This study investigates a novel self-sensing approach for monitoring the structural health of concrete structures by developing hybrid textile-fiber-reinforced concrete (TFRC) elements. The proposed concept offers to use carbon-based textile positioned within electrically conductive concrete medium, functioning both as the primary reinforcement system and as a sensory device for the concrete body. By exploring changes in the impedance spectrum and characterizing the equivalent electrical circuit, measurements of the electrical resistance (R) and capacitance (C) of the concrete are achieved. Both electrical properties are used as indicators for assessing the structural health by two transverse gauge-factors, namely (Formula presented) and (Formula presented). To enhance the electrical conductivity of the concrete body, additive short carbon fibers (CFs) are used, which also enhance the mechanical properties of the element. It is demonstrated that CFs significantly affect the electrical resistivity and permittivity of the concrete. It is observed that the percolation threshold is at a volume fraction of V_f = 0.6%, and the highest electrical permittivity is at V_f = 1.2%. Results showed that the smart hybrid TFRC elements exhibited consistent, repetitive, and sensitive electrical responses associated with straining and cracking of the concrete matrix.

Fatigue damage is one of the primary distresses in hot mix asphalt (HMA) pavements. The complex viscoelastic behavior of the asphalt composition poses challenges in developing robust models for predicting fatigue life and assessing damage. This study aims to explore a relatively direct model to address these challenges. A continuum damage mechanics (CDM)-based model is applied to HMA, in which dissipated energy is defined as the damage variable, while temperature and strain are considered dependent variables. By defining damage in terms of dissipated energy, rather than the conventional approach of tracking the degradation of the stiffness modulus, the model can be calibrated to provide reliable fatigue life predictions. Furthermore, such a model addresses key limitations associated with stress triaxiality and enables direct exploration of the variables governing fatigue damage. Fatigue curves, obtained from repeated loading in four-point bending tests under strain-controlled conditions, are used to calibrate the model’s coefficients. The model is verified through experimental investigation, demonstrating good agreement between the predicted and measured damage evolution and fatigue life, even at relatively high temperatures. The results quantitatively demonstrate that fatigue life increases with the increase in temperature and decreases in high tensile strain levels. Moreover, it is found that temperature plays a key-factor in determining the coefficients of the fatigue damage model. This finding enables the determination of model coefficients for HMA using a limited number of flexural fatigue tests conducted in constant-strain mode. The proposed model’s methodology can be applied to evaluate the fatigue life of various HMA compositions.

The study presents a new methodology to assess the bond mechanism of textile-reinforced concrete (TRC) elements. Since changes in the electrical properties of carbon yarns are correlated to their microstructural bond mechanism, they can be indications of the shear-bond stress-slip relation. The study developed a new setup enabling sensitive electrical measurement without affecting the mechanical response, yet clearly capturing the microstructural mechanism. Carbon yarn is electrically characterized as an RL circuit, comprising a resistor (R) and an inductor (L) connected in series. The study offers to explore both properties by measuring the response spectrum of the impedance at a specified range of electrical current frequencies. Results demonstrated that changes in the electrical resistance and inductance in a localized cracked zone are directly correlated to the shear-bond stress (τ)-slip relation. It was found that the rate of changes (ROC) of both electrical properties reflect and follows the microstructural mechanism and, accordingly, provides new insights on the internal stress distribution. To quantitively estimate the τ-slip relation, a conversion factor (α), that correlates between the ROC and the τ-slip relation, was evaluated by adjusting the ROCs to the structural response from numerical model. It was found that, for the investigated composition, the conversion factor is α = 7.88 ± 0.97 [mΩ·mm/N], yielding that the ultimate shear bond stress is about τ_ultimate = 2.2 ± 0.32 [MPa] which is acceptable value. The proposed methodology can be easily implemented in various compositions and provides a useful method to estimate τ-slip relations.

