/*! 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 89 The article "Reliability-Based S... [FREE SOLUTION] | 91Ó°ÊÓ

91Ó°ÊÓ

The article "Reliability-Based Service-Life Assessment of Aging Concrete Structures" (J. Structural Engr., 1993: \(1600-1621\) ) suggests that a Poisson process can be used to represent the occurrence of structural loads over time. Suppose the mean time between occurrences of loads is .5 year. a. How many loads can be expected to occur during a 2year period? b. What is the probability that more than five loads occur during a 2-year period? c. How long must a time period be so that the probability of no loads occurring during that period is at most .1?

Short Answer

Expert verified
a. Expect 4 loads in 2 years. b. Probability of more than 5 loads is 0.2149. c. The period should be at least 1.15 years.

Step by step solution

01

Understand the Poisson Process

A Poisson process is often used to model the number of events occurring within a fixed period of time. In this case, we want to model structural loads over a time period. The mean time between occurrences of loads is given as 0.5 year.
02

Calculate the Rate of Occurrences

The mean time between occurrences is 0.5 years, indicating a rate, \( \lambda \), of 2 loads per year (since \( \lambda = \frac{1} {0.5} \)). For a 2-year period, the rate becomes \( \lambda_{2\text{-year}} = 2 \times 2 = 4 \).
03

Calculate Expected Loads in a 2-year Period

The expected number of loads during a specific time period is given by the product of the rate of occurrences and the length of the period. Thus, for a 2-year period, the expected number of loads is \( \lambda_{2\text{-year}} = 4 \).
04

Use the Poisson Probability Formula

The probability of observing \( k \) loads in a time period is governed by the formula \( P(k; \lambda) = \frac{e^{-\lambda} \lambda^k}{k!} \).
05

Calculate Probability of More Than Five Loads

To find the probability of more than five loads, we calculate \( P(X > 5) = 1 - P(X \leq 5) = 1 - \sum_{k=0}^{5} P(k; 4) \). Compute the probabilities for \( k = 0 \) to \( k = 5 \) and sum them to find \( P(X \leq 5) \), then subtract from 1.
06

Compute Each Probability Term ',' Description

Calculate - \( P(0; 4) = \frac{e^{-4} \cdot 4^0}{0!} = e^{-4} \)- \( P(1; 4) = \frac{e^{-4} \cdot 4^1}{1!} = 4e^{-4} \)- \( P(2; 4) = \frac{e^{-4} \cdot 4^2}{2!} = 8e^{-4} \)- \( P(3; 4) = \frac{e^{-4} \cdot 4^3}{3!} = \frac{32e^{-4}}{6} \)- \( P(4; 4) = \frac{e^{-4} \cdot 4^4}{4!} = \frac{256e^{-4}}{24} \)- \( P(5; 4) = \frac{e^{-4} \cdot 4^5}{5!} = \frac{1024e^{-4}}{120} \)Sum these values.
07

Calculate the Required Time Period for No Loads

We need the period \( t \) such that the probability of no loads is at most 0.1. This means \( P(X = 0) = e^{-\lambda t} \leq 0.1 \). Solve for \( t \) using \( e^{-\lambda t} = 0.1 \) with \( \lambda = 2 \) (rate per year).
08

Solve for the Time Period Using Exponential Function

From \( e^{-2t} = 0.1 \), take the natural logarithm on both sides to obtain \(-2t = \ln(0.1) \), and find \( t = -\frac{\ln(0.1)}{2} \). Solve for \( t \).

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

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

Probability Theory
The Poisson process is deeply rooted in probability theory, a branch of mathematics concerned with analyzing random events. In probability theory, a Poisson process is a model that represents the occurrence of events over time, valuable when events are rare and sporadic. Each event is independent of the previous one, typical for scenarios like structural loads in engineering. The beauty of the Poisson distribution is that it uses just one parameter, the rate of occurrence (denoted by \(\lambda\)), to define the probability of a given number of events occurring in a fixed interval of time.

This distribution is described by the formula:
  • \( P(k; \lambda) = \frac{e^{-\lambda} \lambda^k}{k!} \)
where \(k\) is the number of events you're examining. The ability to predict the likelihood of multiple event occurrences is powerful, contributing vast applicability across different fields such as environmental science, telecommunications, and here, in structural engineering.
Reliability Engineering
Reliability engineering focuses on ensuring that systems perform consistently over time. The Poisson process comes into play as it helps manage and predict the likelihood of failure events. In the context of structural engineering, reliability often means maintaining the integrity and safety of structures like bridges and buildings that endure various loads over their lifespan.

