Abstract

Durability property is a critical performance indicator of concrete in different environments and locations. However, durability also plays a key role in the sustainability and climate resiliency of concrete structures which is mostly ignored in the context of ways to improve the sustainability of concrete materials and structures. Hence, this paper aims to bring focus to this area by presenting an overview of the critical role of concrete properties especially durability on the sustainability and climate resiliency of concrete structures. This paper first presents a general overview of concrete materials followed by the connection of concrete to sustainability and climate resiliency. Discussions from this paper indicate that to improve concrete sustainability, there is a need to use materials with lower environmental impacts upfront in addition to producing concrete with improved durability to ensure long-term performance. In other words, merely reducing the upfront embodied carbon of materials is not sufficient to achieve sustainable concrete if the impact of such alternative low-carbon materials used to replace the traditional materials in concrete is not considered. On the other hand, the climate resiliency of concrete structures is mostly dependent on improved durability which would sustain their adaptation over time to the impacts of the changing climate conditions. Overall, to achieve sustainability and climate resilience of concrete structures; lower environmental impact, higher durability performance and resilience to applicable climatic conditions must be achieved.

Introduction

Concrete being the most used construction material in the world can be associated with its outstanding performance coupled with its lower cost and availability of raw materials locally in various parts of the world. Concrete has been used extensively to build various infrastructures ranging from transportation systems, health, residential and commercial buildings, water systems, etc. However, the high production and use of concrete have been found to yield negative environmental impacts on the environment due to its contribution to greenhouse gas (GHG) emissions and consumption of natural resources [1] , [2] .

In contrast to other construction materials, such as steel and glass; concrete has a lower unit embodied carbon as depicted in Fig. 1 which shows the carbon emissions per kilogram of each material. However, the production and use of concrete in large quantities have resulted in the concrete industry being a major contributor to the world’s human-induced GHG emissions. A critical part of concrete responsible for the high GHG emission is the production of portland cement (PC) which is the primary binder in concrete and other cementitious materials. Out of all cementitious materials (i.e. concrete, mortar, grout, etc.), concrete consumes PC the most with an estimated amount of 70% while the other 30% is used for other cementitious materials such as mortar, grout, etc.

Conclusion

This paper presents an overview of various properties, specifically the durability of concrete and how it influences concrete sustainability and climate resiliency. Discussions in this paper show that the durability of concrete is very critical to both concrete sustainability and climate resiliency and a holistic approach needs to be employed. Improving the durability of concrete would result in the reduction or elimination of raw material and energy use for rehabilitation and reconstruction resulting in lower environmental impact thereby enhancing sustainability. Similarly, enhanced durability of concrete would ensure that concrete structures can adapt to the changing climate changes thereby improving its climate resiliency.

Thus, to improve the sustainability and climate resiliency of concrete infrastructures; core attention must be placed on the embodied carbon of the materials and the durability performance rather than the former only. Finally, initiatives to improve concrete sustainability and climate resiliency should be specific geographical zone-based rather than a global approach as the availability of raw materials and climate conditions varies with location.

Abstract

     Concrete is one of the most widely used materials in various civil engineering applications. Its global production rate is increasing to meet demand. Mechanical properties of concrete are among important parameters in designing and evaluating its performance. Over the past few decades, machine learning has been used to model real-world problems. Machine learning, as a branch of artificial intelligence, is gaining popularity in many scientific fields such as robotics, statistics, bioinformatics, computer science, and construction materials. Machine learning has many advantages over statistical and experimental models, such as optimal accuracy, high-performance speed, responsiveness in complex environments, and economic cost-effectiveness. Recently, more researchers are looking into deep learning, which is a group of machine learning algorithms, as a powerful method in matters of diagnosis and classification. Hence, this paper provides a review of successful ML and DL model applications to predict concrete mechanical properties. Several modeling algorithms were reviewed highlighting their applications, performance, current knowledge gaps, and suggestions for future research. This paper will assist construction material engineers and researchers in selecting suitable and accurate techniques that fit their applications.

Introduction

     Concrete is the most widely used building material worldwide. With population growth and urbanization, the demand for concrete is expected to reach 18 billion by 2050 [[1], [2], [3]]. In order to improve the design of concrete structures, it is necessary to gain a better understanding of concrete performance, relying on accurate evaluation of its mechanical properties. Among the various properties of concrete, compressive strength has been considered a direct indicator of performance. It is directly related to the safety and performance of the structure throughout its life cycle [1,4,5].

