Abstract:In this paper, the seismic performance of polymeric-housed electrical equipment and the vibration absorption effect of dampers are investigated. To this end, a shaking table test was carried out on a polymeric-housed UHVAC capacitor voltage transformer, and the dynamic characteristics and seismic response of the equipment was analyzed throughout. White noise test results show that the first-order frequency of the equipment slightly reduced from 1.07 to 1.04 Hz after the dampers were mounted, which means that the damping device had a slight influence on the overall stiffness of the structure. The maximum stress and displacement response of the original structure under the input of artificial seismic waves with a peak ground motion acceleration of 0.2g (PAG=0.2g) were 46.33 MPa and 349.12 mm, respectively. The maximum stress and displacement response of a structure with PAG=0.5g after damper installation were 27.64 MPa and 330.06 mm, respectively. Based on simplified equivalent analysis, the reduction rates of the maximum stress and displacement are respectively 62.34% and 49.33% when PAG=0.3g, and 76.14% and 62.18% when PAG=0.5g. This shows that the seismic performance of equipment greatly improves after damper installation. This research can provide parameter data for seismic performance analysis of composite electrical equipment and the application of damper devices.

Abstract:Steel structures are light in weight, high in strength, and suitable for industrial manufacture. In China, there is currently a policy that supports the development of steel structures and their durability is gradually being addressed by designers, users, and researchers. In the design working life, even if a steel structure is maintained with an anti-corrosion coating, it is difficult to avoid corrosion as this is caused by external factors and the influence of corrosion on the performance of steel structures has become an urgent problem. Therefore, in this paper a dynamic time history analysis of multi-age (different degrees of corrosion) steel frame structures is carried out using ABAQUS software and the influence of corrosion damage is studied. The main work progressed as follows:based on the nonlinear finite element analyses from ABAQUS and using the control variable method, the main factors influencing earthquake damage in multi-age steel frames were found to be effective section shrinkage and ultimate strength degradation of the steel. Generalized corrosion damage was defined, and the relationship between corrosion damage and seismic damage in a non-corroded prototype structure explored. Finally, a multi-age structural damage model based on the earthquake damage in the non-corroded prototype structure was established.

Abstract:Based on the OpenSees platform, a model of a concrete-filled steel tubular (CFST) arch bridge is analyzed, and then it is compared with the results of the Midas Civil model. Through the incremental dynamic analysis (IDA) under strong earthquake records, the transverse nonlinear seismic performance of the arch rib of the CFST arch bridge is discussed. The bending moment time history curves of the arch foot and the displacement time history curves of the vault are compared with those of two different arch rib models (elastic beam element and fiber beam element). The yield mechanisms of the key sections of the arch rib are analyzed, and their IDA curves and vault displacement are drawn. The results show that under strong ground motions, the arch foot and vault do not necessarily yield first, but the section-changing position or limped-mass connection of arch rib, which must be carefully considered in the design. With the increase in ground motion, the arch rib gradually yields, beginning with the bracings, and then the arch foot and vault, and then the whole arch rib. The arch rib has a good nonlinear performance and seismic capacity.

Abstract:Refuge buildings often adopt the concrete replacement method to resist earthquakes, which results in a poor seismic performance when the buildings are subjected to strong earthquakes. Therefore, this study investigates the aseismic design method for steel strip refuge buildings under strong earthquakes. A complex network strip steel refuge building reinforcement model was adopted to calculate the strength and load capacity of a reinforced concrete before reinforcement. The section of the frame column was enlarged, and the load of the refuge building was increased. The earthquake resistance of the building wall was improved by a composite wall reinforcement model. When evaluating the collapse risk assessment of the reinforced building model, the full probability of collapse of steel strip refuge building was used to measure the collapse safety of the building during its design life. The experimental results show that the seismic performance of steel strip refuge buildings designed with the proposed method is relatively high when subjected to strong earthquakes.

