Chinese Seismic Code Research Articles

The Vertical and Horizontal Spectra of Near-Fault Ground Motions

Based on the horizontal and vertical components of a set of 30 acceleration records obtained from 10 near-fault earthquakes, the horizontal and the vertical response spectra are established, and have been compared with each other in this study. Statistical analyses show that, for the selected 30 acceleration records, the maximum mean of vertical acceleration spectra is slightly higher than which of horizontal acceleration spectra. That means the near-fault earthquake really have significant vertical effect. Consulting the domestic and international research achievement, the normalized near-fault design spectrum adapted to Chinese seismic design Code (GB50011-2010) is established in horizontal direction. The results show that, within short period range, the horizontal near-fault design spectrum obtained in this paper is obviously higher than which derived from Chinese seismic code. Subsequently, the spectra of horizontal components for the selected 30 records are each scaled to match the horizontal near-fault design spectrum at two periodic points of 1.0 and 1.5 sec respectively, and the corresponding vertical spectra are scaled with the horizontal spectra at the same time. The scaled results reveal that the vertical spectra have much higher discretion than horizontal spectra, hence the study in this paper could initiates the research interest to a new aspect concerned with the randomness of vertical spectra for near-fault ground motions, which would affect the seismic reliability of structures significantly.

Comparison of Base Shear Force Method in the Seismic Design Codes of China, America and Europe

Seismic design response spectrum and earthquake action in Chinese new seismic code (GB50011-2010), ASCE/SEI7-05 and Eurcode8 were gathered in this paper. Using base shear force method of each code, the authors computed the horizontal seismic forces of a three-story reinforced concrete frame building under the same conditions. The results show that the three static methods roughly approach, while the different parameters lead to discrepancies in calculated values.

Seismic performance of a reinforced concrete frame building in China

This paper investigates the seismic performance of a multi-story reinforced concrete frame building designed according to the provisions of the current Chinese seismic code (GB50011-2010). A typical five-story reinforced concrete frame building is designed. Seven natural earthquake acceleration records, selected and adjusted for compatibility with the adopted design spectrum, are used. The frame structure is evaluated using both a nonlinear static (push-over) analysis and nonlinear dynamic time-history analysis. The assessment of seismic performance is based on both global and member level criteria. According to the numerical results, the building frame designed by GB50011-2010 provides the inelastic behavior and response intended by the code and satisfies the interstory drift and maximum plastic rotation limits suggested by ASCE/SEI 41-06. However, the push-over analysis indicated the potential for a soft first story mechanism under significant lateral demands. Design recommendations are provided to help ensure the preferred strong-column, weak-beam damage mechanism.

A Study on Elastic Input Energy Spectra Based on the Compound Intensity Indicator

Determination of a SDOFS elastic input energy is the primary problem to solve for energy-based design approach. The effect of ground motion and damping ratio were analyzed on the input energy spectra. is selected as the compound ground motion intensity indicator to represent the damage potential of strong ground motion. Through inputting of 188 seismic records according to the site classification of Chinese seismic code, three-segment elastic energy spectra are proposed based on normalization methods. The calculation formula of the peak and the value of long-period section of the input energy spectra are presented for four categories of site conditions by statistical analysis. Moreover, calculation procedure of the total energy input is given in the paper.

A Study on Elastic Input Energy Spectra Based on the Compound Intensity Indicator

Determination of a SDOFS elastic input energy is the primary problem to solve for energy-based design approach. The effect of ground motion and damping ratio were analyzed on the input energy spectra. is selected as the compound ground motion intensity indicator to represent the damage potential of strong ground motion. Through inputting of 188 seismic records according to the site classification of Chinese seismic code, three-segment elastic energy spectra are proposed based on normalization methods. The calculation formula of the peak and the value of long-period section of the input energy spectra are presented for four categories of site conditions by statistical analysis. Moreover, calculation procedure of the total energy input is given in the paper.

Modified-modal-pushover-based seismic optimum design for steel structures considering life-cycle cost

A modified-modal-pushover-based optimization technique is presented to design steel moment resisting frame buildings for minimizing the life-cycle cost based on the framework of performance based earthquake engineering. Modified modal pushover analysis (MMPA) procedure capturing the higher mode effect well is utilized to analyze the inelastic seismic demands of the structures subjected to the considered design earthquakes in terms of the Chinese seismic code for buildings, especially for the medium- to high-rise buildings. Furthermore, the life-cycle cost is formulated as the summation of the initial material cost and the future expected damage loss, which can be stated as a function of seismic performance levels and their corresponding failure probability by means of a statistical model. Meanwhile, the damage loss is explicitly and continuously expressed by the defined interstory drift index using the fuzzy-decision theory. Moreover, the powerful adaptive simulated annealing algorithm is applied to solve the discrete optimization problem due to the discreteness of standard steel sections. Finally, a 9-story planar steel frame is provided to illustrate the effectiveness of the proposed optimization design technique, which achieves not only more cost-effective design but greatly improves the robustness of the optimum design as well.

