Abstract:When the uniform damage state of structures is developed under strong earthquakes, each story has an approximately equal story drift ratio and damage, and the material potential of each structural components is fully exploited, which makes for the global yielding mode and energy dissipation mechanism. By considering the global and local damage, the optimization design procedure of seismic uniform damage of reinforced concrete frame structures was firstly constructed based on the optimality criteria method. The analytical model of reinforced concrete frame structures considering the soil-structure-interaction was developed based on the Beam on Nonlinear Winkler Foundation (BNWF) model. Two 5-and 8-reinforced concrete (RC) frame structures were employed as the prototype structures. The uniform damage optimization design was performed and the influence of main convergence parameters were analyzed. The structural reinforcements, component rotations and maximum interstory drift ratio before and after optimization were compared. According to the story shear distribution of two optimized RC frames, a new lateral force pattern for seismic design was proposed using the format of Chinese seismic design code.

Abstract:In order to reduce the damage of the coupling beams in the coupled reinforced concrete shear wall structure under strong earthquake, realizing the rapid recovery of the structural function after earthquake, a new hybrid damping coupling beam with self-centering and energy dissipation functions were proposed. An innovative composite self-centering damper composed of shape memory alloy strands and viscoelastic damping devices was installed in the middle span of the innovative self-centering energy-dissipating coupling beam. A 10-layer coupled shear wall structure was taken as an example. The dynamic time history analysis on the coupled shear walls with the innovative self-centering damper, viscoelastic damper and common RC coupling beam, respectively, were conducted to investigate the seismic response mitigation effect of different damper on the shear wall structure. The calculation results show that the deformation and energy dissipation of the structure are concentrated on the coupling beam damper under the actions of earthquake, while the new self-centering coupling beam damper has better control effect than the viscoelastic damper for the seismic response of the structure, exhibiting excellent re-centering and energy dissipation capacities during the earthquakes.

Abstract:In the shaking table test of steel frames-steel shear wall system, a problem is that the thickness of the steel plate shear wall(SPSW) in the scale model is too small. In order to solve this problem, this paper proposes two equivalent models:concentrically braced frames and I shape of steel plate shear walls. Both of the two models are based on principles of equivalent initial lateral stiffness or bearing capacity of the structure. The finite element analysis program ABAQUS was used to establish the refined model, using the method of numerical analysis. And the stiffness, bearing capacity and other seismic performance of the prototype SPSW and equivalent models were compared and analyzed. The results show the two equivalent substitution models both have good energy consumption capacity and can solve the problem of small thickness. In addition, the concentrically braced frames model can only make sure either stiffness or bearing capacity equivalent, but I shape of steel plate shear walls model can ensure both stiffness and bearing capacity equivalent, which provides some suggestions for the equivalent models of SPSW in shaking table tests.

Abstract:High-strength steel fabricated framed-tube structure with replaceable shear link (HSS-FTS-RSL) was proposed. One 2/3 scaled sub-structure specimen of HSS-FTS-RSL was fabricated. Low cycle reciprocating loading test was carried out for the specimen to study its seismic performance, including failure modes, hysteretic behaviors, and replaceability. The simplified numerical model of HSS-FTS-RSL was established by using OpenSees, and the analysis results of this model had good agreement with the test results. Three simplified numerical models of HSS-FTS-RSL with different layouts of shear links were considered to investigate their seismic performance through the nonlinear dynamic analysis. The results show that the specimen had good seismic performance, with the failure of energy dissipation beam section under cyclic loading. The maximum interstroy drifts could meet the demands in the seismic code under the ground motions. The high-strength steel could reduce the stress in spandrel beams and columns but not increased the amount of steel of the structures. The maximum residual story drifts ranged from 0.028% to 0.148%, which were lower than the maximum residual story drift of 0.41% for replacing shear links obtained from the test. Considering the seismic performance and repairability of the structure, it was suggested that the shear links of HSS-FTS-RSL should be arranged in three-span interval according to the analysis results.

Abstract:A method to connect modular steel frame units(hereinafter referred to “modular units”) was proposed, which is that 2, 4, or 8 modular units can be connected by innovative box connecting component(BCC-1and BCC-2), plates through high strength bolts. Force mechanism of box connections were analyzed, and based on the Chinese code, the design flow and design method of the inovative box connections (hereinafter referred to “box connections”) of modular units were proposed. Taking the 11 layers modular steel frame office as an example, an corner connection and an edge connection were designed, and low cycle reciprocating loading were carried out on the connection using the finite element software Abaqus to verify seismic resistance of modular connections. Results show that:plastic hinge of corner connections and edge connections initialed on web of BCC-1 and BCC-2, which can be quickly replaced after an earthquake to restore the function of connections. Both connections met the requirements of the ANSI/AISC 360-10 specification for semi-rigid connections, and hysteresis curve were full, indicating good seismic resistance. Both ratio of ultimate bending capacity of predicted value and finite element results exceed 90%, indicating that the structure, the idea, and the design method are reasonable.

