Key Engineering Materials Vols. 452-453

Abstract: For the mechanical properties of reinforced concrete under high temperature with large deterioration, the reliability of reinforced concrete beams have been largely discounted. A calculation of fire resistance based on failure probability is given by this paper. Reinforced concrete beam is usually working with cracks. Since each section with cracks has possibility of destruction, the reliability of the beam is calculated by the minimum value of n crack-sections’ resistance. The plastic zone resistance of concrete under high temperature is considered in this paper. A simple and feasible time-variant model of the resistance of reinforced concrete beams under fire and a reliability index analysis method of reinforced concrete beams under fire has been given. The action of ISO834 temperature rising curve on the reliability index of different specifications of concrete beams at different time is analyzed. The action of main parameters on the reliability index changes with time is shown. The fire resistance considers the failure probability is given. The results show that increase the reinforcement ratio and concrete cover thickness appropriately are effective measures to improve the fire resistance limit of reinforced concrete beams.

Abstract: This paper provides approximate fatigue life estimates for aluminum cylinders with a constant ratio of outer to inner radii 2.2 which were subjected to autofrettage pressure. Experimental tests of cylinders made of aluminum alloy are part of this article. Numerical simulations of the cylinders were also performed using the finite element code, ABAQUS. The resulting stresses are then used to calculate stress intensity factors to determine fatigue life. Using standard fatigue crack growth relationship, life of the cylinder is then calculated based on recommended initial and final crack length. The results show that the fatigue life due to autofrettage is more than nonautofrettage cylinder between Py1 and Py2 where, Py1 is the pressure required at the onset of yielding which occurs at the inner surface of the cylinder and Py2 is the sufficient pressure to bring the outer surface of the cylinder to yielding, i.e. the wall of cylinder becomes fully plastic.

Abstract: A mechanical model of the pressure-sensitive dilatant material is established in order to investigate the viscous effect in mode I quasi-static growing crack-tip field. The constitutive equations on the pressure-sensitive dilatant material are deducted. Through asymptotic analysis, it is shown that in the stable creep growing stage, the elastic-deformation and the visco-deformation are equally dominant in the near-tip field, as . The asymptotic solutions of separative variable in the crack-tip field of plane stress mode I quasi-static are aslo obtained. According to numerical calculation, the curves of stress, strain and displacement in terms of various parameters are given. The asymptotic solutions of quasi-static growing crack-tip field gained here can conveniently degenerate the incompressible case, when the Poisson ratio , named as HR field. The conclusions can provide the references for further studying the dynamic growing crack-tip field in the pressure-sensitive dilatant material.

Abstract: In recent years, many earthquakes occurred in our country. Some is big, but most are small or middle earthquakes. Usually earthquake damage ratio of buildings in low intensity area can be attained from on site survey. But it is important that how to evaluate the seismic performance of existing building stock subjected to high intensity in earthquake-affected area. In this paper, the expectation and variance value of damage probability in known intensity is calculated by making the probability disperse. Supposing that the damage probability in each intensity obeys to Beta distribution. The expectation and variance value of damage probability in other intensity is given by comparing to that of criterion earthquake damage matrix. So the parameter of Beta-distribution function is calculated from the expectation and variance in other intensity. Then the probability of each damage grade in other intensity is gained. This approach makes the damage matrix which is suitable for this region complete and provides the reference for earthquake damage prediction and earthquake economic loss evaluation. The result showed that this approach is feasible.

Abstract: More than 30 earthquake loss assessment reports in Yunnan Province in 1993 – 2003 are collected. And the building loss in each intensity recalculated based on the all building area, destruction ratio, loss ratio and replacement cost which are listed in the reports. The relation curves of building loss versus affected population, affected area in each intensity are studied respectively using statistical regression method. After regression significance test, it is found that the relation of building loss and affected population is high; however, there is no obvious relevance of building loss versus affected area. So in this paper, the quantitative relation between the housing loss and earthquake-affected population in each intensity area is established in Yunnan Taking four earthquakes during 2004 ~ 2005 in Yunnan as examples; we estimated their earthquake building economic loss and compared them with the values taken from field investigation. The result shows this regression equations are useful and applicable for evaluating the building loss caused by earthquake.

