TO CRACK SAP , ETABS AND SAFE SOFTWARES SEE BELOW LINK
REDUCIBLE LIVE LOAD :
Q : In ETAB, I defined Live load as reducible live load. I know it reduces live load for column design. But my question is does the live load get reduced for beam and joist design as well?
Because I don't want to recduce live load for beam and girder design- is there a way in ETAB so that it reduces ony for columns and not for beams and other elements?
ans : Yes, by choosing axial force option only. In the live load reduction menu under preferences, choose axial force only and it will reduce only that.
FOLLOW UP QUESTION
This option is ok for column design.But while you design beams and girders,it reduces the live load.
But I want to design beams and girder on the same model but without reducing live load.So far I used to design beams and girder clicking the option No live load reduction and while designing columns click the option 'reduce per ASCE 7 and choosing the axial force option as you mentioned above.
I am wondering how other people are designing and if there is an efficient way to do it.
ans : Live load reduction can be chosen only for axial forces. It won't reduce any moments in beams. I don't know what you mean!
I also got reply from another post. They are recommending to overwrite the LL reduction factor =1.0 for beams and girders.And selecting the axial force only option as mentioned above for application to columns.
It solved the problem.
One more question..
if i am not wrong, even if i define live load as simple live load (not reducable live) live load reduction will be applied by etabs.. rite/?
ETABS does not reduce Live load unless it is assigned as reducible live.
What is an Interaction Diagram?
In short, an Interaction Diagram is a much faster way of analyzing a concrete column for large eccentricities (aka large moments). An example of a Interaction Diagram has been included in Figure below
Fantastic! Now how do I use it?
Don't fret, it's actually a lot simpler to read than it seems. I highly recommend you print out the large version of the Interaction Diagram that you can find here before continuing. It will clarify my explanation of how to use interaction diagrams greatly.
1) The constants:
Before you pick a interaction diagram you have to make sure you have the right one. That upper right hand corner of every diagram has a section that we'll call the constants for now. This section is how you differentiate one column from another. The following will usually be defined in the constants:
f'c = the strength of the concrete (e.g. 4 ksi)
fy = the yield strength of the steel in the column (e.g. 60 ksi)
γ (gamma) = the ratio between the center-point of the steel reinforcement and the outside dimension of the column. For example, if you have #8 bars with a edge distance of 2" on a 20" x 20" concrete column then γ would be: [20" - 2*2" (cover) - 1" (dia. of bar)] / 20" = 15/20 = 0.75
Lastly, it is important to differentiate between square tied columns and circular spiral columns in this section (you'll be able to tell the difference by the shape of the column in the upper right hand corner). In the example i've attached the column is a square tied column.
Note: If any of the variables fall between constants then you can conservatively take the lower of the two interaction diagrams for your numbers.
2) The horizontal and vertical axis:
As you can see the two equations below make up the horizontal and vertical axis' of the interaction diagrams.
Kn & Rn
Pu = Factored axial load on the column (lbs or kips)
ϕ = Strength Reduction Factor
f'c = Strength of the concrete (psi or ksi)
Ag = The gross area of the concrete column (in2)
e = Pue will create the moment acting on the column (in kip-in or lb-in)
h = the dimension of the column perpendicular to the axis of bending (in)
These two variables represent an Axial Force variable and a Moment variable (notice how one contains e/h and one does not). They are your starting point for figuring out where your preliminary point on the interaction curve is. See Section 5 below to see some hints for getting started.
Note: These variables are unitless so make certain that all of the units in both of the above equations cancel out.
3) The Pg and e/h lines:
Two additional pieces of information on these graphs are the pg and e/h lines. These lines provide boundary conditions once you figure out your vertical and horizontal axis variables. As you can see, pg represents the amount of steel in the column. The higher the moment you have, the more steel you will need. Steel will also greatly increase the axial capacity of a concrete column.
The e/h line is a shortcut to not take the moment acting on the column into account. It is not necessary to solve for both the e/h line and the horizontal axis (notice how they both have e/h, which is a variable that takes the moment acting on a concrete column into account. Since I always like solving for both axis' I usually ignore this step.
Note: An e/h of 1.0 represents a much larger moment than an e/h of 0.10
4) Why is ε on there?
