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DSS UNIT 1 Introduction.pdf

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This document provides information about the Design of Steel Structures course taught by Prof. Durgesh Tupe. It includes the course code, credits, teaching scheme, evaluation scheme, course contents organized in 5 modules, outcomes expected after completion of the course, text books and reference books. The key concepts covered are types of connections in steel structures, standard rolled sections, types of loads, permissible stresses and factors of safety, methods of design including working stress method, ultimate load method and limit state method. Connections can be riveted, bolted or welded. Loads include dead, live, wind, seismic, snow etc. Methods of design have moved from working stress to limit state for better economy and safety consideration

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Prof. Durgesh Tupe 1 TY Civil Semester- V SEM V Course Category Cours e Code Course Title Teaching Scheme Evaluation Scheme Credit L T P CA MS E ES E Tota l PCC 10 BTCVC 501 Design of Steel Structures 2 1 - 20 20 60 100 3 PCC 11 BTCVC 502 Geotechnical Engineering 3 1 - 20 20 60 100 4 PCC 12 BTCVC 503 Structural Mechanics –II 2 1 - 20 20 60 100 3 PCC 13 BTCVC 504 Concrete Technology 2 - - 20 20 60 100 2 HSSMC3 BTHM505 Project Management 3 - - 20 20 60 100 3 PEC 1 BTCVPE506 A. Advanced Environmental Engg. B. Applied Geology C. Hydraulic Engineering Design D. Advanced Water Resources E. Geomatics F. Town and Urban Planning G. Material, Testing and Evaluation H. Construction Economics & Finance 3 - - 20 20 60 100 3 ESC10 BTCVES507 Software applications in Civil Engineering 2 - - 50 - - 50 Audit LC 7 BTCVL508 SDD of Steel Structures Lab. - - 2 20 - 30 50 1 LC 8 BTCVL509 Geotechnical Engineering Lab. - - 2 20 - 30 50 1 LC 9 BTCVL510 Concrete Technology Lab. - - 2 20 - 30 50 1 Internship BTCVP410 Internship – 2 Evaluation - - - - - - - Audit Total 17 3 6 230 120 450 800 21
Prof. Durgesh Tupe 2 BTCVC 501 Design of Steel Structures Teaching Scheme: (2 Lectures + 1 Tutorial) hours/week Course Contents Module 1: Introduction and Connections (6 Lectures) Introduction, advantages & disadvantages of steel structures, permissible stresses, factor of safety, methods of design, types of connections, various types of standard rolled sections, types of loads and load combinations Types: Riveted, Bolted, Welded; Analysis of axially & eccentrically loaded connections (subjected to bending & torsion), Permissible Stresses, Design of connections, failure of joints Module 2: Axially Loaded Members (8 Lectures) Tension members: Common sections, net effective area, load capacity, connection using weld / bolts, design of tension splice Compression members: Common sections used, effective length and slenderness ratio, permissible stresses, load carrying capacity, connection using weld / bolt Beams: Laterally supported & unsupported beams, design of simple beams, built up beams using flange plates, curtailment of flange plates, web buckling & web crippling, secondary and main beam arrangement, beam to beam connections. Module 3: Industrial Roofing (8 Lectures) Gantry girder: Forces acting on a gantry girder, commonly used sections, introduction to design of gantry girder as laterally unsupported beam, connection details Roof trusses: Components of an industrial shed, types of trusses, load calculations and combinations, design of purlins, design of truss members, design of hinge & roller supports Module 4: Columns and Column Base (6 Lectures) Simple and built up section, lacing, battening, column subjected to axial force and bending moment, column splices. Column bases: Analysis and design of: Slab base, gusseted base and moment resisting bases, grillage foundation, design of anchor bolt
