former.

Abstract: Taking Clough & Duncan’s hyperbolic model as the transfer function, the influencing factor of super-long single pile’s effective pile length are analyzed. Discussed four kinds factors, which are the pile elastic modulus E_p, the external friction angle σ, the material parameters k₁ and the allowable settlement S_a, effect on the effective pile length. The conclusion has some active meaning to super-long single piles’ the theoretical study and the application to engineering.

Abstract: Based on the assumption of pointed blade of circular cassion, the formulas of the bearing capacity of soil beneath the blade are presented by the slip line method. The values of N_γ are not too sensitive to change for the soil’s internal friction angle, and are significantly greater than those obtained by Terzaghi’s and Berezantsev’s formulas. They decrease with an increase in the value of blade embedment depth and the taper angle.