Abstract:A base-isolated structure is a civil engineering structure with a long natural vibration period and is easily influenced by the long period spectrum characteristics of seismic ground motion. Some research results show that, compared with far-field ordinary seismic ground motion, an isolated structure may experience greater deformation under far-field long-period ground motion, and that this will cause structural damage. Therefore, the seismic performance of isolated structures under long-period ground motion is worth studying. In this paper, nine far-field long-period ground motion records were chosen from the Pacific Earthquake Engineering Research Center (PEER) as seismic input, and a lead-rubber bearing (LRB) base-isolated structure, based on the design code, was taken as the object of study. The seismic response of the structure was analyzed and compared under far-field ordinary and far-field long-period ground motion, and the effect of long-period ground motion on isolated structures was studied. The damage distribution law for base-isolated structures under long-period ground motion is discussed by defining the damage status of the concrete and steel in the structure. The research results show that the probability of damage to base-isolated structure under long-period ground motion is far greater than under ordinary ground motion. Furthermore, the damage distribution in isolated structures under long-period ground motion is uneven and is mainly concentrated in the bottom floors of the structure.

Abstract:In recent years, harvesting offshore wind energy has become a promising option for overcoming the problem of energy supply while still protecting the natural environment. China is rich in offshore wind energy along the east and southeast coastline, so it makes sense to invest in offshore wind farms. With wind turbine construction moving from onshore to offshore and into deeper and deeper waters, high construction standards and maintenance of the foundations and turbine structures are necessary to meet the adverse offshore environment. Therefore, the technological difficulties and costs of installing offshore wind turbines (OWTs) are increasing markedly and are becoming obstacles to the development of offshore wind energy. OWTs are relatively new structures and are meant to produce energy for 25 to 30 years, but we have no records on their long-term performance. The offshore wind turbine is a slender and flexible structure, and its dynamic behavior is strongly affected by environmental loading and the stiffness of its foundation. The first-order natural frequency of an OWT is generally close to the forcing frequencies imposed by environmental loading (wind, waves, and currents) and the onboard machinery. A change in foundation stiffness results in a change in the natural frequency of OWTs; therefore, rational choices regarding OWT foundations and accurate prediction of their long-term performances are very challenging. This paper establishes a simplified wind turbine model comprised of foundation, tower, and top mass. Based on the elastic restrained bottom condition, the coupling effect between the lateral and rotational stiffness is considered. Based on the improved model, differential equations, and boundary conditions, the effect of foundation stiffness and top mass on the structure's first dynamic response, i.e., its four orders of natural frequency, is studied. The conclusions in this paper can be used to predict the development trend of OWT dynamic behavior based on foundation stiffness variation, and can also guide the design of foundations and support structures in the future. However, rational choices of OWT foundations and accurate prediction of their long-term performances are still very challenging.

Abstract:This study aims to establish an integrated theoretical framework of a time-varying power spectral density (PSD) estimation for non-stationary earthquake ground motion excitations. First, time-frequency analysis methods, including the short-time Fourier transform, complex Morlet wavelet, and generalized harmonic wavelet transforms, are adopted to estimate the time-varying PSD in the presence of multiple samples. Priestley's estimation method is also introduced when the number of samples is limited. Second, by regarding the uniformly modulated and general modulated non-stationary Kanai-Tajimi models as the target seismic spectrum, a comparative study and an evaluation of the accuracy and the convergence of different time-varying PSD estimation approaches are performed. The guidance suggestions of the estimation method and the principle of parameter selection are also proposed herein to facilitate engineering application. Finally, a group of samples from three directions, including EW, NS, and UD of the 45th earthquake recorded in Strong Motion Array in Taiwan, Phase I or SMART-I, are used to reveal the typical transient features of the time-varying PSD and the coherence function among different directions. The results show that the complex Morlet wavelet and the generalized harmonic wavelet transforms exhibit a better performance compared to the short-time Fourier transform. The Priestley method also has advantages to one available sample. The earthquake ground motions of SMART-I exhibit dual non-stationary properties of intensity and frequency, and the three directions show a weak coherence. The research conclusions could also extend the application of spectral estimation theory in engineering and provide references for a further study on the multi-dimension and multi-point non-stationary seismic random response of large-span structures.