Prof. Durgesh Tupe 3 Module 5: Introduction to Plastic Analysis and Limit State method (8 Lectures) Introduction to: Plastic Analysis, Hinge Formation, Collapse Mechanism, Recent approaches in Steel Structure design based on Plastic Analysis Method and Limit State Approach, Introduction to Provisions in IS 800-2007 Note: Contents in Module 1 to part of 4 shall be taught with help of relevant text or reference books based on elastic design concept and IS 800: 1984. Unit 5 shall be taught with reference to IS 800 2007 Use of IS 800: 1984 and 2007, IS 875 (All Parts), IS: Handbook No.1 for Steel Section and Steel Table is permitted for theory examination. Text Books • Duggal S. K., “Design of Steel Structures”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Gambhir, “Fundamentals of Structural Steel Design”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Negi L. S., “Design of Steel Structures”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Chandra Ram, “Design of Steel Structures”, Vol. I & Vol. II, Standard Book House, New Delhi • Dayaratnam P., “Design of Steel Structures”, Wheeler Publishing, New Delhi • Subramanian N., “Steel Structures: Design and Practice” Oxford Univ. Press, Delhi • Vazirani V.N. and Ratwani M.M., “Design and Analysis of Steel Structures”, ISBN NO: 978-81-7409-295-3 • Sai Ram K. S., “Design of Steel Structures”, Pearson Education, 2nd Edition Reference Books • Arya A. S. and Ajamani J.L., “Design of Steel Structures”, Nemchand and Brothers, Roorkee • Vazirani&Ratwani, “Design of Steel Structures”, Standard Book House, New Delhi • Duggal S. K., “Limit State Design of Steel Structures”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Publications of Bureau of Indian Standards, New Delhi, IS 800:1984, 2007, IS 875 (Part I to V) • Gaylord E.H. and Gaylord C.N., “Design of Steel Structures” McGraw Hill, New York • Lothers J.E., “Design in Structural Steel” Vol.-I, Prentice Hall New Jersy • Salmon and Johnson, “Steel Structures: Design and Behaviour”, Harper and Row, New York
Prof. Durgesh Tupe 4 • Steel Designers Manual. Course Outcomes: On completion of the course, the students will be able to: CO1: Identify and compute the design loads and the stresses developed in the steel member.CO2: Analyze and design the various connections and identify the potential failure modes. CO3: Analyze and design various tension, compression and flexural members. CO4: Understand provisions in relevant BISCodes.
Prof. Durgesh Tupe 5 Introduction A Civil Engineering Designer has to ensure that the structures and facilities he designs are (i) fit for their purpose (ii) safe and (iii) economical and durable. Thus safety is one of the paramount responsibilities of the designer. However, it is difficult to assess at the design stage how safe a proposed design will actually be – consistent with economy. There is, in fact, a great deal of uncertainty about the many factors, which influence both safety and economy. Firstly, there is a natural variability in the material strengths and secondly it is impossible to predict the loading, which a structure (e.g. a building) may be subjected to on a future occasion. Thus uncertainties affecting the safety of a structure are due to • uncertainty about loading • uncertainty about material strength and • uncertainty about structural dimensions and behaviour. These uncertainties together make it impossible for a designer to guarantee that a structure will be absolutely safe. All that the designer could ensure is that the risk of failure is extremely small, despite the uncertainties. Advantage of steel structure : 1. Steel member have high strength/unit weight 2. Steel being a ductile material does not fail suddenly but give visible evidence of independent failure by large deflection 3. Structural steel is tough i.e. they have both strength and ductility 4. Being light steel member can be easily handle and transport properly, steel structure have long life & property of steel mostly do not change 5. Addition and alteration can be made easily to structure 6. The steel can be erected at fast rate 7. Steel has highest scrap value among all building material 8. Steel is the ultimate recyclable material 9. Addition and alteration can be easily made to structure Disadvantage of steel structure : 1) Steel structure may be more costly than other type of structure 2) The strength of steel reduce subsequently when heated at temperature commonly observed in building fires, hence need fire proof treatment. 3) Steel structure exposed to air and water such as bridges are such suspectical to corrosion and needs regular maintainace.
