International Journal of Civil Engineering
1735-0522
5
4
2007
12
1
Considering different criteria for minimizing torsional response of asymmetric structures under near-fault and far-fault excitations
247
265
EN
H.
Shakib
A.
Ghasemi
An attempt has been made to explore the general trends in the seismic response of planasymmetric
structures when subjected to near-fault and far-fault ground motions. Systems with
structural wall elements in both orthogonal directions considering actual and common nonlinear
behavior under bi-directional excitation were studied. Idealized single-storey models with uni-axial
eccentricity were employed. The main findings are: The rotational response trend considering
actual behavior method would be different from common behavior method assumption, when the
system subjected to near-fault motions. In the former case, the minimum rotational response could
be achieved, when stiffness and strength centers are located on opposite side of the mass center. In
the latter case, stiffness eccentricity determines the minimum and maximum rotational response.
General trends in the rotational demand for far-fault motions, considering two type behavior
assumptions, are similar to the last case. Moreover, in near-fault motions, when stiffness and
strength centers are located on opposite side of the mass center, stiff side displacement demand
would be greater than that soft side which is contrary to the conventional guidelines. While, in farfault
motions similar to near-fault motions which stiffness and strength centers are located on one
side of the mass center, displacement demand would be according to conventional guidelines.
International Journal of Civil Engineering
1735-0522
5
4
2007
12
1
A comparision between plastic shrinkage of concrete containing silica fume and the normal concrete
266
273
EN
P.
Ghoddousi
A.M.
Raiss ghasemi
T.
Parhizkar
Plastic shrinkage is one of the most important parameter which must be considered in hot
weather concreting. If plastic shrinkage is not prevented, cracking will be significant, especialy if
silica fume is used in the mix. In this paper, the effect of silica fume in bleeding and evaporation was
investigated in laboratory. The results showed that in restrained shrinkage, beside relative humidity,
temperature and wind velocity, sun rediation also is very important factor in evaporation rate. It is
found that under solar radition condition, the evaporation was much larger than the estimated value
in ACI 305 Nomogram. The rate of evaporaion under solar radiation was about two folds of
evaporation rate under shade condition.
The results showed that in terms of crack initiation time, crack width and total cracking area,
concrete containing silica fume is more severe than concrete with no silica fume. Reduction of water
cement ratio in concrete with silica fume makes the concrete more sensitive in cracking. The results
of this project also showed that the severity of the cracking is not related only to rate of bleeding
but all environmental factors including like sun radiation or shading and also mix compositions
have important roles.
International Journal of Civil Engineering
1735-0522
5
4
2007
12
1
Strength evaluation of wet reinforced silty sand by triaxial test
274
283
EN
S.N.
Moghaddas Tafreshi
A.
Asakereh
Conventional investigations on the behavior of reinforced and unreinforced soils are often
investigated at the failure point. In this paper, a new concept of comparison of the behavior of
reinforced and unreinforced soil by estimating the strength and strength ratio (deviatoric stress of
reinforced sample to unreinforced sample) at various strain levels is proposed. A comprehensive set
of laboratory triaxial compression tests was carried out on wet (natural water content) non-plastic
beach silty sand with and without geotextile. The layer configurations used are one, two, three and
four horizontal reinforcing layers in a triaxial test sample. The influences of the number of
geotextile layers and confining pressure at 3%, 6%, 9%, 12% and 15% of the imposed strain levels
on sample were studied and described. The results show that the trend and magnitude of strength
ratio is different for various strain level. It implies that using failure strength from peak point or
strength corresponding to the axial-strain approximately 15% to evaluate the enhancement of
strength or strength ratio due to reinforcement may cause hazard and uncertainty in practical
design. Hence, it is necessary to consider the strength of reinforced sample compared with
unreinforced sample at the imposed strain level. Only one type of soil and one type of geotextile
were used in all tests.
International Journal of Civil Engineering
1735-0522
5
4
2007
12
1
Multi-reservoir operation by adaptive pheromone re-initiated ant colony optimization algorithm
284
301
EN
Hon.M.
ASCE
M.R.
Jalali
A.
Afshar
M.A.
