Despite the fact that applying constructability concepts in building designs have led to savings estimated within a range of 1% to 14% of the capital cost, the construction industry still lacks an advanced tool to assess and check for constructability implementations in designs. Therefore, the objective of this research is to propose a quantitative assessment of building constructability, which transforms the subjective assessment of constructability knowledge to a quantified value so that it is easy to analyze and improve building design. The proposed methodology uses the advancement of object oriented Building Information Model (BIM) and 4D simulation model to serve as a data repository models for the constructability assessment platform. Factors affecting constructability of building designs have been identified and relatively weighted using Analytical Hierarchy Process (AHP) technique based on a questionnaire survey collected throughout the Canadian provinces. Evaluation criteria are also developed to assist the designer to evaluate the design proposals. The outcome shows that the proposed method provides the designer an accurate and faster mode in evaluating project constructability by using the parametric features from BIM and taking the advantage of spatial relationship between building components.
Construction is a dynamic, complex, as well as fragmented process, and the traditional system of construction separates the two main disciplines of design and construction, where designers and contractors rarely communicate before the initiation of the construction phase. Early in 1982, The Business Roundtable defined a “constructability program” where a potential return on investment of 10:1 was reported by applying constructability [
The commonly quoted definition of constructability by the Construction Industry Research and Information Association (CIRIA) is “the extent to which the design of a building facilitates ease of construction, subject to the overall requirements for the completed building” [
With the continuous advancement in technologies, new techniques are constantly being developed in order to improve engineering implementations for the construction industry. One of these promising developments is Building Information Modeling (BIM) where it facilitates a more integrated design and construction process that results in better quality buildings at lower cost and reduced project duration [
The benefits of improved constructability have been associated with the time, cost, quality, and safety performance of a project, together with other intangible benefits. Quantifying assessment of designs, constructability review, and implementation of constructability programmers are the three most commonly employed approaches. Quantifying assessment of designs enables an objective evaluation of constructability attributes since results are comparable. Using this approach, two issues were addressed. On one hand, it is reasonably practicable and manageable for assessments to be made because it is done using the finished design product rather than evaluating the design process. On the other hand, it is difficult to comprehensively take into account all relevant factors affecting constructability into the assessment system [
Singapore has pioneered in the field of quantifying constructability based on a scheme known as the Buildable Design Appraisal System (BDAS). The concept is based on a “3S” design principle in which a design is tested for constructability issues with respect to Standardization, Simplicity and Single Integrated Elements. A similar approach was used for assessing constructability proposed for the Hong Kong construction industry in 2007 [
It was found that previous assessment platforms were in complex calculations, dependent on governmental benchmarks, and lack of time factor. Detailed comparison can be found in [
As discussed in the Introduction, BIM is playing a crucial role in research and development fields of construction information integration and interoperability. BIM is defined as the creation and use of coordinated, consistent, computable information about a building project. These various forms of information had a parametric nature where they can be used for design decision making, production of high-quality construction documents, prediction of building performance, cost estimating, and construction planning [
As stated earlier, certain constructability factors are of a qualitative nature which makes it exceptionally difficult to quantify their impact on design. For example, many studies have been done on analyzing material access throughout the construction site, and all the contributions included only ideas and knowledge bases to improve proper material accessibility ( [
In addition, time information can be integrated into the BIM model, which utilizes a three-dimensional project geometry into an environment where the effect of time schedule over construction can be visualized. A virtual object-oriented 4D model had the potential to support automated constructability assessment and to assist a project team in identifying constructability issues early in the design and construction phases [
The authors of the present paper have been exploring the integration of quantitative constructability assessment with BIM and 4D models for a long time. Based on our previous research results ( [
The objectives of the present paper are:
1) to propose a new methodology for assessing constructability of building designs quantitatively considering both quantitative and qualitative issues;
2) to explore the added value for using BIM/4D concept in constructability assessment;
3) to develop a platform to integrate all factors that affect constructability to be associated with BIM components.
simplicity, flexibility, sequencing of installation, and labor skill and availability; (5) Construction efficiency is considered in specification development including prior review of specs by construction personnel; (6) Designs promote construction accessibility of personnel, materials, and equipment; (7) Designs facilitate construction under adverse weather; and (8) Design and construction sequencing facilitates system turnover and start-up. From those principles, all design-relevant factors affecting constructability of design can be identified.