Prof. Durgesh Tupe 6 Permissible Stresses: The permissible stress is defined the ratio of yield stress to factor of safety. So as to keep the stresses within permissible value. Thus Yield Stress Permissible Stress = Factor of Safety Factor of Safety: The factor of safety is a termed describing the structural capacity of as steel beyond the expected load or actual load. The safety factor are often calculated using detailing analysis because compressive is impractical on many structures , such as bridges, buildings but the structure ability to carry load must be determine to responsible accuracy. Many systems are purposefully deal much stronger than needed for normal uses to alone for emergency situation, unaccepted load, needs or degradation. Factor of Safety is defined as yield stress to working stress Yield Stress Factor of Safety = Working Stress Methods of Design: The aim of design is to design, shape, size and connection details of the members so that the structural beam design will performed satisfactory during its right span. Following methods of design are used in steel structures 1) Working Stress Method (WSM) 2) Ultimate Load Method (ULM) 3) Limit State Method (LSM) 1) Working Stress Method (WSM) : Working Stress Method is the traditional method of design not only for Reinforced Concrete but also for structural steel and timber design. The conceptual basis of the WSM assumes that the structural material behaves in a linear elastic manner and that appropriate safety can be ensured by suitably limiting the stresses in the material due to the presumed working loads (service loads) on the structure. WSM also assumes that both the steel reinforcement and concrete act together and are perfectly elastic at all stages, and hence the modular ratio can be used to determine the stresses in steel and concrete. The stresses under the working loads are obtained by applying the methods of ‘strength of materials’ like the simple bending theory. The limitations due to non-linearity and buckling are neglected. The stresses caused by the ‘characteristic’ or service loads are checked against the permissible (allowable) stress, which is a fraction of the ultimate or yield stress. The permissible stress may be defined in terms of a factor of safety, which takes care of the overload or other unknown factors.
Prof. Durgesh Tupe 7 Limitations of Working Stress Method 1.The main assumption of a linear elastic behavior and the implied assumption that the stresses under working loads can be kept within the ‘permissible stresses’ are found to be unrealistic. Many factors are responsible for this, such as the long-term effects of creep and shrinkage and other secondary effects. 2.The use of the imaginary concept of modular ratio results in larger percentage of compression steel and generally larger member sizes than the members designed using ultimate load or limit states design. However, as a result of the larger member sizes, they result in better performance during service. 2) Ultimate Load Method (ULM) This is also known as load factor method or ultimate strength method. In this we make use of the nonlinear region of stress strain curves of steel and concrete. The safety is ensured by introducing load factor. “Load factor is the ratio of ultimate strength to the service loads” The ULM makes it possible to consider the effects of different loads acting simultaneously thus solving the shortcomings of WSM. As the ultimate strength of the material is considered we will get much slender sections for columns and beams compared to WSM method. But the serviceability criteria is not met because of large deflections and cracks in the sections. The fall-back in the method was that even though the nonlinear stress strain behaviour of was considered sections but the nonlinear analysis of the structural was not carried out for the load effects. Thus the stress distribution at ultimate load was just the magnification of service load by load factor following the linear elastic theory. 3) Limit State Method (LSM) In limit state design method, the structure shall be designed withstand safety. All loads likely to act on it throughout its life span. It shall not suffer total collapse under accidental load such as from explosion or impact or human error to an extend beyond the local damages. The acceptable limit for safety, serviceability requirement before failure occurs it called limit state. Steel structure are to be design and constructed to safety. The design requirement with regard to stability, strength, serviceability, brittle, fracture, fatigue, fire and durability such that they need the following points. a) Remain free adequate re-ability be able to sustain all loads. b) We have adequate durability under normal maintenance c) Do not suffer overall damage as collapse The current revision of the code of practice IS 800-2007 recommended limit state method for design of structure using hot rolled section.
Prof. Durgesh Tupe 8 Sl. No. Working Stress Method Limit State Method 1. This method is based on the elastic theory which assumes that concrete and steel are elastic and the stress strain curve is linear for both. This method is based on the actual stress-strain curves of steel and concrete. For concrete the stress-strain curve is non-linear. 2. In this method the factor of safety are applied to the yield stresses to get permissible stresses. In this method, partial safety factors are applied to get design values of stresses. 3. No factor of safety is used for loads. Design loads are obtained by multiplying partial safety factors of load to the working loads. 4. Exact margin of safety is not known. Exact margin of safety is known. 5. This method gives thicker, sections, so less economical. This method is more economical as it gives thinner sections. 6. This method assumes that the actual loads, permissible stresses and factors of safety are known. So it is called as deterministic method. This method is based upon the probabilistic approach which depends upon the actual data or experience, hence it is called as non-deterministic method. 7. Working stress method is also known as the plastic method Limit State method is also known as the Elastic design 8. In working stress method, the material follows Hooke’s law as stress is not allowed to cross the yield limit. Limit state method, stress is allowed to cross the yield limit. 9. This method gives more large sections, therefore less economical. This method is more economical since it gives thinner sections. 10 This method assumes that the actual loads, permissible pressures and factors of safety have been understood. So it's called a deterministic method. This way is based upon the probabilistic approach that depends upon the real data or expertise, thus it's referred to as a non-deterministic method.
