Time-Cost Tradeoff and Resource-Scheduling Problems in Construction: A State-of-the-Art Review

Duration, cost, and resources are defined as constraints in projects. Consequently, Construction manager needs to balance between theses constraints to ensure that project objectives are met. Choosing the best alternative of each activity is one of the most significant problems in construction management to minimize project duration, project cost and also satisfies resources constraints as well as smoothing resources. Advanced computer technologies could empower construction engineers and project managers to make right, fast and applicable decisions based on accurate data that can be studied, optimized, and quantified with great accuracy. This article strives to find the recent improvements of resource-scheduling problems and time-cost trade off and the interacting between them which can be used in innovating new approaches in construction management. To achieve this goal, a state-of-the-art review, is conducted as a literature sample including articles implying three areas of research; time-cost trade off, constrained resources and unconstrained resources. A content analysis is made to clarify contributions and gaps of knowledge to help suggesting and specifying opportunities for future research

BEHAVIOUR OF HIGH STRENGTH CONCRETE COMPOSITE SLABS WITH DIFFERENT END ANCHORAGES

This study is performed to investigate experimentally the behaviour of steel deck composite slabs with different end anchorages. End anchorage as a type of shear connection for composite slabs plays an important role to prevent relative slip between concrete and steel deck. The presented composite slab specimens are made of high strength concrete and loaded at a specific shear span. Objectives of this study is to evaluate experimentally load carrying capacity, end slip, mode of failure, shear bond capacity, and the end anchorage contribution to the whole composite slab behaviour. Research also presents a comparison between the experimental results and the theoretical results derived according to m-k and partial shear connection methods included in these standards (BS 5950-4:1994, CSSBI S3-2003, and EC4 EN 1994-1-1:2004)

Study of Optical, Electrical and Photocatalysis Properties of SrMnO3 Synthesized by Solid-State Reaction

SrMnO3 was prepared by solid-state reaction method to obtain powder then thin films by a thermal evaporation method. XRD diffraction, Optical and electrical properties were investigated. Photocatalysis process was implemented as an interesting application of SrMnO3. XRD diffraction results were used to study the compound structure and to calculate some other parameters such as crystallite size, D, microstrain, e, and dislocation density, d. XRD results revealed that SrMnO3 has a polycrystalline structure such as hexagonal structure for SrMnO3 phase and tetragonal structure for MnO2 phase. The optical energy band for the powder and thin film were equal to 2.28 eV and 2.92 eV respectively, which candidates this compound to be a solar cell transparent window, especially for deposited thin films. The electrical resistivity behaved as semiconductor-like where it decreases with the temperature with electrical activation energy equal 0.960 eV when heating and 0.663 eV when cooling. The result of the Methylene blue absorption showed that the SrMnO3 powder does work very well as a Photocatalyst. The efficiency of the powder of SrMnO3 as a Photocatalyst increases with the illumination time and its best value is about 56% at 120 min

Study of Optical, Electrical and Photocatalysis Properties of SrMnO3 Synthesized by Solid-State Reaction

SrMnO3 was prepared by solid-state reaction method to obtain powder then thin films by a thermal evaporation method. XRD diffraction, Optical and electrical properties were investigated. Photocatalysis process was implemented as an interesting application of SrMnO3. XRD diffraction results were used to study the compound structure and to calculate some other parameters such as crystallite size, D, microstrain, e, and dislocation density, d. XRD results revealed that SrMnO3 has a polycrystalline structure such as hexagonal structure for SrMnO3 phase and tetragonal structure for MnO2 phase. The optical energy band for the powder and thin film were equal to 2.28 eV and 2.92 eV respectively, which candidates this compound to be a solar cell transparent window, especially for deposited thin films. The electrical resistivity behaved as semiconductor-like where it decreases with the temperature with electrical activation energy equal 0.960 eV when heating and 0.663 eV when cooling. The result of the Methylene blue absorption showed that the SrMnO3 powder does work very well as a Photocatalyst. The efficiency of the powder of SrMnO3 as a Photocatalyst increases with the illumination time and its best value is about 56% at 120 min

Bond Strength of Concrete Containing Different Recycled Coarse Aggregates

Some of the remnants of construction demolition wastes could be used after recycling as coarse aggregate in concrete industry. Among these wastes are ceramics, shale bricks and hardened concrete. This research was carried out to determine the effect of using such recycled aggregate (RA) as total or partial replacement of the natural dolomite coarse aggregate in concrete mixes on their compressive and bond strength with steel bars. Two types of concrete were investigated in this research which included normal concrete and self-compacted concrete. The main variables taken into consideration wee, the type of concrete, the type and percentage of the recycled aggregate and the age of testing. The consistency of the normal fresh concrete was measured by the slump test. However, the workability and flowability of the self-compacted fresh concrete were measured using slump test, V-funnel test. Out of the experimental test results, equations were predicted which correlated between the concrete compressive strength and bond strength of both the recycled aggregate ordinary concrete and the recycled aggregate self-compacted concrete. These equations were completely different than that of the steel-concrete bond equation of concrete with natural aggregate. Out of this research results, the recycled aggregate concrete could be used in both non structural applications and in some structural applications with special precautions

