Abstract:Liquefaction of saturated silty soil can easily occur during strong earthquakes.To investigate the liquefaction of a saturated silt mixture, a series of cyclic triaxial tests is conducted.Some factors such as clay particle content, relative density, effective confining stress, and cyclic stress ratio are examined by analyzing the cumulative dissipated energy for triggering liquefaction.The results show that for low (high)values of clay particle content, an increase in clay particle content with the same relative density leads to a decrease (increase) in cumulative dissipated energy.The effective confining pressure and relative density have strong effects on the cumulative dissipated energy.However, the cumulative dissipated energy is independent of the cyclic stress ratio for the specimens with constant relative density and confining pressure.

Abstract:Field observations and laboratory studies indicate that sand with a certain amount clay can be easily dynamically liquefied under certain conditions and that the amount of clay has a complex impact on the liquefaction resistance of sand.Using a CKC dynamic tri-axial test system, the liquefaction resistance of sand samples with different clay content (0%, 5%, and 10%) was investigated.The results show that the sand sample with 5% clay had the lowest liquefaction resistance;the generation of pore water pressure is obviously effected by the clay content.The liquefaction mechanism of the sand-clay mixture is explained according to the experimental results.

Abstract:The cracking of soil has resulted in significant geological engineering and environmental problems.Indoor experiments on water loss ratio and the desiccation cracking of clay were carried out at room temperature.The research results indicate that:(1) the cracking progress can be divided into pre-cracking, rapid cracking, and cracking stagnation stages, (2) the cracking process is influenced by the buried hill of basement, and (3) though the surface cracking persists, the pattern of cracking has not significantly changed.The later cracks were approximately perpendicular to the early cracks, especially in the basement zone.The change in metric suction and surface shrinkage through water loss leads to the desiccation and cracking of the clay and the cracking process is controlled primarily by the boundary and geomorphologic form of the basement.

Abstract:Research on soil liquefaction under in-situ conditions will be an important branch in soil dynamics.At present, in-situ liquefaction test under artificial dynamic loading remains at the research stage;there have been only a few studies.This paper presents a method for in-situ liquefaction test based on a remolded saturated sand model.Many technological problems related to this method are discussed, which include five parts:(1)test apparatus, (2)ground motion stimulation, (3)test pit arrangement, (4)saturated soil model preparation, and (5) data measurement and acquisition.An in-situ liquefaction test using this method was performed in this study.The surface soil acceleration and pore water pressure data indicate that soil liquefaction occurs under artificial dynamic loading.The main points are:(1)A dynamic loading system can simulate strong ground motion with an acceleration from 0 to 7 m/s².(2)Under a loading frequency of 13 Hz to 15 Hz, the soil liquefaction test can be performed relatively easily when the distance between the soil model and loading base is 0.5 m to 2.5 m.(3)Measurement positioning and water-proofing are key factors during the preparation of the saturated soil model.(4)More request in data measurement and acquisition should be raised because of little acknowledges for soil liquefaction at site.(5)Experimental results indicate that this technology is practically feasible.Studies on special liquefaction problems can be performed using this method. It also paves the path for further studies on geotechnical in-situ testing techniques under artificial dynamic loading.

Abstract:The seismic capacity of residual deformation of the fine-grained soils which are buried deeply in super-deep overburden layer is poor, and a great seismic settlement of dam-foundation system may be produced by the earthquake when the thickness of soil layer is large.So it is significant for the anti-seismic design of dam to study the seismic residual deformation characteristics of soil and determine the corresponding characteristic parameters.In the paper, a series of dynamic triaxial tests on silty sands buried deeply in the super-deep overburden layer foundation of an earth-rock fill dam in China are carried out, and the seismic residual deformation characteristics of soils in earthquake are analyzed.The results show that:(1)the grading curve of testing soil is consistent with the mean grading curve of corresponding drill on field soils, and the grain composition properties of field soils can be represented by the testing soil;(2) the seismic residual deformation characteristics of testing soil is influenced by the density of soil and the stress condition, and the consolidation ratio is a significant influencing factor;(3) the influencing laws of factors on axial deformation characteristics and those on residual volumetric deformation of soils are different.

Abstract:Wave load causes continuous rotation of the principal stress axes of seabed soil.Unlike seismic load and traffic load, under the action of cyclical wave load, stiffness softening of soft clay is much more obvious.Numerical simulation is applied to obtain the stress response of undisturbed and disturbed seabed soil, and to analyze the characteristics of the stress path.Under wave loads, the main feature of the seabed soil is the continuous rotation of its maximum principal stress axis;the maximum principal stress' cycle is similar to the wave load cycles.Under the influence of the structure in the seabed disturbance, the soil's stress path changed under the wave load, and the factors that affect the stress path can be generalized using the initial principal stress orientation, the initial stress ratio, the angle of the major principal stress direction, and other factors.To describe the relation of a soil's stress and strain after stiffness softening, two parameters were introduced to the Haridin-Drnevich model to reflect the stiffness softening and cumulative plastic strain phenomenon, and these two parameters are a function of the soil's initial status, which influences its stress path under wave load.The cyclic coupling shear tests can probably simulate the wave load and therefore, this modified Haridin-Drnevich model should be compared with the results of cyclic coupling shear tests where wave loads can be applied to verify its reliability.