Meanwhile, BIM model is developed based on the design. The BIM model includes all the details of Dimensions, Specifications, Resources, Functions, etc. Construction schedule is also integrated to form a 4D model. The integrated Data Model will combine the BIM/4D model with Design Attributes, Construction Attributes and the External Impacts to for the Constructability Input.
Constructability factors cannot be easily evaluated by traditional measurement methods or mathematical models due to their qualitative or subjective nature based on review. To address this challenge, a questionnaire survey is proposed to assess the relative importance of the selected factors and to assign weights to them. The survey is forwarded to experienced professionals in the field of design, construction and management disciplines. The relative weight of each factor is calculated using Analytical Hierarchy Process (AHP) [
Another aspect of building an assessment model is to develop evaluation criteria that assist the design team in their subjective evaluation of their design proposals. These criteria can aid the designers to rate the output data from BIM and 4D models using a scale that ranges from very bad (VB) to very good (VG), as shown in the bottom part of
Using Simple Multi-Attribute Rating Technique (SMART), rating criteria are converted to utility values. SMART was originally developed and formally named by Edwards [
Factors affecting constructability of designs are studied and identified based on literature reviews, published journal papers, and scientific and academic reports. As shown in
After identifying the sixteen constructability factors, a survey questionnaire is done throughout different Canadian provinces.
Since constructability is a knowledge based abstract, stakeholders always have different interpretations on how to understand its impact on design. From this sense, what seems easy to construct for a particular construction team, may be difficult for another team. In other words, contractors may execute the work in different manners, but at the end they have to follow a generic construction knowledge based on a specific rationale to get the work properly done. From this perspective, each factor presented in the model is provided with specific rationale criteria in order to assist the user in rating the various constructability factors. These rationales are extracted from the literature and published journal papers. The present research proposes 16 rationale criteria so as to match the 16 identified constructability factors. All of the attributes presented in the section are integrated in the BIM model or identified from the 4D model so that the designer can input the values of these attributes when designing his/ her project. The rationale attributes proposed for each factor are discussed as follows:
Level #1 | Level #2 | Level #3 | Factor Description | Relation to Constructability Concepts | Reference | |
---|---|---|---|---|---|---|
Design Attributes | Standardization | Prefabrication | Precast Concrete, Prefabricated utility products, etc.… | A repeated grid layout will leads to faster construction sequences and reduce production waste. | [ | |
Grid Layout | Horizontal/Vertical/Radial Grid dimensions | |||||
Standard Dimensions | Dimensions for door, windows, partitions, tiles, etc.… | Dimension of building elements should reflect material sizes and should be designed to minimize labour requirements and wastage of material by special cutting. | [ | |||
Resources’ Availability | Availability of materials or special equipments. | Designers should use widely available materials that can be economically feasible. | [ | |||
Labour’s Skills | Availability of special labour skills | Designs should improve constructability by designing for economical use of available skilled workers. | [ | |||
Construction Attributes | Installation | Construction Sequence | Sequence of installation of components. | Appreciating the sequence of operations and trade interrelationships on site can enhance constructability of design. | [ | |
Time under Ground | Construction time under ground level. | Reducing the construction time below ground level can improve constructability. | [ | |||
Building Envelope | Construction of the whole building envelope. | Designers should facilitate the enclosure of building at the earliest possible stage to exclude hind rage and damage because of bad weather. | [ | |||
Weather Effect | Effect of climate conditions on construction work. | |||||
Safety | Effect of construction sequence of workers’ safety. | The design should be arranged so as to facilitate safe working in foundations and earthworks. | [ | |||
Accessibility | Material Access | Space for material storage and transportation on site. | The efficient location and distribution of temporary works and storage areas are necessary for good buildability. | [ | ||
Personnel Access | Accessibility of equipments and tools for and from different site locations. | |||||
Equipment Access | Accessibility of personnel for different site locations. | Designers must consider the contractor problems of access to and around construction sites. | [ | |||
