Name: safety factors in structural design
Uploaded: 2024-03-07T13:22:33.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Human Sustainability

3.3.9-12.O

Design Consideration

בעת תכנון מבנה, השיקולים מתחילים בחוזק הסופי של החומר, אשר נקבע באמצעות בדיקות, מדידת שינויים תחת עומס מוגבר עד שהוא מגיע לקצה גבול היכולת שלו או נשבר.
העומס המקסימלי שמעבר לו נשבר החומר הוא העומס האולטימטיבי. היחס בין העומס האולטימטיבי לאזור החתך המקורי מספק את הלחץ הנורמלי האולטימטיבי או את הכוח האולטימטיבי.
שיקול חשוב נוסף הוא גורם הבטיחות, שהוא היחס בין העומס האולטימטיבי למותר, המבטיח עתודה של יכולת נשיאת מטען לפעולה בטוחה.
גורם בחירת הבטיחות כרוך בהתחשבות בשינויים בתכונות החומר, עומסים, סוגי כשל פוטנציאליים, אי ודאויות בשיטות אנליטיות, הידרדרות עתידית, חשיבות מבנית וסיכון לחיים ולרכוש.
שיטת הלחץ המותרת הקונבנציונלית מקבצת את כל אי הוודאות לגורם בטיחות אחד, אך שיטה חלופית הנקראת שיטת תכנון גורמי עומס והתנגדות מבחינה בין אי ודאויות הקשורות למבנה לבין העומס שלו ומבדילה בין עומסים חיים ומתים.

שיקול עיצובי

<div style="direction: rtl;">
תכנון מבנה כרוך בשורה של שיקולים, בעיקר החוזק הסופי של החומר, המחושבים באמצעות בדיקות המודדות שינויים בכוח מוגבר עד שהחומר מגיע לנקודת השבירה או הגבול שלו. העומס האולטימטיבי, שבו החומר נשבר, מחולק לפי שטח החתך המקורי שלו, וכתוצאה מכך המתח או החוזק הנורמליים האולטימטיביים. מתח הגזירה האולטימטיבי הוא גורם משמעותי נוסף שנלקח בחשבון.

גורם הבטיחות הוא היבט מרכזי נוסף המקשר בין העומס הסופי לעומס המותר. הוא מבטיח חיץ ביכולת נשיאת העומס לפעולה בטוחה. בחירת גורם הבטיחות דורשת התחשבות בשונות בתכונות החומר, סוגים שונים של כשל פוטנציאלי, אי ודאות בשיטות אנליטיות, הידרדרות עתידית, חשיבות מבנית וסיכון לחיים ולרכוש. גורם בטיחות קטן מדי מסתכן בכשל, בעוד שגורם גדול מדי יכול לגרום לתכנונים לא כלכליים או לא פונקציונליים.

באופן מסורתי, נעשה שימוש בשיטת המתח המותר, המגבשת את כל אי הוודאות לגורם בטיחות אחד. עם זאת, שיטה חלופית, שיטת עיצוב פקטור עומס והתנגדות (Load and Resistance Factor Design), מבדילה בין אי ודאויות הקשורות למבנה ולעומס שלו ומבחינה בין עומסים חיים ומתים. 
</div>

בעת תכנון מבנה, השיקולים מתחילים בחוזק הסופי של החומר, אשר נקבע באמצעות בדיקות, מדידת שינויים תחת ...

Education

JoVE Core

Mechanical Engineering

הנדסת מכונות

Unit 1

יחידה 1

Concept of Stress

מושג הלחץ (Stress)

KEY TERMS AND CONCEPTS

מונחים ומושגי מפתח

safety factors in structural design

Safety factors in structural design help engineers choose a material and loading limit that can be used safely. The process begins with a material’s ultimate strength. This value comes from tests that increase force until the material reaches its breaking point or limit.

The ultimate load is then divided by the original cross-sectional area to find the ultimate normal stress, or strength. Ultimate shearing stress is another key value used in design. These limits show how much stress a material can resist before failure.

