Advanced Materials Research Vols. 163-167

Abstract: The mechanical properties of high strength concrete(HSC) were experimentally investigated under mixed erosion and freeze-thaw cycling according to ASTM C666(Procedure B), the erosion solution was mixed by weight of 3% sodium chloride and 5% sodium sulfate. The mass loss, relative dynamic modulus of elasticity, compressive strength, elastic modulus and other relative data were measured. The results showed that with the increasing number of freeze-thaw cycles, the surface scaled more seriously; the mass loss, compressive strength and elastic modulus continued to decrease; the relative dynamic modulus of elasticity increased slightly in the first 225 freeze-thaw cycles, then decreased in the following 75 cycles; the corresponding strain to peak stress decreased with the increase of freeze-thaw cycles. After 200 cycles, the rate of deterioration of concrete accelerated obviously.

Abstract: The temperature cracking of early-aged concrete is often met by constructors in recent years, because of large temperature difference of core and surface of concrete. Experimental study on temperature field of concrete under different environmental conditions is conducted. Different environmental conditions such as wind speed, formwork removal, sun radiation and conservation are involved. The influence of environmental conditions on the peak value of rising temperature, temperature difference of core and surface and descending speed of temperature of concrete is studied. Result obtained from this study can be used in controlling of early-age cracking of concrete.

Abstract: : Performance of high strength concrete and ordinary concrete under alternating action of mixed erosion and freeze-thaw cycling were compared. The erosion solution was mixed by weight of 3% sodium chloride and 5% sodium sulfate. Results showed that, after 200 freeze-thaw cycles, the effect of surface scaling of ordinary concrete was more significant than that of high strength concrete, and the mass loss rate of ordinary concrete was much higher; The relative dynamic modulus of elasticity of high strength concrete slightly increased by 2.99%, while that of ordinary concrete decreased more than 13%. Compressive strength and elastic modulus of high strength and ordinary concrete behaved almost in the same way in the first 50 freeze-thaw cycles, with the increase of freeze-thaw cycles in the following test, the compressive strength and elastic modulus of ordinary concrete showed larger reductions than these of high strength concrete. As the freeze-thaw cycles increased, the corresponding strain to the peak stress of high strength concrete decreased, but it increased for ordinary concrete.

Abstract: Based on a steel reinforced concrete composite post crack under the torque simplified calculation method was studied. Using the simplified formula derived for H steel reinforced concrete structures under the action of compound and cracking torque is calculated. And simplify the calculation compared with the experimental value. The result is calculated with the testing results.

Abstract: Nine push-off specimens were designed, constructed, and tested. Test variables included reinforcement ratio of shear reinforcement, interface preparation, loading method and eccentricity of applied load. The failure pattern, hysteretic characteristic and degradation characteristic of capacity and stiffness of the specimens were analyzed. The effects of moment and cyclic reversed loading on interface shear capacity were studied. The results indicated that applied moment less than or equal to the flexural ultimate moment of shear plane has little influence on the interface shear capacity, and the effect of cyclic reversed loading on the interface shear capacity of new and existing concrete is bigger. The test value and the calculated value of current Code and Specification of China were compared. Results showed that the current JGJ 1-91 interface shear capacity provisions gave a very conservative estimate for interface shear capacity, while for the new and existing concrete interfaces under the action of cyclic reversed loading, the calculated value according to GB 50010-2002 tended to be unsafe.

Abstract: With the application of the composition material-concrete-filled-steel-tube (CFST) in civil engineering, the crossing ability of arch bridge gets advanced development. Therefore, it is of interesting to study the stability of such long-span arch bridges, especially which have small width, for the bridge’s safety under long term operation. The present study focuses on studies the transverse stability of long-span arch bridges with small width. To this purpose, a deck type CFST arch-bridge in Gansu Province is adopted as an example. The arch bridge has a span of 180 m, and its width-span ratio is 1/25.7. The finite element method with a special beam element is employed to analyze the stability. The analyses are carried out for the transverse stability of the bridge during construction and under service, respectively. Furthermore, the influence of the spandrel structure and deck elastic restraints to the stability is investigated taking account of geometrical and material nonlinearity.

Abstract: Internal force of a concrete member duo to temperature variation is related to stiffness. A reduction of stiffness occurs and the magnitude of the internal forces drops from the values existing before cracking when cracking occurred due to temperature variation. Internal force of axial tension member due to temperature variation developed in a jagged style with cracking. Calculation method of internal force and stiffness reduction coefficient of axial tension member due to temperature variation was presented accounting for cracking. Given example shows stiffness reduction coefficient has a close relationship with number of cracks and steel ratio. Member with high steel ratio subjected to the same temperature variation has more cracks and smaller crack width.

Abstract: As the stress measurement of interior concrete is hard in the construction control of the cable- stayed bridge, a new method fitted for stress measurement in large span PC concrete cable-stayed bridge is proposed in this paper. This method is based on the principle that the normal stress in neutron-axis of girder is only decided by the horizontal part of the cable force. First, the normal stress on the neutron-axis of girder is calculated by the measured cable force, and then the creep coefficient is identified, and finally the other stresses are worked out. This method has been applied to a large span PC cable-stayed bridge constructed in process with favourable results and thus proves its accuracy and efficiency.

Abstract: Based on Timoshenko beam theory, a section model for the ultimate load analysis of RC beam under combined action of axial force, bending and shear force is presented in this paper. Especially, the transverse deformation is considered with the appearance of diagonal cracks. The validity of the model is established by comparing its results with several tests. These simulations include ultimate bending moments of pure bending tests and ultimate shear loads with different shear-span ratios. The analytical results show excellent agreement with experimental data.

Abstract: Deterioration mechanism of concrete suffered slowly freeze-thaw and eroded in different mixed liquor (3%NaCl+5%NaSO₄, 3%NaCl+1.5%NaSO₄, 5%NaSO₄, water) were experimental investigated. The hydration product and microstructure of concrete specimen after 100 circles of freeze-thaw was tested and analyzed with SEM (Scanning Electron Microscope). The result indicated that under the interactions of freeze-thaw and mixed erosive solution, there were not only physical changes but also chemical reactions occurred in concrete, which exacerbate the mechanical properties deterioration of concrete. The mechanical performance and microstructures of concrete deteriorated most significantly in the mixed solution 3%NaCl+5%NaSO₄, and deteriorated more significantly in the mixed solution 3%NaCl+1.5%NaSO₄.