     Concrete is a complex system of combinations of different components (coarse and fine aggregates, water, cement, and additional mixtures) that are randomly distributed throughout the concrete matrix [[6], [7], [8], [9]]. This heterogeneous feature makes it difficult to accurately predict certain mechanical properties, especially compressive strength [[10], [11], [12]]. The most direct way to evaluate the compressive strength of concrete is through physical tests performed on specimens cured to the desired age [13,14]. Such a method for evaluating the compressive strength needs time while being affected by other factors related to specimen fabrications and test operators. Moreover, the test tends to damage the specimens. Empirical regression methods were therefore proposed to predict compressive strength [[15], [16], [17]], but the disadvantage of this method is the non-linear relationship between the concrete mixture and the concrete’s compressive strength. This prevents an accurate regression expression. Numerical simulation is another method that can predict the behavior of concrete. However, a good prediction of concrete behavior is not easy to achieve due to the non-linearity and randomness [[18], [19], [20]].

Conclusions and recommendations

     The present study investigated the performance of different ML/DL models to predict the mechanical properties of concrete. Among the wide range of ML/DL models, support vector machines, decision trees, evolutionary algorithms, and artificial neural networks were examined due to the popularity of these models as well as their frequent use in the field of civil engineering. Therefore, the performance of these models in various studies to evaluate the compressive strength, tensile strength, shear strength, flexural strength, and elastic modulus was evaluated. A comparison of experimental models with ML/DL methods shows that ML/DL models with better updating capability and the ability to analyze large datasets perform better. On the other hand, statistical models are not good for predicting complex structures due to their high cost and time-consuming nature. According to ML/DL methods, selecting the appropriate model for predicting the target strength of concrete should be made by considering different criteria. A review of various studies shows that the relationship between concrete components and mechanical strength is influential in choosing the forecasting model. Therefore, models that can respond in nonlinear space should be used if the relationship is nonlinear. In these cases, SVM and ANN models can be used for their acceptable performance in a non-linear environment with fewer errors. To achieve more accurate results, optimization of these models with metaheuristic algorithms can also be used. But if we need the transparency of the model and the explicit mathematical formula between input and output, we can use decision tree models and evolutionary algorithms. On the other hand, the use of ensemble models to optimize these models, although it results in higher accuracy, increases computation time and model complexity. The combined SVM and ANN models, although they increase the computation time, have accurate results in the face of extensive data. Therefore, based on the study, the best option for predicting the strength of concrete in terms of model accuracy and model implementation is the combined use of SVM and ANN combined models.

Highlights

Abstract

Graphical abstract

Keywords

1. Introduction

2. Overview of cloud computing

3. The need for cloud computing in the construction industry

4. Methodology

5. Findings

6. Use cases of cloud computing in construction industry

7. Insight from the systematic review

8. Challenges of cloud adoption by construction industry

9. Future opportunities of cloud computing in the construction industry

10. Implications for practice

11. Conclusion

Declaration of Competing Interest

References

Abstract

Cloud computing technologies have revolutionised several industries for several years. Although the construction industry is well placed to leverage these technologies for competitive and operational advantage, the diffusion of the technologies in the industry follows a steep curve. This study therefore highlights the current contributions and use cases of cloud computing in construction practices. As such, a systematic review was carried out using ninety-two (92) peer-reviewed publications, published between 2009 and 2019. A key highlight of the findings is that cloud computing is an innovation delivery enabler for other emerging technologies (building information modelling, internet of things, virtual reality, augmented reality, big data analytics) in the construction industry. As such, this paper brings to the fore, current and future application areas of cloud computing in the construction industry. The paper also identifies barriers to broader adoption of cloud computing in the construction industry and discusses strategies for overcoming these barriers.

1. Introduction

The construction industry is data intensive as heterogeneous data are continuously generated as the project progresses. The data from different stages of the project are usually stored in silos; team server or desktop, individual desktop, laptops, smartphones, etc. Data integration is thus required for the overall project coordination because the inability to access a holistic view of data often leads to wrong decisions that could delay the project and also impact on performance and profitability of the project [1]. The traditional Information and Communication Technologies (ICT) solution is to acquire high-end capacity system to store, process and analyse data from its subcontractors. Deploying on-site solutions require a massive overhead (power, cooling, security, availability, updates) which comes with huge operational cost burden. Therefore, it is impractical to commission on-site ICT infrastructure for all projects due to the huge initial investment requirement. Besides, in-house computing provision is static in capability and usually more expensive to upgrade to meet a sudden upsurge in computing needs. The construction industry is about 90% small and medium enterprises (SME) [2] and cannot afford to invest heavily in the state-of-the-art ICT infrastructure that is a prerequisite to benefit from the current digital innovations. Hence, construction industry is one of the least digitised industry.