Prof. Durgesh Tupe 9 Types of connection: The connection provided in steel structure can be classified as following 1) Riveted Connection 2) Bolted Connection 3) Welded connection 4) Pinned connection 1) Riveted Connection: Riveted connection absolute understanding of riveted connection is essential for strength, evaluation and rehabilitation of old structure. The analysis and design of riveted connection as that of bolted connection. 2) Bolted Connection: A bolt metal pin with a head at a one end and the shank is threaded at the outer end in order to receive a nut. Bolts are used for joining together piece of metal by inserting them through the bolts in metal and tightening the nut at the threaded end. 3) Welded connection: Welding is a process of joining to metal pieces at the faces. Render plastic by pressure or heat or both. 4) Pinned connection: When structural members are connected by means of cylindrical shape. Pin the connection is called pinned connection. Various types of standard rolled section: [1] Structural steel can be loaded into various shape and size usually having larger modular of section in proportion to their cross-section area are preferred [2] Steel sections are simply design by cross-sectional shape [3] The cross section and size are governing by a number of factor such as arrangement of material dimension and capacity of rolling meals and material properties 1. Rolled steel T-section:- [1] I.S.J.T. (I.S. Junior T-section) [2] I.S.N.T (I.S. Normal T-section) [3] I.S.H.T (I.S. Heavy T-section) T-section are used to transmit the bracket load to column as tension member. 2. Rolled steel Angle-section:- As per I.S. code angle section are divided into two category I. Equal angle section II. Unequal angle section It is denoted by I.S.A.
Prof. Durgesh Tupe 10
Prof. Durgesh Tupe 11 Types of loads on steels structure: 1) Dead Load: Dead loads are permanent and stationary load which are transferred to the structure thought there their life span. Dead load is primaralily due to self weight of structural member. Permanent partition wall fixed permanent equipment and weight of different material.
Prof. Durgesh Tupe 12 Plain concrete- 25 KN/m3 R.C.C concrete-25 KN/m3 Soil-18 KN/m3 Rolled steel-79 KN/m3 IS Code used for dead load is IS 875-1987 Part-I 2) Live Load : Live load are either moveable or moving load without any impact. These are assumed to be produced by the intended use or occupancy of the building including weight of movable portion. Live load is consider according to i.s.875 part-II. Sr.no Type of load Maximum live load 1 Residential building 2 KN/m2 2 Bank, office 3 KN/m2 3 Classroom assembly hall 4 KN/m2 4 Workshop, factory:- Light weight- Medium weight- Heavy weight- 5 KN/m2 7.5 KN/m2 10 KN/m2 3) Wind Load: Wind load basically horizontal load causes by movement of air. Wind load is required to be consider in the design specially when the height of building exceeds the two times of dimensions transferred to expose surface. Wind depend upon intensity of wind pressure and shape of structure in case of truss design two type of wind type of wind pressure considered 1) Internal air pressure:-it depend on permeability of structure 2) External air pressure:-it depend on location of structure Internal air pressure depends upon permeability of structure and external air pressure depends upon location. IS Code used for wind load is 875 part-III. 4) Earthquake Load: If structure is situated in earthquake prone area, earthquake load may be considered due to earthquake shock structure vibration. Earthquake load are horizontal load caused by earthquake and shall be calculated in accordance with IS 1983 and revised IS 2017.
Prof. Durgesh Tupe 13 5) Snow Load: This depend upon latitude of placed. Design snow load depends upon shape of roof and this load act vertically and this load can be taken as 2.5 KN/m2 per mm depends of snow. 6) Imposed Load: Imposed load caused by vibrator or impact or acceleration of person walking, produce live load but soldiers marching or frame supporting lifts produced impact load. Thus impact load is equal to imposed load incremental by some percentage depending on the intensity of impact. 7) Hydrostatic Pressure: Pressure of water is to be taken into account which are below the ground level. Hydrostatics pressure is calculated from established theories. 8) Temperature Effects: Due to change in temperature in structural member, extract or contract and produced the loading effects in member. Load Combination: The combination of the loads are necessary to ensure the required safety and economic design. Load combination as per IS 875 Part IV Dead Load (DL) Live Load (LL) Wind Load (WL) Earthquake Load (EL) Temporary Load (TL) Combination 1) 1.5 (DL + LL) 2) 1.2 (DL+LL+EL) 3) 1.2 (DL+LL-EL) 4) 1.5 (DL + EL) 5) 1.5 (DL - EL) 6) 0.9 DL+ 1.5 EL 7) 0.9 DL-1.5 EL etc.

