Toward Sustainable Engineering Structures for Better Safety in Built-Environment

The concept of safe design in architectural and civil engineering is of importance to protect humanity considering our economic, environment and sociality to maintain and improve its quality of life without degrading the quantity and quality. This Special Issue covers a broad range of research topics from small scale to large structural system level, related to the safety and sustainability issues in our engineering-built environment. The results disseminated in this Special Issue are believed to be helpful in understanding and making our society a better place by utilizing scientific and engineering methods, and it would be of interest for potential readers working in this area.

Currently, the so-called ESG (Environment, Social, and Governance) is emphasized for a better-built environment in the near future as a rising agenda, for which we can get started with research at the material level. Ghadr et al. [1] show the feasible applicability of nano-silica hydrosols in practice, which can reduce any harmful effect to humans in concrete structures with improved material performance. In addition, Hong et al. [2] study the use of shape memory alloy (SMA) as a new high-tech reinforcement for concrete. With its excellent recovery performances, SMA shows a great potential as a smart and sustainable pre-stressing system for concrete structures in a permanent manner under certain temperature and service stress conditions. In addition, Jeon et al. [3] provide material test results of pre-stressing steel considering corrosion damage. Corrosive damage is one of the key influential factors in service-life evaluations of the built environment, and therefore it is also of great concern on the long-term performance of existing buildings and bridges. This research investigates the tensile behavior of 86 corroded pre-stressing strands obtained from existing bridges, and proposes a flexural strength evaluation method of PSC beams with a single corroded strand. Song et al. [4] then also present a non-destructive method to measure the near-surface shallow delamination in concrete by using a noncontact micro-electromechanical system (MEMS) ultrasonic sensor array and an optimization-based data processing approach, which is believed to be usefully adopted in practices.

Good air quality is an essential condition to ensure the safety and high-quality life of human beings. These days, air pollution and bad indoor air quality due to micro dusts have become a serious environmental issue through the world. Efforts have been made to initiate and open new engineering approaches to solve this issue. Woo et al. [5] and Song et al. [6] develop a new way of measuring fine-dust particle density in the air through the innovative application of the multiple scattering theory, and a series of numerical simulations are also presented to generate multiply scattered ultrasonic wavefield data.

In recent years, advanced computational techniques from computer sciences (CS) are being actively adopted in civil and environmental engineering fields. This Special Issue also keeps up with the current developments, and appreciates the significance and critical role of the CS techniques in our research area. Park et al. [7] introduce a vision-based health monitoring technique linked with a traditional finite element (FE) analysis method. The objective of this study is to enable a more accurate performance evaluation of damaged structures through the combination of vision-based health monitoring and optimization-based FE model updating techniques. When structural members are damaged, their status and the corresponding structural behavior are reflected by updating parameters of FE models based on an effective optimization method known as genetic algorithm. Lee et al. [8] show an automatic design approach by utilizing a realistic building information modeling (BIM) model, where point cloud data (PCD) are used through the scan-to-BIM process. The automatic bridge-design parameter extraction system developed in this study can reduce time and effort required in the conventional scan-to-BIM process, and it enables the construction of a BIM model based on the current state of the structure. In addition, an adaptive neuro-fuzzy inference system (ANFIS) is proposed by Cho et al. [9] to estimate the effective load-carrying capacity of high-strength concrete columns and normal-strength concrete slab systems in buildings. According to the analysis, an ANFIS model trained by a total of 50 test data is more accurate in estimating the compressive strength of concrete columns compared to the current code-based equation. Over materials and component levels, Dudzik and Potrzeszcz-Sut [10] newly present a hybrid reliability analysis, where neural network models are combined with FE models for spatial structures.

With the significant population increase and urbanization, demands have been growing on irregular and complex buildings to allow more efficient use of space in urban areas. However, the design of those systems can be time- and cost-consuming as it may require an iterative or demanding design process. To this end, Choi et al. [11] introduce a new optimal design method for an underground space structure known as a double-beam floor system. The proposed method adopts a length-moment index as an indicator for reaching a minimum cross-section of the steel beams, and it allows users to reach optimized material quantity without relying on the iterative design process. In addition, Meng et al. [12] also propose a computational algorithm to find out optimized column layouts for more sustainable architectural and structural design. With this new optimization approach based on the optimality-criterion (OC) method, more efficient column distributions can be easily estimated for various shapes of roof-column structural systems.

