Research on the seismic fortification level of offshore platform in Bohai Sea and adjacent areas

API code is introduced at first, and then a comparison of seismic character and seismic hazard between Bohai and Southern California is carried out. The analysis indicates both the seismic frequency and intensity and the seismic hazard of Bohai are much weaker than that of Southern California. API code states the strength level and deformation level of permanent structures in Southern California takes 200 a and several hundred to a few thousand years respectively. But in the reference codes in China, the seismic levels take 500 a and 10000 a for strength design and deformation design, and it seems too conservative. In China, the deformation level of class A structure takes 2%-3% probabilities of exceedance in reference period 100 a, and that of class B and C often takes 2%-3% in 50 a. Now that offshore platforms may cause server subsequent risk, it is safe to take 1% in 30 a as its deformation design level. On the basis of the above analyses and social economic level and the consistency with present codes, the strength design level and deformation design level of Chinese offshore platforms is suggested to take 200 a and 3000 a respectively.

Lectotype optimization of mid-highrise residential building based on site conditions and seismic fortification intensity

A multi-objective lectotype optimization model based on site conditions and seismic fortification intensity is presented for mid-highrise residential buildings taking into account multiple items such as the original investment, disaster losses and maintenance cost, the integral stiffness, the total ductility, the construction period, and so on. A Three-Scale Fuzzy Analytical Hierarchy process is proposed by introducing the Three-Scale Analytical Hierarchy process and the trapezoid fuzzy number. The result of a calculation example shows that the T-FAHP is practical.

Large, moderate, small earthquakes and seismic fortification criterion

This paper discusses the relation between two-step seismic design and the standard of probability of exceedance, and the relation of three-levels seismic ground motion parameters given by probability method and comprehensive probability method. The relative size relations of the ground motions with 2%, 10%, 63% probability of exceedance in 50 years, namely large earthquake, moderate earthquake, and small earthquake, are discussed through a practical example of seismic hazard analysis. The methods to determine seismic fortification criterion are discussed.

A Comparison of Domestic and Foreign Seismic Fortification Standards for Electrical Equipment

It is of great significance to make comparative analyses of seismic fortification criteria at home and abroad for improving the anti-seismic capability of electrical equipment and revising the relevant national standards.A brief overview of American,Japanese,IEC standards and Chinese seismic design codes for electrical equipment is presented.Differences between these seismic fortification standards of electrical equipment are compared and analyzed in respect of the goal and level of seismic fortification and the seismic design spectrum.The advantages and disadvantages of Chinese standards are pointed out.Through learning from foreign experience on the determination of seismic fortification standards,recommendations are made for the improvement and revision of Chinese seismic fortification standards for electrical equipment.

Study on the Seismic Fortification Criteria of Offshore Platforms in the Bohai Sea

This paper analyzes the seismicity and seismic risk distribution in the Bohai Sea. Based on the seismic design parameters of 46 platforms in the Bohai Sea, a statistic analysis is made on the ratios of the peak accelerations for different probability levels. In accordance with the two-stage design method, a scheme of two design seismic levels is proposed, and two fortification goals are established respectively for strength level earthquakes and ductility level earthquakes. Through analogy and comparison to the Chinese seismic code for buildings, it is proposed that the probability level for the strength and ductility level earthquakes takes return periods of 200a and 1000～2500a respectively, and we further expounded on its rationality. Finally, the fortification parameters in the sub-regions of Bohai Sea area are given in the light of seismic risk zonation and ground motion division. This article is a summary of experiences from many years of offshore platform seismic fortification work, and an exploratory study on the seismic fortification standards of offshore platforms in China, which may provide some references for the establishment of the standard.

Evaluation of collapse resistance of RC frame structures for Chinese schools in seismic design categories B and C

According to the Code for Seismic Design of Buildings （GB50011-2001）, ten typical reinforced concrete （RC） frame structures, used as school classroom buildings, are designed with different seismic fortification intensities （SFIs） （SFI=6 to 8.5） and different seismic design categories （SDCs） （SDC=B and C）. The collapse resistance of the frames with SDC=B and C in terms of collapse fragility curves are quantitatively evaluated and compared via incremental dynamic analysis （IDA）. The results show that the collapse resistance of structures should be evaluated based on both the absolute seismic resistance and the corresponding design seismic intensity. For the frames with SFI from 6 to 7.5, because they have relatively low absolute seismic resistance, their collapse resistance is insufficient even when their corresponding SDCs are upgraded from B to C. Thus, further measures are needed to enhance these structures, and some suggestions are proposed.

Probability-consistent spectrum and code spectrum

In the seismic safety evaluation (SSE) for key projects, the probability-consistent spectrum (PCS), usually obtained from probabilistic seismic hazard analysis (PSHA), is not consistent with the design response spectrum given by Code for Seismic Design of Buildings (GB50011-2001). Sometimes, there may be a remarkable difference be-tween them. If the PCS is lower than the corresponding code design response spectrum (CDS), the seismic fortifi-cation criterion for the key projects would be lower than that for the general industry and civil buildings. In the paper, the relation between PCS and CDS is discussed by using the ideal simple potential seismic source. The re-sults show that in the most areas influenced mainly by the potential sources of the epicentral earthquakes and the regional earthquakes, PCS is generally lower than CDS in the long periods. We point out that the long-period re-sponse spectra of the code should be further studied and combined with the probability method of seismic zoning as much as possible. Because of the uncertainties in SSE, it should be prudent to use the long-period response spectra given by SSE for key projects when they are lower than CDS.