The synergy between textile and fibers reinforcement systems and high strength cementitious matrices offers the development of advanced and sustainable thin concrete structures. The focus has been on the effect of the properties of the textile, fibers, or the concrete on the structural mechanism of the elements. This study aims to enhance the understanding of the unique mechanisms of these composites by exploring the mutual effects of the reinforcement systems (textiles and/or fibers) and the matrix compositions (Portland cement—PC or Magnesium Phosphate cement—MPC) on the mechanical behavior. The study involves micro- and macro-scale experimental investigations. Nine different compositions are investigated under uniaxial and flexural loading setups. The study demonstrated that by adequate composition of fibers, textile, and advanced cementitious technologies and, especially, by leveraging synergies between them, an enhanced composite can be achieved. Due to the improved rheological and strength properties, MPC is a preferable matrix in case of TRC elements. The effectiveness of the reinforcement system is governed by a tradeoff mechanism between the elastic modulus and the compactness of the yarns. Textiles that consist of both AR-glass and carbon yarns can benefit from the advantages of the two mechanisms.

This study explores the capability of smart self-sensory carbon-based Textile Reinforced Concrete (TRC) elements to locate and detect cross-sectional degradation. The concept involves connecting carbon yarns into electrical circuits using Time Domain Reflectometry (TDR) technique to measure electrical changes caused by wetting events. To detect cross-sectional degradation, the monitoring approach compares measurements from the current wetting event to those of a healthy reference measurement. The study presents the capability of the new monitoring concept by experimental investigation. It is demonstrated that the smart sensory carbon yarns successfully detect the location and estimate degradation of the cross-section of the elements.

The goal of this study is to explore the use of carbon-based textiles to sense strain in fiber-reinforced concrete (FRC) elements. To answer this goal, the study investigates a new electrical configuration in which the carbon yarns function as internal devices within the FRC body. An impedance spectrum analysis is used to monitor changes in both electrical resistance and capacitance, focusing on tensile stresses in the healthy state of the element. The results show that the electrical responses consistently follow the mechanical loading and can be correlated to them for the purpose of strain sensing.

Contemporary building envelopes primarily rely on repetitive elements that fulfill mainly a singular purpose-a barrier between interior and exterior spaces. Implementing building envelopes featuring intricate geometries and non-repetitive tiles can significantly enhance the environmental performance of the structure. However, the current manufacturing processes for the required moulds are plagued by high costs, time consumption, labor-intensiveness, and mainly by using non-recyclable moulds. To address these challenges, the paper presents an innovative solution for designing and fabricating building envelope tiles with complex geometries by employing stay-in-place 3D knitted moulds. The moulds are digitally fabricated using innovative knitting procedures implemented on an industrial flat double-bed machine. The paper presents preliminary research out-comes, including a new digital design methodology for creating knitted moulds and a new fabrication method for buildings’ envelope tiles.

The study develops textile-reinforced concrete (TRC) trusses, reinforced with 3D textiles. It is argued that, by taking advantage of textiles’ ability to conform to complex shapes and their corrosion resistance, TRC truss structures enable a substantial reduction in material and weight through efficient load transfer mechanisms. An experimental investigation explores the design methodology and manufacturing possibilities, as well as the macro-structural response and the cracking and failure mechanisms under flexural loading. Additionally, the study investigates the effects of various reinforcement layouts associated with different anchoring feasibilities and reinforcement ratios on the structural performance. It was found that TRC trusses maintain their structural performance compared to full cross-sectional rectangular TRC beams while achieving significant material savings and weight reduction (about 50 %). It was also found that effective anchoring is a dominant parameter governing structural response. Results from this study highlight the high potential of TRC trusses as a sustainable alternative for structural components.

The current study aims to handle the challenge of identifying the location of cracks in carbon-based textile reinforced concrete (TRC) elements by using their smart self-sensory capabilities. To answer this challenge, the study offers to adopt the concept of the Time Domain Reflectometer (TDR) analysis. Yet, direct implementation of the TDR analysis to smart sensory carbon yarns is not a straightforward act and requires facing some inherent challenges. Therefore, the study offers an advanced monitoring methodology that handles the various challenges. A special electrical setup is proposed that uses a pair of carbon yarns, in which one yarn is used as the electrical conductor that transmits the electrical current, and the other as insulation. Two calibration processes that consider the unique micro-structural mechanism and its correlation to the electrical characterization are developed. The efficiencies of the calibration processes are investigated by a designated identification technique. Results from this study demonstrate the potential and capabilities of the proposed smart self-sensory carbon-based TRC concept to monitor its health by detecting the cracks’ locations.