Abstract:In order to study the influence of the horizontal steel bar connection method on the seismic performance of the composite shear wall joints, this paper designed two types of composite joints, which were horizontal reinforcements with or without embedded column. Under cyclic loading, a total of four specimens of two types of joints were subjected to seismic tests. By studying the deformation, failure characteristics, hysteretic characteristics, ductility and energy dissipation capabilities of the composite shear wall node, the seismic performance of the composite shear wall connection node is analysed. Through comparative analysis of bearing and deformation, ductility, energy consumption and other indicators, it is obtained that the cracking, yielding and ultimate load of the joints of horizontal steel bars are increased by 2.42%, 10.84% and 9.25% respectively; the ductility coefficient is increased by 10.26%; the energy consumption coefficient has been increased by 8.70%. It can be seen that the overall seismic performance of the joint specimens can be effectively improved by reasonable reinforcement and connecting the shear wall nodes.

Abstract:The aging eccentric compression, and even void of plate rubber bearings are very important for the seismic safety of bridges. The elastic modulus of plate rubber bearing was measured by indoor aging test. According to the degree of aging and eccentric compression the quasi-static test is divided into 16 cases, and the seismic performance indexes and change rules of the bearings under thermal aging, eccentric pressure and coupling are compared and analyzed. The results show that the hysteresis curve of the bearings under eccentric compression is relatively narrow. The area and equivalent damping ratio of the hysteresis curve decrease, and the horizontal equivalent stiffness of bearing increases. After aging, the shear deformation of the bearings decreases, the hysteresis curve is fuller with the increase of slip ratio for the given displacement amplitude, and the corresponding equivalent damping ratio increases. Under the condition of aging and eccentric compression, the slope of hysteresis curve is more gentle, and the energy dissipation capacity of bearing is obviously weakened. It is found that the beam end or the common plate rubber bearing that is under eccentric compression for a long time has the risk of falling off due to the excessive unidirectional accumulative slip in earthquake. It is suggested that in bridge maintenance, a limit device should be set on the underside of the bearing and timely adjust the bearing with severe eccentric compression.

Abstract:To enhance the seismic performance of precast-reinforced concrete frame structure, and aim at the severe damage of beam and column members after earthquake, an innovative construction at beam end called artificial dissipative plastic hinge (ADPH) is proposed. ADPHs are constructions that connect precast beam and column though an embedded mechanical hinge, and additional steel plates are installed to carry the load and dissipate energy. Eight groups of additional steel plate specimens with different sections and structures were designed and fabricated. The low-reversed loading tests are carried out on the artificial dissipative plastic hinge structures with different additional steel plates, the failure modes are analysed, and the seismic performance of ADPH are studied through the hysteresis curves, skeleton curves, equivalent viscous damping coefficient and ductility. The results show that the plastic damage will concentrate only on middle part of steel plates, and prove the effectiveness of energy dissipation by bending, ADPH construction possesses the features of damage-control and rapid-replacing, and the U-shape steel plates could enhance the capacity of buckling-delayed and energy-dissipating.

Abstract:A Kelvin-Voigt type passive control unit was set up between the equivalent two-body single-degree-of-freedom simplified models of adjacent isolated structures. Based on the Kanai-Tajimi spectral stochastic seismic motion model, by taking the minimum of the total vibration energy of the structures as the optimal control objective, the influence rules of the connection control parameters on the control effect have been drawn on basis of detailed analyses, as well as the optimal control parameters. According to the equivalent two-body single-degree-of-freedom model, the optimal parameters of connection control between adjacent high-rise isolated structures were obtained; The response expressions of adjacent high-rise isolated structures were derived from the time domain and frequency domain; The influences of connection control devices on the natural vibration characteristics and random responses of the structures under different layout schemes were analyzed. Finally, it is proved by numerical analysis that, this control method can be applied to adjacent isolated structures, which has control effect on each structure. It shows that the control method is effective for the adjacent isolated structures.