Abstract:Under seismic loading, sliding bands originating from landslides are usually composed of coarse and fine grains.The dynamic features of sliding-band soils and the development of dynamic pore water pressure during the cyclic loading process are extremely important to the stability of slopes.Dynamically cyclic triaxial tests on gravels including fine particles smaller than 0.5 mm were conducted to investigate the influence of fine particles on the dynamic pore water pressure features of these mixed soil gravels of 6~20 mm.Three groups of specimens with fine contents of 0%, 20%, and 40% were tested using a triaxial dynamic apparatus wherein the consolidation confining pressure was 100 kPa, the ratio of consolidation was 1.0, and the frequency was 1.0 Hz.Dynamic axially cyclic stress of 0.50 kN, 0.55 kN, 0.60 kN, and 0.65 kN was applied to each group.The specimen shape was cylindrical, and the specimen size was 100 mm × 200 mm.The dry densities of the specimens with fine contents of 0%, 20%, and 40% were 1.605 g/cm³;1.741 g/cm³, and 1.570 g/cm³, respectively.After the tests were concluded, the development of dynamic pore water pressure and its evolution laws were obtained and analyzed in detail. It was experimentally determined that under the same dynamic load, a more rapid increase in dynamic pore water pressure occurs when the fine soil particle content is small;when the content is high, the speed is lower.For the same fine grain content, a small dynamic load resulted in a low speed increase of dynamic pore water pressure; when the dynamic load was high, the increase was rapid. Moreover, a larger dynamic load and smaller fine grain content resulted in relatively larger dynamic pore water pressure of soil specimens that tended to be stable.The number of the dynamic cycles was largest (smallest) when the specimen with fine content of 20% (40%) was wreck.At the end of the experiment, the pore water pressure of the soil specimen was close to the consolidation confining pressure with fine contents of 0% and 20%.For the specimens of 40% fine content, the pore water pressure was close to the consolidation confining pressure under a high dynamic load.

Abstract:This study addressed the influence of the shear-wave velocity test standard deviation on ground motion.The Shake 2000 program and site model of Turkey Flat were used to analyze the response spectrum of ground and peak acceleration under a variety of engineering conditions by inputting different types of multi-intensity seismic waves.The study concluded the following:(1)the impact of the shear wave velocity test standard deviation on ground motion in the shallow stiff soil site is related to the intensity and frequency of the input seismic waves, and the calculated value of shear wave velocity;(2)if the response spectrum residuals or peak acceleration D-value exceed 20%, the effects of the velocity test standard deviation cannot be ignored in most situations;(3) when the predominant period of the input ground motion is similar to the characteristic site period, the changes of the response spectrum caused by the shear wave velocity test standard deviation in the shallow stiff soil site is significant;(4)only when the predominant period of the input ground motion with weak intensity and the characteristic site period are largely different, can the changes in the response spectrum caused by the test standard deviation be omitted;and (5)if the shear wave velocity in the shallow stiff soil is lower than the statistical mean value, the calculated value deviation of ground motion is larger than the measured value of shear wave velocity which is higher than the calculated mean value, and the ground response is more obvious with higher intensity of the input ground motion.

Abstract:The dynamic shear modulus ratio and damping ratio are two important parameters in seismic risk assessment and can directly affect the soil dynamics of engineering sites.The analysis of seismic hazards and soil layer seismic response showed that dynamic soil parameters were the key aspects that influenced the results of the analysis.In this study, 66 recent seismic risk assessment reports in the Tianjin area were collected, which contained representative and complete experimental data of soil dynamics parameters.Using two statistical methods, the dynamic parameters of experimental soils in these reports (e.g., silty clay, clay, silt, sand, silt soil, etc.) were statistically analyzed by depth and the average value of the dynamic shear modulus ratio and damping ratio.Next, the soil analysis models of two representative engineering sites (located at the Tianjin urban district and Tangu suburban district) were developed and the soil layer seismic response was calculated.The analysis showed that the two statistical values were representative and adaptable in the Tianjin area, and were more consistent with the practical measured values.Therefore, the two statistical values that were derived could be used to conduct the soil seismic response analysis for sites in which it was difficult to acquire undisturbed soil samples, especially for the thin interbed soil.

Abstract:During earthquakes, piles undergo stresses due to both the motion of the superstructure(inertial interaction)and that of the surrounding soil (kinematic interaction).Based on the artificial viscoelastic boundary, a 3D numerical model of seismic performance for superstructure-pile-soil interaction was developed to analyze the kinematic response of PHC pile (prestressed high concrete pipe pile) during earthquakes.The kinematic seismic interaction of single piles embedded in soil was evaluated by focusing on the bending moments induced by the transient motion.Considering the conditions of layered soil, factors influencing the analysis included PHC pile diameter, the ratio of shear wave velocities between two soil layers, the depth of embedded soil, and the inertial loading of the superstructure.The results indicated that pile diameter affects the amplitude of bending moments at the pile head.Specifically, at the interface between layers for a given soil deposit, the bending moment increased as the pile diameter increased, especially at the interface of two soil layers.In soil profiles where the transition between layers was distinct, the bending moments in the pile were significant, especially near the interface of soil layers with highly contrasting stiffness.The bending moment at the interface between two soil layers of soil increased when the ratio of shear wave velocities increased.An increase in the depth of overlying soil in two soil layers would also cause an increase in the pile bending moment at the interface between the two layers.The fixed head of a pile and the interface of two soil layers would increase the bending moment.The superstructure had an important influence on the bending moment of the pile head, but not for the deep section of the pile.The conclusions of this study will lead to recommended reference criteria for the seismic design PHC piles

