Abstract:This paper investigated the issue of fluid-structure interaction (FSI) for fixed offshore wind turbines. The model for a 5 MW monopile wind turbine built by the National Renewable Energy Laboratory (NREL) was selected as an example. The stochastic inflow turbulence code written by NREL-TurbSim, the Kaimal spectrum and exponential wind profile were used to generate stochastic and full field turbulent wind. The aeroelastic code FAST developed by NREL was then used to calculate the aerodynamic load on the wind turbine. The time histories of shear force and bending moment at the top of the tower were obtained. The random wave was simulated using the Pierson-Moskowits spectrum through the harmony superposition method. Two cases were considered in this study, namely, the case that considered the effect of FSI and the case in which the effect of FSI was neglected. Kinematic equations and numerical models under the two cases were developed respectively, and the comparison between the two cases was made to investigate the effect of FSI. The results indicate that distinct deviations affected by the intensity of the wind and wave exists in both wave force and dynamic responses in the two situations.

Abstract:Super-high-rise buildings experience aeroelastic effects under the action of design wind velocity for its low mass and structural damping, and significant aerodynamic damping arises. Considering the first order linear sway mode, a single degree-of-freedom aeroelastic model of super-high-rise buildings with square cross section was made with a geometrical scale of 1∶600, and a series of wind tunnel tests were carried out to measure the accelerations on the top of the building model. Random Decrement Technique (RDT) was adopted to identify the aerodynamic damping of the building model. The aerodynamic damping in along-wind and across-wind directions obtained agrees well with that from literatures. The results show that the aerodynamic damping within the wind direction of 84°~90° is similar to that in the across-wind direction (90°), and the aerodynamic damping within the wind direction of 0°~12° is similar to that in the along-wind direction (0°). It should be noted that critical wind velocity decreases under some special wind directions, such as a reduced wind velocity of 7.2 in wind direction of 16.5°. Moreover, negative aerodynamic damping is found at low wind velocities.

Abstract:The wind pressure distribution of cooling towers with different rough strip parameters was tested, and the influence of roughness on both mean and fluctuating wind pressure was investigated. The experiment results show that the width of rough strip has little effect on the distribution of wind pressure, while the height and number have a greater impact, and the roughness coefficient k/s can describe the size of roughness accurately. Even though the number n and height k of rough strip is different, as long as the roughness coefficient k/s is consistent, the mean pressure distribution is basically the same, but the peak fluctuating pressure is smaller with higher height of rough strip. Furthermore, roughness has little effect on both the distribution of positive pressure and the size of back pressure. However, the amplitude of the smallest negative pressure coefficient and the peak fluctuating pressure decrease with the increase of roughness, while the width of back pressure expands slightly. Although the mean pressure at high Reynolds number can be simulated effectively at low Reynolds number by increasing surface roughness, the simulation accuracy of fluctuating pressure should be checked with field tests in the future.

Abstract:By testing painted ordinary cement mortar and composite cement mortar on the dorsal surface of concrete，the effect of ordinary cement mortar and composite cement mortar on concrete impermeability was compared. The influence of composite cement mortar thickness and additive content on impermeability effect was studied.Test results have indicated that composite cement mortar improves concrete impermeability more significantly than ordinary cement mortar.Within a certain range，the thicker the additive content or composite cement mortar，the better the permeability effect. Painting the composite cement mortar on the dorsal surface of concrete is easy to operate in basements and tunnels，which greatly facilitates the construction，so there is a wide range of practical engineering applications.

Abstract:A kind of high-damping mortar layer applied to damped infill wall was designed, and the pseudo-static experiments were carried out, also its mechanical properties were studied. The results reveal that: compared with common mortar layer, high-damping mortar layer has greater energy dissipation and horizontal shear deformation capacity in damped infill walls. When the polymer-cement ratio is in the range of 0.38~0.53, with the increase of polymer content in high-damping mortar layer, the energy dissipation and horizontal shear deformation capacity of mortar layer in damped infill walls will be enhanced; the optimal polymer-cement ratio is 0.45. With the increase of the thickness of high-damping mortar layer, horizontal shear deformation capacity of mortar layer in damped infill walls will be improved, the slip between the upper masonry and high-damping mortar layer will be delayed, this enhancing its energy dissipation capacity; however, with the increase of the thickness of high-damping mortar layer, the ultimate bearing capacity of mortar layer in damped infill walls will be reduced, the better value of thickness of high-damping mortar layer is about 9 mm.