Abstract:To systematically evaluate seismic performance of reinforced concrete frame structure designed with lead viscoelastic damper (LVD), a 6-layer RC frame (RCF) and LVD-damped RC frame (LVDF) in 8 degree (0.2g) were designed and established. Finite analysis models of the RCF and LVDF were built using OpenSees. Incremental dynamic analysis (IDA) was conducted to both RCF and LVDF using a total of 22 far field ground motion records as recommended from ATC-63. Based on results of IDA, probabilistic seismic demand analysis followed with the seismic fragility analysis was carried out for RCF and LVDF, and the probability of achieving different damage states of RCF and LVDF were quantitatively evaluated. The analysis results show that lead viscoelastic damper can be used to seismically control structural dynamic behavior so that structural response of LVDF is smaller than that of RCF under the same earthquake. As shown in results of probabilistic seismic demand analysis, LVD reduce dispersion of structural dynamic analysis results due to differences characteristics of ground motion records. As shown in seismic fragility analysis results, LVDF has lower probability of exceedance under different damage states than that of RCF, indicating that LVD can significantly both release structural damage and improve seismic performance of the structure.

Abstract:Based on the influence rule of the structural natural vibration period and the damping ratio on the seismic excitation of the structure, the calculation formula of displacement reduction rate and seismic shear reduction rate of SDOF system of the combined damping structure with BRB and VD are derived and the damping performance curve of combined energy dissipation structure under target displacement reduction rate and target shear reduction rate is established. In addition, the performance-based combined energy dissipation design method is proposed and the validity is verified with a practical engineering example. The simplified application mode of the combined energy dissipation design method in multi-degree-of-freedom system is proposed. The results show that there exists unique performance point under the case that the target displacement reduction rate and target shear reduction rate are determined, and the combined damping structure could achieve excellent displacement response and seismic shear reduction control effects if designed reasonably. The calculation example structure designed according to the design method achieves the expected damping target. The simplified application method based on the first-order mode can be used for the combined seismic design of multi degree of freedom system with uniformly distributed mass and stiffness along the height.

Abstract:Through a quasi-static test of three beam-column joint scale models extracted from the high-rise frame-shear wall structure designed according to the “strong joint” principle in the current national code, the seismic performance of beam-column joints at different positions in frame structures is studied. The test adopts column end loading, considering the influence of the floor slab on the seismic performance of the joint, and analyzes its ductility, stiffness, bearing capacity, energy consumption and other performance indicators. During the test, the development of the cracks was recorded in detail and compared with the mechanical indexes of the components to relate the damage state with the mechanical indexes. The test provides test basis for improving the vulnerability curve and relevant consequence information of the reinforced concrete frame beam-column joints. It is found that the failure modes of the joints at different positions of the frame structure are different. The failure modes of the bottom nodes are shown as bending failure, and the failure is mainly concentrated in the beam ends and column feet toe. No obvious failure in the joint area, while the shear failure occurs in the top joint area. The test results show that the strong joint coefficient and the column end bending moment amplification factor at an extremely high level can completely avoid the damage that needs to be repaired in the beam column joint area, achieve the elasticity of the node, and will not weaken the ductility of the assembly.

Abstract:An innovative resilient rocking (IRR) column was developed to achieve the rapid recovery of the performance of the frame structure after earthquakes. Quasi-static cyclic tests on two full-scaled IRR columns were carried out to further investigate the influence of stiffener height at the column end on the seismic performance of IRR columns. The test results show that the hysteresis curves of the two specimens are full, which shows good hysteresis performance and deformation ability. When the height of the internal stiffener of the IRR column root is insufficient, the horizontal load will cause out-of-plane buckling of the side panel of the steel column, which will further cause the plastic deformation of the steel plate damper lags behind. When the height of the internal stiffener is sufficient, the column body is always in an elastic state. And the steel dampers finally ruptured after full development of plastic deformation, achieving the design philosophy of “strong column and weak damper”. As the stiffener height increased from 100 mm to 420 mm, the maximum loading capacity and the initial stiffness of IRR columns increased by 11.5% and 25.1% respectively, while the ultimate deformation dropped by 39.3%. The findings can be referenced for application of earthquake resilience structures.

Abstract:In design of super high-rise structure, the ground motion intensity index guides the seismic design of the structure and is very important for safety of the structure,but there is no unified conclusion on the ground motion intensity index of super high-rise mixed structure. Therefore, it is of great significance to study the ground motion intensity index of the super high-rise structure. Based on the review of the current research status of the effectiveness of seismic intensity index in the incremental dynamic analysis of building structures, this article proposes a seismic intensity index a%, which is suitable for the incremental dynamic analysis of super high-rise building structure. The ground motion intensity index S_a% is the geometric average of the spectral acceleration corresponding to the natural vibration period of a% mode mass participation coefficient before considering the translational direction of the structure. In order to verify the effectiveness of the seismic intensity index S_a%, PERFORM-3D elastoplastic analysis software was used to establish a nonlinear model of an actual super high-rise building and perform incremental dynamic analysis. Based on the discrete analysis of θ_max and V_max results of various ground motion intensity indexes, it is concluded that S_a% of ground motion intensity index proposed in this paper can effectively reduce the discreteness of θ_max and V_max when applied to incremental dynamic analysis of super-high-rise structures, which improves the validity of calculated data and provides reference for the application of actual super high-rise structures.