Construction industry is investment intensive hence may not be too willing to experiment with new technology and thus being observed to be slow in technology adoption. While there is a huge potential for cloud computing in the construction industry, such applications are not widespread [3]. Cloud computing technology provides affordable and scalable computing facilities using a pay as you go pricing model [4]. Hence the suitability of cloud computing functionality to the SME. As cloud computing eliminates acquisition, installation and maintenance cost of computing facilities [5], which has been a significant hindrance to the adoption of ICT in the construction industry [2]. To assist the construction industry to adopt cloud computing technology, researchers need to expose the potential benefits of the cloud computing technology to the construction practitioners. The need to fill this knowledge gap led to the research question of this study.

Highlights

Abstract

Keywords

1. Introduction

2. Designing and calibrating public transport models

3. Optimal supply policies

4. Emerging technologies and related policies

5. Conclusions

CRediT authorship contribution statement

Acknowledgement

Appendix.

References

Abstract

Public transport provision requires substantial organisational efforts, careful planning, financial contributions from the public, and coordination between millions of passengers and staff members in large systems. Efficient resource allocation is critical in its daily operations. Therefore, public transport has been among the most popular subjects in transport economics since the infancy of this discipline. This paper presents an overview of the literature developed over the past half century, including more than 300 important contributions. With a strong methodological orientation, it collects, classifies, and compares the frequently used analytical modelling techniques, thus providing a cookbook for future research and learning efforts. We discuss key findings on optimal capacity provision, pricing, cost recovery and subsidies, externalities, private operations, public service regulation, and cross-cutting subjects, such as interlinks with urban economics, political economy, and emerging mobility technologies.

1. Introduction

Public transport, defined in this paper as high-capacity vehicle sharing with fixed routes and schedules, is the backbone of urban transport systems in global cities, especially in densely populated metropolitan areas. It is unlikely that mobility will become completely private in the near future, simply because of the inevitable traffic congestion and the difficulties of storing individual vehicles when they are not in use. In other words, even though technological development may transform the appearance of public transport, the fundamental challenge of coordinating between individual travellers who share vehicles of high capacity will remain. The purpose of public transport economics is to make this coordination more efficient, ensuring optimal resource allocation to unlock all societal benefits of mass mobility.

This work reviews more than 300 papers, including the most influential contributions that shaped our understanding of the economics of public transport over recent decades. The earliest studies date back to the 1960s and the 1970s when advanced quantitative methods were not available to calibrate disaggregate supply models, estimate sophisticated demand models, and simulate policy interventions’ impact on large urban networks. Did public transport economics significantly change over half a century? Interestingly, the main messages and policy recommendations of the economists in this field are still the same. Scale (density) economies, road pricing, substitution with underpriced car use, socially optimal subsidies, and the peak load problem are still on the research agenda in various forms, just like decades ago. However, the prevalence of popular subjects does not imply that theoretical and empirical results have achieved maximum impact on policymaking. Despite the surrounding consensus among members of the scientific community, the links between scale economies and subsidisation or the limitations of public transport pricing in congestion mitigation are not obvious in the wider transport industry, to mention only two examples. One of the challenges of public transport economics as a sub-discipline will emerge in knowledge dissemination and cross-fertilisation with related disciplines and professions. We believe that a critical overview of past research efforts is crucial in making impactful discoveries in the future.

1- Introduction

2- Microstructure of RAC

3- Defects in RAC microstructure

4-  Enhancement treatments

5- Conclusions

References

Abstract

Recycled concrete aggregate (RCA) differ from natural aggregate as the former contains attached mortar. Given the recycling process of RCA, that is, by crushing, the microstructure presents several disadvantages, such as porosity, micro-cracks, as well as weak interface transition zones (ITZs), which will also damage the mechanical properties and durability of recycled aggregate concrete (RAC). According to current literature, the microstructure of RAC is mainly affected by ITZs and the porosity of RCA. This paper summarises the principles, advantages and disadvantages of the methods for improving the microstructure of RCA from four aspects, such as removal of attached mortar in the RCA, surface coating on RCA, different mixing methods and CaCO3 precipitation. Methods are also discussed from the aspects of environment, RCA particle size and application, which provide readers with a reference for improving the microstructure of RCA.

