Abstract:In this paper, the low reversed cyclic loading tests of three PVA-ECC columns were carried out, and the influence of the stirrup ratio change on the seismic performance of the columns under the high axial load ratio was studied, and the hysteretic performance, ductility, energy dissipation capacity and stiffness degradation of the test PVA-ECC columns and the ordinary reinforced concrete columns were compared. The test results indicate that, under high axial load, the test specimen exhibited flexure failures with better ductility, and bond splitting, spalling of ECC as well as composite disintegration due to cyclic loading were prevented. With the decrease of the stirrup spacing of PVA-ECC columns, the seismic ductility was also improved greatly. Compared with the PVA-ECC column with stirrup spacing( 90mm),the displacement ductility, the maximum drift ratio and the equivalent viscous damping ratios of the PVA-ECC columns with stirrup spacing 70 mm and 50 mm were improved by 15.6%～16.3%,17.1%～20.6% and 15.6%～17.8%, respectively. Minimum stirrup ratio that can satisfy certain seismic requirement on displacement ductility and drift ratio were put forward.

Abstract:Various uncertainties of the FE modeling may have significant impact on structural identification and result in obvious discrepancy between FE model analysis and field test results. In order to eliminate epistemic uncertainty and aleatory uncertainty during model calibration procedure, which contributes to achieve reliable condition assessment and response prediction, two long-span bridges were taken for examples, and several critical issues were discussed. By means of field inspection and blueprint review, simultaneously combined with the precise modeling, uncertain parameter selection was carried out based on sensitivity analysis, and parameter optimization was eventually performed by the least square method to complete the working condition assessment and response prediction. Research in this paper consists of in-situ experiments, precise finite element modeling, model calibration, and model admissibility check. Discrepancies between FE model and field test results can be mitigated by efficient model calibration method, and initial design model generally shows 20% and 23% relative difference.

Abstract:This paper proposes a new multi-objective hybrid swarm optimization method for active control system based on particle swarm algorithm and differential evolution algorithm, in which the parameters of controller, and the number of and allocation of actuator are synchronously optimized. The basic idea is as follows: The different algorithms are used to complete the evolution of corresponding population, the non-dominated solution set is achieved based on the dealer principle, and the leader selection based on boundary point geometry center is adopted. Meanwhile, the simulated annealing algorithm is used for the secondary local search, the two indexes reflecting the structural vibration control effect and performance of control strategy are used as the optimization objective function. Finally, a ASCE 9-story benchmark model is used as a numerical example to validate the effectiveness of the proposed method. Compared with the conventional MODE, MOPSO, and MOHA algorithm, the MOHO-SA algorithm has better convergence curve and distribution of the pareto solution sets.

Abstract:To study the seismic performance of a new concrete filled tube-confined sandwich shear wall (CFT-SSW), cyclic loading tests were carried out on three CFT-SSW specimens with different depth-thickness ratios and one conventional concrete shear wall specimen for comparison. The load-carrying capacity, ductility, stiffness and their degradation, hysteretic and energy dissipation characteristics, and failure modes of the specimens were investigated and compared. Equations for prediction of the strength of CFT-SSWs were also proposed. The calculated strengths were in good agreement with the test results. The results show that CFT-SSWs exhibited both the high lateral stiffness and strength due to reinforced concrete shear walls and the superior ductility due to concrete filled tubes. The strength, ductility, and stiffness of CFT-SSW specimens were greater than those of the cast-in-situ concrete shear wall specimens. In addition, the depth-thickness ratio has only marginal effects on the seismic behavior of the CFT-SSWs within the test range of the current tests.

Abstract:Combined with domestic and international research on the mechanical properties of concrete and steel after fire, a three-step model and a two-step model were used to calculate the elastic modulus of concrete and steel simply, respectively. According to the simplified calculation model and the equivalent elastic modulus method, an equivalent cross-section elastic modulus of reinforced concrete beams was obtained after fire. Based on the effective moment of inertia method, the cross section of the reinforced concrete beam was equivalently translated before and after the reinforced concrete beam cracked. Area of the whole cross-section mortar and the reinforced area of tension zone were translated to the effective area whose modulus of elasticity is the concrete modulus of elasticity. Through the experiment data, design formula of the stiffness and deflection of the reinforced concrete beam with high-performance ferrocement laminate after fire was deduced and verified. The calculation results are in good agreement with the experimental ones.

