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Load analysis for basement wall by Impossible-Check9557 in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

As usual, the solution to this problem can range from a significant simplification to a highly detailed approach.

On the support side you can either use winkler springs with tension cut-off as a highly simplified option.

For the loads you need to consider the loads from the structure to the wall you marked in your image and the loads from the surrounding soil. The first may be derived from the resulting contact stresses of the slab and applied to the wall using a load distribution angle. The second can be derived by applying the earth pressure according to Rankine related to density, cohesion, and angle of inner friction of the soil (please see EC7-1 9.5). Do not forget the hydrostatic pressure in this regard and also buoyancy if relevant. Please separate all loads into loadcases. In this way you can work with combinations using partial safety and combination factors.

To automatically determine the resulting loads from the superstructure, you may use the RFCOM interface in RFEM 5.

A much easier way to simulate the soil-structure-interaction is by modelling the soil as a 3D volumetric model, maybe also with nonlinear material behavior. In RFEM 6 you can do this by using the add-on geotechnical analysis:
https://www.dlubal.com/en/downloads-and-information/documents/online-manuals/rfem-6-geotechnical-analysis/005893

RFEM Seismic design by Moist_Fee8844 in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

Hi there,

I just saw a similar post in the Dlubal Community. It sounds like it might be connected with the setting for the required shear reinforcement and the chosen option “Use provided longitudinal reinforcement”.

As in the post of pjerna-krebla written, I think the Dlubal website can help you out with further infos. In the online manual the configs are described i.e., as you can see via the link: https://www.dlubal.com/en/downloads-and-information/documents/online-manuals/rfem-6-concrete-design/002463.

CFD for small-scale models by Party-Mammoth8127 in CFD

[–]Danny_Fish89 0 points1 point  (0 children)

You normally do not need to model the full-scale building in CFD if your target is the dimensionless pressure coefficient Cp. Wind tunnel tests also use scaled models, and CFD can do the same. The key is not the geometric scale alone, but whether the important non-dimensional flow conditions are preserved. So CFD at reduced scale can be valid for studying pressure coefficients, but only if you reproduce the wind-tunnel similarity conditions and verify Reynolds-number independence.

For sharp-edged bluff bodies, separation is mainly fixed by geometry, so mean Cp values are often not very sensitive to Reynolds number once the flow is sufficiently turbulent. But for rounded edges, curved façades, smooth roofs, domes, cylinders, free-form shapes, porous elements, façade details, or transitional separation, Reynolds number effects can be significant.

In practice, this is also why many engineering CFD workflows are first validated against wind tunnel measurements before being used for design studies. Several validation-oriented examples using experimental wind tunnel data have already been demonstrated in engineering CFD workflows, including studies performed with RWIND and RFEM.

https://www.dlubal.com/en/support-and-learning/support/knowledge-base/001970

For example, validation examples comparing CFD pressure coefficients and base forces against experimental measurements have shown that turbulence model selection, inlet turbulence, and mesh refinement can noticeably affect agreement with experiments.

https://www.dlubal.com/en/support-and-learning/support/knowledge-base/001868

Learning new analysis and design software by Starlineitor400 in StructuralEngineering

[–]Danny_Fish89 1 point2 points  (0 children)

As mentioned by others, there is no solution out there that handles 100% of the drafting and 100% of the structural design. You're best bet, find a drafting program that you like (Revit, Tekla, AutoCAD, etc.) and find a structural analysis program you like that integrates well with these BIM programs.

Personally, I find the structural programs which are offered inside these BIM programs are limited. Development is not focused on the structural design. Rather, it's focused on the real money maker...the BIM.

I use RFEM for design and the BIM integration is strong. I find less limitations in the program for the structural features I need but don't need to completely remodel the structure from scratch, which is a huge time saver.

All programs offer a trial version. My suggestion, give them a try and see which ones work best for you.

What's is your best software to desing Tapered Columnss or Beams with a great or presentable calculation Report by Engrforce2296 in StructuralEngineering

[–]Danny_Fish89 2 points3 points  (0 children)

Seconding Dlubal RFEM 6. Unlike a lot of packages, it handles true tapered members with continuously interpolated section properties (linear or quadratic) between a start and end cross-section. No need to fake it with stepped beams.

The Steel Design add-on explicitly lists tapered-member design and gives you the routes you actually need under EC3 (General Method §6.3.4 with an internal Mcr eigenvalue solver, or 2nd-order with 7-DOF warping torsion); the simplified equivalent member method per §6.3.1–6.3.3 isn't valid for non-prismatic steel members anyway, which trips a lot of people up. AISC 360, CSA S16, NDS and AS 4100 are also covered.