This study investigates the monitoring capabilities of a carbon yarn embedded in cement as a smart strain sensory system by means of gauge factors (GF). In the proposed configuration, the yarn serves both as the structural system and as the sensory platform, yielding efficient and intelligent reinforced concrete elements. The study focuses on exploring the strain-sensing capabilities at a single cracked zone of carbon-based textile-reinforced magnesium phosphate cement (TR-MPC) specimens. The results reveal consistent mechanical and electrical responses with a strong correlation. The study demonstrated that the electrical resistance and inductance of the carbon yarn can be correlated using GF, denoted as GF_R and GF_L, respectively. The GFs reflect the micro-structural mechanism at different mechanical stages, enabling self-strain sensing in intelligent TRC elements.

The current study presents an identification procedure to locate cracks within textile reinforced concrete (TRC) elements by their smart self-sensory capabilities. The study offers to integrate the Time Domain Reflectometer (TDR) analysis and the concept of smart water leakage detection methodology. By connecting a pair of carbon yarns to the data acquisition (DAQ) system and performing wetting events, the identification procedure monitors changes in the electrical characterization of the electrical circuit. The measured changes in the impedance spectrum are analysed by using the TDR technique and are correlated to the crack's location. It is presented that the proposed procedure enhances the sensing capabilities, particularly the range of the measurements, and enables to detect the location of cracks with relatively high accuracy.

Structural health monitoring (SHM) is the automation of the condition assessment process of an engineered system. When applied to geometrically large components or structures, such as those found in civil and aerospace infrastructure and systems, a critical challenge is in designing the sensing solution that could yield actionable information. This is a difficult task to conduct cost-effectively, because of the large surfaces under consideration and the localized nature of typical defects and damages. There have been significant research efforts in empowering conventional measurement technologies for applications to SHM in order to improve performance of the condition assessment process. Yet, the field implementation of these SHM solutions is still in its infancy, attributable to various economic and technical challenges. The objective of this Roadmap publication is to discuss modern measurement technologies that were developed for SHM purposes, along with their associated challenges and opportunities, and to provide a path to research and development efforts that could yield impactful field applications. The Roadmap is organized into four sections: distributed embedded sensing systems, distributed surface sensing systems, multifunctional materials, and remote sensing. Recognizing that many measurement technologies may overlap between sections, we define distributed sensing solutions as those that involve or imply the utilization of numbers of sensors geometrically organized within (embedded) or over (surface) the monitored component or system. Multi-functional materials are sensing solutions that combine multiple capabilities, for example those also serving structural functions. Remote sensing are solutions that are contactless, for example cell phones, drones, and satellites. It also includes the notion of remotely controlled robots.

This study investigates the effect of the matrix properties on the structural and sensory capabilities of smart self-sensory textile reinforced cement composites, in which carbon rovings are simultaneously used as the main reinforcement system and as the sensory agent. The investigation focuses on two different cementitious matrices: Portland cement (PC) and Magnesium Phosphate cement (MPC). The differences are associated with the matrix electrical and micro-structural behaviors. It is demonstrated that compared to PC matrix, MPC matrix is characterized by a relatively high electrical resistivity, which enhances the electrical signal. It is further demonstrated that the advanced material properties of the MPC matrix improves the textile-matrix interaction, and, as a result, the structural performance of the composites. The characterization is affected and reflected by the measured electrical resistance change (ERC). The integrative gauge factor (GF) concept was chosen to demonstrate the different structural – electrical correlations associated to the matrices. It is presented that the matrix type is reflected by the value and trend of the GF. While carbon-based textile reinforced PC elements are characterized by nonlinear and lower GF values, in the case of textile reinforced MPC elements, the GF is linear and its value is about 2.5 times higher.

This study explores advanced capabilities of smart carbon-based textile reinforced cement-based elements to monitor its structural health. The goal is to enhance and amplify the electrical measurements and the sensitivity of the electrical readings. To answer these goals, the study develops advanced alternating current (AC) based electrical measurement setups. The study also offers to use a new cementitious matrix with enhanced mechanical, rheological and electrical properties. To amplify the measurement, the study suggests measuring the electrical changes at the resonance frequency of the system, which can be done by connecting external capacitors to the embedded carbon roving. A comparison investigation is performed to explore the monitoring capabilities of four electrical measurement setups at various structural states. Eight textile and fibers reinforced cement-based beam specimens were investigated under flexural loading. It is found that by connecting an external parallel capacitor to the roving, amplified, stable and sensitive electrical measurements are achieved.

