Showing papers in "Ksce Journal of Civil Engineering in 2013"

Improvements in Engineering Properties of Soils through Microbial-Induced Calcite Precipitation

Abstract: Microbial-Induced Calcite Precipitation (MICP) has recently emerged as a sustainable technique for soil improvement. This paper aims to study the effectiveness of MICP in improving the shear strength and reducing the hydraulic conductivity of soils. A species of Bacillus group, B. megaterium was used to trigger the calcite precipitation. The experimental variables included soil types (tropical residual soil and sand), soil densities (85%, 90%, and 95% of their respective maximum densities), and treatment conditions (untreated, treated with cementation reagents only, treated with B. megaterium only, and treated with B. megaterium and cementation reagents). The results showed that MICP could effectively improve shear strength and reduce hydraulic conductivity for both residual soil and sand. The improvements, however, varied with soil densities, soil types, and treatment conditions. With MICP treatment, the improvement ratios in shear strength of the residual soil specimens were significantly higher (1.41–2.64) than those of the sand specimens (1.14–1.25). On the contrary, the sand specimens resulted in greater hydraulic conductivity reduction ratios (0.09–0.15) than those of the residual soil specimens (0.26–0.45). These observations can be explained by the particle-particle contacts per unit volume and pore spaces in the soil specimens. Both soil specimens when treated with cementation reagents only exhibited slight alterations in the shear strength (ranging from 1.06–1.33) and hydraulic conductivity (ranging from 0.69–0.95). The results implied that natural calcite forming microorganisms only exist for insignificant amount. The amount of calcite precipitated in the treated residual soil specimens ranged from 1.080% to 1.889%. The increments of calcite content in the treated sand specimens were comparatively higher, ranging from 2.661% to 6.102%. The results from Scanning Electron Microscope (SEM) analysis confirmed the experimental findings.

Application of Excel Solver for Parameter Estimation of the Nonlinear Muskingum Models

Abstract: The Muskingum model continues to be a popular procedure for river flood routing. An important aspect in nonlinear Muskingum models is the calibration of the model parameters. The current study presents the application of commonly available spreadsheet software, Microsoft Excel 2010, for the purpose of estimating the parameters of nonlinear Muskingum routing models. Main advantage of this approach is that it can calibrate the parameters using two different ways without knowing the exact details of optimization techniques. These procedures consist of (1) Generalized Reduced Gradient (GRG) solver and (2) evolutionary solver. The first one needs the initial values assumption for the parameter estimation while the latter requires the determination of the algorithm parameters. The results of the simulation of an example that is a benchmark problem for parameter estimation of the nonlinear Muskingum models indicate that Excel solver is a promising way to reduce problems of the parameter estimation of the nonlinear Muskingum routing models. Furthermore, the results indicate that the efficiency of Excel solver for the parameter estimation of the models can be increased, if both GRG and evolutionary solvers are used together.

A Newly Developed State-of-the-Art Geotechnical Centrifuge in Korea

Abstract: The first large scale geotechnical centrifuge in Korea has recently been developed at KAIST under the Korea Construction Engineering Development (KOCED) Collaboratory program. A 5 m platform radius, 240 g-tons state-of-the-art geotechnical centrifuge has been installed in a new facility. The centrifuge has the unique feature of an automatic balancing system and includes parts for general testing purposes such as fluid rotary joints, slip rings, a fiber optic rotary joint and an Ethernet network system. In addition, a four degree-of-freedom in-flight robot can be equipped to simulate complex construction or in-situ testing process during centrifuge flight. In order to simulate earthquake motion during operation, a self-balancing type biaxial shaking table has also been developed. Since the KOCED program promotes collaboration and remote use, tele-presence and tele-participation environments have been implemented in this facility.