Feasibility of using self-compacting concrete in civil engineering applications

This research aimed to investigate the feasibility of using self-compacting concrete in civil engineering applications as a producing a precast hollow unit. The behavior of the hollow sections cast with self-compacted concrete beneath line-load was evaluated. An experimental work was carried out and a finite element model with ANSYS (version 15) was adopted. A total of fourteen hollow beams were cast and tested. The most variables taken into thought were; the types of reinforcement (reinforced steel bar and steel wire meshes), the types of steel wire meshes (expanded and welded steel wire mesh), number of layers of steel meshes (one layer and two layers), cross section thickness of concrete (40 mm and 60mm), concrete cover thickness (15mm and 20 mm) and also the shapes of cross section (square or circular). Special attention to initial cracking load, ultimate load, deflection, cracking pattern, energy absorption and ductility index were investigated. Good agreement was found compared with the experimental results. Out of this research; this paper presents applications of self-compacted concrete for casting skinny structural hollow members. These members can be used as precast units within the construction of the tunnel to decrease the problems in highway roads due to the difficulty of using crossing bridges particularly for kids and old people which are very useful for developing countries with great economic advantages

Residential area characteristics and disabilities among Dutch community-dwelling older adults

Background: Living longer independently may be facilitated by an attractive and safe residential area, which stimulates physical activity. We studied the association between area characteristics and disabilities and whether this association is mediated by transport-related physical activity (TPA). Methods: Longitudinal data of 271 Dutch community-dwelling adults aged 65years and older participating in the Elderly And their Neighbourhood (ELANE) study in 2011-2013 were used. Associations between objectively measured aesthetics (range 0-22), functional features (range 0-14), safety (range 0-16), and destinations (range 0-15) within road network buffers surrounding participants' residences, and self-reported disabilities in instrumental activities of daily living (range 0-8; measured twice over a 9months period) were investigated by using longitudinal tobit regression analyses. Furthermore, it was investigated whether self-reported TPA mediated associations between area characteristics and disabilities. Results: A one unit increase in aesthetics within the 400m buffer was associated with 0.86 less disabilities (95% CI -1.47 to -0.25; p<0.05), but other area characteristics were not related to disabilities. An increase in area aesthetics was associated with more TPA, and more minutes of TPA were associated with less disabilities. TPA however, only partly mediated the associated between area aesthetics and disabilities. Conclusions: Improving aesthetic features in the close by area around older persons' residences may help to prevent disability. © 2016 The Author(s)

Modeling of CPM/LOB integrated Scheduling Technique for Repetitive Construction Projects: Case of Multiple-Crews with Fuzzy Time Data

Project scheduling provides a good insight for the manager to complete the project on time. Project scheduling gives complete timing analysis of activities involved and identifies the critical ones. Critical Path Method (CPM) is the most widely used in planning and scheduling method for traditional (non-repetitive) projects to determine the critical path which determines the minimum completion time of a project.Some construction projects consist of several similar or identical units, which are called repetitive projects. LOB technique has some drawbacks such inability to generate a clear critical path of the project schedule and calculating the total float because it is a graphical technique. LOB used for scheduling repetitive typical projects because this technique considered work continuity and resource availability constraints to avoid unnecessary crew idle time.Some of the previous studies have been made to combine the benefits of CPM and LOB techniques in planning and scheduling repetitive construction projects, so, there is a model that was developed for this objective (schedule repetitive projects in an easy non-graphical manner). But, in real life, more conditions contributed to varying activity duration. Thus, the duration of project activities contains some sort of uncertainty affecting the estimating of project duration. Previous studies used fuzzy set theory instead of probability theory for quantifying the uncertainty associated with the duration of project activities.In this paper, a developed integrated model of CPM and LOB with fuzzy time data for scheduling repetitive projects is presented. The developed model provides a new technique to schedule repetitive projects with fuzzy time data in an easy non-graphical manner

Behavior improvement of self-compacting concrete in hot weather

The main aim of this research is studying the effect of hot weather on the properties of self-compacting concrete and conventional concrete in both fresh and hardened state. Also, this research extends to improve the behavior of self-compacting concrete in hot weather. The main parameters were surrounding weather temperature (5°C, 20°C and 35°C), concrete materials temperatures’ (25°C, 50°C), curing temperatures (25°C and 50°C) and admixtures (using a retarder). Two stages were carried out to achieve the research aim. The behavior of self-compacting concrete compared to conventional concrete was evaluated in the first stage. Based on the first stage, attempts to enhance the concrete properties were evaluated in the second stage. Precautions on mixing and placing concrete in these climates are considered. Results are a drive in terms of; workability tests, compressive strength, splitting tensile strength, and flexural strength. Test results showed that self-compacting concrete behavior and strengths were better than conventional concrete. Slump test, J-ring and V-funnel test were used to evaluate the fresh properties of the self-compacting concrete. Drying shrinkage of self-compacting concrete in hot weather were also evaluated