This paper demonstrates the development of lightweight textile-reinforced concrete (TRC) trusses. The innovative element expands the boundaries of the traditional TRC structures towards a new standard of sustainability in the field of constructive concrete structures. The proposed TRC trusses are composed of high-performance concrete (HPC) matrix and three-dimensional (3D) textiles. The combination provides high compressive and tensile strengths for the slender truss members and thus allows the efficiency of the truss mechanism. The experimental investigation presents the design and manufacturing processes of three truss layouts and explores their structural responses under flexural loading. The presented preliminary investigation demonstrated the efficacy of the TRC truss.

The study aims to investigate the ability of smart self-sensory carbon roving to detect damaged zones in TRC structures. State of the art monitoring procedures are based on integrative measurements and accordingly are limited in detecting only the occurrence of damage. This study aims to handle this limitation and offers to adopt the Time Domain Reflectometer (TDR) technique. The TDR concept is widely used in Bayonet Nut Coupling (BNC) cables to identify defects along the cable (opens, shorts, etc.). The current study adopts its principle to carbon rovings. To simulate the BNC cable configuration, the study offers to connect two parallel carbon rovings to the TDR Data Acquisition (DAQ) system. The proposed monitoring technique is investigated by loading two textile reinforced MPC beams under uniaxial tensile loading. Results show the potential of the suggested technique to locate damage zones in TRC structures and highlights its limitation.

The goal of the study is to develop an identification procedure that identifies the location of cracks within textile reinforced concrete (TRC) elements by using their smart self-sensory capabilities. To answer this goal the investigation offers to adopt the principles of the time domain reflectometer (TDR) analysis and to explore the changes of the spectrum of the impedance. In order to use the concept, the study considers the electrical characterization of the sensory carbon yarns, mainly the dependency of the impedance with the yarn's length and offers a calibration procedure. It was found that the procedure has the capabilities to identify all cracking events but also involved additional false alarm scenarios. It is further demonstrated that only the location of the first crack was accurately identified.

This study develops novel intelligent composite structural elements combining three advanced technologies: magnesium phosphate cement (MPC) matrix, smart-self sensory carbon-based textile reinforcement system, and additive short-dispersed fibers. In such system, the carbon rovings simultaneously serve as the main reinforcement system and the sensory agent. The material properties of the MPC matrix include minimization of environmental effects, high flexural strength and enhanced rheological properties which is an advantage in textile reinforcement system. From the sensory point of view, MPC is electrically insulated matrix which enhances the measured electrical signal from the carbon rovings. Experimental investigation demonstrates the advanced capabilities of the new hybrid structures. The investigation compares between the structural and electrical responses of textile reinforced MPC elements and TRC elements under flexural loading. The structural-electrical correlation enables to further explore new composite configurations and to develop enhanced smart self-sensory systems. The study demonstrates that by merging MPC mixture with textile and fiber reinforcement systems, it is possible to design and construct thin-walled, elements with advanced structural and self-sensing capabilities.

The study aims to develop sustainable smart self-sensory infrastructures with leakage detection capabilities. To answer this goal the study offers to combine two advanced technologies, namely: smart textile reinforcement (TR) and magnesium phosphate cement (MPC). The TR is produced with AR-glass and carbon yarns, in which the electrical conductivity of the carbon yarns enables them to be used also as smart self-sensory agents. The study presents the feasibility of the TR-MPC smart pipe concept by demonstrating its production possibilities, as well as its sensory capabilities to detect and distinguish between the magnitude of leakage events.

