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I work in a project with large spans (9.2m X 8m) and large service loads (4kn/m^2 SDL+Partitions), (7.5kn/m^2 Live load) In modeling the project on ETABS I set the property modifiers for slab (thin shell as 0.25) and this affected the deflection in slabs ( about 5 cm deflection from service loads) Hence: Slab thickness is 22 cm and interior beams 50X50 and the owner didn't allowed to increase the thickness Any suggestions to solve the problem.

increasse the compression reinforcement (top) and see the long term sustaineddeflection in safe.this one is second alternative,but i think in your case deflection is quite high due to heavy loads,it may not control as much as you wanted.bcz reason is slab thickness is low.

dear ahmed !THIS IS ALARMING SITUATION. there are certain things which i dont know about your project,but i have assumed and calculated required thickness of your panel,which comes to be AT LEAST 9.2 INCH.REFERENCE ACI318-14 (TABLE 8.3.1.2) 1-THIS 5cm deflection is immediate,the long term will be approximately 12 cm,but you can calculate exactly by yourself. i dont know what is allowable deflection in your case. 2-i have considered your panel interior ,and taken 9.2m clear span. • L/480 for the part of the total deflction that occurs after attachment of elements, that is, the sum of the long-time deflction due to all sustained loads and the immediate deflction due to any additional live load, for flors or roofs supporting elements likely to be damaged by large deflctions.

1. How are you calculating slab deflections from ETABS? 2. Are deflection elastic or long-term? 3. Perform long-term non-linear deflection analysis in SAFE. 4. Then if deflection is excessive, try increasing top and bottom reinforcement. 5. If nothing is working and you cannot increase thickness or decrease loads, then try using another type of slab. For example ribbed slab, hollow cores etc.

Dear Ahmad, Please follow forum rules. A simple search of old forum posts would have been helpful. For example see below;

Selection of the size of a steel beam depends upon the design moment to be resisted and the structural steel grade of the beam material. Knowing these two parameters & design requirements of the steel design code, you can calculate section modulus of the beam required to resist the applied moment safely. Any steel section (e.g., 8"x4", 10"x5", etc.) having a section modulus equal or more than the required section modulus should be Ok to use, provided it satisfies all other relevant design & serviceability requirements of the applicable design code as well. Regards.

Hello Everyone. I am Engr. Zulfiqar Ali. I am working as Senior Civil Design Engineer in a multinational company Tecnicas Reunidas Engineering Consultancy (TR Engg. Consultancy) in Oman for last five years. I always like to learn new things and just know about this website, so i decided to join. Hopefully we can discuss any structural design issue here. Thanx in advance. With Best Regards, Engr. Zulfiqar Ali