Civil Engineering Infrastructure Research Articles

5th International Conference on Environmental Science and Civil Engineering (ESCE2019)

Preface5th International Conference on Environmental Science and Civil Engineering (ESCE2019) has been held in Nanchang, P.R. China from April 13th-14th, 2019, organized by Nanchang Institute of Technology, Civil Engineering Academy of Jiangxi Province and Hubei Zhongke Institute of Geology and Environment Technology, co-organized by journal of Rock and Soil Mechanics, Key Laboratory for Safety of Water Conservancy and Civil Engineering Infrastructure in Jiangxi Province, Jiangxi Provincial Engineering Research Center of Special Reinforcement and Safety Monitoring Technology in Hydraulic & Civil Engineering.ESCE2019 proceeding tends to collect the most up-to-date, comprehensive, and worldwide state-of-art knowledge on Environmental Science and Civil Engineering. All the accepted papers have been submitted to strict peer-review by 2-4 expert referees, and selected based on originality, significance and clarity for the purpose of the conference. The conference program is extremely rich, profound and featuring high-impact presentations of selected papers and additional late-breaking contributions. We sincerely hope that the conference would not only show the participants a broad overview of the latest research results on related fields, but also provide them with a significant platform for academic connection and exchange.The Technical Program Committee members have been working very hard to meet the deadline of review. We have collected more than 180 submissions during the conference period. The final conference consists of 68 papers divided into 5 sessions.We would like to express our sincere gratitude to all the TPC members and organizers for their hard work, precious time and endeavor preparing for the conference. Our deepest thanks also go to the volunteers and staffs for their long-hours work and generosity they’ve given to the conference. The last but not least, we would like to thank each and every of the authors, speakers and participants for their great contributions to the success of ESCE2019.Qing Quan LiangVictoria University, Australia

SORTING SUBCONTRACTORS’ ACTIVITIES IN CONSTRUCTION PROJECTS WITH A NOVEL ADDITIVE-VETO SORTING APPROACH

Selection processes in civil engineering infrastructure projects might require more time and effort than the decisionmakers involved in these projects are normally prepared to devote to running them. A novel approach is proposed to sort these activities into classes that represent their impact on the project, namely additive-veto sorting model, which should be considered before any bidding procedure. Therefore, problems regarding the client’s satisfaction caused by subcontractors can be avoided, and the decision-makers involved in the selection problem can devote to each class an effort compatible with the impact that activity might have on the project. The novelty of this method is that it was built to reflect the quasi-compensatory rationality of decision-makers in the construction industry; it provides them with insights on subcontractors’ activities, and it is grounded on and inspired by a real case study. The new parameters proposed within this model introduce the idea of vetoing an activity being assigned to a class when this activity is incompatible with the decision-maker’s preferences. By using this novel method, the authors succeeded in finding results that avoided a complete compensation amongst the factors considered, taking into account ranges that would be of significant importance in the decision process.

Numerical study of full-scale CFRP strengthened open-section steel columns under transverse impact

In recent years, externally bonded fibre reinforced polymer (FRP) material has gained popularity as an efficient means of strengthening existing civil engineering infrastructure. In the case of steel structures, FRP has frequently been deployed to strengthen against static and fatigue loads. However, the understanding of the effect of impact load on strengthened structures is still in its early stages. In parallel with this, most of the existing studies on impact have concentrated on small scale elements. Thus, the study presented here is aimed at examining the effectiveness of carbon fibre reinforced polymer (CFRP) in strengthening full-scale steel I-section columns against impact load. To achieve this aim, a non-linear finite element model built using ABAQUS was validated against experimental tests and then used to simulate the strengthening technique. The model included failure criteria of all investigated materials (steel, CFRP and adhesive material). Various parameters including boundary conditions, preloading level, kinetic energy, impact location and impact direction were examined. The CFRP strengthening technique was found to be highly effective in preventing column failure whether by global buckling failure or transverse shear failure. In addition the strengthened columns exhibited a reduced axial and transverse displacement by more than 70% in many cases.