In order to plot a point on the graph, you have to assume a phi (ϕ). The ε t = 0.002 (compression controlled section) and et = 0.005 (tension controlled section) are on the diagram to be used as guides when assuming a value for your strength reduction factor. At this point you may have to revisit your horizontal and vertical axis variables and update your location on your interaction diagram (if you originally assumed compression controlled and it ends up being somewhere between the two).
5) Any other hints for getting started?
To get started assume a ϕ and check back later to make sure your assumptions were correct.
A good place to be is to have pg fall between 0.02 and 0.025
If the point is outside the last curve (pg = 0.08) then the section size is to small. The 8% steel content keeps the column from getting to congested.
If your moment is inside the fist curve (pg = 0.01) then your section size is to big.
Transverse reinforcement can be found the same way it's found for columns with small eccentricity (see Concrete Tied Columns & Concrete Spiral Columns)
Where can i find them?
Most often these interaction diagrams are found in the Appendices of your Concrete books. Here are a few websites where I have found additional ones:
LOADS TO BE DEFINED IN MODEL
1) DEAD LOAD = DO NOT ASSIGN LOAD IN THAT STATIC LOAD CASE Because THis Static load case is for self weight of structural elements and no load is to be assigned in that Dead Load
2) Finishes Load = either 2 inch thick or 3 inch thick finishes depends upon architectural requirement , if 3 inch thick finishes then
Finishes Load = (3"/12) x 144(density) = 36 psf
3) Sunk Load = Sunk load is provided in Toilets or washrooms or bathrooms , it is also depends upon architectural or plumbing engineer's requirement to provide that much amount of sunk ,
for Example 12 inch sunk is to be provided then
Sunk Load = (12"/12)* 120(density) = 120 psf
4) Live load = For this there are tables in Ubc code 1997 and in Asce 7-05 code
In UBC 1997 See Tables 16-A and 16-B
in ASCE 7-05 see Table 4-1
Asce 7-05 is having Detailed and wide variety of Live loads for Different Occupancy or use
You can refer both COdes at same time for Live Loads
PART 1 OF NADEEM HASSOUN BOOK
PART 2 OF NADEEM HASSOUN BOOK
UNSUPPORTED HEIGHT OF MASONARY AND LOAD BEARING WALLS , SEE BELOW
see below search link to see Limitations of different codes
go to above link and buy it online
CAMBERING OF SLAB OR BEAM
WE RAISE SLAB WHICH IS KNOWN AS CAMBERING , CAMBERING IS DONE IN SUCH A WAY THAT SLAB OR BEAMS ARE RAISED BY SOME INCHED UPWARD SO THAT WHEN LOADS COMES THIS BEAM OR SLAB COMES BACK TO ITS ORIGINAL STATE , BUT THIS CAMBERING IS DONE WHERE THERE ARE LARGE PANEL OF SLABS AND IN THOSE SLABS DEFLECTIONS ARE EXCEDDING ALLOWABLE DEFLECTIONS WHATS WHY WE PROVIDE CAMBER IN SLABS , AND IN BEAMS WE INTRODUCE CAMBER WHEN THERE IS LARGE SPAN BEAMS AND DELFECTIONS ARE EXCEEDING ALLOWABLE DEFLECTIONS AND WE CANNOT INCREASE DEPTH OR CHANGE THE SIZE OF BEAMS
Soil Bearing capacity does not depend on city wise , in one city different areas has different bearing capcities , no general bearing capcity for any city
it depends upon soil condition , for sandy soil means poor soil , take bearing capcity of 0.5 tsf , wherase for rockey area means good soil , you can take 1.5 tsf
for sandy soil go for raft foundation or pile foundation
for rocky area go for isolated footing
Difference between cracked and uncracked section is that , in uncracked we are assuming that there is no cracking occurs on tension side means concrete and steel (reinforcement) are interlocked with each other wherease in reality when concrete cracks tension will be taked by reinforcment in tension side and thats why we have to use cracked section not uncracked sections
QUESTION : "CALCULATING & ASSIGNING MODIFIER VALUES IN ETABS"
Property modifiers in etabs are used to model cracked behaviour of concrete sections. They are only applied to concrete members because of cracking.
