In my case, using the auto rectangular option with a meshing factor of 0.25 effectively maintains a regular mesh pattern across walls and slab elements because their dimensions are divisible by 0.25. However, in scenarios where elements have varying dimensions that do not uniformly divide by a single factor like 0.25, opting for the general meshing option is preferable. This approach provides flexibility to adjust mesh sizes according to specific element sizes and structural requirements, thereby ensuring optimal mesh quality throughout the model.

In older versions of ETABS, using the automatic wall mesh option often resulted in incorrect lumping of masses across story levels. In this case the manual meshing of walls is necessary, where walls are divided into smaller elements manually to ensure accurate structural analysis. However, in the newer version of ETABS, this issue has been successfully resolved. The software now handles automatic wall meshing more effectively, ensuring that masses are correctly distributed and calculated across each story level.

Hello Sir I mentioned at the end of this video that you can use the load combos for checking the Drift limits. In my opinion, gravity loads will not make a big difference in these computations, however it's ok to include them.

@@Eng.tarekyoussef Thank you very much!

For concrete structures, it’s essential to estimate reasonable values for axial and bending stiffnesses that account for cracking, yield, and creep. As referenced in Dr. Powell's book *Modeling for Structural Analysis: Behavior and Basics* (2010), using effective stiffness values is critical for accurate modeling, particularly in capturing second-order effects like P-delta behavior. Adjusting for these factors ensures that the structural analysis reflects realistic performance under loads. For further details on the appropriate stiffness modifiers to use before including and checking P-delta effects, please refer to tutorials number 5 and 12. These resources provide valuable insights into the necessary adjustments for effective modeling.

Hello, If you're using the second technique, which involves shifting the center of mass using the modal load case, you don't need to calculate the Ax factor (this factor amplifies eccentricity), because the effect of shifting the center of mass is already included in the analysis. However, the Ax factor can still provide insight into how much the structure would rotate if the center of mass were shifted. If you find that the Ax factor is notably high, approaching 3, I advice you to modify your structural configuration to mitigate these torsional effects and enhance stability.

@@Eng.tarekyoussef thankyou tarek, and then why did we must change the load case type to nonlinear static? since the approach of RSA method is the linear dynamic analysis method?thankyou

@@anandito6833 we need to define the nonlinear static load case to be able to add a new modal load case. Please note that for RSA method, the type of load case defined is Response spectrum and not nonlinear static.

I forgot to delete this statement. Just use the equivalent lateral forces explained in tutorial 9

@@Eng.tarekyoussef Thank you very much.

Check ASCE 7-10, Commentary Appendix CC for serviceability considerations or check the end of this video "Load combo for checking drifts": kzbin.info/www/bejne/qITGmYCro8uLntEsi=F-ip5p147RvyvO_S

Thank you

More to come!

Glad it was helpful!

In structural design, the stiffness of steel beams and columns is generally not reduced in the same way as it is for reinforced concrete beams and columns. In reinforced concrete design, the stiffness reduction often refers to considerations such as cracking of concrete and the non-linear behavior of reinforcement under load. Steel members are less affected by load-induced cracking or yielding compared to reinforced concrete. Steel beams and columns are designed to resist bending and axial loads primarily through elastic behavior, where the material remains within its elastic range and returns to its original shape once the load is removed. However, in practical design, factors such as local buckling, lateral-torsional buckling, and stability under various loading conditions are critical considerations that may indirectly affect stiffness calculations. These factors are addressed through appropriate design checks and may influence the effective length and moment of inertia used in the analysis, but they are not typically described as a direct reduction in stiffness similar to what is considered in reinforced concrete design.

@@Eng.tarekyoussef thank you for your information👍🏻

IF the base shear from RSA is greater than the base shear from ELF (VRSA>VELF), then you do not need to scale (match) the base shear from RSA.

Thank you! finally here

Thank you

Noted

Your videos are really helpful, Thanks for sharing knowledge, It will be great if you explain it a little bit deeper and not skip even simple steps, thanks again

All types of slabs should be reduced

docs.google.com/spreadsheets/d/18FiLBQWWy7jos9mwz_7gbIcLF6DpP7Wt/edit?usp=drive_link

Thanks a lot! I think you might find this video interesting: kzbin.info/www/bejne/Zoe4ooCtiJl5edEsi=3ICYsUkyqmPIHyP-

شكرا جزيلا على ملاحظتك. يمكنك إبطاء سرعة الفيديو لمتابعة الشرح بشكل أفضل

Sure!