SHM of Reinforced Concrete Elements by Rayleigh Backscattering DOFS

This document showcases the latest research conducted within UPC – BarcelonaTech on the performance of distributed optical fiber sensors (DOFS), more specifically the case of the optical backscattered reflectometry (OBR) system, in the structural health monitoring (SHM) of bridges and large scale structures. This technology has demonstrated promising results for monitoring applications in a wide range of fields but due to its novelty, still presents several uncertainties which prevent its use in a more systematic and efficient way in civil engineering infrastructures, being this even more evident in the case of concrete structures. Therefore, different laboratory experimental campaigns were devised where multiple aspects of the instrumentation of DOFS technology in civil engineering applications were assessed and scrutinized. Such as the study of new implementation methods, comparison and performance analysis of different bonding adhesives and spatial resolution. Additionally, the fatigue performance of this sensing typology was also assessed. Furthermore, the use of the OBR system technology was applied in a real world structure in Barcelona, Spain, where new challenging conditions had to be addressed. Consequently, with this work, different conclusions are obtained related to the proficiency and limitations on the use of this particular type of optical sensing system in concrete structures.

Big Data Analytics in Civil Engineering : Use Cases and Techniques

Big data analytics has brought about positive change to civil engineering infrastructure monitoring, project control and management, and envisioning smart cities. ensors along with more sophisticated data processing methods enable engineers to gather massive amounts of data which in turn can be utilized making useful decisions, carry out predictive analyses on when machinery might require maintenance, or where resources should be utilized to the maximum. This paper focuses on analysing the way big data is used and applied in civil engineering and the advancement that can be made in safety, costs and sustainability of an infrastructure project. Nevertheless, issues including the quality of data, cost sensitivity, and scarcity of talent are also presented.

Effect of near and far Field Earthquakes on performance of various base isolation systems

Civil engineering infrastructures are prone to natural disasters like earthquakes, floods and strong winds. Base isolation is one of the effective structural controlling technique for protection of structure during earthquake events. The concept of Base isolation is to insert a flexible layer between foundation and superstructure thus decoupling the building from damaging action of ground motion. This modifies the dynamic characteristics of the system. This paper presents comparative study of near and far field earthquakes on the performance of three types of passive base isolators namely High Damping Rubber bearing (HDRB, Damping Ratio: 13%), Low Damping Rubber Bearing (LDRB; Damping Ratio: 3%) and Lead Core Rubber Bearing (LCRB, Damping Ratio: 25%). For this purpose, an 8-storey structure has been analyzed using state space approach in MATLAB. Parameters like peak global drift, inter-storey drift, transmissibility of acceleration are compared for various base isolation systems under near and far field earthquakes. It is concluded that the dynamic response of the structure depends on the source of excitation and designer must consider this effect for efficient design. Moreover, the damping of the base isolator should be so adjusted that both the deformation and transmissibility ratio are minimized or in some cases a combination of different dampers may be used.

Design and field implementation of an impact detection system using committees of neural networks

Many critical societal functions depend on uninterrupted service of civil engineering infrastructure. Railroads represent important infrastructure components of the transportation sector and provide both passenger and freight services. Railroad bridges over roadways are susceptible to impacts from overheight vehicles and equipment, which may damage bridge girders or supports and must be investigated after each event. One method of monitoring for vehicle-bridge collisions utilizes accelerometers to monitor for abnormal bridge vibrations corresponding to abnormal activity. Passing trains under normal operating conditions frequently produce significant bridge responses that have similar response characteristics to bridge strikes, but do not need to be investigated. This paper presents an expert system which comprises committees of artificial neural networks trained to interrogate data collected from accelerometers mounted on the bridge, assess the nature of the acceleration signal, and classify the event as either a passing train or a potentially damaging impact. This system is trained using acceleration time histories from accelerometers installed on 8 low-clearance rail bridges; no finite element model simulations were used for network training or data stream creation. The presented system accurately detects and classifies impacts with average impact detection performance ranging from 91–100% with average false positive rates limited to 0.00–0.75%.