Site Impacts | Adjacent Structures | To Adjacent Foundation | Effect of current construction to adjacent constructions. | Site conditions should be thoroughly investigated to avoid subsequent delays thoroughly after construction has commenced. | [ | |
To Infrastructure | Effect of current construction to adjacent or nearby infrastructure constructions. |
Prefabrication: Prefabrication has a direct impact on three main construction drivers: cost, schedule and workforces issue. From a constructability point of view the more fabricated components are involved in the design, the more the positive impact is on constructability. The attributes related to this factor are:
a) Prefabrication: Prefabrication is defined as “a manufacturing process, generally taking place at a specialized facility, in which various materials are joined to form a component part of a final installation” [
b) Preassembly: A common definition for preassembly is “a process by which various materials, prefabricated components, and/or equipment are joined together at a remote location for subsequent installation as a unit” [
Grid Layout: According to Code of Practice on Buildability [
Standard Dimension: this factor checks all components of the buildings if its constitute parts have a standard dimension or not. The attributes are: Standard components, and Custom made components.
Component Flexibility: Flexibility is characterized as the ability of a system to cope with unforeseen changes [
a) Potential for change: The user has to identify each component whether a particular component has a potential to change or not.
b) Effect of change: If the component has a potential to change, the user must identify the effect of the change from a 3 point scale; Low, Moderate or High. Otherwise he/she will state NA for not applicable.
c) Readiness for change: If the potential for change was positive, the user must state if the construction team is ready for the change or not. For example, the construction team must identify whether they are ready to change an internal partition 125 mm to a 145 mm thick with a 2 hour fire rated protection or not.
d) Position flexibility: This attribute addresses flexibility more specifically concerning orientation and horizontal display.
Resources Availability: Availability of resources is considered one of the main factors for addressing constructability of a given design. Resources here mean ordinary labor, material or equipment. Thus attributes related to this factor are: Equipment availability, Personnel availability, and Material availability.
Labor Availability: Labor here stands for a specialized skilled labor or talent. Some activities needs a particular kind of labor and the unavailability of this resource can cause a delay of a construction activity. Those attributes related to this factor are: Special skill needed, and Special skill unneeded.
Construction Sequence: Attributes related to this factor are [
a) Physical relationships among components: Building components are spatially restricted; weather protected, or gravity supported by other components. Activity sequencing has to respond to these inter-component relationships.
b) Trade interaction: Activity sequencing also responds to different ways in which trades affect each other during construction phase.
c) Path interference: Building components have to be moved around jobsite in order to be installed. Activity sequence has to guarantee an interference-free path for installation of any component.
d) Code regulation: Activity sequencing is also response to construction-phase safety considerations.
Time underground: must be calculated as its value must be taken into consideration to assess the overall constructability. The attributes used for this factor are: Total construction time for activities at the underground level, and Total project duration.
Building Envelope: The study of building envelope can ensure proper enclosure analysis of the project. This factor is used in the overall constructability assessment. The attributes used for this factor are: Number of days to finish all external activities, and Total project duration.
Weather Effect: The two attributes needed to analyze this factor are: Number of days with expected bad weather, and Number of planned dates that match the same bad weather days.
Safety: Safety issues must be recognized throughout all stages of the design phase [
a) Hazardous locations: Chemical materials, gas containers or unsafe openings must be well identified as to be prevented when planning for work spaces and material access.
b) Parapet height: Height of minimum 42 inch should be provided immediate guardrail thus eliminating the need to construct one and improving safety during construction phase.
c) Window sill height: The same rule for parapet height is applied here.
d) Identify components to be fabricated on ground then placed in place: In order to reduce exposure to falls from elevation and the risk of workers being struck by falling objects.
e) Identify permanent stairways and walkways (have priority to be constructed first): To minimize the use of temporary scaffolding.
f) Identify overhead power lines for cranes: To reduce contact with high voltages.
g) Overtime periods: Overtime periods may cause fatigues that reduce the alert of workers during construction.
