Horizontal load represents that arising from equivalent static analysis (earthquake load)as obtained from IS 1893:2002. As for the other two structures, The governing criterion isstrength. Combined axial and flexural check show that beam (1) is critical with the ratio of0.98 and column (2) is critical with the ratio of 0.99.Figure 14 shows the pushover graph for the frame when subjected to incremental statichorizontal loads. One point to be noted here is the decrease in the base shear capacity of thestructure prior to collapse (not shown). This maximum value is considered as the ultimatebase shear.Figure 15 show the IDA curves when the structure is subjected to Bhuj and Uttarkashirecords respectively. In case of Bhuj record, the structural failure occurs when IDR becomes10% (see Sect. 2.4). In case of Uttarkashi record, the structure exhibits a phenomenon called weaving where in the structural response decreases at a certain step even when Sa increases.In this case, the structural slope falls almost to 0.3∗Se (see Sect. 2.4) and at that point it isassumed that the structure fails. The pushover, time-history and IDA results are summarizedin Table 4 below.The R factor is a serious source of underdesign in this structure. Both Bhuj and Uttarkashiearthquakes are moderate when compared to earthquakes like Kobe, 1995 where PGA was1.28 g. It can be seen that the structure yields under unscaled Uttarkashi earthquake groundmotion record. A stronger earthquake can prove disastrous for this kind of structure.4 Discussion of results—true demand and capacity versus codal provisionsIS1893 prescribes design base shear for structures below 40m. Three steel moment resisting2-D framed structures were analyzed, all in Seismic Zone V, subjected to Bhuj and Uttark-ashi records. Here, we compare the codal provisions with the actual performance of the threestructures. Four response categories are chosen: peak IDR, total base shear, critical beammoment and critical column moment. In each of these categories, and for each structure, thecomparisons are made in terms of four ratios given below. The numbers in parentheses referto column entries of Tables 1, 2 and 3.A. Codal CDR. (Code specified factored capacity / code specified factored demand) =(2)/(3).B. Capacity ratio. (Actual capacity / code specified factored capacity)=min((10),(11))/(2)for shear and moments, and min((8),(9))/(2) for IDR. C. Demand ratio.(Actual demand/ code specified factored demand)= max((6),(7))/(3)D. Actual CDR. (Actual capacity/ actual demand)= min((10)/(6),(11)/(7)) for shear andmoment, and min((8)/(6),(9)/(7)) for IDR.In the above ratios, the code specified factored capacity refers to column 2 while the codespecified factored demand refers to column 3 of Tables 1, 2 and 3. The actual capacity refersto the ultimate capacity in column 10 and 11 for base shear and moments, and to the yieldcapacity in columns 8 and 9 in case of IDR. The actual demand refers to columns 6 and 7of the three Tables. For a ratio involving the actual capacity, the lower result between thetwo records—Bhuj and Uttarkashi, is adopted; while for a ratio involving actual demand, thehigher result between the two earthquake records is selected.Figure 16 describes the four ratios in each of the four response categories for the threestructures. The first set of bars in each figure shows the codal CDRs. Since the code specifiedcapacities and demands include the respective design factors in them, it is not surprising thatthe critical codal CDR for each structure is very close to one.The second set of bars in each figure shows the capacity ratios. Clearly the ratios are ataround 2.0 or higher for each structure and might (erroneously) suggest an amount of conser-vatism in the codal provision. Such false sense of security is lost when one looks at the thirdset of bars—the demand ratios. The demand ratios are greater that one in most cases, and 5 ConclusionsThis study looked at the adequacy of the current Indian seismic design code for low-rise steelstructures by subjecting three representative 2-D frames to incremental dynamic analysisunder Uttarkashi and Bhuj earthquake records. It is seen that the equivalent static methodrecommended by the IS code for low-rise structures significantly underpredicts both seismicdemands and structural capacities in four different response categories. 通过增量动态分析评估设计低层钢框架英文文献和中文翻译(6):http://www.751com.cn/fanyi/lunwen_56527.html