A digital twin approach for geometric quality assessment of as-built prefabricated façades

Highlights

• A comprehensive framework for evaluating geometric quality of prefabricated façades.

• Measurement of geometric quality in terms of completeness, correctness, and accuracy.

• One-to-one correspondence mapping of as-built elements to as-designed counterparts.

• An efficient solution for localization and visualization of construction errors.

Abstract

We develop a new framework for geometric quality assessment of as-built prefabricated façades during construction process using a 3D as-designed model and a 3D as-built semantic model. The framework is based on a digital twin approach which facilitates an automatic quantitative comparison between the 3D as-built digital replica, reconstructed from the 3D as-built lidar point cloud, and the 3D as-designed model. The framework consists of automated correspondence identification and element-based comparison on three new criteria, which ensure comprehensive measurement of the geometric quality of as-built façades regarding accuracy, completeness, and correctness. Experiments on a synthetic façade system and a prefabricated façade of an actual construction project demonstrate the ability of the framework to detect inconsistencies and perform a quantitative evaluation and localization of geometric errors in as-built prefabricated façades in an efficient and timely manner. Ultimately, the proposed framework enables efficient visual quality assessment during construction process for prefabricated construction.

Introduction

Today prefabricated and modular construction are becoming increasingly popular and recognized as key components to improve productivity in the construction industry [1,2]. In comparison with on-site construction, prefabricated construction promises to achieve faster production and reductions in time and cost [3,4], while offering safer and cleaner construction environments [5,6]. In practice, this construction method strictly requires precise production of structural components in a factory environment, as well as accurate assembly of the components at construction sites [6]. Incompliances and discrepancies between as-built [7] and as-designed (AD) prefabricated constructions result in considerable rework and disruptions [6]. Therefore, an efficient quality inspection solution, which enables detection and identification of these inconsistencies and mismatches between the AD and AB components at an early stage, can significantly reduce the negative impacts on construction projects. To date, there have been intensive research efforts dedicated to the fabrication verification process, which aims to ensure the accurate production of each individual prefabricated element and smooth assembly of the elements at the fabrication stage [8,9]. However, only a few research works have focused on geometric quality assessment of AB prefabricated components during construction, and they usually focus on one quality aspect (e.g., accuracy). In fact, the existing solutions often encapsulate the quality of the whole AB prefabricated construction in a few quality indices, which are insufficient for localization and visualization of construction errors. Therefore, there is an urgent need for a more comprehensive and efficient solution for assessment and visualization of geometric quality of AB prefabricated construction that can be used in practical situations.

Traditionally, the inspection of as-built conditions of constructions mainly relies on contact surveying devices (e.g., tapes and callipers). Several simple non-contact solutions, such as total stations, are also widely adopted and can produce data with higher accuracy [7]. However, these techniques usually require manual single-point measurement, which is laborious, time-intensive, and thus is feasible for inspecting only a small number of components. Recently, the development of state-of-the-art data acquisition techniques, including range-based and image-based techniques, enable non-contact and a more comprehensive inspection of physical structures [10,11]. These techniques enable the rapid capture of a 3D geometric representation of AB constructions as a point cloud, which contains millions of measured points, with a high level of accuracy (millimetres to a few centimetres) [10]. However, point clouds are often incomplete and unstructured and lack semantic information. Therefore, a reconstruction process to convert the surveying data into a 3D semantic digital counterpart of an AB construction is often needed and a prerequisite for many practical construction applications, including automated quality assessment and inspection [[11], [12], [13]].

A prefabricated façade system is one of the most popular and important components in modern prefabricated construction. Within the fields of urban reconstruction and digital construction, there have been intensive research efforts aimed at generating a 3D digital counterpart of an AB façade system from lidar point clouds or imagery data captured at construction sites [13]. Meanwhile, quality evaluation and detection of incompliances and inconsistencies of AB prefabricated building façades with respect to their designs during construction process have not garnered much attention and still rely on visual and manual inspection [6,14]. In practice, during the construction process, the quality inspection and identification of construction errors need to be frequently conducted in a timely manner, so as to facilitate rapid repair whilst reducing disruption. Contrary to its state at a fabrication plant [9], an AB prefabricated façade panel at a construction site is not an isolated element, but is installed and assembled with other panels and structural components of a building. Likewise, differently from cast-in-place construction [15], one-to-one mapping between an AB prefabricated façade panel and its corresponding design is required for drawing comparisons between them. Without a proper correspondence mapping, the geometric quality of an AB prefabricated element might be compared with an irrelevant AD element. Therefore, existing quality evaluation solutions for cast-in-situ construction cannot directly be applied in prefabricated construction, and vice versa. To date, an automated evaluation method, which efficiently facilitates quantitative measurements of an AB prefabricated façade system with respect to its design during construction, is not available.

In this paper, we propose a comprehensive framework for geometric quality evaluation of AB prefabricated façades using a 3D AD model and a 3D AB model. The framework is developed based on a digital twin concept, which facilitates quantitative measurements of the geometric quality of an AB physical façade through the comparison between its 3D AD digital model and the 3D semantic digital counterpart reconstructed from the AB point cloud. The approach enables automated identification one-to-one correspondence and element-based comparison between AD and AB elements guided by semantic information (i.e., label of elements). Consequently, the approach enables independence of the assessment on data quality and ensures measurement of geometric discrepancies between relevant AB and AD prefabricated pairs. The proposed approach not only provides a first comprehensive framework for evaluating the geometric quality of prefabricated facades in terms of three quality aspects - completeness, correctness, and accuracy - but also provides an efficient solution for localization and visualization of construction errors that can be applied in practice. Ultimately, this information provides insight into the quality of each individual component of an AB prefabricated façade system, and thus is useful and efficient in assisting builders in making decisions and applying suitable adjustments on the physical construction products.

The remainder of the paper is organized as follows. Section 2 provides a review of the literature, which covers the quality inspection of prefabricated components in construction and the quality assessment of building façades. Section 3 elaborates on our proposed approach for the quality assessment of as-built prefabricated building façades. Section 4 describes the details of an experiment for an actual construction project utilizing prefabricated façades to evaluate the feasibility of the proposed approach. The experimental results are presented and discussed in Section 5. Section 6 concludes the paper and provides directions for future work.