Performance of self-compacting concrete containing different mineral admixtures

Abstract: Self-Compacting Concrete is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement. One of the disadvantages of self-compacting concrete is its cost, associated with the use of high volumes of Portland cement and use of chemical admixtures. One alternative to reduce the cost of self-compacting concrete is the use of mineral admixtures such as silica fume, ground granulated blast furnace slag and fly ash, which is finely, divided materials added to concrete during mixture procedure. When these mineral admixtures replace a part of the Portland cement, the cost of self-compacting concrete will be reduced especially if the mineral admixtures are waste or industrial by-product. Moreover, the use of mineral admixtures in the production of self-compacting concrete not only provides economical benefits but also reduces heat of hydration. The incorporation of mineral admixtures also eliminates the need for viscosity-enhancing chemical admixtures. The lower water content of the concrete leads to higher durability, in addition to better mechanical integrity of the structure. This paper presents an experimental investigation on strength aspects like compressive, flexural and split tensile strength of self compacting concrete containing different mineral admixtures and workability tests for different mineral admixtures (slump, L-box, U-box and T50) are carried out. The methodology adopted is that mineral admixtures are replaced by 30%, 40% and 50% for Portland cement and performance is measured and compared. The influence of mineral admixtures on the workability, compressive strength, splitting tensile strength and flexural strength of self-compacting concrete was investigated. The mix proportion is obtained as per the guidelines given by European Federation of producers and contractors of special products for structure. The following inferences were made; optimum dosage of super plasticizer enhanced the flow property of the concrete. As a result, overall improvements in the flow and filling ability of the self-compacting concrete were observed. It is observed that when mineral admixtures used in self-compacting concrete, can reduce the amount of super-plasticizer necessary to achieve a given fluidity. It should be noted that the effect of mineral admixtures on admixture requirements is significantly dependent on their particle size distribution as well as particle shape and surface characteristics. From this view point, a cost effective self-compacting concrete design can be obtained by incorporating reasonable amounts of silica fume, fly ash, and ground granulated blast furnace slag.

Establishment of Structural Similitude for Elastic Models and Validation of Scaling Laws

Abstract: Scaled down models are widely used for experimental investigations on huge structures due to the limitation in the capacities of testing facilities, and, moreover, the experimentation on scaled models is less expensive. Also small scale models are often built with materials dissimilar to those of the prototype. However, only few studies have been carried out on the similitude laws for the prototype structures with small scale models built with a different material. In the present study, an attempt has been made to develop a scaling law for models to carry out the free vibration analysis of structures, based on the similitude requirement. The established scaling laws are validated analytically using simple test problems. The similitude relationship between the prototype and the model is validated with the aid of a case study using finite element analysis software.

Enhancing the Durability Properties of Concrete Containing Recycled Aggregate by the Use of Pozzolanic Materials

Abstract: This study concerns properties of concrete containing Recycled Aggregate (RCA). To compensate for a reduction of properties for the RCA concrete, 30% Pulverised Fuel Ash (PFA) and 60% Ground Granulated Blast furnace Slag (GGBS) were used for replacement for Ordinary Portland Cement (OPC). The compressive strength for RCA concretes was measured for 180 days, and simultaneously the durability against chloride, frost and sulfate environment was evaluated. As a result, the RCA concrete always revealed the lower strength and resistance to chloride, frost and sulfate attack. However, the RCA concrete containing 30% PFA and 60% GGBS enhanced the strength to the level for control concrete containing natural aggregate. The rate of chloride transport was lowered by addition of 30% PFA and 60% GGBS in the RCA concretes after 91 days of curing, presumably due to the refinement of pore structure and further formation of hydration products. As for the frost damage, 30% PFA concrete containing the RCA showed the greatest resistance to frost, while 60% GGBS concrete containing RCA to the similar level of the control. It was found that the RCA concrete containing 30% PFA and 60% GGBS were slightly more resistant to sulfate attack than control.

