Study On Failure Modes For RC Frame-bent Structure Of Thermal Power Plants Under Earthquake

The seismic performance of the frame-bent structure for thermal power plants ispoor as its quality and rigidity are distributed non-uniformly on the spatial distributionand integral performance of the structure is poor and it has many weaknesses. Asimportant lifeline engineering, the frame-bent structure must have good seismicperformance. In order to reduce the adverse influence of seismic damage and ensure thenormal work of the frame-bent structure, it’s very vital significance to research thefailure modes of the frame-bent structure and improve the frame-bent structure.The frame-bent structural system with end shear wall is comprised of steam-engineroom, deaerator room and coal bucket room three-rankedly. In this paper, the finiteelement analyze model of the frame-bent structure for main mill building is establishedby SAP2000. Then the Pushover curve of the model is got by Pushover analysis.According to the failure criterion, the structural failure mode can be got. Through thestudy of failure modes the structural failure path and the weak position can be got. Thenon this basis the performance of the structure is evaluated and improved. Finally, bycomparing the elastic-plastic time history analysis results of the improved structure withthat of the original structure and the main conclusions can be drawn as follows:(1) The first mode of the structure is lateral translation and then the second modeof the structure is torsion. The ratio of the torsion of the first period to the translation ofthe first period is74.6%and each mode has a certain torsion reaction.(2) The Pushover analysis of the structure is made. According to the failurecriterion, the structural failure mode can be got. Then the structure’s weakest failuremode is discussed based on the comparison and analysis of the failure modes of each working condition. The failure path and the weak position of beam-column element ofthe structure’s weakest failure modes are studied. Analysis results show that while thestructural damage occuring, the platform column at the bottom of the platform and thedeaerator layer and the coal bucket layer are weak positions, the damage is the mostserious. The failure mode of beam-column element is beam-column hinging mixedmode. The damage of the NO.1of the transverse frame-bent structure is the mostserious.(3) According to the energy spectrum method of ATC-40, the structuralperformance at unusual earthquake Ⅶ and unusual earthquake Ⅷ is evaluated. Theinter-story displacement angles are not more than the concrete frame structure’slimitation of inter-story displacement.(4) The weak positions of the most serious three transverse frame-bent structuresare improved. The improved schemes are compared and analyzed through Pushoveranalysis. This study shows that by taking into account the improved results of eachimproved scheme, process requirements, and the difficulty and operability of theconstruction, this paper suggests that improving the platform column at the bottom ofthe platform and the deaerator layer and the coal bucket layer of the NO.1of thetransverse frame-bent structure can achieve relatively good improvements.(5) The elastic-plastic time history analysis of the original structure and theimproved structure are made after inputting4kinds of seismic wave with accelerationpeak of100gal,220gal,400gal,510gal respectively. Their seismic performance iscompared and analyzed by considering the biggest inter-story displacement angles asseismic index of structure. The results show that the improved results of scheme3ispoorer with the growth of acceleration peak at the same seismic wave. In view of themaximum and the minimum of the improved results of scheme3, the difference of themaximum and the minimum of the improved results of scheme3is the biggest at theacceleration peak with100gal and while it is the smallest at the acceleration peak with510gal at the same seismic peak acceleration. So the difference of the improved resultsof scheme3is reduced with the growth of acceleration peak value. The difference ofseismic performance indicators with different seismic waves is relatively small atunusual earthquake and can ensure the accuracy of structural performance evaluation, the results shows that the improved result of scheme3tends to be stable.