Yes, it’s okay to define earthquake loads for combination using the equivalent static method. This method is widely used for its simplicity and effectiveness, especially for low-rise buildings that are fairly symmetric.

@@Eng.tarekyoussef thank you sir, i see

To accurately model the behavior of the portal frames as bracing elements, you typically release moments at the ends of beams where they connect to columns. This approach acknowledges that the beams are hinged (or nearly hinged) at their ends where they meet the columns (not at the start and end of the columns). The decision to release moments depends on the structural design and the intended behavior of the portal frame system under lateral loads. If the frame is designed assuming hinge behavior at the beam-column connections (for example, for moment redistribution under lateral loads), you release moments. If the design assumes rigid connections to transfer moments and shear without significant rotation, you do not release moments. In summary, you do not necessarily release moments to all beams in all types of portal frame systems. It depends on the type of the beam-column connection (fixed or hinged connection).

I am designing this building for a site in Bangkok, Thailand. The Mapped Long-Period Transition Period, (TL), is not used in the Thai building code, which is why I ignore the formula for "Cs" that includes "TL" However, let me provide a brief explanation: “TL” is the period at which the response of the structure transitions from being controlled by velocity to being controlled by displacement. You can find the values of the long-period transition period (TL) in the ASCE 7-16 standard in Figures 22-14 through 22-17. However, these values are specific to the United States and may not be applicable to other regions, including Thailand. If the fundamental period of the structure "T" ≤ "TL", use Eq. 12.8-3. If the fundamental period of the structure "T" > "TL", use Eq. 12.8-4.

Lebanon

When the difference between the center of mass (CM) and the center of rigidity (CR) exceeds 5%, it can lead to significant torsional effects in the structure during seismic events. Here are some steps you can take to address this issue: 1- Re-evaluate Structural Design: This might involve adjusting the layout of the structural elements. 2- Increase Stiffness: Add or enhance structural elements such as shear walls or bracing to increase the rigidity and reduce the eccentricity. 3- Mass Distribution: Adjust the distribution of mass within the structure to bring the CM closer to the CR. 4- Torsional Analysis: If the techniques in points 1 to 3 do not solve the problem, perform a detailed torsional analysis to understand the impact of the eccentricity and design accordingly. This includes: * Computing the Ax Factor: Check for torsional irregularity and amplify the eccentricity by the Ax factor if needed. * Code Compliance: Ensure all design modifications comply with relevant building codes and standards to ensure a safe design. 5- Nonlinear Analysis: For irregular buildings, nonlinear analysis is recommended as it provides a clearer understanding of the structural behavior under seismic loads.

To calculate the lumped mass matrix, consistent mass matrix, and stiffness matrix for a 3D space frame, you'll need to follow a systematic approach that involves understanding the physical properties of the frame and applying the principles of structural dynamics. Here's an overview that might help: 1. Lumped Mass Matrix Definition: The lumped mass matrix assumes that the mass is concentrated at the nodes. Calculation: - Identify the nodal points of the structure. - Sum the masses (such as dead load, live load, partition wall load, etc.) that are associated with each node. - Construct a diagonal matrix where the diagonal entries represent the lumped masses at each node. 2. Consistent Mass Matrix Definition: The consistent mass matrix distributes the mass over the entire structure, taking into account the shape functions used in the finite element method (FEM). Calculation: - Use the shape functions for the elements to distribute the mass. - Integrate these shape functions over the volume of the elements to construct the mass matrix. - This matrix is typically more complex and requires numerical integration. 3. Stiffness Matrix Definition: The stiffness matrix represents the relationship between the nodal displacements and the forces in the structure. Calculation: - Derive the element stiffness matrix using the material properties (Young’s modulus, Poisson’s ratio) and geometric properties (length, cross-sectional area). - Assemble the global stiffness matrix from the element stiffness matrices using the connectivity of the nodes. Applying Gravitational Loads For the lumped modal mass matrix and consistent mass matrix: - Gravitational loads (such as dead load, live load, partition wall load) are considered when determining the masses to be lumped at the nodes or distributed over the elements. - These loads influence the inertial properties of the structure and should be included in the mass calculations. #Resources • Structural Analysis by R.C. Hibbeler • McGuire, Gallagher, Ziemian, “Matrix Structural Analysis,” 2nd Edition, Wiley. • Ghali, A., Neville, A.M., Structural Analysis - a Unified Classical and Matrix Approach, Second edition, Chapman and Hall, London, 1978. • Sack, R.L., “Matrix Structural Analysis,” PWS-KENT, Boston, 1989. • McCormac, J.C., Nelson, J.K., “Structural Analysis-A Classical and Matrix Approach,” Second Edition, Addison-Wesley, 1996.

