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Strategically Preparing Design of Steel Structures for GATE Civil Engineering

This article on Design of Steel Structures has been written by Rohit Sachdeva. He graduated from Delhi College of Engineering (now DTU) in 2012 (a gold medalist in his batch) in Civil Engineering branch. Then he appeared in Civil Engineering (CE) paper in GATE 2017 and secured an All India Rank (AIR) of 93.

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In this blog, I will be discussing Steel Design. Despite being a very vast topic, its weightage in recent years in GATE has been less. On the other hand, studying this topic in detail is important for people who want to enter Structural Engineering domain as their career option.

However, I will be focusing how to prepare this subject from GATE point of view, and which topics to target so that unnecessary time is not wasted in studying this subject in too much detail. Many students tend to skip this subject because of its vastness; but if targeted approach is followed, then questions from this topic can be answered with almost 100% accuracy.

A rough breakup of questions of various topics in last 30 years in GATE is as follows:

Sl No Topic No. of Questions
1 mark 2 marks
1 Materials & Specifications 2
2 Riveted Joints & Bolted Joints 4 2
3 Welded Joints 1 6
4 Eccentric Joints 1 5
5 Tension Members 3 6
6 Compression Members 5 2
7 Column Bases and Column Splices 1 1
8 Beams 10
9 Plate Girder 1 2
10 Gantry Girders 1
11 Plastic Analysis 10 20

An analysis of last 5 years of GATE papers reflect that Steel Design carries only 2-4 marks. Although Indian Standard IS 800:2007 is a reference material, it is recommended that class notes & topics mentioned below be studied thoroughly rather than going too much in-detail for this subject. The textbook(s) to be referred are mentioned in a separate comprehensive blog which you should refer.

Time required for preparation

10-12 days (if you have 8-10 month of preparation) with 4 hours daily
5-6 days (if you have 4-5 months of preparation) with 7-8 hours daily

In this blog, I will try to mention the important topics which you should definitely do to secure those extra marks in GATE (most important ones in bold & italics). Topics no. 1 to 4, and 11 are more important. If you have less time, try to study at least these ones properly.

1. MATERIALS & SPECIFICATIONS (1/2 DAY)

Although no direct questions are usually asked from this topic, it contains very important concept of permissible stresses in steel in various conditions (axial compression/tension, bending compression/tension, bearing & shear in bolt and FOS for these conditions, etc), and both in WSM & LSM. This will be used in almost all the questions later. Therefore it is very important to learn these formulae and note them in formula sheet; it will come handy later.

 

2. RIVETED & BOLTED JOINTS (1.5 DAYS)

Lap joint and Butt joint (single cover or double cover), strength of a joint (failure of bolt/rivet, bearing of plate, tearing of plate based on gross area or net area), single shear of double shear, no. of bolts required at a joint, efficiency of a joint, maximum pitch of rivets/bolts in compression and tension, dia of bolt hole, Unwin’s formula for nominal dia of bolt used for plate, s2/4g rule.

3. WELDED JOINTS (1 DAY)

Relation b/w size of weld & throat thickness based on fusion angle, effective length of weld, permissible shear stresses in weld, slot welding, designing of moment-free welded connection (finding P1 & P2 and then l1 & l2).

4. ECCENTRIC JOINTS (2 DAYS)

This topic has become very important recently. It contains 2 parts:

Bolted/Rivet Eccentric Connection

a) In-plane eccentricity: finding location of most critical bolt & stresses in it (finding resultant of shear force due to direct load & shear force due to twisting/torsion).

b) Out-of-plane eccentricity: this is like interaction b/w shearing & tension (due to moment); hence interaction equation is used.

Welded Connection

a) In-plane eccentricity: finding CG of weld line, calculation of stresses (resultant of stress due to direct load & that due to twisting moment using polar moment of inertia)

b) Out-of-plane eccentricity: calculation of resultant stress due to direct load & bending moment.

5. TENSION MEMBERS (1 DAY)

Slenderness ratio & limits for tension members in various loading cases, staggered or zig-zag bolting (finding least Anet using s2/4g rule), effective area when 2 or more angles are place together, opening of an angle as a plate for calculation of area.

6. COMPRESSION MEMBERS (1 DAY)

Slenderness ratio & limits for tension members, effective length of column with various end conditions, Euler’s critical load & stress, Design of LACING SYSTEM (single/double, effective length, width, min thickness, forces in lacing members), Design of BATTENING (similar to Lacing).

7. COLUMN BASES & SPLICING (1/2 DAY)

 

Formula of thickness of base plate (in WSM & LSM) for slab base is important.

8. BEAMS (1 DAY)

This is a vast topic & contains a lot of content. Bending formula (calculation of section modulus Z), laterally supported & unsupported beams, permissible deflections, flange buckling criteria, web buckling criteria, web crippling criteria, design of built-up beam (area of plate required on top & bottom of beam), b/tf ratio for plastic, compact, semi-compact & slender sections.

9. and 10. PLATE GIRDER & GANTRY GIRDER (1/2 DAY)

There is very less chance of question from these topic, they can be skipped. Just go through them once to understand how plate girders & gantry girders function. Detailed study can be avoided.

 

11. PLASTIC ANALYSIS (3 DAYS)

This topic is important & very scoring; numericals should be practiced in this. Shape factor for different cross-sections, elastic & plastic N.A, formation of plastic hinge, collapse load for various loading cases (principle of virtual work), plastic hinge in fixed/indeterminate beams and propped beams, plastic hinge length, plastic analysis of frames (beam, sway & combined mechanisms).

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