Abstract:In order to study the influence of exterior cladding walls on the seismic performance of frame structure，especially the impact on siding horizontal stiffness of structures, strength and deformation capacity, three full-scale reinforced concrete frame structures including pure cast, siding with the beam and siding with both the beam and the column were tested under cyclic loading to a maximum inter storey drifter angle of 1/16 rad. The experiment results indicate that three specimens exhibit steady hysteretic behavior and excellent ductility. After the connection with the column was disengaged, the impact on the strength of the structure can be ignored. The cladding walls have a significant impact on the initial stiffness of the structure, and the siding with the frame and beam increases the stiffness more obviously than the effect when the siding is only connected to the beam. The connections between the cladding panels and the beam have no noticeable damage, and the panel remains intact when the inter storey displace angle reaches 1/16, indicating that the connections between the structure and the exterior cladding walls can meet the design requirements of major earthquakes.

Abstract:Full-scale model test method was used to investigate the seismic behavior of cast in place beam-column assembly and four new precast concrete beam-to-column connections under low-cycle reversed loading. The estimation was given for the seismic performance of new precast connection on the basis of the failure mechanism on the beam-column connections, as well as hysteretic loops, ductility, energy dissipation, etc. The results indicate that, by setting additional reinforcement in the core area of the node, it can achieve the relocation of the plastic hinge at the end of beam. The hysteresis curve of the new precast connection is plumpy, and in the pre-load, the equivalent viscous damping coefficient was smaller than the cast in place connection. However, when loaded into the ultimate load, the equivalent viscous damping coefficient of precast connections was roughly equal and even exceeded cast in place connection. It has been shown that the new connection has a better energy dissipation capacity, and can meet the requirements of “strong column weak beam, stronger joint”.

Abstract:It is pointed out that the Tri-linear Model in Concrete Structure Design Code GB 50010-2010 for calculating the bearing capacity of reinforced concrete members under the combined action of shear and torsion enlarges the 1/4 Circular Arc Model and leads to an unsafe design. The formula proposed by Ding Dajun using the 1/4 Circular Arc Model understates the bearing capacity of concrete in choosing the reduction factor of concrete shear capacity. The formula proposed by Huang Liang using the Linear Model makes the design conservative. On the basis of the 1/4 Circular Arc Model, two modified formulas were provided. Practical examples show that Formula 1 and Formula 2 are more secure than the Code formula. Numerical examples show that Formula 1 and Formula 2 not only totally conform to the 1/4 Circular Arc Model , but also approximately conform to the Linear proposed by Huang Liang, and their calculation results are quite similar.

Abstract:Referring to the methods and equipment of concrete compressive strength testing, the cast-in-place pull-out test was conducted on concrete specimens, which were reinforced by Polypropylene-Engineered Cementitious Composite, Polyvinyl Alcohol-Engineered Cementitious Composite, steel fiber cement mortar with nine strength grades. And the cube compressive strength test was conducted on fiber reinforced cement mortar specimens, which were reserved. Choosing linear relationship to fit the experimental data by using the method of least squares, this paper obtained three kinds of fiber reinforced cement mortar strength curves. At last, the relevant evaluation between them was carried out. The test data showed that there was a good linear relationship between them. This method has been proved to have very high precision, and can be used to predict fiber reinforced cement mortar compressive strength.

Abstract:Based on the tests of sixteen unbonded partially prestressed concrete beams under low cyclic reversed loading, the constitutive relations under cyclic loadings of every material were selected reasonably. After an in-depth analysis on the mechanical characteristics of unbonded partially prestressed concrete beams, unbonded prestress actions were converted to their equivalent loads by setting short rigid arms. Then, a nonlinear full range hysteretic analysis method for unbonded partially prestressed concrete beams was proposed by combining the step deforming method and the step loading method, and a MATLAB program was developed. Through comparisons and analyses, the calculated results coincide well with the testing results. So it has theoretical and practical engineering significance.