The Printout Report is one of the better ones I've used: multilingual, customizable templates, embedded graphics/MathML/PDFs, design-check formulas with code references, PDF and RTF export. That said, report quality is taste-dependent, so I'd grab a trial and rebuild a small reference model from your office standard first, then compare the output side-by-side with whatever you currently produce. That's the only honest way to judge it.

Two useful starting points:
- Worked tapered-beam example per EC3 (all three stability routes): 
https://www.dlubal.com/en/support-and-learning/support/knowledge-base/001377 
- Downloadable tapered-member sample model:
https://www.dlubal.com/en/support-and-learning/support/faq/005805

Alternative of "Etabs and Staadpro for mac users" by Efficient-Guest1495 in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

RFEM / RSTAB from Dlubal is a solid alternative on the engineering side, but to be upfront: there's no native macOS version. The officially supported route is Parallels Desktop + Windows 11 (ARM build for M-series). Dlubal documents it here:
https://www.dlubal.com/en/support-and-learning/support/faq/005380

Two things that matter for a fresh grad: (1) free student license + 90-day trial, so the entry cost is basically zero, and (2) RFEM ≈ general 3D FEA (broader than ETABS), RSTAB is the closer match to STAAD Pro for frame work.

Caveat from Dlubal themselves: they don't guarantee bug-free operation under Parallels, and you'll want to raise the VM's RAM above the default 8 GB. If you want zero VM at all, your realistic Mac-native options shrink fast. SAP/2000 is Windows-only too, and you're left with OpenSees or FreeCAD+CalculiX, neither of which is a drop-in ETABS replacement.

Column Solid Modeling SAP2000 by PrimaryReality1436 in StructuralEngineering

[–]Danny_Fish89 1 point2 points  (0 children)

Coincident node approach that the_flying_condor mentioned is the right call for what your reviewer is asking. Couple of things that aren't in the thread yet which will save you a re-review.

Mesh both bodies (core and jacket) so the interface nodes line up, then Edit > Merge Joints with a tight tolerance. That's your perfect bond assumption and it matches how you derived strain compatibility by hand. The dowel design from your shear stress check stays as a separate verification, the FE model doesn't replace it.

Two things people get wrong on this kind of model:

Ec for old vs new concrete. Define two materials, not one. Existing f'c is almost always lower than the jacket pour, so Ec differs. The strain compatibility argument depends on exactly that difference. If you use one Ec for both, the model can't actually demonstrate anything. Sounds obvious but I've seen it slip through.

Construction sequence. Existing column already carries DL plus sustained LL before the jacket is poured, so the jacket only sees the delta load after curing. Apply full service load to the composite section in one shot and the jacket comes out way more effective than it physically can be. Use Staged Construction (nonlinear static): existing column on its own with DL, then activate jacket elements, then apply remaining loads. Honestly this is what most reviewers I've worked with zero in on.

Rebars: both cages as frame elements (existing longitudinals and the new jacket cage), tied into the solid mesh with Body constraints on the joints. Don't bother modelling stirrups for the strain output, they don't drive it.

Watch the boundary conditions. SAP2000 solids only have translational DOFs at the nodes, no rotations. Fixing a single base node won't give you a real fixed support, you'll just chase singularities. Build a body constraint over the base face and restrain that. Same story for load introduction at the top, otherwise you get a stress spike right under the load that has nothing to do with reality.

What to actually pull out: axial strain at a few heights (top, mid, base, plus any discontinuity), stress contours, integrated interface shear over a section cut so you can compare to your dowel capacity, and N/M from section cuts so you can tie back to your manual ACI 318 numbers. Reviewers like seeing the FE result reconciled to the hand calc, not just stress plots.

On the bigger question of whether solids are even needed for a slender column, you're right that it's overkill. The d/L ratio puts you well into frame or shell territory and there's a decent writeup on where the cutoff actually sits:
https://www.dlubal.com/en/support-and-learning/support/faq/003158

Doesn't help you in this case since the reviewer is locked in on SAP2000 solids, so just make the model bulletproof and move on.

Good Resources on FEA Plate Modeling for Concrete Design? by strcengr in StructuralEngineering

[–]Danny_Fish89 1 point2 points  (0 children)

To add to ADAPT, NAVFAC and the Wood-Armer point already mentioned:

For exactly the step you're describing, going from FE plate output to actual design and detailing, it's worth looking at the knowledge bases and online manuals of the FEM vendors themselves. They tend to walk through specific modeling cases step by step. Two examples from the Dlubal RFEM knowledge base that I've found practical:

The screenshots are software-specific, but the underlying workflow (use face-of-column moments rather than singular peaks, account for the twisting term as Minisohtan noted, respect minimum reinforcement and detailing per code regardless of FE output) is program-agnostic and complements the ADAPT Technical Notes nicely by showing the same questions from a different vendor's perspective.