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DSS UNIT 1 Introduction.pdf

  • 1. Prof. Durgesh Tupe 1 TY Civil Semester- V SEM V Course Category Cours e Code Course Title Teaching Scheme Evaluation Scheme Credit L T P CA MS E ES E Tota l PCC 10 BTCVC 501 Design of Steel Structures 2 1 - 20 20 60 100 3 PCC 11 BTCVC 502 Geotechnical Engineering 3 1 - 20 20 60 100 4 PCC 12 BTCVC 503 Structural Mechanics –II 2 1 - 20 20 60 100 3 PCC 13 BTCVC 504 Concrete Technology 2 - - 20 20 60 100 2 HSSMC3 BTHM505 Project Management 3 - - 20 20 60 100 3 PEC 1 BTCVPE506 A. Advanced Environmental Engg. B. Applied Geology C. Hydraulic Engineering Design D. Advanced Water Resources E. Geomatics F. Town and Urban Planning G. Material, Testing and Evaluation H. Construction Economics & Finance 3 - - 20 20 60 100 3 ESC10 BTCVES507 Software applications in Civil Engineering 2 - - 50 - - 50 Audit LC 7 BTCVL508 SDD of Steel Structures Lab. - - 2 20 - 30 50 1 LC 8 BTCVL509 Geotechnical Engineering Lab. - - 2 20 - 30 50 1 LC 9 BTCVL510 Concrete Technology Lab. - - 2 20 - 30 50 1 Internship BTCVP410 Internship – 2 Evaluation - - - - - - - Audit Total 17 3 6 230 120 450 800 21
  • 2. Prof. Durgesh Tupe 2 BTCVC 501 Design of Steel Structures Teaching Scheme: (2 Lectures + 1 Tutorial) hours/week Course Contents Module 1: Introduction and Connections (6 Lectures) Introduction, advantages & disadvantages of steel structures, permissible stresses, factor of safety, methods of design, types of connections, various types of standard rolled sections, types of loads and load combinations Types: Riveted, Bolted, Welded; Analysis of axially & eccentrically loaded connections (subjected to bending & torsion), Permissible Stresses, Design of connections, failure of joints Module 2: Axially Loaded Members (8 Lectures) Tension members: Common sections, net effective area, load capacity, connection using weld / bolts, design of tension splice Compression members: Common sections used, effective length and slenderness ratio, permissible stresses, load carrying capacity, connection using weld / bolt Beams: Laterally supported & unsupported beams, design of simple beams, built up beams using flange plates, curtailment of flange plates, web buckling & web crippling, secondary and main beam arrangement, beam to beam connections. Module 3: Industrial Roofing (8 Lectures) Gantry girder: Forces acting on a gantry girder, commonly used sections, introduction to design of gantry girder as laterally unsupported beam, connection details Roof trusses: Components of an industrial shed, types of trusses, load calculations and combinations, design of purlins, design of truss members, design of hinge & roller supports Module 4: Columns and Column Base (6 Lectures) Simple and built up section, lacing, battening, column subjected to axial force and bending moment, column splices. Column bases: Analysis and design of: Slab base, gusseted base and moment resisting bases, grillage foundation, design of anchor bolt
  • 3. Prof. Durgesh Tupe 3 Module 5: Introduction to Plastic Analysis and Limit State method (8 Lectures) Introduction to: Plastic Analysis, Hinge Formation, Collapse Mechanism, Recent approaches in Steel Structure design based on Plastic Analysis Method and Limit State Approach, Introduction to Provisions in IS 800-2007 Note: Contents in Module 1 to part of 4 shall be taught with help of relevant text or reference books based on elastic design concept and IS 800: 1984. Unit 5 shall be taught with reference to IS 800 2007 Use of IS 800: 1984 and 2007, IS 875 (All Parts), IS: Handbook No.1 for Steel Section and Steel Table is permitted for theory examination. Text Books • Duggal S. K., “Design of Steel Structures”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Gambhir, “Fundamentals of Structural Steel Design”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Negi L. S., “Design of Steel Structures”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Chandra Ram, “Design of Steel Structures”, Vol. I & Vol. II, Standard Book House, New Delhi • Dayaratnam P., “Design of Steel Structures”, Wheeler Publishing, New Delhi • Subramanian N., “Steel Structures: Design and Practice” Oxford Univ. Press, Delhi • Vazirani V.N. and Ratwani M.M., “Design and Analysis of Steel Structures”, ISBN NO: 978-81-7409-295-3 • Sai Ram K. S., “Design of Steel Structures”, Pearson Education, 2nd Edition Reference Books • Arya A. S. and Ajamani J.L., “Design of Steel Structures”, Nemchand and Brothers, Roorkee • Vazirani&Ratwani, “Design of Steel Structures”, Standard Book House, New Delhi • Duggal S. K., “Limit State Design of Steel Structures”, Tata McGraw Hill Pub. Co. Ltd., New Delhi • Publications of Bureau of Indian Standards, New Delhi, IS 800:1984, 2007, IS 875 (Part I to V) • Gaylord E.H. and Gaylord C.N., “Design of Steel Structures” McGraw Hill, New York • Lothers J.E., “Design in Structural Steel” Vol.-I, Prentice Hall New Jersy • Salmon and Johnson, “Steel Structures: Design and Behaviour”, Harper and Row, New York
