Civil Engineering Reference
In-Depth Information
Table 6.2
Backfill Soil Model Properties
Dry
Density
(pcf)
Internal Friction
Angle
(Degrees)
Dilatancy
Angle
(Degrees)
Elasticity
Modulus
E
ref
(ksf)
Elasticity
Modulus
E
oed
(ksf)
Elasticity
Modulus
E
50
(ksf)
Soil Model
Mohr Coulomb
110
38
8
648
720
N/A
Hardening Soil
110
38
8
N/A
720
800
Poisson's ratio
ν
= 0.2; power m (HS model) = 0.5; E
ur
= 2160 ksf; K
0
= 0.384
6.2.3 The Analysis Procedure
The numerical analysis of the full-scale structure is composed of three parts. The
first part consists of a plain strain analysis of a selected frame along column line D
under temperature loading without the presence of soil backfill on either side of
the structure. This analysis is used as a benchmark to compare the strains
developed in the frame due to thermal stresses versus the strains developed for the
same structure retaining the backfill soil.
The second part of the analysis includes the frame with the backfill soil
idealized using the elastic-plastic Mohr-Coulomb constitutive model. The retained
soil is added at the initial stage of the analysis using a staged construction
simulation, followed by the application of 50ºF thermal expansion load, and
several 90ºF contraction and expansion load-cycles subsequently.
The third analysis procedure repeats the second part described above, with the
exception that the backfill soil is modeled using the Hardening Soil model.
6.3 Numerical Analysis
The three analysis procedures are further introduced and presented herein.
6.3.1 Thermal Analysis of Rigid Frame (Part 1)
6.3.1.1 Description of Analysis Procedure
The rigid frame with the properties shown in Fig. 6.1 is analyzed independently of
any soil loading or restraint for thermal strains. The first temperature cycle
consists of simulating an increase in temperature of 50ºF assuming the
construction of the reinforced concrete structure was concluded towards the end of
the spring season. The second and subsequent temperature loading cycles simulate
an alternating decrease and increase in temperature of 90ºF. These thermal loads
are in-line with the average temperature changes in the building locale, and are
obtained from averaging the range of temperatures measured on-site for nearly
fifty-four months and presented earlier in Chapter 4.
