Abstract
Selecting the construction delivery method during the contracting period is one of the most important decisions determining the quality of large-scale infrastructure projects. Infrastructure projects have the most complex production processes in civil engineering. Infrastructure projects are among the most complex and resource-intensive endeavours in civil engineering due to their size, scope, multidisciplinary nature, regulatory requirements, financing challenges, environmental considerations, and the need for long-term planning and maintenance. Effective project management, collaboration, and a deep understanding of these challenges are crucial for the successful execution of infrastructure projects. Implementing such projects inevitably demands proper quality management throughout the project lifecycle. Two primary types of construction contracts are under implementation worldwide: Design-Bid-Build (DBB) and Design–and–Build (DB) contracts. In the Western Balkans region, both types of contracts are utilized for infrastructure projects, A noticeable trend is emerging toward transitioning from DBB to DB contracts. This paper provides a comprehensive analysis of quality management within the context of construction contracts with a focus on the roles and responsibilities of key stakeholders and how these factors affect the achievement of quality objectives while managing constraints related to cost and time. This research aims to improve construction practices by selecting an adequate type of contract for construction practices and ensuring successful project outcomes.
1 Introduction
The selection of the construction project delivery method is an important decision that the client must take during the initial stages of the project planning. The choice of an appropriate contracting method for construction significantly impacts the overall project performance, construction quality, budget, and time of completion [1]. Numerous studies have focused on optimizing the selection of the suitable type of construction contract, particularly for large-scale infrastructure projects. Under the DBB (Design-Bid-Build) type of contract, the project owner or client divides tasks into two major components: design and construction. This type of contract requires issuing separate tenders to independently select both the designer and the contractor [2]. For the DB (Design – Build) contract type, the client solicits only a single tender, selecting a design-and-build contractor as illustrated in Fig. 1.
The conceptual model for design-bid-build and design-and-build contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
The conceptual model for design-bid-build and design-and-build contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
The conceptual model for design-bid-build and design-and-build contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
As shown above, under the DBB type of contract there is no contractual relationship between the company responsible for the detailed design, and the company executing the design during construction – the contractor. In this setup these two parties typically operate independently, making decisions remotely from each other during different phases project. Specifically, the designer completes the detailed design in advance, submits it to the owner, and then the contractor constructs that design [3]. In contrast, the DB type of contract involves the project owner engaging a single contractor for both the design and construction of the project. In this setup, the selected contractor undertakes the overall design responsibility as well as liability for project implementation as presented in Fig. 1. A comparison of major obligations between DBB and DB for project stakeholders presented below shows risks and obligations associated with each contract type:
As presented in the table, the DBB is a traditional method of project delivery widely used in engineering projects until recently. It is a delivery approach with which project owners are most familiar. DBB follows a linear process in project management where each task follows the completion of the previous one with no overlap. The process commences with the owner selecting an architect or design company to prepare construction documents. In this type of contracting, the architect releases these documents either publicly to any general contractors or to prequalified contractors invited to bid on what they estimate the total construction cost will be. For DB contract type the general contractor (GC) usually serves as the design-builder. However, the general contractor and the designer can form an association under an internal contracting agreement for which the project owner is not affected. With the general contractor approach, a primary position is generally assumed by an architect or engineer who undertakes overall project responsibility. From the project inception up to the completion, the GC is the key organizational entity. They are accountable to the owner for the design, defects, quality assurance, and quality control for defects, delays, and losses that may arise during the construction. As a result, the overall project liability concerning the time of completion and quality management falls on the GC as presented in Table 1.
