Difference Analysis Of Seismic Performance Of Reinforced Concrete Buildings Based On China And Ethiopia Seismic Code

Reinforced concrete(RC)structure has been widely used as an important building form.However,each country has promulgated and implemented the corresponding different RC building seismic code according to its seismic hazard conditions.This will create barriers to technical communication between professionals from different countries.Therefore,in the rapid development of globalization,it is necessary to make a comparative study of the advantages and disadvantages of the norms of various countries for learning from one another,to achieve the best practices applicable building standards in the economy,safety,and effectiveness.Based on the seismic design codes of Ethiopia(ES8-2015)and China(GB50011-2010),this research paper explores the seismic performance and soil-structure dynamic interaction of reinforced concrete buildings.The paper consists of three important parts.First of all,the background of the development of the seismic standards is studied,and the model buildings are designed according to the seismic code and concrete code of Ethiopia and China.Secondly,the model building seismic performance analysis is made by using the pushover method and verified by using the Incremental Dynamic Analysis method(IDA).Thirdly,the dynamic analysis of soil-structure interaction is studied.Finally,some important conclusions are summarized.In the first part,the design response spectrum regulations in the seismic code of Ethiopia(ES8-2015)and China(GB50011-2010)are reviewed.To make a comparison,a comprehensive consideration has been made with previous studies,and various item settings of the two specifications are involved.The elastic response spectra of horizontal ground motion and equivalent ground motion under the same design earthquake risk are compared.The results show that there is no significant difference between the two in the vibration period of less than 2.0s,but in the longer vibration time T > 2.0s,the results of China(GB50011-2010)code are significantly larger than those of Ethiopia(ES8-2015),which is consistent with the previous research conclusions in the context of ES8-2015.In addition,the design response spectrum comparison shows that the absence of ductility reduction coefficient in response spectrum of China(GB50011-2010)is not only the reason for the difference,but also the long-period region response spectrum curve provision.In general,this study highlights the advantages of response spectra of the two national codes,which can be used for future comparative studies,as well as for guidance and performance evaluation of seismic design of buildings.The second part of the study presents the seismic performance evaluation of the Reinforced Concrete(RC)frame designed as per Ethiopian(ES8-2015)(based on EN1998-1)and Chinese(GB50011-2010)seismic codes to realize best practices within them.In the study,three model RC frames with 4-,8-,and 12-storey are designed with the respective codes.Then,their seismic performances are evaluated using the nonlinear static(pushover)and procedures of FEMA-356 and ATC-40 provisions and verified with Incremental Dynamic Analysis(IDA).The comparison parameters include elastic stiffness,peak strength,target displacement,and plastic hinge formation patterns in the structures.The results display many similarities in the global and local performance of the structures.Despite these,the important findings are the observation of some noteworthy discrepancies that are presented as follows.(1)For Pushover analysis up to 2% roof drift as per ATC-40 Life safety structural performance level,GB50011-2010 designed frames show a larger pushover capacity curve,however,more plastic hinges form in the columns,which affects inter-story drifts,while ES8-2015 designed frames,more plastic hinges(energy dissipation)form in beams than in the columns,which exhibits better strong column-weak beam scenario,also distributed uniformly along with the height of the structure.(2)For Pushover analysis with the roof drift up to the performance point(target displacement)of the corresponding codes,the target displacement in ES8-2015 is greater than GB50011-2010 with smaller height frames 4 and 8-story,but become less for the 12-story frame.These variations are directly associated with the codes elastic spectrum uniqueness,the demand spectrum of GB50011-2010 considerably larger than ES8-2015,particularly for period of vibration T>2.0s.(3)However,for the aforementioned arguments in(1)and(2),it has to be noted that,the performance point analysis in(2)of both codes satisfy the design requirement,despite their structural performances discrepancy for 2% roof drift in(1).Nevertheless,these are important witnesses for the benefits gained while comparing various seismic codes as they have their own merits over one another.To sum up,although this study is limited to the flexural dominant reinforced concrete frame,it is of great significance to further study these two seismic standards by extending this research to various structural forms and establishing a correlation between them.In the third part,the dynamic analysis of soil-structure interaction(SSI)of multi-story reinforced concrete frame structure under two-dimensional and three-dimensional founded soft soil(flexible foundation)is carried out.The soft soils type IV and type D with a shear velocity less than 150m/s are considered respectively according to China Seismic standard(GB50011-2010)and Ethiopia seismic standard(ES8-2015).In the two-dimensional SSI analysis,with the help of the SAP2000 computer program,the SSI dynamic analysis of 7-story and 12-story reinforced concrete frames is carried out by using SSI models of the Winkler Spring and the half-space direct method.The analysis results of the two SSI models show the basic vibration periods and the story displacements are larger than the fixed base foundation;while the base shear force is smaller.In addition,the flexible foundation model has a large inter story-displacement and a second-order effect(P-△)at the bottom of the story.This shows that the reduction of base shear due to SSI does not mean always beneficial.Because for all types of foundation,the gravity load(P)on the fixed and flexible foundation is the same,the increase of the inter-story drift and the decrease of the inter-story shear force of the flexible foundation will increase the(P-△)effect of the bottom layer,making the vertical members of the bottom stories to be over-stressed and may cause stability problem leading to collapse.On the other hand,the three-dimensional SSI dynamic analysis of the 20 story shear wall-frame system is carried out.Using FORTRAN user subroutine,the seismic input model,Viscous Spring Boundary(VSB)with artificial boundary is applied to ABAQUS software for SSI dynamic analysis of the model wall frame building.Also,the SSI model of viscoelastic boundary is compared with that of constrained degree of freedom boundary,and the results are in good agreement.On the other hand,the overall response of three-dimensional SSI analysis is similar to that of two-dimensional analysis.However,the three-dimensional model analysis has higher calculation requirements despite its accuracy.In addition,the effect of SSI on wall frame interaction is well noted wall and frame have different stiffness in the building response as compared to the fixed base.The stress distribution within the wall and frame system changes along the height of the structure and vice versa either increasing or decreasing.The change of structural response along the height of the building is presented in chart form,and the correlation between SSI and fixed foundation response is obtained.Finally,the results of SSI analysis show the importance of SSI in the seismic design of buildings,so it is necessary to include SSI in the simplified P-△ effect seismic code.To summarize,according to FEMA 356 and ATC-40,the seismic performance of reinforced concrete frames designed by China(GB50011-2010)and Ethiopia(ES8-2015)were evaluated.The results will be of guiding significance for the code updating and other relevant seismic codes application in China and Ethiopia in the future.In addition,it highlights the importance of SSI in the seismic code,especially the P-(35)effect in the simplified form.