The paper aims to prove the feasibility of smart concrete pipe systems with integrated monitoring capabilities. The development of such systems is motivated by functional, structural, sustainability and monitoring requirements of underground and buried pipelines with limited accessibility. To answer these challenges, the study adopts the textile reinforced concrete (TRC) technology that allows the production of effective, durable, and lightweight structural elements with integrated monitoring systems. In such systems, by utilizing the electrical conductivity of the carbon rovings, the carbon-based textile can simultaneously serve as the main reinforcement system and as the sensory agent. The proposed hybrid monitoring system aims to detect the occurrence of leakage and to distinguish its severity, which is directly correlated to the structural health. Smart TRC pipes were designed, constructed, and experimentally investigated from structural and sensory points of view. The design considers the multifunctionality of the carbon rovings and the hybrid performance of the textile cage, from both aspects - reinforcement and sensing. An experimental investigation explores the mutual structural, functional, and sensory capabilities of the hybrid system, which reflect and affect each other. It is presented that the strong correlation between the structural-functional and sensory responses reveals an efficient smart TRC pipes. The presented results take a major step toward the realization of the smart TRC concept and exceeded beyond small 1D scale elements to 3D structures.

The study electrically characterizes a smart-self sensory carbon-based textile reinforced concrete (TRC) structure and explores its sensory capabilities by various electrical properties. The hybrid system is based on implementing electrically conductive carbon rovings, within a textile mesh made of alkali resistant (AR) glass yarns, that simultaneously serve as part of the reinforcement system and as the sensory agent. The study uses an AC based electrical circuit and offers to characterize changes in the electrical properties of the sensory carbon rovings by exploring the electrical response spectrum of the impedance. It is found that, since each carbon roving consists of thousands of electrically conductive filaments that are bundled together, each roving is electrically characterized by a resistor and an inductor that are influenced by the concrete body. The AC based sensory system is experimentally investigated by monitoring changes in the measured electrical properties, that is resistance and inductance, of TRC beams under monotonic loading and correlating these changes to the micro- and macro-structural responses. It is demonstrated that a sensory system that is based on an AC electrical circuit yields additional sensitive and important sensory information on the structural health of the beams.

The study proposes a new method to assess the bending stiffness distribution in plate- and slab- like reinforced concrete (RC) structures based on spatially distributed strain data. Specifically, the study aims to provide an adequate structural interpretation of the readings, which infers the structural health. It is especially relevant for RC structures, that are designed to be cracked during their service life. To meet this goal the study correlates damage induced by cracks and curvature computed from strains to analyze 2D RC structures characterised by directional strains, and moment redistribution. The study also considered the installation possibilities and the limited and thus averaged strain data. To exclusively correlate changes in curvatures, by means of curvature index factors, and residual bending stiffness distribution, the study proposed an iterative identification algorithm. The paper demonstrates the effectiveness of the algorithm by numerical simulations of strain measurements and considers the various limitations of the adopted strain measurements along large 2D RC structures. It is presented that the procedure succeeds in localising the damaged regions and provides less accurate, but still contributive, assessment of their severity. Thus, the proposed method can support engineers in decision making regarding the structural health of the structure.

The study investigates the capabilities of various configurations of self-sensory carbon-based textiles to detect and distinguish between the severity of water infiltration through cracked zones along textile reinforced concrete (TRC) elements. The investigation aims to explore whether an optimal smart textile configuration can improve the structural performance while providing sensitive sensory capabilities. Such an investigation is needed for the development of intelligent TRC structures. Specifically, the study experimentally investigates the effect of two types of bindings and the effect of coating on the mutual structural-sensory performances. The sensory concept is based on changes of the electrical mechanism of two adjacent carbon rovings due to infiltration of water through cracked zones. Eight TRC beam samples were cast and mechanically loaded up to cracking. The cracked zones were monitored, and each zone was separately examined by performing a wetting event. It is demonstrated that the type of binding and coating, which significantly affect the structural response, reflect and affect the measured electrical signal. It is found that there is a tradeoff mechanism between the structural response and the sensory capabilities. While specific textile configuration improves the structural performance, it may reduce its sensory capability to distinguish between the magnitude of water infiltration.

The study aims to develop the required methodology for the design, analysis and experimental testing of textile reinforced concrete (TRC) pipes. To answer this goal, experimental and analytical investigations are performed and cover various aspects related to the construction, experimental testing, and structural analysis of TRC pipes. The experimental investigation presents the production and operation feasibilities with respect to acceptable standards and codes of concrete pipes. The loading scheme, the construction materials, and the unique structural mechanism of TRC elements that affect the mechanical performance of the structure, are requirements that should meet and adjust each other and are considered in the proposed methodology. A special analytical model is developed, which considers the geometrical properties, the nonlinearity of the concrete and the unique micro-structural mechanism of the textile within the concrete matrix. The model is validated by an experimental investigation. Results and outcomes from this study aims to take a significant step forward into realization of TRC pipes.