Abstract:Suction anchors are widely used in deep sea oil and gas engineering as a foundation for spars and TLPs because of their considerable uplift capacity and convenient installation.The suction anchor mainly sustains dynamic loads transmitted from the mooring line except for steady loads.The dynamic loads can be divided into two, wave-frequency loads with smaller amplitude and shorter period, and the second-order slow drift loads with larger amplitude and longer period.When the suction anchor is subjected to dynamic uplift loads with different frequencies and amplitudes, pore pressures increase in the soil around the anchor.In this study, to investigate the development of oscillatory pore-pressure and the accumulation mechanism of residual pore pressure in the seabed soil, a finite element model of a suction anchor embedded in a porous seabed subjected to dynamic uplift forces is constructed.On the basis of a steady uplift load, the pressure distribution and development under dynamic loads with different amplitudes and periods are contrasted.The results indicate that oscillatory and residual pore-pressure responses are significant around the anchor.Negative oscillatory pore-pressures mainly appear at the lower part of the anchor.Residual pore-pressure builds-up in the shallow soil, reducing the soil effective stress and the friction between the anchor and soil.Consequently, the failure mechanism may change and the uplift capacity is reduced.

Abstract:The point-peak method has been used for many years to analyze the linear displacement amplitude-frequency response curve of dynamic foundation. In this method, however, the subsoil damping ratio is low and is thus low in the code for dynamic foundation design.In this study, a multi-peak method is presented for measurement and analysis to increase the damping ratio.This method is used in the design of a hydraulic vibrator foundation with better economic results and has been also been used in well operation.This paper describes the differences in the two methods, including stiffness.The point-peak method has limitations.With increasing frequency, the damping ratio unusually decreases.The ratio value is zero at peak frequency but is 0.707 at the origin.Moreover, stiffness is larger at peak frequency but smaller at the origin.Therefore, the damping ratio is smaller in the peak area, and thus in our code for design of dynamic machine foundation, resulting in an excessively large and wasteful foundation.In addition, one parameter group is obtained by analyzing the single response curve with the point-peak method, and different groups from other curves of one foundation unusually appear because there is only one group for one foundation.On the contrary, in the multi-peak method, the parameters obtained by analyzing two curves, namely two by two, are generally very close and may be averaged.This method is more economical, and stiffness is decreased along an increase in frequency, and the static stiffness is larger than dynamic stiffness.This result agrees with the half space theory of foundation.The code for design of a dynamic machine foundation is mainly applied to the foundation design of a reciprocating compressor with a single working frequency.Resonance can be avoided if the natural frequency is larger or smaller than the working frequency.In such cases, the effect of damping is less, and the damping ratio may be small. In hydraulic vibrators with a wider working frequency zone, however, resonance cannot be avoided.In such cases, the damping ratio must be larger to control the resonance.

Abstract:Using the finite element liquefaction program based on Biot's dynamic theory for fluid-saturated porous media and a multimechanism constitutive model for sandy soils, dynamic effective stress analysis of an earth dam on deep sandy alluviums during an M6.8 earthquake is conducted.A comparison of calculated and measured values shows some differences in acceleration and permanent deformation.Because the calculated values essentially reflect actual distribution, the accuracies of the numerical and constitutive models are validated.On the basis of the numerical analysis results, it can be concluded that a reinforcement measure for the dam and its underlying foundation is unnecessary because liquefaction in only a small area may occur in these zones. However, an anti-liquefaction reinforcement measure should be taken because liquefaction in large areas may occur in the shallow layers of sandy alluviums near the dam toe.

Abstract:To meet the requirements of bearing capacity and anti-liquefaction of liquefiable foundations, the reinforcement of liquefiable soil using CFG piles combined with gravel piles is used in engineering.In this study, a composite foundation with multi-type piles composed of gravel piles and CFG piles was analyzed.In composite foundations with multi-type piles, gravel piles are supplemented piles that are mainly used to accelerate the foundation drainage consolidation.CFG piles are the main piles that undertake greater seismic load and reduce the dynamic pore pressure and post-earthquake settlement of the foundation.A composite foundation with multi-type piles composed of gravel and CFG piles can improve the bearing capacity and liquefaction resistance of a liquefiable foundation.A three dimensional numerical model was established and the dynamic characteristics of a composite foundation with multi-type piles was studied through numerical simulation;the influence of design parameters such as the ratio of pile type, pile diameter, pile length, CFG pile body stiffness, and gravel pile body permeability on dynamic characteristics of a composite foundation with multi-type piles was analyzed.The results show that the dynamic deformation of a composite foundation, including gravel pile composite foundation, CFG pile composite foundation, and composite foundation with multi-type piles is obviously smaller than that of a natural foundation during earthquakes, and the dynamic deformation decreases with increase in the number of CFG piles.When the ratio of gravel piles and CFG piles is 4:5, the dynamic deformation curve of a composite foundation with multi-type piles is close to that of the CFG pile composite foundation and the influence of the increase in the amount of CFG piles on the reduction in the dynamic deformation of the composite foundation is no longer obvious.When the ratio of gravel piles and CFG piles is 4:5, the dynamic pore water pressure of the composite foundation with multi-type piles is relatively small compared to that of the CFG pile composite foundation, and the composite foundation settlement caused by the earthquake is also relatively low.In engineering design, an appropriate ratio of gravel piles to CFG piles is 4:5.The pile diameter, pile length, CFG pile body stiffness, and gravel pile body permeability can affect the dynamic deformation of a composite foundation with multi-type piles.With increase in the pile length, pile diameter, and CFG pile stiffness, the vertical dynamic deformation of the composite foundation with multi-type piles decreases gradually.With the increase of the permeability of the gravel pile body, the excess dynamic pore water pressure in the composite foundation with multi-type piles and the deformation after an earthquake decrease.