MariĆ±o
Through a collection of cooperative agents called ants, the near optimal solution to the
multi-reservoir operation problem may be effectively achieved employing Ant Colony Optimization
Algorithms (ACOAs). The problem is approached by considering a finite operating horizon,
classifying the possible releases from the reservoir(s) into pre-determined intervals, and projecting
the problem on a graph. By defining an optimality criterion, the combination of desirable releases
from the reservoirs or operating policy is determined. To minimize the possibility of premature
convergence to a local optimum, a combination of Pheromone Re-Initiation (PRI) and Partial Path
Replacement (PPR) mechanisms are presented and their effects have been tested in a benchmark,
nonlinear, and multimodal mathematical function. The finalized model is then applied to develop an
optimum operating policy for a single reservoir and a benchmark four-reservoir operation problem.
Integration of these mechanisms improves the final result, as well as initial and final rate of
convergence. In the benchmark Ackley function minimization problem, after 410 iterations, PRI
mechanism improved the final solution by 97 percent and the combination of PRI and PPR
mechanisms reduced final result to global optimum. As expected in the single-reservoir problem,
with a continuous search space, a nonlinear programming (NLP) approach performed better than
ACOAs employing a discretized search space on the decision variable (reservoir release). As the
complexity of the system increases, the definition of an appropriate heuristic function becomes more
and more difficult this may provide wrong initial sight or vision to the ants. By assigning a
minimum weight to the exploitation term in a transition rule, the best result is obtained. In a
benchmark 4-reservoir problem, a very low standard deviation is achieved for 10 different runs and
it is considered as an indication of low diversity of the results. In 2 out of 10 runs, the global optimal
solution is obtained, where in the other 8 runs results are as close as 99.8 percent of the global
solution. Results and execution time compare well with those of well developed genetic algorithms
(GAs).
International Journal of Civil Engineering
1735-0522
5
4
2007
12
1
Optimal design and operation of irrigation pumping systems using particle swarm optimization algorithm
302
311
EN
M.H.
Afshar
R.
Rajabpour
This paper presents a relatively new management model for the optimal design and
operation of irrigation water pumping systems. The model makes use of the newly introduced
particle swarm optimization algorithm. A two step optimization model is developed and solved with
the particle swarm optimization method. The model first carries out an exhaustive enumeration
search for all feasible sets of pump combinations able to cope with a given demand curve over the
required period. The particle swarm optimization algorithm is then called in to search for optimal
operation of each set. Having solved the operation problem of all feasible sets, one can calculate
the total cost of operation and depreciation of initial investment for all the sets and the optimal set
and the corresponding operating policy is determined. The proposed model is applied to the design
and operation of a real-world irrigation pumping system and the results are presented and
compared with those of a genetic algorithm. The results indicate that the proposed mode in
conjunction with the particle swarm optimization algorithm is a versatile management model for
the design and operation of real-world irrigation pumping systems.
International Journal of Civil Engineering
1735-0522
5
4
2007
12
1
Evaluating the potential for tsunami generation in southern Iran
312
329
EN
M.
Heidarzadeh
M.
Dolatshahi Pirooz
N.
Hadjizadeh Zaker
M.
Mokhtari
Makran Subduction Zone (MSZ) offshore of Iran and Pakistan is one of the most
tsunamigenic sources in the Indian Ocean. Historically, the MSZ has generated some tsunamigenic
earthquakes like that of 28 November 1945 with the death tool of more than 4000 people along the
coasts of Iran, Pakistan, India, and Oman. In this study, the tsunami hazard associated with the
MSZ is investigated. At first, a review of historical tsunamis in the Indian Ocean basin was
performed which reveals the Makran region has experienced al least 4 tsunamis including events of
326 BC, 1897, 1008, and 1945. Consequently, since the pattern and extent of vertical ground
deformation from an earthquake determines whether or not a tsunami is formed, a computer
program is developed to predict the seafloor deformation due to the earthquake occurrence in the
MSZ. The model was verified through run of it on some actual tsunamis so far occurred. Then, using
the data of the 1945 Makran tsunami, the seismic parameters of the MSZ were calibrated. Finally,
we used the developed computer program to calculate seafloor deformation at the location of
Makran subduction zone for several earthquake scenarios with moment magnitudes ranging
between 6.5 and 8.5. The results of this research show that the risk of tsunami generation from MSZ
can be classified into three main categories, as follows: (1) very little risk for tsunami generation
in the case of the occurrence of an earthquake having magnitude up to 7 (2) little to medium risk
for moment magnitudes ranging between 7 and 7.5 and (3) high risk for moment magnitude greater
than 7.5. At the end of the paper, modeling of tsunami propagation is performed for an earthquake
scenario with magnitude of 8 offshore Chabahar, in order to give preliminary information about
tsunami behavior in this region.