Civil Engineering Infrastructures Journal
Volume:51 Issue: 1, Jun 2018

The only way to test the ability of concrete plants to produce high quality concrete is to test their final products. Also, the process of testing and controlling concrete quality is time consuming and expensive. In this regard, having a quick, cheap and efficient way to predict the readiness of concrete plants to produce high quality concrete is very valuable. In this paper, a probabilistic multi-attribute algorithm has been developed to address this problem. In this algorithm, the goal is to evaluate readiness of concrete plants to produce high quality concrete based on the error rate of concrete compressive strength. Using past information and data mining techniques, this algorithm predicts the readiness level of concrete plants by similarity of their production factors to past information. Readiness alternatives for plants are ranked using data mining techniques for order preference based on their production factors (PF) and by evaluating the similarity/difference of each PF to past information. A case study of 20 concrete plants is used to illustrate the capability of the new algorithm; with results showing that the algorithm generated nondominated solutions can assist plant managers to set efficient production plan, a task both difficult, cost and time-consuming using current methods. In the case study, lab test totally confirm the algorithm outcomes thus it has been successfully verified.

Vertical drains and stone columns which have been used in infrastructure construction for highways, ports, coastal regions, etc., provide significant benefits for improving soil characteristics such as reducing the drainage length and accelerating the consolidation process. So the investigation of the radial consolidation is inevitable. Soils may be subjected to cyclic loading such as silos, tanks, etc. This paper presents semi-analytical solutions for radial consolidation and investigates the consolidation behavior under three types of cyclic loading. Consolidation under cyclic loads was calculated using the superimposition rule. Barron (1948) and Olson (1977) have presented theories for calculating radial consolidation under static and ramp load respectively. In this study, by using a set of continuous static loads or a series of infinite ramp loads, with alternatively positive and negative signs, we have extended these theories for rectangular, triangular and trapezoidal cyclic loads. The obtained analytic results demonstrate that the average degree of consolidation at the steady state depends on the integral of the load-time curve for each cycle and it increases with increase of the integral and the results indicate that change in cycle period of time does not effect on the time of getting steady state. Radial and vertical consolidation under rectangular cyclic loading have also compared and the effect of the distance between vertical drains on the time of getting steady state have investigated.

In the case of problematic soils and tall buildings where the design requirements cannot be satisfied merely by a raft foundation, it is of common practice to improve the raft performance by adding a number of piles so that the ultimate load capacity and settlement behavior can be enhanced. In this study, the effect of spatial variability of soil parameters on the bearing capacity of piled raft foundation is investigated based on the random field theory using the finite difference software of FLAC3D. The coefficient of variation (COV) of the soil’s undrained shear strength, the ratio of standard deviation to the mean, was considered as a random variable. Moreover, the effect of variation of this parameter on the bearing capacity of piled raft foundation in undrained clayey soils was studied taking the Monte Carlo simulation approach and the normal statistical distribution. According to the results, taking into account the soil heterogeneity generally results in more contribution of the raft in bearing capacity than that of the homogenous soils obtained by experimental relationships, which implies the significance of carrying out stochastic analyses where the soil properties are intensively variant.

One of the numerous methods recently employed to study the health of structures is the identification of anomaly in data obtained for the condition of the structure, e.g. the frequencies for the structural modes, stress, strain, displacement, speed, and acceleration) which are obtained and stored by various sensors. The methods of identification applied for anomalies attempt to discover and recognize patterns governing data which run in sharp contrast to the statistical population. In the case of data obtained from sensors, data appearing in contrast to others, i.e. outliers, may signal the occurrence of damage in the structure. The present research aims to employ computer algorithms to identify structural defects based on data gathered by sensors indicating structural conditions. The present research investigates the performance of various methods including Artificial Neural Networks (ANN), Density-Based Spatial Clustering of Applications with Noise (DBSCAN), Manhattan Distance, Curve Fitting, and Box Plot in the identification of samples from damages in a case study using frequency values related to a cable-support bridge. Subsequent to the implementation of the methods in the datasets, it was shown that the ANN provided the optimal performance.

