| Ever since the Ronan Point collapse case, the issue on how to resist progressivecollapse through structural robustness has attracted a lot of attention. For forty years,huge numbers of study and research has done worldwide. However, there are hardlyever any papers discussing progressive collapse of step-terrace frame structures.Step-terrace frame structure is a representative structural types of mountainousbuilding. Uneven height grounding ends led to the vertically irregular for this structure.The lateral stiffness for columns of upper ground floor differs a lot, which results thedifferent in progressive collapse property betweenstep-terrace frame structureandordinary structure. On the other hand, the slope failure may cause the progressivecollapse. Thus, it is necessary do some study about resist progressive collapse propertyfor the step-terrace frame structures.The main contents herein are as followed:①Summarized methods for design and analysis about structureresist progressivecollapse. Among them, alternate path method is under detailed analysis and some thekey problems during application have been pointed out and tested.②Refer to GSA2003, the software SAP2000, alternate path method are used tofind out the effects the following4aspects, number of off layers, span of off layers,kinds of support, seismic fortification intensity and slope failure, may have on theperformance of resist progressive collapse of step-terrace frame structures.③On account of the stress features of the step-terrace frame structures, threemeasures to improve the capacity of resist progressive collapse are carried out,respectively are brace-setting, improve reinforcement ratio of beams of some certainfloors, and connect off layers’ beam to retaining wall. These measures are studied, andsuggestions of design are proposed according to the analysis results.Conclusions in this paper are drawn as followed:①Compared with ordinary structure, the performance of resist progressivecollapse of step-terrace frame structure is more unfavorable. When the total layers’number stays invariant, the larger the number of structure’s off layer is, the lower thecapacity of resist progressive collapse of the structure will be; When the total spannumber is same, the larger the span number of off layer is, the higher the capacity willbe; The structures whose columns on the upper ground are fixed supported have better resistant ability than the ones whose are articulated supported; The destructive effect isthe strongest when the collapse happens due to the inside column invalidation. The mostinfluential component in deciding the capability of resisting possessive collapse is thebeam connected to the failure upper column.②In the area whose seismic fortification intensity is6, the capacity of resistprogressive collapse of step-terrace frame structure is low. With the improvement ofseismic fortification intensity, the contribution of the seismic load is greater than gravityload on reinforcing frame structure, and structure’s capacity of resist progressivecollapse is significantly improved.③For braced step-terrace frame structure, only when the brace setting is in thebay where the column is removed, the structure’s resist progressive collapse capacitymay improve. Besides, when the brace is seated above the removed column one layer, itis most advantageous for structure’s resist progressive collapse capacity. And when thebrace’ location is higher and higher, the brace’s contribution to structure’s resistprogressive collapse capacity will decrease gradually.④For the step-terrace frame structure which is designed with6degrees (0.5g)seismic fortification, when of30percent of the layers above the upper ground and thelayers parallel to upper ground, the layers beam’ reinforcement improve30%~35%, thestep-terrace frame structure can almost have the capacity to resist progressive collapse.Besides, for the removed column on the lower ground, the increase of beams’reinforcement makes greater contribution to improve the capacity of resist progressivecollapse of the remain structure of removed column on the upper ground.⑤The connection between beam and barricade can only affect the capacity ofresist progressive collapse of the remained structure when the columns close tobarricade on lower ground are removed. Here what is needed to point out is that thisoccasion can only happen when the one special-shaped column frame is invalid, and asthe layer number of upper ground increases, beam and barricade use rigid connectionhas a weaker influence on improving the structure’s capacity of resist progressivecollapse. |
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