The goal of this study is to develop a structural health monitoring methodology for smart self-sensory carbon-based textile reinforced concrete elements. The self-sensory concept is based on measuring the electrical resistance change in the carbon roving reinforcement and by means of an engineering gage factor, correlating the relative electrical resistance change to an integral value of strain along the location of the roving. The concept of the nonlinear engineering gage factor that captures the unique micro-structural mechanism of the roving within the concrete matrix is demonstrated and validated. The estimated value of strain is compared to a theoretical value calculated by assuming a healthy state. The amount of discrepancy between the two strain values makes it possible to indicate and distinguish between the structural states. The study experimentally demonstrates the engineering gage factor concept and the structural health monitoring procedure by mechanically loading two textile reinforced concrete beams, one by a monotonic loading procedure and the other by a cyclic loading procedure. It is presented that the proposed structural health monitoring procedure succeeded in estimating the strain and in clearly distinguishing between the structural states.

Coastal areas are earthquake-prone zones where giant ruptures have been materialized throughout history. Coastal areas are also the first line of impact in a Tsunami event. Today when 40% of the global population (2.4 billion) live in coastal communities the threat for either disaster or both is imminent. This study offers an alternative approach to address coastal cities resilience to seismic shocks and Tsunamis, by the employment of modular floating structures (MFS), which can be utilized for urban development in the adjacent marine environment. The MFS concept is based on modular floating units, consolidated into a large structure to provides an adequate surface for mixed-use urban development. Floating structures are inherently base isolated; therefore, seismic loads are not transmitted to the structure foundation. This principle was tested successfully during the 1995 Great Hanshin Earthquake where the floating Kobe City Air Terminal (K-CAT) suffered no damage. In addition, Tokyo Bay, Osaka Bay and Ise Bay are all equipped with emergency floating platforms for evacuation in case of disaster. Which raise the query as to why not use floating platforms for urban development in pre-disaster condition? The design of MFS is an interdisciplinary endeavor, which encompass by few disciplines, mainly: architecture, naval architecture and civil engineering. Building a viable urban development on floating structures can help mitigate, or even eliminate, the disastrous effects of Tsunami, which accumulates into a destructive order only when approaching the shore. The hypothesis is that floating structures can offer a unique avenue to explore new and sustainable ways to mitigate structural damaged related directly to earthquake and/or Tsunami. This study examines the potential urban development and dwelling solutions for three mega-coastal-cities, such as Jakarta, Tokyo and Manila – all which are susceptible to major earthquakes. The study presents a feasibility model for an MFS preliminary design. The limit service state is achieved by implementing international regulations from a coherent statutorily guidelines, that are merged to fulfil the requirements for the special context of urban floating structures. The service limit state is achieved by extensive hydrodynamic analysis that evaluates the compatibility to occupant comfort acceptable in residential buildings.

The concept of Modular Floating Structures (MFS) presents a unique alternative to increase the available land resources in the adjacent marine environment of coastal cities. It offers a sustainable technological adaptation that can help mitigate overdevelopment and urban growth limitations. This study examines the comfort range of a suburban offshore MFS module, by using a novel methodology that reconciles residential comfort criteria with seakeeping. The investigation is performed by characterising the hydrodynamic structural response and analysing its compatibility for offshore dwellings. It is demonstrated that the MFS module complies to marine regulations, including seakeeping and comfort, but when evaluating its hydrodynamic response to the accepted accelerations in residential buildings, it reaches performance limits at a certain sea state. This may influence the choice of environment, based on the allowable significant wave height, or call for better hydrodynamic performance using multi-body configuration.

The concept of Modular Floating Structures (MFS) offers a unique avenue to explore new and sustainable ways for addressing issues of coastal urbanization and sea level rise in the proximity of coastal cities. This concept is easily implemented in calm waters without the interference of waves. Yet, its implementation in open water, poses greater challenges, particularly in terms of habitability and comfort. The current study examines the feasibility of the concept in two locations: in mild sea zone near Singapore and in open water conditions at the Eastern Mediterranean Sea. Both conditions are examined in operational and extreme storms. It is shown that the MFS configuration can attenuate incident waves of short periods. This reduces the motion amplitudes of the inner modules with respect to the exterior modules facing the waves. It is also presented that during extreme storms, the chosen configuration is less effective, and the motion amplitudes of all modules within the MFS fabric are almost identical. To further increase the acceptable sea states, the study proposes a unique floating seawall design, which provides a substantial wave reduction in long wave periods. The study presents the efficiency of the new configuration in operational weather and a 100-years storm.