  • 4. Prof. Durgesh Tupe 4 • Steel Designers Manual. Course Outcomes: On completion of the course, the students will be able to: CO1: Identify and compute the design loads and the stresses developed in the steel member.CO2: Analyze and design the various connections and identify the potential failure modes. CO3: Analyze and design various tension, compression and flexural members. CO4: Understand provisions in relevant BISCodes.
  • 5. Prof. Durgesh Tupe 5 Introduction A Civil Engineering Designer has to ensure that the structures and facilities he designs are (i) fit for their purpose (ii) safe and (iii) economical and durable. Thus safety is one of the paramount responsibilities of the designer. However, it is difficult to assess at the design stage how safe a proposed design will actually be – consistent with economy. There is, in fact, a great deal of uncertainty about the many factors, which influence both safety and economy. Firstly, there is a natural variability in the material strengths and secondly it is impossible to predict the loading, which a structure (e.g. a building) may be subjected to on a future occasion. Thus uncertainties affecting the safety of a structure are due to • uncertainty about loading • uncertainty about material strength and • uncertainty about structural dimensions and behaviour. These uncertainties together make it impossible for a designer to guarantee that a structure will be absolutely safe. All that the designer could ensure is that the risk of failure is extremely small, despite the uncertainties. Advantage of steel structure : 1. Steel member have high strength/unit weight 2. Steel being a ductile material does not fail suddenly but give visible evidence of independent failure by large deflection 3. Structural steel is tough i.e. they have both strength and ductility 4. Being light steel member can be easily handle and transport properly, steel structure have long life & property of steel mostly do not change 5. Addition and alteration can be made easily to structure 6. The steel can be erected at fast rate 7. Steel has highest scrap value among all building material 8. Steel is the ultimate recyclable material 9. Addition and alteration can be easily made to structure Disadvantage of steel structure : 1) Steel structure may be more costly than other type of structure 2) The strength of steel reduce subsequently when heated at temperature commonly observed in building fires, hence need fire proof treatment. 3) Steel structure exposed to air and water such as bridges are such suspectical to corrosion and needs regular maintainace.
  • 6. Prof. Durgesh Tupe 6 Permissible Stresses: The permissible stress is defined the ratio of yield stress to factor of safety. So as to keep the stresses within permissible value. Thus Yield Stress Permissible Stress = Factor of Safety Factor of Safety: The factor of safety is a termed describing the structural capacity of as steel beyond the expected load or actual load. The safety factor are often calculated using detailing analysis because compressive is impractical on many structures , such as bridges, buildings but the structure ability to carry load must be determine to responsible accuracy. Many systems are purposefully deal much stronger than needed for normal uses to alone for emergency situation, unaccepted load, needs or degradation. Factor of Safety is defined as yield stress to working stress Yield Stress Factor of Safety = Working Stress Methods of Design: The aim of design is to design, shape, size and connection details of the members so that the structural beam design will performed satisfactory during its right span. Following methods of design are used in steel structures 1) Working Stress Method (WSM) 2) Ultimate Load Method (ULM) 3) Limit State Method (LSM) 1) Working Stress Method (WSM) : Working Stress Method is the traditional method of design not only for Reinforced Concrete but also for structural steel and timber design. The conceptual basis of the WSM assumes that the structural material behaves in a linear elastic manner and that appropriate safety can be ensured by suitably limiting the stresses in the material due to the presumed working loads (service loads) on the structure. WSM also assumes that both the steel reinforcement and concrete act together and are perfectly elastic at all stages, and hence the modular ratio can be used to determine the stresses in steel and concrete. The stresses under the working loads are obtained by applying the methods of ‘strength of materials’ like the simple bending theory. The limitations due to non-linearity and buckling are neglected. The stresses caused by the ‘characteristic’ or service loads are checked against the permissible (allowable) stress, which is a fraction of the ultimate or yield stress. The permissible stress may be defined in terms of a factor of safety, which takes care of the overload or other unknown factors.
