Abstract:In order to identify the impact echo response characteristics of two kinds of void-existed defects induced by the interface debonding between the grouting medium and duct's inner surface due to the shrinkage of grouting material and initial void in grouting medium within the duct of post-tensioned concrete members, four grouted specimens with different interface debonding state were fabricated by using interfacial bonding agent, expansive agent and curing ways after grouting, and another specimen with void defect in grouting medium was formed by presetting a foam in the duct. The spectrum response was continuously measured by impact echo system within five days after grouting. The results show that the spectrum within first 2 days after grouting of well grouted specimens without any preset void in the grouting medium were almost identical and similar to that of solid specimens without duct, and obvious interface debonding in specimens without expanding agent in the grouting material was observed, resulting in the lower thickness frequency and more complicated spectrum at the third and following days after grouting, which can be considered the principle to ascertain the occurrence of interface debonding for specimens with well grouted duct. In the specimen with a preset void in the grouting medium but without any interface debonding, although its thickness frequency was always lower than that of well grouted specimens without interface debonding, its spectrum form was very similar to that of the latter and its thickness frequency ratio almost kept unchanged as about 0.85. The thickness frequency development curves with the grouting age between the specimens with a preset void and interface debonding intersected, and both had the same frequency at about the third day, which indicates that the two different defects of interface debonding and existing void cannot be identified uniquely only by the thickness frequency at some moment. To distinguish these two defects mentioned previously through the response characteristics and the development curves of thickness frequency during about 4 days after grouting is necessary.

Abstract:The multi-zone network model method, together with the wind tunnel test and CFD numerical simulation results, was employed to simulate the combined wind and stack effects of a high rise building with the height of 340 m. It was concluded that: 1）The differential pressure curves between the indoor elevator and outdoor were linear under pure stack effect, which were consist with the theoretical result. The differential pressure between the indoor elevator and outdoor was gradually dominated by the wind effect with the increase of wind speed, and its curve gradually changed from linear distribution to nonlinear distribution. Higher wind speed would lead to significant nonlinear feature. 2）The neutral plane level of the building was hardly affected by the outdoor wind speed，and the refuge floors had great influences on the differential pressure elevators on the refuge floor and its neighboring floors; 3) Different wind on different seasons would have different impacts on the stack pressures. For one high frequency ENE wind in winter, the wind pressure would depress the stack pressure generally，while for another N wind，the wind pressure would strengthen the stack pressure by contrast. Under the ESE wind in summer，the wind pressure would depress the stack pressure on the floors except for the refuge floor，while an opposite effect would occur on the refuge. 4） Measures such as improving the sealing level of the glass curtain and/or adding additional partitions were helpful to mitigate the excessive differential pressure caused by stack effect.

Abstract:Two semi-rigid beam-column connection specimens with T-stubs of steel frame were designed. The impact tests using drop-hammer were conducted to simulate the collapse behavior under impact loading. The influence of thickness of T-stubs flange and web for the beam-column connection on the impact resistance of steel frame substructure was investigated. The failure modes and time histories of impact load and deformation were obtained，and the dynamic responses of the impact load and deformation time histories were analyzed as well as the dynamic rotation and energy dissipation of the substructures. Test results show that the failure modes of T-stub beam-column connection specimens mainly include the fracture and bending deformation of T-stub flange and web as well as distortional deformation of steel beam web. The rotation capacity of two connection specimens were dominated by the T-stubs，and their maximum rotations are less than the FEMA350 design limit （θ = 0.109 rad） due to the premature failure of T-stubs. The energy dissipation and ductility of semi-rigid beam-column connection specimens with T-stubs are inferior to the ordinary welded rigid beam-column connections. The finite element （FE） analysis model of T-stub beam-column connection was established using ABAQUS software. The internal force development of specimens during the impact loading was analyzed and it demonstrated that the T-stub beam-column connection with design of partial strength and semi-rigid connection degraded the formation of catenary action.