Removal of Hazardous Cationic Salt Pollutants During Electrochemical Treatment from Contaminated Mixed Heterogeneous Saline Soil

Salt-affected soils are found mainly in arid and semiarid regions. In these areas, weak precipitation rate causes salt accumulation at high level on the soil surfaces, leading to drastic modifications in soil properties, affecting hence the environment, human health and civil engineering infrastructure and facilities. This research aimed to study the performance of the electrochemical treatment on removal of hazardous cationic salt including sodium, potassium and magnesium cations. The novelty of this work lies in the investigation of the potential of electroosmosis phenomenon as a driving vector in the removal of cationic hazardous salt during its regularized path toward the cathodic area. Therefore, a controlled-permanent analysis of contaminated catholyte water over processing time was achieved, in order to understand the evolution of contaminant removal during treatment time via the electroosmosis process. For this purpose, five relevant indices were evaluated, including electric current, electroosmotic flow, pH, electrical conductivity and cationic hazardous salt removal efficiency. Experimental tests were conducted in laboratory-designed cell using different electric potential difference for a total period of 8 days. Owing to the electroosmosis phenomenon, salt contaminants migrated and accumulated in the catholyte chamber, facilitating thereby their removal. Among these contaminants, sodium and potassium exhibit the highest decontamination efficiency with a rate of 88 and 85%, respectively. Magnesium ions show moderate removal with a percentage of 53%, due to the pH gradient, degree of hydration, ionic valence and mobility. The results demonstrate that the electrochemical treatment may be an efficient method for remediation of saline low-permeable heterogeneous soils.

Infrastructure construction in developing countries: a shared approach to sustainability

The oil and gas and extractive industries face the constant challenge of locating new resources in remote parts of the developing world. Skill shortage, inhospitable locations and outdated engineering practices and technology characterise these projects. Companies operate under fixed-period concessions, which place huge time pressures on the exploration and production cycle. Construction of the associated civil engineering infrastructure is often on the critical path. These projects typically use pools of foreign skilled workers and large volumes of imported materials and equipment. The cost and carbon dioxide emissions associated with logistics alone are enormous. Overcoming these challenges calls for a critical rethink in the way traditional civil engineering construction practice is undertaken. This paper reports on the implementation of a sustainability management and resource training framework by a foreign consulting and advisory firm. The framework examines in-country labour skill sets, natural resource and technology relevant to project needs, identifying constraints and knowledge gaps. Innovative engineering solutions that maximise use of local workforce, materials and technology are subsequently designed in line with project timelines. Case studies from Central Asia, the Middle East and Africa, demonstrate that the framework is an effective tool for human resource development and sustainability management.

Laboratory investigation on solutes removal from artificial amended saline soil during the electrochemical treatment

Soil salinity has become one of the environmental issues around the world, compromising thus land ecosystems as well as civil engineering infrastructures and facilities. This hazard is further aggravated, primarily when dealing with low permeable soils, where conventional remediation techniques are inadequate and mostly ineffective. Electrochemical treatment is an innovative and green technology for restoration of saline soils. This process has been proven to be the most efficient, promising technique, offering an optimal and sustainable remediation of salt-affected soils. The originality of this method involves application of an electric current through inserted electrodes into the soil matrix, inducing mobilization and transport of salts toward the electrodes of opposite charge via electro-migration process. The electrical current also induces a net water flow by electro-osmosis mechanism, allowing better draw and removal of solutes within the porous medium. This paper investigates the performance of the electrochemical treatment in remediation of salt-affected soil. Sodium, potassium and calcium were used as selective contaminants with targeted concentration of 0.5 M. In this aim, a laboratory bench scale was designed. It consists of soil box, anolyte and catholyte reservoirs, current monitoring devices, pH and electrical conductivity probe controller. The highest removal was for sodium and potassium with an extraction of 88 and 82%, respectively. Calcium exhibits lower removal rate of 57%, due to the development of the pH gradient, hindering therefore their mobility. This study demonstrated that electrochemical treatment can be advantageous in remediation of salt-affected soils, for enhancing agricultural productivity as well as soil constructional uses.

Challenging the Limits of Nanoscale Simulations: Modeling Joule Effect and Piezoresistivity in Carbon Nanotubes Enforced Polymers