Importance and ranking evaluation of delay factors for development construction projects in Benin

Abstract: This study focuses on the analysis of delay factors which affect the delay in construction completion in Benin in order to teach construction project managers a specific managerial method that would be very useful for the success of new development projects. In this respect, some Beninese construction experts have been interviewed about some construction projects: departmental hospital, administration office, school, community health care center and community market done in the past and located in Cotonou, Porto-Novo, Abomey and Parakou. After statistical data of frequency, severity and importance was analyzed, an index of thirty-five delay factors were identified and used in structured questionnaires that were sent to the construction managers (contractor, owner, consultant and architect). The top ten important delay factors by their rank were further identified as: Financial capability by contractor, financial difficulties by owner, poor subcontractor performance, materials procurement of contractor, changes in drawings of architect, inadequate planning and scheduling of contractor, slow inspection of completed works by the consultant, equipment availability of contractor, preparation, approval of drawings of consultant and acceptance of inadequate design drawings by consultant. A comparison of the top five delay factors of Benin construction projects requiring a time extension with selected construction projects in Asia and other African countries shows that financial difficulty is most common, especially in African countries. Other causes of delay are very similar for developing countries and related to lack of technology, management, skills and competencies of project participants. Therefore it has been concluded that construction time overrun depends on economic, political stability and management implementation in each country. The study can be extended to compare other African countries development construction project delay factors to Asian countries.

Model Studies of Bearing Capacity of Strip Footing on Sand Slope

Abstract: An experimental investigation into the ultimate bearing capacity of strip footing on sand slope is reported. The parameters investigated are the effect of setback distance of the footing to the slope crest, slope angle, relative density of sand and footing width on the ultimate bearing capacity of strip footings. A series of finite element analyses was additionally performed on a prototype slope to ascertain the validity of the findings from the laboratory model tests and to supplement the results of the model tests. The agreement between observed and computed results is found to be reasonably well in terms of load-settlement and general trend of behavior. The results show that the ultimate bearing capacity increases with increase in setback distance, relative density of sand, footing width and decrease in slope angle. At a setback distance of five times of the width of the footing, bearing capacity remains constant like that of a footing on level ground.

Palm Oil Fuel Ash: Promising supplementary cementing materials

Abstract: Palm Oil Fuel Ash (POFA) is by-product obtained by burning of fibers, shells and empty fruit bunches as fuel in palm oil mill boilers. In this investigation, three ashes were collected from different palm oil mills around Malaysia and namely CAPOFA, ALPOFA and KTPOFA. The ashes were ground to 45 μm before replace 20% by weight of cement in concrete and mortar. The compressive strength of concretes containing POFA was tested at ages of 7, 28 and 90 days. For durability aspects, concretes and mortars were prepared to investigate the chloride and sulfate resistance respectively in accordance with appropriate ASTM standards. Rapid Chloride Penetration Test (RCPT) was conducted in accordance with ASTM C1202 to investigate the ability of concretes containing POFA to resist the penetration of chloride ions. Change in length and microstructure study for mortar bars containing POFA immersed in sodium sulfate were conducted to evaluate the effects of sulfate attack on POFA mortars. Concrete and mortar specimens were prepared using plain portland cement in order to use as control specimens. At age of 90 days, the results of compressive strength of all POFA concretes were higher than control concrete. All concretes containing POFA showed higher potential to resist chloride ions penetration compared to control concrete. All mortar bars containing POFA showed lower expansion and less porous structure than control mortar. Depending on the results of this investigation, it could be concluded that POFA could be successfully used as supplementary cementing materials to replace 20% of cement in concrete and mortar.

Using ANP and AHP for the supplier selection in the construction and civil engineering companies; Case study of Iranian company