Abstract:A large number of buildings and transportation facilities have been constructed in recent years. Residential areas, commercial centers, industrial areas, and highways have formed a three-dimensional transportation network, and artificial vibrations are generated with high frequency and large cycle numbers.Artificial vibration has become a new type of environmental pollution, and is listed as one of the world's seven major environmental hazards.All the various types of artificial vibrations involve the generation and dissemination of elastic waves.Setting up of barriers between vibration sources and protection zones can block the elastic wave propagation path, attenuate the vibration energy, and reduce the vibration amplitude;this has become one of the most effective vibration isolation measures.Based on the geometric structures, normally-used barriers can be divided into two types:(1)continuous barriers, which are integrated structures, such as open trench, concrete walls, and trenches filled with mud, sawdust, or foam;and (2)discontinuous barriers, which are composed of individual elements, such as one row of cylindrical cavities, solid piles, or hollow pipe piles.In this study, theoretical and experimental studies of these two types of isolation barriers are reviewed and some important conclusions are drawn;(1)the effectiveness of continuous isolation barriers is better, but the depth of the barriers is usually required to be more than ten meters for vibration sources with low frequencies, which approaches half the wavelength of a Rayleigh wave, and so high construction costs and large construction difficulties are caused when constructing in soft soils or regions with high groundwater levels;(2)discontinuous barriers can be easily constructed, are not limited to depth and space, do not need additional support and maintenance, and so several rows of discontinuous barriers have more application prospects.In the future, isolation studies should focus on three-dimensional theoretical analysis and experiments on new absorbing materials with several rows of discontinuous barriers.

Abstract:As unique underground structures, submerged tube tunnels have been subject to vehicle loads for long periods of time.As the loads change, the underwater tunnel will show cyclical changes in displacement, bending moment, and ground reaction force.These periodic changes represent a significant potential threat to the integrity of tunnel structures.The purpose of this study was to assess the impacts of vehicle load on those tunnels.The modal superposition method was used to analyze three characteristics of vertical displacement, bending moment, and ground reaction force in underwater tunnels.In this method, two conditions were assumed:(1)the underwater tunnel in soft soil areas is the foundation of the Kelvin model, and (2)vehicle loading is the fluctuation of load form changing with time.The impact of vehicle speed and the foundation soil modulus on the tunnel's vertical displacement and bending moment was analyzed.Using the Beam-On-Elastic-Foundation (BOEF) model, combined with data from the Tianjin Haihe River tunnel engineering, the results of the analysis showed that:(1)the midpoint pipe vibration amplitude induced by vehicle loads was up to 5 mm, the midpoint pipe bending moment was approximately 15 500 kN·m, and the vibration cycle was 0.25 s;(2)the higher the vehicle speed, the shorter the pipe vibration cycle time, the more intense the vibration, and the lower the effect on amplitude;and, (3)the greater the modulus of foundation soils, the smaller the amplitude of vibration and bending moment, and the lower the effect on the cycle.

Abstract:This article briefly introduces the seismic safety community and the composition and performance parameters of buckling-restrained braces.The seismic safety community is the community that experiences small destructive earthquakes.Specifically, these communities have carried out effective seismic fortification of all buildings in compliance with seismic hazard regulations.In the seismic safety community, improving the seismic performance of buildings is the primary goal.Local seismic fortifications meet the minimum seismic requirements, and the level of fortification of buildings is increased using certain technical measures.The traditional method of seismic fortification is to increase the size of major structural components, such as beams, columns, and shear walls, and to improve the ratio of reinforcements to buildings.However, increasing the amount of material increases cost and reduces the usable area of buildings.The new method calls for change to the seismic characteristics of the structure itself and improvements to its capacity for energy dissipation through the use of isolation and dissipation technologies.In the structural system, the seismic sections generally remain the same, and cost increases are small.Buckling-restrained braces have gained widespread application as measures for energy dissipation and earthquake resistance.They also overcome the disadvantages of traditional energy dissipation braces.The component's full section will yield during compression, effectively minimizing local buckling failure and overall buckling failure.Therefore, the energy dissipation capacity of the components is maximized and the seismic response of the structure is reduced.The Dalian Aonan Mingxiu manor project described in the paper is a pilot project undertaken in the Dalian earthquake safety community.The project addresses building security and earthquake safety at the design stage.By installing buckling-restrained braces, the seismic characteristics of the structure itself are changed.To determine whether the structure can achieve the goals of seismic fortification, the project conducts an elastic-plastic analysis by installing buckling-restrained braces in the original frame structure.In this study, the ABAQUS software was used to conduct the dynamic and time-history analysis of two models of reinforced concrete framework: the origin structure and the structure with buckling-restrained braces added.The shock absorption effects of the buckling-restrained braces were analyzed.The results of the analysis showed that buckling-restrained braces could significantly reduce the inter-storey drift angle of a reinforced concrete frame during rare earthquakes and improve the level of seismic fortification buildings.

