Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

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Introduction 3
Within a few hours after concrete is placed for girders, beams,
and slabs, it begins to set and to bond with the reinforcing steel, thereby
developing strength to support itself. Although the forms are usually
left in place for several days, magnitudes of the unit stresses in the
forms will gradually decrease as the concrete gains strength. Thus,
the maximum unit stresses in the formwork are temporary and of
shorter duration than the time the forms are left in place.
The allowable unit stresses specified for lumber are generally
based on a full design load that is applied for a normal load duration
of approximately 10 years. If the duration of the load is only a few
hours or days, such as with formwork, the allowable unit stress may
be adjusted to a higher value. For loads that are applied for a short
duration, less than 7 days, the allowable unit stresses may be increased
by 25%. The examples and tables contained in this book are based on
using increased allowable unit stresses, assuming loads are applied
for a short duration.
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Care of Forms
Forms are made of materials that are subject to considerable damage
through misuse and mishandling. Wood forms should be removed
carefully, then cleaned, oiled, and stored under conditions that will
prevent distortion and damage. At periodic intervals, all forms should
be checked to determine whether renailing, strengthening, or replacing
parts is necessary.
Patented Products
There are numerous patented products for concrete structures that
have been produced by companies in the construction industry. Many
of these products are contained in this book. However, it is not practical
to include all of the products that are currently available. Inclusion
of the products of some manufacturers and the exclusion of
similar products of others should not be interpreted as implying that
the products included in this book are superior to those not mentioned.
The products described in this book are intended to illustrate
only the types of products available for use in concrete formwork.
For most of the products that are included in this book, the manufacturers’
specifications, properties, dimensions, and other useful
information are given in tables.
Arrangement of This Book
There are 17 chapters in this book. The following paragraphs briefly
describe each one.
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