Gross moment of inertia is bd^3/12 for a rectangular section, but when you make this member of concrete, it will experience cracking when loaded after some time. This cracking will happen when concrete reaches its tensile capacity which is about 7-10% of its compressive strength. Formula to calculate cracking moments are given in ACI. For example 3000psi will have only 300psi of tensile strength. Actually the reinforcement starts its work when concrete cracks because of tension. After cracking concrete is no longer able to carry tension so steel starts taking the tension.
So now if concrete cracks after 300psi the moment of inertia will be reduced because of cracking. If moment of inertia is reduced, its stiffness is reduced, taking less moment, and its deflection increases because of less stiffness.
This moment which the cracked beam is not taking anymore will be re distributed to other structural members based on their stiffness.
If you read ACI chapter 10, there are many sets of modifiers used for different types of analysis.
Stiffness modification for concrete members are recommended in most of the international codes like, ACI,UBC,IBC, BS and other.
Stiffness modifiers are primarily used to take into account cracking and inelaticaction that has occured along each memebr before yielding. Different members have different stiffness modification for e.g., Beam 0.5Ig, Column 1.0Ig for braced frame (see cl 8.6 ACI-318)
Frames that are free to sway stiffness modifications for Beam 0.35Ig, column 0.7Ig like for other elements (see cl 10.11.1 ACI- 318)
MODELLING RAMPS AND STAIRS IN ETABS
Ramps can be modelled from plan to below plan , means if your ramp is starting from ground to basement then first open ground floor plan then assign slab horizontally then go to Draw then Draw reshape object then click on this horizontal slab then white dots will apear around 4 corners of slab then right click on that point which you have to drop from this ground to basement and window will appear and put in Z-ord box value of Basement floor level and do same thing for second point and open 3d view , ramp will be modelled
same thing applied for stair modelling in etabs , means drop down modelling , means if you have two floors , one is ground and other is first floor then , in between there will be landing level , now if your ground floor is at level 3' and first floor is at 15' then your landing level will be 3 + 15 / 2 * 9 feet , now make reference plane at 9 ft , go to edit then edit reference plane and there in z-ord box put 9 feet , then click ok , now make landing slab area in first floor plan by null lines then select that null lines and move that lines to 9 feet means to get to 9 feet from 15 feet you have to type -6 in Delta z and then click ok , now open reference plane and you will see null lines here now select draw points objects and click on bottom left portion of this null lines in reference plane and here in Plan offset X type width of stair flight slab , if your stair flight slab is 4 feet then type 4 here and point will be made in this plane at4 feet from bottom left of null lines , now select these two points that is bottom left and this point at 4 feet and then replicate that point to that dimension which is your flight stair slab length then click only on that points which will be at supose 8 feet from these points of null lines and move that points to ground floor level means ground floor is at level 3 feet and you have to go from 9 feet to 3 feet means you have to type 6 feet in Delta z box then assign slab from bottom left point and at 4 feet from bottom left point in reference plane to points at 8 feet from these points in ground floor , your stair flight slab will be assigned now and same thing you will do for flight which is coming down from first floor slab to landing level
ACI-5.6 2008 requires that all the tests to be performed on fresh, hardened or old concrete are to be performed by qualified field testing technicians. They should collect and prepare all the specimens for testing and should record temperature and other important information about the fresh concrete.
1. Frequency Of Testing
A strength test is considered as the average of the strengths of at least two 150 by 300 mm cylinders or at least three 100 by 200 mm cylinders made from the same sample of concrete and tested at 28 days or at test age designated for determination of fc’.
As mentioned in the earlier chapters, samples for strength tests of each class of concrete placed each day must be taken not less than all of the following:
a) Once a day
b) Once for each 110 cum of concrete
c) Once for each 460 sqm of surface area for slabs or walls. Only one side of the slab or wall should be considered in calculating the area. This criterion requires more frequent sampling than once for each 110 m3 of concrete placed if the average wall or slab thickness is less than 240 mm.
d) At least five randomly selected samples for a given class of concrete.
e) According to ACI, when total quantity of a given class of concrete is less than 38 m3, strength tests are not required when evidence of satisfactory strength is submitted to and approved by the building official.