Abstract:The variable and strong random vibration caused by natural disasters such as earthquakes can cause great damage to the large-span concrete-filled steel tube column structures, resulting in life periodic attenuation of the whole structure of related buildings. This paper proposes a seismic performance testing method for large-span concrete-filled steel tube columns under random vibrations. Under the environment of variable and strong random vibrations, a test model was established; then, the vibration signal was separated from the noise by using the signal covariance matrix. The vibration signal was then processed by calculating the intensity, posterior density, and weight coefficient, and then the single life attenuation parameter was obtained. Afterwards, the particle swarm optimization (PSO) algorithm was introduced to solve the life attenuation suppression cycle of long-span concrete-filled steel tubular columns to judge their seismic resistance. The experimental results show that the judgement method for life attenuation suppression cycle of long-span concrete-filled steel tubular column structures can be used in the seismic test of relevant building structures under variable and strong random vibrations.

Abstract:In the traditional stereo-mechanical method based on the collision resilience coefficient, the energy loss caused by pile foundation collision is not considered in the analysis of settlement and displacement of building pile foundation, resulting in low accuracy and reliability of the analysis results. Therefore, this study proposes an improved Kelvin settlement analysis method for building pile foundation collision to solve this existing problem in the stereo-mechanical method. The Kelvin model is established with linear damping to analyze the damping of the pile foundation during the close and rebound stages of collision. The pile foundation collision is then transformed into the vibration of a single degree of freedom system. The vibration model is established to realize the effective calculation of relative settlement velocity and relative settlement displacement of the pile foundation. The maximum settlement displacement of the pile foundation is calculated based on the conservation laws of energy and momentum at the initial and end moments of the pile foundation collision settlement. The results indicate that the proposed method can improve the accuracy and reliability of the settlement analysis of the ground pile foundation.

Abstract:Previous studies on the factors influencing the seismic performance of buildings are confined to external conditions such as construction materials and technical methods. The influence of the safety factor of foundation soils and foundation pit conditions is often neglected, and this weakens the seismic performance of buildings. Therefore, in this study, the influence of foundation pit pile rows on the seismic performance of buildings is analyzed. Through the finite element strength reduction method, the safety factor of soil and the judging standards of the foundation pit condition were obtained, which helped to obtain the calculation parameter of each soil layer. Based on these parameters and the ABAQUS finite element software, the Mohr-Coulomb elasto-plastic soil model and a two-dimensional elastic pile model were adopted to establish a finite element analysis model of pile rows in a foundation pit. An experimental analysis method was used to analyze the seismic performance of a building from the aspects of row spacing and stiffness of the foundation pit. The experimental results show that if the foundation pit pile row spacing is properly selected, the seismic performance of the building would be effective. The greater the stiffness of the double-row piles, the better the seismic performance of the building, which tended to be stable with the increase of piles stiffness.

Abstract:The seismic performance of the pile foundations of bridges is very important in earthquake and geotechnical engineering. At present, the seismic design of a pile foundation only considers structural measures to ensure its seismic performance, which can lead to overestimation or underestimation of the seismic performance. Therefore, this study investigates the seismic design of a bridge using a three-dimensional finite element model. Under different seismic waves, the seismic response of a pile foundation was calculated, considering the soil-pile structure interaction, and the results were compared and checked. The results show that:(1) The internal force response of the pile is related to the frequency spectrum characteristics of the input ground motion; (2) for the pile foundation in a site, the result of finite element analysis is similar to that of the m method; (3) when the depth of pile cap is zero, the internal force of the pile body is relatively large, so it is necessary to take corresponding measures to reinforce the soil around the pile cap.