The use of composite structural systems is beneficial in enhancing structural performance and durability of structures, leading to better sustainability in the built environment. In this sense, an innovative solution is presented by Lim et al. [13] by using steel folding truss and reusable formworks. With the improved constructability of the proposed composite system, fast-built construction and high quality of the buildings can be assured. Zhao and Andrawes [14] focus on repairing and rehabilitation of existing shear-damaged precast bridge girders by implementing fiber reinforced polymer (FRP), one of the sustainable materials that has high corrosion resistance. The current study carries out three-point bending tests for the full-scale precast bridge girders, and presents a strut-and-tie model to predict the shear capacity of the FRP-repaired precast girders.

For the better safety of our built environment under probable manmade and natural disasters, this Special Issue addresses various extreme loading conditions, including earthquakes, impact threats, and fire, etc. To examine the effects of strong earthquakes on buildings with rectangular hollow section (RHS) trusses, Yoon et al. [15] conduct lateral cyclic loading tests on three plate-to-RHS K-truss specimens. It is found that the specimens show increased initial stiffness and ultimate strength when it is provided with chord face stiffeners. The structural responses of the specimens with different connection details are analyzed and compared with those predicted by the current design codes. On the other hand, Mohamed and Mehana [16] assess the effects of accidental torsion and increased responses of buildings subjected to seismic loads. Various parameters, including the ratio of torsional frequency between uncoupled and uncoupled systems and the floor plan aspect ratio, are included in static and dynamic analyses of a set of 72 multistory buildings. For estimation of damage status and limits of concrete structures subjected to impact loading, Kim and Kang [17,18] carry out experimental and analytical studies and present their findings in two series of papers. A total of 402 impact test results are collected and compared with their proposed method for verifications. An energy-based impact model developed based on the experimental data is found to be more effective in predicting the penetration depth, scabbing depth, scabbing limit, and perforation limit of concrete panels, compared to existing formulae. Kubicka and Radoń [19] focus on the effect of boundary conditions on thermal expansion of steel structures exposed to high temperature, and investigate the fire performance evaluation of the steel truss system depending on the support conditions. For this research, kinematically admissible failure mechanisms of selected steel truss systems are first identified, and then behaviors of the trusses under fire conditions, such as axial force and load-carrying capacity of individual elements, are estimated through a reliability analysis. It is concluded that additional supports can prohibit thermal expansion of the truss system, deteriorating its fire resistance.

Finally, structural performance evaluation of underground infrastructure is one of the remaining areas that require substantial research. Ban et al. [20] conduct 3-D FE analysis for concrete pipes buried in soil. The numerical simulations adopt a nonlinear elastoplastic model for backfill materials, and include various effects such as groundwater table and voids around pipes to obtain more accurate and realistic soil pressure distributions. Propagation of concrete cracking is also studied through the numerical simulations. Shaldykova et al. [21] conduct a comparative study on design solutions of Kazakhstani (SP RK 5.01-102-2013) and European (Eurocode 7) codes for shallow foundations. The design outcomes from the two different approaches are compared in terms of various aspects such as bearing capacity and elastic settlement of the soil, and over-design factors. It is found that the European code tends to yield a more conservative design outcome for the design of shallow foundations.

In closing, the guest editors are really pleased to take this opportunity to manage and share the state-of-art research results with the potential readers of Applied Sciences in the world. The guest editors also would like to thank all the authors who shared their interesting work during the serious pandemic to make our society a better place, and special thanks should also go to the reviewers. Without their voluntary dedications, this special could not be timely completed.

Based on the successful completion of the 1st phase of the Special Issue, the second series issue of Toward Sustainable Engineering Structures for Better Safety in Built Environment II is now open and awaiting your contributions (https://www.mdpi.com/journal/applsci/special_issues/Sustainable_Engineering_Structures_II (accessed on 7 July 2021)).