International Journal of Civil Engineering

Experimental and Numerical study on the Effect of Core Shape and Concrete Cover Length on the Behavior of BRBs

A. R. Rahai

During the past years the use of buckling restrained braces (BRBs) have had a dramatic growth due to their better performance comparing to conventional braces. BRBs have more ductility and energy absorption capacity by excluding the overall brace buckling. However, even these kinds of braces have some problems restricting their use in some projects, i.e. high tolerance of applying unbonding material, concrete placing difficulties and their weight. Accordingly, many researchers have conducted experiments to find the possibility of shortening or even eliminating the infill material of the braces. The following study has addressed the effect of debonding material friction ratio, shortening the concrete fill, and finally eliminating it if possible, by reshaping the core element with constant section area. The operated analysis has been carried out both numerically and experimentally. ABAQUS finite element software was applied for numerical analysis and the results were verified by an experimental study in two groups of models each including four full-scale brace models. With a constant core section area, results revealed that without the risk of buckling, the concrete cover length could be reduced. With a special core profile, the infill may be fully omitted and the restrainer would be made up of only a steel tube, which may happen without any changes made to the cross sectional area of the core profile.

Risk Assessment of Construction Projects for Water Conveyance Tunnels Using Fuzzy Fault Tree Analysis

A. Ardeshir

In the water industry tunnels can be used to transfer water from a basin to other areas over varying distances. The construction of such tunnels is inherently risky and can result in unpredicted events and incidents. It is therefore necessary that thorough risk assessments are carried out as a priority of the owner, contractor and consultant organization. This is so that, through a systematic and logical plan, they can risk posed by these unforeseen events and incidents. In this paper, the risks and their main causes which are often encountered in such projects are identified and assessed. A fault tree method is applied in order to identify the main causes of events and incidents. By its nature a Risk assessment cannot be defined by absolute values and so fuzzy data must be used in order to calculate the probability of incidence and the severity of the risk. This is done on the four main criteria of time, cost, quality and safety. In order to estimate the significance of each criterion and to calculate the significance of the total influence of risk Analytic Hierarchy Process (AHP) is applied. In this paper the case study of Dasht-e Zahab water conveyance tunnel has been selected for discussion as it was subjected to severe and multiple hazards. The results obtained using the method were validated by conducting different interviews with the field experts. It was concluded that by applying the proposed methodology on the case study the risks of the project can be evaluated in a more methodical and accurate way than could be done without using the method. This approach is therefore recommended for similar types of projects where there are complicated risks that must be thoroughly investigated and understood.

Seismic protection of vulnerable equipment with semi-active control by employing robust and clipped-optimal algorithms

T. Taghikhany

Critical non-structural equipments, including life-saving equipment in hospitals, circuit breakers, computers, high technology instrumentations, etc., are vulnerable to strong earthquakes, and the failure of these equipments may result in a heavy economic loss. To guarantee function of vulnerable equipment during earthquake peak acceleration and peak base displacement response of system should be limited to allowable levels. Traditional and passive control strategies cannot afford these contradictory targets in same time for broad range of ground motions. In recent years, semi-active control systems have been introduced as an adaptable and reliable alternative to control response under both limitations with low power supply. In this paper, efficacy of smart semi-active controlled floor isolation system which consists of a rolling pendulum system and a semi-active controlled magnetorheological (MR)-damper to control seismic response of equipment has been investigated by using clipped-H_2/LQG and clipped-H_∞ algorithms. The effectiveness of these algorithms was examined for equipment stand on raised floor due to floor motions in seven stories building. The results demonstrate semi-active control effectively decrease response acceleration and velocity of equipment in compare to passive strategy and hold its relative displacement to floor in least value. Furthermore it was shown semi-active control strategy with clipped-H_∞ algorithm in controlling seismic response of equipment compare to clipped-H_2/LQG algorithm and passive strategy (isolation system) have better performance in protecting equipment.

