Building Structures

STRUCTURAL FUNCTIONS 13
Figure 1.20 Buildings above ground.
and records of previous seismic activity. A principal
force on the building structure is generated by the
momentum of the building mass once it is moved.
Application. Consideration of the building mass as
a horizontal or vertical force with the necessary
resistance of the building’s bracing system.
Hydraulic Pressure
Source. Principally from groundwater when the free water
level in the soil is above the bottom of the building
basement floor.
Computation. As fluid pressure proportional to the depth
of the fluid.
Application. As horizontal pressure on walls or upward
pressure on floors.
Soil Pressure
Source. Action of soil as a semifluid exerting pressure on
buried objects or vertical retaining structures.
Computation. By considering the soil as a fluid with the
typical hydraulic action of the fluid pressures.
Application. As for hydraulic pressure; horizontally on
walls.
Thermal Change
Source. Temperature variations in building materials from
fluctuations in outdoor temperature.
Computation. From weather histories, indoor design
temperatures, and the coefficients of expansion of
the materials.
Application. Forces on the structure if free movement
due to expansion or contraction is prevented; stresses
within the structure if connected parts have different
temperatures or different rates of thermal expansion.
Other Potential Load Sources
Shrinkage. Volume reduction in concrete, plaster, stucco,
or mortar in masonry joints as the materials dry out
and harden. Dimensional and form changes in large
timber members as the wood dries out from the green,
freshly cut condition.
Vibration. Oscillations caused by machinery, vehicles,
high-intensity sounds, and people walking.