Introduction

Since the beginning of the 21st century, with the rapid development of urbanisation and industrialisation, the construction industry has consumed large amounts of natural resources and produced large amounts of construction and demolition waste [1]. The impact on the environment according to Oikonomou [2] is ‘‘Take 50% of raw materials from nature, consume 40% of total energy, and create 50% of total waste”; and construction became the industry with the largest impact on the environment [3]. Concrete is widely used in the construction industry because of its low price, wide application and the ability to take any shape [3,4]. It is a composite material prepared from a certain proportion of cementitious materials, water, aggregates and admixtures [5]. The construction industry produces about 25 billion tons of concrete annually worldwide [6]. Developing countries, such as China and India, which are among the top 10, are the biggest consumers of concrete [3,5].

1- Introduction

2- Previous studies on geopolymer concrete

3- Taxonomy on geopolymer concrete research

4- Performance assessment methods

5- Assessing variables and assessing approaches

6- Structural tests for performance of geopolymer concrete

7- Performance design of geopolymer concrete

8- Conclusions and remarks

References

Abstract

Off late, the continuously depletion of the ozone layer and global warming issue have increased the awareness of the construction industries in using more eco-friendly construction materials. Against this background, geopolymer concrete has started to gain significant attention from the research scholars and construction practitioners, due to its advantageous in using by-product waste to replace cement and reducing greenhouse gas emission during its production. It also possesses better mechanical properties and durability compared to conventional concrete. Despite its advantageous, the use of geopolymer concrete in practical is considerably limited. This is mainly due to the lacking in the studies in terms of structural elements, design and application studies. This paper reviewed the material and structural performances of geopolymer concrete to identify the research gaps in this area for future research development. Analysis shown that geopolymer concrete can replace conventional concrete as they presented better mechanical properties, higher durability and more desirable structural performances compared with conventional counterparts. More studies are still needed for practical design standards and finally, the full scale studies on the structural elements should be established to ensure its feasibility in practical.

Introduction

Geopolymer is adjudged as the latest wave of cement, after gypsum cement and ordinary Portland cement (OPC). It has appeared to be one of the major construction material internationally. ‘Geopolymer’ can be referred as amorphous alkali aluminosilicate or alkali-activated cements [1]. Geopolymer concrete can be produced by polymerizing the aluminosilicates such as fly ash (FA), metakaolin (MK), slag (SG), rice husk ash (RHA), and high calcium wood ash (HCWA) through activation using alkaline solution. Hence the efficiency in producing geopolymer concrete is highly dependent on the activators as well as types of aluminosilicates resources [2]. In general, geopolymer is one of the inorganic polymers. It is amorphous rather than crystalline compared to other natural zeolitic materials [3]. The polymerization requires a considerably quick reaction of silica (Si)-alumina (Al) under alkaline condition which subsequently create three-dimensional polymeric chain of SiAOAAlAO bonds. Dissimilar to OPC or pozzolanic cements, geopolymer utilizes the polycondensation of silica and alumina and a high alkali content to attain compressive strength [4]. On the other hand, geopolymer incorporating OPC develops calcium silicate hydrates (C-S-H) as well as polycondensation of silica and alumina and a high alkali content to attain compressive strength. The following reactions occur during geopolymerization [5].

1- Introduction

2- Fundamentals of piezoelectric material

3- Advanced methods to improve the piezoelectricity of cement-based material

4- Applications of piezoelectric material in sustainable building structures

5- Performance of piezoelectric materials and THeir future development

6- Conclusions

References

Abstract

Piezoelectric materials are capable of transforming mechanical strain and vibration energy into electrical energy. This property allows opportunities for implementing renewable and sustainable energy through power harvesting and self-sustained smart sensing in buildings. As the most common construction material, plain cement paste lacks satisfactory piezoelectricity and is not efficient at harvesting the electrical energy from the ambient vibrations of a building system. In recent years, many techniques have been proposed and applied to improve the piezoelectric capacity of cement-based composite, namely admixture incorporation (e.g. lead zirconate titanate, barium zirconate titanate, carbon particles, and steel fibers) and physical treatments (e.g. thermal heating and electrical field application). The successful application of piezoelectric materials for sustainable building development not only relies on understanding the mechanism of the piezoelectric properties of various building components, but also the latest developments and implementations in the building industry. Therefore, this review systematically illustrates research efforts to develop new construction materials with high piezoelectricity and energy storage capacity. In addition, this article discusses the latest techniques for utilizing the piezoelectric materials in energy harvesters, sensors, and actuators for various building systems. With advanced methods for improving the cementitious piezoelectricity and applying the material piezoelectricity for different building functions, more renewable and sustainable building systems are anticipated.

