Advanced Materials Research Vols. 261-263

Abstract: Utilizing the large static-dynamic triaxial test system, 7 proportional loading biaxial tensile and compressive tests of concrete were conducted. The proportional loading paths are 0 (uniaxial compression), -0.05, -0.1, -0.15, -0.2, -0.25 and ∞ (uniaxial tension). Compressive and tensile strength were measured as well as the strains at two loading directions. Considering the ratio to tension and compression, failure criteria of ordinary concrete under biaxial tension and compression was established, which has a good agreement with test value.

Abstract: Traxial compressive tests on concrete samples subjected to such stress ratios as 0.1:0.25:1, 0.1:0.5:1, 0.1:0.75:1and 0.1:1:1, were performed. Based on mechanical properties measured from the tests, strength and deformation behaviors of concrete under triaxial compression were explored, and then the failure criterion was proposed. The result indicated that the bearing capacity of concrete under triaxial compression is greater than that under uniaxial stress state. Construction material can be greatly reduced considering this factor in design.

Abstract: This paper mainly focuses on the cracking problem of concrete structures, researches on the biaxial tensile strength of cement concrete. The biaxial tensile instrument is used for material test, the biaxial tensile strength formula is proposed, and the theoretic formula is deduced by Hill criterion. With the test data analysis, it shows that the calculating value and the testing value fit well. The biaxial tensile strength of cement concrete is about 15%~30% lower than its uniaxial tensile strength, putting up significant biaxial tensile strength weakening effect. This kind of weakening effect is important for designs of large-span beam, plate and shell structures under complex stress.

Abstract: The experimental study on the failure behavior of cement test block in sodium sulfate solution and strength change of specimen in early stage. The microstructure of cement test block attacked by sodium sulfate is observed by means of scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD). The mechanism of erosion damage in the sodium sulfate solution is analyzed. It is found that in the early period corrosion intensity will not suffer, but increase, and on the surface no obvious changes can be seen. However, in the attack later coarse surface cracks appear, then there is a serious off and the cement test block eventually collapses.

Abstract: The influence of grinded blast furnace slag (GBFS), high-calcium fly ash (HF), desulfurized gypsum (DG) and Na₂SO₄ (NS) on dissolvable ion Moore concentration and pH value of hardened cement is researched. In liquor with hardened cement powder, the dissolvable ion Moore concentration of Mg, Si or Al is according to each ion content in raw materials of cement paste. In materials system of cement-slag-HF, NS reduces the ion Moore concentration of Al and increases that of Mg or Si. PH value of hardened cement is mostly controlled by dissolvable Ca ion Moore concentration in the material system of cement-BBFS-HF. Alkali metal ions, which is introduced with additional materials, effect pH value more remarkably than the dissolvable Ca ion Moore concentration. PH value of hardened cement decreases a little if 50% cement is replaced by same weight of GBFS and HF. HF can reduce pH value more seriously than GBFS. DG enhances S and Ca ion Moore concentration, and decreases pH value of hardened cement.

Abstract: This paper presents a 2-D nonlinear and non-steady equation for the diffusion reaction of sulfate ion in concrete column subjected to couplings of random excitations and sulfate attack. Taking the diffusion reaction of sulfate ion in concrete column as an example, the time-variation behaviors of the ion concentration and its diffusion coefficients under white noise excitations are numerically analyzed. The results show that with the increasing of diffusion time, the sulfate ion concentration in the concrete column section has a gradual increase to reach a plateau in which the diffusion and reaction is in dynamical equilibrium state. Under random excitations, the sulfate ion concentrations in the column section increase with the excitation amplitudes, and the sulfate ion diffusion coefficients in concrete change randomly with the excitations and increase with its amplitudes. This work will provide a basis for analyzing the diffusion reaction behaviors of the corrosive medium in concrete structure and the damage evolution of concrete structure durability.

Abstract: Standard impermeability test is used to evaluate the impermeability of concrete without bearing history. For having no test to evaluate fiber concrete with load-supporting history under service environment, a new test, splitting tensile permeability test is proposed in the paper. The proposed test method involves two parts called splitting tensile test and load holding permeability test. The splitting tensile test is used to get fiber concrete specimen with tiny crack which impermeability measured by the load holding permeability test. Based on the concept of water proof grade in underground engineering, a new method for defining fiber content is proposed to improve the impermeability of fiber concrete. The new test and method is used to define the fiber content in a subway station of shanghai metro line 7, which have well impermeability upon engineering completion. So splitting tensile impermeability test is proved to have good reliability and feasibility for evaluating fiber concrete servicing in underground engineering.

Abstract: Based on Moelands-Reinhardt single parameter power exponent constitutive equation and Equivalent stain hypothesis, preliminary damage evolution equation of polypropylene fiber concrete is derived. To eliminate mesh correlation of element characteristic length and reflect the action of tensile strength and fracture energy to damage evolution, modified polypropylene fiber concrete’s damage evolution equation is deduced from the preliminary damage evolution equation. The modified damage evolution equation is proved by comparing the Load-displacement curve get from splitting test and theoretical Load-displacement curve obtained by damage FEM calculation. Through the splitting test, it is showed that the modified damage evolution equation reflects the action of polypropylene fiber volume ratio and aspect ratio to polypropylene fiber’s damage evolution.

Abstract: Pedestrian loads are affected by such uncertain parameters as walking step frequency, step length, dynamic load factors and phases of harmonic components, which lead to the uncertainties of structural response. A new method for calculation random response spectrum based on uniform design is introduced to reduce calculation work. A few representative samples of loads time histories are simulated using uniform design, and then the RMS acceleration response spectrums are obtained by dynamic time-history analysis of beam structures with different spans and damping ratios. The RMS acceleration response spectrums which have certain percentiles are obtained by reliability analysis based on response surface. Ultimately the general forms of RMS acceleration response spectrums are deduced from the analyses of sensitivities for damping ratio and span.

Abstract: Mining explosions and railway transportation generally result repeated intermission vibrations (RIV). These vibrations, with relatively shorter duration and larger peak acceleration, often repeat several times in a day. A proper evaluation method of human response should consider both the non-stationary nature and the occurrence frequency of RIV. This result the evaluation process has some differences compared with that for ordinary stationary vibration. Current evaluation method for human vibration comfort is first reviewed in this paper. Then the vibration dose value (VDV) and frequency of vibration events are introduced to evaluate vibration comfort under RIV. At last part of the paper, two vibration cases, one for blasting and one for railway transportation, are analyzed to explain above evaluation process.