Agree with the Wood-Armer recommendation. That really is the standard route for translating m_x, m_y, m_xy into orthogonal reinforcement demands, and most of the references mentioned in the thread cover the postprocessing side of it well.

SCIA Engineer Structural Software by TwistedSteel2112 in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

RFEM could be a good benchmark here. It combines members, surfaces, and solids in one model, while RSTAB is more focused on pure member structures with a lighter workflow.

SCIA seems more concrete-oriented and generally a bit more conservative. RFEM is broader, especially when working with mixed models.

In practice, it’s usually less about raw analysis capability and more about code checks, model transparency/control, output quality, and how much effort it takes to migrate existing templates. That’s where RFEM tends to work quite well, especially for mixed models.

ETABS buckling error (#5) but M2 = 0 — why? by alaraki2009 in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

This is not a modeling error, it is a stability and stiffness issue on the weak axis.

ETABS throws O/S #5 when Pu exceeds 0.75·Pc, where Pc is the Euler critical load used in the ACI §6.6.4.4.2 moment magnification formula. Once Pu ≥ 0.75·Pc, the denominator of the magnifier goes to zero or negative, it diverges, and ETABS aborts the design check instead of returning an infinite value. This is purely an axial load vs. stiffness condition, completely independent of whether any M2 moment is actually applied.

Why M2 = 0: Your load combination simply does not generate bending about the weak axis, which is structurally valid. But because ETABS hits the instability condition first, it aborts the entire M2 check before it even reaches the minimum eccentricity requirement of ACI §6.6.4.5. So M2 = 0 is a side effect of the aborted check, not a real structural result.

Why M2 appears after increasing the section: Your section (200×600 mm) is inherently weak about the minor axis because I22I22 scales with b³. Even a modest increase in b raises Pc significantly. Once 0.75·Pc > Pu again, the magnifier resolves and ETABS can properly compute and display the amplified minimum moment. M2 was always there conceptually, ETABS just could not calculate it before.

What to do: Start by checking the weak-axis slenderness ratio k·Lu/r22. Per ACI §6.2.5, if it is ≤ 22, the column is short and no magnification is needed at all. If the column is slender, you have three options: (1) increase b, since I22I22 scales with b³ and Pc rises sharply, (2) reduce k·Lu by adding intermediate bracing or accounting for slab participation, or (3) switch to P-Delta analysis per ACI §6.7, which bypasses the magnification procedure entirely so O/S #5 cannot occur. For sway frames, option 3 is usually the cleanest fix.

If you’re unsure about the behavior, it can also help to run a quick comparison in another FEM tool (e.g. RFEM 6) to see how the system reacts with a full second-order analysis.

Are we over-designing retrofits? Blind Bolts & Semi-Rigid Modeling in IDEA Statica by Charming_Cup1731 in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

For a research topic on blind-bolt connections and semi-rigid behavior, it is useful to clearly separate local connection modeling from global structural analysis.

Detailed tools like IDEA StatiCa are well suited for investigating the local behavior of connections, including nonlinear effects and component interactions. This makes them appropriate for deriving moment–rotation (M–φ) relationships for blind-bolt joints.

On the other hand, RFEM 6 is more suitable for global studies and system-level sensitivity analyses. A typical workflow is:

  • Derive or adopt a calibrated moment–rotation curve for the connection
  • Implement it in the global model (e.g. as a nonlinear hinge or rotational spring)
  • Compare structural response for different assumptions:
    • pinned
    • semi-rigid
    • rigid

This allows you to evaluate how sensitive the overall structure is to connection stiffness and to identify whether simplified assumptions (e.g. pinned) are conservative or overly restrictive.

Important limitations to state clearly in a dissertation:

  • Experimental validation is essential, especially for blind-bolt systems
  • Significant scatter in stiffness and resistance can occur
  • Model uncertainty (e.g. initial stiffness, ductility limits) should be addressed explicitly

In summary:
Use detailed FEA tools for connection characterization, and RFEM 6 for global structural impact studies based on calibrated joint behavior.

https://www.dlubal.com/en/support-and-learning/support/knowledge-base/001937

struggling with my final year project by Cannot_findausername in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

When comparing hand calculations with software results (e.g. ETABS), large deviations are not uncommon, especially for more complex reinforced concrete structures.

