mod 1

Flange vs Web

Flange is the top/down part, web is the middle part.

Duggal¶

A steel structure is an assemblage of a group of members (elements) expected to sustain their share of applied forces and to transfer them safely to the ground. Depending on the orientation of the member in the structure and its structural use, the member is subjected to forces, either axial, bending, or torsion, or a combination thereof. Axial load can be either tensile or compressive, and accordingly the members are called tension members or compression members. An example of a tension member is a tie and that of a compression member is a strut. These are used in trusses. Another example of a compression member is a column or post used in buildings. Primarily, all the steel structures are constructed with elements such as tension members—members subjected to tensile forces; compression members—members subjected to compressive forces; or flexural members—members subjected to bending. The elements of a steel structure, as discussed above, are rolled to a basic cross section in a mill, and worked to the desired size and form in a fabricating shop or site. These elements are connected by using rivets, bolts, pins or welds to form the structure, and the connections so formed are called joints. Depending upon the fixity provided, the connections are classified as rigid—can transfer moments; flexible—can transfer axial loads (shears); or semi-rigid—that fall in between rigid and flexible.

The main advantages of steel structures are their smaller weight-to-strength ratio, speed of erection and dismantling, and its scrap value. However, the faster degradation of their strength in the events of fire, requirement of skilled, personnel and the accuracy desired in fabrication are the major drawbacks.

Steel, as a building, material, has been used extensively in various types of structures. Some of the examples of civil engineering works in steel are high-rise building skeletons, industrial buildings, transmission towers, railway bridges, overhead tanks, chimneys (stacks), bunkers and silos. Figure 1.1 illustrates some of the typical steel structures. Steel structures can be divided into two principal groups:

simple civil tamil¶

Theory¶

1) Explain the advantages and disadvantages of steel as a structural material

Advantages of Steel as a Structural Material: * High strength and durability * Versatile and can be customized to fit different designs and applications * Fire-resistant * Low maintenance * Resistant to environmental factors such as moisture and pests * Recyclable and sustainable * Faster construction time due to prefabrication * High load-bearing capacity * Improved seismic resistance * Reduced foundation requirements * Lightweight compared to other materials * Better quality control due to standardized manufacturing processes * Good aesthetic appeal * Resistant to termite and other pest attacks * Longer lifespan compared to other materials

Advantages of Steel as a Structural Material: * High cost compared to other building materials * Corrosion can occur over time * Vulnerable to rust in certain environments * Can be affected by extreme temperatures * Poor insulation properties * High thermal conductivity * Conducts electricity which can be dangerous in some situations * Prone to fatigue and stress fractures over time * Heavy and difficult tonove on-site * Requires skilled labour for fabrication and installation * Sound transmission can be an issue * Not suitable for some historical or traditional building styles * More complex fireproofing and insulation requirements * Limited design flexibility due to weight restrictions * Risk of galvanic corrosion when used with other metals.

2) Explain the type of loads on structures and load combinations. (AU-Nov/Dec-2021/Reg-2017) (AU-Nov/Dec-2021/Reg-2017)

Refer IS800-2007, C.3.2, and Page. No: 15

3) Compare working stress method and limit state design method for steel structures. (8Marks) (AU-Nov/Dec-2021/Reg-2017)

Working Stress Method (WSM):

Definition: The working stress method is a traditional design approach that assumes the material is behaving elastically and limits the maximum permissible stress to a fraction of the yield stress of the material.

Merits: * The design process is simple and easy to understand. * The method is well-established and widely used in India. * It is cost-effective compared to other design methods. * The design is based on actual stress and strain distribution in the material. * The method considers the uncertainty associated with material properties.

Demerits: * The method does not account for material strgin hardening. * The design is based on out-dated engineering practices and does not reflect the latest research and understanding of materials. * The method does not consider the ultimate strength of the material. * The method is not as accurate as other modern design methods. * The method is not suitable for complex and large-scale structures.

Limit State Method (LSM)

Definition: The limit state method is a modern design approach that considers the ultimate limit state (ULS) and serviceability limit state (SLS) of a structure. The method assumes that the material behaves plastically and uses a partial safety factor to account for uncertainties in the design process.

Merits: * The method is more realistic as it accounts for the actual material properties and the behaviour of the structure under load. * The method considers both the ultimate and serviceability limit states. * The method uses a partial safety factor to account for uncertainties in the design process. * The method is more accurate than other traditional design methods. * The method is suitable for complex and large-scale structures.

Demerits: * The design process is more complex and requires more advanced analysis methods. * The method is more expensive than other traditional design methods. * The method requires a better understanding of material properties and the behaviour of the structure under load. * The method is not well-established in some countries. * The method may require more time and effort to obtain design results.