Abstract:Corrosion of rebar significantly affects the transfer path of chloride ions in concrete, and the penetration of chloride ions as well as the erosion of rebar in concrete are two nonlinear mutually strengthening and coupling processes. This paper proposed numerical methodologies to solve the nonlinear problem. An efficient iterative algorithm was established for simultaneously analyzing the penetrating process of chloride ions into concrete and the evolution of concrete damage, and was subsequently implemented and integrated into ABAQUS with user subroutine. Efficiency and reliability of the proposed method was certified with the test data from literatures. Numerical results clearly demonstrated that the coupling process between chloride ions penetration and concrete damage evolution greatly affected the assessment of the integrity of reinforced concrete structures. The developed method could give more comprehensive evaluation of the service life of reinforced concrete structure, and provide new guidelines for the durability analysis of concrete structures under marine environment.

Abstract:The main building of three-tower ultra high-rise connecting buildings is significantly interfered by the podiums and annexes. Large eddy simulation was adopted for three-tower ultra-high-rise connecting buildings. The shape coefficients of the main building were calculated, and the computational results were compared with the wind tunnel test results. The wind fields, wind pressure coefficients, and the interference effects between tall buildings were discussed. It is found that the large eddy simulation was a feasible way, and the turbulent wind velocity was higher in condition with single building. The field of flow separation is more lasting in condition with three buildings. The interference effect might have beneficial sheltering effect on the wind-induced vibration response of the main building when the main building was in the upstream. On the contrary, the wind pressure of main building might have been magnified when the main building was in the downstream.

Abstract:The durability of the interface between NSM FRP and concrete under freeze-thawing cycles was examined. The pull-out tests were conducted to investigate the influence of freeze-thawing cycles on the bond performance between NSM FRP and concrete with normal strength, high strength, or additional frost resistance. The mechanism of the bond degradation between NSM FRP and concrete under the freeze-thawing cycles was also discussed. Moreover, the influences of the distance between concrete edge and groove (edge distance) and the thickness of epoxy adhesive on the bond durability of the NSM FRP were studied. The test results show that freeze-thawing cycling resulted in the strength deterioration of ordinary concrete, while the high strength concrete and the concrete with frost resistance showed no significant deterioration under freeze-thawing cycles. Freeze-thawing cycling also caused the transformation of failure mode and the relatively significant decrease in bond capacity for specimens using ordinary concrete. Nevertheless, it had no substantial impact on the bond performance of specimens made by concrete with high strength or frost resistance. This result indicates that the bond deterioration of NSM FRP under freeze-thawing cycles was caused by low strength of concrete. Moreover, the decrease of edge distance resulted in cone-shape cracks at the loading end. When the thickness of epoxy adhesive was reduced, the bond strength degradation induced by freeze-thawing cycles was more significant compared with that of specimens with thicker epoxy adhesive.

Abstract:Compaction degree is an important factor that affects the mechanical property of reinforced soil. In this paper, two kinds of geogrids were adopted to study the compression performance of cylinder reinforced soil without lateral confinement. Through a single-stage loading/unloading way, the variation rules of vertical deformation for reinforced specimens with the compaction degree of 85%, 90%, and 100% were tested. The following conclusions can be drawn from the present study. 1) Improvement of the compaction degree effectively enhances the soil resistance to deformation, makes the soil deformation stable faster, and makes the velocity curve of deformation more smooth; 2) The impact of compaction degree on the mechanics performance of reinforced soil is closely related to the tensile modulus of reinforced materials and the effective contact area between reinforced materials and soil. Reinforced material with higher tensile modulus provides more effective restrain on the soil.