Abstract:To improve the transverse seismic capacity of continuous skewed girder bridges with elastomeric pad bearings and reveal their transverse seismic behaviors under different design parameters, the OpenSees was used to establish a three-dimensional finite element model of a typical continuous skewed girder bridge, while considering the sliding effect of elastomeric pad bearings, the hysteretic mechanical properties of reinforced concrete retainers, and the abutment-backfill interaction. The transverse seismic performance of the bridge was investigated for different combinations of retainer strength and gap. The results indicate that with an increase of both retainer strength and gap, the displacement of the bearings decreased in the transverse direction, but increased in the longitudinal direction. The transverse displacement of the main beams decreases with an increase of retainer strength. The increase of the plane rotation angle of the girder is detrimental to the shear safety of the bearings at the both sides of abutments. With greater strength and smaller gaps of retainers, the pier columns are more likely to be at an elastoplastic stage. In this paper, all the seismic performance indices of the modeled bridge satisfy the requirements in the design codes with a retainer strength of 40% of the reaction force and gap of 0.08 m.

Abstract:Based on basic theory of the seismic response of a multi-degree-of-freedom spatial structure system, the spatial seismic responses of a long-span continuous steel truss flexible arch bridge under uniform and non-uniform excitations are analyzed using the dynamic time-history analysis method and spatial finite element model created by ANSYS software. Results of analysis show that the peak value of the arch rib's axial force and the main truss's bending moment appear around the arch foot and side of pier under non-uniform excitation. Further results are as follows:the maximum axial force at the arch foot and the in-plane bending moment under the multi-directional input of a seismic wave are 1.28 and 8.32 times greater than those under single-directional input, respectively; the axial force at the arch foot and the in-plane bending moment under non-uniform excitation are 2.5 and 8.4 times greater than those under uniform excitation, respectively; the peak value of lateral displacement at the arch rib under the a transverse direction input is 2.4 times greater than that under a longitudinal direction input; while the peak value of longitudinal displacement at the arch rib under the input of longitudinal direction is 2.6 times greater than that under the input of transverse direction. The bearing form also has some influence on the seismic response of structure. Results show the necessity of considering the space and time effect of seismic waves during the seismic design of long-span steel truss arch bridges.

Abstract:Although China has established a relatively complete seismic design system for buildings and structures on land areas, minimal research has been conducted on seismic problems associated with marine engineering, particularly with respect to seismic response analyzes of reef sites. With the rapid development of the South China Sea in recent years, it is necessary to conduct a seismic hazard analysis during the design of reef sites. This study introduces typical engineering geological conditions and seismic activity characteristics of reef sites in the South China Sea. Through a comparison with common methods employed in site seismic response analysis at home and abroad, four critical factors and relevant solutions are proposed:(1) the terrain on islands and reefs in the South China Sea is distinct and it requires (2) specialized geo-technical engineering material; (3) the dynamic interaction between the seawater and reef should be considered; and the (4) input ground motion in the seabed of the South China Sea needs to be determined. This study provides research ideas for conducting stability analyzes of reef sites with respect to earthquakes, and also acts as a reference for seismic hazard analyzes during construction on islands and reefs in the South China Sea.

Abstract:Focal mechanisms of small and micro earthquakes are used as basic data for studies on regional stress fields and for other geodynamics studies. The Shaanxi region is at the intersection of several seismic zones, and abundant waveform data of small to microseismic events have been accumulated in recent years. This study uses the recently developed generalized polarity and amplitude technique (GPAT), together with a 2015 crustal velocity model of Shaanxi, to invert the focal mechanisms of 121 small and micro earthquakes with a range between M_L1.5 and M_L3.5 that occurred between April, 2011 and December, 2015, that were recorded by the seismic network of Shaanxi. Inversion results show that focal mechanisms of these events were mostly strike-slip and normal-fault types (64.5%) and thrust faulting types (22.3%). In addition, there is a good consistency between the focal depth inverted from the focal mechanism and the location depth. However, there is a difference between the moment magnitude and local magnitude, and this difference increases with a decrease in magnitude. Furthermore, compared with other study results conducted within the Weihe fault zone, this study verifies that normal fault types mainly control the focal mechanisms of earthquakes, and they are in a state of tensile stress.

