JNTU
JNTU B.Tech III DESIGN OF STEEL STRUCTURES Previous Question Paper (November/December - 2020 - R16)
Answer any five questions. All questions carry equal marks.
IS 800-2007 code book and steal tables are permitted.
Main
A tie member of a roof truss consists of 2 ISA 100×75×8 mm. The angles are connected on either side of a 10mm gusset plates and the member is subjected to a working pull of 400kN. Design the welded connection. Connections are made in the workshop.
Answer
Given: Factored load (P) = 400 kN × 1.5 = 600 kN. The member consists of 2 ISA 100x75x8 mm angles connected on either side of a 10 mm gusset plate. The design strength of the weld is determined based on the shop welding condition.
1. Design Strength of Weld:
2. Size of Weld (s):
For 8 mm thick angles, the minimum size of the weld is 3 mm and the maximum size is 8 - 1.5 = 6.5 mm. Provide a weld size of 6 mm.
3. Effective Throat Thickness (tt):
4. Required Length of Weld (L):
5. Distribution of Weld Length:
The load is shared by two angles. For each angle, the required length is 377.15 mm. Since the angles are connected on both sides of the gusset, the load is distributed based on the centroidal distance of the angle. For ISA 100x75x8, the centroidal distance from the longer leg (Cyy) is approximately 31.3 mm. Let L1 be the length at the top and L2 be the length at the bottom:
Provide a 6 mm fillet weld with lengths of 260 mm and 120 mm on the respective sides of each angle.
List the advantages and disadvantages of bolted connections.
Answer
Bolted connections offer several advantages: they allow for rapid assembly and erection on-site without the need for skilled labor or specialized equipment like welding sets. They facilitate easy dismantling or replacement of members during maintenance or modifications. Furthermore, bolted joints do not require pre-heating or post-weld heat treatment, and they are not affected by the adverse weather conditions that can compromise weld quality.
The disadvantages include the reduction of the effective cross-sectional area of the connected members due to the necessity of drilling or punching bolt holes. The process of making holes can lead to stress concentrations around the hole edges. Additionally, bolted connections are susceptible to loosening under vibration or dynamic loading unless locking devices are used, and they require more material due to the need for gusset plates and overlap, which increases the overall weight of the structure.
How will you calculate strength and efficiency of a bolted joint?
Answer
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Design a built-up column 7m long to carry factored axial load of 1000 kN. The column is restrained in position but not in direction at both the ends. Design the column with two channels placed toe-to-toe. Provide single lacing system with 20mm diameter bolted connection. Assume steel of grade Fe 410 and bolts of grade 4.6.
Answer
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Design a single angle section for a tension member of a roof truss to carry a factored tensile force of 250kN. The member is subjected to the possible reversal of stress due to the action of wind. The length of the member is 3m. Use 20mm shop bolts of grade 4.6 for the connection.
Answer
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A compound beam is to carry a uniformly distributed dead load of 300kN and an imposed load of 500kN. The beam is simply supported over a span of 12meters. Allow 30kN for the weight of the beam. The overall depth should not exceed 700mm. The bearing plate width is 300mm and full lateral support is provided for Compression flange. Design the beam.
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An ISLB 350 @495 N/m transmits an end reaction of 350KN to the web of an ISMB500 @869N/m. Design a framed connection and give neat sketch.
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List the steps involved in the design of a roof truss clearly.
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List the steps involved in the design of plate girders with stiffeners.
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