Introduction

Building structures are constructed for the purposes of residential, official, and commercial activities, all of which make great contributions to the socio-economic development of a nation. During their life cycle, buildings demand a large amount of energy, including the direct energy consumed during construction, operation, rehabilitation, and eventually demolition, as well as the indirect energy required for manufacturing the building’s materials and components [1–3]. From recent literature [4,5], it is estimated that building energy has been reported to occupy about 35% of total energy consumption worldwide. Additionally, carbon dioxide emission from the building industry is responsible for 40% of the total amount of carbon dioxide emitted worldwide [6]. In considering the energy challenges and environmental problems associated with building construction, it is essential to balance the advantages and disadvantages of using energy in buildings and to develop various schemes of achieving sustainability. Self-sustaining building systems thus seek to minimize their negative impacts on the environment through consuming fewer resources, such as materials, energy, water and so on. Among these resources, energy consumption is the primary concern, as it is associated with the entire building lifecycle and carbon dioxide emission. Building energy consumption can be compensated by on-site generation infrastructures or reduced by selfsustained building components. Recently, timber has been increasingly recognized as an environmentally friendly resource and renewable building material. Construction of timber building is conducted within industry plants where little production and processing energy is required. Furthermore, timber buildings allow carbon dioxide storage, performance reproducibility and fast assembly, and their market trend is growing [7]. Timber building will be treated as one of the sustainable building styles, as stated in a recent ASCE report [8]. To promote the application of timber building as a robust alternative to traditional heavyweight infrastructure, acoustic and vibration emissions and management for timber building have recently been studied.

1- Introduction

2- Stainless steel material and tubes

3- Bond behaviour of concrete filled stainless steel tubes

4- Static performance

5- Dynamic performance

6- Fire performance

7- CFSST composite joints

8- Concluding remarks

References

Abstract

Concrete filled stainless steel tubular (CFSST) columns have attracted increasing research interests in the last decade. This paper briefly introduces the material properties of stainless steel and reviews recent research on behaviour of CFSST columns and joints at both ambient and elevated temperatures. The reviewed studies include tests of bond behaviour between the stainless steel tube and core concrete, and the static behaviour of CFSST stub columns, slender columns, beams, stainless steel-concrete-carbon steel double-skin tubular columns, and concrete filled bimetallic tubular columns. The cyclic behaviour of CFSST beam-columns under combined axial and lateral cyclic loading as well as the impact behaviour of CFSST columns is also introduced. Fire test results of full-scale CFSST columns are presented along with finite element analysis results. The behaviour of composite joints with CFSST columns is also briefly reviewed in this paper. Based on the previous research, future research directions on CFSST are summarised and discussed.

Introduction

In the last few decades, the application of stainless steel in construction has attracted increasing interests among researchers and structural engineers. Compared with conventional carbon steel, stainless steel has several advantages, such as extremely high durability and corrosion resistance, easiness of maintenance and improved fire resistance. However, the high cost of stainless steel prevents its wide application as a structural material. To make more economical use of stainless steel, it is advisable to develop stainless steel-concrete composite structures. A good example is to fill stainless steel hollow sections with concrete to form concrete filled stainless steel tubes (CFSST). Fig. 1 shows typical cross-sections of circular and square CFSST columns, where D is the diameter of the circular steel tube, and B is the width of the square steel tube. In the past, extensive studies have been conducted on conventional concrete filled carbon steel columns and their behaviour has been well understood. Since the material behaviour of stainless steel is different from that of conventional carbon steel, some recent studies have been carried out to investigate the behaviour of CFSST members and joints. This is necessary to allow the development of any rational design guidelines for this type of innovative composite structure.