Abstract:Lingzhao Veranda (also called Crystal Palace) is located in the eastern part of the Palace Museum (the Forbidden City), which was planned for the amusement of the royal family in 20^th century.However, construction of the building lasted only three years, and the building has lain idle until the present.The building is composed of a center bearing frame and four surrounding white marble verandas.The frame is composed of I-section steel beams and a ring of iron columns.In addition, on top of the bearing frame and verandas, there are five iron booths.Because the building has been idle for nearly 100 years, structural problems have appeared on the frame due to a number of factors, such as shortage of bolts, slack in joint connections, and cracks in the iron columns.The National Center for Quality Supervision and Testing of Building Engineering has conducted on-site inspections of the steel structure, and concluded that the beams and columns are structurally sound.However, the joints need to be strengthened.As a historic building, the Lingzhao Veranda is worth protection for its artistic, historical, cultural, and architectural values.To effectively protect this historic building, it is necessary to assess its current structural safety.Such an assessment may provide a direction for future maintenance and restoration of the building.The status of the structure can be determined through simulation methods.For the purpose of this study, the ANSYS program was used to study the aseismic performance of the steel structure.Beams and columns of the frame are connected by steel bolts, which form a type of semi-rigid joint to release part of moment of the joint.Three spring elements of the ANSYS program are used to simulate rotation stiffness values of the beam-column joints.The degradation of rotation stiffness in the joints is also considered.In addition, because some steel beams are embedded in the white marble walls, the embedded locations of the beams are considered as a fixed boundary.Accordingly, the finite element model of the steel structure is developed.Using modal analysis, the structure's basic frequencies and primary modes are determined.Using response spectrum analysis, the distribution of its deformation as well as internal forces under Ⅷ-degree intensity of frequently occurred earthquakes are analyzed.Using time history analysis, the structure's anti-collapse performance under Ⅷ-degree intensity of rare earthquake events is estimated. Results of modal analysis show that the basic frequency of the steel structure is 5.31 Hz.The structure's primary modes focus on mode 5 in x direction and mode 1 in y direction.Both modes behave as a local vibration of the steel booths in level directions, which relates closely to degradation of the stiffness in its beam-column joints.The response spectrum analysis shows that, under Ⅷ-degree intensity of frequently occurred earthquakes, values for deformation as well as stress in the steel structure are within permissible ranges.This is attributable to many factors, including several beams embedded into walls that serve as additional supports for the center frame, and the high strength of the steel (iron) material.In addition, the locations of the peak deformation and stress are near the top of the columns, reflecting the ease with which the slack in the joints can easily cause lateral deformation or failure of the columns.The results of time history analysis show that, under the Ⅷ-degree intensity of rare occurred earthquakes, displacement response curves of the typical nodes in the steel structure reflect a nearly even fluctuation based on balance locations.In turn, this means that the steel structure maintains a stable vibration status.Because the peak deformation value of the weak layer of the structure is still within permissible ranges, the structure is not expected to collapse.

Abstract:The focus of this study was the characteristics leading to failure of frame structures in recent major disasters.This study analyzed a new system for energy dissipation using a stiff frame rocking structure.Energy consumption during seismic oscillations was analyzed using the energy method, and a systematic study of the system's the anti-seismic properties was conducted.With a six-floor frame structure as the research object, a calculation model for the new energy dissipation rocking structure was developed.The dynamic responses of the new system under different seismic oscillations were obtained using the OpenSEES software.Energy consumption and its role in the new were analyzed.Results of the research showed that the mechanism for energy consumption in the new rocking structure was more reasonable, and its anti-seismic properties were an improvement over traditional structural systems.

Abstract:Since the beginning of the 1990s, performance-based seismic design theory has entered the mainstream of structural seismic research.The purpose of performance-based seismic design theory is to determine the seismic performance objectives of a building based on its use, importance, and level of seismic fortification.Buildings designed in accordance with those objectives will safely withstand earthquakes that may occur in the future.On the bridge, plastic hinges placed on the piers were used to consume earthquake energy.Design for ductility can avoid collapse of the bridge.However, permanent deformation of the plastic hinges could cause serious damage to the pier.It is difficult to immediately repair bridges following earthquakes.Many transportation functions are significantly slowed or lost.In order to ensure that the transportation capacity of bridges is recovered quickly after a strong earthquake, many structural systems have been proposed, including rocking bridge piers and self-centering bridge piers.The continuous rigid frame bridge system with displacement-restricted piers was consistent with the concept of rocking piers.This structure can realize three important functions:(1) limit the maximum displacement of pier, (2) prevent the bridge from overturning, and (3)adjust the coefficient of friction at the pier bottom.By adhering to these objectives between the pier bottom and the pier cap, the displacement-restricted system allowed the bridge to move with under the action of the earthquake.In so doing, this method can reduce the input of energy to the bridge structure and achieve the purpose of earthquake mitigation.This study concluded that the continuous rigid frame bridge system with displacement-restricted piers could reduce ductility and strength demands on the bridge piers.This paper compared the displacement limits of 2 cm, 5 cm, 8 cm and traditional piers.The results showed that the displacement of the pier top, the bending moment at the pier bottom, and the bending moment of the pier at the bridge beam with the displacement-restricted 2 cm, 5 cm, 8 cm piers were much less than the piers of a traditional continuous rigid frame bridge.The results also show that the amount of displacement restrictions is important.Choosing the appropriate displacement restriction can ensure that the elastic working state of the bridge will be maintained under severe earthquake conditions.This can improve the effectiveness of earthquake relief work and greatly reduce the cost of repairs.

