Explaining the complete process of generating an Interaction Diagram

After achieving a successful axial and moment design, the program creates an axial resistance, Pr, vs. moment resistance, Mr, diagram. The calculation procedure followed in the P-M diagram depends on whether the wall is reinforced or not.

Unlike for out-of-plane walls, the shear wall P-M diagram provided by MASS does not include separate curves depending on whether or not the effect of the grout is included. However, the program allows users to check the shear wall design with loads applied in both directions. This feature is important for asymmetrical shear walls (shear walls with different flanges configurations). If loading in both directions is selected, the P-M diagram would include a curve for loads applied from left to right, and another curve for loads applied from right to left. The program also provides an envelope curve indicating the bounds of acceptable Pr and Mr combinations, always selecting the lower moment resistance from the two plotted curves. If loading in both directions is not selected, the P-M diagram only displays one curve, for loads applied from left to right.

 In the P-M interaction diagram, and for every load combination, the program displays points representing the factored axial force and moment (Pf, Mf,total).

P-M Interaction Diagram (Unreinforced Masonry)

Same as for out-of-plane walls, in the shear wall P-M diagram for unreinforced masonry, the moment resistance Mr is determined and plotted for incremented values of the axial resistance, Pr. The moment resistance calculations vary depending on whether the wall is designed as an uncracked or a cracked section.

The P-M interaction diagram is created in three separate stages. The first stage, where the wall must remain uncracked (the curve is under the elimit line). The second stage is governed by the elimit line, and how this line intersects with stages one and three. The third stage, where the wall can be designed as a cracked section (the curve is above the elimit line) and the moment resistance is calculated using the equivalent rectangular stress block. MASS also performs the grey zone check for shear walls.

P-M Interaction Diagram (Reinforced Masonry)

 The axial resistance, Pr, and the moment resistance, Mr, are determined and plotted for incremented values of the neutral axis depth, c. The neutral axis depth begins with c=1 mm, and is incremented up by 1 mm with each iteration, terminating when the compression zone is equal to the length of the shear wall (when β1c=ℓ).

MASS does not account for reinforcement in compression in the moment resistance calculations, since tying bars in walls is not easily accomplished.

Continue Reading: Self Weight Shear Walls

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