Abstract: The experts of the construction and civil engineering companies are responsible for selecting an appropriate supplier. Evaluation and selection of appropriate suppliers may decrease quality deficiency, cost overrun, environmental problems and etc. In this research a decision support system is developed to select appropriate supplier for construction and civil engineering companies. The effective criteria on the supplier selection process have been investigated and accommodated to internal structure of the Iranian construction and civil engineering companies by questionnaire survey. For this purpose, the current research carries out among logistics managers of the first grade Iranian construction and civil engineering companies or those with having ISO certification. After completion of questionnaires, the effectiveness of criteria is evaluated using t-student test. Five criteria are excluded, and 18 criteria are selected as effective criteria. To select appropriate supplier, the AHP and ANP approaches are utilized simultaneously. Since, these two methods use a limited number of criteria, it is essential to prioritize criteria. So, Friedman test is applied and finally five of the most important criteria have been employed. Unfortunately environmental issues are not attended by construction and civil engineering companies. To illustrate concept and performance of proposed decision support system three candidate suppliers are ranked using AHP and ANP models. Although the final results of AHP and ANP methods are the similar, the values of variation between suppliers are different. Therefore, it is recommended to employ the ANP method considering internal relations between criteria.

Effect of Fly Ash and Silica Fume on compressive strength, sorptivity and carbonation of SCC

Abstract: In this paper, ASTM C 618 Class F Fly Ash (FA) at 25%, 30%, 35% and 40% and Silica Fume (SF) at 5%, 10%, 15% and 20% replacement of Portland Cement (PC) CEM I 42.5 in SCC was used to evaluate the effect of types and quantity of powder additions on compressive strength and permeations properties of SCC. To this end, eight types of SCC were designed, in comparison with Vibrated Traditional Concrete (VTC). The results indicated that SCC specimens with SF15 had the highest compressive strength with 73.87 MPa for 130 days. The sorptivity values of SCC specimens with FA and SF were lower than those of VTC specimens regardless of type and quantity of powder additions. On the other hand, the carbonation resistance of VTC was higher than that of SCC specimens containing both SF and FA for all accelerated carbonation periods. Consequently, it can be said that type and quantity of powder additions had an important effect on the correlation among the compressive strength and permeation properties of SCC.

Understanding the Critical Variables Affecting the Level of Political Risks in International Construction Projects

Abstract: Contractors in the international marketplace are experiencing more severe political risks than ever before They have also in response endeavored to mitigate the high degree of political risk exposure in order to survive It is important however to identify and manage the critical variables affecting political risks associated with international construction projects Relatively few studies of political risks, particularly in the context of international projects, have been carried out The objective of this paper is to examine how international contractors attempt to identify and manage the critical variables which affect the level of political risks when they venture out of their home countries 85 variables contributing to the level of political risks encountered by international contractors were identified in this paper Based on the findings from an international survey on political risks, this study reveals that the variables, such as degree of stability of the government, project desirability to the host country, policy uncertainty, racism and xenophobia, and unfavorable attitude towards foreign businesses are the most significant variables Several recommendations are also provided for international contractors in this paper This research will assist international contractors to manage the political risk factors when expanding overseas

Load Rating of Highway Bridges by Proof-loading

Abstract: Aging and lack of maintenance are a matter of increasing concern for most bridges that are part of the road and railway systems of the European Union. Many of these bridges are very old and without documentation and as a consequence load rating by analytical tools is not possible. This paper explains how a possible way to assess their capacity is by means of a so-called “proof load test”. The work was developed as part of the Project ARCHES (Assessment and Rehabilitation of Central European Highway Structures) funded by the VI Framework Program of the European Union. A methodology of proof load testing for existing highway bridges is proposed and applied to the traffic conditions of several European Countries. The final objective is to provide guidance on the appropriate target proof load to be used based in very simple parameters of the bridge as span-length and percentage of heavy traffic.

Self-balanced earthquake simulator on centrifuge and dynamic performance verification

Abstract: This paper describes some details of a self-balanced earthquake simulator on the centrifuge in KAIST and results of a series of proof tests for verifying its dynamic performance and excitation capacity. The main feature of the earthquake simulator is the dynamic self-balancing technique adopted to eliminate a large portion of the undesired reaction forces and vibrations transmitted to the centrifuge main body. This feature is achieved by embarking counter-weight platform and two back-to-back hydraulic bearings. The maximum base shaking acceleration of the earthquake simulator is 20 g in horizontal direction under 40 g of centrifuge acceleration with a maximum payload of 700 kg, corresponding to 0.5 g of horizontal shaking acceleration in the prototype scale. The loading frequency ranges from 40 Hz to 200 Hz (300 Hz) for sinusoidal (real earthquake) inputs. The dimension of slip table is 670 mm × 670 m in length and width. The proof test results show that the earthquake simulator can reproduce mono-frequency sinusoidal inputs in a wide band of frequencies as well as multi-frequency real earthquake inputs at the bottom of soil models with satisfactory fidelity, and the dynamic self-balancing contributes to the safety of the centrifuge structure.

