2.1 disaster management
Traditionally, disaster management is generally considered a spiraling cyclical process [8], from pre-disaster preparation to emergency response and then reconstruct various facilities in the disaster-stricken area to finally achieve a higher degree of disaster preparedness. Alexander believed that disasters are often recurring events. He considers disaster management a cycle formed by the four stages of mitigation, preparation, response, and recovery[9]. In recent years, the concept of resilience has been introduced and integrated into disaster management theory and has become a positive measure for disaster management [10, 11], which is defined as the ability of a system, community, or society to adapt to dangers, through resistance or change, to achieve and maintain an acceptable level of function and structure [12],
Among the four stages of disaster management, the recovery stage usually occurs after the disaster relief stage, ranging from three months to five years, or even longer [13]. Generally, the recovery includes psychological recovery and socio-economic recovery. The socio-economic recovery emphasized by FEMA contains five categories, namely: economic, health and social services, housing, infrastructure systems, and natural & cultural resources [14]. The reconstruction of housing and infrastructure systems with appropriate advanced functions and reliable quality is the physical basis for social services and economic recovery. At the same time, the restoration goals of economic and social services have guided the upgrading of the functions and construction methods of housing and infrastructure.
2.2 the process of post-disaster reconstruction
Most of the existing researches on post-disaster reconstruction projects focus on funding[4, 15, 16],reconstruction idea[17, 18],successful factors[19-21],community participation[22, 23],Availability and effective management of resources [24, 25]. These studies are less concerned about the project's implementation process, so it isn't easy to guide the behavior of managers.
Post-disaster reconstruction projects should be regarded as special projects and implemented according to the guidance of project management knowledge [26]. Silva believed that the reconstruction project still needs to include three stages: planning, design, and construction. Scholars and practitioners have identified many goals and challenges for post-disaster reconstruction, such as deliver on time, within budget, higher quality standards, multiple participants, etc. [27-30]. Time or speed has become a standard for measuring the success of reconstruction [5]. Gradually replacing the normal process in the built environment in a very short and tight time was considered the critical difference between post-disaster and normal conditions [31].
Although post-disaster reconstruction might be a relatively long process (more than twelve months) compared with disaster response, it still needs to make rapid progress. Many scholars agree that time has a positive effect on reconstruction projects. Still, only a few studies have focused on adjusting the construction process to achieve the goal of shortening the construction period [5, 31]. Norling believed the first step in implementing an effective time management process was to create a schedule list that reflected the action plan [5]. Fatazi&Arefian revealed the causes and effects of four different segmentations on the time compression of the reconstruction project[32]. Olshansky&Hopkins argued the time compression could improve the design of planning processes and structure of institutions following disasters[31].
PMI proposed crashing and fast-tracking techniques to shorten the project time, which has become the starting point of many studies[6]. Crashing shortens the duration by increasing resources, including working overtime, inputting additional resources, or paying to speed up activities on the critical path[6]. The traditional CPM scheduling optimization is based on this method. Scholars have developed different methods of shortening project time based on crashing [33-35] to cope with various constraints, such as resources constraints and time-cost tradeoffs.
The fast-tracking technique overlaps part or all of the activities or stages usually completed sequentially[6]. For example, the foundation of the building is constructed before all architectural drawings are complete. Researchers value this method more because it breaks through resource constraints and emphasizes optimizing the management process[36-39]. The time reduced caused by overlapping activities depends on two aspects: the reduced time of overlapping activities and the increased time of rework caused by insufficient information [40, 41].
When activities overlap, specific project delivery methods are required to cooperate. DBB, DB(and similar EPC), and CMR are currently the three most mainstream delivery methods in the industry[42], which affect the project's delivery time by varying the number of contractors, responsibility distribution, and process. In DBB, the owner signs contracts with three different entities respectively and awards the contracts at different times in sequence. Limited by contract authorization, it is difficult for authorized entities to participate in the activities of other entities. DB and CMR have a manager who assumes the main responsibility or risk, and the builder provides constructability suggestions at the early stage of the design process. In two later project delivery processes, the designer/builder controls the details of the design[43], and it is possible to integrate construction and design into a whole rather than fragmented work.
2.3 the design structure matrix (DSM) method
The design structure matrix (DSM), also called the dependency structure matrix, has become a widely used modeling tool in many areas such as product development and system design[44, 45]. In project management, DSM can be used to express and analyze activity dependencies [46-48]. The project schedule results from the superposition of the activities sequence and the feedback to a certain extent. Traditional CPM and PERT tools can no longer handle much activity information feedback and iterative loops of complex projects [49]. DSM overcomes these shortcomings and is used to improve project schedule performance [50-52].
The DSM is a graphical modeling tool used to represent a system's elements and their interactions[53]. The DSM can be four categories: component-based DSM, team-based DSM, activity-based DSM, parameter-based DSM[54]. The activity-based DSM is usually used in Project scheduling, activity sequencing, and cycle time reduction[46]. The DSM approach allows the project or engineering manager to represent meaningful task relationships to determine a sensible sequence for the modeled activities [55]. The DSM has been identified as a potential tool to model interdependent activities (or loops), to identify suitable assumptions, formulate and evaluate the resulting sequence [47]. The DSM types and analysis methods are shown in Table 1.
Table 1 Four Different Types of Data in DSM [adapted from 54]
DSM Data Types
|
Representation
|
Application
|
Analysis Method
|
Activity-based
|
Task/Activity input-output relationship
|
Project scheduling,
activity sequencing,
cycle time reduction
|
Partitioning,
Tearing,
Banding,
Simulation and Eigenvalue Analysis
|
Parameter-based
|
Parameter decision points and necessary precedents
|
Low-level activity sequencing and process construction
|
Partitioning,
Tearing,
Banding,
Simulation and Eigenvalue Analysis
|
Team-based
|
Multi-team interface characteristics
|
Organizational design, interface management, team integration
|
Clustering
|
Component-based
|
Multi-component relationship
|
System architecting, engineering and design
|
Clustering
|
The basic representation of task DSM is an N-square matrix containing a list of activities in the rows and columns in the same order. The order of activities in the rows or columns indicates the execution sequence. The marks represent the information flow between activities. The relationships among the activities are represented with the help of 'X' marks in the off-diagonal cells. An 'X' mark above the diagonal indicates that an assumption of information is required to start the activity. The DSM is particularly well suited to model the sequential and iterative informational relationships between activities in a product development process [56-58].
There are three possible relationship types between activities, so there are three corresponding DSM representation patterns, as is shown in Figure 1. When feed-forward information flows from A to B, place the mark at the intersection of column A and row B of the lower triangle. Conversely, when feedback information flows from B to A, the mark is placed at the intersection of row A and column B of the upper triangle. When there is no information flow between A and B, the corresponding position is empty.
Partitioning is the manipulation of the matrix to eliminate or reduce feedback marks [58]. This process reorders activities so that dependencies are either below or close to diagonals. When this is done, a transparent structure for the network starts to emerge, allowing better planning of the project. We can see which activities are sequential, which ones can be done in parallel, and which ones are coupled or iterative [54].
Tearing is the process of choosing the set of feedback marks that, if removed from the matrix (and then the matrix is repartitioned), will render the matrix lower triangular [54]. Once the assumptions are made through tearing, the matrix is repartitioned for determining the preferred execution sequence [55].
Banding is the addition of alternating light and dark bands to a DSM to show independent (i.e., parallel or concurrent) activities (or system elements) [44]. The collection of bands or levels within a DSM constitutes the system/project [54].