Civil Engineering Reference
In-Depth Information
in the earth pressure coefficient with temperature change is valid for the instru-
mented building (PG-1) only. Therefore, the insights derived from this case histo-
ry are applicable to all rigidly framed earth retaining structures, including jointless
(segmental) bridges.
5.10 Conclusions
This case history demonstrates that rigidly framed earth retaining structures un-
dergo complex temperature-dependent soil-structure interaction. Displacements of
a four-story rigidly-framed structure that retained 36 ft of fill on one side only
were monitored along with temperature for a period of 4.5 years. During periods
of temperature decrease, the structure contracts, and the soil follows it. During
periods of rise in temperature, the structure undergoes limited expansion move-
ments into the soil mass at the restrained end, causing larger expansion move-
ments, and stresses, at the other end. This is not surprising since the energy needed
to overcome the soil's passive resistance is vastly larger than the energy stored in
the building when it contracts under active earth pressure conditions. Expansion
of the structure toward the retained soil induce an increase in earth pressure,
and possibly in soil stiffness, causing it to deflect away from the soil mass to
maintain the required force equilibrium, while still undergoing thermal expansion
movements.
The observed building displacements were correlated to the coefficient of lat-
eral earth pressure,
K
.
K
was found to be linearly dependent on the building tem-
perature; it changed by approximately 0.005/°C varying in the range of 1.25 to
1.5, depending on the season. A residual translation away from the restrained soil
is observed at the end of each thermal cycle. It is the thermal cycles rather than
the high earth pressure that caused some of the structural elements of the building
to distress and fail, in order to release some the built in pressure.
The measurements presented in this topic demonstrate that after the first cold
cycle, RFERS contract and the retained soil typically follows the structure. As
temperature increases, the structure attempts to expand, but is restrained by the
soil, causing it to drift away from the retained soil. Repeated cycles of contraction
and expansion may cause distress of the structure.
