/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 11 A two-axle carriage that is part... [FREE SOLUTION] | 91Ó°ÊÓ

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A two-axle carriage that is part of an overhead traveling crane in a testing laboratory moves slowly across a simple beam \(A B\) (see figure). The load transmitted to the beam from the front axle is \(9 \mathrm{kN}\) and from the rear axle is \(18 \mathrm{kN} .\) The weight of the beam itself may be disregarded. (a) Determine the minimum required section modulus \(S\) for the beam if the allowable bending stress is \(110 \mathrm{MPa}\) the length of the beam is \(5 \mathrm{m},\) and the wheelbase of the carriage is \(1.5 \mathrm{m}\) (b) Select the most economical I-beam (IPN shape) from Table E-2, Appendix E.

Short Answer

Expert verified
Required section modulus is approximately 122.73 cm³. Select an I-beam with a section modulus greater than this value.

Step by step solution

01

Identify Key Values

First, identify and list the provided values: - Front axle load: 9 kN - Rear axle load: 18 kN - Allowable bending stress: 110 MPa - Beam length: 5 m - Carriage wheelbase: 1.5 m.
02

Determine Reaction Forces

When the front or rear axle is located at any point along section AB, the maximum moments occur when one axle is at the support and the other is on the beam. The beam reactions when the loads are produced across whole beam are not required; we use the loads being directly under the support.
03

Calculate Maximum Bending Moment

For maximum bending, the front axle should be at one support and the rear axle 1.5 m away from it.Use the formula for maximum moment:\[M_{max} = 9 \, \mathrm{kN} \cdot 1.5 \,\mathrm{m} = 13.5 \, \mathrm{kNm}\]Convert to Newton-meter:\[M_{max} = 13,500 \, \mathrm{Nm}\]
04

Calculate Minimum Required Section Modulus, S

Using the formula for the section modulus:\[S = \frac{M_{max}}{\sigma_{allowable}}\]Substitute the values:\[S = \frac{13,500}{110} \approx 122.73 \, \mathrm{cm^3}\]
05

Select an I-beam

Select an I-beam from Table E-2, which has a section modulus greater than or equal to 122.73 cm³. A suitable beam choice might be a beam with section modulus close to but more than 122.73 cm³.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Section Modulus
The section modulus is a critical parameter in the design of beams subjected to bending. It is a measure that represents the strength of a beam's cross-section. The section modulus is calculated as the ratio of the beam's bending moment capacity to the bending stress that it can withstand. This value is vital for ensuring that the beam does not exceed its allowable stress under load.
Given a maximum bending moment, the section modulus can help in determining the minimum dimensions and shape of a beam needed to safely support loads without bending excessively. The formula used to find the minimum required section modulus is: \[ S = \frac{M_{max}}{\sigma_{allowable}} \]Where:
  • \( S \) is the section modulus.
  • \( M_{max} \) is the maximum bending moment.
  • \( \sigma_{allowable} \) is the allowable bending stress.
This gives engineers a straightforward calculation to assess and select appropriate beam sizes, keeping construction materials efficient and cost-effective.
Bending Stress
Bending stress occurs in a structural element when a bending moment is applied to it. This stress can lead to the distortion or failure of the structure if it exceeds the material's capacity to withstand it.
Bending stress is determined by the internal forces and the cross-sectional dimensions of the beam. It is typically calculated using the formula:\[ \sigma_{bending} = \frac{M}{S} \]Where:
  • \( \sigma_{bending} \) is the bending stress.
  • \( M \) is the moment applied to the beam.
  • \( S \) is the section modulus.
In overhead crane design, ensuring that bending stress remains below the allowable limit is crucial for maintaining structural integrity. This balance ensures safety and performance while preventing material fatigue over repeated use.
Overhead Crane Design
Overhead cranes are sophisticated pieces of equipment used in many industrial and laboratory settings for lifting and moving heavy loads. The design of these cranes involves careful consideration of several factors, including load capacities, mechanics, and structural elements like the beams.
An integral part of overhead crane design is the appropriate selection and analysis of the beam that carries and distributes the load. Designing for optimum performance involves understanding:
  • The maximum loads the crane will bear.
  • The configuration and span of the moving gantry.
  • The impact of moving loads on bending moments across the beam.
Designing for an overhead crane involves not just ensuring material strength but also optimizing the efficiency and safety of operations across its work area.
Structural Engineering
Structural engineering is a field of engineering focusing on the design and analysis of structures that must withstand loads and environmental forces. Engineers in this field apply physics and mathematical principles to ensure structures do not fail under stress.
Every structure is subject to various forces, such as compression, tension, bending, and shear. The primary goal is to create a robust framework that maintains safety and functionality. Concepts such as section modulus and bending stress are pivotal in evaluating if a beam or frame will suffice under specified loading conditions.
Considerations in structural engineering include:
  • Selecting appropriate materials and cross-sections for structural members.
  • Calculating the internal forces and moments in structural elements.
  • Conducting safety and serviceability checks to prevent failures.
Understanding these principles ensures that designs meet regulatory requirements and suit operational purposes.