The goal of this study is to characterise the piezoresistive capabilities of self-sensory carbon roving reinforcements by means of integrative gauge factors (GFs). The correlation between the measured integrative electrical resistance of the carbon rovings and the distributed strain is experimentally investigated by two different textile reinforced concrete beams under monotonic flexural loading. Because the microstructural mechanism of the rovings within the concrete matrix affects the electrical resistance, the GF is a function of the structural health. Two approaches to explore the GF are suggested: the first is by considering the design and damaged states separately and accordingly defining a constant GF for each state, and the second is by considering the entire structural response which leads to a continuous non-linear correlation. The potential of the two representations of GFs is presented by investigating the two beams. It is demonstrated that similar ranges of GFs are obtained for both beams, which further demonstrates the potential of using the proposed methodology for quantitative monitoring purposes.

This study investigates the mutual effects of binding and pretreatment procedure (coating) on the structural performance of textile-reinforced concrete (TRC) composite beams under flexural loading. The goal is to choose an optimal reinforcing textile configuration that yields a better design of the textile performance. The investigation was performed by correlating between the microstructural mechanism, which is associated to the textile configuration, and the macrostructural response according to various structural parameters, such as the ultimate load, the relative structural ductility, and the equivalent fracture energy. An experimental investigation is presented on four different binding types of warp-knitted structures: Pillar and counterlaid tricot, characterized by relatively circular roving cross section, and plain and tricot, characterized by elliptical roving cross section. Each type was investigated in uncoated configuration and by coating with 50% styrene-butadiene rubber (SBR). In total, 32 TRC beam specimens were designed, cast, and monotonically loaded. Results demonstrated that generally the type of binding is significantly pronounced in uncoated textiles and that coating considerably improves the structural performance of all types of textile binding. It is also concluded that relatively flat and elliptical cross-sectional areas of the rovings are preferable in the case of uncoated textile, while in the case of coated textile the preferable binding configurations are the ones characterized by a relatively circular roving cross section.

The paper presents a non-linear structural model for evaluating the macro-structural response as well as the distribution of the internal stress resultants of textile reinforced concrete composites under uniaxial static loading. The equilibrium equations and the appropriate boundary conditions are derived on the basis of the variational principle of the minimum potential energy approach. Various aspects related to the unique micro-structural behavior associated to the bonding mechanism of the yarns and the concrete matrix, as well as the nonlinearity of both materials, are taken into consideration and implemented in the variational principle. The obtained set of nonlinear equilibrium equations is formulated according to the mixed formulation which yields a set of first order nonlinear ordinary differential equations. The solution procedure is conducted by the mixed-half-station interlacing-grid finite-difference scheme and by Newton–Raphson method. Results provided by the proposed model are compared to experimental tests from the literature and demonstrate its generality, accuracy, simplicity, and its easy implementation in various experimental setups. It is further demonstrated that the presented structural model can successfully capture the macro-structural response and gives an insight into the micro-structural mechanism involved in the load carrying capacity of the TRC composite element.

The study examines the use of hybrid carbon-based textile-reinforced concrete elements with self-sensing capabilities to quantitatively detect wetting events within cracked zones. The self-sensory structural element combines the advantages of AR-glass and carbon-based textile-reinforced concrete for thin-walled structural elements with those stemming from the electrical properties of reinforced carbon rovings. The article investigates the sensitivity of sensory carbon rovings to distinguish between the magnitudes of various wetting events, which is associated with the severity of the cracking, according to two electrical setups (DC and AC circuits). The sensing concept takes advantage of the continuous configuration of the carbon rovings, which enables direct connection of the roving ends to the data acquisition system, and of the manufacturing process that two carbon rovings are placed adjacent to one another. Therefore, it is assumed that wetting events electrically short-circuit the two adjacent rovings. The sensitivity of the two electrical setups is experimentally investigated and performed on a couple of bared carbon rovings and on a cracked textile-reinforced concrete beam. Test results demonstrate the sensitivity of the sensing capabilities of the carbon rovings to detect and distinguish between the magnitudes of the wetting events and consequently the severity of the cracking.

