MODELLING OF BRICK MASONRY WALL IN ETABS ,STRUT ANALOGY, (PART -2)

Summary

In this detailed tutorial, Muhammad Ubad walks viewers through the process of modeling unreinforced brick masonry infill in ETABS, a widely used structural analysis software. The video covers key parameters like concrete strength, column and beam sizes, and masonry prism strength, all of which are essential for creating accurate structural models. After defining the material properties and dimensions, the video demonstrates how to set up a 2D frame, apply supports, and model the masonry strut. Additionally, the tutorial discusses how to apply earthquake loads and run the linear analysis to determine the structural response. Perfect for engineers looking to improve their modeling skills.

Takeaways

• 😀 In this video, Muhammad Ubad explains how to model unreinforced brick masonry infill using ETABS software for earthquake engineering analysis.
• 😀 The video builds on previous content, revisiting parameters and guidelines for modeling masonry infill as discussed in IS 1893 (2016) Part 1.
• 😀 The concrete strength (fck) is assumed to be 25 N/mm², with an elasticity modulus of 25,000 N/mm², while the masonry prism strength (fm) is 6 N/mm².
• 😀 The elasticity modulus of the masonry infill is calculated to be 3300 N/mm² using the formula: 550 times the prism strength.
• 😀 For simplicity, a 2D frame is chosen for analysis, and the height of the infill wall is calculated based on the building's story height and column depth.
• 😀 The thickness of the masonry infill is assumed to be 230 mm, and the model uses a strut to represent the behavior of the infill.
• 😀 The angle theta and diagonal length of the strut are calculated using trigonometry based on the height and length of the masonry infill.
• 😀 A detailed procedure is demonstrated for defining materials, including concrete and masonry, and assigning rebar material (Fe415) for both columns and beams.
• 😀 The strut section is modeled as a rectangular shape with dimensions of 230 mm by 390 mm, corresponding to the masonry wall thickness and diagonal length.
• 😀 The video shows how to apply earthquake loading (IS 1893-2016) to the model, define diaphragms, and perform linear analysis to determine the structural response under seismic conditions.
• 😀 After running the analysis, the axial forces and moments in the strut are observed to validate the accuracy of the model, providing a more realistic simulation of masonry infill behavior.

Q & A

What is the purpose of modeling unreinforced brick masonry infills in ETABS?

The purpose of modeling unreinforced brick masonry infills in ETABS is to improve the accuracy of earthquake analysis by properly simulating the behavior of masonry walls as strut members, which helps in understanding the structural response during seismic events.

How do we determine the masonry strength (fm) for modeling purposes?

Masonry strength (fm) can be determined either through prism testing as outlined in IS 1905, or it can be estimated using a formula. In this example, the masonry strength is assumed to be 6 Newton per mm² for the modeling process.

Why is the modulus of elasticity (E) important for masonry infills?

The modulus of elasticity (E) is important because it determines the stiffness of the masonry material. A higher modulus indicates a stiffer material, which impacts how the masonry infill will resist deformation under seismic loads. For this modeling, E is calculated as 550 times the masonry strength (fm).

What are the key parameters used for modeling in ETABS, as discussed in the video?

Key parameters for modeling include concrete strength (fck), modulus of elasticity for concrete, column and beam sizes, masonry prism strength (fm), and dimensions for the masonry strut such as width and height.

How do we calculate the height and length of the masonry infill in ETABS?

The height of the masonry infill is determined by subtracting the depth of the beam and column from the total story height. The length of the infill is calculated by measuring the distance between the center-to-center of the column sections.

What formula is used to determine the width of the strut in the masonry infill model?

The width of the strut is determined using a specific formula based on the angle of the strut and the diagonal length. The angle (theta) is found using trigonometry, and the width (wds) is calculated based on the diagonal length (lds) and the formula given in the script.

What is the significance of using the eccentric bracing option for modeling the strut?

The eccentric bracing option simulates the behavior of the masonry infill as a compression member (strut), which helps in accurately representing the infill’s load transfer to the surrounding structural elements during seismic events.

What type of analysis is used in this modeling example, and why?

A linear analysis is used in this example, as earthquake analysis is being performed with the assumption of linear behavior. This simplifies the modeling process and is sufficient for the scope of this video, where non-linear behavior is not being considered.

How are diaphragm conditions assigned in the ETABS model?

Diaphragm conditions are assigned by selecting the relevant story levels in the plan view and assigning rigid diaphragms. This ensures that the floors behave as rigid bodies during lateral load applications, such as earthquake forces.

What steps should be taken if the model encounters issues during the analysis in ETABS?

If the model encounters issues during analysis, it's important to check for modeling errors, such as incorrect material properties, missing diaphragms, or inconsistent load cases. Verifying the degree of freedom settings and ensuring proper boundary conditions for supports and joints also helps troubleshoot common errors.