Sulfate attack is a series of physico-chemical reactions between hardened cement paste and sulfate ions. Sulfate ion penetration into the hydrated cement results in the formation of voluminous and deleterious phases such as gypsum and ettringite which are believed to cause deterioration and expansion of concrete. Concrete deterioration due to sulfate attack depends on many parameters, however, in experimental studies, the implementation of the parameters and obtaining the results in a short time are too difficult. In this paper the effect of wollastonite, with and without silica fume, on the performance of cement based materials during hydration and magnesium sulfate attack was studied by thermodynamic modeling. Thermodynamic modelling was carried out using the Gibbs free energy minimization program GEMS. By this method, in addition to investigating the type and volume of the produced material, the optimal substitution percentage of wollastonite and silica fume were studied as well. In sulfate attack, especially at higher percentages of substitution, wollasonite is not very effective in itself. Wollasonite replacement has a reverse effect on monosulfate and ettringite phases. Volume of these phases increases with addition of the substitution percentage. Substituting a portion of the cement with wollastonite and silica fume would improve sulfate resistance. Substitution of 5% of wollasonite and 10% of silica fume has shown the best performance, highest increase in C-S-H gel volume and reduction in harmful phases such as gypsum, ettringite and brucite.

Trapezoidal prestressed unbonded retrofit (TPUR) systems have been recently developed and tested. The authors have already developed a comprehensive and accurate analytical solution for the TPUR system that takes many system parameters into account. The main aim of this paper is to develop a simplified analytical solution for predicting the behavior of metal beams that have been strengthened with the TPUR system. The developed analysis method can be useful to engineers because of its simplicity. An energy approach based on Castigliano’s theorems is used to study the flexural behavior of a steel beam retrofitted with the TPUR system. A parametric study was performed and the comparative results showed that the results using Castigliano’s first theorem are in agreement with the results using the flexibility approach.

Hybrid fiber reinforced concrete (HFRC) consisting of two or more different types of fibers has been widely investigated because of its superior mechanical properties. In the present study, the effect of the addition of steel (0.25%, 0.5%, 0.75%, and 1% of concrete volume) and Polypropylene (0.2%, 0.4%, and 0.6% of concrete volume) fibers on the surface scaling resistance of concrete, depth of penetration of water, and compressive strength of concrete is investigated. The permeability test is conducted for all the specimens to measure the depth of penetration of water under pressure. Moreover, scaling resistance of concrete subjected to freezing and thawing cycles in the presence of salt solution is assessed to simulate the durability of concrete under field exposure conditions. The results showed that the addition of fibers increases the permeability of concrete. However, it enhances the scaling resistance and compressive strength of concrete. The mixture containing 0.4% of Polypropylene (PP) fibers and 0.75% of steel fibers demonstrated the highest scaling resistance since the scaled materials in this mixture were almost half weight of the materials scaled from the control mixture after 84 cycles of freezing and thawing. Increasing the scaling resistance of concrete leads to a better long-term serviceability performance of HFRC compared to plain concrete, making these composites a great choice for application in environments exposed to cold weather.

Clayey soils are the most common material used for water sealing and undertake an important role in controlling landfill-related pollution. Organic liquids can adversely affect the effectiveness of clay liners by drastically increasing their hydraulic conductivity. The aim of this study is to investigate and compare the permeability in two types of clay with different plasticity, exposed to the flow of kerosene and diesel as non-polar immiscible liquids and ethanol as a miscible liquid with an intermediate dielectric constant. The effects of plasticity and water content for a given compactive effort are also investigated. Two different clayey soils with different plasticity were provided and their physical properties determined. Next, modified constant-head permeability tests were conducted on the samples. Results show that the lower dielectric constant of the organic fluids, leads to an increase in hydraulic conductivity. Research has shown that organic fluids shrink the diffuse double layer due to their lower dielectric constant and reduce its thickness. Shrinkage of the double layer leads to higher permeability and lower plasticity in the soil. As a result, the void space for the passage of the fluid increases. With the decrease the dielectric constant from 80.1 to 1.8, permeability is increased up to 1800 times. On the other hand, results show that for a clay with a higher liquid limit and plastic limit, permeability for all the liquids investigated in the research is lower.

