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Workability and Quality Control of Concrete

The word workability is a term that refers to properties of fresh concrete, that is, of the concrete before it has set and hardened, and it is legitimate to ask why any attention should be given to these properties at all.

The performance of concrete will in practice be assessed in terms of whether the hardened material performs in the way intended and continues to do so: it will be judged in terms of shape and finish, strength, deflection, dimensional changes, permeability and durability.

So why should the properties of the fresh concrete be considered to be important, and why should they be the concern of the practising engineer?

The answer to the first of these questions lies in the fact that the properties of any finished material are affected by the properties at an earlier stage and by the processes applied to it, while the answer to the second one is that all, or a major part of, the processing of concrete is actually carried out on site.

The first stage is, of course, the making of a homogeneous mix and then, assuming this has been done properly, the material is subjected to other processes as follows.

The concrete must be capable of giving a good finish direct from the formwork, withouth oneycombing or an excessive number of blowholes or other surface defects.

If there is a free surface, it must also be capable of giving a good finish in response to an operation such as floating or trowelling.

A workable concrete is one that satisfies these requirements without difficulty and, ingeneral, the more workable it is, that is, the higher its workability, the more easily it can be placed, compacted and finished.

Workability can be increased by simply increasing the water content of the mix but, if that method is used, a point will be reached at which segregation and/or bleeding become unacceptable so that the concrete is no longer homogeneous and, before that, the water/cement ratio may have reached a level such that the hardened concrete will not attain the required strength.

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Failures in Concrete Structures

Many failures, when investigated, have been found to arise from a combination of causes.

The traditional design sequence starts with the sizing of members.

These are determined from the loading (permanent and variable actions) with reference to bending moments and, for beams, shear forces.

The reinforcement is then calculated to cater for these forces.

Much of the reinforcement is detailed only after completion of the contract documents.

Later, if problems are found in fitting the required reinforcement into an element or joint, it is difficult to change the size of section on which the architect and services engineers agreed.

Many such problems could have been avoided by producing sketches early on to show how the joint details could work before sizes were finalised.

This book is a personal selection of incidents that have occurred related to reinforced and prestressed concrete structures.

Not all have led to failures and some of the mistakes were discovered at the design stage.

Each incident required some form of remedial action to ensure safety of the structure.

Some of the incidents were caused by mistakes in design or construction or both.

Some involved collapse of part of the structure, but in such cases the cause was from mor than one unrelated mistake or problem.

A few of the errors and incidents were caused by deliberate intent.

Chapters 1 to 11 describe specific incidents such as structural misunder standing, extrapolation of codes of practice, detailing, poor construction, and other factors.

When a particular incident involved more than one of these causes, it is described in the most relevant section.

Chapters 12 and 13 discuss issues related to procurement and research and development.

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Why buildings fall down how structures fail

Why buildings fall down: how structures fail

Once upon a time there were Seven Wonders of the World.

Now only one survives: the mountainlike Pyramid of Khufu in the Egyptian desert near Cairo.

The other six have fallen down.
It is the destiny of the man-made environment to vanish, but we, short lived men and women, look at our buildings so convinced they will stand forever that when some do collapse,

we are surprised and concerned.

Our surprise may be partly due to the fact that most of us judge buildings by their facades:

They look beautiful when very old and ugly when very young, the opposite of human faces.

But this kind of judgment is superficial and misleading; a much better metaphor
for a building is the human body.

A building is conceived when designed, born when built, alive while standing, dead from old age or an unexpected accident.

It breathes through the mouth of its windows and the lungs of its airconditioning system.

It circulates fluids through the veins and arteries of its pipes and sends messages to all parts of its body through the nervous system of its electric wires.

A building reacts to changes in its outer or inner conditions through its brain of feedback systems, is protected by the skin of its facade, supported by the skeleton of its columns, beams, and slabs, and rests on the feet of its foundations.

Like most human bodies, most buildings have full lives, and then they die.

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Structural Vibration Analysis and Damping

The analysis of structural vibration is necessary in order to calculate the natural frequencies
of a structure, and the response to the expected excitation.

In this way it can be determined whether a particular structure will fulfil its intended function and, in addition,

the results of the dynamic loadings acting on a structure can be predicted, such as the dynamic stresses, fatigue life and noise levels.

Hence the integrity and usefulness of a structure can be maximized and maintained.

From the analysis it can be seen which structural parameters most affect the dynamic response so that if an improvement or change in the response is required,

the structure can be modified in the most economic and appropriate way.

