Previous Questions
Quesion # 55
Question by RKALC Member:
Hi Admin,
Please explain below total area both faces is in Ast (mm2/m) or length of left strut for rebars?
It mentions total both faces – please confirm for each faces, it will be divided by half Ast?
Below is sample cals for Wall STM.
Is below Reo Ast in mm2 total bottom Area of rebar in both ways?
Reply by RKALC Admin:
Hi ,
In all cases, the bursting reinforcement in the X direction, for example, should be divided by 2 to distribute it between two faces. The resulting number should then be divided by the wall height, and that number will be the reo needed in square millimetres per metre of height.
For example, if the default wall height is 3 metres and the total bursting reo is 3000, you need 1500 sq. mm per face. Divide this by 3, and you will get 150 sq. mm per metre of height. However, if you provide N12-200, you will be providing 565 sq. mm,... Read MoreReply by RKALC Admin:
Follow up by the user:
Does the application allow for 1 support or minimum 2 supports are required - this is for a case that pile is eccentric (moved in perpendicular direction of capping beam due to construction > tolerance of 75mm)?, and there is additional shear due to torsion.
What if there are tension reversal forces on pile - I could not do for uplift loads?
... Read MoreReply by RKALC Admin:
Further clarification by RKALC:
Hi,
The application requires 2 supports. You may look at the corbel calculator, that one could help on your case.
More generally if you have (equilibrium) torsion on capping beam due a pile moving out of the capping beam line, I assume load comes from columns above capping beam, you can simply draw the torsion diagram of the beam (just like shear diagram) and reinforce it with closed ties + longitudinal bars. See RC beam calculator for working beam reo.
The decision that the torsion can't be taken by any element but the capping beam needs some judgement.
I am... Read MoreReply by RKALC Admin:
further question by the user:
Hi,
I carried out an example from text book - the STM application gives different output. Please verify.
... Read MoreReply by RKALC Admin:
Further clarification by RKALC
I have had a look at this previously, no the calculations they are doing for the strut length or lb is incorrect, also the tie force is incorrect if you work the truss depth which is 1552 mm corresponding to an angle of 32.6.
it also adopts the 2009 code (fi factor)
best example found is the Lonnie Oack book.
look at the attachment for the input that works with geometry assumptions they made. you need to minus the covers to get the wall and node dimensions right
... Read MoreReply by RKALC Admin:
further quetstion by the user
Why changed the width of applied load to 875mm instead column is 600x600 for this example?
In the example you have shown in guide online has 420mm width of strut? why 1000mm width of pile cap is not used?
further clarification by RKALC:
the width of applied load is not changed, remained as in the example you mentioned. at 875 mm.
With regards to the column width of 600, this is a question to the example writer. He might have reduced the width of the node to claim development length past the node. In real life the width of... Read MoreReply by RKALC Admin:
final comment by the user:
Thanks you for in depth clarification.
Really appreciated your assistance. This was interesting as NZS and AS also specifies to do STM rather than rational simplied formular method of designing RC elements. STM is now mandatory as well as FEM.
... Read More
Quesion # 47
Question
What is the significance of P-Delta analysis in short, and tall buildings?
Reply by RKALC Admin:
P-Δ effects play significant role in any building or structure,
We usually undertake P-Δ analysis in ETABS using either an iterative or non-iterative approach. The first method involves including the gravity component of the lateral load combination that results in maximum lateral sway. The second method is non-iterative, where ETABS performs the second-order analysis automatically.
For very tall buildings with a slenderness ratio greater than 5, P-Δ effects can contribute an additional sway of 5-15%, particularly if the building is not very stiff or if the mass is not well distributed (for example, when the building sets back). However, P-Δ effects... Read More
Quesion # 46
Sample Question
What is the universal deflection formulae for beams?
Reply by RKALC Admin:
1- For Pin-Pin Δ = M × L² / (10 × EI) - Reduce I to 0.25I for long term effects in concrete beams
2- For Pin-Fix Δ = M × L² / (13 × EI) - Reduce I as above
3- For Fix-Fix Δ = M × L² / (16 × EI) - Reduce I as above... Read More
Quesion # 45
Sample Question
How do we estimate moments applied onto transfer slabs without modeling (approximate analysis)?
Reply by RKALC Admin:
The issue can be resolved as follows:
1- Calculate the point load (P, the transfer load) from the upper levels using the tributary area method (you can use the TribKALC online software).