Irregularities in bridge pier stiffness concentrate the ductility demand on short piers; while not operating on the longer and more flexible ones. The existence of non-uniform, ductility demand distribution in bridges significantly influences seismic response. As such, this paper proposes a new approach for balancing the ductility demand in irregular bridges by utilizing shape memory alloys (SMAs). An irregular, single column bent viaduct with unequal pier heights is modeled and used as a reference bridge. To enhance seismic behavior of the bridge, a fixed bearing at the top of the short pier is replaced by a sliding bearing and two groups of SMA bars. SMAs are designed to keep their maximum strain within the super-elastic range. The seismic response of the controlled bridge is compared with a reference bridge through parametric studies using a set of suitable ground motion records. Study parameters include SMA lengths, short pier reinforcement ratios, design strain of SMA elements, and the heights of the medium and long piers. The proposed method successfully reduced the response of the short pier and, hence, improved the overall seismic behavior.

A general initial-boundary value problem of one-dimensional transient wave propagation in a multi-layered elastic medium due to arbitrary boundary or interface excitations (either prescribed tractions or displacements) is considered. Laplace transformation technique is utilised and the Laplace transform inversion is facilitated via an unconventional method, where the expansion of complex-valued functions in the Laplace domain in the form of general Dirichlet series is used. The final solutions are presented in the form of finite series involving forward and backward travelling wave functions of the d’Alembert type for a finite time interval. This elegant method of Laplace transform inversion used for the special class of problems at hand eliminates the need for finding singularities of the complex-valued functions in the Laplace domain and it does not need utilising the tedious calculations of the more conventional methods which use complex integration on the Bromwich contour and the techniques of residue calculus. Justification for the solutions is then considered. Some illustrations of the exact solutions as time-histories of stress or displacement of different points in the medium due to excitations of arbitrary form or of impulsive nature are presented to further investigate and interpret the mathematical solutions. It is shown via illustrations that the one-dimensional wave motions in multi-layered elastic media are generally of complicated forms and are affected significantly by the changes in the geometrical and mechanical properties of the layers as well as the nature of the excitation functions. The method presented here can readily be extended for three-dimensional problems. It is also particularly useful in seismology and earthquake engineering since the exact time-histories of response in a multi-layered medium due to arbitrary excitations can be obtained as finite sums.

Since the structure and foundation are built on soil, the soil is the major platform by which seismic vibrations are transmitted to the structure, and has noticeable effects on the response and behavior of structure during earthquakes. In this research, the recently introduced Performance-based plastic design (PBPD) and its modified Performance-based plastic design (MPBPD) method in which soil and structure interaction effect has been considered underwent the seismic evaluation. In order to do evaluation, a twenty-floor concrete structure with MPBPD method and conventional PBPD was designed and analyzed in accordance with the time history of the 22 far-field quake records. In this study, cone model is employed for modeling the soil and foundation. With a detailed three-dimensional finite element model of a twenty-story high-rise structure constructed and exploited in the OpenSees software, it is attempted to consider a more realistic behavior of the structure. The results of six related parameters with the maximum response of the structure demonstrate the efficiency and performance of the MPBPD method for the purpose of considering the SSI effect, compared with the conventional method of PBPD. The Results show that, in the MPBPD design method, maximum displacement, acceleration, inter-story drift and shear force dropped leading to a better distribution of energy in the structure compared to the PBPD method.

Current approach for designing of reinforced concrete members is based on the load and resistance factor. However the load and resistance parameters are random variables, the constant values have been designated for them in the designing procedure. Assuming these factors as the constants, will be led to the unsafe and uneconomical designs. Safe designing of structures requires appropriate recognition of the effective parameters and their uncertainties. Therefore, this achievement is possible through clarifying the effective design parameters and applying risk-based design methods. The main purpose of this paper is reliability based design of the reinforcement concrete structures under bending action. Rectangular sections with tension rebars (singly reinforced), rectangular sections with tension and also compression rebars (doubly reinforced) and T-shape sections are designed based on probabilistic methods. The appropriate tool for reliability calculations is selected based on pros and cons of each method. Evaluation of the load and the resistance factors for all mentioned beams is the next goal of this investigation. In this research, the steel usages for desired safety level are determined through the produced graphs. Using the proposed methodologies, the economic and fully probabilistic design of the concrete beams for bending is now available.