Material Access: To insure proper material accessibility throughout different site locations, specific space allocations must be properly defined. Diverse space areas based on literature findings [
Personnel Access: Similar to the previous factor, four attributes are proposed here to insure proper personnel path: Hazardous path, Hazardous locations, Stair cases accessibility, and Scaffolding area.
Equipment Access: Equipment space is defined as a space occupied by a resource or temporary facility which is used to support other activity work elements. The analysis of equipment space can lead to the analysis of the equipment access using these attributes: Unloading area, Storage area, Working area, and Equipment occupied place.
Effect to Adjacent Foundation: Like adjacent building structures (basement, retaining walls, foundations, etc...). Two attributes are identified for this factor: Identify exciting adjacent foundation, and Distance between adjacent foundation and new building.
Effect to Infrastructure: Like adjacent sewage system or underground power line installations. The two attributes identified for this factor are: Identify exciting adjacent infrastructure, and Distance between adjacent infrastructure and new building.
To insure proper and accurate output of constructability data to the proposed assessment model, a special technique is proposed and developed to insure proper constructability input to the design. This aspect is achieved by modifying certain aspects of the BIM and 4D models. The technique also must be generic so that whatever kind of BIM vendor the user is working on, the assessment method works properly.
Each constructability attribute identified is linked to the BIM model in the form of a shared parameter. A shared parameter is saved in a universal format with the intention that each design component in the BIM model has the possibility of acquiring constructability inputs. The purpose of this approach is to facilitate the designer adding accurate constructability information to the model while designing the building. Only attributes that can be modified from BIM models are saved in the shared parameter file. These parameters and their input types criteria are: Labor availability (Yes/No), Material availability (Yes/No), Equipment availability (Yes/No), Spe cial Skill Labor (Yes/No), Prefabrication (Yes/No), Preassembled (Yes/No), Standard dimension (Yes/No), Flex_Effect of change (Low/Moderate/High), Flex_Position Flexibility (Yes/No), Flex_Potential for change (Yes/No), Flex_Readiness for change (Yes/No).Shared parameters are saved in a text file (*.txt) so that they can be loaded and used easily by any BIM vendor.
The output of the 4D model is in the form of either a simulation video or snap-shot pictures captured on a pre- planned time schedule.
The constructability factors previously incorporated with the 4D model needs two main visual aspects to insure proper evaluation:
Components: The relationship between the time duration and the physical characteristics of each building component is clear in the 4D model and is used to study the following factors: Construction sequence, Time underground, Building envelope, Weather effect, Safety, To adjacent foundation, and To infrastructure.
Space Volumes and Paths: By identifying work spaces and worker’s path in the BIM model, as mass volumes and polylines, working space allocations and resource accessibility can be studied from the 4D model. These aspects will be used to study the following factors: Material access, Personnel access, and Equipment access.
The general idea behind developing the assessment model is based on transforming the subjective assessment of constructability knowledge to a quantified value so that it is easy to analyze and improve. From this perspective, the model has to take into consideration two main attributes, the weight of each factor and the utility value of each factor. Constructability index reflects the impact value of a particular factor on the overall constructability score and is calculated in a way that is presented in [
A questionnaire was sent to sixty-two experts (architects, designers, consultants), among which fifteen feedbacks were received, giving a response rate of 24%. The relative weight of each factor at each level of the hierarchy is collected. This could be the answer to the question of “What is the importance of each factor in contributing to impact on constructability?” The questionnaire survey asked the participants to perform a pair wise comparison for each factor found under each level. They were provided with a 9 point scale that ranges from “Equally Preferred” to “Extremely Preferred” as proposed by Saaty [
Reliability analysis is applied to the collected data to estimate the reliability of the questionnaire responses. Cronbach’s alpha is the most widely used measure of reliability [
Based on the 15 received responses, pair wise comparison matrixes are developed for each hierarchy level based
Main Attributes | Cronbach’s (α) | Reliability |
---|---|---|
Standardization | 0.949 | High |
Economical Impact | 0.651 | High |
Accessibility | 0.572 | Low (within acceptable range) |
Constructability Consideration | 0.866 | High |
Effect on Constructability | 0.624 | High |
Installation Sequence | 0.596 | Low (within acceptable range) |
on the AHP methodology proposed by Saaty [
1 = Equal importance or preference.