Abstract:Aiming at spanwise correlation of vortex-induced forces (VIFs) of the main deck of bridges, wind tunnel experimens of an oscillating and stationary streamlined box girder were conducted under different wind attack angles in the smooth flow. The VIV responses, spanwise correlation of vortex-excited forces, and surface pressures of the streamlined box girder were investigated. The research results showed that the spanwise correlation coefficients of the vortex-excited forces of the streamlined box girder were related to the amplitudes and wind speeds in the lock-in region. The spanwise correlation coefficients of the vortex-excited forces of the main deck at ascending stage of the lock-in region were larger than that of the main deck at the maximum amplitude of the lock-in region. The spanwise correlation coefficients of the pitch moments of the main deck in torsional VIV were larger than that of the lift forces of the main deck in vertical VIV. Meanwhile, the spanwise correlation coefficients of the pressures on measure points of the main deck were related to the amplitudes of the oscillating main deck, and the spanwise correlation coefficients increased with the increase of the amplitudes.

Abstract:The yield strength of the steel component gradually decreases under high temperature. As a result, the structural performance of the steel component on the bridges will be greatly affected by the on-deck fire disaster. Taking the steel pylon of a three-pylon suspension bridge as an example, this paper mainly studied the influence of the fire disaster on the structural performance of the steel pylon and the entire bridge. First of all, the temperature distribution inside the fire and steel pylon was obtained by the numerical simulation of different on-deck fire scenarios near the middle steel pylon. Secondly, the change of the structural static performance of the bridge under different fire scenarios was obtained by a nonlinear analysis. The results showed that under the effect of a serious vehicle fire, larger than 80 m2 area of the middle steel pylon was under the temperature up to 800 ℃, and the maximum temperature would exceed 1 000 ℃, which can greatly affect the structural performance of the steel pylon. Obvious changes of stress and formation of the middle steel pylon were discorverd, which means 4.6 mm vertical residual deformation, 53.8 mm lateral residual deformation and 70 MPa stress reduction. However, the stress and deformation of the main cable and girder only showed minor changes.

Abstract:Considering the cross-anisotropy properties of asphalt concrete (AC), finite element numerical analysis was introduced to develop the three-dimensional (3D) Finite Element Model (FEM) of AC overlay placed on old asphalt pavements. The AC overlay and old asphalt layer were assumed to be cross-anisotropic, and the temperature field characteristics of AC overlay as well as the variations of its modulus versus temperature were considered. And the mechanical behaviors of AC overlay at high and low temperatures and the effects of the cross-anisotropy properties of AC on its deformations and strains were then investigated. The results show that the cross-anisotropy properties and modulus gradients of AC induced by temperature fields both had great effects on its mechanical behaviors.

Abstract:Through the conventional low temperature performance test and Superpave low temperature performance test, the structural performance of different polyphosphoric acid(PPA) modified asphalt binder was investigated at low temperature, and the corresponding relationship of its performance evaluation index was analyzed. Further, the anti-cracking performance of asphalt mixture at low temperature was verified by the improved trabecular bending test and TSRST, and the correlation of low temperature performance between the asphalt binder and the mixture was studied. Finally, the rationality and deficiency of the evaluation index of different low temperature performance were analyzed. The results show that PPA reduced the ductility and stiffness modulus of asphalt, and the aging had great influence on the structural performance of PPA modified asphalt at low temperature. The strain energy density index shows that PPA can improve the cracking resistance of asphalt mixture at low temperature, the anti-cracking performance of PPA compound SBR modified asphalt was better than that of SBR modified asphalt, and the freezing temperature and freeze fracture strength can more accurately evaluate the low temperature performance of PPA modified asphalt.

Abstract:In order to reveal the response characteristics of the laminated fabric for airships under plane stresses, a series of biaxial tensile tests were first conducted on high-performance envelope materials Uretek3216LV. Based on the stress-strain data obtained from the biaxial tensile tests, the response surfaces of strain and elastic parameters were displayed using the MATLAB program. Using an integrated weighting method, the characteristics of elastic parameters affected by the stress levels and stress ratios were analyzed.The results indicate that reciprocal relationship doesn’t apply to the constitutive model of laminated fabrics, and obvious orthotropy of the elastic parameters can be observed for different stress levels and stress ratios. In addition, the large value of Poisson’s ratio (>0.5) can be attributed to the complex interaction and deformation mechanism of warp and weft yarns which make the laminated fabrics different from homogeneous materials which makes the laminated fabric different from homogeneous materials.