Very often the dynamic response can only be effectively controlled by changing the damping in the structure.

Structural Vibration: Analysis and Damping benefits from my earlier book Structural Vibration Analysis: Modelling,

Analysis and Damping of Vibrating Structures which was published in 1983 but is now out of print.

This enhanced successor is far more comprehensive with more analytical discussion, further consideration of damping sources and a greater range of examples and problems.

The mathematical modelling and vibration analysis of structures are discussed in some detail, together with the relevant theory.

It also provides an introduction to some of the excellent advanced specialized texts that are available on the vibration of dynamic systems. In addition,

it describes how structural parameters can be changed to achieve the desired dynamic performance and, most importantly,

the mechanisms and methods for controlling structural damping.

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Analysis and Design of Shallow and Deep Foundations

Advances in foundation engineering have been rapid in recent years. Of note
are the maturity of the concepts of soil–structure interaction, the development
of computer codes to deal with advanced topics, the advent of new methods
for the support of structures, and the proliferation of technical publications
and conferences that present a variety of useful information on the design and
performance of foundations.

This book takes advantage of these advances by presenting methods of analysis while being careful to emphasize standard methods such as site visits and the role of engineering geology.

The goals of the engineer in the design of foundations are to achieve a
system that will perform according to stipulated criteria, can be constructed
by established methods, is capable of being inspected, and can be built at a
reasonable cost.

Builders have realized the need for stable foundations since structures began
rising above the ground. Builders in the time of the Greeks and the Romans
certainly understood the need for an adequate foundation because many of
their structures have remained unyielding for centuries.

Portions of Roman aqueducts that carried water by gravity over large distances remain today. The Romans used stone blocks to create arched structures many meters in height
that continue to stand without obvious settlement.

The beautiful Pantheon, with a dome that rises 142 ft above the floor, remains steady as a tribute to builders in the time of Agrippa and Hadrian. The Colosseum in Rome, the
massive buildings at Baalbek, and the Parthenon in Athens are ancient structures
that would be unchanged today except for vandalism or possibly
earthquakes.

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Design and Control of Concrete Mixtures

Design and Control of Concrete Mixtures has been the cement and concrete industry’s primary reference on concrete technology for over 85 years. Since the first edition was published in the early 1920s, the U.S. version has been updated 15 times to reflect advances in concrete technology and to meet the growing needs of architects, engineers, builders, concrete producers, concrete technologists, instructors, and students.

This fully revised 15th edition was written to provide a concise, current reference on concrete, including the many advances that occurred since the last edition was published in 2002. The text is backed by over 95 years of research by the Portland Cement Association. It reflects the latest information on standards, specifications, and test methods of ASTM International (ASTM), the American Association of State Highway and Transportation Officials (AASHTO), and the American Concrete Institute (ACI).

Concrete’s versatility, durability, sustainability, and economy have made it the world’s most widely used construction material. The term concrete refers to a mixture of aggregates, usually sand, and either gravel or crushed stone, held together by a binder of cementitious paste. The paste is typically made up of portland cement and water and may also contain supplementary
cementing materials (SCMs), such as fly ash or slag cement, and chemical admixtures Understanding the basic fundamentals of concrete is necessary to produce quality concrete. This publication covers the materials used in concrete and the essentials required to design and control concrete mixtures for a wide variety of structures.

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Railway Geotechnics

Railway Geotechnics is written by four colleagues who studied at the University of Massachusetts, Amherst, in an academic program advised by Professor Ernest T. Selig.

Our collective time at the university spanned over a decade, during which we were individually inspired by Professor Selig to work on and further advance the subject of railway geotechnology, whichhe pioneered and developed into a rigorous field of study.

Since graduation, the aggregate of our professional experience includes railway operations,
consulting, research, and education.

The field of railway geotechnology was in its infancy when we were in our early careers.

Because the engineering behavior of track substructure was not well understood up to that point, perspectives on the causes and cures of substructure instability were often informed by anecdote rather than by verifiable fact. Mystique surrounded the subject in the absence of critical thinking,

often resulting in costly applications of remedial methods that did not address the root causes of track substructure problems.

Advancing the field of railway geotechnology by the writing of this book is a natural step for each of us in our careers.

The book continues the work Track Geotechnology and Substructure Management by Selig and Waters (1994) and provides an update to this field of study so that current railway
engineers and managers have easier access to new and emerging best practices.

During years of writing and discussions, we each had moments that challenged some of our beliefs while we debated the merits of emerging technology and practices.The goal of this book is to provide a better understanding track substructure in order to enable more effective design, construction, maintenance, and management of railway track so as to ensure the vitality of rail transportation.