3 = Moderate importance or preference of one over another.
5 = Strong or essential importance or preference.
7 = Very strong or demonstrated importance or preference.
9 = Extreme importance or preference.
The “priority vector” (i.e. the normalized weight) is calculated for each criterion using the geometric mean of each row in the matrix divided by the sum of the geometric means of all the criteria. According to Saaty [
For example, Design Attributes (Level #1) are of moderate/ strong importance over Construction Attributes, and are of extreme importance over Site Impacts Attributes. Standardization (Level #2) is of equal/moderate importance over Impacts on Adjacent Structure. Material Accessibility (Level #3) is of moderate importance over Equipment Accessibility. Then normalization is applied to get weights for each pair.
After performing all the needed matrices, the weight of each factor is calculated by multiplying its local weight by the weight of its up-level sub-factor. The weight of each factor is the average of weights of all the 15 responses and the final result is recorded in
Consistency Ratio (CR) calculations are performed on all weights to check the internal consistency of the judgments that have been entered to the AHP matrix calculations. Saaty [
Based on the definition of BIM, data used for executing the construction drawings are linked to their respective design components. The following points show how building elements’ specifications are used and modified as to provide constructability input for the assessment model.
Impact to Infrastructure | Site Impacts | ||||
---|---|---|---|---|---|
Impact to adjacent site structures | 6 | ||||
Grid Layout | Standardization Dimension | Standardization | |||
Prefabrication | 2 | 5 | |||
Availability of Resources | Availability of Labors’ Skills | Economic Impact of Design | |||
Flexibility to Change Design Components | 3 | 4 | |||
Works Accessibility | Equipment Accessibility | Accessibility During Construction | |||
Material Accessibility | 2 | 3 | |||
Construction Attributes | Site Impacts Attributes | Constructability Consideration | |||
Design Attributes | 4 | 9 | |||
Economical Aspects | Construction Installation | Space Accessibility | Impacts on Adjacent Structure | Effect on Constructability | |
Standardization | 6 | 4 | 9 | 2 | |
Construction Time under Ground | Priority for Building Envelope | Weather Effect | Construction Safety | Installation Sequence | |
Construction Sequence | 4 | 3 | 3 | 7 |
Level #1 | Weight | Level #2 | Weight | Level #3 | Weight | Decomposed Weight | |
---|---|---|---|---|---|---|---|
Design Attributes | 0.667 | Standardization | 0.788 | Prefabrication | 0.575 | 0.302 | |
Grid Layout | 0.282 | 0.148 | |||||
Standard Dimensions | 0.143 | 0.075 | |||||
Economical Impact | 0.212 | Components' Flexibility | 0.611 | 0.086 | |||
Resources’ Availability | 0.173 | 0.025 | |||||
Labour’s Skills | 0.216 | 0.031 | |||||
Construction Attributes | 0.181 | Installation | 0.514 | Construction Sequence | 0.514 | 0.048 | |
Time under Ground | 0.087 | 0.008 | |||||
Building Envelope | 0.123 | 0.011 | |||||
Weather Effect | 0.151 | 0.014 | |||||
Safety | 0.126 | 0.012 | |||||
Accessibility | 0.486 | Material Access | 0.606 | 0.053 | |||
Personnel Access | 0.214 | 0.019 | |||||
Equipment Access | 0.180 | 0.016 | |||||
Site Impacts | 0.152 | Adjacent Structures | 1.000 | To Adjacent Foundation | 0.720 | 0.110 | |
To Infrastructure | 0.280 | 0.043 |
Design attributes:
Component’s Flexibility: Flexibility rationales identified in previous subsection are interpreted in
Automatic constructability rules: BIM parametric features are very helpful in identifying and modifying constructability aspects in a design. Parametric relationship between design components means that they have a logical interconnection between them. This aspect is considered one of the most important features of a BIM model. In other words, if the user changes a particular building component, any linked component to it will be updated automatically, thus preventing rework, reducing modification time and increasing accuracy of the design.