The present review manuscript examines the most essential phases in the developments of the inorganic class of environmentally benevolent Geopolymer concrete focusing on the valorisation of Waste of Glasses in context of incorporation in the manufacturing of Geopolymer concrete, especially concerning to its properties and applications. Their long-standing applications as structural materials developed through activation of alkali, i.e., Geopolymerization, in the field of sustainable constructions and infrastructures industries, diverse GPC are on the map. Even though, more advanced studies in the context of the said concept will be proved valuable to concerned industries people and of course, to the researchers themselves. Although the available literature in this innovation zone is few and far between, it breaks the surface, for the most of the centre of attention on its, incorporation with other waste materials pointing a finger to its approach to embrace ‘‘waste for the best” strategy. Previously, their character is neither wellfigured out nor aptly welcomed as in the ordinary Portland Cement based edifice materials enjoying. That is the core reason and objective of this article that review of its handy restricted literature to throw lights on the valorisation of blending of Waste of Glasses for the manufacturing of Geopolymer concrete centring its attributes and uses establishing it as a soon-to-be useful lucrative and sustainable global building material. The suggestions pointed out here in this manuscript will confidently be accommodating for potential research works on the topic. However, a modest challenge viz., curing complications, sometimes practical confronts of application, constrained supply chain, and a prerequisite for an observant directive of mix design for its fabricating, are standing up in its tracks to substitute Ordinary Portland Cement counterparts. Even so, when produced by utilizing vast and within reach precursors, activators and waste glass materials under up to the standard quality control of diverse characteristics, predominantly strength and green footprints of alkali activators, valorisation of Geopolymer concrete incorporated with waste glasses are momentous forthcoming part of the prospect toolbox of sustainable and economically reasonable construction materials. Eventually, the paper categorizes promotion of applications and most importantly the properties aspect for this promising novel type of building material.

Introduction

Concrete technology has witnessed a revolution since Romans era. Nowadays, a trend towards less energy-intensive, green, innovative, affordable, sustainable user-friendly building materials with low carbon footprint is the subject of attraction to researchers [1–4]. The application of diverse recycled solid waste is drawing the attention of engineers to incorporate them with construction composites. The market for recycled materials like concrete aggregates has been initiated through a project to develop it by Flemish Public Environmental Agency (OVAM) in 2006. It’s conclusion suggested that top-level recycled aggregates often finish up in substandard applications owing to the lack of certainty about the technical performances of recycled aggregates viz., consistency of properties, porosity, the presence of Chlorides, Sulphates, etc. and deficiency of regulations to encourage their applications with elevated added value [5].

1- Introduction

2- Sustainable control objectives in freeway traffic control

3- The modelling framework for sustainable freeway traffic control

4- Sustainable freeway control strategies

5- Remarks on sustainable freeway traffic control

6- Future steps towards a greener mobility

References

Abstract

Sustainability is a key point in the design and management of mobility and traffic systems, which affects also the development of traffic control strategies for freeway networks. According to sustainability-related concepts, freeway traffic controllers should be devised not only for maximally exploiting the road capacity and decreasing vehicles travel delays, but also for reducing pollutant emissions, fuel consumptions, accidents, noise, and so on. This paper analyses the state of the art of freeway traffic control strategies characterised by sustainability-related objectives, in particular referred to traffic emissions and traffic safety, by providing a classification of the research papers in this area. The final part of the paper highlights the main research challenges for modelling and control techniques brought by the introduction of emerging information and communication technologies, that are becoming more and more widespread and are transforming the concept of vehicles in intelligent and connected agents, able to measure the traffic state and to implement specific traffic control policies.

Introduction

Nowadays, the greater awareness about the dangerous effects produced by myopic policies aimed only at pursuing short-term benefits has brought the issue of sustainable development to the centre of the political agenda of many countries worldwide. In recent years, in fact, the theme of sustainability has been addressed considering various fields of the human activity and proposing several definitions and targets (as those proposed in Kates, Parris, & Leiserowitz, 2005 and Giovannoni & Fabietti, 2014). Although concerning different aspects, such definitions agree that only the actions aimed at achieving the optimal relation between the humans and the environment can ensure a fair development of contemporary and future society. Yet, the concept of sustainability is extremely complex, since it requires the fulfilment of a mix of often conflicting objectives. The creation of sustainable cities, the promotion of a more equitable economic growth and the environmental safeguard represent just some of the objectives identified in United Nations (2017) to accomplish the 2030 Agenda for Sustainable Development (United Nations General Assembly, 2015). The implementation of the 2030 Program requires a rethinking of transportation systems in a more open-minded and environmentfriendly perspective. In this sustainable vision, the transport system should enhance the social equity and ensure a safer mobility by increasing the access to services and to the most disadvantaged areas, without damaging the environment and people’s health. This ambitious journey towards sustainable mobility starts from the awareness that the transport system, in particular the road sector, is today one of the leading sources of greenhouse gases and pollution, involving serious consequences both for human health and for the environment (Hoek, Brunekreef, Goldbohm, Fischer, & Brandt, 2002). A survey developed by the World Health Organization, on the basis of 2012 data, revealed that 3.7 millions of premature deaths may be attributed to environmental pollution. Most of these deaths and diseases are caused by the prolonged exposure to substances resulting from the use of fossil fuels.