We hope that this work will prove useful to current railway engineers and managers as well as college students pursuing careers in the field of railway engineering.

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Principles of Structural Design Wood Steel and Concrete

Buildings and other structures are classified based on the risk associated with unacceptable performance of the structure, according to Table 1.1.

The risk categories range from I to IV, where category I represents buildings and other structures that pose no danger to human life in the event of failure and category IV represents all essential facilities.

Each structure is assigned the highest applicable risk category.

Assignment of more than one risk category to the same structure based on use and loading conditions is permitted.

To safeguard public safety and welfare, towns and cities across the United States follow certain
codes for design and construction of buildings and other structures.

Until recently, towns and cities modeled their codes based on the following three regional codes, which are normally revised at 3-year intervals:

1. The Building Officials and Code Administrators National Building Code
2. The Uniform Building Code
3. The Standard Building Code

The book is appropriate for an academic program in architecture, construction management,
general engineering, and civil engineering, where the curriculum provides for a joint coursework in wood, steel, and concrete design.

The book has four sections, expanded into 17 chapters. Section I, comprising Chapters 1
through 5, enables students to determine the various types and magnitude of loads that will be acting on any structural element and the combination(s) of those loads that will control the design.

ASCE 7-10 has made major revisions to the provisions for wind loads. In Section I, the philosophy of the load and resistance factor design and the unified approach to design are explained.

Wood design in Section II from Chapters 6 through 8 covers sawn lumber, glued laminated
timber, and structural composite or veneer lumber, which are finding increased application in wood structures.

The NDS 2012 has modified the format conversion factors and has also introduced some
new modification factors.

First, the strength capacities in accordance with the NDS 2012 for tensile, compression, and bending members are discussed and the basic designs of these members are performed.

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Steel Design 5th Edition

Steel Design, Fifth Edition covers the fundamentals of structural steel design for buildings.

This book is intended for junior-and senior-level engineering students, although some of the later chapters can be used in a combination undergraduate/graduate course.

Practicing civil engineers who need a review of current practice and the

current AISC Specification and Manual will find the book useful as a reference.

Students should have a background in mechanics of materials and analysis of statically determinate structures.

Knowledge of statically indeterminate structural analysis is not a prerequisite for the use of this book.

Structural design is a complex endeavor, involving the synthesis of many processes.

This book does not cover the integrated design of buildings, but presents some of the “building blocks” for structural steel design.

We focus on the analysis and design of individual members and connections, rather than complete structures.

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Geotechnical Engineering Principles and Practices of Soil Mechanics and Foundation Engineering

This book has the following objectives:
1. T o explain the fundamentals of the subject from theory to practice in a logical way
2. T o be comprehensive an d mee t th e requirements o f undergraduate students
3. T o serve as a foundation course for graduate students pursuing advanced knowledge in the subject

There are 21 chapters i n this book. The first chapter trace s the historical background o f the
subject and the second deals with the formation and mineralogical composition o f soils.

Chapter 3 covers th e inde x properties an d classification of soil. Chapters 4 and 5 explain soi l permeability , seepage, an d th e effec t o f water on stress conditions in soil .

Stresses developed in soil due to imposed surface loads , compressibility and consolidation characteristics , and shear strength characteristics o f soil are dealt with in Chapters 6,7 , and 8 respectively. The first eight chapters develop the necessary tools for computing compressibility an d strength characteristics o f soils.

Chapter 9 deals with methods for obtainig soil samples in the field for laboratory tests and for constructed on an outcrop of sound rock, no foundation is required. Hence, in contrast to the
building itself which satisfies specific needs, appeals to the aesthetic sense, and fills its
matters with pride, the foundations merely serve as a remedy for the deficiencies of whatever
whimsical nature has provided for the support of the structure at the site which has been
selected. On account of the fact that there is no glory attached to the foundations, and that
the sources of success or failures are hidden deep in the ground, building foundations have
always been treated as step children; and their acts of revenge for the lack of attention can be
very embarrassing.
The comments made by Terzaghi are very significan t an d shoul d b e take n not e o f by all
practicing Architects an d Engineers. Architects or Engineers who do not wish to make use of the growing knowledge of foundation design are not rendering true service t o their profession. Since substructures are as important as superstructures, persons wh o are well qualified in

the design ofsubstructures should always be consulted an d the old proverb tha t a ‘stitc h i n time save s nine ‘ should always be kept in mind.

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