Research on Structural Influencing Coefficient of Moment-Resisting Steel Frames

This paper is focused on the evaluation of the structural influencing coefficient in multi-story moment-resisting steel frames involving local bucking effect, with due consideration to both their ductility and overstrength. Ductility and overstrength play an important role in keeping satisfactory performance of structures during strong earthquake. Firstly, moment-resisting steel frames of are designed according to Chinese seismic code. Based on the non-linear shell element method, both inelastic time history and pushover analyses has been performed on these steel frames to get the global capacity envelopes. The results show that number of stores and spans have effect on the behaviour factor values, and that the local buckling affects the ductility capacity of steel frames. Finally, based on the findings presented in the article, tentative influencing coefficient values are proposed for moment-resisting steel frames.

Structural Seismic Performance Evaluation in Consideration of Earthquake Ground Motion Uncertainties Using Convex Set Model

When data is insufficient to support a probabilistic assumption, the structural seismic performance evaluation results with probabilistic approach are suspicious. In this paper, the convex set theory, which requires much less information, is employed to model the uncertainties of peak acceleration and frequency characteristics of earthquake ground motions. The bounds of shear forces are first derived with Chinese seismic code, and then a lateral bound load method for Push-over analysis is conducted. Then the convex analysis is integrated into Push-over analysis to study the bounds of structural capacity. Furthermore, the bounds of earthquake demand are deduced with the bounded convex set model and Chinese seismic code. The bounds of target displacement are obtained using capacity spectrum method. The seismic performance of structure is then evaluated with an interval. Finally, seismic performance evaluation of a three-storey RC building is given to demonstrate the benefits of the proposed method.

Response spectrum of seismic design code for zones lack of near-fault strong earthquake records

It was shown from the study on the recently near-fault earthquake ground motions that the near-fault effects were seldom considered in the existing Chinese seismic code. Referring to the UBC97 design concept for near-fault factors, based on the collected world-widely free-site records of near-fault earthquakes ground motions classified by earthquake magnitude and site condition, the attenuation relationship expressions of the acceleration spectrum demand at the key points within the long period and moderate period were established in term of the earthquake magnitude and the site condition. Furthermore, the near-fault factors’ expressions about the earthquake magnitude and the fault distance were deduced for the area lack of near-fault strong earthquake records. Based on the current Chinese Building Seismic Design Code, the near-fault effect factors and the modified design spectral curves, which were valuable for the seismic design, were proposed to analyze the seismic response of structures.

The Modification of Strength Reduction Factors for MDOF Effect

This paper focuses on the modification of SDOF system strength reduction factors to suit MDOF systems. Firstly, an approach to calculation of the modification factors is presented and a method of determining storey ductility of structures with incremental dynamic analysis is introduced. Then, the modifications of the strength reduction factors to take account of MDOF effect are investigated for four RC frame structures strictly designed according to the Chinese seismic code subjected to 80 earthquake ground motions. The ductility level, structural period and site conditions effects on the modification factors are discussed and a simplified expression to estimate the modification factors is presented, which is a function of the structural period and the ductility level. It is concluded that the modification factors are primarily affected by the ductility level and structural periods and the inverse of the modification factors increases apparently with increasing ductility level and structural period. It also appears that the site conditions have little effect on the modification factors.

Study on strength reduction factors considering the effect of classification of design earthquake

The strength reduction factors are not only the key factors in determining seismic action for force-based seismic design, but also the key parameters to derive the inelastic response spectra for performance-based seismic design. In this paper, with a high quality ground motion database that includes a reasonable-sized set of records from China, a statistical study on the strength reduction factors is conducted and a new expression of strength reduction factors involving classification of design earthquake, which is an important concept to determine design spectra in Chinese seismic design code, is proposed. The expression of strength reduction factors can reflect the ground motion characteristics of China to a certain extent and is particularly suitable for Chinese seismic design. Then, the influence effects of site condition, classification of design earthquake, period of vibration, ductility level, earthquake magnitude and distance to fault on strength reduction factors are investigated. It is concluded that the effect of site condition on the strength reduction factors cannot be neglected, especially for the short-period structures of higher ductility. The classification of design earthquake also has an important effect on strength reduction factors and it may be unsuitable to use the existing expressions of strength reduction factors to the design spectra of current Chinese seismic code. The earthquake magnitude has no practical effect on strength reduction factors and if the near-fault records with forward directivity effect are not taken into consideration, the effect of distance to fault on strength reduction factors can also be neglected.

Optimization and Dynamic Analysis of Frame Structures with Friction Energy Dissipation Device

An analytical solution for a single-damped-storey frame structure system including a friction energy dissipation device under sine wave excitation is presented with an example. A new mathematical model for optimizing some key system parameters in earthquakes is proposed. The model minimizes the sum of brace stiffness that complies with the Chinese seismic code for storey-drift limitations for three given earthquake records. Therefore, the seismic requirements for similar structures can be satisfied with fewer friction energy-dissipation devices. Using the Visual C++ language, a computer program, GAOFF, has been developed to optimize the parameters of a frame structure with friction energy dissipation devices based on three earthquake records using a genetic algorithm. An example of a six-storey RC frame is also presented to demonstrate the effectiveness of the proposed optimal design procedure.