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Found 9 results

  1. Slab deflection in ETABS

    Hello, While I was modeling a 20 story building with symmetrical concrete slab sections and loads in each story, I noticed that the deflection of the slab increases the more I go higher in elevations despite having the same sections, dimensions and loads. I know that floors with symmetrical shapes and loads must endure the same stresses so it has the same reinforcement. Can someone explain this behavior or explains why it occurs if I was wrong ? Thanks in advance
  2. Assalam o alaikum, For assuring deflection check of flexural members, we compare immediate deflection due to live load with L/180 or L/360. Also we compare total deflection (sum of immediate deflection due live load and long term deflection due to "dead +sustained loads") with L/240 or L/480. These deflections are calculated using corresponding effective moment of inertia "Ie" using equation 9-8 of section 9.5.2.3. To find out immediate deflection due to dead load we find out it using Ie calculated using cracking moment due to dead loads. To find out immediate deflection due to sustained loads we find out it using cracking moment due to sustained loads. To find out immediate deflection due to D+L we find out it using cracking moment due to dead + live loads. But to find out immediate deflection due to live load, we don't find it using cracking moment due to live load. We find out it by the difference of deflection due to dead + live load with the deflection due to dead load only. as shown by following results of manual calculations (Results from example 10.1 of PCA notes of ACI 318) Del.dead = 0.098 in (calculated using Ma due to dead load only and corresponding Ie came out to be 10648 in4 = i.e. Ig because Ma is less than cracking moment) Del.live = 0.0744 (calculated using Ma due to live only and corresponding Ie came out to be 10648 in4 = i.e. Ig because Ma is less than cracking moment) Del.(dead+live) = 0.344 in (calculated using Ma due to dead+live combo and corresponding Ie came out to be 5345 in4 < Ig because Ma is greater than cracking moment) Note that 0.344 is not the simple sum of 0.098(Del.dead) + 0.0744 (Del.live) because here for Del.live, Ie used was based on live only i.e. Ig =10648 in4; for Del.dead, Ie used was based on dead load only i.e. Ig = 10648 in4; and for Del.(dead+live) Ie used was based on (dead+live) load combo i.e. 5345 in4. All three "Ie" are different". My question is, how to cater this in etabs modeling because in etabs it simply super impose deflections due to dead and live for D+L combo which must not be the case. More over, does modifier 0.35 is enough to cater effect of effective moment of inertia? Thanks.
  3. While checking the allowable deflection in member in ETABS, which deflection is to be considered, absolute or relative? Which one represents the actual deflection of the member?
  4. Large deflection in two way slabs

    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.
  5. Deflection Control

    Do etabs or sap has allowable deflection checks for beams if it is analysed and designed through these softwares.
  6. This particular slab (19x18 ft) is expereincing too much displacement, giving rise to very close spacing in slab panel in the middle strip. It has three interior beams placed to carry line load of the walls above. How can this displacement be reduced? Slab 19x18.bmp
  7. Hi, I have a problem with a simply supported deep beam which has a uniformly distributed load. The beam is simply supported at both ends but I have to consider the results for the following 3 scenarios - where the support is at the bottom of each end of the beam - where the support is at the mid point at each end of the beam - where support is at top of each end of the beam I have run this using FEA and I'm finding significantly different deflections and stresses when the beam is supported at the midpoint at its end and the other two scenarios...can anyone explain the exact reasoning for this? Sincere thanks Daniel
  8. 1-how to calculate deflection for a t-beam? 2-will it be different from the rectangular beam? 3-will concrete strength effect the deflection?
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