Multi-dimensional Ground Motions Research Articles

Incremental dynamic analysis of SRC frame-bent structures in CAP1400 NPP

Under the earthquake, the collapse or damage of buildings would result in significant casualties and economic losses. Especially when essential lifeline projects such as nuclear power plants and thermal power plants were affected by earthquakes, they also resulted in severe consequences, such as the paralysis of urban functions, delays in post-earthquake disaster relief, and social chaos. In this paper, the conventional island steam turbine main building of the CAP1400 nuclear power plant (NPP) in Shidaowan, Shandong Province was taken as the research object, and the seismic performance of the main building structure of the SRC frame-bent was studied by using the incremental dynamic analysis (IDA) method. Firstly, the dynamic characteristics of the substructure of the steel reinforced concrete (SRC) frame-bent main building structure were obtained by experiments. Then, the prototype structure model of the main building was established and verified with the experimental results. Finally, 15 natural ground motions were selected and the corresponding torsional components were calculated. With peak ground acceleration (PGA) and Sa (T1, ξ) as IM indicators, top displacement of structure (Dt) and maximum inter-story drift ratio (θmax) as engineering demand parameters (EDP) parameters, the IDA of the structure were carried out, and the IDA curve cluster and percentile curve of the structure under multidimensional ground motion were obtained. The results show that the discreteness of the IDA curve cluster with Dt-Sa index was relatively small compared with the other three groups; the discreteness of the IDA curve cluster with Dt-PGA as the index was large. In addition, the results of the IDA conducted on the SRC frame-bent main building structure with PGA as an intensity measure (IM) parameter were deemed more conservative.

Multidimensional Seismic Response Analysis of Large-Scale Steel-Reinforced Concrete Frame-Bent Structures in CAP1400 Nuclear Power Plant

Irregularity in the plane layout of a building structure and the vertical discontinuity of lateral resistance components could lead to torsion and result in the brittle failure of a structure. According to the characteristics of the conventional island main building of nuclear power plants, this paper focuses on the conventional island main building of the CAP1400 nuclear power plant (NPP) in Shidaowan as the research object. A prototype structure model of the main building was developed using ABAQUS software. The seismic response of the structure under multidimensional ground motion was studied by inputting the X-direction and Y-direction translational and torsional components of ground motion in ABAQUS. The results demonstrate that the overall transverse displacement of the structure under bidirectional ground motion was significantly higher than that under unidirectional earthquakes, which was about 20%. Under a multidimensional frequent earthquake, the transverse displacement of the structure increased by about 13% on average compared with that under a bidirectional earthquake; the longitudinal increase was the largest, at about 28%. Finally, the lateral displacement of each layer of the steel-reinforced concrete (SRC) frame-bent main building structure with few walls proposed in this article decreased by an average of about 17% compared to the traditional SRC frame-bent main building structure. The longitudinal displacement was reduced by about 14% compared to the traditional SRC frame-bent main building structure.

Collapse failure analysis and fragility analysis of a transmission tower-line system subjected to the multidimensional ground motion of different input directions

Transmission lines, which are important for maintaining economic and social operations, are vulnerable to collapse damage due to the effect of multidimensional ground motion. In this paper, a three-dimensional finite element model of a transmission tower-line system is established. Twenty ground motion records were selected from the international ground motion database. The acceleration time history is orthogonally decomposed to obtain the acceleration time history along the X direction and Y direction of the model in different input directions. Based on the incremental dynamic analysis method, the influence of different ground motion input directions regarding the collapse failure of transmission tower-line systems is studied. Taking the section draft ratio of the tangent tower as the criterion, the influence of the seismic input direction on the collapse of the peak ground acceleration (PGA) and vulnerable area of the tangent tower is analyzed. The influence of the input direction on the collapse fragility of transmission tower-line systems under different conditions is investigated based on the fragility analysis method, and the collapse margin ratio is used to evaluate the seismic capacity of transmission tower-line systems. A comparison of the results indicates that the input direction of the ground motion has a great influence on the collapse of the PGA, and the difference in the various directions is up to 0.34 g. Additionally, the change in the input direction makes it possible for collapse to occur between the fourth and fifth sections. Last, the results also indicate that the input direction of the ground motion has a great disturbance on the collapse fragility of transmission tower-line systems. The influence of the input direction of ground motion should be considered under the condition of rare ground motion (0.32–0.46 g) and extremely rare ground motion (0.54–0.64 g) in the design of the structure. The direction along and vertical to the tower-line is not the worst input direction of the transmission tower-line system. Considering only the seismic input of these two directions will cause a significant overestimation of the seismic capacities of transmission tower-line systems.

Seismic Response Analyses of Transmission Towers under Multidimensional Ground Motions with Rocking and Torsion Components

AbstractMost current studies on the seismic responses of transmission towers are performed using two or three translational components of ground motion as earthquake inputs. In this study, a novel ...