  • 7. Prof. Durgesh Tupe 7 Limitations of Working Stress Method 1.The main assumption of a linear elastic behavior and the implied assumption that the stresses under working loads can be kept within the ‘permissible stresses’ are found to be unrealistic. Many factors are responsible for this, such as the long-term effects of creep and shrinkage and other secondary effects. 2.The use of the imaginary concept of modular ratio results in larger percentage of compression steel and generally larger member sizes than the members designed using ultimate load or limit states design. However, as a result of the larger member sizes, they result in better performance during service. 2) Ultimate Load Method (ULM) This is also known as load factor method or ultimate strength method. In this we make use of the nonlinear region of stress strain curves of steel and concrete. The safety is ensured by introducing load factor. “Load factor is the ratio of ultimate strength to the service loads” The ULM makes it possible to consider the effects of different loads acting simultaneously thus solving the shortcomings of WSM. As the ultimate strength of the material is considered we will get much slender sections for columns and beams compared to WSM method. But the serviceability criteria is not met because of large deflections and cracks in the sections. The fall-back in the method was that even though the nonlinear stress strain behaviour of was considered sections but the nonlinear analysis of the structural was not carried out for the load effects. Thus the stress distribution at ultimate load was just the magnification of service load by load factor following the linear elastic theory. 3) Limit State Method (LSM) In limit state design method, the structure shall be designed withstand safety. All loads likely to act on it throughout its life span. It shall not suffer total collapse under accidental load such as from explosion or impact or human error to an extend beyond the local damages. The acceptable limit for safety, serviceability requirement before failure occurs it called limit state. Steel structure are to be design and constructed to safety. The design requirement with regard to stability, strength, serviceability, brittle, fracture, fatigue, fire and durability such that they need the following points. a) Remain free adequate re-ability be able to sustain all loads. b) We have adequate durability under normal maintenance c) Do not suffer overall damage as collapse The current revision of the code of practice IS 800-2007 recommended limit state method for design of structure using hot rolled section.
  • 8. Prof. Durgesh Tupe 8 Sl. No. Working Stress Method Limit State Method 1. This method is based on the elastic theory which assumes that concrete and steel are elastic and the stress strain curve is linear for both. This method is based on the actual stress-strain curves of steel and concrete. For concrete the stress-strain curve is non-linear. 2. In this method the factor of safety are applied to the yield stresses to get permissible stresses. In this method, partial safety factors are applied to get design values of stresses. 3. No factor of safety is used for loads. Design loads are obtained by multiplying partial safety factors of load to the working loads. 4. Exact margin of safety is not known. Exact margin of safety is known. 5. This method gives thicker, sections, so less economical. This method is more economical as it gives thinner sections. 6. This method assumes that the actual loads, permissible stresses and factors of safety are known. So it is called as deterministic method. This method is based upon the probabilistic approach which depends upon the actual data or experience, hence it is called as non-deterministic method. 7. Working stress method is also known as the plastic method Limit State method is also known as the Elastic design 8. In working stress method, the material follows Hooke’s law as stress is not allowed to cross the yield limit. Limit state method, stress is allowed to cross the yield limit. 9. This method gives more large sections, therefore less economical. This method is more economical since it gives thinner sections. 10 This method assumes that the actual loads, permissible pressures and factors of safety have been understood. So it's called a deterministic method. This way is based upon the probabilistic approach that depends upon the real data or expertise, thus it's referred to as a non-deterministic method.
