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Purpose The purpose of this paper is to present a newly developed multi-objective optimization method for the time, cost and work interruptions for repetitive scheduling while considering uncertainties associated with different input parameters. Design/methodology/approach The design of the developed method is based on integrating six modules: uncertainty and defuzzification module using fuzzy set theory, schedule calculations module using the integration of linear scheduling method (LSM) and critical chain project management (CCPM), cost calculations module that considers direct and indirect costs, delay penalty, and work interruptions cost, multi-objective optimization module using Evolver © 7.5.2 as a genetic algorithm (GA) software, module for identifying multiple critical sequences and schedule buffers, and reporting module. Findings For duration optimization that utilizes fuzzy inputs without interruptions or adding buffers, duration and cost generated by the developed method are found to be 90 and 99 percent of those reported in the literature, respectively. For cost optimization that utilizes fuzzy inputs without interruptions, project duration generated by the developed method is found to be 93 percent of that reported in the literature after adding buffers. The developed method accelerates the generation of optimum schedules. Originality/value Unlike methods reported in the literature, the proposed method is the first multi-objective optimization method that integrates LSM and the CCPM. This method considers uncertainties of productivity rates, quantities and availability of resources while utilizing multi-objective GA function to minimize project duration, cost and work interruptions simultaneously. Schedule buffers are assigned whether optimized schedule allows for interruptions or not. This method considers delay and work interruption penalties, and bonus payments.

Scheduling of construction projects can be categorized into repetitive and non-repetitive. 47Repetitive scheduling contains cycles of repetitive activities such as those encountered in 48 housing units, highways, pipelines, and railways. Non-repetitive scheduling (network 49 scheduling) fits construction projects that do not require continuity of resources. These two types 50 of scheduling are also referred to as activity-based network scheduling and location-based Method 118The proposed method integrates CCPM and LSM; the aggressiveness of CCPM leads to shorter 119 schedules while LSM visualizes repetitive processes and accounts for continuity of resources. 120The framework of proposed method is illustrated in Figure ( 129Calculation of aggressive and safe durations using CPR leads to identification of the controlling 130 resource for each activity as presented in Equation (3). The controlling resource is defined as the 131 resource that controls the activity duration. Where, 138D i, j (AG), represents the aggressive duration of activity "i" in process "j". 139CPR i (CL), represents constrained productivity rate of activity "i" with resources availability at 140"CL" confidence level. 141CPRi (AG) represents constrained productivity rate of activity "i" with resources availability at 142 50% confidence level. Sequencing activities based on aggressive durations (average schedule):144The aggressive schedule is sequenced using illustrates the developed procedure for maintaining the continuity of resources. Russell and continuity of work for all activities "i" in the same process "j" as well as the continuity of work 160 among consecutive processes using Equations (4) and (5). Equation (4) calculates the SD of an 161 activity "i" as the maximum between the finish date (FD) of same activity "i" in preceding 162 process "j-1" and the FD of its preceding activity "i-1" in the same process "j" to maintain 163 continuity in the same process as well in the consecutive processes. Equation (5) calculates the 164 FD of activity "i" in process "j" as the sum of SD ij calculated using Equation (4) and the duration 165 of activity "i" in process "j" calculated using Equation (1) and (2). As long as "j" remains 166 smaller than the total number of processes (m), this procedure is repeated for all activities "i" in 167 all processes "j" to maintain the continuity of processes in the developed linear schedule. However, the continuity constraint in linear scheduling should be respected. If two or more 179 sequential activities share the same controlling resource, then the priority is given to predecessor 199QC: Resources quantities consumption during normal duration in preceding activity. 200O RC : Overlap due to resources conflicts. 201The variability of resource for preceding activity shifts the start of the succeeding activity by Where, 210O VAR : Overlap of resources quantities variability for preceding activity. 211Q 50%: quantities in preceding activity with 50 % confidence in availability. 212Q 90%: quantities in ...

Modular and offsite construction reduces project duration and cost by synchronizing offsite and onsite work. Project activities are constructed in a controlled offsite facility to minimize effects of inclement weather and site disruptions, while meeting safety and quality requirements. In recent years, many organizations have conducted questionnaires to study characteristics of modular and offsite construction, such as the Modular Building Institute (MBI), Buildoffsite campaigning organisation in the UK, Canadian Manufactured Housing Institute (CMHI), National Institute of Building Sciences, McGraw-Hill Construction, and Fails Management Institute (FMI). This paper introduces a summary of results for a new questionnaire carried out in collaboration between the Department of Building, Civil and Environmental Engineering (BCEE) at Concordia University, MBI, Niagara Relocatable Buildings, Inc. (NRB) in Canada, and the Nasseri School of Building Science and Engineering at the University of Alberta. This questionnaire focuses on two issues: (1) the characteristics of the modular and offsite construction industry, and (2) detected barriers to the increased market share of this industry. For the latter, effort was made to address five factors emanated from a workshop on äóěChallenges and opportunities for modular construction in Canadaäóť held in Montreal in October 2015 to analyze barriers to growth of modular construction in Canada. Key findings of this questionnaire include requests for use of a separate code of modular construction design, innovative financing and insurance solutions, standards that consider procurement regulations, and lending institutions that partner with financial houses to create special lending programs for modular construction.

Modular construction enables delivery of a building as an assembly of a set of modules manufactured offsite in a controlled manufacturing facility environment. Unlike stick-built practices, modular construction enables higher schedule control of construction projects due the inherent concurrency of offsite and onsite construction operations. Literature provides simulation-based scheduling methods that integrate offsite and onsite construction activities. These methods, however, depend largely on availability of data such as productivity rates for offsite and onsite activities. This paper presents an alternative BIM-based framework that integrates linear schedules of onsite and offsite construction operations in a manner that synchronizes work progress of these operations. The proposed framework considers limited capacities of storage areas in the manufacturing facility and on site as well as, the availability of trucks for delivering the fabricated modules from manufacturing facility to the jobsite. The use of BIM provides visualization capabilities for the integrated schedule and allows for monitoring simultaneously the work progress of offsite and onsite activities. Conclusions are drawn concerning the suitability of developed framework for integrated scheduling of modular construction projects. KeywordsBIM, Integration, Scheduling, Modular Construction. IntroductionA recent survey of 800 engineers, architects, and contracting professionals reveals modular construction advantages including shorter project schedules (66% of respondents); lower cost (65% of respondents); and reduced construction waste (77% of respondents) [1]. Independent KPMG research found that financial net savings for offsite construction projects are 7% due to shortened construction period without considering the savings generated from decreasing the interest of borrowing [2]. These savings enable faster rental income and lower escalation in construction costs. The combination of offsite and onsite construction in a "50-storey office building" project in central London generated combined savings of £ 36 million [2].Offsite construction provides other benefits such as; enhanced predictability of time and cost, reduced noise from construction, and improved health and safety. According to size and complexity of manufactured components, offsite construction types are grouped into five categories; 1) modular, 2) hybrid, 3) panelized, 4) prefabricated components, 5) processed material [3]. Modular construction reduces considerably the schedule of construction projects which may generate significant cost savings. Literature reviewParallel scheduling for offsite and onsite construction schedules saves 30 to 50 percent of project duration as compared to stick-built traditional construction processes as shown in Figure 1