Abstract:Using the phase data of Pn, Sn, Pg, and Sg recorded by the Xinjiang seismic network from January 2009 to July 2014, the average traveling velocity of the Pg, Pb, and Pn phase (v_pg, v_pb, and v_pn), and the depth range of Conrad and Moho discontinuities (H_conr and H_moho) are determined in the Xinjiang area using linear fitting, reduced travel time, PTD earthquake location, and HypoSAT location methods. Computational iteration is implemented on the sample data with velocity and depth steps of 0.1 km/s and 1 km, respectively. After analyzing and comparing calculated results between sample data from national unified earthquake cataloging and the existing 3400 model for the Xinjiang area, a 1D velocity model with a minimum average RMS is established. The parameters of the new model include v_pg, v_pb, and v_pn of 6.10 km/s, 6.70 km/s, and 8.20 km/s, respectively, and H_conr and H_moho of 26 km and 54 km, respectively. Through tests and comparisons, the new model is found to be superior to the existing 3400 model for the Xinjiang area.

Abstract:Researching on seismic sand liquefaction is one of the important methods of studying historical earthquakes and paleoearthquakes. Its result has great meaning in evaluating regional seismic risk. The horizontal and sectional characteristics of sand liquefaction in the Huangjiagou and Changxing villages in Xianyang City, Shaanxi Province were investigated. The sand liquefaction was clearly induced by earthquakes. According to the archaeological identification of the cultural layers, where the dikes of the two sites both pass through, the sand liquefaction might have formed during the Ming Dynasty. Moreover, the corresponding earthquake was the 1556 Huaxian M8¼ earthquake, the 1568 M6¾ earthquake in eastern Xi'an, or the 1487 Lintong M6¼ earthquake. The controversial epicenters of the Qishan M ≥ 7 earthquake in 780 B.C. and the Qin-Long M=6~7 earthquake in 600 A.D. were discussed based on the other sand liquefactions we found in the Weihe Basin before. Defining the epicenter of the 780 B.C. earthquake as magnitude 8 needed more evidence. The epicenter of the 600 A.D. earthquake should not be near Xi'an. The conclusion provides new circumstantial data for the seismic hazard evaluation of several main active faults in the Weihe Basin.

Abstract:This paper analyzes characteristics of strong ground motion recorded during the August 24, 2016, Italy M_W6.2 earthquake. Regression analysis is used to obtain the amplitude attenuation of ground motion occurring during this earthquake. A comparison is then conducted with other models and attenuation characteristics are found to be in basic agreement with those of other prediction equations; however, the far-field actual observed values are lower than those of predicted values. The response spectra during different periods and with differing site conditions are subsequently calculated using a damping ratio of 5%. Results show that large amplitude response spectra at four near-source stations are higher than the design response spectrum of the Europe seismic design code of 2008, and that peak values of response spectra are focused on a range between 0 and 0.5 s. The earthquake caused relatively serious damage to Rieti, Italy, particularly to short-period structures; this is mainly because:(1) the earthquake was a shallow destructive event and local buildings were built with un-reinforced bricks and cement; and (2) the seismic fortification level was not high enough. In relation to these earthquake damage characteristics, it is evident that the central Italian region needs to improve seismic fortification during practical construction to ensure the security level of structures.

Abstract:In this study, the temporal variation and spatial distribution characteristics of geomagnetic total intensity in mobile geomagnetic observation were analyzed using the mobile geomagnetic observation data from Hebei province between 1986 and 2009; in addition, the characteristics of mobile geomagnetic anomalies were discussed. The results show that there is a certain relation between the mobile geomagnetic changes and earthquakes in the area. The precursory anomalies usually appear 1~2 years before the earthquake. The δ_F value has the variation characteristic of "continuous sharp rise-impending sharp decline." The bigger the magnitude the larger is the geomagnetic anomaly. In this study, only M_L ≥ 4.0 earthquakes occurring in the monitoring area can reveal seismic change information that can better predict the earthquake.

