## RETAIN CAPABILITIES

Retain may be used to design or review cantilevered concrete
retaining walls and bridge abutments with either spread footing or
pile foundations.

Program input may be supplied interactively by filling in the GUI
tab control form or via an externally created file. Input files may
be saved for later editing and reuse. The input may be supplied in
either English or SI (metric) units. The program is not
dimensionless due to the concrete design formulas, therefore
dimensions should be input as specified under Program units in the
Program options section.

Concrete design may be performed using either the ultimate strength
design procedure or the working stress design method. For working
stress design and ultimate strength design the specified load
factors are used for calculation of material stress. The load
factors for working stress design should be reduced below 1.0 to
account for allowable stress increases (ie. use load factor = 0.75
for 33% stress increase). For external stability calculations
(sliding, overturning, bearing pressure, etc.), the load factors are
internally changed to 1.0 for each specified load. For further
information refer to the Load Combinations section.

The soil configuration may either be constant sloped backfill with a
uniform surcharge loading or an irregular backfill and surcharge
load. The constant sloped backfill uses the user-input lateral
pressure coefficients to calculate the force on the wall. The
irregular backfill option uses the trial wedge solution procedure
with the user-input soil friction angle to calculate the wall
forces.

A variety of loads may be specified on the wall, including axial
dead and live load at the top which allows the program to simulate a
bridge abutment loading. Other top-of-wall loads include moment and
shear from wind and earthquake, which allow the program to simulate
sound wall loadings. A seismic lateral earth pressure coefficient
may be included for use using the Mononabe-Okabe method for constant
slope backfill, or an acceleration in G’s may be specified to
accelerate the trial wedge for the irregular backfill configuration.

Safety factors for external stability and soil parameters such as
friction coefficients and allowable bearing pressure may be
specified separately for regular load, wind loads and seismic loads.
This gives the user the flexibility necessary for checking multiple
load conditions in one design run.