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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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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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Design of Reinforced Concrete : ACI 318-05 Code

With this bestselling book, readers will quickly gain a better understanding of the fundamentals of reinforced concrete design.

The author presents a thorough introduction to the field, covering such areas as theories, ACI Code requirements, and the design of reinforced concrete beams, slabs, columns, footings, retaining walls, bearing walls,

prestressed concrete sections, and framework. Numerous examples are also integrated throughout the chapters to help reinforce the principles that are discussed.

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Design of Concrete Structures,14th ed,Nilson

The 14th edition of the classic text, Design of Concrete Structures, is completely revised using the newly released 2008 ACI (American Concrete Institute) Code.

This new edition has the same dual objectives as the previous editions;

first to establish a firm understanding of the behavior of structural concrete, then to develop proficiency in the methods used in current design practice.

Design of Concrete Structures covers the behavior and design aspects of concrete and provides updated examples and homework problems.

New material on slender columns, seismic design, anchorage using headed deformed bars, and reinforcing slabs for shear using headed studs has been added.

The notation has been thouroughly updated to match changes in the ACI Code.

The text also presents the basic mechanics of structural concrete and methods for the design of individual members for bending,

shear, torsion, and axial force, and provides detail in

the various types of structural systems applications, including an extensive presentation of slabs,footings, foundations, and retaining walls.

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Reinforced Concrete Design of Tall Buildings

Design concept is an impressive term that we use to describe the intrinsic essentials

of design. The concept encompasses reasons for our choice of design loads,

analytical techniques, design procedures, preference for particular structural systems,

and of course, our desire for economic optimization of the structure.

To assist engineers in tackling the design challenge, this introductory chapter is

devoted to developing a “feeling” for behavior of structural systems.

It is this “feeling” for the nature of loads and their effect on structural systems that

paves the way for our understanding of structural behavior and allows the designer

to match structural systems to specific types of loading.

For example, designers of tall buildings, recognizing the cost premium for carrying

lateral loads by frame action alone, select a more appropriate system such as a belt

and outrigger wall or a tubular system instead.

As structural engineers, our primary task is to take someone else’s vision of a project,

convertit into analytical and numerical models, and then produce a set of buildable

documents.

However, the current trend in engineering education seems to focus more on the behavior

of computer-based mathematical models while seldom acknowledging their fallibilities.

Given this scenario, one may wonder if the era of engineers who endorsed structural

attitudes based on their qualitative knowledge of the behavior of the structures is gone.

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Design of Low-Rise Reinforced Concrete Buildings

The purpose of Design of Low-Rise Reinforced Concrete Buildings—based on
the 2009 IBC/ASCE/SEI 7-05/ACI 318-08 is to help engineers analyze, design
and detail low-rise cast-in-place conventionally reinforced concrete buildings in
accordance with the 2009 edition of the International Building Code® (IBC®).
Because the 2009 IBC references the 2008 edition of Building Code
Requirements for Structural Concrete (ACI 318-08) and the 2005 edition of
ASCE/SEI 7, Minimum Design Loads for Buildings and Other Structures, the
narrative and examples are based on these current standards wherever
applicable. Section numbers and equation numbers from the 2009 IBC, ACI 318-
08 and ASCE/SEI 7-05 that pertain to the specific requirements are provided
throughout the text.

Although the book is geared primarily for practicing structural engineers,
engineers studying for licensing exams, structural plan check engineers and civil
engineering students will find the book a valuable resource because of its
straightforward approach.
Chapter 2 summarizes floor systems commonly used in concrete buildings with
guidance on the advantages of various systems and practical framing layouts
and formwork. Information on the selection of economical floor systems for
various span and gravity load conditions is provided along with methods to
determine preliminary member sizes.

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Concrete Properties (Advanced Concrete Technology Set)

Description

Based on the Institute of Concrete Technology’s advanced course, this new four volume series is a comprehensive educational and reference resource for the concrete materials technologist.

An expert international team of authors from research, academia and industry has been brought together to produce this unique reference source. Each volume deals with different aspects of the properties, composition, uses and testing of concrete.

With worked examples, case studies and illustrations throughout, this series will be a key reference for the concrete specialist for years to come.

Key Features

Expert international authorship ensures the series is authoritative
Case studies and worked examples help the reader apply their knowledge to practice
Comprehensive coverage of the subject gives the reader all the necessary reference material

Readership

Practitioners in the concrete and cement industry. Academics and postgraduate students of civil engineering and related subjects

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