The role of organic acids in the mobilization of heavy metals from soil

Abstract: Batch laboratory experiments were performed to determine the effectiveness of organic acids in mobilizing heavy metals (Cu, Pb, Zn) from contaminated soils. Because the direct measurement of all of the species that are extracted by an organic acid is not possible, we calculated the speciation of Cu, Pb, and Zn in the presence of oxalate with regard to the primary distribution of metals and oxalate in solution using GEOCHEM-PC. Significant amounts of copper and zinc were removed from contaminated soil at higher initial concentrations of oxalic and succinic acids in solution. For the viewpoint of lead immobilization in soil, citric acid was the most effective among organic acids. Our speciation calculations by GEOCHEM-PC for metal-oxalate complex imply that significant amounts of the Cu, Pb and Zn that was extracted from the soil existed as oxalate complexes and free metal ionic form.

Effects of particle shape on shear strength of clay-gravel mixture

Abstract: Soils containing gravel-sized particles attract much less attention from researchers than clay and sands, though they may be the most commonly encountered materials in geotechnical engineering practice, especially in mountainous area. Large direct shear tests are carried out in this study to investigate the shear behavior of such soil mixtures, with emphasis on influences of shape properties (symmetry and smoothness) of gravel particles. The tested samples are prepared by mixing kaolin and gravel-sized particles (2.0 mm < d < 15 mm) of different shapes at various volumetric proportions (40, 70 and 100%). Three types of gravel are used, i.e., glass beads, river cobbles and crushed granite fragments. The applied normal stresses is 150 kPa and the shearing rate is 0.006 mm/min. Results are presented in terms of shear dilatancy, and peak and constant volume friction angle. Based on the analysis of the test results, it is found: (1) increasing gravel content increases both peak and constant volume friction angle; (2) both particle symmetry (quantified by elongation) and surface smoothness (quantified by convexity) play an important role in peak and constant volume friction, though they work in different ways; (3) increasing convexity decreases constant volume friction angle, while increases peak friction angle; and (4) increasing elongation increases constant volume friction angle, but decreases peak friction angle.

Numerical modelling study of the load sharing law of anti-sliding piles based on the soil arching effect for Erliban landslide, China

Abstract: This paper presents a new model of the load sharing law with a three-stage load sharing pattern via a representative case study in the Three Gorges reservoir region, China. A definitive new three-stage load transfer pattern is presented, including end-bearing soil arching, friction soil arching and the sliding mass in front of the pile. By means of the soil arching effect between the anti-sliding pile and landslide mass, the law of the load sharing ratio under different cases, including different intervals, section dimensions, driving forces, and shearing parameters of the sliding mass and the pile-soil interface, is presented by using the explicit finite-difference numerical modelling method. The results show that (a) the effect scale of the soil arching effect is within the scale of four times of the width of the pile; (b) the soil arching only exits within a certain pile interval, and it will become inefficiency beyond the maximum pile interval; (c) there is a threshold value for the cohesion strength parameters of the sliding mass, beyond which the load sharing ratios of soil arching keep in a steady level.