Abstract:he hysteretic constitutive model is used to predict the structural elasto-plastic seismic behavior of materials accurately. Chinese 6082-T6 and 7020-T6 aluminum alloy were tested under cyclic loading, and their stress-strain curves under monotonic and cyclic loading were obtained. Secondly, the expressions of monotonic tensile curves, hysteretic curves and skeleton curves were fitted based on the piecewise Ramberg-Osgood model. As a consequence, the uniaxial hysteretic constitutive model of Chinese aluminum alloy was proposed. The obtained hysteretic constitutive model was validated against the test curves, and the results showed that the uniaxial hysteretic behavior of Chinese aluminum alloy can be accurately described by the proposed model.

Abstract:This paper investigates the parameter evaluation of mechanical behavior of high strength structural steels in fire-resistance design. In order to reveal the elevated-temperature mechanical properties of high strength steel S460N, tensile tests were conducted under both fire conditions of steady state and transient state. The elevated-temperature reduction factors of elastic modulus, yield and ultimate strengths of S460N were obtained and compared to those in the current design standards and available literature. According to the comparison between the research results on S460N, the available research results in literature on S460N, S460M, Q460 and various mild steels, it is found that the deterioration of mechanical properties of structural steels at elevated temperatures is dependent on steel grades and manufacturing method. Therefore, the recommendations in current design standards are not applicable to high strength structural steels. Moreover, unique predictive equations for the deterioration of S460 mechanical properties at elevated temperatures were proposed and validated against the available literatures.

Abstract:Real-time hybrid simulation is a new method of structural seismic test. A hybrid simulation test system is established, which includes the numerical simulation computer based on OpenSees finite element software, the target computer with time delay compensation function and the electro-hydraulic servo control system. Furthermore, the Simulink numerical simulation model is established in MATLAB, and an adaptive feedforward time-delay compensator based on displacement prediction is proposed. Finally, a single story and three span high-strength steel composite eccentrically braced steel frame structure was considered as the prototype, the single story steel frame with the eccentric brace was considered as the test sub-structure, and a real-time hybrid simulation test of a 1/2 scaled model was carried out. The experimental results show that the maximum time-delay compensation error and maximum amplitude error of the system increase with the increase of overall response peak acceleration of the model, but all of them are within the tolerance allowable range. At the same time, the hybrid simulation test system has good stability and accuracy, and can be used to test the seismic performance of the eccentrically braced frame as the test sub-structure.

Abstract:In order to investigate the load distribution and settlement characteristics of large scale piled raft foundation in practical engineering, a nonlinear analysis method for the rigid piled raft foundations under vertical loading is presented based on the pile-soil-raft interactions theory. Four types of interactions, i.e., pile-soil interaction, pile-pile interaction, raft-soil interaction and raft-pile interaction, are considered for the pile-soil-raft interactions herein. The hyperbolic attenuation pattern of soil modulus is considered for the nonlinear elasto-plastic analysis. Based on the comparisons with the field tests of piled raft foundation with different scale，a method to determine the soil parameters is specified, and the validity of the proposed method is verified by comparing the settlement and load participate ratio with the measured results. The optimized analysis of a piled raft case shows that the number of piles can be reduced significantly, provided that the load distribution of the raft is considered, and when the pile number is reduced to 1/3 of the original, the piled raft settlement does not increase remarkably.

Abstract:The impact on construction period is ignored in all existing research results on wind load of cooling towers. Taking the 220 m the world's highest super large cooling tower under construction as the example, the flow field information and three-dimensional aerodynamic forces during construction period are obtained based on large eddy simulation（LES） method. The validity of numerical simulation is verified through comparing the average wind pressure distribution of the entire tower with the standard curve and the measured curve. On this basis, the average wind pressure distribution and flow field characteristics under construction period are investigated. At the same time, the flow field characteristics and action mechanism are extracted from the velocity and vorticity changes of the cooling tower under different working conditions. The distribution regularities of the pulsating wind pressures and extreme wind pressures, lift/resistance coefficients and the correlations between points are revealed. Finally, the fitting formula of extreme wind pressures is given based on the nonlinear least square method. Studies show that the pressure extreme value on cooling tower firstly increases from -3.91 to -1.75, then decreases to -2.28 with the increase of construction height, the lift coefficient decreases with the increase of construction height, and the correlation of fluctuating wind loads firstly increases, and then decreases with height increase. Main conclusions can be used as reference to design wind loads on such large cooling towers during the construction.