Abstract:In the actual seismic record formation process, there is a superposition of high and low frequency components of seismic waves. The composition of high and low frequency components of ground motion is an important reflection of the characteristics of the response spectrum of ground motion. This study is based on the digital filtering technology, taking the average period of acceleration response spectrum (T_avg) 2 s as the cut-off period and combining with empirical mode decomposition(EMD), and it extracted the intrinsic mode function(IMF) and residual component which the cut-off period above 2 seconds as long-period components of long period ground motions(LPGM) after refactoring and baseline correction. The remaining IMFs were reorganized into short-period components; The validity of the extraction method is verified by correlation between seismic records and their components and the discreteness of the original ground motion and the response spectrum. It also compare this method with existing methods. The results show that the extraction method for LPGM components in this paper can better extract the long and short period components of the seismic response spectrum that are less discrete and have a good correlation with the original ground motions in the long and short periods respectively. It better reflects the spectral characteristics of original ground motions and has better adaptability in the LPGM component separation.

Abstract:The seismic design of nuclear equipment is an important topic in the anti-seismic field of nuclear power plants. In order to achieve the ground motions fitting design of nuclear power plant equipment to meet the requirements of the typical response spectrum (RRS) matching and the standard power spectral density (PSD) envelope, a standard PSD generation method based on the ground motion fitting method for nuclear power plant site design recommended in the 2014 edition of the Standard Review Program (SRP) is proposed, which considers the effects of iteration correlation and random phase spectrum on the iterative convergence efficiency. The method realizes the artificial seismic wave synthesis with RRS matching and standard PSD envelope by controlling the Fourier amplitude in the process of fitting the artificial wave in the traditional frequency domain method, which provides a test basis for the seismic wave of the floor of the nuclear equipment anti-seismic design. The pressure vessel is selected as the prototype for seismic research of nuclear equipment. And the theory that artificial ground motions matching RRS and envelope PSD will stimulate greater response of equipment is verified by the shaking table test comparing the response peak parameters of the specimen and the power spectral density function in response acceleration time history. It shows that the significance of enveloping PSD requirements in the ground motion fitting design, which can be used as a suggested requirement in seismic design process.

Abstract:In order to effectively identify the early fatigue cracks of the steel bridge deck under vehicle loads, the numerical and experimental research on the nonlinear Lamb wave detection of steel plate fatigue cracks were carried out. Based on the non-linear theory of acoustic contact, three damage indexes were proposed, which are first wave energy, pseudo sound velocity and nonlinear parameter. Three types of defects including hole defect, macro crack and fatigue crack were considered in the specimens. Among them, the fatigue growth crack was generated by the fatigue loading test. In the three-dimensional numerical model, the “breathing effect” of closed crack is simulated by a zero-length nonlinear spring element to simulate the local nonlinear interaction process between Lamb waves and fatigue cracks. In the experiment, the nonlinear Lamb wave stepped scanning was performed, and the harmonic response was extracted through a band pass filter. The research results show that the first wave energy and pseudo sound velocity are sensitive to macro defects, while the harmonic waves energy and nonlinear parameter are sensitive to fatigue cracks. Combining the three damage indexes can simultaneously achieve the identification and location of macro defects and fatigue cracks.

Abstract:The transmission tower-line systems play a vital role in power transmission. However, since most of the transmission tower-line systems are situated in rural areas subjected to various extreme weather conditions, transmission conductors are prone to be broken. In order to investigate the dynamic impact of conductor breakage on the transmission tower, a finite element model is established in ABAQUS, and the global state of the transmission tower is determined according to the base reaction. By calculating the impact coefficient of the main members in different parts of the tower under different working conditions, the changes of axial forces of the main members in different positions are shown, and the most severely impacted parts of the tower are identified. Finally, the simulation results are compared with the current norm, and the shortcomings of the criteria are pointed out. The results show that the main failure modes of transmission tower caused by wire breakage are bending failure and torsion failure, and the bending failure is more serious. When a single wire is broken, the impact caused by the rupture of the upper wire is the most serious, and the place suffering the greatest impact is the section between the crossarm connected with the broken wire and the adjacent crossarm. With the increase of the number of broken wires, the proportion of torsion failure increases, and the sections between two adjacent crossarms are damaged seriously. In addition, it is necessary to use dynamic methods to analyze structures, because using current codes and static methods to calculate the influence of wire rupture on structures cannot ensure that structures are still safe under the dynamic impact of wire rupture.

