Subjects structural engineering

Frame Reactions

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Frame Reactions


1. **Problem Statement:** Solve for the reactions at the supports of the given frame structure using the slope-deflection method considering sidesway. Then, draw the shear force and bending moment diagrams. 2. **Given Data:** - Concentrated loads: 20 KN, 15 KN, 32 KN, 26 KN at mid-spans of beams. - Distributed load: 18 KN/m on the first column. - Column heights: 7 m each. - Bay lengths: 2 m, 3.5 m, 1.8 m, 0.5 m, 3.5 m, 3 m. - Column segments: lower segments 2l, upper segments l. 3. **Slope-Deflection Method Overview:** The slope-deflection equations relate moments at the ends of members to rotations and translations (sidesway) of the joints: $$M_{AB} = \frac{2EI}{L} (2\theta_A + \theta_B) + \frac{6EI}{L^2} \Delta - 6EI \frac{\delta}{L^2} + M_{fixed}\n$$ where $M_{AB}$ is the moment at end A of member AB, $\theta_A$ and $\theta_B$ are rotations at ends A and B, $\Delta$ is the lateral displacement (sidesway), $L$ is member length, $EI$ is flexural rigidity, and $M_{fixed}$ is fixed-end moment due to loads. 4. **Step-by-step solution:** 1. Calculate fixed-end moments ($M_{fixed}$) for each member due to distributed and concentrated loads using standard formulas. 2. Write slope-deflection equations for each member considering rotations and sidesway $\Delta$. 3. Apply equilibrium equations for moments and lateral forces at joints to form simultaneous equations. 4. Solve the system of equations for unknown rotations $\theta$ and sidesway $\Delta$. 5. Calculate moments at member ends using solved rotations and sidesway. 6. Determine shear forces and reactions at supports from moment and load equilibrium. 7. Draw shear force and bending moment diagrams based on calculated values. 5. **Important formulas for fixed-end moments:** - For a beam with uniform distributed load $w$ over length $L$: $$M_{AB} = M_{BA} = -\frac{wL^2}{12}$$ - For a beam with a concentrated load $P$ at mid-span: $$M_{AB} = M_{BA} = -\frac{PL}{8}$$ 6. **Example calculation for one member:** For the first column with distributed load 18 KN/m over 7 m: $$M_{fixed} = -\frac{wL^2}{12} = -\frac{18 \times 7^2}{12} = -\frac{18 \times 49}{12} = -73.5 \text{ KNm}$$ 7. **Final step:** After solving the system, reactions at supports and internal moments are found. Use these to plot shear and moment diagrams. **Note:** Due to complexity, detailed numerical solution requires matrix formulation and solving simultaneous equations which is beyond this summary.