Abstract:Recently, vibration in buildings in old residential districts has been increasing.These buildings are brick-concrete structures, and are multi-story residences, generally with 6 ~ 7 floors.In this study, the natural frequency of buildings in a district is empirically estimated.Combining with the in-situ test results, the vibration caused by heavy vehicle traffic or braking and starting of vehicles at bus station, whose frequency is close to the natural frequency of buildings in the district, is the main reason of vibration in buildings.Considering the characteristics of the study district, popular methods to reduce the vibration here are analyzed to obtain the most suitable method for the district.Cast-in-place bored piles in rows are selected for this district and a preliminary solution for vibration reduction is presented.

Abstract:The purpose of this study was to analyze the seismic vulnerability of the post-earthquake reinforced concrete frame structure in Wenchuan, China.High earthquake intensities and large areas that are affected increase grievous personal and economic losses.Based on disaster investigations, reinforced concrete frame structures accounted for the high proportion of buildings destroyed. Researchers at Cornell University in the United States proposed a probabilistic method that considers the influence of different seismic intensities in the same area.From a quantitative standpoint, this method can evaluate the seismic hazard level of the target area within a given time period using ground motion parameters and probability analysis to facilitate the engineering seismic design process.A simplified method for assessing vulnerability based on ground motion parameters was proposed, and vulnerability curves for the reinforced concrete frame structure in Wenchuan were drawn to describe the probability of the various levels of damage.The curve between the ground motion parameters and the annual probability based on the Cornell University theory is accurate, reasonable, and somewhat conservative.This study used the finite element software OpenSEES to conduct nonlinear static and dynamic history analyses.The OpenSEES software is widely used because of advantages in its fiber model division, higher computing speed, and better accuracy.Approximately 300 samples of the structure were established using the OpenSEES software in order to perform the nonlinear static analysis.During the analysis, the yield displacement and the maximum story drift were chosen as a measure of the level of seismic capacity in the structure.The two-fold energy equivalent yield displacement method proposed by FEMA273 was also used to determine the yield displacement of structures and maximum story drift.Research methods that consider the probability of earthquake ground motion parameters by combining Latin hypercube sampling, nonlinear static analysis, dynamic time history analysis, and statistical regression analysis are effective for the assessment of seismic vulnerability. The relationship between the ground motion parameters and failure probability curve can intuitively represent the seismic performance of the structure.Because the method is based on probabilistic seismic demand and aseismic capacity, the prospect is good for its application in seismic vulnerability analysis.The level of damage table and corresponding inter-story displacement angle limit table contained in this paper reflect the characteristics of the building structures and seismic features in earthquake disaster area.The table was based on Wenchuan earthquake survey data and structural seismic codes in China.Combined with the results of the HAZUS risk assessment, it represents an effective standard for evaluation.We also concluded that the proposed method for vulnerability assessment based on ground motion parameters is feasible.With the inputting parameter of the PGA, the correlation of the maximum response of the structure decreases with increases in the natural period and the corresponding probability of structural failure is enhanced.

Abstract:At present, analyses of seismic damage to tunnels have focused on the tunnel portal and portal section.However, there are still many deeply-buried tunnels that have been badly damaged by earthquakes;an important reason for this is the existence of voids behind the lining or because the lining backfill is not dense.However, studies on the relationship between voids behind the lining and the dynamic characteristics of earthquakes are few.In this study, the seismic performance of a tunnel with voids behind the lining are studied using the finite element software ABAQUS.The analysis reveals the following:if the lining is tightly and firmly stuck to the surrounding rocks, even under larger seismic action, the lining remains in a good state of compression.Once voids are present behind the lining, the lining that does not have the support of the surrounding rock comes under great tensile stress, resulting in cracking of the lining, which causes tunnel collapse.In addition, during earthquakes, larger plastic deformation appears in the surrounding rock without lining support than in those with lining support, causing the rock to more easily relax and fall off.

Abstract:Referring to the site classification principles in the code for seismic design for buildings, China, site categories for the stations selected from Kik-Net, Japan, were determined.Using the current equivalent linear programs, Shake2000 and LSSRLI-1, for site seismic response analysis, the peak acceleration, response spectra, and shear strain were calculated for different site categories.The calculated results for the different site categories were compared and the calculation discrepancy between Shake2000 and LSSRLI-1 was obtained for the different site categories.In addition, the numerical results were compared to those of real seismic records.The analytical results show that the nonlinearity of the soil dynamic modulus ratio, damping ratio, and site categories have a significant influence on the calculation results.For class I and II sites, the calculated results by Shake2000 and LSSRLI-1 were similar for most cases, while for class III and IV sites, the calculated results by Shake2000 and LSSRLI-1 were similar for the majority of the cases.With respect to real seismic records, the results by SHAKE2000 are better than those by LSSRLI-1, especially for class III and IV sites.For strong nonlinear soil, the results by SHAKE2000 are noticeably better than those by LSSRLI-1.Preliminary analysis indicates that the difference in the calculated results by SHAKE2000 and LSSRLI-1 is due to the difference in the calculated shear strains.