The unique electric properties of carbon nanotubes (CNT)1, have opened new scientific and technological fields2 based on the investigation and optimization of CNT filled polymers3. CNTs, when added to polymer matrices (such as epoxy, bitumen, concrete) make them conductive once they overcome a specific (so-called percolative) concentration4. When this percolative threshold is reached, a CNT electric circuit is formed and the composite materials become conductors. Based on such peculiar behavior, smart materials able to monitor their own conditions could be realized and employed for several applications ranging from automotive and aeronautics to civil engineering infrastructures. The main goal of this work is to understand, through a theoretical-computational approach, the electric behavior of CNT based composites5 and help in improving their performances. In particular, the Joule effect, i.e. the heat dissipation of the conductive CNTs is simulated. The CNTs Joule effect can be employed to build smart materials able to have specific properties (i.e. self-deicing under certain temperatures) or to repair their own cracks (self-healing). The piezoresistivity, i.e. the change in the electric resistance of the CNTs due to an applied strain or stress, is also investigated. This feature allows these composites to be sensitive to an external stress or damage (self-sensing), in this way an immediate and efficient repair can be performed. A computational protocol to understand the behavior, the sensitivity and the limits of such materials at the nanoscale is proposed. This will improve the materials performances and efficiency on larger scales. For the first time, a computational modeling strategy along with preliminary results is built and presented to simulate at the nanoscale the Joule effect and the piezoresistivity of CNTs filled polymers. Obtaining a widely applicable strategy to model electric properties of CNTs and characteristic behavior trends of such materials is the final goal of this project. [1] Iijima, Nature, 1991, 354, 56-58. [2] W. Nan, Y. Shen, J. Ma, Annu.Rev.Mater.Res., 2010, 40, 131-151. [3] M. Ajayan, O. Stephan, C. Colliex, D. Trauth, Science, 1994, 265, 1212-1214. [4] M. Mutiso, K. I. Winey, Prog. Polym. Sci., 2015, 40, 63.84. [5] Zhao, M. Byshkin, Y. Cong, T. Kawakatsu, L. Guadagno, A. De Nicola, N. Yu, G. Milano, B. Dong, Nanoscale, 2016, 8, 15538-15552.

A comparative study of the thermophysical and mechanical properties of the glass fiber reinforced polymer bars with different cure ratios

Cure ratio is a key property for the acceptance and use of glass fiber reinforced polymer bars in civil engineering infrastructure. Yet, there have been no reported studies investigating the effect of cure ratio on the physical, thermal, and mechanical properties of the fiber reinforced polymer bars. This paper presents an interlaboratory test program involving four laboratories to evaluate the cure ratio and glass transition temperature of glass fiber reinforced polymer bars from different production lots. The effect of cure ratio on the physical, mechanical, and microstructure of the glass fiber reinforced polymer bars was also evaluated. The results of this study show that the cure ratio significantly affected the glass transition temperature ( Tg) of the glass fiber reinforced polymer bars tested. The results also show that interlaminar shear strength of the glass fiber reinforced polymer bars was affected by the cure ratio but not the physical and tensile properties, microstructure, or chemical composition. The fully cured glass fiber reinforced polymer bars had interlaminar shear strength up to 8% higher than the partially cured bars. Nonetheless, the glass fiber reinforced polymer bars with a cure ratio of only 96% still had properties well above the minimum prescribed physical and mechanical properties for the reinforcing materials in concrete structures.

Effect of crumb rubber on the mechanical properties of crushed recycled pavement materials

The low-carbon footprint of using recycled construction and demolition (C&D) aggregates in civil engineering infrastructure applications has been considered to be a significant solution for the replacement of conventional pavement aggregates. Investigations regarding the use of crumb rubber in the base and subbase layers of pavement have been well documented. However, information on the effects of crumb rubber and its size within C&D aggregates as the base/subbase layers is still very limited. In this study, crumb rubber with particle sizes ranging from 400 to 600 μm (fine) to 10–15 mm (coarse), 20 mm recycled crushed concrete (RCC), and 20 mm crushed rock (CR) were used. The crumb rubber was added to the two groups of C&D aggregates at 0.5, 1 and 2% by weight percentages of the aggregates. The effect of crumb rubber on the mechanical properties (such as California bearing ratio, unconfined compressive strength, aggregate crushing value, dynamic lightweight cone penetrometer, Clegg impact value, Los Angeles abrasion values, and resilient modulus) of the C&D aggregates was then examined. Based on the experimental test results, it was found that crumb rubber can be recycled as a waste material for the base and subbase layers in the pavement.