You should have "P" as it corresponds to the design vertical loads (gravity loads exist in all floors). In this video I used the load combo of "DL+0.25LL" to get P.

ETABS does not lump the masses correctly to floor level if the mesh option for shear wall is used. This issue is also announced through the CSI website. In reality, the mass of a building is not only concentrated at the floor levels but is distributed throughout the structure. Lumping masses at the center of each floor, which is done by the use of a rigid diaphragm, is an approximation to simplify the analysis. Thus, the mass matrix generated in ETABS will be affected by the way the masses are lumped.

@@Eng.tarekyoussefThanks Tarek. I think this issue solved with Etabs 20. I’m just using etabs as 3rd party reviewer. Back to topic, using the lumped mass or consistent mass is something the designer can decide it but basically if the vertical elements or lateral resisting system is about same or higher than the weight of floor e.g, shear wall systems then lumped mass is not valid means the consistent should be used because the mass is distributed over the height of the structure

You are welcome

In a bearing wall system, the walls primarily carry vertical loads, known as gravity loads. So, when considering modifiers for such walls, it's important to assume an un-cracked section, as cracking can occur due to gravity loads alone, even without considering lateral loads. This ensures that the design adequately accounts for potential cracking under gravity loads.

You are most welcome

Thank you

In practical design, it is challenging to prevent all cracks in a shear wall. Minor cracks are often acceptable and expected due to the nature of concrete and the stresses it undergoes. When cracks exceed acceptable limits, one common approach is to adjust the stiffness modifier of the affected zone. This adjustment helps to account for the reduced stiffness of the cracked section and provides a more accurate representation of the wall's behavior. While these modifiers offer a practical solution, they may not always be entirely accurate, particularly in capturing highly nonlinear behavior. Performance-Based Design (PBD) allows for a detailed understanding of the nonlinear behavior of structural members. This includes evaluating the level of nonlinearity and determining whether the wall is performing safely despite cracking. Linear vs. Nonlinear Analysis: 1- Linear Analysis: In linear analysis, the material is assumed to remain within its elastic range. This assumption limits the ability to accurately assess cracking and nonlinear behavior. For regular buildings, linear analysis is typically sufficient, as it provides a reasonable approximation of the structure's response. However, it may not capture all aspects of cracking and nonlinearity. 2- Nonlinear Analysis: For irregular buildings or those expected to experience significant nonlinear behavior, nonlinear analysis is essential. This type of analysis captures the real response of the structure, including the effects of cracking and stiffness degradation. I hope I answer your question

When designing a building with extreme torsional irregularity and a seismic design category D, it's crucial to account for the torsional effects accurately. Since the Equivalent Lateral Force (ELF) procedure is not suitable due to the complexity and irregularity, the Response Spectrum Analysis (RSA) method could be appropriate, but the NLRHA is the best ! RSA in X & Y Directions: You need to define RSA load case for X and Y directions. RSA in Z Direction (Vertical RSA): In most cases, RSA for the Z direction is not necessary unless specified by your building code or project requirements. Vertical seismic effects are generally less critical than horizontal effects for typical buildings. However, if your specific code or project requirements mandate it, then you must include RSA for the Z direction. Understanding Torsional Effects: The torsional irregularity is primarily due to the asymmetric distribution of mass and stiffness within the building. This causes the building to rotate about its vertical axis (Z-axis) when subjected to lateral loads. Improving Building Response to Torsion: Adjust the location of structural elements such as columns, shear walls, and bracing to reduce torsional irregularity. Aim for a more symmetric distribution of stiffness and mass. Summary: 1- Define RSA for X and Y directions to accurately capture the lateral seismic response. 2-Define RSA for Z direction only if required by your building code or project specifics. 3-Focus on torsional analysis to understand rotational behavior. 4-Adjust structural configuration to minimize torsional effects, ensuring a more uniform distribution of stiffness and mass.

Thank you

kzbin.info/www/bejne/f6SVp6V-gcpmepIsi=mKcNeRqQiG_a8sbK

@@Eng.tarekyoussef yes I am aware of the two method the issue is if you want to check the torsional irregularity in response spectrum you simply cannot

Hope you enjoy it