Abstract:When the construction of tunnels encounters with the filled Karst cave, the instability of confining rocks normally causes the geological hazards like water or mud inrush. Based on the limit analysis theorem, a calculation method to investigate the stability of confining rocks was proposed. In view of latent filled karst cave existing in the circumferential direction of the tunnel, transformed strength parameters of Hoek-Brown nonlinear failure criterion were obtained by virtue of the generalized tangent technique, and the two-dimensional model was constructed as well. In order to characterize the stability of the confining rocks, safety factor was introduced into the energy dissipation analysis on the basis of upper bound theorem and strength reduction technique. The variations of safety factor with respect to the diverse parameters were then discussed through optimization analysis. The computed results show that the parameters, including thickness of rock plug, pressure in Karst cave, tunnel supporting pressure, diameter of the circular cross section, uniaxial compressive strength, and parameters of Hoek-Brown failure criterion had significant influence on the variations of safety factor. And it is found that the safety factor was insensitive to the change of unit weight of surrounding rock. Moreover, the proposed method was applied to engineering projects, and reasonable results were obtained, which verified the validity of the proposed method.

Abstract:The shield tunnel of Lanzhou metro undercrossing the Yellow River was driven under through high permeability sandy cobble stratum and under high water pressure. A device for external loading test was therefore developed, which introduced a controllable air pressure between the linings and grouting layer, and by regulating the pressure difference, the equivalent water pressure can be then simulated. Using this device together with a tunnel-ground simulation facility, a model test with a geometric similarity ratio of 1∶10 was conducted. The device can reach the point that the water pressure and earth pressure were controlled separately. The mechanical characteristics of segment lining with different external water pressures, soil pressure, coefficient of side earth pressure and segment assembling methods was analyzed. The results suggest that, as external water pressure increased, a significant increasing trend of axial force and a gentle decrease trend of bending moment were observed while eccentricity decreased obviously; as soil pressure increased, a gentle increase of axial force, bending moment and eccentricity was observed; Given a fixed water pressure, increasing effects on the bending moment and decreasing effects on axial force were shown with the increase of soil pressure; Given a normal pressure level, axial force of segment linings increased while bending moment decreased when the coefficient of side earth pressure increased, which made the eccentricity decrease. In addition, the coefficient of side earth pressure shows decreasing effects on the mechanical characteristics of segment linings with the increasing of water pressure; Under staggered assembling, internal force of the segment will produce a mutation at some parts of circumferential and longitudinal joints, besides, internal force of the segment under staggered assembling is larger than that under straight joint assembling.

Abstract:In order to study the seismic response of underground structures when liquefied soil layer is located in different positions, the PL-Fin constitutive model proposed and developed in FLAC3D was used in this paper. The time when large deformation occurred, liquefied area distribution, the law and difference of pore water pressure and excess pore water pressure ratio, the law of the displacement characteristics, and differential settlement of structure were summarized. Their differences were also compared and analyzed when the structure is on non-liquefied soil layer. The primary conclusions are as follows: the displacement of structure was the largest when liquefied soil layer was under structure and caused the structure sink; the liquefied soil on both sides of the structure caused the structure float upward, and increased the displacement between the layers of side walls in the horizontal direction as well as between the roofs and floors in the vertical direction; the soil displacement and the displacement and differential settlement of structure were all not the largest when structure was all located over the liquefied soil, so it was not enough to only study the law when structure was embedded in liquefied soil; the law of the y-displacement of story drift on top plate was similar when the liquefied soil was located at six different positions including around the structure, on its two sides, in its bottom, in 45 degrees at the bottom of the location, on its two sides and 45 degrees at the bottom of the location, and in its bottom and 45 degrees at the bottom of the location, but the response of liquefied soil and the influence on the structure performance were different; and the large deformation caused by liquefaction occurred in 1 to 3 seconds after the jump of pore water pressure and the excess pore water pressure ratio, so their mutation can be considered as judgement on whether the large deformation occurred or not.