When assessing reliability, engineers often consider the expected frequency of loads based on historical data and models, such as those used in the Poisson process. By understanding the probability of load occurrences over a given period:
  • Engineers can better predict maintenance schedules.
  • They can enhance the design specifications to meet safety standards.
  • They optimize resources for repairs or reinforcements.
Reliability engineering provides a framework that enhances structural safety by combining theoretical models with practical assessments.
Statistical Modeling
Statistical modeling employs mathematical theories to analyze complex data patterns, supporting decision-making processes. In the context of this exercise, statistical modeling involves using the Poisson distribution to model and predict the frequency of events (like structural loads).

With statistical models, engineers and researchers can:
  • Estimate event rates over time.
  • Determine crucial thresholds, like when the excess of load could jeopardize a structure.
  • Create simulations to visualize potential outcomes.
The Poisson model's simplicity and effectiveness at handling count data make it a powerful tool in statistical modeling. It assists in interpreting data in a reliable manner, guiding informed engineering decisions that align with expected reality.
Structural Engineering
Structural engineering is a discipline that delves into the design and analysis of buildings, bridges, and other structures. The core of structural engineering lies in ensuring that these structures can withstand the loads they will encounter over time. By using models like the Poisson process, structural engineers can better understand load patterns and frequencies, helping to design structures that are safe and efficient.

Key considerations in structural engineering when dealing with loads include:
  • The expected frequency and magnitude of loads.
  • The durability of materials under repeated stress.
  • The impact of unforeseen events, like natural disasters, on structural integrity.
Structural engineers must ensure that their projects are designed with a buffer for uncertainty, using models to predict and factor in potential future scenarios. This proactive approach helps in maintaining safety and functionality throughout a structure's life.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Suppose that \(90 \%\) of all batteries from a certain supplier have acceptable voltages. A certain type of flashlight requires two type-D batteries, and the flashlight will work only if both its batteries have acceptable voltages. Among ten randomly selected flashlights, what is the probability that at least nine will work? What assumptions did you make in the course of answering the question posed?

Suppose that you read through this year's issues of the \(N e w\) York Times and record each number that appears in a news article-the income of a CEO, the number of cases of wine produced by a winery, the total charitable contribution of a politician during the previous tax year, the age of a celebrity, and so on. Now focus on the leading digit of each number, which could be \(1,2, \ldots, 8\), or 9 . Your first thought might be that the leading digit \(X\) of a randomly selected number would be equally likely to be one of the nine possibilities (a discrete uniform distribution). However, much empirical evidence as well as some theoretical arguments suggest an alternative probability distribution called Benford's law: \(p(x)=P(1\) st digit is \(x)=\log _{10}(1+1 / x) x=1,2, \ldots, 9\) a. Compute the individual probabilities and compare to the corresponding discrete uniform distribution. b. Obtain the cdf of \(X\). c. Using the cdf, what is the probability that the leading digit is at most 3 ? At least 5 ? [Note: Benford's law is the basis for some auditing procedures used to detect fraud in financial reporting-for example, by the Internal Revenue Service.]

Suppose that the number of drivers who travel between a particular origin and destination during a designated time period has a Poisson distribution with parameter \(\lambda=20\) (suggested in the article "Dynamic Ride Sharing: Theory and Practice," J. of Transp. Engr., 1997: 308-312). What is the probability that the number of drivers will a. Be at most 10 ? b. Exceed 20 ? c. Be between 10 and 20 , inclusive? Be strictly between 10 and 20 ? d. Be within 2 standard deviations of the mean value?

Suppose that \(30 \%\) of all students who have to buy a text for a particular course want a new copy (the successes!), whereas the other \(70 \%\) want a used copy. Consider randomly selecting 25 purchasers. a. What are the mean value and standard deviation of the number who want a new copy of the book? b. What is the probability that the number who want new copies is more than two standard deviations away from the mean value? c. The bookstore has 15 new copies and 15 used copies in stock. If 25 people come in one by one to purchase this text, what is the probability that all 25 will get the type of book they want from current stock? [Hint: Let \(X=\) the number who want a new copy. For what values of \(X\) will all 15 get what they want?] d. Suppose that new copies cost \(\$ 100\) and used copies cost \(\$ 70\). Assume the bookstore currently has 50 new copies and 50 used copies. What is the expected value of total revenue from the sale of the next 25 copies purchased? Be sure to indicate what rule of expected value you are using.

The College Board reports that \(2 \%\) of the 2 million high school students who take the SAT each year receive special accommodations because of documented disabilities (Los Angeles Times, July 16, 2002). Consider a random sample of 25 students who have recently taken the test. a. What is the probability that exactly 1 received a special accommodation? b. What is the probability that at least 1 received a special accommodation? c. What is the probability that at least 2 received a special accommodation? d. What is the probability that the number among the 25 who received a special accommodation is within 2 standard deviations of the number you would expect to be accommodated? e. Suppose that a student who does not receive a special accommodation is allowed 3 hours for the exam, whereas an accommodated student is allowed \(4.5\) hours. What would you expect the average time allowed the 25 selected students to be?

See all solutions

Recommended explanations on Math Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.