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Assalam-o-alaikum! Step wise process, for ETABS version 9, is as under: 1. Go to 'Analyze' -> Set Analysis Options' 2. Check 'Dynamic Analysis' 3. Click on 'Set Dynamic Parameters' 4. Select 'Ritz vectors' in 'Type of Analysis' portion. 5. Press 'OK'. Regards.

you have to consider yield line theory for non rectangular slab

Assalam-o-alaikum! Narrating, what Umar has said, in another form and in some detail, my comments are as under: From structural point of view, the design information we require (from a manual calculation, or a structural software), is somewhat DIFFERENT in case of Structural Steel and reinforced concrete (RC) members. In case of structural steel frame design, we are interested in knowing the 'capacity ratio' (= maximum stress, caused by applicable load combinations / permissible stress) of a member, to decide whether the member has passed (indicated by 'capacity ratio' <= 1), or failed (capacity ratio > 1). On the other hand, for the RC frame members, we want to know whether a particular member has failed? (so that its size could be revised). And, if it is passed, what is the required reinforcement ratio / percentage? The failure or passing of a RC member is based on the reinforcement ratio (or percentage). For passing of a member, the reinforcement ratio (or percentage) MUST be within code prescribed limits. For the steel members, ETABS does provide values of capacity ratios DIRECTLY. However, in case of RC members it does so INDIRECTLY by provides required reinforcement quantities / percentages and warning / error messages, to indicate whether the member has passed or failed. A 'passed' member is indicated by 'required reinforcement being WITHIN code-prescribed limits' and 'NO error / warning messages'. On the other hand, a member will 'fail', if the required reinforcement is OUTSIDE code-prescribed limits, accompanied by error / warning messages, indicating structural deficiencies in relevant respects_shear, torsion etc). In case of RC Shell elements (slabs, walls etc) however, it is possible in ETABS to check various type of stresses. This can be done using following (ETABS version 9) menu command (for the defined load combinations): 'Display --> Show Member Forces/Stress diagram --> Shell Stresses/Forces' (Select Component Type 'Stresses') Regards.

This warning message appears in cases, where the calculated value of shear and torsion stresses, EXCEEDS the value permitted by the code. Generally, it requires increase in the member cross-section. Regards.