Abstract:Single tuned mass damper (STMD), being an effective vibration absorber, is generally installed at the top of a flexible structure for vibration control. Due to the limited space, the design and installation of the STMD may be greatly restricted, especially for slender structures such as wind turbine towers. More importantly, the effect of STMD has been proved to be limited for the involvement of multiple modes. For the reasons above, the multiple tuned mass damper (MTMD) has been proposed. In the present work, the constrained parameter optimization of the MTMD system designed for the wind turbines is performed, based on the initial configuration given in advance. The transfer function from the ground motion to the response of the wind turbine tower is derived by means of modal superposition. A proper objective function is developed by comprehensively considering displacement, acceleration as well as based reaction forces. The genetic algorithm (GA) is employed for searching the optimal design parameters of the MTMD system. A wind turbine model is adopted as an example, and the working efficiency of the MTMD system is finally verified by comparing with the classical Den Hartog's formula. Results reveal that the designed MTMD system is feasible for control of multi-mode vibration, having potential value for broader practical applications.

Abstract:To evaluate the seismic performance of utility tunnel wall-slab joints using anchorage button-head reinforcement, pseudo-static tests were carried out on six full-scale wall-slab joint specimens. Bearing capacity, failure mode, hysteretic energy dissipation, displacement ductility and other seismic performance indexes of utility tunnel wall-slab joints were investigated. Comparing the test results of the cast-in-place wall-slab joint specimens with that of composite fabricated wall-slab joint specimens, reasonable anchorage length of upsetting steel bar was determined. The finite element model of these wall-slab joints was established and its validity was checked. The results show that the composite fabricated wall-slab joint using anchorage button-head reinforcement has the same bearing capacity as that of the cast-in-place joint, and displacement ductility and energy dissipation capacity are good, indicating that the composite fabricated wall-slab joints can meet the seismic performance requirements. When the anchorage length of upsetting steel bar is longer than 0.5l_abE, the seismic performance of joint specimens can meet seismic design requirements. However, as the anchorage length of upsetting steel bar decreases, the bearing capacity and deformation capacity of wall-slab joints gradually decrease, and the ductility and energy dissipation capacity also decrease gradually. The crack propagation at the composite surface of prefabricated wall-slab joints is greater, and damage in the core area of the joint is severe. Consequently, necessary reinforcement measures need to be taken and the connection measures of the joint area need to be strengthened in engineering practice.

Abstract:In order to study the seismic response of group silos stored materials to the dynamic lateral pressure of the silo wall, column-supported group silos and independent single silo models with a scale ratio of 1:25 were designed and manufactured, and shaking table tests with different ground motion levels under three seismic waves were carried out. The seismic response characteristics of the two models, the variation law of dynamic lateral pressure and over-pressure coefficient of the silo wall were obtained. The results show that:1) during the earthquake, the phase difference between the storage and the wall of the silo is relevant with the position of the silo body and the location of the measuring point; 2) the distribution law of the dynamic lateral pressure on the wall of the side silo and the middle silo is relevant with the direction of seismic wave input; on the whole, the over-pressure coefficient of the silo is generally smaller than that of the independent single silo; 3) the over-pressure coefficient of the side silo is larger than that of the middle silo, both of which are larger than the values adopted by the code, and the comprehensive correction coefficient adopted in the current code is relatively small; 4) the storage seismic response characteristics of the vertical silo cannot be fully reflected only via the independent single silo, therefore it is essential to consider the different positions of the silo and the direction of seismic action to design the strength of the silo wall structure.

Abstract:In order to investigate the mechanical characteristics of high strength stainless steel wire mesh in Engineering Cementitious Composites (ECC) and to determine the reasonable lap length, the pullout tests of 39 specimens were carried out by considering the influential factors such as transverse strand spacing, lap length and strand diameter. The results show that there are two failure modes in the lap connection of steel wire mesh in ECC, namely pull out and pull off. The setting of transverse strand has little effect on the ultimate pull-out force, but the slip decreases with the decrease of the transverse strand spacing. With the increase of lap length, the slip amount and “lap stiffness” to peak load increase, while the ultimate bond stress decreases. Based on the experimental analysis, the critical lap length of steel wire mesh is determined, and the calculation formula of lap length considering the correction coefficient β is established.