Comparison between DBB and DB delivery methods and projects
| Metrics | DBB type of contract | DB type of contract |
| Payment | The project owner pays the designer and the contractor under separate contracts | The project owner pays the DB contractor |
| Involvement and the responsibility of the owner | High | Low |
| Owner risk during the project implementation | High | Low |
| Risk of design failure | High | Low |
| Cooperation between the designer and the contractor | Low | High |
| Cost for the designer and the Contractor | Uncertain | Uncertain |
| Design changes during the construction | Slow, costly, and complicated | Fast, no cost, and easy |
| Cooperation between designer and contractor | Slow and complicated | Fast and easy |
| Management cost for design changes | High | Low |
| Overall management cost | Medium | High |
| Time for project implementation | Larger period | Shorter period |
| Quality Management | Complicated | Simplified |
| Quality Assurance | Strict | flexible |
| Design and the Construction liability | The designer and the contractor | Contractor |
2 Quality management for DBB versus DB projects
DBB type of contract commences with the design stage, progresses through the bidding (or tendering) stage, and is completed in the construction stage. The entire process is overseen directly by the owner or their representative which may include a consultant or an engineering company. Simultaneously, an agent or consulting firm can be chosen for construction supervision. The invitation procedure for builders during the bidding stage begins with the coordination between the architect and the owner, resulting in the release of completed bid documents to general contractors (refer to Fig. 2). The overall design quality assurance remains within the owner's purview. Throughout the construction stage, the quality assurance process for the construction process can either remain under the owner's control or can be delegated to an independent engineer responsible for construction supervision. Their role ensures that expected quality, cost, and project timeline are met. The services of this independent engineer can also extend into the defect notification period following the project completion which typically ranges between 12 and 24 months. During this period, significant construction defects may become apparent. These defects fall under the contractor's liability and warranty ensuring that works are completed as per design and specifications prepared by the architect during the design stage [4–6].
Design-bid-build quality model assurance for construction contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Design-bid-build quality model assurance for construction contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Design-bid-build quality model assurance for construction contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
DB contracts require the general contractor to propose a firm fixed price for a project. The scope of work is defined by the technical specifications prepared by the designer, who simultaneously develops the design component of the project. Consequently, the design details become the variable leg in the design–and–build stool, and the general contractor faces the challenge of balancing both schedule and budget constraints while ensuring a requested level of quality. This makes it particularly important for both project participants the owner and general contractor have clear and comprehensive construction requirements outlined in the project Request for Proposal (RFP). This ensures that proposals that are generated align not only with the owner's needs and preferences but also with the budgetary, technical, and schedule constraints of the project. One of the most complex aspects of this contract type is for the project owner to define the project requirements including a well-defined allocation of quality management responsibilities between the owner and the general contractor [7]. The overall quality management is supervised by a specialized company often referred to as the Engineer appointed and financed by the project owner. The Engineer's role revolves around guaranteeing that the works and project's overall quality adhere to the specifications outlined in the RFP released during the initial stage of the project initiation. It is crucial for the engineer and the contractor to collaboratively define QA/QC plans and the comprehensive Quality Management (QM) for the project within the bid document [8, 9]. This ensures that these requirements are transparent and clearly understood by all involved parties in the project.
The model of QA for a DB-type construction contract is presented in Fig. 3.
Design-and-build project model assurance for construction contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Design-and-build project model assurance for construction contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Design-and-build project model assurance for construction contracts
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
3 Comparison of quality between DBB and DB types of contracts in infrastructure projects
In the past, contracting authorities worldwide predominantly relied on the DBB delivery method for infrastructure construction, commonly recognized as the traditional method of contracting. However, in recent times institutions embraced innovative delivery methods, including DB, aiming to complete more infrastructure projects within budget and schedule [10].
A similar trend has been observed in Europe and Balkan countries, where traditionally, infrastructure projects were primarily designed by specialized design companies rather than being executed by separate companies, as previously explained. The current trajectory demonstrates a movement from the conventional contracting method towards adopting more innovative contracting strategies.
For this paper, we have undertaken an analysis of three infrastructure projects developed in the last decade within Kosovo: two motorways and one railway:
Kosovo Motorway Route 7: Morine-Merdare Motorway, Length 80 km, constructed between 2010–2015 using the design-bid-build type of contract,
Kosovo Motorway Route 6: Prishtine-Hani i Elezit Motorway, Length 60 km, constructed between 2014 and 2019 using the design-and-build type of contract,
Kosovo Railway Rehabilitation Project Phase I: Fushe Kosove-Hani i Elezit Railway, Length 66 km, initiated in 2019 and currently ongoing under the design-bid-build type of contract [11].