2. Acceptance Based On Standard-Cured Specimens
Strength of a new concrete determined by standard-cured specimens is considered satisfactory if both of the following conditions are satisfied:
a) Every arithmetic average of any three consecutive strength tests equals or exceeds fc?
b) No strength test falls below fc? by more than 3.5MPa when fc? is 35 MPa or less; or by more than 0.10 fc? when fc? is more than 35 MPa.
If the above conditions are not satisfied, steps must be taken to increase the average of subsequent strength test results.
3. Acceptance Of Field-Cured Specimens
Field-cured test cylinders should be molded at the same time and from the same samples as laboratory-cured test cylinders. These results are not directly used as acceptance criterion but give idea about the field curing procedure. Procedures for protecting and curing concrete are to be improved when strength of field cured cylinders at test age designated for determination of fc? is less than 85 percent of that of companion laboratory-cured cylinders. The 85 percent limitation need not to be applied if field-cured strength exceeds fc? by more than 3.5 MPa.
4. Investigation Of Low-Strength Test Results
If the strength tests of laboratory-cured cylinders do not satisfy the criterion for acceptance or if tests of field-cured cylinders indicate deficiencies in protection and curing, immediate actions are required to avoid under-strength construction. If it is almost confirmed that the concrete may be of low strength, three cores must be taken for each under-strength test. Cores are tested after 48 hours but not, later than 7 days after coring unless approved by the licensed design professional. The strength of concrete may be considered satisfactory if the average of three cores is equal to at least 85 percent of fc? and if no single core is less than 75 percent of fc?. If these criteria are not satisfied, it is allowed to extract and test additional cores. Cores taken to confirm structural adequacy are usually taken at ages later than those specified for determination of fc?. If the core test also fails and the doubt about the concrete strength still exists, structural strength evaluation / load test may be recommended.
Before the concrete is poured into the formwork, it must be checked by someone who has been trained to inspect formwork. Depending on how big or complicated the pour is, the inspection may just take few minutes or it could take hours. Only when the formwork has been approved, may the pour take place.
Formwork pressures are function of height (including the height from which concrete is dropped into the forms) and are affected by concrete workability, rate of stiffening and rate of placing. One task of the temporary works co-ordinator is to consider such factors as ambient temperatures and concrete composition, when calculating maximum permissible rate of concrete placing.
Exceeding this limit may lead to unacceptable formwork deflections, loss of grout / concrete at joints, or even collapse. The cost of remedial work due to formwork deflection will usually exceed the original cost of doing the job properly.
Below are the checks that should be verified before pouring begins:
Is the formwork erected in accordance with the approved drawings?
Is the formwork restrained against movement in all directions?
Is it correctly aligned and leveled?
Are all the props plum, and at the right spacing?
Are bolts and wedges secure against any possible looseing?
Has the correct number of ties been used? Are they in the right places and properly tightened?
Are all inserts and cast-in fixings in the right position and secure?
Have all stop ends been properly secured?
Have all the joints been sealed to stop grout loss (especially where the formwork is against the kicker)?
Can the formwork be struck without damaging the concrete?
Are the forms clean and free from rubbish such as tie wire cuttings, and odd bits of timber or metal?
Has the release agents been applied, and is it the correct one?
Are all projecting bars straight and correctly positioned?
Is there proper access for placing the concrete and compacting?
Have all the toe-boards and guard rails been provided?
RELEASE AGENTS FOR FORMWORK:
Formwork needs to be treated with a release agent so that it can be removed easily after the concrete has set. Failure to use a release agent can result in the formwork sticking to the concrete, which may lead to damage of the concrete surface when it is prised off.
A single application of release agent is all that is required when forms are then used. Care must be taken to cover all the surface that will come in contact with the surface of concrete. However, if there is an excess of release agent, it may cause staining or retardation of the concrete.
There are different release agents depending on what material is used for the formwork. The three most common release agents for formwork are:
Neat oils with surfactants: used mainly on steel surfaces, but also suitable for timber and plywood.
Mould cream emulsions: good general purpose release agents for use on timber and plywood.
Chemical release agents: recommended for high quality work, applied by spray to all types of form face.