Game Analysis on Moral Hazard of Construction Project Managers in China

L. Ma

This paper aims to develop a quantitative game model for preventing construction project managers from moral hazard problem from the standpoint of construction enterprises in China. The authors analyze the sources of construction managers’ moral hazard behaviors under China’s specific situation on the basis of the principal-agent theory, establish a game theoretic model to analyze the moral hazard problem between construction enterprises and construction project managers, and calculate the equilibrium solution through building up the payoff matrix. Our crucial contribution is a quantitative characterization of risk deposit system and performance appraisal system which help to resolve the moral hazard problem of construction project managers. The solution results show that the probability of moral hazard problem of construction project managers can be reduced after implementing risk deposit system and performance appraisal system. Thus the two systems we proposed can be taken by China’s construction enterprises as the effective measures to resolve moral hazard problem of construction project managers.

RETRACTED ARTICLE: APPLICATION OF SMALL-SCALE EXPERIMENTAL MODELS FOR THERMAL COMFORT ASSESSMENT OF SUSTAINABLE BUILDING MATERIALS

R. Ralegaonkar

It has been brought to our attention that the article [1], published in International Journal of Civil Engineering, is a republishing material from a previous publication published in Journal of Energy Engineering[2]. The editorial board of IJCE consider this action as an infringement of professional ethics and therefore the decision has been made to retract of the article.

The authors’ response provided by Journal of Energy Engineering to us, was not satisfactory from this journal's point of view for this unfortunate situation (the documents are kept in the journal’s offices). Any inconvenience this may have caused by authors to the Readers due to improper action of the authors should be apologized by them.

[1] “Application of Small-Scale Experimental Models for Thermal Comfort Assessment of Sustainable Building Materials” by S. P. Raut, S. A. Mandavgane, and R. V. Ralegaonkar. International Journal of Civil Engineering, Vol. 12, No. 4, Transaction A: Civil Engineering, December 2014
Received: May 2013, Revised: December 2013, Accepted: January 2014. This article should be considered as retracted.

[2] Thermal Performance Assessment of Recycled Paper Mill Waste–Cement Bricks Using the Small-Scale Model Technique” by Sanjay Raut, Sachin Mandavgane, and Rahul Ralegaonkar. J. Energy Eng., 2014, 140(4): 04014001. http://dx.doi.org/10.1061/(ASCE)EY.1943-7897.0000171
Submitted on April 9, 2013; approved on October 25, 2013; published online on October 29, 2013.

Shape-size optimization of single-layer barrel vaults using improved magnetic charged system search

A. Kaveh

In this paper, the problem of simultaneous shape and size optimization of single-layer barrel vault frames which contains both of discrete and continuous variables is addressed. In this method, the improved magnetic charged system search (IMCSS) is utilized as the optimization algorithm and the open application programming interface (OAPI) plays the role of interfacing analysis software with the programming language. A comparison between the results of the present method and some existing algorithms confirms the high ability of this approach in simultaneous shape and size optimization of the practical and large-scale spatial structures.

A dynamic model for adjusting contemporary construction projects behaviors in today changeable environments

M. H. Sebt

Project Management knowledge has been used in many project oriented organizations in last two decades across the world. Despite, rate of project success did not change during these years. We believe there is a basic challenge in projects environment for managing them based on its inherent characteristics. In fact, project management knowledge use theories and concepts that are belong to process management world, as a different world. There is no enough attention to project characteristics as a fundamental differentiation for coping projects. Identification of construction projects nature in order to discern variables that create the project behaviors is main concern of the paper.Considering project characteristics in this research revealed construction project nature creates from combination two aspects. First, detecting environmental changes to develop a need and second prepare resources structure to respond the need. Important management challenge in this model is environmental continuous changes that alter the need and exchange resources structure. So, the paper considers how these aspects can be operationalized for developing a dynamic project management model. It gives some ideas about why project complexity might be considered to be increasing, and how construction projects move towards shorter timescales. The effectiveness of the model is verified by applying it for predicting some construction projects behavior. The results of the paper may capable future project managers to test any decision before its applying and lead to a new project management tool for construction projects management.