A factor of safety compares the ultimate load with the allowable load. It creates a buffer in load-carrying capacity for safe operation. Choosing this factor requires attention to changes in material properties, possible failure modes, uncertainty in analysis, future deterioration, structural importance, and the risk to life and property.

If the factor of safety is too small, the structure may fail. If it is too large, the design may become uneconomical or unusable. The traditional allowable-stress method combines the uncertainties into one safety factor. The Load and Resistance Factor Design method separates uncertainties in the structure and in the load, and it also distinguishes between live loads and dead loads.

Safety Factors in Structural Design

normal stress

Normal Stress in Axial Loading

Normal stress acts perpendicular to a material’s cross-sectional area. It appears when a force is applied along the axis of an object, which is called axial loading. Bridge truss members are a practical example of this kind of loading. When a rod carries axial load, internal forces develop across the section. Because these forces act normal to the plane of the section, the stress is called normal stress. Stress here means the average stress over the whole cross-section, not the value at one...

shearing stress

Shear Forces in Bolts and Rivets

Shearing stress is caused by transverse forces acting on an object. These forces create internal forces in the plane where the external forces are applied. The total internal force in that section is called the shear. Average shearing stress is found by dividing the shear by the cross-sectional area. This value is only an average, because shear stress is not spread evenly across the section. It can be zero at the surface and much higher than the average in other areas. Bolts, pins, and rivets...

bearing stress

Bolt-to-Plate Contact Pressure

Bearing stress is the contact pressure between two separate bodies. A common example is a bolt pushed through a plate. The bolt applies a force to the plate, and the plate pushes back with an equal and opposite force. That force is not a single point load. It is made up of many smaller forces spread across the contact surface between the bolt and the plate. Because these microforces are complex, engineers use an average value called bearing stress. Bearing stress is found by dividing the...

applications of stress

Boom and Rod Stress Analysis

Boom and rod stress analysis shows how a pinned support structure carries a load. The boom and the rod are connected by a pin and held in place by brackets and pins. The structure is then separated from its supports so the forces can be studied clearly. A free-body diagram is drawn to identify every force on the boom, the rod, and the load. The reaction forces on both members are found using equilibrium equations. At point P, the reaction causes compression in the boom. At point R, the...

stress on an oblique plane

Axial Load Stress on Inclined Sections

Axial loading creates stress in a material along its central axis. This kind of load can cause compression or elongation, and it produces normal stress. Normal stress acts perpendicular to the material area and can be either tensile or compressive. When the section is not perpendicular to the load, it becomes an oblique plane. On this inclined plane, the stress state includes both normal stress and shearing stress. Shearing stress acts parallel to the area and changes shape without changing...

stress: general loading conditions

Stress Components on a Loaded Body

Stress components on a loaded body can be found by cutting the body through a point with a plane parallel to the xy plane. That section carries the original loads, along with normal forces and shearing forces. The result is a simple way to describe how a structure responds under combined loading. The shearing force in the section can point in different directions within the plane. It is split into two parts that run parallel to the x and y axes. Each part is divided by the area, and as that...

components of stress

Stress Components on a Cube at a Point

Stress components on a small cube help describe how a body behaves under multiple loading. The cube is centered at point O and has stress acting on all six faces, whether the faces are visible or hidden. Normal stress components σx, σy, and σz act perpendicular to the x, y, and z axes. Shearing stress components also act on the cube faces. The visible faces carry shear stresses such as τxy and τxz. The hidden faces carry equal and opposite stresses. This balance keeps the cube in equilibrium.

design consideration

Safety factors in structural design help engineers choose a material and loading limit that can be used safely. The process begins with a material’s ultimate strength. This value comes from tests that increase force until the material reaches its breaking point or limit. The ultimate load is then divided by the original cross-sectional area to find the ultimate normal stress, or strength. Ultimate shearing stress is another key value used in design. These limits show how much stress a material...

key terms and concepts

Learn how ultimate strength, ultimate stress, and factor of safety guide structural design. Compare allowable-stress and Load and Resistance Factor Design methods.

