Scientia Iranica
Year:2015 | Volume:22 | Issue:3 (TRANSACTIONS A: CIVIL ENGINEERING)|Papers Count:11

Metakaolin (MK) is produced by the suitable thermal treatment of either kaolin or paper sludge. MK can be used to modify some properties of Portland Cement (PC). Many authors have studied the effects of blending PC with MK on durability characteristics, and the current investigation focuses on a review of the effect of MK on the durability of blended PC. A review on the resistance to abrasion, fire, freeze thaw, seawater, chloride-ion diffusion, carbonation, acid, sulfate, chloride, corrosion, creep, shrinkage, Alkali-Silica Reaction (ASR) and near surface is presented. This overview can be considered as a short guide for civil engineers.

The seismic behavior of concrete end diaphragms of bridges has not been studied before and there are no significant design provisions available. According to the American Association of State Highway and Transportation Officials (AASHTO), the end diaphragms being part of the seismic load path have to remain elastic under the prescribed seismic design forces, regardless of the type of bearings used. In this paper, using a three dimensional finite element model and nonlinear time history analyses, the behavior of reinforced concrete end diaphragms in straight single-span slab-girder bridges has been investigated. The results are compared to AASHTO's design provisions. It is concluded that for slab-girder concrete bridges, the concrete diaphragms remain elastic under design earthquake loading. It is also concluded that AASHTO's recommended seismic design force for end diaphragms could be unsafe in most cases.

Strengthening reinforced concrete members by bonding fiber reinforced plastics on the tension face has become a viable alternative to address strength deficiency problems. This paper investigates rectangular composite slabs subjected to a distributed load using Abaqus finite element software. A parametric study, using appropriate constitutive models, is generated to stimulate the nonlinear material behavior of the reinforced concrete and FRP. The numerical analysis examines the behavior and maximum capacity of the composite slabs. The paper presents the finite element analysis results for concrete slabs strengthened with FRP material. The proposed fitted equation is applicable in the preliminary investigation for engineering applications.

Piles in structural foundations that are used to load transmissions from the main structure to the bed are generally subjected to lateral loads. In order to study the effect of concrete pile geometry on its structural behavior, several models with different shapes and dimensions were selected and analyzed, assuming nonlinear behavior for soil. The behavior of the pile models was studied, evaluated and tabulated using numerical analysis under different conditions, such as changes in the pile geometry and shape, and soil properties. Therefore, the displacements of pile heads situated in granular soil, with different compaction levels, under a lateral load, were studied in loading and unloading cycles. The dissipated energy was calculated based on pile head displacements in different load steps in the first and second cycles of loading. The "performance index" is defined as the ratio of dissipated energy to the maximum pile head displacement, and these two factors effects on different pile model behavior were compared, concurrently. It was observed that piles with rectangular cross sections and smaller width have the maximum dissipation of energy, and the minimum displacement occurs in dense soil.

The objective of this study is to develop a material-nonlinear-analysis algorithm based on the Transfer Matrix Method (TMM). This newly developed algorithm can be used to perform nonlinear analyses of continuous beam systems. The nonlinear transfer matrix is derived from the general frame stiffness matrix, and the Gauss-Lobatto integration scheme is employed for numerical integration. In the TMM, the system equation has a constant number of system unknowns, regardless of the total degree-off-freedom number in the structure and the system response (either linear or nonlinear). As a result, TMM can be used efficiently, both for linear and nonlinear structural analyses. In this study, a secant nonlinear algorithm, required in nonlinear TMM, is employed, due to its good compromise between the convergence rate and numerical stability. To verify the accuracy and efficiency of the developed TMM, four numerical examples are selected and analyzed. The analysis results are compared with those obtained by the highly accurate flexibility-based frame model, in terms of global and local responses.

The aim of this paper is to deal with Resource-Constrained Multiple Project Scheduling Problems (RCMPSP), which consider the complex hierarchical organization structure and fuzzy random environment in the decision making process. A bi-level multiobjective RCMPSP model with fuzzy random coefficients is presented, taking into account the strategy and process in the practical RCMPSP. In the model, the project director is considered the leader at the upper level who aims to minimize the total tardiness penalty of all sub-projects and the consumption of resources. Meanwhile, the sub-project manager, a follower at the lower level, regards the target to minimize the duration of each sub-project. To deal with the uncertainties, fuzzy random parameters are transformed into trapezoidal fuzzy variables first, which are subsequently de-fuzzified by the expected value index. A multi-objective bi-level adaptive particle swarm optimization algorithm (MOBL-APSO) is designed as the solution method to solve the model. The results and analysis of a case study are presented to highlight the practicality and efficiency of the proposed model and algorithm.