  • 9. Prof. Durgesh Tupe 9 Types of connection: The connection provided in steel structure can be classified as following 1) Riveted Connection 2) Bolted Connection 3) Welded connection 4) Pinned connection 1) Riveted Connection: Riveted connection absolute understanding of riveted connection is essential for strength, evaluation and rehabilitation of old structure. The analysis and design of riveted connection as that of bolted connection. 2) Bolted Connection: A bolt metal pin with a head at a one end and the shank is threaded at the outer end in order to receive a nut. Bolts are used for joining together piece of metal by inserting them through the bolts in metal and tightening the nut at the threaded end. 3) Welded connection: Welding is a process of joining to metal pieces at the faces. Render plastic by pressure or heat or both. 4) Pinned connection: When structural members are connected by means of cylindrical shape. Pin the connection is called pinned connection. Various types of standard rolled section: [1] Structural steel can be loaded into various shape and size usually having larger modular of section in proportion to their cross-section area are preferred [2] Steel sections are simply design by cross-sectional shape [3] The cross section and size are governing by a number of factor such as arrangement of material dimension and capacity of rolling meals and material properties 1. Rolled steel T-section:- [1] I.S.J.T. (I.S. Junior T-section) [2] I.S.N.T (I.S. Normal T-section) [3] I.S.H.T (I.S. Heavy T-section) T-section are used to transmit the bracket load to column as tension member. 2. Rolled steel Angle-section:- As per I.S. code angle section are divided into two category I. Equal angle section II. Unequal angle section It is denoted by I.S.A.
  • 11. Prof. Durgesh Tupe 11 Types of loads on steels structure: 1) Dead Load: Dead loads are permanent and stationary load which are transferred to the structure thought there their life span. Dead load is primaralily due to self weight of structural member. Permanent partition wall fixed permanent equipment and weight of different material.
  • 12. Prof. Durgesh Tupe 12 Plain concrete- 25 KN/m3 R.C.C concrete-25 KN/m3 Soil-18 KN/m3 Rolled steel-79 KN/m3 IS Code used for dead load is IS 875-1987 Part-I 2) Live Load : Live load are either moveable or moving load without any impact. These are assumed to be produced by the intended use or occupancy of the building including weight of movable portion. Live load is consider according to i.s.875 part-II. Sr.no Type of load Maximum live load 1 Residential building 2 KN/m2 2 Bank, office 3 KN/m2 3 Classroom assembly hall 4 KN/m2 4 Workshop, factory:- Light weight- Medium weight- Heavy weight- 5 KN/m2 7.5 KN/m2 10 KN/m2 3) Wind Load: Wind load basically horizontal load causes by movement of air. Wind load is required to be consider in the design specially when the height of building exceeds the two times of dimensions transferred to expose surface. Wind depend upon intensity of wind pressure and shape of structure in case of truss design two type of wind type of wind pressure considered 1) Internal air pressure:-it depend on permeability of structure 2) External air pressure:-it depend on location of structure Internal air pressure depends upon permeability of structure and external air pressure depends upon location. IS Code used for wind load is 875 part-III. 4) Earthquake Load: If structure is situated in earthquake prone area, earthquake load may be considered due to earthquake shock structure vibration. Earthquake load are horizontal load caused by earthquake and shall be calculated in accordance with IS 1983 and revised IS 2017.
  • 13. Prof. Durgesh Tupe 13 5) Snow Load: This depend upon latitude of placed. Design snow load depends upon shape of roof and this load act vertically and this load can be taken as 2.5 KN/m2 per mm depends of snow. 6) Imposed Load: Imposed load caused by vibrator or impact or acceleration of person walking, produce live load but soldiers marching or frame supporting lifts produced impact load. Thus impact load is equal to imposed load incremental by some percentage depending on the intensity of impact. 7) Hydrostatic Pressure: Pressure of water is to be taken into account which are below the ground level. Hydrostatics pressure is calculated from established theories. 8) Temperature Effects: Due to change in temperature in structural member, extract or contract and produced the loading effects in member. Load Combination: The combination of the loads are necessary to ensure the required safety and economic design. Load combination as per IS 875 Part IV Dead Load (DL) Live Load (LL) Wind Load (WL) Earthquake Load (EL) Temporary Load (TL) Combination 1) 1.5 (DL + LL) 2) 1.2 (DL+LL+EL) 3) 1.2 (DL+LL-EL) 4) 1.5 (DL + EL) 5) 1.5 (DL - EL) 6) 0.9 DL+ 1.5 EL 7) 0.9 DL-1.5 EL etc.