Civil Engineering Reference
In-Depth Information
During the next temperature drop cycle of nearly 40ºC, the northern sensor
recorded elongation movements leading to a relative movement at the end of the
cycle of nearly 0.2 mm. Both structures underwent contraction and reverted to
nearly the same position. Subsequent temperature cycles indicate that PG-1 moved
cumulatively relative to PG-1 in the direction away from the soil mass, with a total
relative movement recorded at the end of the monitoring period of 5 mm.
This movement trend was similar to that recorded by the electrolytic tiltmeter at
level D.
The data of the southern sensor at the roof level, shown in Fig. 4.23, also show
relative movements between PG-1 and PG-2. During the period of temperature
rise, after installation, the southern sensor recorded a shortening of about 1.8 mm,
indicating that the expansion movements of building PG-1 were larger than PG-2
at the southern side. The additional expansion recorded for PG-1 is the sum of the
magnitude of the restrained expansion at the northern edge and the lateral
movement resulting from any increase in earth pressure.
During the temperature drop cycle of nearly 46ºC (6ºC larger than the
temperature drop recorded by the northern sensor), the relative movements
recorded by the southern sensor indicate that the two structures, PG-1 and PG-2,
assumed the same position corresponding to a zero reading, followed by an
elongation of the sensor of approximately 2.8 mm. This elongation signifies that
PG-1 underwent larger movements in the direction of contraction when compared
to PG-2. This may be due to the fact that the contraction of the structure induced a
relaxation of earth pressure leading to a total or partial elimination of the lateral
movements undergone due to increase in earth pressure.
The data discussed thus far indicate that the presence of the soil mass retained
by the rigidly framed building induce a complex soil-structure interaction
dependent on many factors including soil stiffness, lateral structural stiffness,
thermal movement properties of the structure, displacement and earth pressure
relationship, among others.
In an effort to quantify the movements of PG-1, we make use of the thermal
study presented earlier where several values the Apparent Coefficient of Thermal
Expansion (ACTE) of the structure in service were derived. The values obtained
for the seasonal ACTE would be most appropriate to determine the magnitude of
movements undergone by PG-1. To do so, we calculate the magnitude of thermal
movements undergone by PG-2 based on the seasonal values of the ACTE, and
add the recorded movement of the sensor (in vector form) from the calculated
PG-2 movements.
The calculated displacements of building PG-1,
PG-1
, derived from the data
collected by the roof level sensors are shown in Fig. 4.25, along with the change
in temperature,
δ
T
. During the first temperature rise cycle, the northern end of
PG-1 underwent an expansion of about 1 mm, while its southern end expanded by
nearly 4.5 mm. Through the subsequent temperature drop cycle, PG-1 displaced
approximately 5 mm away from the soil mass at the northern end, and 9 mm in the
Δ