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Most popular questions from this chapter

A wood beam \(A B C\) with simple supports at \(A\) and \(B\) and an overhang \(B C\) has height \(h=300 \mathrm{mm}\) (see figure). The length of the main span of the beam is \(L=3.6 \mathrm{m}\) and the length of the overhang is \(L / 3=1.2 \mathrm{m}\). The beam supports a concentrated load \(3 P=18 \mathrm{kN}\) at the midpoint of the main span and a moment \(P L / 2=10.8 \mathrm{kN} \cdot \mathrm{m}\) at the free end of the overhang. The wood has weight density \(\gamma=5.5 \mathrm{kN} / \mathrm{m}^{3}\) (a) Determine the required width \(b\) of the beam based upon an allowable bending stress of \(8.2 \mathrm{MPa}\) (b) Determine the required width based upon an allowable shear stress of \(0.7 \mathrm{MPa}\)

\mathrm{A}\( simple beam \)A B\( of span length \)L=7 \mathrm{m}\( is subjected to two wheel loads acting at distance \)d=1.5 \mathrm{m}\( apart (see figure). Each wheel transmits a load \)P=14 \mathrm{kN}\( and the carriage may occupy any position on the beam. (a) Determine the maximum bending stress \)\sigma_{\max }\( due to the wheel loads if the beam is an I-beam having section \\[ \text { modulus } S=265 \mathrm{cm}^{3} \\] (b) If \)d=1.5 \mathrm{m},\( find the required span length \)L\( to reduce the maximum stress in part (a) to \)124 \mathrm{MPa}\(. (c) If \)L=7 \mathrm{m}\(, find the required wheel spacing \)s\( to reduce the maximum stress in part (a) to \)124 \mathrm{MPa}$.

Each girder of the lift bridge (see figure) is \(50 \mathrm{m}\) long and simply supported at the cnds. The design load for each girder is a uniform load of intensity \(18 \mathrm{kN} / \mathrm{m}\). The girders are fabricated by welding three steel plates so as to form an I-shaped cross section (see figure) having section modulus \(S=46,000 \mathrm{cm}^{3}\) What is the maximum bending stress \(\sigma_{\max }\) in a girder due to the uniform load?

A short column of wide-flange shape is subjected to a compressive load that produces a resultant force \(P=55 \mathrm{kN}\) acting at the midpoint of one flange (see figure). (a) Determine the maximum tensile and compressive stresses \(\sigma_{t}\) and \(\sigma_{c},\) respectively, in the column. (b) Locate the neutral axis under this loading condition. (c) Recompute maximum tensile and compressive stresses if a \(120 \mathrm{mm} \times 10 \mathrm{mm}\) cover plate is added to one flange as shown.

A plain concrete wall (i.e., a wall with no steel reinforcement) rests on a secure foundation and serves as a small dam on a creek (see figure). The height of the wall is \(h=2 \mathrm{m}\) and the thickness of the wall is \(t=0.3 \mathrm{m}\). (a) Determine the maximum tensile and compressive stresses \(\sigma_{i}\) and \(\sigma_{c},\) respectively, at the base of the wall when the water level reaches the top \((d=h) .\) Assume plain concrete has weight density \(\gamma_{c}=23 \mathrm{kN} / \mathrm{m}^{3}\). (b) Determine the maximum permissible depth \(d_{\max }\) of the water if there is to be no tension in the concrete.

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