Abstract: In this paper, the vulnerability of the multi-storey reinforced concrete is classified and analyzed according to three control factors: construction age, story and uses. And the different categories vulnerability matrices of multi-story reinforced concrete are obtained from the monomer sample buildings which are already evaluated. The proportion of construction area of different categories can be attained from buildings census statistics. Then the vulnerability matrix of concrete building group in study region can be established by sum-product of construction area ratio of each vulnerability class in study region and each class vulnerability matrix. Finally, the vulnerability matrix of reinforced concrete structure of Xi'an Yanliang District was obtained using this approach. After comparing with the traditional earthquake damage prediction method, it is shown that this method is feasible, simple idea and high reliable and can be used for rapid assessment of post earthquake.

Abstract: On 12 May 2008, a magnitude 8.0 earthquake happened in Wenchuan, Sichuan province, China .It was the most serious earthquake in china since 1949, causing very huge casualties and engineering damages to the buildings. In the earthquake, a reinforced concrete frame structure of Beichuan Hotel in Beichuan County collapsed completely because of the unsuitable arrangement of column network, and the engineering damage was characteristic. In the paper, the properties of material nonlinearity were considered ,the nonlinear analysis model of reinforced concrete frame structure was established, the time history analysis and nonlinear static analysis were used during inelastic stage, the main cause of structural destruction was obtained, the influence of the arrangement of column network on the structure was discussed.Therefore ,the results can provide valuable reference for the seismic design of reinforced concrete frame structure.

Abstract: The in-situ tests have been widely used to directly assess the strength and deformability of rock mass, along with which, various numerical approaches were proposed to give rational interpretations to the mechanical phenomenon happening during these tests. In this study, the so-called potential cracks are introduced into DEM model, leading to expanded DEM (EDEM) approach which is capable of simulating the cracking in intact rocks. The EDEM is applied to an in-situ triaixal compression test on a fractured rock sample. The simulation has well represented the failure mode, peak stress and elastic modulus obtained from tests as well as the cracking phenomenon and the slips on fracture planes during the loading process.

Abstract: Injection-molded bamboo fiber/PBS (polybutylene succinate) composites were studied; especially much attention was focused on their fracture behavior. The effects of filling rate and size of the bamboo fiber (BF) to the resin on fractural behavior were evaluated by tensile and Izod impact tests. The tensile strength of the composites of BF particle size the range from +75 to -180 m and from +180 to -250 m were higher than those of -75 m and those of +250 to -500 m. However, there are many pull-out fibers on fracture surface. The surface of the fiber had no sticking of PBS resin. The impact strength of the composites increased with increasing BF content except for the case that BF particle size was -75 m. After impact tests, in the case of the composites prepared using large BF, the fractural surfaces became bumpy. The changes in shapes of the composites derived from immersion in boiling distilled water were examined by using a digital microscope. After immersion in the hot water, many cracks appeared on the outer surface of the composites. These cracks might be responsible for the brittle fracture behavior of the water-absorbed composites.

Abstract: The low pressure die casting machine has been used in industries because of its low-cost and high efficiency precision forming technique. In the low pressure die casting process is that the permanent die and filling systems are placed over the furnace containing the molten alloy. The filling of the cavity is obtained by forcing the molten metal, by means of a pressurized gas, to rise into a ceramic tube, which connects the die to the furnace. The ceramics tube, called stalk, has high temperature resistance and high corrosion resistance. However, attention should be paid to the thermal stress when the ceramics tube is dipped into the molten metal. It is important to reduce the risk of fracture that may happen due to the thermal stresses. To calculate the thermal stress, it is necessary to know the surface heat transfer coefficient when the ceramics tube dips into the molten metal. In this paper, therefore, the three-dimensional thermo-fluid analysis is performed to calculate surface heat transfer coefficient correctly. The finite element method is applied to calculate the thermal stresses when the tube is dipped into the crucible with varying dipping speeds and dipping directions. It is found that the thermal stress can be reduced by dipping slowly when the tube is dipped into the molten metal.