Applied Mechanics and Materials Vols. 94-96

Abstract: With gap elements modeling the gap contact condition between jacket platforms guided supports and the conductor pipe, the deflections of the conductor pipe induced by the motions of Jackup in cantilever mode, and offsets of the jacket platforms under operating conditions are investigated. The limiting relative excursions between the jacket out of phase or in phase with the jackup and the distributions of the moment are quantified by the strength and stability analysis of the conductor systems. The results show to avoid an overload for given conductor strength and dimensions, the maximum relative displacement between jackup and jacket platform with guide offsets is about 75.0cm.

Abstract: The water absorption and desorption process of different prewetting degree ceramsites embedded in ceramsite concrete was obtained by a U-tube micro pressure measurement device. The internal relative humidities of ceramsite concrete using different prewetting degree ceramsites were monitored by humidity sensors. The study reveals that, with the increase of ceramsite prewetting degree, the internal relative humidity of ceramsite concrete increases because the reservoir function of ceramsite is more obvious.

Abstract: In order to study the mechanical behaviors of post-tensioned unbonded prestressed concrete hollowed floors, a 1/4 scale post-tensioned unbonded prestressed reinforced concrete hollow slab-column structure model is used to act uniform distributed load on the floor. The test results showed that the load carrying capacity is enough. The points of maximum displacement are at the centers of slabs. By means of the experimental studies and elastic finite element analysis methods, the results showed that post-tensioned unbonded prestressed concrete hollowed floor presents anisotropy with layout of circular-tubes in one way. In direction parallel to layout of hollowed tubes, the continuity of floor is destruction and bending stiffness of slab is weakened. For studying the deformations of slab, it can still be considered continuous cross-slab in two directions.

Abstract: Through the experiment of the four RC beams strengthened with SWR externally prestressing, the shear resistant effect of Strengthened beams under cracking width of the original beams is studied in the paper. The ultimate load was confirmed by the test of the basic beam. First the presplitting load were respectively 50%, 60%, 70%, 80% of the ultimate load of basic beam, and seconly cracks were repaired with JN-L low viscosity pouring sealant, lastly experiment beams were strengthened by shear reinforcement of the external prestressing with steel wire rope. Loading method is the single point loading, and the shear span ratio is 2.0. The results show that: the cracking width of original beam has certain effect in shear resistant capacity. When the cracking width was less than 0.2 mm, the effect of injecting glue was not ideal and the shear resistant capacity is lower. When the crack width was bigger, the effect of injecting glue was more ideal, so the effect of reinforcement was better. When the cracking width was greater than 0.28 mm, the ultimate load was no longer improved. The smaller inclined cracking width in strengthening is, the worse repairing effect and the bigger strain value of stirrup is. Each strengthened beams’ wire rope strain increment was nearly close before cracking. As the decrease of original beams crack width, crack repair effect was weak, and the external strain increment of wire rope becomes bigger under the same load. The trend was very clear after the stirrup yielding.

Abstract: A new kind of prestressed concrete beams with spiral broken line cables subjected to torsions is present based on the fundamental principle of equivalent loads of prestressed reinforcement. It carried out the emulation analyses and load tests of the beams on spiral broken line cables and the general prestressed concrete beams with longitudinal cables. The results showed that the spiral broken line cables effectively postpone the cracking of the beam and increased both crack torsional moment and ultimate torsion moment, and kept some ductility.

Abstract: Centrifugal compressors are power machineries used widely. Fully understanding of the complex three-dimensional flow field is very important to design higher pressure ratio, higher efficiency centrifugal compressor. In this paper, time marching method is adopted to solve the three-dimensional viscous N-S equations under the relative coordinate system. The internal flow field of the “full controllable vortex” high speed centrifugal impeller is analyzed and the medial velocity vector distribution and the development of the velocity of each section in the impeller are showed. From the figures, it can be seen that the “wake” phenomenon, such as Ecckart described, caused by the curvature, Coriolis force and the boundary layer is exist

Abstract: The bottom interaction stress distribution of circular foundation on rock subgrade is generally nonlinear. Different from in soil, it is more complex and have no common conclusion. But it is important for design of this kind foundation. According to the circular foundation’s axial symmetry, using the homogeneous Lame equation in the circular cylindrical coordinates, and the Boussinesq-Galerkin’s general solution, selecting the Love’s strain function as a trial function, the analytic expressions of the bottom stress distribution of the circular foundation on rock subgrade is obtained by the trial Love’s strain function satisfying the boundary conditions. The results of field model tests and numerical simulation analysis are discussed here. It is provided about the bottom interaction stress distribution of circular foundation that is based on rock subgrade by compared the theoretical analysis with the test and numerical calculation. This study conclusion is valuable for design and practice of this foundation engineering.

Abstract: Based on the analytical method, the failure function is obtained for reinforced concrete (RC) frame columns with large eccentric compression under vertical and horizontal loads together. A special characteristic is found that the whole correlative curve of vertical and horizontal loads may contain some rising parts under limit state, and the corresponding determinant condition is also proposed. With the approximate linearization of rising parts, the practical limit state function is also obtained. Then, the seismic reliability is calculated for RC frame columns with large eccentric compression under different combined ratios of gravity and horizontal earthquake loads according to the current Chinese design code. The results indicate that its reliability is lower than the reliability of RC frame beam when the strong column coefficient adopts low values. This provides some useful references for engineers to design RC columns with large eccentric compression reasonably.

Abstract: In this study, the flexural behavior of the reinforced concrete beams attacked by acid rain environment is investigated. The objective is to discover the deterioration mechanism of the concrete beams servicing in the acid rain environment. An artificial rainfall device was designed. Eleven reinforced concrete beams, 120mm×200mm in cross-section were prepared in the laboratory. Three accelerating corrosion methods, which inclusive of immersion method, dry-wet cycle method, and artificial rainfall method, were applied to simulate the action of the real acid rain respectively. The acid solutions with pH level 1.5 and 2.5 were prepared by the mixture of sulfate and nitric acid solution respectively. One of the beams was tested in the natural condition to serve as reference; the remaining ten beams were tested after being exposed to the simulated acid environments for certain periods. Ultrasonic technology was applied to evaluate the damage depth and the compressive strength of the concrete. Dynamic test was applied to estimate the integrity of the beam. Three-point bending tests were performed to investigate the load carrying capacity of the beams. Mechanical properties of concrete and load carrying capacity of the beams exposed to different accelerated corrosion methods are obtained and compared. It is illustrated that the designed artificial device is efficient to simulate the real acid rainfall. It is shown that the strength of concrete, frequency and ultimate load of the beams, have a direct relationship to the damage degree of the beams.

Abstract: The total porosity of the high performance concrete under cyclic loading was measured in this present paper. Results show that finite cycles of cyclic axial tensile load causes permanent damage to concrete, which can be measured after unloading. The higher the applied upper load level or the more the cycle number is, the more obvious will be the connection and development of micro cracks. Then the higher will be the total porosity. Especially, with the increase of cyclic load number, the total porosity of the concrete shows obvious stage characteristics. And there is a linear relationship between the total porosity and cyclic loading cycles in the second developing stage of fatigue strain.