Omar Khalid

Thank you

Hey, I’ve recently graduated from University with no real experience in work and was looking for a site engineering position to gain experience in the field. However couldn’t find one. So do you recommend me searching for a designer position in a consultant firm ?

1- Place shear walls opposite to each other, let's say you put a wall at the far right of a building, put another one with the same length and thickness at the far left one, .. etc that is to ensure the center of rigidity ( governed by walls mostly) coincides with the center of mass of the building to eliminate torsional movement of the building. 2- The far the wall is placed from the center of the building the better, as walls near the center doesn't resist much shear force as walls at the outer perimeter and the latter is good to prevent torsional movement. 3- The following is copied directly from the ACI design hand book: '' Shear walls should be located within a building plan to efficiently resist lateral loading. Locating shear walls in the center half of each building is generally a good location for resisting lateral forces. This arrangement, however, can restrict architectural use of space. Although shear walls are commonly located at the ends of a building, such wall locations will increase slab restraint and shrinkage stresses, especially in long buildings and buildings such as parking structures that are exposed to large temperature changes. Symmetrical wall arrangements provide good flexural and torsional stiffness. Walls at the perimeter resist torsional forces most effectively. Walls away from the perimeter, however, could have a higher tributary area and, consequently, larger gravity axial force to resist uplift or overturning. They are, however, less efficient in resisting horizontal torsion An unsymmetrical arrangement, however, does not usually provide predictable torsional stiffness due to their eccentricity. Such a shear wall layout should be designed explicitly for torsion. A symmetrical arrangement is preferable to avoid designing walls for torsion.''

If I calculated for an example the total area of rebars in a beam and I got let's say 433 mm2 I can now choose let's say 4 - 12 diameter bars or 2 - 16 diameter bars in a 300 mm width beam both will satisfy the minimum reinforcement and the maximum and minimum spacing due to ACI code. Does it matter if I chose any of them ? I know that the lesser the spacing between rebars the better to resist internal cracks in concrete. What are your thoughts ?

Hey guys, I think I have found what's wrong but don't know how to fix it. I drew the slab on SAFE and I have obtained the beams moments and slab deflections and they were very far away from ETABS results. However, there is an option to check it for columns and walls in SAFE it's called : ''Automatic rigid-zone area over column'' When I uncheck it, it gives nearly the exact deflection and beams moment in ETABS This option means the following from CSI america's website : ''Rigid zones are used to model the physical overlap between columns/walls and slab, which prevents deformation of the slab at the column location. This also will have the effect of producing maximum design moments at face of columns/walls instead of center line of columns/walls. This in turn will produce less reinforcement and hence a more economical design, and allowed by most codes(i.e ACI-318). Deformations also will be more realistic in this case.'' So I assume applying a rigid zone is more realistic but somehow it's not assigned in ETABS and I don't know how to assign it in ETABS. What are your thoughts ?

This is the slab it continues like this to the 20th story. Columns 60 X 60 cm Walls 30 cm Slab 20 cm Beams 60 X 30 cm

It's not entirely symmetrical I have 4 L shaped shear walls at the corners. Same thickness and nearly close lengths the columns are symmetrical right and left sides with the same dimensions but not symmetrical in the Y axis That's why I have a displacement of 1 cm at the roof in the y axis but that shouldn't cause vertical displacement note that the first floor has 8.4 mm vertical deflection while when I export the story to safe it gives me 2 mm deflection

That's what I was thinking, but the maximim reinforcement of a column at the base is 1.3-2 % which indicates which indicates small loads I will try to screen shot it when I get home

No. It's maximum vertical displacement absolute not relative

Hey My name is Omar I'm Jordanian and Palestinian and currently a civil engineering student at Jordan University of Science & Technology in my last semester. I've found this forum while searching for people to help me and I hope I can contribute to this community too Greetings

The location is in the panel with the largest span in a story which is predictable nearly in the center of the panel

Maximum deflection in the first floor is 8.4 mm 2nd floor is 9.4 mm 3rd is 10.6 mm 4th is 11.65 mm 5th 12.6 mm etc the 20th 20.5 mm These are maximum deflections in each slab (same place) with dead load only (self weight only)

Hello, I'd like to contribute to this forum three excel sheets of my design, Nothing too fancy but that's what I'm capable of The first is a singly reinforced concrete beam - one layer. (Don't use the shear design it's not complete) with ACI 318-14 The second is a hollow core pretension-ed slab analysis using PCI to check the stresses limits, design strength and Mcrack The third excel is an analysis method for seismic design of reinforced concrete water containing structures. ( I've done this very recently if you spot any error in it please inform me ) with ACI 350.3-06 and IBC/ ASCE 7-10 Sheets.rar

Moment release in SAFE doesn't work regardless the model. probably a bug in the program. checked it with another model and lap top. Thanks by the way

Can you tell me how to check it ?

1) due to dead load only (own weight) the building tends to undergo a displacement in the x axis (horizontal displacement) the maximum displacement is 1 cm at the roof. Cause I have a stair wall with 2 elevator cores at one side of the building. 2) No earthquake or wind loads being applied yet. Only dead and live and slab deflections still increases when you go up. 3) No errors in my model.

Hello, I exported a story from etabs to safe and checked the results it turned out safe always gives me lower moment result for beams and by exporting it doesn't import neither property stiffness modifiers nor end releases assigned in etabs. After I have assigned moment release manually in safe nothing happens. The negative moments is still present why is that ? Thanks

Regardless the combination I choose to look for settlements. it's always increasing the higher I go. I've seen people modeling on youtube having the same problem except they don't talk about it like it's a normal thing. does it have anything related to vertical settlements of columns and walls ? You can try it by yourself on etabs to check I'm right or not.

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