4) Explain the mechanical properties of structural steel. (AU-Nov/Dec-2021/Reg-2017)

(page no. 12 IS800 2007)

The values of some mechanical properties of structural steel as per IS800-2007:

Fe 250 grade steel: - Minimum yield strength (f,): 250 MPa - Minimum ultimate tensile strength (f,): 410 MPa - Minimum percentage elongation: 23% - Modulus of elasticity (E): 2.1 x 10° MPa - Poisson's ratio (u): 0.3

Fe 415 grade steel: - Minimum yield strength (fy): 415 MPa - Minimum ultimate tensile strength (fu): 485 MPa - Minimum percentage elongation: 14.5% - Modulus of elasticity (E): 2.1 x 10° MPa - Poisson's ratio (u): 0.3

5) Write notes on partial safety factors for loads with respect to strength and serviceability and partial safety for materials for limit state method. (AU-April/May-2022/Reg-2017)

Definition: (Partial safety factor)
Refer C.1.3.69, Pg.No-4, 1IS800-2007

Partial safety factors for loads with respect to strength and serviceability
Refer C.5.2.1 & 5.2.2 and T-4, Pg.No-28, 1S800-2007

Partial safety for materials
Refer C.5.4.1, Pg.No-30, 1S800-2007

6) What is mean by hot rolled sections? List out any five numbers of hot rolled section with neat sketch and mark their salient feature. (AU-April/May-2022/Reg-2017)

Hot rolled sections refer to steel sections that are made by rolling heated steel billets or blooms through a series of rollers to shape them into the desired cross- section. These sections are commonly used in the construction of steel structures due to their high strength and durability. Here are five commonly used hot rolled sections:

I-Beams (ISMB) (1):

I = Indian, S = Standard, M = Medium (could be L/Light or H/Heavy), B = Beam

I-beams are used for structural applications such as beams and columns. They have a wide flange and a narrower web (1), giving them a distinctive "I" shape.

Salient features include:

High strength-to-weight ratio
Efficient use of material
Can support heavy loads

Channels (ISMC):

Channels are used for various applications such as framing, supports, and bracing. They have a C-shaped cross-section with a wide flange and a shorter web. Salient features include:

Good torsional resistance
Can be used for Iightweigh't applica'tions
High bending strength

Angles (ISA)

Angles are used for various applications such as supports, braces, and lintels. They have an L-shaped cross-section with equal or unequal legs. Salient features include:

High strength-to-weight ratio
Can be used for both compression and tension loads
Versatile in their use

Round Bars (ISCR):

T Round—bars—are used for various applications such as shafts, axles, and fasteners. They have a circulzr cross-section and come in various diameters. Salient features include:

High tensile strength
Can be easily machined
Good ductility

Flat Bars (ISFL):

Flat bars are used for various applications such as supports, braces, and frames. They have a rectangular cross-section with a flat surface and come in various widths and thicknesses. Salient features include:

Easy to fabricate and weld
High tensile strength
Can be used for both compression and tension loads

Sketches with salient features:
Figure.2 Pg.No19 IS800-2007

Problems¶

⚡ Problem 1¶

Solution 1Solution 2

The welded section shown below is used as column of 3.5m height. Calculate the permissible compression load, according to the allowable stress method of section 11 in the code.

Answer:

Effective length = Height = KL = 3.5m = 3 x 10^3 mm

Solution:

We are asked to find the permissible compression load. We know there is a formula formula for finding actual compressive stress in page 84 of codebook.

Actual compressive stress (IS800, C.11.3.1, Pg. No: 84)

Actual compress stress fc = Ps / Ae
Permissive compressible sterss = fac = 0.60fcd

where Ae = Effective sectional area
fcd = design compressive stress

We see that there are multiple tables to find out fcd, namely for buckling class a, b, c and d resptively. All these tables show that as a pre-requisite to finding out fcd (design compressive stress) we need to know KL/r and yield stress fy. We know that the yield stress for steel if 250N/mm2.

To find out the buckling class we need to refer to table no 10 (the page right after all these tables).

We know that we have a welded I section:

The thickness of the flange is 8 mm, which is less than 40. So along the zz axis we have buckling class b and along the yy axis we have buckling class c.

What about the critical axis. The critical axis is gonna be

But y is the critical axis, hence the buckling clas is C.

Now we know we should use table c.

Actual compressive stress: Mentioned in page 84 of book.

⚡ Problem 2¶

source: https://www.youtube.com/watch?v=NUujcJYErwM