Ontology-based construction knowledge retrieval system

Abstract: Managing knowledge effectively is critical to the competitive power of a company. Knowledge is used as an important resource in many industrial areas, and so it follows that there is a growing interest in knowledge management within the construction industry. Yet because of the unique characteristics of construction knowledge created during projects, there are limitations to its capture and reuse. The knowledge produced during construction projects is project-oriented, experiential, and context specific; due to these characteristics, the reuse of knowledge is difficult. In this research, research team focus on capturing and identifying the characteristics of construction knowledge, then propose a method for applying these characteristics to the development of an ontology-based construction knowledge retrieval system. Moreover, research team developed a system prototype that applies ontology in suggesting related search words during the search process and validated the effectiveness of the prototype in terms of precision and recall rate. By applying the prototype, the precision and recall rate was improved by approximately 10∼30%.

Success evaluation factors in construction project management : some evidence from medium and large portuguese companies

Abstract: The construction industry plays a very important role in the Portuguese economy. In 2009, it was among the top five economic sectors, representing 13% of total employment. Nevertheless, project failures are still frequent mainly due to inadequate management practices and to the intrinsic characteristics of projects of the construction industry. Even though Portuguese construction has improved in recent years, cost and schedule overruns, low productivity and final product quality problems are still common. In this context, project management is a crucial tool for improving construction operations and for the overall success of projects. The aim of this article is to contribute to the discussion on success evaluation factors in a field where little has been written — the construction industry. Through a survey of 40 medium and large Portuguese companies several factors were identified which are currently considered in the evaluation of project success, as found in the literature review. The results show that the traditional factors, often referred to as the “Atkinson elements triangle” (cost, time and quality), are still the most relevant for evaluating the success of a project, but others, such as customer involvement and acceptance, have gained importance in recent years.

A new adaptive importance sampling Monte Carlo method for structural reliability

Abstract: Monte Carlo simulation is a useful method for reliability analysis. But in Monte Carlo, a large number of simulations are required to assess small failure probabilities. Many methods, such as Importance sampling, have been proposed to reduce the computational time. In this paper, a new importance sampling Monte Carlo method is proposed that reduces the numbers of calculation of the limit state function. On the other hand, the proposed algorithm does not need the knowledge about the position of the design point or the shape of the limit state function. The key-idea of the proposed algorithm is that the mean of sampling density function is changed throughout the simulation. In fact, in random point generating process each point with lower absolute value of limit state function and nearer distance from space center is considered the mean of the sampling density function. Based on this, the centralization of the sampling will be on the important area.

Simulation-optimization model for non-point source pollution management in watersheds: Application of cooperative game theory

Abstract: A new cooperative watershed management methodology is designed for developing an equitable and efficient Best Management Practice cost allocation among landowners in a watershed. The approach intends to control the total sediment yield in the watershed, considering landowners’ conflicting interests. Wet detention ponds, are considered as the only available options to the landowners. The quality of the storm water is evaluated by the Total Suspended Solid loading from the watersheds. The proposed methodology combines a watershed simulation model, named Soil Water Accounting Tool (SWAT), with an Ant Colony Optimization (ACO) module and the cooperative game theory approach. Integration of SWAT and ACO modules provide the best set of designs for any constraints on target sediment removal set forth by non-cooperative and cooperative behaviors of the stakeholders to participate in the coalition to minimize the total cost of management practice. Nash Bargaining Theory is used to investigate how the maximum saving on cost of the participating players in a coalition can be fairly allocated. The proposed method is illustrated by a hypothetical example. The results demonstrate the applicability of the methodology. For the hypothetical case example, the proposed methodology with grand coalition leads to approximately 48 percent cost saving.

Efficiency analysis on bus companies in Seoul city using a network DEA model

Abstract: This study aims to develop a network Data Envelopment Analysis (DEA) model for evaluating the efficiency of bus companies of Seoul, Korea. The proposed model is formulated by combining a network DEA model with the Banker, Charnes, and Cooper (BCC) model. The model can reflect the non-storable nature of public transportation services by sequentially considering transportation services provided by operators and consumed by users. The model also reflects simultaneously both desirable and undesirable outputs and thus provides more sufficient information with which to evaluate the efficiency of bus companies than the traditional DEA model does. The proposed model is estimated based on data regarding bus companies in the city of Seoul. Findings suggest several policies to improve the efficiency of bus companies, such as expansion of bus rapid transit systems and establishment of additional stops of median bus lanes for express and arterial bus routes. Furthermore, specific tax-cut polices related to environmental issues should be implemented to encourage inefficient bus companies to operate more pro-environmental vehicles. The developed model and criteria can assess the overall efficiency of bus companies and provide direction for the efforts of inefficient bus companies.