Safety Factors in Structural Design | JoVE K12

JoVE Core Mechanical Engineering offers concise, easy-to-understand animated videos covering key topics such as equilibrium, forces, truss analysis, and structural mechanics. Explore their real-world applications, and witness these concepts in action through scientist-led experiments.

mechanical engineering

3.3.9-12.P

Louisiana Student Standards for Science

High School

Earth Science

HS-ESS3-2

HS-ESS3-4

Chemistry

Matter And Its Interactions

HS-PS1-6

Energy

HS-PS3-3

HS-PS3-6

Texas Essential Knowledge and Skills

Specialised Topic in Science

112.51.c.1.

112.51.c.2.D.

Next Generation Science Standards

Physical Science

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

HS-PS2-3

Biology

BIO.2

BIO.2.A

BIO.2.D

Physics

PHYS.2

PHYS.2.A

PHYS.2.D

Chemistry and Physics

IPC.2

IPC.2.A

IPC.2.D

Climate Change

The certainty of climate change remains a public controversy despite the consensus among approximately 97% of active climate researchers, who not only ...

Global Climate Change

Throughout its ~4.5 billion year history, the Earth has experienced periods of warming and cooling. However, the current drastic increase in global ...

What is Climate?

Climate refers to the prevailing weather conditions in a specific area over an extended period. As the saying goes, &#8220;Climate is what you expect. ...

an-overview-of-bgdgt-biomarker-analysis-for-paleoclimatology

An Overview of bGDGT Biomarker Analysis for Paleoclimatology

Source: Laboratory of Jeff Salacup&#160;- University of Massachusetts Amherst
Throughout this series of videos, natural samples were extracted and ...

extraction-of-biomarkers-from-sediments-accelerated-solvent-extraction

Extraction of Biomarkers from Sediments - Accelerated Solvent Extraction

Source: Laboratory of Jeff Salacup&#160;- University of Massachusetts Amherst
The distribution of a group of organic biomarkers called glycerol-dialkyl ...

The Carbon Cycle

Carbon is the basis of all organic matter on Earth, and is recycled through the ecosystem in two primary processes: one in which carbon is exchanged among ...

Melting Land and Sea Ice
ExpandNOTE: This activity is a simulation of land- and sea-ice melting and their effects on water levels.
First, label one ...

What are Biogeochemical Cycles?

The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited ...

What is Weather?

Overview

Weather refers to the current state of atmospheric conditions at a specific time and place. Weather is temporary and is influenced by the ...

Students who demonstrate understanding can use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity. [cite: 88] Clarification Statement: Examples of Earth systems to be considered are the hydrosphere, atmosphere, cryosphere, geosphere, and/or biosphere. [cite: 89] An example of the far-reaching impacts from a human activity is how an increase in atmospheric carbon dioxide results in an increase in photosynthetic biomass on land and an increase in ocean acidification, with resulting impacts on sea organism health and marine populations. [cite: 90] Assessment Boundary: Assessment does not include running computational representations but is limited to using the published results of scientific computational models. [cite: 91]

3.3.9-12.M

Sustainable Development

As the human population continues to grow and use resources, we must be mindful of our planet&rsquo;s natural limits. Sustainable development provides a ...

Private Goods and Common Resources

Private goods are items that a person can buy and use, which then prevents others from using them.
For example, a slice of pizza. It is a private good ...

Negative Externalities

A negative externality is a cost suffered by an unrelated third party due to an economic transaction.
The costs created by negative externalities are not ...

The Efficient Level of Pollution

Producing goods often results in pollution as a byproduct, but eliminating all pollution isn&#39;t practical. Doing so would mean halting the production ...

Biodiversity and Human Values

Human civilization relies on biodiversity in many ways. Sudden changes in species biodiversity result in environmental changes that can modify weather ...

While designing a structure, the considerations start with the ultimate strength of a material, which is determined through tests, measuring changes under ...