Abstract:It is important to study seismic wave propagation through fractures in the field of earthquake engineering. Based on elasticity mechanics and wave motion theories, the propagation law of an anti-plane SH-wave across a ground fissure interface is analyzed using time-domain and frequency-domain calculation methods in this paper. Recursion equations are established and a contrast verification between the two methods is conducted. The influence of certain related parameters on the propagation law of anti-plane SH-waves are discussed, including the equivalent shear stiffness of the ground fissure interface, incidence wave frequency, incident angle, and shear strength of the fissure surface. Furthermore, a cross-comparison of these parameters is performed, and recursion equations considering the shear strength of fissure are established. Results indicate that the transmission coefficient increases with an increase in equivalent shear stiffness and the incident angle, but decreases with an increase in incident frequency. In addition, the low-pass filtering effect of the ground fissure interface is more evident with a decrease in equivalent shear stiffness and the incident angle. Under the input of a real seismic wave, there is a decrease of transmission coefficient but no obvious decrease in the amplitude of the transmission wave. However, the waveform change is obvious. The amplitude and wave form of the reflection wave gradually approach the incident wave, but the effect of hysteresis occurs in the phase relative to incident wave. To obtain an effective and real propagation law of wave motion, fluctuation time-history data were processed using linear interpolation, and results indicate that there are no changes to the precision of calculation results using this method.

Abstract:When using the traditional static analysis method to analyze the influence of strong motion on the variation of the attribute parameters of rocks in mountainous areas, the interaction between the bottom and top of the rock fragment is neglected, which leads to inaccurate analysis results of rock density and other attribute parameters. Therefore, in this study, an influence analysis method is proposed to analyze the influence of strong motion on the attribute parameters variation of rocks in mountainous areas. With the proposed method, the degree to which the rock was subjected to strong motion can be effectively shown through the elevation control effect. Indoor and outdoor measurements of the original and fragmented rock densities are carried out, and the unloading and pressure between gravels are added to the measurement results. Then the variation in the results of various parameters such as density, porosity, natural water absorption rate, permeability coefficient, and softening coefficient of rock are obtained with the wax-coated method, and then, they can be effectively analyzed. The experimental results that show the proposed method is highly accurate for analyzing the attribute parameters variation of rocks in mountainous areas subjected to strong motion.

Abstract:The traditional location method based on cloud computing needs to analyze a large amount of geographic data, leading to a complex location process and errors in the location results. Therefore, this study puts forward a new unmanned aerial vehicle (UAV) global positioning system (GPS) remote sensing location method in a post-earthquake area. Its functions include the sensing subsystem, remote sensing air control subsystem, UAV platform, UAV ground control subsystem, three-dimensional (3D) model image reconstruction, and target location analysis. In reconstructing the 3D image model of the earthquake disaster area, we first extracted the digital elevation model (DEM) data of the area, then mapped the image texture measured by UAV GPS remote sensing to the DEM. We used the ranging target positioning method to perform the target localization analysis. The UAV was used in different positions to locate the target to realize the location analysis of the post-earthquake area and obtain the target coordinate. The experimental results showed that the proposed method can improve the precision of the target location and shorten the time of the target location.

Abstract:Destructive earthquakes often lead to serious economic losses and casualties, so it is important to evaluate the value of earthquake loss, for it can help to improve the seismic capacity and reduce the loss of earthquake disasters. In seismic data processing, traditional spatial models cannot deal with the interference of big data on the spatial scale selection, and drawbacks of large deviation and high volatility of seismic loss assessment results must be faced. Therefore, this study designs a seismic loss assessment model based on the cloud computing platform, HAZ-China. The service levels, seismic application service layer, and system structure of the cloud computing platform, HAZ-China, were designed to provide pre-, co-, and post-seismic loss value evaluation services. The model can realize the storage and analysis of big data, then design the building damage database and cloud computing model using the distributed database, HBase. The model can accurately evaluate the seismic loss value through a comprehensive assessment of the seismic disaster loss. The experimental results showed that the designed model can realize an accurate evaluation of the value of earthquake loss, and had high convergence, efficiency, and stability.