1- Introduction

2- Recently developed methods

3- Applicability

4- Cost

5- Duration time

6- Conclusions and recommendations

References

Abstract

Triggered liquefaction in earthquakes, that soil displays fluid-like characteristics caused by an on-going increase of pore water pressure and reduction of the effective stress, can damage existing building foundations and other structures and result in significant economic losses. Many previous studies have investigated methods, which effectively control sand liquefaction while minimizing cost, environmental impact and other related disturbances. Recently, the rapid development of materials technology and multidisciplinary approaches has made available new materials suitable for improving the liquefaction resistance and enabling other liquefaction mitigation techniques. To raise some important questions and encourage further research and discussions, investigations on the recently developed liquefaction mitigation methods are reviewed in this study. The review first analyzed and discussed the characteristics of the newly developed methods including the mitigating mechanism, effectiveness, and possible executive problems for purpose of building sufficient understanding into the progress of liquefaction resistance. Then, the applicability and uniformity in the soil with different pore size, possible disturbance to nearby structures are discussed. Additionally, the potential cost and duration time of the mitigation measures for site constructions are briefly described. Through this review, some important questions and discussions are raised; the readers will fully understand the research trend of liquefaction mitigation and further explore new methods and techniques that could be effective, easy for on-site construction, low cost, environment-friendly and highly durable. This study recommends long-term in-situ investigation on mitigation effectiveness, duration time and quantitative cost assessment.

Introduction

Liquefaction induced by static or dynamic loading in saturated sandy soil can cause significant damage to building foundations and existing structures, such that the sudden instability may result in the destruction of structures, economic losses and even loss of human life [1–3]. Liquefaction problems have been reported frequently after earthquakes, such as the earthquakes that occurred in 1964 Niigata, Japan, 1976 Tangshan, China, 1999 Kocaeli, Turkey, 2008 Wenchuan, China, and 2011 the Tohoku Region Pacific Coast Earthquake, Japan. This has motivated increasing research into improving liquefaction resistance and other liquefaction mitigation methods. The main cause of liquefaction is the loss of shear strength due to an increase in pore water pressure and a reduction of the effective stress of soil, which eventually leads to the phenomenon where sandy soil displays fluid-like characteristics [4,5]. Soil improvement methods are most commonly employed to reduce or eliminate the effects of liquefaction. Research on the physical properties of liquefiable sand shows that the density of sand [6], content of fines [7,8], coefficient of uniformity [9] and other factors [10–12] has a great influence on liquefaction. However, control of these factors was not the best way to improve liquefaction resistance. Earlier studies have shown that the addition of metal strips and bars, existing plant roots and soil densification can improve liquefaction resistance [13–15]. However, the use of metal strips present problems including reduced ductility and uncertainty of the influence of environmental factors. Additionally, the durability of liquefaction alleviation is poor when utilizing plant roots. Soil densification through dynamic compaction is energy intensive. Moreover, this method has a great impact on the surrounding infrastructures, and the depth of compaction is limited. Therefore, researchers continue to explore new mitigation methods to prevent the occurrence of liquefaction.

1- Introduction

2- Conceptual definitions

3- Bibliometric details

4- Progressive collapse and structural robustness in international codes

5- Quantification of structural robustness

6- Progressive collapse risk

7- Experimental testing

8- Numerical modelling

9- Conclusions and needs

References

Abstract

Extreme events (i.e. terrorist attacks, vehicle impacts, explosions, etc.) often cause local damage to building structures and pose a serious threat when one or more vertical load-bearing components fail, leading to the progressive collapse of the entire structure or a large part of it. Since the beginning of the 21st century there has been growing interest in the risks associated with extreme events, especially after the attacks on the Alfred P. Murrah Federal Building in Oklahoma in 1995 and on the World Trade Center in New York in 2001. The accent is now on achieving resilient buildings that can remain operational after such an event, especially when they form part of critical infrastructures, are occupied by a large number of people, or are open to the public. This paper presents an ambitious review that describes all the main advances that have taken place since the beginning of the 21st century in the field of progressive collapse and robustness of buildings. Widely diverse aspects are dealt with, including: (1) a collection of conceptual definitions, (2) bibliometric details, (3) the present situation and evolution of codes and design recommendations, (4) quantification of robustness, (5) assessing the risk of progressive collapse, (6) experimental tests, (7) numerical modelling, and (8) research needs. Considering the comprehensive range of these aspects, this paper could be of great use to professionals and researchers who intend to enter the field of the progressive collapse of building structures and also to other experts who require an extensive and up-to-date view of this topic.