Abstract:A study on the evolution of crustal strain in the eastern Tibetan Plateau not only provides a perspective regarding regional crustal strain characteristics but is also very useful for analyzing the relationship between earthquakes and strain rates.Here, we first calculate the crustal strain in spherical coordinates around the eastern Tibetan Plateau in different periods based on a multi-surface function using regional GPS velocities for the periods 2001 to 2004, 2004 to 2007, and 1999 to 2013.Then, we study the characteristics of the evolution of surface strain and maximum shear strain in this area, analyzing its relationship with the large earthquakes (>M_S6.0) that occurred during each period. It was determined that during the years 2001 to 2004, the eastern Tibetan Plateau generally suffered surface compression.The value of the surface compression of the southern part of the Longmenshan sub-block was lower than the northern part.The Sichuan-Yunnan rhombus-shaped block generally suffered surface compression, but the value of the Baoshan sub-block's surface compression was lower than the other three sub-blocks.From the distribution and focal mechanisms of the earthquakes (>M_S6.0), we found that the three strike-slip earthquakes between the Baoshan and Dianzhong sub-blocks might be a response to the considerable difference in surface compression between the two sub-blocks.The normal-slip earthquake in the Yajiang sub-block might be a response to the difference of the N-S orientation in the surface compression of the sub-block.During the years 2004 to 2007, the emergence of two areas of strong surface compression formed a "strong-weak-strong" pattern of compression along the Longmenshan Fault, which could have triggered the May 12, 2008, Wenchuan M_S8.0 earthquake.The surface strain in the Sichuan-Yunnan rhombus-shaped block changed dramatically from 2004 to 2007;this may have had some impact on the occurrence of earthquakes after 2008. From the surface strain rate of 1999 to 2013, we found the evidence of strain responses to the Wenchuan earthquake, manifested as the uniform surface compression around the Xianshuihe faults.Generally, the distribution of surface strain rate agrees well with the scope of the sub-blocks, but the distribution of maximum shear strain rate agrees with the fault systems among the sub-blocks.The areas of high values of maximum shear strain rate correspond to the fault zones of strong tectonic activity, where it is difficult for the strain accumulation to grow and no large earthquakes occur.From the distribution of maximum shear strain rate during 2001 to 2004, we found that most earthquakes were located around the area of low values.This means that lower the maximum shear strain rate, greater the strain accumulation, and higher the risk of large earthquakes.During 2004 to 2007, the low-value area of maximum shear strain rate was located around the Longmenshan Fault, as was the situation during 2001 to 2004.This means that the Longmenshan Fault is not active and it can accumulate considerable strain energy over a very long period, which is an important requirement for the occurrence of the M_S8.0 Wenchuan earthquake.

Abstract:Peak ground acceleration (PGA) in the near field is associated with earthquake damage, but practical instances of the impact of PGA distribution in the near field of different types of focal mechanism is rarely reported.Using the intensive digital seismic records of the capital circle strong motion network, this paper studies two earthquakes that occurred in April 2003 with an epicenter located in Tangshan.Using data from the strong motion network and the temporary seismic network in Sichuan, Gansu, and Shanxi, it also studies two earthquakes that occurred in July and August 2008 with an epicenter located in Wenchan.By using a function of the thematic map in ArcGIS software, the distribution of both the horizontal synthesis and vertical PGA is established, obtaining the differences in earthquake PGA distribution in the near field from the faults and strike-slip faults, and the thrust and strike-slip faults.In this paper, we study the impact of different focal mechanisms in the Ninghe and the Wenchuan earthquake on PGA;the difference in the influence of various focal mechanisms to PGA is especially striking.The results show that this difference is prominent, and that the distribution of major earthquakes PGA is complex in the near field, while that of medium-small earthquakes is also complex.The most crucial place for death and destruction is in the near field.Spectrum analysis established that there are differences in the lower frequencies of seismic waves.Now that there are more buildings and that a greater proportion are multistory and large, the self-vibration period is longer.High values in PGA of nearly vertical strike-slip earthquakes are symmetrically distributed along the fault, while normal faults and reverse faults are concentrated in the hanging wall.The distribution of PGA is complex in the near field, and it is worth noting that the phenomenon of low frequency dip-lip earthquakes is crucial to the input of power and materials in emergency rescue following destructive earthquakes.

