SSC-JE CIVIL ENGINEERING STRUCTURAL ENGINEERING STUDY MATERIAL STEEL STRUCTURE STEEL STRUCTURE

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1 Page 1 o 138 SSC-JE STAFF SELECTION COMMISSION CIVIL ENGINEERING STRUCTURAL ENGINEERING STUDY MATERIAL

2 Page 2 o 138 CONTENT 1. STRUCTURAL STEEL, LOADS AND STRESSES STEELWORK CONNECTIONS COMPRESSION MEMBERS COLUMN BASE TENSION MEMBERS BEAMS PLATE GIRDERS AND GIRDERS PLASTIC ANALYSIS

3 Page 3 o 138 TCHAPTER-1 STRUCTURAL STEEL, LOADS AND STRESSES Structural Steel: Main components o steel are: (i) Metallic iron, (ii) Carbon and others like Si, Cr, Mn, Cu etc. Generall steel consists o more than 98% o iron and carbon content 0.04% to 2.1% Cast iron has high carbon content (2.1% to 4%) which makes it brittle. Wrought iron has low carbon content (less than 0.08%). It is tough, malleable, ductile, corrosion resistant and easil welded. Steel has carbon content intermediate between cast iron and wrought iron. Depending upon chemical composition, steel is classiied as: (i) Mild steel (ii) Medium carbon steelare Knows as structural steel and is used in steel structure. (iii) High carbon steel (iv) Low allo steel (v) High allo steel Note: As carbon content increases, strength, hardness and brittleness increases but the ductilit decreases. Mild steel is used or manuacture o rolled steel section, rivets and bolts. Phsical properties o mild structure are. (i) Mass : 7850 Kg/m 3 (ii) Young s modulus o Elasticit (E): N/mm 2 or MPa (iii) Modulus o rigidit (G): N/mm 2 (iv) (v) Poisson s ratio () : 0.3 (in elastic range) : 0.5 (in plastic range) Co-eicient o thermal expansion or contraction : /ºC Table : Chemical Composition o Structural Steels

4 Page 4 o 138 Fe = steel, C = carbon, S = sulphur, P = phosphorus, Mn = Manganese, Si = silicon Structural Elements o a Steel Structure :The steel rame work or the skeleton consists o ollowing elements. (i) Flexural members beams or girders (ii) Tension members ties (iii) Compression members columns, struts (iv) Torsional members The members o the design are made up o commonl used shapes and built b members made o the common shapes. Following are the common shapes. (a.) (b.) (c.) (d.) (e.) (.) (g.) Rolled steel I-section Rolled steel channel section Rolled steel T-section Rolled steel angle section (equal or unequal) Rolled steel circular section (solid or hollow) Rolled steel bars (circular or rectangular) Rolled steel plates Flexural members: (Beams and Girders): A beam or girders is a structural component which supports loads normal to its axis. The are both same but girder is primaril used to describe a built up member or a main beam which supports other beams.

5 Page 5 o 138 Tension Members (Ties) : It is used to resist axial tension. The are usuall called ties or hangers. The cross-section o a tension member is important onl to the context o its quantit. The shape is immaterial to resist the tensile orce. Compression Members (Columns, Struts): The primaril resist the compressive stress. The shape o a compression member plas an important role in its determination apart rom the area required. The material properties also plas an important role in its selection. Torsional Members: The are primaril provided to resist torsion or twisting orces. Note: (Important o ESE) 1. ISLBIndian standard low beam. The are used as roo beam where loads are relativel less. 2. ISMBIndian standard medium beam. The are used as loor beam, the have high moment o inertia about x- axis as compared with -axis. Lateral buckling strength o these beams is not highh (can be overcome b laterall restraining o compression lange o the beam). 3. ISWB Indian Standard Wide Flange Beam. The have high M.I about - axis also. So the have higher lateral buckling strength. Indian standard wide lange beam. So the are used as column. 4. ISHB Indian standard heav beam. Design methods: Design o steel structures consists o the design o steel members and their connections. A steel structure can be designed b an one o the ollowing methods: (i) Working stress design: Also known as the elastic design method, it assumes that the acceptable behaviour in a steel member is up to the ield stress. It also takes into account the actor o saet. Yield stress Permissible stress Factor o saet (ii) Plastic design : In this method, the material is considered acceptable upto the ultimate load. It is mainl used in the analsis and design o staticall indeterminate structure. The actor o saet in this method is known b the name o load actor. Working load = (iii) Limit state method: Limit state method is similar to plastic design which considers most critical limit states o strength and serviceabilit. Load actors are applied to the service loads and then theoretical strength o member is reduced b application o resistancee actor. The criteria to be satisied in selection o member is actored load actored strength. Collapse load Load actor

6 Stress Strain Relationship or Mild Steel: Page 6 o 138 The curve starts rom the origin showing that there is no initial stress or strain upto point A, Hooke s law is obeed and stress is proportional to strain. Point A is called the limit o proportionalit. Point B is called the elastic limit. Upto this point i the load is removed, the material returns to its original shape and size, i.e., no strain is let in the specimen. Beond point B, the material behaves as a plastic material until point C which is the upper ield point. Ater point C the cross-sectional area o the material starts decreasing and the stress decreases to a lower value to point D, called the lower ield point. Beond D, the specimen elongates without a considerable increase in stress and reaches a maximum value o stress called the ultimate strength. This is denoted b point E. Ater point E, necking o the material starts and the cross-sectional area decreases at a rapid rate. At last, the material ractures at point F. Elastic Plastic range Strain hardening Stresss Strain This igure is an enlarged view o a part o the graph given above. It shows that the range o working stress design is onl upto the proportional limit while the range or plastic design is large and upto a strain 10 times than what occurred upto the proportional limit. Beond plastic range is the strain hardening or which a structure is not designed.