Abstract:The fire resistance performance of concrete component is very important for building structure safety. A test method was proposed for concrete column at high temperature under compressive loading. Firstly, a concrete column was placed under constant compressive loading, and then, the performance of the concrete column was tested at different constant temperatures after heating. The performance of the concrete column at high temperature was evaluated by first spalling temperature, spalling degree, fracture shape and axial compressive strength in the course of heating. Test results of three groups of concrete prisms show that this method can reflect the performance of concrete column at high temperature under compressive loading, and also has the advantages of low requirements for test instruments, convenient testing methods and reliable results.

Abstract:To evaluate the deformation and stress distribution of cement-concrete pavement under no-uniform temperature distribution along the depth direction, finite element analysis method was used in this research to simulate nonlinear temperature gradient load， and the nonlinear temperature distribution index was adopted to represent the degree of nonlinear distribution and to evaluate its effect on stress distribution. Models with different nonlinear temperature index parameters were constructed. The results indicate that, although the deformation caused by linear temperature gradient models was almost identical with that from nonlinear temperature gradient models, the linear temperature gradient models have overestimated bottom-up stresses and underestimated top-down stresses. When the nonlinear temperature gradient is negative, the influence of nonlinear temperature gradient on slab stress increases with the increase of slab thickness and elastic modulus. Besides, the effect of nonlinear temperature gradient is reduced with the increase of the base reaction module. What is more, based on the regression analysis of a large database, the formula of maximum tensile stress of the slab top was obtained.

Abstract:This paper studied the influence of cooling regimes on the residual mechanical properties of ECC (Engineered Cementitious Composites) after high temperatures. The ECC specimens were heated to different temperatures (200, 400, 600 and 800 ℃) and cooled in different regimes (cooling in air and quenching in water). The residual mechanical properties were tested. The results indicated that the specimens quenching in water gained better mechanical properties than the one cooling in air and the influence of cooling regimes increased with temperature. The micro structural characterization was examined before and after exposure to fire deterioration by using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) test. The results from the micro test explained the mechanical property variation of post-fire specimens.

Abstract:To address the deficiencies of new design methods of underground supporting structure, which lacks stability index of definite physical meanings, a study was conducted with the convergence-confinement theory. First the Kastner formula and the Duncan formula based on the Mohr-Coulomb failure criterion were selected to analyze the elastic-plastic of rock to establish ground characteristic curve. Each support unit was analyzed in series to establish the support characteristic curve of bolt-shotcrete support structure. Then, the stability coefficient of the support structure was derived in accordance with the principle of convergence-confinement and the principle of loat, which build up the quantitative evaluation of the stability of underground structure method for different stratigraphic characteristic curves. Finally, the otherness between different ground characteristic curves was demonstrated by other examples under similar conditions for rock mass mechanical parameters. Different modes of operations and operation processes were also shown.

Abstract:Bladder-type inflatable anchor is the improved and innovated inflatable anchor. In order to analyze the influencing factors of the ultimate up-lift bearing capacity and ultimate displacement, a series of laboratory model tests were carried out on bladder-type inflatable anchor. From experiments, we obtained uplift capacity-displacement curves. Test results have shown that the influencing factors include inflation pressure, embedded depth, length and thickness of rubber membrane, number of airbags, the distance between airbags and so on. However, the influence degree is different on bladder-type inflatable anchor. Through the contrast test with single capsule inflatable anchor, it is concluded that, under the same conditions, the ultimate up-lift bearing capacity of bladder-type inflatable anchor increases 1.2~1.7 times, and the ultimate displacement is 0.37~0.66 times of the single capsule inflatable anchor, which controls the displacement effectively.

Abstract:The construction of tunnels beneath mined-out coal seam disturbs the stratum nearby and influences the stability of surrounding rocks and primary support. Similar indoor model tests were carried out to simulate the excavation of tunnels beneath inclined mined-out thin coal seam. Benching method and side heading method were compared on the basis of the measured data such as subsidence of mined-out coal seam, internal force of primary support and so on. The test results indicate that excavation method has a significant effect on the subsidence of mined-out area. Benching method leads to bigger subsidence than the side heading method, which has a deeper and wider subsidence trough. In both methods, the biggest surrounding rock pressure are located in right arch foot, the biggest bending moment in the arch foot and axial force of the steel frame on the haunch or spandrel. Under the same condition, surrounding rocks pressure, internal force and the eccentricity of steel frame measured in side heading method are generally greater than those in benching method. Although side heading method can reduce the disturbance of surrounding rocks, the primary support of the tunnel should be strengthened to ensure the stability of surrounding rocks and the structure.