What lies beneath? A decade of underground construction in Hong Kong

Over the past decade Hong Kong has seen a rapid expansion in the use of underground space for Civil Engineering infrastructure projects (Fig. 1). Forty-eight kilometres of rail tunnel has been or is in the process of being constructed with associated shafts (Fig. 2) for access and ventilation and mined caverns for stations (Fig. 3). The catalyst for this expansion may be due to the integration of the Hong Kong Special Administrative Region with China, which commenced in 1997 (with the handing back of Hong Kong and the New Territories to China) and has accelerated over the last decade in line with the global aspirations of China. This integration has been the catalyst for three new major road border-crossing projects (Deep Bay Link; Hong Kong to Macau Bridge; and Liantang/Heung Yuen Wai crossing) and connection into the mainland express rail link (Hong Kong High Speed Rail Project) (Fig. 1). The population has also risen over this period from c. 6.9 million in 2005 to c. 7.3 million in 2016 (tradingeconomics 2016) fueling, in part, the expansion of mass transit rail systems: the Kowloon Southern Link (3 km – complete); the West Island Line (3 km – complete); Sha Tin to Central Link (17 km – under construction); the South Island Line East (7 km – under construction); the Kwun Tong Line extension (3 km – under construction) and the Hong Kong Express Rail Link (26 km – under construction) (Fig. 1). Pressure on valuable land resources has seen the emergence of the innovative use of underground space for: explosives magazines; sewage treatment systems; service reservoirs (Fig. 4); urban drainage and flood protection projects (Fig. 5); and new road networks, such as the Central–Wan Chai Bypass (Fig. 6). Fig. 1. Simplified outline map of the Hong Kong SAR showing the location of the projects referred to in this …

Technical Specifications of Structural Health Monitoring for Highway Bridges: New Chinese Structural Health Monitoring Code

Governments and professional groups related to civil engineering write and publish standards and codes to protect the safety of critical infrastructure. In recent decades, countries have developed codes and standards for Structural Health Monitoring (SHM). During this same period, rapid growth in the Chinese economy has led to massive development of civil engineering infrastructure design and construction projects. Consequently, China has become the leading country of civil engineering. In 2016, the Ministry of Transportation of the People’s Republic of China published a new design code for SHM systems for large highway bridges. This document is the first technical SHM code by a national government that enforces sensor installation on highway bridges. This paper summarizes the existing international technical SHM codes for various countries and compares them with the new SHM code required by the Chinese Ministry of Transportation. The paper outlines the contents of the new Chinese SHM code and explains its relevance for the safety and management of large bridges in China, introducing key Chinese-US SHM vocabulary, definitions and technical significance. Finally, this paper discusses the implications for the design and implementation of a future US SHM code, with suggestions for similar efforts in other countries and governments.

A survey on problems encountered in current concrete construction and the potential benefits of self-healing cementitious materials

The annual costs for repair, maintenance and replacement of civil engineering infrastructure attracts significant expenditure in the UK. Anecdotal evidence suggests that a significant number of existing and new concrete structures suffer from repair and maintenance problems, but a lack of objective construction industry supported data concerning these problems makes it difficult to establish, with any certainty, the actual problems encountered in current concrete construction in the UK. To address this lack of data, a market research exercise was commissioned by the Materials for Life (M4L) EPSRC funded research project. The market research has shown that damage in the form of cracking in concrete structures was experienced by more clients, design team members and civil engineering contractors than any other problem. Structures requiring articulation and subject to dynamic loads such as bridges were noted as being the most vulnerable to damage, with this damage mostly occurring in the joints and half joints, bearings and the deck of such structures. The main consequential effects of damage in concrete structures were the need for the contractor to return for repairs as well as the need for regular monitoring. The current approaches taken to enhance a structure’s longevity mainly involve the use of additional cementitious material to improve the barrier between the environment and the steel reinforcement. However, an alternative could be to use the self-healing cementitious materials that have been proposed by the M4L research team. Until now there has been insufficient evidence regarding how these materials may be deployed in the construction industry, and the applications to which they may be best suited in terms of added-value. The market research results show that highways and infrastructure generally and water retaining structures would benefit most from self-healing cementitious materials, with reduced maintenance costs over a structure’s lifetime justifying a premium in the capital material cost. Reduced whole-life costs and fewer repair and maintenance interventions will have a significant influence on the economic, environmental and social impact of repair and maintenance events, which will be of benefit to the UK as a whole.