The primar purpose o an structure is that it should be strong enough to carr all tpes o oreseeable loads.

7 Page 7 o 138 Example: Which o the ollowing statements is incorrect regarding steel? (a) It can be reused. (b) Being heav, it is quite hard to transport. (c) Steel has a ver long lie when maintained properl. (d) Steel is a ductile material. Sol. (b) Being light, steel can be handled convenientl thus it oers ease in transportation. The primar purpose o an structure is that it should be strong enough to carr all tpes o oreseeable loads. For the purpose o designing an element or a structure as a whole, the ollowing loads and their eects should be taken into account, where applicable, with partial saet actors and combinations. (i) Dead loads ; IS 875 (Part I) (ii) Live loads : IS 875 (Part II/IV) (iii) Wind loads ; IS 875 (Part III) (iv) Earthquake loads ; IS 1893 (v) Erection loads (vi) Accidental loads such as those due to blast (vii) Secondar eects due to contraction or expansion resulting rom temperature changes, dierential settlement o structure as a whole or o its components, eccentric connections, rigidit o joints diering rom design speciications. (i) Dead loads: It is the weight o the walls, partitions, roos, etc. and other permanent construction in the building. Dead loads do not change their position and do not var in magnitude. (ii) Live loads: It consists o variable loads, due to people, urniture, stores, machiner etc. It is also known as the super-imposed loads. In broader sense, it includes. Movable machiner Snow load Earth pressure Earthquake orces Thermal orces. (iii) Wind loads: Wind produces wind pressure on the exposed vertical suracess o wall, towers, etc. and acts horizontall. The wind velocities are measured with the help o anemometers which are installed at a height o 10 to 30 meters. Load combinations: The ollowing combination o loads with appropriate load actors speciied in the code ma be considered. (a) Dead load + Imposed load (b) Dead load + Imposed load + Wind or earth quake load (c) Dead load + Wind or earthquake load (d) Dead load + Erection load

8 Permissible Stresses: 1. Axial tensile stress: Permissible axial tensile stress () : at Page 8 o 138 at 0.6 Where ield stress o steel (N/mm 2 ) 2. Axial Compressive Stress: Permissible axial compressive stress 0.6 For direct stress in compression o a axiall loaded column ac Or, According to Rankine sormula: ac Where, 0.6 ()() cc cc n cc. n 1/ n E elastic critical stress in compression 2 Slenderness ratio n 1.4 E = Young s modulus The value o ac l r shall exceed neither o the above two values Bending Stress: Permissible bending stress in tension or in compression: or 0.66 bt bc Permissible bending compressive stress in beams and plate girders: bc 0.66 () cb n cb. n 1/ n Where, n =1.4 cb Elastic critical stress in bending. 4. Shear Stress: Permissible shear stress, v 5. Bearing Stress: vm 0.45 Permissible bearing stress, p 0.75

9 Factor o saet (F.O.S.)F: It is deined as the ratio o ield stress to maximum expected stress. F max Page 9 o 138 I.S. Code permits the value o F as As carbon content increases, strength, hardness and brittleness increases but ductilit decreases. 2. For mild steel, Mass = Ke Points kg/ m E = N/ mm 5 G MPa Permissible stresses: Axial tension, 0.6 at Axial compressive, 0.6 or, b Rankine s ormula, ac ac 0.6. [()() ] cc 1 n n n cc bt Bending stress, 0.66 bc Shear stress, VM 0.45 Bearing stress, P 0.75

10 Page 10 o 138 SSC-JE Practice Set & Previous Year Question 1. Pick up the correct statement rom the ollowing: (a) Dead load includes sel-weighstructure o the structure and super-imposed loads permanentl attached to the (b) Dead loads change their positions and var in magnitude (c) Dead loads are known in the beginning o the design (d) None o these 2. The rolled steel I-sections are most commonl used as beams because these provide (a) large moment o inertia with less cross-sectional area (b) large moment o resistance as compared to other section (c) greater lateral stabilit (d) all the above 3. Rolled steel beams aredesignated b Indian Standard series and its (a) weight per meter and depth o its section (b) depth o section and weight per meter (c) width o lange and weight per meter (d) weight per meter and lange width 4. The Indian standard code which deals with steel structures, is (a) IS : 875 (b) IS : 800 (c) IS : 456 (d) IS : 1893 To bu Complete Course Materials Contact: , eiidelhi@gmail.com Website : Classroom Coaching Program Postal Coaching Program Online Test Series

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twenty one steel construction and design Steel Steel Construction Steel Construction APPLIED ARCHITECTURAL STRUCTURES: STRUCTURAL ANALYSIS AND SYSTES DR. ANNE NICHOLS FALL 018 lecture twent one steel construction and design http://nisee.berkele.edu/godden Steel cast iron wrought iron -