Steel Structures: Purlin Design Quiz

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Questions and Answers

What is the primary function of purlins in steel structures?

To anchor vertical columns

To distribute dead loads on the foundation

To carry roof sheeting and cladding (correct)

To support lateral loads in bending and shear

What spacing is recommended for the channel sections to be used as purlins in the given design?

6 meters

2 meters (correct)

1 meter

4 meters

What is the maximum slope angle for which the frame may be analyzed as a rectangular single portal frame structure?

6°

5°

12°

10° (correct)

Which materials constitute the dead load and imposed load on the purlin design?

0.45 kN/m² and 0.75 kN/m² respectively Signup and view all the answers

In the context of steel purlins, what is meant by 'conservative design details'?

Designs that provide extra strength against unexpected loads Signup and view all the answers

What are beams primarily used to resist?

Bending, shear, and deflections Signup and view all the answers

Which type of beam is characterized by having one end fixed and the other supported?

Fixed supported beam Signup and view all the answers

What type of buckling can occur in the projecting flange of an I-beam?

Lateral buckling Signup and view all the answers

Which of the following is NOT a type of beam mentioned?

L-shaped beam Signup and view all the answers

What factor is most crucial in ensuring the serviceability of a beam under imposed loads?

Deflection limits Signup and view all the answers

Which material is specified for the design of the beam in the example?

S275 steel Signup and view all the answers

What is the design moment (M) given for the example beam?

585 kNm Signup and view all the answers

What value is taken as Young’s modulus (E) in the example?

205 kN/mm² Signup and view all the answers

What is the calculated ultimate design load (w) for the given purlin design?

21.96 kN Signup and view all the answers

What is the moment (M) calculated for the given loads and span?

16.47 kNm Signup and view all the answers

What shear capacity (Pv) was determined based on the given shear area (Av)?

136.13 kN Signup and view all the answers

What is the result of checking the moment capacity against the plastic modulus?

The section is adequate. Signup and view all the answers

What determines whether the shear is classified as low or high shear?

If Fv is less than or greater than 0.6Pv. Signup and view all the answers

Which value of d/t indicates section classification?

19.3 Signup and view all the answers

What is the value used for calculating the design moment capacity (Mc) for class 1 plastic?

36.3 kNm Signup and view all the answers

What is the deflection limit for the given span, according to the specifications?

30 mm Signup and view all the answers

What is the value of w, when calculated for the UDL from the ultimate design load?

3.66 kN/m Signup and view all the answers

What was the basis for determining the shear area related to the shear capacity?

Av = tD Signup and view all the answers

What is the calculated shear capacity, $P_v$, for the given steel section?

888.41 kN Signup and view all the answers

What is the condition for determining if shear is considered low?

If $F_v < 0.6P_v$ Signup and view all the answers

What is the $d/t$ ratio in this instance, and is it necessary to check for shear buckling?

$47.2$ and no Signup and view all the answers

Which statement about moment capacity, $M_c$, is true for a simply supported beam?

$M_c$ must exceed $M_x$ for serviceability Signup and view all the answers

What is the formula used to determine the moment capacity, $M_c$?

$M_c = p_y S_x$ Signup and view all the answers

At the center of the beam, what is the calculated value of $F_{vc}$?

67.8 kN Signup and view all the answers

What is the basis for determining whether the web bearing capacity is adequate?

$F_x < P_{bw}$ Signup and view all the answers

What is the value of $M_{cx}$ calculated for moment capacity, and is it adequate?

649 kNm, adequate Signup and view all the answers

What is the basic requirement to determine the buckling resistance of the unstiffened web?

Fx ≤ Px Signup and view all the answers

If Fx is 136kN and Px is 472.73kN, what conclusion can be drawn regarding buckling resistance?

The buckling resistance is adequate. Signup and view all the answers

What is the value of the bearing capacity of the unstiffened web?

296.08kN Signup and view all the answers

Calculate the maximum allowable deflection if the limit is set to 18.1mm.

8.69mm Signup and view all the answers

Which material and grade is used for the beam design mentioned in the homework?

Steel grade S275 Signup and view all the answers

What load value represents the imposed point load Wi in the deflection calculation?

50kN Signup and view all the answers

What is the formula used to calculate deflection under the given serviceability loads?

$rac{wiL^4}{384EI} + rac{WiL^3}{48EI}$ Signup and view all the answers

What is the significance of 25εt in the buckling resistance formula?

It is the thickness of the unstiffened web. Signup and view all the answers

What is the main reason compression members must be stocky?

To resist buckling Signup and view all the answers

Which type of section is considered ideal for compression members?

Tubular (hollow) sections Signup and view all the answers

What is the formula to calculate slenderness ($λ$) of a column?

$λ = L / r$ Signup and view all the answers

What does the radius of gyration indicate?

The elastic stability of a cross-section Signup and view all the answers

Which of the following is a requirement for the slenderness ratio just before a column is considered safe?

$λ$ must not exceed 180 Signup and view all the answers

In buckling analysis, which radius of gyration value should be used?

Least value of the radius of gyration Signup and view all the answers

The effective length of a compression member is determined by which factors?

Actual length and positional restraints Signup and view all the answers

What is a universal column (H-section) primarily used for?