Abstract:The earthquake emergency surveying and mapping information is of great significance for overall acquisition of earthquake disaster information in the earthquake-stricken area. However, the current surveying and mapping information for seismic area exists in the form of independent classification, lacking of data correlation, and has a large defect in the whole information acquisition, so its ability of earthquake emergency response is poor. We propose herein an intelligent comprehensive processing method for earthquake emergency surveying and mapping information to obtain comprehensive earthquake disaster information and effectively deal with immediate earthquake disasters. Based on the method, we can establish an earthquake emergency linkage information service platform and design the discernment frame of earthquake disaster. According to the judgement of earthquake disaster discernment frame, the eigenvector of earthquake disaster surveying and mapping information can be extracted, and the rule set of earthquake disaster information can be obtained. By using the surveying data fusion algorithm, the intelligent fusion of multi-source earthquake disaster information can be realized, and the fusion results of multi-source earthquake disaster surveying and mapping information can be obtained. Then the intelligent comprehensive processing of an earthquake disaster can be realized. The experimental results showed that the proposed method has a strong ability of information acquisition and analysis in the intelligent comprehensive processing of earthquake emergency surveying and mapping information.

Abstract:Uplift bearing capacity is an important part of pile foundation design. In ocean engineering, there is a growing demand for piles that have enough uplift bearing capacity for construction in offshore wind farms. The method for calculating the uplift bearing capacity of pile foundations given in current codes is rooted in the modification of the compressive bearing capacity of pile foundations, and the theoretical research is limited to semi-empirical and limit equilibrium methods. Therefore, there is big difference between calculated and measured values. This paper systematically explains the current calculation methods for the uplift bearing capacity of pile foundations, then uses different methods combining them with practical projects. The results show that:the uplift bearing capacity calculated by the method given in the API code is closer to the measured value in clay; the Meyerhof and Das algorithms are ideal for uplift piles with a small length-diameter ratio; and Chattopadhyay and Shanker's algorithms are suitable for piles in sand. We also found that the current methods for calculating uplift capacity ignore the adhesion force and negative pore water pressure, resulting in great differences between calculated and measured values.

Abstract:In element and model tests, high-accuracy measurement for the internal displacement field of a sample is crucial in investigating the mechanical property of the material under loading. In this study, a frequency-domain finite element method based on the energy minimization principle is developed for elastic wave CT. Through solving the wave equation numerically, the displacement fields are estimated and then compared with their actual values. Thus, the renewal gradients of the parameters of every element are obtained, including the density (ρ) and the Lame constant (λ). Furthermore, the distribution of density (ρ) and the Lame constant (λ) can be acquired upon several iterations. The new method can avoid solving the Jacobi matrix, leading to a great improvement in calculation efficiency. In addition, the numerical inversion iteration of the Lame constant (λ) shows high efficiency and accuracy when the whole displacement field is known, and the efficiency and accuracy gradually decrease with an increased number of unknown displacement nodes.

Abstract:Rock is a typical brittle non-uniform material that is rich in various internal defects (cracks, pores, joints fissures), which make the rock damage and failure mechanism very complex. Theoretical and laboratory experimental studies indicate that energy plays an important role during rock deformation and failure and abrupt energy release causes rock failure. Under certain conditions, this energy release can constitute an energy dissipation catastrophe. From the thermodynamics perspective, the process of rock damage is irreversible and energy release, the essential characteristic of rock deformation and failure, reflects the process of the propagation of internal defects and decreasing strength. The process of rock damage is one of constant energy evolution, so rock deformation and fracture can be well described from the energy viewpoint. Based on previous studies of rock damage, we know that the elastic modulus decreases while plastic strain emerges in the loading process. Based on the above analyses, we can define the damage variable with respect to energy. By relating the effective and total stress in the unloading stage of the stress-stain curve, we can determine a method for calculating the damage modulus. We conducted a statistical analysis of the damage parameters of rock under uniaxial and triaxial states to calculate and contrast the damage moduli. The results show the damage modulus to have a gradual decreasing trend with increasing confining pressure, whereby the damage modulus first decreases and then tends to stabilize. In addition, our method for calculating the damage modulus takes full account of the influence of the confining pressure. Building on the studies mentioned above, the analysis results of this paper promote further understanding of rock damage and failure.