Abstract:In order to control the influence on deformation parameter estimation in Excavation Deformation Monitoring when geometric observations are anomalous, mechanic information about excavation slope is considered to be unknown information, and a filtering model with unknown parameter is given. In the fixed observation window, unknown parameters do not change with time, which can be fitted with the prediction of observation residuals and residuals. At the same time, algorithm improves the reliability of the state estimations. In a real example, by using the prior geometry and physics of information to deformation monitoring, the given algorithm can significantly improve the reliability of state parameter estimation.

Abstract:As a self-insulating building material which can meet the 65 percent energy-efficiency requirements in cold regions of China, aerated concrete blocks often go moldy, suffer frost heaving, or cause plaster layer hollowing at thermal bridge parts in extremely cold regions due to the restrictions of environmental climate and construction technique. Outer-corner part and T-shaped part of aerated concrete walls are most influenced by thermal bridge effect. In this paper heat transfer calculation models for outer-corner wall and T-shaped wall were developed, and their temperature fields were simulated. According to the simulation results, insulation measures of the thermal-bridge position of self-heat-insulting walls were designed to weaken or even eliminate thermal bridge effect and to improve the temperature of thermal-bridge position. And the influences of the thickness and location of the local insulation layer on the temperature field were analyzed. Consequently, the condensation inside self-thermal-insulating wall and frost heaving caused by condensation and low temperature were reduced, avoiding damage to the wall body from condensation. The research results can provide theoretical basis for the application and extension of self-thermal-insulating wall in extremely cold regions.

Abstract:To enhance the heating performance of the air source heat pump (ASHP) system in the low ambient temperature surroundings, the triple-sleeve energy exchanger (TRESE) for space heating mode was proposed. The running stability and the coefficient of performance (COP) of the energy storage heat pump system (ESHP) in the TRESE heating mode, the TRESE combined ASHP system heating mode, and the solar hot water assisting TRESE heating mode, were compared and discussed.The results demonstrate the substantial advance in the heating performance of the ESHP system in the TRESE heating mode and the ASHP system heating mode. For instance, when the temperature and volume flow of the solar hot water are 28 ℃ and 300 L/h, respectively, the evaporating temperature and COP achieves -2.8 ℃ and 2.8 respectively.

Abstract:Using the methods of questionnaire and field measurement, this paper analysed the characteristics of the thermal and humidity environment of every season in mid and low altitude rural tourist areas of Chongqing. By comparing the measured value with the thermal comfort limit value of the national standards, we find out that the departure degree of temperature and humidity range is small in summer and the transition season and the large in winter. Through large-scale sample questionnaire survey, we conclude that, in each season the PMVe values are +0.67 in summer, +0.32 in the transition season and -1.20 in winter. The TSV values are +0.63 in summer, -0.64 in transition season and -1.53 in winter respectively. The thermal comfort is better in summer and transition season and the worst in winter. Through further calculation of APMV and contrast with PMVe, TSV values, we find out that the most unfavorable factors to impact thermal comfort in summer, transition season and winter are indoor temperature, indoor humidity and indoor temperature respectively. Therefore, in order to improve the thermal comfort of residences in rural tourist areas, we can take the following measures: ventilation cooling in summer, adding moisture-proof material in the exterior wall in the transition season and adopting the air source heat pump with solar house or the surface water source heat pump when conditions permit.

Abstract:Owing to the artificial backfill uncertainty, the air gap may emerge in the backfill process, which will influence the soil initial temperature distribution, and it will also influence the horizontal buried pipe heat transfer performance. The initial soil temperature numerical model with backfill air gap was set up. Using CFD software, the numerical calculation result was analyzed and compared with the theoretical calculation value without air gap and practical experimental test data. The soil initial temperature with backfill air gap in the deep of 2.2 meters presents about one degree higher than that without backfill. Then, the horizontal buried pipe coupled numerical models with the deep of 2.2 meters were established on the boundary conditions of the initial soil temperature with air gap and that without air gap. Using CFD software, the horizontal buried pipeimport/export temperature and the average heat transfer coefficient changing along with time were analyzed and compared with experimental operating data. The result shows that the soil with air gap will lead the import/export temperature rise and reduce the heat transfer performance, and the average heat transfer coefficient reduces from 2.71W/(m·℃)to 2.22 W/(m·℃).