Abstract:Liupanshan is located at the border of the Ningxia Hui autonomous region, Gansu and Shanxi provinces.It belongs to the northern section of the north-south seismic structural zone, and according to its geological structures, it is located in the transitional region between the Ordos block of the western North China Plate and the Qilianshan orogenic belt of the northeastern Qinghai-Tibetan block.Its structures and landform development have their own specificity and sensitivity.Under the premise of the rapid uplift of the Tibetan Plateau and northeastern extension in the late Cenozoic, the Liupanshan area experienced strong deformational tectonic processes.These processes have controlled the development of regional landforms and evolution of rivers.The Liupanshan Fault zone includes the eastern and western Liupanshan piedmont faults, and based on the interpretation of aerial and satellite photos and data from field surveys, we undertook a detailed investigation of its activities.The total length of the eastern Liupanshan piedmont fault is ~90 km.The fault extends southward from Xiaokou to Majiaxinzhuang with an overall NW trend.The fault topography is very clearly defined along the fault.Analyses of its geomorphological features and of a typical fault section suggest that the eastern Liupanshan piedmont fault has characteristics of left-lateral thrust and that it moved in the late Holocene.According to the measurement of the offset terrace at Houmohe, the displacement of the T₂ is about (25±3) m.The age of the T₂ is about (9372±86) a based on 14C dating and therefore, we estimated the slip rate to be about (3.2±0.5) mm/a.This result was consistent with a previous study.The total length of the western Liupanshan piedmont fault is ~60 km.The fault extends southward from the Sanlidian Reservoir to the Taoshan Reservoir, then its trend changes from N-S to NNW-SSE.The fault topography is very clearly defined along the fault.Analyses of its geomorphological features and of a typical fault section suggest that the western Liupanshan piedmont fault is a high-angle reverse fault that moved in the early late-Pleistocene, but that has not dislocated since the middle late-Pleistocene.In this paper, we also discuss the geomorphologic response to the tectonic activity.Based on SRTM data, we established the Jinghe and Shuiluohe drainage basins and river systems that lie either side of Liupanshan, and we also obtained the hypsometric interval (HI) values of the drainage basins.In general, the HI values of bigger drainage basins reflect the influence of different regional neotectonic activity, while those of smaller basins reflect the influence of lithology and local tectonic activity.According to the map of HI values, there is a clear difference either side of Liupanshan;the two sides have similar lithologies, but the HI values to the east of Liupanshan are lower than those to the west.The reason for this might be connected to the different levels of activity between the eastern and western Liupanshan piedmont faults.Through the above research and geomorphological analysis, we provide basic data and interpretations to better understand the geomorphological evolution of the Liupanshan area.

Abstract:In this paper, based on the seismicity and seismic structural analysis of the margin of the Bayan Har block, we discuss the risk of large earthquakes in the Maqu-Maqin seismic gap with regard to spatial seismicity patterns and temporal evolution of event sequences.According to paleo-earthquake and historical earthquake seismicities, there was an initial seismic gap at Maqu-Maqin along the east Kunlun fault, and therefore, large earthquakes will recur in this area.A second seismic gap, the seismic quiescence of no M_L≥5.0 earthquakes, has been detected in the same area since 2008.A comparison with previous earthquake cases showed that a similar period of seismic quiescence formed in the region of Gansu-Qinghai-Sichuan provinces before the 1990 Gonghe M7.0 earthquake. The distribution of M_L≥4.0 earthquakes in the current seismic quiescence is also similar to that of the Gonghe M7.0 case;hence, we think there is a risk of a large earthquake in the current gap.From the temporal sequences evolution analysis (M-T relations), we found that seismicity in the Gonghe gap had undergone strong-weak-strong stages prior to the Gonghe M7.0 earthquake. However, the seismicity in the current seismic gap in the region of Gansu-Qinghai-Sichuan provinces has also undergone the first two stages, and therefore, we conclude that it will soon reach the strong seismicity stage.We scanned the b-value distribution in this region, which showed that the b-values are very low around the east Kunlun fault and that there is locking in this area.We also calculated the spatial correlation lengths (SCL)and multiple fractal dimensions from the earthquake catalog of the Bayan Har block using GeoTaos.All the statistical seismicity parameters indicate that the risk of a large earthquake on the Maqu-Maqin segment of the east Kunlun fault is increasing, and therefore, researchers should monitor and study this area.

Abstract:An M5.6 earthquake struck Nima, in Tibet, on July 24, 2009.According to the displacement of the earthquake surface rupture and destruction of buildings, the earthquake macroscopical epicenter lay between Juncang Town in Nima County and Cishi Town in Cuoqin County.The intensity of seismic area was VII.This article studies the basic parameters of earthquake sequence features, source parameters, seismogenic structure, and so on, making use of related parameters to discuss the focal mechanism solutions identified as consistent with the event by Harvard University.The results are confirmed by field investigation.An inspection of the scene of the earthquake recorded the seismic characteristics of every type of building in the region, and the reasons for damage are summarized, and suggestions made for earthquake disaster prevention and mitigation.This article establishes that the earthquake occurred within the Kailash-Lhasa block, displaying NNW trending mainly under tensile stress generated by a sinistral strike slip with normal faulting. In addition, this article analyzes minor earthquake activity and the imaging features of regional seismicity in Nima before the M_S5.6 earthquake, and compares these with regional seismicity during the M_S5.0 earthquake here in 2009.One to two years before the M_S5.6 earthquake, Nima experienced strong earthquake bursting, and moderate earthquakes of magnitude 3.0 and 4.0 were assigned a state of "Significantly Enhanced" across the area.Twelve months before the M_S5.6 earthquake, a seismogenic gap of earthquakes of magnitude 3.0 and 4.0 occurred in the source area, with abnormal images of almost adjoining distribution.Before the M_S5.6 earthquake, the strong seismic status and abnormal images of small earthquakes in Tibet were the same as associated with the M4.9 earthquake in 2009.The outcomes of this paper are a scientific basis with which to predict earthquakes in future.