Structural damage detection using incomplete modal data and incomplete static response

Abstract: This paper presents novel approaches to structural damage detection and estimation using incomplete modal data and incomplete static response of a damaged structure The proposed methods use modal data or static displacement to formulate objective functions Damage location and severity in structural elements are determined using optimization of the objective functions by the simulated annealing algorithm The presented methods are applied to a simply supported beam and a three-story plane frame with and without noise in modal data and containing several damages Moreover, the performance of the proposed methods has been verified through using experimental modal data of a mass-stiffness system The results indicate that the proposed methods perform quite well using different objective functions in spite of the incomplete data

Definitions, concepts and new directions in Industrialized Building Systems (IBS)

Abstract: Nowadays, industrialization of construction is important due to increase in quality, mass production and etc This subject is much discussed in periods of time from various points of view, so it has various definitions and concepts in each period by changing trends in and views to industrialization The main objective of this paper is to study new directions of industrialization in construction, which leads to discuss contemporary and progressive trends of this subject, so this paper offers a background for the subject of industrialization In this paper, new definitions and attitudes are presented by comprehensive review of previous researches with an explanatory and analytical method to extract new directions in building industrialization; also questionnaires and interviews are used to extract criteria and suggestions of new directions The directions have been discussed in three sections, requirements (quality and economical advantages), social trends and sustainability; so contemporary industrialized building systems are focused on sustainability as a new comprehensive direction For sustainability direction a conceptual model is presented to explain the Sustainable Industrialized Building Systems (SIBS) as a new trend and presenting some practical suggestions

WIM-based live load for bridges

Abstract: Calibration of the AASHTO LRFD Code required the statistical parameters of load and resistance parameters. The basic load combination includes dead load, live load and dynamic load. In 1980’s, there was no reliable Weigh-in-Motion (WIM) data base and, therefore, the development of live load factors was based on a small scale truck survey. In the meantime, the WIM technology was improved and millions of vehicles were recorded in various geographical locations. The objective of this study is to review the available WIM data of about 35 million trucks and determine the statistical parameters of Gross Vehicle Weight (GVW) and live load moment. Moments were calculated for simple spans using influence lines. The span length range is from 30 to 200 ft (9 to 60 m). The Cumulative Distribution Functions (CDF) were plotted on the normal probability paper for an easier interpretation. CDF’s of GVW and moments show a considerable variation depending on WIM station location. Maximum expected values of live load depends on the considered time period and, in general, for strength limit states the time periods can be 75 or 100 years, and for service limit states they are much shorter, few days or weeks. Therefore, the statistical parameters are determined for time periods from 1 day through 100 years and for traffic volumes with ADTT from 100 through 10,000. For longer time periods, the results were obtained by extrapolation of the available WIM data. The statistical analysis of moments provides a basis for the development of national live load parameters and live load factors in the bridge design code.

Numerical analysis of consolidation of soft soils fully-penetrated by deep-mixed columns