The tendering procedures for all three infrastructure projects adhered to international procurement standards, resulting in the selection of international companies as general contractors. The client for these projects were the Kosovo Ministry of Spatial Planning and Infrastructure for two motorway projects, and the Railway Authority Infrakos, a distinct entity under the Government of Kosovo for the railway projects. See maps of all three projects presented in Figs 4 and 5.
Motorway route 7 and route 6
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Motorway route 7 and route 6
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Motorway route 7 and route 6
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Railway route 10
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Railway route 10
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Railway route 10
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
Quality tools for monitoring the construction activities during the construction of all three projects were aligned with FIDIC requirements: Field Site Instructions (FSI) and Non-Conformities (NCR). FSI and NCRs were released to the contractors whenever work was found non-compliant with stipulated specifications, or method statements, or if there were issues with materials or qualities of workmanship. The various infrastructure works during the execution were divided into categories, and the released NCRs were assigned based on these categories or not meet the quality requirements of material or works [12, 13]. The number of NCRs released on each infrastructure project is presented in Table 2. Results are presented using the comparison method for similar works (Fig. 6).
Number of NCRs and percentages for the Motorway route 7, Motorway route 6 and the Railway project
 |
NCRs in three projects
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
NCRs in three projects
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
NCRs in three projects
Citation: International Review of Applied Sciences and Engineering 2023; 10.1556/1848.2023.00730
4 Results and discussions
This paper contains limited studies of data analysis by comparing infrastructure projects for Kosovo only, this limitation was due to resource constraints such as budget and time constraints.
As presented in Table 3, projects executed under the DBB procedures, such as Kosovo Motorway Route 7 and the Kosovo Railway Rehabilitation Project Phase I, exhibited higher non-conformities (NCR) during their implementation. This can be attributed to various factors such as poor coordination between the Designer, Client, and Contractor, differences in approaches to resolving construction details between designers and contractors, and a lack of knowledge within the Client's implementation unit for large-scale infrastructure projects. An additional challenge that contributed to difficulties in achieving the desired quality level as per clients' expectations was the absence of coordination and sometimes a complete lack of communication between the designer and the contractor. The DBB projects suffered from inadequate quality assurance oversight throughout the project implementation phase, resulting in an increased number of defects.
Comparison of NCR projects
| Projects | Type of contracts | Time for completion (days) | Ext of time (days) | Time exten. (%) | Project completion | Cont. amount | Nonconformities for the whole project NCR | Average completed amount of works without NCR |
| Kosovo Motorway Route 7 Project | Design-bid-build (DBB) | 1,249 | 52 | 4.2% | November 2013 | ∼€825 MEUR | 2,048 | €402,456 |
| Kosovo Motorway Route 6 Project | Design-and - Build (DB) | 1,277 | 499 | 39.1% | May 2015 | ∼€705 MEUR | 624 | €1,130,793 |
| Kosovo Railway route 10 - I Section | Design-bid-build (DBB) | 730 | 579 | 79.3% | Ongoing | ∼€78.6 MEUR | 480 | €96,093 |
The last column of the table presents the average completed amount of work without NCR, which is significantly higher for the projects executed under DB-type contracts compared to DBB–type contracts.
Kosovo Motorway Route 6, which was implemented with a DB type of contract, exhibited less defects, or NCR, during the construction, this can be attributed to the direct and consistent communication between the designer and the contractor throughout the construction period, which was not the case for two other types of contracts implemented under DBB.
Upon comparing the recorded number of quality issues with the number of contracts for projects, it becomes evident that DB types of contracts result in a significantly larger volume of work being completed without encountering quality issues. This does not imply that contractors under DBB-type contracts lack the commitment to quality, but rather highlights that quality-related concerns during construction are more promptly addressed through designer-contractor collaboration, a dynamic that is often not as effective within DBB-type contracts [14]. Particularly when dealing with flawed designs for which the responsibility rests on the client.
5 Conclusions
These conclusions can serve as a basis for further analysis of contracting methods in large-scale infrastructure projects and other construction projects. As a summary conclusion regarding the selection of the construction contract concerning the quality of construction, it can be concluded that:
DB-type construction contracts exhibit faster project implementation in terms of completion time, aligning well with the triple project constraints of cost, schedule, and quality than traditional DBB-type construction contracts.
