Civil Engineering Reference
In-Depth Information
example. This unbalanced force is likely to be much larger than
all other loads on the structure and its magnitude needs to be
established early on as it will drive many aspects of the design.
the load paths to support at the ground. These diagrams are an
important way for the engineer to think through all the elem-
ents and connections along the path that will need detailed
design later. They also importantly convey to other team mem-
bers the way the structure works, letting them appreciate the
impact on the design if things later need to change and move.
Anything that interrupts, cuts or deviates this flow of force will
need to be thought through and justified or modified.
Although seemingly a statement of the obvious it is import-
ant to emphasise that all load paths must be complete. Simple
examples of incomplete paths are shown in
Figure 7.2
. There
must be a capable member or connection at every stage of the
load's journey and this must be a key focus of early technical
reviews as this is often where problems occur. Load path dia-
grams are a key tool in such reviews.
Computer tools now allow an engineer to build a three-
dimensional structural model at an early stage, apply loads and
then let the computer establish how the forces flow through
the structure. However, this is an extremely dangerous prac-
tice as the engineer has no idea of whether the results they
are given are either correct or appropriate. The computer is
fully in charge and the operator has lost control of the design.
'Designer' would be the wrong word for their role here.
7.3.2 Load paths
All loads must have a load path. Before decisions are made on
the form of the structural elements the designer must be clear
what role these elements play in the building's load paths.
A structural designer is someone who chooses the load path
along which loads flow from their point of application to their
point of support. They investigate options for this path and
choose an optimal configuration. They must know the load
path of every load applied and load path diagrams demonstrate
this understanding.
A structure transfers loads through load paths that span to
points of support. Buildings are three-dimensional objects, and
the load paths can be so as well, but often load paths through
parts of a structure can be considered as two-dimensional plans
or sections. Simpler 'one-way spanning' solutions often give
easier design and straightforward construction but the efficien-
cies of 'two-way spanning' should also be understood.
It is important that clear diagrams are produced early in the
design life-cycle that show the way that loads flow through
Figure 7.2
Incomplete load path diagrams