Abstract:In order to investigate the topographic factor of single hill with different slopes and the influence of wind flow over hill on transmission tower-line system, wind tunnel tests of three hill models with different slope were carried out and the results were compared with several different codes in China and abroad. The topographic factor at hilltop and along the hillside were analyzed, together with the vertical wind component and turbulence of wind field. The results show that the topographic factors at hilltop for different slopes are the largest in the Load code for the design of building structures and Code for design of high-rising structures. The topographic factor at hilltop does not always increase with the increasing slope of the hill，and it gradually decreases when the slope increases from 0.577 to 1. Additionally，The topographic factors of cross-wind at the surface of the hill calculated by the existing fitting formula are smaller than the measured ones, while the calculated values in the upper area are larger than the test one. Moreover, the maximum value of the vertical wind speed component decreases as the slope of the hill increases, and the ratios between the maximum vertical wind speed component and the inflow velocity are 0.523 and -0.542 for the windward and leeward side of the three types of slopes, respectively. The turbulence at the surface increases with the increasing slope of the hill, which is most obvious at the leeward side of steep hill. For example, when the slope is 1, the turbulence at the leeward side of the hill reaches to 35% at the 0.6 times height of the hill.

Abstract:This paper aims to investigate the optimal transverse position for overweight trucks to cross the simply-supported multi-girder bridges. Finite element analysis is performed for a group of prefabricated concrete T-beam bridges commonly used in China under the action of overweight trucks with varying transverse positions. The maximum bending stresses at the mid-span of the girders are extracted from finite element analysis and compared with each other. The optimal transverse position is determined from the point of optimizing the structural response. The effects of a few important parameters, including the length of bridge spans, number of girders and type of girder connections on the optimal transverse truck position are investigated. It is found that the transverse loading position of overweight trucks has a significant impact on the responses of multi-girder bridges. For the T-beam bridges with odd number of girders, the optimal transverse position for overweight trucks is in the middle between the center girder and the adjacent girder; for the T-beam bridges with even number of girders, the optimal transverse truck position is the centerline of the bridge. The influence of the girder connection condition on the bridge responses is significant.

Abstract:In order to master the temperature stress variation of lightweight composite bridge decks and to avoid interlaminar failures between TPO-UHPC， the thermal expansion coefficient and elastic modulus of TPO materials were investigated by strain gauge method and ultrasonic method respectively; the interface temperature stresses of the composite pavement system were calculated by using ABAQUS finite element software. The parameter sensitivity analysis was performed on the main factors that affect the interface temperature stress of the pavement system. The effects on interface thermal stress between TPO-UHPC were discussed， referring to thermal expansion coefficient ratio， TPO thickness and construction temperature. The experimental results show that the thermal expansion coefficient of TPO is much larger than that of cement-based materials， and the elastic modulus of TPO decreases with the increase of temperature. The simulation results show that，under the condition of uniform temperature， the interlaminar shear stress and the normal tensile stress decrease with decreasing the expansion coefficient ratio and the thickness of the TPO layer; the interlaminar shear stress plays a more dominant role than the normal tensile stress in the pavement system. The influences of construction temperature on the interlaminar stress of TPO-UHPC are different for high and low temperature. It is possible to reduce the interface temperature stress amplitude by a suitable construction temperature and TPO thickness.