State-of-the-Art Review of Railway Track Resilience Monitoring

In recent years, railway systems have played a significant role in transportation systems due to the demand increase in conveying both cargo and passengers. Due to the harsh environments and severe loading conditions, caused by the traffic growth, heavier axles and vehicles and increase in speed, railway tracks are at risk of degradation and failure. Condition monitoring has been widely used to support the health assessment of civil engineering structures and infrastructures. In this context, it was adopted as a powerful tool for an objective assessment of the railway track behaviour by enabling real-time data collection, inspection and detection of structural degradation. According to relevant literature, a number of sensors can be used to monitor track behaviour during the train passing under harsh environments. This paper presents a review of sensors used for structural monitoring of railway track infrastructure, as well as their application to sense the performance of different track components during extreme events. The insight into track monitoring for railways serving traffic with extreme features will not only improve the track inspection and damage detection but also enable a predictive track maintenance regime in order to assist the decision-making process towards more cost-effective management in the railway industry.

Distributed fiber optics sensors for civil engineering infrastructure sensing

Distributed Fiber Optic Sensing (DFOS) is one of the promising tools for structure health monitoring. It can measure physical quantities (such as temperature, strain, and vibration) of the fiber continuously (say 5 cm interval) along its length for long distance (say 10 km) due to its low-loss characteristic. By attaching an optical fiber cable to a structure or embedding it inside a structure, it is possible to monitor the changes of ambient parameters of the structure. In this paper, the measurement principles and their state-of-the-art status in terms of their capabilities are discussed. The main advantage is its high sensitivity over large distances and the ability to interface with a wide range of measurands in a distributed manner. The systems provide thousands of “strain gauges”, “thermo-couples”, or “accelerometers” along a single fiber optic cable connected to or embedded in structures, which can then serve as a civil infrastructure nerve system. It can be applied to flexible geometries, providing the ability to design a whole range of sensors with tremendous information carrying capacity. DFOS can provide a highly effective monitoring system for both short and long term to realize our concept of “smart infrastructure”.

Immediate and long-term effects of lime and wheat straw on consistency characteristics of clayey soil

Clayey soils with swelling and shrinkage characteristics have been major causes for many problems in roads, buildings and other civil engineering infrastructure in various areas of Pakistan, particularly where there are several patches of such soils on either side of Indus River. As the consistency characteristics are directly related with the variation of moisture content; therefore, this study was explicitly focused to investigate the effect of lime and wheat straw on the consistency characteristics of clayey soils with relatively high swelling and shrinkage characteristics. The consistency test results indicate that by the increase in lime content there is a decrease in the plasticity index of soil; for instance, 10% lime content resulted to 59% decrease in the plasticity index value. On the other hand; the addition of wheat straw resulted in a significant increase in the plasticity index; for instance, 10% wheat straw content resulted to a 120% increase in the plasticity index. This study has further shown that the shrinkage and swelling of clayey soils which resulting to several problems in the civil engineering infrastructures may adequately be managed through mixing an appropriate amount of lime and wheat straw as soil stabilizing agent for both immediate and long-term effects.

Upscaling the pollutant emission from mixed recycled aggregates under compaction for civil applications.

In general terms, plant managers of sites producing construction wastes assess materials according to concise, legally recommended leaching tests that do not consider the compaction stage of the materials when they are applied on-site. Thus, the tests do not account for the real on-site physical conditions of the recycled aggregates used in civil works (e.g., roads or embankments). This leads to errors in estimating the pollutant potential of these materials. For that reason, in the present research, an experimental procedure is designed as a leaching test for construction materials under compaction. The aim of this laboratory test (designed specifically for the granular materials used in civil engineering infrastructures) is to evaluate the release of pollutant elements when the recycled aggregate is tested at its commercial grain-size distribution and when the material is compacted under on-site conditions. Two recycled aggregates with different gypsum contents (0.95 and 2.57%) were used in this study. In addition to the designed leaching laboratory test, the conventional compliance leaching test and the Dutch percolation test were performed. The results of the new leaching method were compared with the conventional leaching test results. After analysis, the chromium and sulphate levels obtained from the newly designed test were lower than those obtained from the conventional leaching test, and these were considered more seriously pollutant elements. This result confirms that when the leaching behaviour is evaluated for construction aggregates without density alteration, crushing the aggregate and using only the finest fraction, as is done in the conventional test (which is an unrealistic situation for aggregates that are applied under on-site conditions), the leaching behaviour is not accurately assessed.