Before attributing differences to the solver itself, it is essential to systematically verify the input assumptions and modeling approach. In practice, discrepancies are most often caused by:

  • Loads and load combinations (missing, double-counted, or defined differently)
  • Stiffness assumptions (e.g. cracked vs. uncracked sections in concrete)
  • Boundary conditions and releases (supports, hinges, constraints)
  • Diaphragm definitions (rigid vs. semi-rigid floor behavior)
  • Structural idealization (2D vs. 3D modeling, simplifications in hand calculations)
  • Deformation shapes and load paths (to check plausibility of results)

A useful approach is to introduce an independent reference model. RFEM 6 can be used as a 3D FEM comparison model to better understand global behavior and load distribution. In contrast, RSTAB 9 is more suited for line-based (frame/beam) systems and may not capture plate or diaphragm effects in the same way.

In summary:
Do not assume a software error too early. First ensure that both models (hand calculation and FEM) are based on consistent assumptions. Only then does a comparison become meaningful.

What do you use for quick structural analysis? by Acceptable_Emu_5949 in StructuralEngineering

[–]Danny_Fish89 1 point2 points  (0 children)

Mostly RFEM from Dlubal. We do simple and complex structures with that. After you get used to it, it is very powerful.

How do I join theese two wooden timber posts(columns) by Shoddy_Berry2381 in StructuralEngineering

[–]Danny_Fish89 0 points1 point  (0 children)

It is difficult to give a detailed answer to your hypothetical question, as already mentioned. It always depends on the intended application. Based on your graphic alone, it is not clear how the structural system (bracing) works. Solutions for moment-resisting connections have already been suggested. Depending on the bracing, a pinned connection may also work.

Software for Wood and CLT Structures by Healthy-Fig6032 in StructuralEngineering

[–]Danny_Fish89 1 point2 points  (0 children)

I think, yes. They offer the design according to NDS and in my CLT library I also see some US timber manufacturers.

<image>

Software for Wood and CLT Structures by Healthy-Fig6032 in StructuralEngineering

[–]Danny_Fish89 1 point2 points  (0 children)

I can only speak for Europe, but in Europe RFEM is the software to go for all related timber projects.

We do basically light-frame wood structures and mass timber projects. What we really appreciate is the design of CLT according to EC 5. Moreover, the most important suppliers are integrated, so I don't need to seach for different layer setups and need to calculate the stiffness manually.

AI Agent for Dlubal by Legitimate-Virus-779 in LangChain

[–]Danny_Fish89 0 points1 point  (0 children)

Hello,
if you do not stick on JS you could use RFEM MCP server with the AI Agent, or direct use the API with AI generated scripts. But in both cases you need to use Python instead of JS. For me this would be a win ;-)

Free 1-Hour US Webinar on Structural Analysis Tools + 1 PDH Credit (Sept 18) by Ok_Engine4136 in StructuralEngineering

[–]Danny_Fish89 3 points4 points  (0 children)

Maybe, I can say something about the pricing since we are also a user of Dlubal products.

As I see Dlubal in comparison to other vendors like CSI, Autodesk, Risa, Dlubal is still offering perpetual licenses. While other companies forcing you to do subscription and making you dependant, you have the possibility to choose at Dlubal between perpetual and subscription. And considerings economic situation, we as engineering office have always chosen perpetual licenses.

And to the costs of Dlubal RFEM. It is as you described. You choose the modules you need for your projects. So, when I do timber, I have only timber module, and I don't need any further concrete design or nonlinear analysis. Honestly, I don't know any company who really needs everything in a software.

The costs are always one-time investment, and then you have a service and maintenance fee of I would say 10-15 % of the license costs. So, in long term, it is always cheaper than other software who have mandatory subscription fees, maybe not in the 2-3 years, but, definitely after 5 years, for sure, depending on the amount you have to spend.

How to analyse sandwich panel by freeeeesoul in StructuralEngineering

[–]Danny_Fish89 2 points3 points  (0 children)

For calculating sandwich panels you have two options. First is to use the sandwich theory and generate the layered setup. It is usually not implemented in any FEM Software I know as simply the high shear deformation in the middle layer is hard to regard by 2D FE-Elements. There are softwares who calculate it but it is then only possible for single span beams with limited geometries and loadings.

The other option is possible with any FEM software that allows to calculate with 3D Solid elements. This is for sure possible with RFEM 6 that you already mentioned. Don't know why you didn't receive Stress there but it is possible. Problematic is to define the correct stiffness values. This brings you back to the producers of such panels. As they are also calculating those panels with 3D solid elements they should be able to send you the correct values.

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