Abstract:In order to investigate the effect of proportion of buton rock asphalt on the performance of modified asphalt mixture with wet method，Penetration 70 Grade A petroleum asphalt was used as base asphalt for preparing the modified asphalt binder containing rock asphalt up to 40% of the base asphalt. Limestone aggregate was used in designing the AC-20C asphalt mixture of various percentages of rock asphalt by using Marshall method. Laboratory tests were carried out to determine the properties of the asphalt mixture modified with Buton rock asphalt. These properties include dynamic stability from rutting test， retained Marshall stability from immersion Marshall test， tensile strength ratio from freeze-thaw indirect tension test， failure strain from low temperature flexural test， water permeability coefficient from permeability test， compressive resilient moduli from compression tests at 20 ℃ and 15 ℃， and tensile strength from indirect tension test at 15 ℃. The test results and analyses indicate that with the increase of rock asphalt percentage，the high temperature rutting resistance， moisture damage resistance，permeability resistance，stiffness， and strength of the modified asphalt mixture improve gradually to varying degrees.On the other hand，with the increase of rock asphalt percentage，the low temperature cracking resistance of the modified asphalt mixture improves to a peak value and then falls back slightly.The recommended maximum percentage of Buton rock asphalt for paving asphalt mixture is 30% of the base asphalt.

Abstract:To examine the effect of volume of grouting reinforcement body， namely the size of the expanded foot， on the bearing capacity of pile tip， indoor single-pile static-load model tests were conducted through injecting grout into PVC pipe and changing grout amount and PVC pipe size to control the size of the expanded foot. Finally， the pile tip resistance-displacement curves were calculated by the traditional pile tip settlement formula and compared with the measured curves. The results show that when comparing with the pile without grout injection， the piles that form expanded foot after being injected cement soil show the significantly improved bearing capacity， and dramatically reduced settlement under the same load; As the diameter of expanded foot increases， the bearing capacity continues to rise; However， the bearing capacity improved with the increase of per unit diameter at first and then decreased， and its effect on reducing displacement under working load shows a decline trend; The sharing ratio of tip resistance tends to be stable after a displacement of 5 cm. The cement soil expanded foot on pile tip has high ratio of tip resistance and the ratio rises as expanded foot diameter increases. In practical engineering， more importance should be attached to the strength of cement soil on pile tip for the high stress of cement soil， and the pile tip resistance-displacement curves calculated by using traditional pile tip settlement formula fit the measured curves well.

Abstract:To analyze the influence law of existing vertical force（V） on the horizontal bearing capacity of piles in the medium sand and soft clay subsoil， a 3D finite element analysis model of a single pile was set up firstly by ABAQUS and then validated by using available loading test results. By keeping various constant values of V at the pile top and using the probe method， the horizontal load （H） was sequentially applied to obtain the lateral displacement， ultimate bearing capacities and bearing capacity envelopes of the shaft with two kinds of slenderness ratios （L/D） in homogeneous medium sand and soft clay， respectively. It was shown that， under the same variation range of V from 0.2 Vult to 0.8 Vult， the ultimate horizontal bearing capacity（Hult） of the pile in medium sand was increased by 13.6%~41.2%， while the value of Hult for soft clay subsoil was decreased by 2.2% to 6.5%. Furthermore， a more obvious effect was observed for the piles with a smaller L/D. Finally， the different influencing mechanisms of the existing vertical load on the horizontal bearing capacity of a single pile in the medium sand and soft clay subsoil were discussed in detail by analyzing the distribution and variation characteristics of the vertical stress in the subsoil， the side friction and lateral resistance along the pile shaft during the loading process.

Abstract:Conventional second-order second-moment reliability method (SORM) is only applicable to the engineering where the first and second order partial derivative of performance functions can be easily calculated by analytic method，which results in the difficulty in solving reliability problems of complex geotechnical engineering structures.Aiming at above limitation， firstly，approximate calculation expressions for partial derivatives on the checking point are deduced based on finite difference principle. Combine with conversion method of random variables between X space and Y space， solving method for gradient vectors is formed. Secondly， calculation criterion of gradient in Breitung′s SORM is substituted by the above solving method， and then，an improved SORM which is suitable for arbitrary form of performance function is proposed. The limitation of the conventional SORM is eliminated. Finally，reliability problem of two slopes which performance functions are implicit and indefinable are solved by using the proposed method， and it shows the accuracy and availability of the proposed method to deal with complex structures reliability problem. Meanwhile，the value of step length coefficient c = 0.01 in the benchmark space（Y-space) which possess the universal meaning is also achieved.