To achieve the requested quality during the construction, the Contractor must prepare a comprehensive quality management plan for project execution. The Engineer acting as the client's representative, should review and comment on these plans if necessary.
Before commencing construction activities alignment between the contractor and the engineer is imperative for the implementation of the QA/QC plan. This plan should adhere to the technical specifications outlined in the Request for Proposal (RFP) document, and adjustments can be made as needed during the construction stage.
For government-funded projects, including infrastructure projects the approval process of materials faces delays. In contrast, DB-type construction contracts tend to streamline and expedite the material approval process.
In DBB-type contracts unclear technical specifications prepared by the designer create significant conflict between the contractor's representatives and the engineer and/or the Client. DB type of construction contracts have a better approach for this subject because specification and design run in parallel and they are managed by general contractors. The engineer makes sure that quality requirements are met on-site during the construction.
Inflation-prone economies necessitate considering the price adjustment factor of the contractual price during the project implementation ensuring that the contract price holds its actual financial value at the payment stage. Price adjustment must be an integral part of the contract for large infrastructure projects for both contract types.
Different construction standards related to the group of project specifications for the DBB type of contract are more complicated for implementation than for the DB type of contract.
Design changes are more frequent in infrastructure projects due to terrain conditions. DB-type contract manages design changes more effectively, as the contractor has overall responsibility and liability for design and construction, minimizing the need for extensive communication with the Engineer and/or designer.
DBB is a three-leg contract where design is completed by the design company, therefore not adequate design, mistakes at the design stages, and design omissions create risk for implementing this type of contract. DB-type provides a better approach regarding the quality of the design and design changes. If a design mistake happens correction of that mistake is performed without dense communication between the engineer and contractor because the contractor retains overall responsibility and liability for design and construction [15].
As a recommendation, project owners are advised to consider adopting DB-type contracting over DBB-type. The global trend toward DB-type contracts for infrastructure projects is on the rise, and this trend is echoed in the construction sector of Western Balkan countries as well [16].
References
- [1]↑
E. Gashi, “Management of defective works in infrastructure projects,” Int. Rev. Appl. Sci. Eng., vol. 9, no. 1, pp. 73–80, 2018.
- [2]↑
E. S. Danlami, “Comparing performance quality of design-bid-build (DBB) and design build (DB) project delivery method,” Afr. J. Earth Environ. Sci., vol. 2, no. 2, 2020.
- [3]↑
E. Chan and A. Yu, “Contract strategy for design management in design and build, Paperwork PM 4094,” Int. J. Project Manage., May 2005.
- [4]↑
Z. Satterfield, “Design – build; national environmental service centre,” Tech. Brief, vol. 9, no. 2, 2009.
- [5]
R. Khalef and I. F. El-Adaway, “Advancing airport project delivery: a comparison of design-build and traditional methods in terms of schedule and cost performance,” J. Manage. Eng., vol. 39, no. 6, July 2023.
- [6]
Quality Assurance in Design and Build Projects; National cooperative highway research; Synthesis 376, 2009.
- [7]↑
H. V. Ch Edwin and T. W. Y. Ann, “Contract strategy for design management in the design and build system,” Int. J. Project Manage., vol. 23, no. 8, Nov 2005.
- [8]↑
Q. Chen, Zh Jin, Zh Xia, P. Wu, and M. Skitmore, “Time and cost performance of design-build projects,” J. Eng. Manage., vol. 142, no. 2, 2015.
- [10]↑
H. A. Chakra and A. Ashi, “Comparative analysis of design/build and design/bid/build project delivery in Lebanon,” J. Ind. Eng. Int., pp. 147–152, 2019.
- [11]↑
Completion project report, August 2015, Kosovo Motorway Project Route no. 7, Morinë – Merdare Motorway (Ibrahim Rugova Motorway), Hill International.
- [12]↑
Progress Report, Rehabilitation of Railway Route 10, Fushë Kosovë – Hani i Elezit, Hill International.
- [13]↑
Completion project report, October 2019, Kosovo Motorway Route no.6: Prishtinë – Hani i Elezit Motorway (Arben Xhaferi Motorway), Hill International.