2 - Assume your transfer slab spans a 6x7 column grid, with end spans on each side (i.e., fixed-pin support conditions).
3- The moment in the long direction would be:
M = P × Long Span / 6 / (0.65 × Short Span)
Note that the "6" in the denominator accounts for the fixed-pin support condition. If you have pin-pin supports, you would divide by 4 instead.
This gives the moment per unit width... Read More
Quesion # 44
Sample Question
How can we rapidly determine the appropriate dimensions for concrete columns based on their section size, MPa rating, and slenderness, without the need to draw interaction diagrams or calculate moment magnifiers to account for buckling?
Reply by RKALC Admin:
Essentially look after 3 values:
1-Squash Load = Is approximately 0.55Ac*fc
2- Pure bending Point = Calculated based on the golden ratio M/BD² (anywhere between 1.5 and 2.5) (about weak column axis)
Or by establishing Mu=0.7*d*fy*As
3- Balanced point = Roughly 1.3 of pure bending capacity
And some 0.25 of the squash load
Slenderness effects appear when the Height to column width ratio is above 10 for unbraced structures, and 12 for braced, so when the column stockey, estimated section area would be within the 0.8 of squash load (say 0.45F'c*Area)
if column is slender, then take 0.3 to 0.4 of squash load
Watch this... Read More
Quesion # 43
Sample Question
How do we determine section modifiers in ETABS for walls (piers and coupling beams), columns, and slabs?
Reply by RKALC Admin:
I have tweaked the numbers to align with Australian Standards.
Assuming beams and columns are modelled as frames, the stiffness modifier table is as follows:
AS3600 ETABS
Beams.......................................0.40Ig I22 = I33 = 0.35 (would use 0.40 for link beams per Australian Standards)
Columns....................................0.80Ig I22 = I33 = 0.70 (would keep columns at 1)
Walls-Uncracked.......................0.80Ig modelled as shell – f11, f22 = 0.70 (would use 0.80 for wall piers per Australian Standards)
Walls-Cracked...........................0.40Ig (would use 0.40 for wall piers per Australian Standards)
NOTE:
Walls are generally not designed for out-of-plane bending to avoid excessive longitudinal reinforcement. In this case, use a small modifier, say (0.25), for m11, m22, and... Read More
Quesion # 53
Question by MG (LinkedIn)
"I had a question in regards to your Bearing Theory for Column Transitions.
In regards to A1 and A2, How do you calculate A2 as AS3600 notes that A1 and A2 should be geometrically similar yet from your analogy it doesn't appear they are?
Reply by RKALC Admin:
The A1/A2 analogy originates from ACI . This analogy is essentially used to disperse stress from a smaller area (A1) to a larger area (A2), as the surrounding concrete confines. The stress limit on A1 can be increased by the factor (A2/A1)^0.5, but not beyond a factor of 2, or ultimately the upper bound of factor*fc, as this is the maximum crushing or squashing stress concrete can withstand.
ACI does not specify a depth for the dispersion prism or frustum, except in cases where the underlying area is limited, such as a column near an edge. In such cases, the dispersion... Read More
Quesion # 42
Sample Question
What are the parameters for long term deflection in CSI Safe according to AS3600-2018? I am referring to non-linear analysis with creep and shrinkage allowance, and some NL load combinations.
moreoever how does safe compare to Ram Concept in relation to this matter?
Kind regards
Reply by RKALC Admin:
Sample Answer to the Sample Quesion:
If the question pertains solely to the software application, the following steps should be taken:
1- Define the concrete materials accurately by navigating to Define > Materials. Provide concrete properties to be assigned to slab sections, such as the Modulus of Elasticity in accordance with table 3.1.2 under item 3.1.2 of the AS3600-2018. Most importantly, feed the software with the modulus of rupture (concrete tension capacity under 3.1.1.3), which is 0.36*f’c^0.5. I always reduce this number by 30%. If you keep the default program calculations, the modulus of rupture will be calculated to a different standard... Read More
Quesion # 48
Question
What is soil-structue interaction in tall buildings?
Quesion # 49
What is the appopriate over-strength factor to be used for the design of wall piers, then coupling beams according to the Australian Standard AS3600-2018
Quesion # 50
When do we need to calculate cross wind moments in buildings?
Quesion # 51
what are the APPARENT PRESSURE DIAGRAMS for anchored shoring walls?
Quesion # 52
what is the difference between COULOMB and RANKINE theories in lateral pressure onto retaining walls?