Ecological Niches

All organisms have a position within an ecosystem. The complete set of living and nonliving factors&#x2014;including food resources, climate, and ...

Habitat Fragmentation

Habitat fragmentation describes the division of a more extensive, continuous habitat into smaller, discontinuous areas. Human activities such as land ...

Ecological Disturbance

An ecological disturbance is a temporary disruption in the environment resulting from abiotic, biotic, or anthropogenic factors, causing a pronounced ...

applications-of-gis-disaster-management-and-emergency-response

Applications of GIS: Disaster Management and Emergency Response

Geographic Information System (GIS) technology is essential for risk identification, action prioritization, and resource optimization in critical ...

Migration

Migration is long-range, seasonal movement from one region or habitat to another. This common strategy, carried out by many different organisms around the ...

Students who demonstrate understanding can construct an explanation based on evidence for how the availability of natural resources, occurrence of natural hazards, and changes in climate have influenced human activity. [cite: 167] Clarification Statement: Examples of key natural resources include access to fresh water (such as rivers, lakes, and groundwater), regions of fertile soils such as river deltas, and high concentrations of minerals and fossil fuels. [cite: 168] Examples of natural hazards can be from interior processes (such as volcanic eruptions and earthquakes), surface processes (such as tsunamis, mass wasting and soil erosion), and severe weather (such as hurricanes, floods, and droughts). [cite: 169] Examples of the results of changes in climate that can affect populations or drive mass migrations include changes to sea level, regional patterns of temperature and precipitation, and the types of crops and livestock that can be raised. [cite: 170] Assessment Boundary:

Factors Affecting Budget Constraint II

A budget constraint or budget line is affected by a change in the income of the consumer.
For instance, a student receives a weekly allowance of $100 that ...

Social Cost and Benefit

Private costs and benefits are the financial impacts on individuals or businesses directly involved in a transaction.
However, when an additional unit of ...

Budget Constraint II

The slope of the budget constraint represents the rate at which a consumer can trade one product for another. For example, a student spends his weekly ...

Students who demonstrate understanding can evaluate competing design solutions for developing, managing, and utilizing energy and mineral resources based on cost-benefit ratios. [cite: 30] Clarification Statement: Emphasis is on the conservation, recycling, and reuse of resources (such as minerals and metals) where possible, and on minimizing impacts where it is not. [cite: 31] Examples include developing best practices for agricultural soil use, mining (for coal, tar sands, and oil shales), and pumping (for petroleum and natural gas). [cite: 32] Science knowledge indicates what can happen in natural systems-not what should happen. [cite: 33] Assessment Boundary: N/A [cite: 34]

Threats to Biodiversity

There have been five major extinction events throughout geological history, resulting in the elimination of biodiversity, followed by a rebound of species ...

Students who demonstrate understanding can create a computational simulation to illustrate the relationships among management of natural resources, the sustainability of human populations, and biodiversity. [cite: 181] Clarification Statement: Examples of factors that affect the management of natural resources include costs of resource extraction and waste management, per-capita consumption, and the development of new technologies. [cite: 182] Examples of factors that affect human sustainability include agricultural efficiency, levels of conservation, and urban planning. [cite: 183] Assessment Boundary: Assessment for computational simulations is limited to using provided multi-parameter programs or constructing simplified spreadsheet calculations.. [cite: 184]

3.3.9-12.Q

Students who demonstrate understanding can evaluate or refine a technological solution that reduces impacts of human activities on natural systems. [cite: 75] Clarification Statement: Examples of data on the impacts of human activities could include the quantities and types of pollutants released, changes to biomass and species diversity, or areal changes in land surface use (such as for urban development, agriculture and livestock, or surface mining). [cite: 76] Examples for limiting future impacts could range from local efforts (such as reducing, reusing, and recycling resources) to large-scale geoengineering design solutions (such as altering global temperatures by making large changes to the atmosphere or ocean). [cite: 77] Assessment Boundary:

3.3.9-12.R

Safety Factors in Structural Design

Description

Transcript

More videos by Standards