Seismic partitioned fragility analysis for high‐rise RC chimney considering multidimensional ground motion

SummaryIn order to identify the vulnerable parts and areas of the high‐rise reinforced concrete chimney, this paper presents an effective method, which called partitioned fragility analysis. One 240‐m‐high reinforced concrete chimney was selected as the practical project, and its analytical model was created with ABAQUS software. The selected high‐rise chimney structure was divided into 17 parts, and then the damage probability of each part in different damage states was obtained with the fragility analysis considering multidimensional ground motions. Twenty ground motion records were taken from the Next Generation Attenuation database as the input motions, and the peak ground acceleration was selected as the intensity measure. The response of the chimney structure under multidimensional ground motions was obtained based on incremental dynamic analysis. The maximum strains of concrete and steel bars were defined as the damage limit states of the chimney structure. The fragility curves and surfaces obtained from this analysis showed that the vulnerable areas of the chimney structure appear at 0–20 m, 90–130 m, and 150–200 m along the height of the chimney respectively. Based analytical results, these vulnerable parts can be retrofitted to enhance the seismic resistance of existing chimney structures. And the partitioned fragility analysis method can also be used to improve the design of new chimney structures.

Intensity Characteristics of Ground Motion Vectors

The Code for Seismic Design of Buildings stipulates that the ratio of combined values should be 1:0.85:0.65 when considering three-way seismic action. However, it is sometimes found that the difference between the horizontal records and the vertical records in the characteristics of ground motion and peak vibration is very different from those of the two. With the development of the seismic theory of the engineering structure, more complex structural systems have put forward more specific requirements for ground motion input. And the simple application of the three-dimensional seismic action to the combination of the 1:0.85:0.65 pairs of earthquakes is of limited applicability. In order to unify the ratio relationship of ground motion input components in multi-dimensional ground motion, the vector signal was constructed by the components of the ground motion vector. The components of the vector signal were orthogonal to each other in a complex space. So the correlation limit of bainite's theorem and Nuttall theorem was avoided when the orthogonal vector was constructed by Hilbert. At the same time, the problem of one dimension ground motion intensity characteristics to reflect the incomplete surface of the structure response was solved. Firstly, the ratio of the horizontal component and the vertical component to the three-dimensional envelope was calculated by the model fitting, and compared with the law of the traditional multi-dimensional ground motion ratio, and the reliability and practicability of the ratio rule calculated by the new method were clearly defined. Then the time-history characteristics of the ratio were obtained by the function fitting. The corresponding model parameters were obtained by the optimization algorithm and the attenuation law was studied. It is proved that the fitting model is correct and effective in the time-history analysis of ratio.

Comparative Analysis of Torsion Resistance Performance between Traditional Support Structure System and Structure with Diagonal Brace

Traditional support structure system of air-cooled condense adopts hybrid structure system of steel truss and reinforced concrete pipe column, and this type of structure has a remarkable torsion effect because that the quality and rigidity is badly non-uniform at the vertical direction. In order to study the natural vibration period, vibration type and dynamic response under multidimensional ground motions, this paper chooses the support structure system with diagonal brace to analysis the dynamic characteristic and lateral-torsional coupled seismic response of the structure, and compares the results with the traditional structures to study the reasons of these changes so as to make recommendations on the designing of structure. The results show that this new-type structure could reduce the torsional effect, lateral displacement and strengthen overall seismic capacity.

Selection of Ground Motion Prediction Equations for the Global Earthquake Model

Ground motion prediction equations (GMPEs) relate ground motion intensity measures to variables describing earthquake source, path, and site effects. From many available GMPEs, we select those models recommended for use in seismic hazard assessments in the Global Earthquake Model. We present a GMPE selection procedure that evaluates multidimensional ground motion trends (e.g., with respect to magnitude, distance, and structural period), examines functional forms, and evaluates published quantitative tests of GMPE performance against independent data. Our recommendations include: four models, based principally on simulations, for stable continental regions; three empirical models for interface and in-slab subduction zone events; and three empirical models for active shallow crustal regions. To approximately incorporate epistemic uncertainties, the selection process accounts for alternate representations of key GMPE attributes, such as the rate of distance attenuation, which are defensible from available data. Recommended models for each domain will change over time as additional GMPEs are developed.

Experimental study on horizontal performance of multi-dimensional earthquake isolation and mitigation devices for long-span reticulated structures

Earthquake excitation is a kind of complicated multi-dimensional ground motion. Therefore, anti-earthquake measuresfor complex and important engineering structures, such as long-span structures and high rise buildings under multi-dimensional earthquake excitations, have become an extremely important research topic. In this paper, a new multi-dimensional earthquake isolation and mitigation device (MEIMD) is proposed for protecting long-span reticulated structures due to strong earthquake motions. It consists of a viscoelastic bearing and several viscoelastic dampers. Property tests on the MEIMD under different excitation frequencies, excitation amplitudes and vertical pressure forces are carried out. Then, a mathematical simulation is carried out for the equivalent stiffness and the equivalent damping of the device, and the numerical results agree reasonably well with the experimental data. Experimental and numerical results show that the MEIMD has a fine energy dissipation capacity, and can be used for anti-earthquake purposes for long-span reticulated structures.

The Non-Stationary Characteristic Study of Multidimensional Ground Motion by HHT Method: A Case Study from the Chi-Chi Earthquake

Based on HHT method, the influences of site conditions and epicenter distance on non-stationarity of multidimensional ground motion were studied. Additionally, preliminary statistics were carried out on frequency characteristics of multidimensional ground motion under different site conditions. The analysis results showed that HHT method was more accurate in a quantitative description of frequency-domain non-stationarity of ground motion than zero-crossing rate method, and also can reflected the non-stationarity of multidimensional ground motion better.