Fatima Khalid

Thank you EngrUzair and Baz

Anyone can explain what is smeared crack models? Fixed or rotating models? I have searched on google but I couldn't understand what exactly they mean. If any one can explain in simple way or refer any book which can help me understand the cracking models and their behavior. Thank you

Model is stable. But thank you for highlighting an important issue, I will surely look into this matter. If I get any information regarding it, I will inform you.

Not really, I am modelling concrete beam as a 3D solid element and making reinforcement as a line element. I think it would be quite tough if i will make reinforcement as a 3D element. I didn't give any boundary condition to the reinforcement. Do I have to give any boundary condition to the edge of reinforcement? I am assuming reinforcement is embedded in concrete so there will be no bond slip effect.

Thank you Reactions and deflections matches. I am modelling the reinforced concrete beam. I was using the von mises model for reinforcement. So when increasing the load the stresses in reinforcement reaches yield strength and further increasing load cause no effect on stress. It become constant as it is ideal plastic model. But the same does not happens for concrete. I put the 28 days compressive and tensile strength. And after nonlinear analysis, Concrete shows elastic behavior. It does not make the stress constant in tensile region. I found that for finite element modelling, I have to use the material models to define the crack patterns in concrete. there are some plasticity models i.e tresca,von mises, mohr coulomb, drucker prager, rankine principle. and for cracking, the models are smeared cracking and total strain crack models. I am confused that should I use plasticity model or the cracking model to model the concrete non linear behavior. Do you have any idea when do we use plasticity models and cracking models. For steel, I always use plasticity models.

yes, my beam span/depth ratio is 10... so does it means that it will consider shear deformations... ??? Should I make the beam span/ depth ratio smaller than 2??

well, I don't know whether it works or not.. It is reinforced beam and stresses are not matching with the manual values. But yes, for roller i have to uncheck the horizontal reactions. Anyway, Thanks for the help

I have to model a simply supported beam using finite element modelling. What support conditions should I put for roller and hinge? Attached is the picture of software options for constraints and also the beam which I modeled as Simply Supported *If I make a cantilever beam with fixed support, Solid beam gives correct result of stresses. But I think that I am doing something wrong when making 3D solid simply supported beam.

Yes they both are carrying different load therefore they have different stresses. Thank you

I got the solution. For any other who want the solution so they can see this link http://www.ce.memphis.edu/6136/PDF_notes/i1__axial.pdf Someone told me to calculate the stiffness using the concept of spring in series or spring in parallel. and then use this stiffness to find the deflection. This deflection will be the same for concrete and steel. Anyone have any idea what is the procedure for this approach?

I have a column whose length is 1m and cross section is 100x100mm. It has 2 reinforced bars of 16mm dia. I want to calculate the stress in reinforcement and concrete at a specific load i.e 10KN. For stress in concrete, i calculated deflection using PL/AE and then calculated strain i.e deflection/original length (A=Area of concrete and E=Modulus of Elasticity of Concrete) For stress in steel, I did the same but using area of steel and modulus of elasticity of steel But for axial loads, strain in the reinforcing bar must be the same as strain in concrete. And by using above method, I am obviously getting different strain results. So what method or formula should I use to calculate strain in concrete and reinforced bar? I am doing this so I can verify the manual and software result.

You can calculate centre of rigidity by calculating stiffness of each column i.e 6EI/L^2 and multiplying by the distance from the origin. Adding all these values and then divide by sum of all column stiffness. Do the same for both directions. Remember to see the column orientation while calculating inertia.

Try Response2000 or ReCCSA... they are free and can be downloaded from internert. ReCCSA is better

Thank you sir, do you have any link to download the soft copy of Robert D. Cook?

http://docs.csiamerica.com/help-files/etabs/Menus/Assign/Frame/Insertion_Point.htm There is a set of pre-defined locations within the section, called cardinal points You can further offset the cardinal point from the joint by specifying joint offsets. The joint offsets together with the cardinal point make up the insertion point assignment. The total offset from the joint to the centroid is given as the sum of the joint offset plus the distance from the cardinal point to the centroid Hope it helps..

What is the difference between stress at integration point and stress at nodes? Which one is better to use? Thankyou

Thankyou

I have read the description in previous forums about shell, membrane and plate in Etabs. (Thanks for the great info) When using finite element software, to make a beam, we can use line element(1D so 1D stresses), plate element(2D so give 2D stresses) or solid element(3D give 3D stresses). when analyzing the beam using all these 3 elements, the result of deflection is different. why? how do we know whether to use 3D solid element for beam or 1D line element for beam? Manual results matches when I use line elements as a beam.

Khair Mubarak

Thankyou

How to assign the displacement in the centre of 3D solid beam? If i have to put 2mm displacement and at centre i have 25nodes so should i put at centre node the displacement value or should i put the displacement value on all nodes?? e.g for load of 25N, I divide it to 25 nodes and assign each node 1N load. Should I do the same for displacement? *Attach is the picture of beam

i am modelling steel. i have used the von mises yield criterion. i have taken these values from an example on internet. 220N/mm^2 is the yield strength and i am using this value in equation 8fyz/L i have verified the displacement manually using the formula displacement= PL^3/(192EI) = 306000*1000^3/(192*206842*(100^4)/12)=0.926mm (same as software) and stress calculated from flexure formula is 230N/mm2 which is also matching the software result Thanks

No i am not using any load factors. I have applied displacement based loading.

I have calculated the yield load by using stress=My/I=293.3KN where stress is 220N/mm2 and for load at which plastic hinge will be created is calculated using 8fyz/L=440KN i have used perfectly plastic model. Following are the result showing load v/s displacement i dont understand why the load showing straight line at 306KN.. why not it showing results till 440KN??

For nonlinear analysis it gives the error: "too small step in Automa. Check your model and decrease minsiz if it is correct" i have change the minimum size step from 0.001 to 0.000001. but there is no change. It still shows the same error and result is generated for the load i.e 306KN. But the applied load is 500KN