Introduction

All types of public and private buildings may be subjected to extreme events, caused, for example, by hurricanes, tsunamis, earthquakes, explosions, vehicle impacts, fires and human errors, or even terrorist attacks. Such events usually cause local damage to the structure of buildings, which can lead to a complete collapse. This is where the term progressive collapse comes in, understood as the process by which local damage sets in motion a chain of failures, leading to the collapse of the entire building or a large part of it. A progressive building collapse is always accompanied by serious personal and material losses [1]. In recent years the press has spotlighted a number of notorious progressive collapses; the most important for the numbers of victims, extent of the damage or social impact at the time include the classics Ronan Point (London, 1968) and Capitán Arenas (Barcelona, 1972), the U.S. Marine Barracks (Beirut, 1983), the Argentine Israelite Mutual Association (Buenos Aires, 1994), the A.P. Murrah Federal Building (Oklahoma, 1995), the Sampoong Department Store (Seoul, 1995), the buildings of the World Trade Center (New York, 2001), and the Achimota Melcom Shopping Centre (Acra, 2012). From the attention given to these and many other collapses, the idea has become generally accepted that there is a need for robust buildings that can sustain local damage without suffering disproportionate collapse. This performance objective may be further expanded in the case of buildings that form part of critical infrastructures (e.g. hospitals, power stations, passenger terminals), are occupied by a large number of people or are open to the public (e.g. schools, sports and commercial centres). In those situations, there is even the need for resilient buildings, which can be defined as buildings that are able to absorb and recover from an extreme event, maintaining operation and functionality, according to what is generally defined as physical resilience at the larger scale of urban infrastructure systems. Therefore, the resilience of a building includes not only the structural property of robustness, which contributes to the capacity of absorbing an extreme event, but also a recovery capacity that allows the pre-event performance level to be quickly restored or even improved.

Introduction

At 14:27:59 local time, on May 12, 2008, an MS 8.0 earthquake struck Wenchuan County in Sichuan Province of southwestern China [1, 2]. The Wenchuan earthquake was noted as being one of the most destructive earthquake events to occur in China since 1949, due to its widest recorded region of influence and greatest disaster- triggered losses. The Wenchuan earthquake also caused major casualties. Estimates from August 25, 2008 show that 69,226 people had been killed, along with 374,643 reported injured, and 17,923 lost. The earthquake caused a total direct economic loss of 845.1 billion yuan. During the earthquake event, numerous urban and rural buildings were devastated. The Ministry of Civil Affairs (June 25, 2008) states that approximately 23 million housing units were broken down duo to the earthquake (one house being equivalent to four housing units on average), with as many as 6,525,000 left completely destroyed. Also, a vast number of villages in the vicinity of the earthquake were razed to the ground. The Wenchuan earthquake affected all aspects of local society completely. The infrastructures of the area were severely damaged by the earthquake event, and systems providing transport, logistics and daily-life service were paralyzed over a large area. Since all of the facilities were out of operation for at least one week following the earthquake event, there were no landline communication connections available. A large number of hospitals and schools suffered severe damage, as did many historical sites and natural heritage. Moreover, many important industries and corporations were destroyed by the event resulting in severe impediment of industrial progress. The earthquake also effectively destroyed a lot of forested land and wildlife habitats to break down the eco-environment and degrade the area’s ecological functions. These enormous losses left seismologists and engineers many questions to consider. First of all, they needed a clear scientific understanding of the earthquake rupture, including the nature and size of the seismic waves and the ground accelerations they produced. Also, the secondary post-earthquake hazards which had been generated by the main earthquake event required examination, so that the seismic hazards could be better assessed and guarded against in the future. In this research study, the previous research study results which had been made available regarding this particular earthquake during recent years were summarized and reviewed in an attempt to obtain new insights into the disaster. Also, this study focused on the current related challenges to seismology and earthquake engineering following major earthquake events.