Civil Engineering Reference
In-Depth Information
Most structural systems that we design will be highly indeterminate structural systems.
Thus, they will exhibit hybrid structural action. When designing, we must always be
aware of the effect that design changes in one part of the structure have on other parts of
the structure. We must also be mindful of the conditions under which the participation
stress can become significant and affect the load-carrying capacity of the system.
Use of Force Envelopes
When loads are applied to a structure, the structure responds to those loads. The forces in
a particular component in the system are caused by (1) the loads acting on the structure,
(2) the location of those loads, and (3) the combinations of those loads which act simul-
taneously. By determining the response of the structural system to the various forces act-
ing, we can determine the maximum and minimum forces that can exist along the length
of any component. This range of forces is called a
force envelope
and is indicative of the
forces for which we must design. Force envelopes were discussed in Chapter 14 as part
of the discussion about limit states design and about the ACI force coefficients. That
chapter should be reviewed again if the principles discussed there have become fuzzy
with time.
Preparation of Engineering Drawings
An important topic often overlooked when talking about structural design, particularly
when talking about design of components, is the preparation of drawings to illustrate the
final design and enable the structure to be constructed. This is a very important part of
system design because without design drawings the structure will never be built. Three
types of drawings are involved in design of the system:
• Engineering sketches and drawings to illustrate the design.
• Construction drawings from which the structure is actually constructed.
• Shop drawings from which the individual components in the structure are fabricated.
Of these three types, the ones we are concerned with here are the drawings and sketches
necessary to prepare the construction drawings. These are the drawings prepared by the
design engineer; a draftsperson normally prepares the construction drawings from these
drawings. Throughout the discussion in this chapter, we will illustrate some fundamental
criteria for preparing engineering drawings.
21.2
DESIGN OF A REINFORCED CONCRETE BUILDING
As we study structural system design in this chapter, we will be examining the fundamen-
tal concepts of system design. Typical components of the structure will be included in the
process so that we can understand the basic principles. The design that we prepare here is
not a complete design. It is intended to demonstrate the philosophy and principles of sys-
tem design. We will design a typical frame rather than the entire building.