A model for prediction of compressive strength of chemically activated high phosphorous slag content cement

A. Allahverdi

It was found out that the logarithmic models fit the cement–slag blend systems well. In the present study, based on the experimental results, a logarithmic model has been developed to predict the compressive strength of chemically activated high phosphorous slag content cement. Mixes of phosphorous slag (80 wt.%), Portland cement (14 wt.%) and compound chemical activator (6 wt.%) were prepared at different Blaine finenesses using a laboratory ball mill. Compressive strengths of mortar specimens cured in lime-saturated water were measured at different curing times. Mathematical model was prepared in terms of curing time and water-to-cement ratio as independent variables and compressive strength as dependent variable. The comparisons between the model reproductions and the experimentally obtained results confirm the applicability of the presented model.

Load displacement behavior of concrete beam under monotonic static and low velocity impact load

Ö. Anıl

Experiments were carried out to observe the influence of loading type on concrete beam specimens. Beam specimens made of similar concrete mixture with the same geometry were tested under three point static loading and low velocity drop weight impact loading. Load – displacement behavior, absorbed energy dissipation capacity, stiffnesses, failure modes of beam specimens were obtained and discussed. A finite element (FE) model was prepared in ANSYS Explicit STR software and the results of FE analysis were compared with experimental results. The loading type and loading rate have significant influence on the maximum load, stiffness and energy dissipation capacity. Numerical results obtained from ANSYS Explicit STR FE models are consistent with the experimental results.

Experimental studies on the use of mobile cylinders for measurement of flow through rectangular channels

A. Ghare

The objective of field water measurement is to conserve water by improving management of its distribution and field application. A simple mobile flume to measure a discharge through small rectangular open channels in agricultural fields has been experimentally investigated. The flume consisting of a vertical cylinder inserted axially into the horizontal prismatic rectangular channel, referred as a simple cylindrical flume, has been calibrated. The flow rate in rectangular channel can be measured by constricting the flow due to presence of cylinder, resulting in critical flow conditions. Experiments have been performed on two simple cylindrical flumes of different diameters, to evaluate the hydraulic characteristics of subcritical incoming flow under free flow conditions. The results of laboratory experiments on the flume have been analysed and two different discharge prediction models have been developed. The two models developed for the prediction of discharge for simple cylindrical flumes developed for use in rectangular channel sections, are based on the energy concept and the direct regression approach, respectively. Both the proposed models have been validated using the limited experimental data available in the literature. Formation of critical depth at the throat section has also been verified. Plots have also been developed for the dimensionless column head and the corresponding Froude number of the incoming flow. The discharge prediction model giving the least error has been proposed for use in practice.

Impact characteristics of high-performance steel fiber reinforced concrete under repeated dynamic loading

K. NAGAMANI

An experimental study on the impact performance of silica fume concrete and steel fiber reinforced concrete at 28 days and 56 days under the action of repeated dynamic loading was carried out. In this experimental investigation, w/cm ratios of 0.4 and 0.3, silica fume replacement at 10% and 15% and crimped steel fibers with an aspect ratio of 80 were used. Results indicated that addition of fibers in high-performance concrete (HPC) can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths, toughness and ductility of HPC. Pulse velocity test was carried out for quality measurements of high-performance steel fiber reinforced concrete. Steel fibers were observed to have significant effect on flexural strength of concrete. The maximum first crack strength and ultimate failure strength at 28 days were 1.51 times and 1.78 times, respectively at 1.5% volume fraction to that of HPC. Based on the experimental data, failure resistance prediction model was developed with correlation coefficient (R) = 0.96 and absolute variation determined is 1.82%.