Jawaharlal Nehru Technological University Hyderabad B.Tech III Year STRUCTURAL ENGINEERING - II (STEEL) Previous Question Paper (August - 2022 - R18)

To design the seat angle connection for a reaction of 85 kN, we follow these steps:

1. Bolt Capacity: For M16 black bolts (Grade 4.6), the ultimate strength f_ub = 400 MPa. The shear capacity V_dsb = (f_ub / (sqrt(3) * γ_mb)) * A_nb. With A_nb = 157 mm², V_dsb = (400 / (1.732 * 1.25)) * 157 = 29.01 kN. The bearing capacity V_dpb = 2.5 * k_b * d * t * f_u / γ_mb. Assuming standard edge/pitch distances, V_dpb is typically higher than shear capacity; thus, shear governs.
2. Number of Bolts: Required bolts = 85 / 29.01 = 2.93. Provide 4 bolts in the column flange to ensure stability.
3. Seat Angle Selection: Use ISA 100x100x10 mm. The length of the angle is taken as the width of the beam flange (125 mm). The load is assumed to be distributed over a length b = (width of beam flange / 2) + 10 mm.
4. Moment Calculation: The bending moment M = R * (a - b/2), where 'a' is the length of the outstanding leg. Check the moment capacity of the angle: M_d = (β * Z_e * f_y) / γ_m0. Ensure the thickness of the angle is sufficient to resist this moment.
5. Cleat Angle: Provide a top cleat angle (e.g., ISA 60x60x6 mm) to provide lateral restraint to the beam top flange, though it is not designed to carry the vertical reaction.

The connection is safe provided the angle thickness satisfies the bending requirement and the bolts are spaced according to IS 800:2007 requirements (minimum pitch 2.5d and edge distance 1.5d₀).

To design a tension member carrying a factored load of 500 kN using double angles back-to-back on either side of a 10 mm gusset plate, we proceed as follows:

1. Design Strength Requirement: The design strength of the member must be at least 500 kN. Assuming the design is governed by the gross section yielding, the required gross area A_g is calculated using the yield strength of steel (f_y = 250 MPa) and a partial safety factor (γ_m0 = 1.10):

2. Section Selection: For a double angle section, the area of one angle should be at least 1100 mm². Selecting two ISA 75x75x8 mm (A = 1138 mm² each, total A_g = 2276 mm²).

3. Bolt Design: For 20 mm diameter bolts (grade 4.6, f_ub = 400 MPa), the shear capacity V_dsb and bearing capacity V_dpb are calculated. Assuming a standard pitch of 50 mm and edge distance of 30 mm, the capacity per bolt is determined. With a 10 mm gusset plate, the bearing capacity is usually the limiting factor.

4. Net Section Rupture: The design strength T_dn is checked using the net effective area A_ne, considering the reduction factor β for out-of-plane connections:

5. Verification: Ensure the slenderness ratio (λ = L/r_min) does not exceed 300 for members under tension. Check that the chosen section satisfies both the yielding and rupture criteria, and that the bolt group capacity exceeds 500 kN.