As a compression member Signup and view all the answers

Study Notes

Steel and Timber Design Lecture Notes

Lecture 2: Covers steel purlins and steel beams. Steel structures are primarily comprised of purlins (roof sheeting and cladding carriers) and beams/girders (supporting lateral loads in bending and shear).
Rolled and Formed Sections: Different types of steel sections are presented, including Universal beams, Universal columns, parallel flange channels, equal angles, unequal angles, structural tees, circular hollow sections, square hollow sections, and rectangular hollow sections. Specific dimensions and ranges are provided for each section type.
Purlins: Cold rolled sections, angles, channels, joists, and structural hollow sections are common purlin types. These parts are used for roof support and sheeting rails. Diagrams depict typical purlin roof layouts, including sheeting, insulation, decking, and ceiling systems for sloping and flat roofs. Purlin spacing (s) is discussed, as well as sag rods and roof trusses. Force diagrams (normal and tangential) show important design details for purlins.
Purlins: Angle at full plasticity: Diagrams show the centroid of the compression area, the eccentricity section, and stress distribution for purlins at full plasticity. Diagrams illustrate the layout of typical anti-sag ties and eaves beam struts.
Question (Lecture 2): The student needs to design a purlin (a steel support beam for a roof deck) in S275 steel for a given single portal frame structure. The question specifies column/rafter spacing, purlin spacing, roof angle, and imposed/dead loads.
Lecture 2 (beams): Beams are horizontal members mainly horizontal supporting structures. They are often used to support floors and columns and carry roof sheeting. Cantilevered, simply supported, fixed-ended and continuous are various support types for beams. Section types such as universal beam, compound beam, channel, and rectangular hollow section are presented. Force diagrams show bending moment diagrams for simple and fixed beams. Important considerations are provided on web and flange buckling.
Stress-Strain Curve: Explains elastic limit, yield point, ultimate tensile strength, necking, and breaking stress for materials.
Question (Lecture 2, beams): The question for beam design gives a fully restrained beam with specified support and point load conditions. Given conditions (serviceability loads, materials, and specified moments) are used to design the part. The provided question involves the design of a beam.
Lecture 3, column design: Explains columns as structural components under axial load and bending. Discusses types of columns (universal columns, built-up, box columns). Includes strut sections used in trusses, lattices, girders, and bracing. There is information on column connections in factory, and single or multi-story buildings. Notes identify different types of crane columns (uniform, laced, compound). Provides the idea of classification of cross-sections. Explains concepts of effective lengths (and K).
Column Design Procedure/Question: Steps the student should follow for column determination and adequacy checks are outlined. A question to design a column is laid out.
Lecture 4, continued column design: Covers column design for axial load and bending in both directions in continuous structures.
Question 1 (Lecture 4, continued column design): Students design a column subjected to axial and factored concentric bending moments. This part is related to a continuous column. The column's adequacy must be verified, and S275 steel is specified.
Lecture 5, tension members: The design process of tension members should be carried out. The tension capacity is primarily determined by material properties, hole presence, and connection eccentricity. The various types of tension members involved are mentioned. Connections, including threaded bars, angle connections, bolted splices, and welded splices, are explained.
Summary of Tension Member Design Procedure: Steps that are important to take in designing tension members are laid out. This covers selecting the section and its grade, calculating gross, net, and effective areas, and determining tension capacity. It also covers applying the required approach for eccentric connections and combined tension-bending.
Question 3 (Lecture 5, tension members): Design a single angle in S275 steel that can carry a given dead and imposed load through a specified leg. Bolted and welded connections are taken into consideration, and a suitable shape, along with its required dimensions, is decided upon.
Example 1 (Bolted Connections): The question specifies a lap joint with four 20mm diameter Grade 8.8 bolts. Students check minimum spacing, maximum spacing, clearance holes, minimum end/edge distances, bolt shear capacity, bolt bearing, plate bearing, block shear, and plate tension capacity. This section covers the required design based on the specified loads and properties.
Example 2 (Welded Connections): A 65x50x5 angle tie is welded to a gusset plate, receiving dead and imposed loads of 50kN and 60kN respectively. Students design suitable 6mm fillet welds, taking the centroid and shear forces into account, and calculate effective welding length.
Lecture 6, Connections: Covers bolted connections (bolt strengths, assembly details, bolt types and terms) and welded connections (fillet and butt welds, quality inspection and classification methods), and describes the advantages and disadvantages of both types of connections. The distinctions between simple, continuous, and semi-continuous connection designs are explained. Diagrams illustrate essential beam-to-column connection types (portal beam moment-resisting connection). Column-to-beam joint details are described with accompanying diagrams. Diagrams illustrate beam-to-column simple connections (portal beam). Information is provided on welded connections and gusset plate connections. Notes summarize the benefits and drawbacks of bolted and welded connections.
Lecture 7, column bases: Introduces column bases, explains their purpose and the different types (slab, gusset, pocket bases), and differentiates between fixed and pinned bases. Provides information about design considerations for base plates, holding-down (anchor) bolts, and the concrete bedding material for column bases. Illustrates these different styles and their applications.

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Description

Test your knowledge on the critical role of purlins in steel structures. This quiz covers functional characteristics, recommended spacing, slope analysis for portal frames, and load considerations. Explore the details of conservative design practices in purlin applications.