Abstract: Deep mixing is a common ground improvement technology that can be used to increase bearing capacity and stability and reduce total and differential settlements of foundations constructed on soft soils. Field data have shown that deep mixed column foundations had a higher consolidation rate than untreated foundations even though deep mixed columns had similar or lower permeability than untreated soils. The consolidation mechanisms and behavior of deep mixed column foundations have not been well understood. In this study, the consolidation of soft soils fully penetrated by deep mixed columns was investigated using a mechanically and hydraulically coupled three-dimensional finite element method. One quarter of a unit cell was used considering its symmetry and the column and the surrounding soil were modeled as elastic materials. A case study for a stone column foundation in the literature was first used to verify the numerical model and then this model was adopted to analyze the stress transfer, settlement, and consolidation of the soft soil fully penetrated by a deep mixed column. A parametric study was conducted to evaluate the influence of four key factors, soft soil thickness, area replacement ratio, column modulus, and column permeability, on the stress concentration ratio (the ratio of the average vertical stress on the column to that on the soil), settlement, and average degree of consolidation of the deep mixed column foundation. The numerical results show that the average degree of consolidation calculated based on the settlement or the excess pore water pressure was identical. The stress concentration ratio increased with the column modulus and time, but the effect of the soft soil thickness, area replacement ratio, and column permeability was not significant. The simplified method based on a composite foundation concept could conservatively estimate the consolidation settlement. An increase of the column modulus, area replacement ratio, and/or column permeability increased the rate of consolidation.

Effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing class F fly ash

Abstract: Sustainability of concrete can be improved by using large volume of fly ash as a replacement of cement and by ensuring enhanced durability of concrete. Durability of concrete containing large volume of class F fly ash is dependent on the design of mixture proportions. This paper presents an experimental study on the effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing large volume of local class F fly ash. Concrete mixtures were designed with and without adjustments in the water to binder ratio (w/b) and the total binder content to take into account the incorporation of fly ash up to 40% of total binder. Concretes, in which the mixture proportions were adjusted for fly ash inclusion achieved equivalent strength of the control concrete and showed enhanced properties of drying shrinkage, sorptivity, water permeability and chloride penetration as compared to the control concrete. The improvement of durability properties was less significant when no adjustments were made to the w/b ratio and total binder content. The results show the necessity of the adjustments in mixture proportions of concrete to achieve improved durability properties when using class F fly ash as a cement replacement.

Validation of a model measuring the effect of a project manager’s leadership style on project performance

Abstract: This study validates a model for assessing the relationships among a project manager’s leadership style, teamwork, project performance, and stakeholder satisfaction. It determines whether the effect of leadership style on project performance can be mediated by teamwork. An industry-wide survey measured a project manager’s leadership style, teamwork, and project outcomes in project performance and stakeholder satisfaction. Structural Equation Modeling (SEM) approach confirmed this research model. Analyses show that a project manager who adopts transactional and transformational leadership can improve teamwork and capital facility project performance. Additionally, stakeholder satisfaction can be achieved with high levels of project success in schedule, cost, and quality performance. These findings show that teamwork can partially mediate relationships between leadership style and project performance.

Estimating time performance for building construction projects in Vietnam

Abstract: Time performance is one of the most important aspects to be benchmarked in project management. Many factors arise during the project implementation process affecting the project time. Identifying the problems that are significant to executing construction schedule and incorporating them into a comprehensive model will be useful in project management. Based on a data set of 70 projects (outliers discarded), the multiple regression technique is applied to integrate significant variables into a model used to predict or evaluate the project time index. The result suggests that six variables, namely underground site condition, project management works, estimating works, competency of subcontractor(s), accuracy and completeness of design, and owner’s project financing emerged as important factors in regression model. The constructed regression model has a good performance when compared with an artificial neural network model developed for purpose of cross validation.

A toxicological review on potential microbial degradation intermediates of 2,4,6-trinitrotoluene, and its implications in bioremediation

Abstract: In this article, current knowledge on the potential fate, biodegradation, and toxicity of 2,4,6-Trinitrotoluene (TNT) was thoroughly reviewed, focusing on the toxicological evaluation of a variety of potential TNT microbial degradation routes. The present review on microbial degradation pathways and toxicities of biodegradation intermediate products suggests that aerobic TNT degradation pathways may be advantageous from a toxicological perspective, while anaerobic degradation pathways may be preferred over aerobic degradation due to its potential for complete TNT mineralization. Our review on TNT-degrading bacterial and fungal isolates suggests that the ecological understanding of TNT-degrading microbes in subsurface environments must be significantly improved to select an appropriate TNT bioremediation strategy.