Quantitative approaches to risk allocation have been developed to overcome the limitation of qualitative approaches, and to determine how the responsibility of risk should be shared between contracting parties. This paper integrates a system dynamics simulation scheme with fuzzy bargaining game theory for quantitative risk allocation. The behaviour of contracting parties in the quantitative risk allocation negotiation process is modelled as player behaviour in a game. A system dynamics based model is employed to determine the contractor and client costs (players' payoffs) at different percentages of risk allocation. Having determined the player payoffs, the common interval between player acceptable risk allocation percentages is determined. The bargaining process is then performed between two parties accounting for the common interval, and a desirable and equitable percentage of risk allocation is determined.

A triaxial testing system is described for measuring the wave velocity, stiffness, damping and stress-strain behavior of layered granular materials and rock specimens under impact, cyclic and monotonic loading. The system is equipped with high-frequency GAPSENSORs (GSs) in front of target plates connected on the side of a specimen surface to measure wave velocity, axial and radial deformations locally, LDTs to measure axial and radial deformations locally, and a load cell. Based on the first arrival of compressional wave of the deformation time-histories under impact loading, the pulse velocity is evaluated. In addition, using a reduced deformation amplitude technique at different elevations of the specimen, damping ratio is calculated. Results indicate that measurement of the wave velocity and damping ratio using low noise level GSs is a simple, nondestructive and reproducible method. Comparing the results of small strain shear modulus and damping ratio using local axial and radial strains measured by LDTs and GSs in the cyclic loading, with those of the proposed method, the high precision of the used innovative method is confirmed. Using this system, a continuous stress-strain relation for a strain range of 0.0001% to several % can be obtained from a single test using a single specimen.

One of the most common options for structural strengthening and rehabilitation is the use of FRP sheets for shear-torsion strengthening of Reinforced Concrete Beams (RCBs). Their widespread use owes much to their ease of application in addition to many other advantages. The availability of technical references and construction codes today makes it easy to calculate the shear and torsion capacities of strengthened beams. Practically, however, it is combined shear and torsion rather than pure torsion that develops in beams. The present article investigates the use of FRP sheets in strengthening RC beams. For the purposes of this study, 14 RC beams were used that were classified into three different sets: one set consisted of 5 non-strengthened (plain) beams and two sets (one with 5 and the other with 4 beams) consisted of RC beams strengthened with CFRP sheets in two different strengthening patterns. The shear-torsion interaction curves were derived for them by loading the beams under a variety of eccentricities ranging from 0 (pure shear) to infinity (pure torsion). The supports were constructed with flexure and torsion rigidity. Laboratory tests revealed that the shear-torsion interaction curves for all the three sets of beams were close to straight lines.

In the present study, the extent of riprap layer with different sizes around bridge piers is investigated. Rectangular pier with or without an attached protective collar aligned with the flow and skewed at different angles are tested. The optimal configurations of riprap extent for each pier condition with different sizes are determined. Experiments showed that in case of aligned rectangular pier without a collar only 8% of the area around the pier is critical and the remaining 92% area can be protected with about 60% smaller riprap stones. As the skew angle of the pier increases up to 20, the critical area increases up to 23% of the riprap extent. In case of protected pier with collar, the collar prevents the critical region around the pier in aligned and 5o skewed pier. However, by increasing the flow attack angle up to 20, only a small area up to 30% in the riprap extent around the collar is critical and the remaining area can be placed with 40% smaller riprap size. Finally, the design algorithm for riprap extent with different sizes is presented.

A multi-objective Optimality Criteria (OC) is used to obtain optimum design of metal cylindrical shells under combined external loading. The objectives are to maximize the axial and hoop stiffness and minimize the mass of stiffened cylinders subject to the constraints, including functions of weight and buckling load, in such a way that the stiffened shell has no increase in weight and no decrease in buckling load, with respect to the initial unstiffened shell. The optimization process contains six design variables, including shell thickness, number of circular ring stiffeners, number of longitudinal stringer stiffeners, height of ring stiffeners, width of ring stiffeners, and longitudinal stiffener eccentricity from the shell centerline. In the analytical solution, the Rayleigh-Ritz energy procedure is applied and the ring stiffeners are treated as discrete elements. The shapes of the ring and stringer stiffeners are assumed rectangular and Z, respectively. The shell is subjected to uniform axial and non-constant external pressure, simultaneously. The longitudinal stringers are placed in equal spacing, whereas the rings can be placed in an unequal space, due to the non-constant of external pressure over the cylinder length. The results show that the iteration numbers depend on the ring stiffener space states.