building. Design specification, rules and regulations or any other needed construction data are linked to this particular space and used for the constructability analysis. For example, details like finishing material, ceiling height, construction equipment involved, utilities, etc., are used in identifying the space characteristics. Constructability input is added to this space and used as a basic rule for the project; thus all spaces with the same name and function have the same constructability input. The benefit is that a single data modification for a specific defined space will be automatically applied to all spaces that have the same specification. The same concept is applied to all kind of spaces: toilets, kitchens, corridors, emergency exists, etc. In
Working space allocation: Working spaces like storage areas or fabrication area can be identified in the design phase and linked to their associated design components.
As explained in previous subsection, a 4D model is used to test the effect of time on any given 3D model so that factors like resources accessibility and construction sequence or building envelope can be analyzed. Time schedule is developed based on the plan for executing the project. The more details the schedule has, the better the output gained from the 4D model. Each scheduled activity is linked to its corresponding building component. Since the whole constructability assessment is done during early phases of the project, it is not necessary that the schedule is in its final form. In the present research, NavisWorks© is used for developing the 4D simulation. The simulation is in the form of a video where the user can see the sequence of construction in an animated form. Snap-shots from the model can also be used for detailed analysis. The visualization output of the 4D model can be adjusted as to meet the specific requirements of the constructability test proposed by the design team. For example, if activities underground are considered a single phase and needs to have a separate constructability feedback, the 4D model can be adjusted to only simulate the underground activities.
BIM models save each design component’s information with a unique component ID, so that no conflicts occur when dealing with data exchange. Based on this ID uniqueness feature, all components’ characteristics can be exported from the BIM model and imported to the data model. Microsoft Access© is used to develop the data model which will be needed for both the assessment model and the user-friendly tool. After importing all the building data to the Access© based model, each constructability factor will have a “one to many” relationship with all BIM components that are associated with this particular factor. Thus, when it comes to the assessment of a certain constructability factor, only the needed information will be presented for that factor and not the entire output of the BIM model. In addition to the unique ID that each design component has, BIM components also have 2 important characteristics: family and type. Family represents the main description of components like wall, door, window, etc… while type represents a specific kind of family component like: internal wall 1 hour fire rated or wooden door single flush panel. The developed data model used these 2 aspects of BIM components to categorize the whole design components.
After developing the BIM and the 4D model, all the output are exported to a single data model in the form of general constructability output. In the data model, which is generated using Access©, the general data is categorized and distributed based on the proposed criteria rationale for each factor and as per the data model development process. Using Access© application, constructability information is analyzed using one of the two techniques: Quarry and Checklist. Quarries are based on simple mathematical calculations (sum, average) and are used to simplify the generated quantities from the BIM model. The output of these queries is used to evaluate constructability attributes based on the project rating criteria that are proposed in the present paper. Checklist is another method to analyze the output data and t it contains attributes related to only 4 constructability factors. This method is proposed because the rationale behind these factors is based on specific identified points. By identifying the number of checked or unchecked attributes found in the lists the analysis of the corresponding factor is possible. Thus, by evaluating the results of either the quarries or the checklists, the user can rate the impact of the constructability factor on design using the rating scale and criteria provided for the studied factor.