Abstract:Using the fractal theory， the preparation method on the scale sample with same fractal dimension of the in-site filling material produced by ball mill was studied. Based on the requirements of simulating the in-site repetitive crush mechanism， the ball mill was selected to prepare the scale sample. The effects of the experimental influence parameters such as the number of rotation， number of steel balls and initial particles size on the goodness of the fractal simulation and fractal dimensions were investigated by using the orthogonal tests. The effect of secondary crushing on the filling material during the preparation of middle Triaxial specimen was further examined. The results show that with the following crushing parameters: the number of ball mill rotation is 100 rad， the number of steel ball is 9， the initial particle size of the rock is 20mm， the middle Triaxial specimen scale sample with the same fractal dimension as the in-site filling material can be prepared.

Abstract:In order to study the applicability of different long-term strength prediction equations for different soils， the long-term strength of saturated frozen sandy soil， silt and clay were tested using a spherical template indenter. At the same time， the long-term strength prediction equations of three kinds of soils were used to predict their long-term strength. The applicability of the three long-term strength prediction equations for different soils was studied by comparing the measured values with the predicted values. The long-term strength prediction equation of Vyalov can accurately predict the long-term strength of silt and clay. For the sand， the prediction values of the three long-term strength prediction equations have some deviation， which recommends that the weighted average of the three predictive equations can be taken as the predictions.

Abstract:The fault fracture zone is one of the key influencing factors on the structural stability of a tunnel in high earthquake-intensity area. Aimed at dynamic interaction characteristics between surrounding rock and fault under seismic action，a dynamic contact force method considering various contact states was established. The method considers point-to-point contact and point-to-surface contact in finite element model， and it can simulate four contact states between the rock and fault: bonded contact， static contact，separation and sliding contact. Therefore，it is suitable to study the nonlinear large slip problem of dynamic contact system composed of the rock and fault under seismic load. First，the rationality of the method was verified by a sliding block example. Then， the method was applied to the anti-seismic stability calculation of Xianglushan tunnel in Dianzhong water diversion project. The influences of three working conditions on seismic response of the tunnel were contrastively analyzed: without fault， with fault but without dynamic contact，and with fault and dynamic contact. The results indicate that the existence of fault fracture zone aggravates the seismic reaction of the tunnel，which mainly appears as displacement and stress increase of the lining as well as failure zone enlargement of the rock. When considering the dynamic contact，the evident alternate displacement forms between the rock and fault during seismic loading procedure，and then exerts destructive effects on the lining. The damage zone of the lining mainly distributes in the place where the fault passes through and within about 10 m range of distance from both sides of the fault， and the lining in hanging wall is greatly affected by the fault. Under the motivation of horizontal seismic motion，the stress and displacement of the lining haunch are significantly larger than that of the top and bottom arch，so that the haunch is considered as the weak part of the lining structure.

Abstract:The excavation of subway tunnel will induce the extra deformation or even damage of pipelines that lies above. The jointed pipeline was regarded as a beam on elastic foundation. By introducing the equivalent loads to consider the reduction of rigidity at joints， the governing differential equation for the deformation of jointed pipeline was established. Fourier series method was used to solve the governing differential equation. Expressions of the unknown coefficients of Fourier series were derived， and then a set of linear equations for determining relative joint rotations was obtained. Meanwhile， assuming that the soil settlement fits a Peck curve， the settlement of pipeline was computed and compared with that obtained from numerical simulation， which verifies the correctness of the Fourier series method. Results show that， with the loading of soil displacement， the pipeline deforms and rotates largely around its joints. The settlement of soil has small influence on pipe segments beyond 3i (where i is the width of settlement trough)， where joints can be ignored to reduce unknowns because relative joint rotations are far less than the tolerant value. When a joint is located above the excavation center， the soil subsidence can induce the maximum relative rotation at this joint. Therefore， if the locations of joints are unknown， one joint can be set right above the tunnel centerline in order to assure a conservative result.