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Introduction
Roller compacted concrete (RCC) dams have large quantities of concrete that
release large quantities of heat, being generated from the cement hydration process.
The heat generated due to cement hydration requires careful temperature control
during placement of mass concrete for several days after placement. Uncontrolled
heat generation could result in excessive tensile stresses either due to extreme
temperature gradients within the mass concrete or temperature reductions as the
concrete approaches its annual temperature cycle. Reduction in the cement content
and/or cement replacement with pozzolan or fly ash have reduced significantly the
temperature – rise potential and accordingly controls the thermal stresses in a
monolithic structure.
Several techniques are reported in the literature for designers to evaluate the
thermal performance of concrete, the structural configuration, and the construction
requirements. These techniques range from complex three dimensional finite element
analysis methods to simple manual computations. Ayotte et al. (1997) presented
details of an experimental and numerical study of thermal strains and induced stresses
in large – scale mass concrete. Three large scale monoliths were built on a dam
construction site in the James Bay Territory to monitor the thermal behavior of mass
concrete subjected to heat of hydration development and subsequent freeze and thaw
cycles. The monoliths were instrumented with thermocouples and mechanical strain
gages. One of these monoliths was modeled using the computer program ADINA.
Excellent agreement between measured and computed temperature was obtained.
Tatro and Schrader (1992) provided specific guidelines for performing thermal study
for RCC structures.
The U.S. Army Crops of Engineers, Engineer Technical Letter (ETL) 1110-2-
542 (1997) provides guidelines for performing thermal studies of mass concrete
structures (MCS) and provide methodologies for the first two levels of thermal
studies. Background and examples for several levels of less complex analyses were
presented in this (ETL) letter.
Ishikawa (1991) used ADINA to analyze thermal stresses for a concrete dam.
As an example, temperature and stress distributions were simulated in a concrete dam.
He demonstrated numerically that thermal cracks might be avoided to a certain degree
by determining the optimum construction method. Truman et al. (1991) used the finite
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element program ABAQUS along with user – developed subroutines and experi-
mentally derived material constants to analyze a pile–founded mass concrete lock and
dam structure, with an incremental construction analysis including thermal load. Chen
(2001) developed 3–D finite element relocating mesh method for simulating
temperature and thermal stress distribution in a roller compacted concrete dam during
the construction period. Forbes and Williams (1998) discussed the thermal stress
modeling, using high sand RCC mixes and in-situ modification RCC for construction
of the Candiangullong dam. They showed that the finite element program ANSYS can
be conveniently used to examine the thermal conditions and stresses. Crichton et al.
(1999) presented a thermal structural analysis using the ANSYS computer program to
assess the effect of heat of hydration in RCC structural stresses. The effect of using
simple linear elastic material properties on the calculated stresses was compared to a
more complex time variant material modulus and creep analysis. They concluded that
simple models overestimated the initial stresses and underestimated the long term
tensile stresses.
Nollet et al. (1994) described the general aspect of design of the Lac
Robertson dam, its thermal characteristics, and the methodology and results of the
thermal analysis. The analysis was performed with the program COSMOS/M and
consisted of a series of consecutive analyses using the previous temperature results as
initial conditions. Malkawi, et al. (2003) determined the thermal and structural
stresses and temperature control requirements for the 60 meter high Tannur RCC dam
in Jordan. They also studied temperature distribution with time, concrete placement
temperature limits, and joint spacing requirements to minimize cracking in the Tannur
dam. The coupled thermal–structural analysis was carried out using both two and
three– dimensional finite element method (FEM). The computer program ANSYS
was used to simulate the construction process of a roller compacted concrete dam
(RCC). The actual temperature distribution in the body of the dam also was measured
by thermocouples and was compared with results obtained by ANSYS, and generally
good agreement was obtained. Giesecke et al. (2002) presented some main features of
the ongoing development of a computationally effective method to analyze and
calculate the transient temperature field and thermal stresses in large RCC dams.
Numerical procedures based on the research results were developed and implemented
in the program TESAR. With this program the construction process of an RCC Dam
in China was simulated, and a series of parametric studies were conducted. Aufleger
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et al. (2002) presented and discussed the temperature distribution measured using
fiber optic temperature in RCC dams in an international research project. This
technology was applied and examined for its reliability for practical operations using
a 60m high concrete dam in Turkey constructed since 1997. Wiegrink. (2002)
installed a stress-meter instrument in the Mujib Dam body to evaluate the actual stress
distribution in the dam due to heat of hydration.
The objective of this paper is to present 2D and 3D thermal and structural
analyses of an RCC dam in Jordan, using the actual thermal properties, actual climatic
conditions, and the actual placement schedule of RCC layers. Linear and nonlinear
stress strain behavior regarding its temporal variability is considered in the structural
analysis. The numerically computed temperatures are compared with the actual
temperature of the RCC dam which is instrumented with fiber optic cables for DFOT
and thermocouples.
Mujib RCC Dam
The recently completed RCC Mujib Dam, was built to impound floodwater in
order to augment supplies of water for industrial and agriculture needs. The dam was
designed as a central RCC gravity dam with adjacent earth fill dams at the valley
flanks, see Figure 1. The dam is approximately 60 m high and the total volume of the
RCC structure is about 720,000 m³. The dam is categorized as lean RCC dam with
w/c ratio of about 1.61 (Malkawi, 2001). RCC mix designation follows low
cementitious content mix with 85 kg/m³ Ordinary Portland Cement (OPC) and no
pozzolan. At the facings, CVC with 335 kg/m³ OPC is placed against the shutters with
a thickness of 0.3 m. Additionally, a PVC membrane is fixed below elevation 150
mASL. Bedding mortar between each RCC layer is spread at the upstream at one third
of the dam width and to 2.0 m from the downstream face and a nominal contraction
joint spacing of 60 m is applied at Mujib Dam. Only below the gallery, these joints
extend completely from upstream to downstream; above they reach from the faces
into the mass by one fourth of the dam width. The crest length is about 500 m with
embankment sections at both abutment; the upstream face of dam has a slope of
0.1(H):1(V) the stepped downstream face has a slope of 0.8(H): 1(V). Figure 2 shows
the cross section for Mujib Dam, showing the location of the distributed fiber optic
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temperature measurement (DFOT) and the stress-meter for in-situ stress
measurement. About 4000 m of fiber cables were installed at the dam body.
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