The last step in this process is to transform the ratings into utility values using the unified SMART rating scale and weights shown in
The proposed methodology is applied to a construction project located in Montreal (Carterville), Canada. Revit© is used to generate the BIM model, while NavisWorks© is used to simulate the schedule in the 4D model. Only architectural aspects were considered in this case study for simplicity reasons. The BIM model was developed based on completed plans and available construction data (material, partition specification, dimensions, etc…). All unavailable data needed to generate the BIM model were assumed. The Revit© software used contains the modified shared parameters that are explained in previous subsection. Since all design components have parametric relationship with each other, sections, elevations and other details were generated automatically as shown in
cated components are, the more the positive impact on constructability is. Based on the project rating scale for this factor, 49.72% falls in the average criteria. The average criteria as per the constructability rating scale is equivalent to a utility value of U = 0.5. The weight of this factor W = 0.313, thus the Constructability index Ci = 0.5 × 0.313 = 0.157. The weight calculated in the assessment model is given as 0.157.Detailed report for prefabricated and non-prefabricated components are generated and used to identify what elements can be modified as to improve the prefabricated components’ percentage and thus improving constructability. The same process is applied for all the other factors.
The factor Components’ Flexibility was also studied. The BIM model identified 76.89% as a flexibility ratio of the design. Three reports were provided for this factor so identify which components had low, medium or high negative impact on the design in case a change in the components’ specification is required. The weather effect factor was studied using the 4D model. Sixty-seven days during the construction project period were assumed to be extremely bad weather days where a high probability of interruption or delay can affect exterior works activities. The 4D model showed that there are exterior work activities in 26 days out of the 67 days which gives a ratio of 38.8%. This ratio falls in the good rating criteria and gives a utility value of 0.75. The safety factor was assessed using the constructability checklist. Based on the output of the two models, 7 out of 9 identified safety issues were checked which gives a ratio of 77% and thus the safety rating was concluded to be good. The personnel access factor was assessed in the same manner. The analysis of 4 construction phases identified the need for 14 different space allocations. The visual simulation of the 4D model showed a conflict in 6 spaces only which gives a ratio of 42.8% and thus the rating of this factor is average.
These assessments were done for the first proposed design alternative and the constructability score showed an overall score of 0.740 out of 1 which is evaluated as good based on the scale provided with the report. This scale uses the same ratings as the SMART scale. The interpretation of the final score is based on the constructability requirements proposed for this design and thus this design rated good. Improving constructability of design can be done by studying the indexes achieved from the 1st assessment.
This work proposes a methodology that addresses the challenge faced by construction stakeholders concerning constructability improvement of projects. It offers a platform to assess constructability of building designs. The assessment model considers many design relevant factors, which can be divided broadly into 3 main categories: design, construction and impact on site attributes. Based on 8 constructability principles, 16 design factors are incorporated in the model (qualitative and quantitative factors). In addition to the assessment model, a platform to improve constructability of design is proposed. This method relies on the use of advanced technology tools used in the construction field, which are BIM and 4D models. AHP is used to relatively weight the factors incorporated in the model based on a survey questionnaire done throughout different Canadian provinces. Based on the developed assessment model and the proposed implementation method, an Access©-based tool is developed to assess and evaluate constructability of designs. Owners, designers and contractors can use the developed application to improve the constructability of proposed building designs and thus reduce overall time and cost consumption during construction phases. The developed platform addresses the problem of assessing the abstract nature of constructability principles in any given object oriented BIM. It contributes to the field of construction management by achieving the following: (1) A new assessment model to quantitatively evaluate constructability of designs; (2) A new technique to check for constructability implementation in designs that helps owners, designers and contractors integrate their ideas based on state of the art advancement in the construction industry; (3) An automated tool that helps project stakeholders evaluate many design alternatives to achieve maximum possible constructible projects in a quantified manner; and (4) Broadens the usage of objected oriented models as to follow up with the state of the art of BIM evolution in the construction industry and promotes the integration between BIM and 4D models tools for the purpose of constructability analysis.
Cheng Zhang,Tarek Zayed,Wissam Hijazi,Sabah Alkass, (2016) Quantitative Assessment of Building Constructability Using BIM and 4D Simulation. Open Journal of Civil Engineering,06,442-461. doi: 10.4236/ojce.2016.63037