Assessment of P-Delta Effect on High Rise Buildings

P-delta effect is secondary effect on structure .it is also known as ‘Geometric nonlinearity effect’. As number of stories increases, P-delta effect becomes more important. If the change in bending moments and displacements is more than 10%, P-delta effect should be considered in design. In this study the P-delta effect on high rise building is studied. Linear static analysis (without P-delta effect) on high rise building having different number of stories is carried out. For the analysis G+14, G+19, G+24, (i.e 15, 20, and 25storey) R.C.C. framed building are modeled. Earthquake load is applied on model of structure as per IS-18939(2002) for zone III in E-Tab software. Load combination for analysis is set as per IS-456(2000).All analysis is carried out in software ETAB. Bending moment, story displacement with and without p-delta effect is calculated and compared for all the models. Then by trial and error method suitable cross-section are provided for unsafe building to bring within acceptable limit by increasing stiffness of a building. The result shows that it is essential to consider the P-delta effect for 25storey building. So buildings having height more than or equal to 75m, should be designed considering P-delta effect. Also we can say that up to 25storey building, it is not necessary to consider P-delta effect in design and primary or first order analysis is sufficient for design. By increasing stiffness of building by providing suitable cross section or by increasing stiffness building can bring within acceptable limit.[7] DOI: 10.17762/ijritcc2321-8169.150515

Pushover Analysis of Steel Seismic Resistant Frames with RWS and RBS Connections

The widespread brittle failure of welded beam-to-column connections caused by the 1994 Northridge and 1995 Kobe earthquakes highlighted the need for retrofitting measures effective in reducing the strength demand imposed on connections under cyclic loading. Researchers presented the reduced beam section (RBS) as a viable option to create a weak zone away from the connection, aiding the prevention of brittle failure at the connection weld. More recently, an alternative connection known as a reduced web section (RWS) has been developed as a potential replacement, and initial studies show ideal performance in terms of rotational capacity and ductility. This study performs a series of non-linear static pushover analyses using a modal load case on three steel moment-resisting frames of 4-, 8-, and 16-storeys. The frames are studied with three different connection arrangements; fully fixed moment connections, RBSs and RWSs, in order to compare the differences in capacity curves, inter-storey drifts, and plastic hinge formation. The seismic-resistant connections have been modeled as non-linear hinges in ETABS, and their behavior has been defined by moment-rotation curves presented in previous recent research studies. The frames are displacement controlled to the maximum displacement anticipated in an earthquake with ground motions having a 2% probability of being exceeded in 50 years. The study concludes that RWSs perform satisfactorily when compared with frames with fully fixed moment connections in terms of providing consistent inter-storey drifts without drastic changes in drift between adjacent storeys in low- to mid-rise frames, without significantly compromising the overall strength capacity of the frames. The use of RWSs in taller frames causes an increase in inter-storey drifts in the lower storeys, as well as causing a large reduction in strength capacity (33%). Frames with RWSs behave comparably to frames with RBSs and are deemed a suitable replacement