The study investigates the sensitivity of hybrid coated and un-coated carbon-based textile reinforced concrete (TRC) beams to detect and distinguish between different and accumulated levels of cracking. The sensing concept is based on using the electrical conductivity of embedded carbon rovings reinforcement as the monitoring system. The focus is on the influence of coating on the structural-electrical response and its capabilities to detect the severity of cracking. Two TRC beams reinforced with uncoated and coated AR-glass/carbon-based textile were investigated under cyclic mechanical loading. The study demonstrates that the micro and macro structural mechanisms of both beams are reflected in the electrical signal and can be quantitatively correlated to the level of damage. The sensing capabilities of the textile yields stable, repeatable, sensitive and consistent electrical readings for monitoring needs. However, in case of coated textile, while coating improves the structural performance, it limits the sensing capabilities in distinguishing macro-cracking scenarios.

Land scarcity in and around coastal cities is a growing problem in both industrialized and developing nations. The lack of development areas increases the tension between infrastructure needs, urban needs and nature – impacting both growth and quality of life. This study advocates that floating structures can offer a unique avenue to explore new and sustainable ways of addressing these issues. Recognizing that no comprehensive analysis or study on the legal requirements needed for the realization of such projects has yet been conducted, the study's first aim is to define the required design guidelines by synthesizing statutory requirements, building codes and international regulations. From a statutory perspective, these encompass two disciplines: civil engineering and naval architecture. To this end, a preliminary design of a Modular Floating Structures (MFS) module is presented, reconciling the design requirements of the two disciplines, in order to proof the feasibility of the MFS technology for urban use offshore. The study mainly focuses on structural and safety aspects, and sheds light on other crucial factors for offshore dwelling feasibility, such as occupant comfort.

This study presents the concept of a carbon based-sensory textile reinforced concrete (TRC) element that combines an advanced material/structural system with sensing capabilities. The concept is based on the use of glass and carbon fiber based textile for the reinforcement of thin-walled concrete elements and, at the same time, to use the electro-mechanical properties of the carbon components as a sensory device. This combination aims to provide the structure with the structural and sensory features required for an intelligent load bearing system. The research presents the applicability of the concept to crack detection and damage quantification, and to detection of water infiltration. The study presents the feasibility of the hybrid TRC structures and reviews the challenges that should be faced in order to bring the technology into realization in the future.

The study investigates the electrical mechanism of hybrid carbon-based textile-reinforced concrete (TRC) elements with self-sensing capabilities to detect infiltration of water within cracked zones. The concept is based on carbon rovings that simultaneously serve as the reinforcement system as well as the sensory agent. The main goal of the study is to characterize the mechanism of the electrical signal obtained by exposure carbon rovings to wetting events. To meet this goal, the study uses alternating current circuits, which yield, additionally to the resistance or voltage changes, the characterization of the capacitance and inductance of the system. Two sensing concepts are investigated. Both concepts take advantage of the continuous configuration of the carbon rovings, which enables direct connection of the roving ends to the data acquisition system. The first sensing concept assumes that the electrical properties of a single carbon roving is affected by wetting, while the second assumes that wetting the interface between two adjacent carbon rovings links them electrically. The experimental investigation is performed on bare carbon rovings, and on a cracked carbon based TRC beam. Test results characterize the electrical mechanism of the wetting events and reveal its potential use as a basis for smart textile-reinforced systems with integrated monitoring functions.

A well-maintained water distribution system is an important asset for any community that supplies water from its source to consumers. Installation and maintenance of water pipes are expensive in terms of transportation, handling logistics and monitoring. Textile reinforced concrete (TRC) offers a lighter, stronger and more durable alternative to conventional building materials. The use of carbon fiber as a leakage sensor allows integrated crack monitoring. This paper presents the possibilities to use TRC as a construction material for smart water pipes with inherent sensory functions. Therefore AR-glass and carbon rovings were warp knitted in to a reinforcement textile for a TRC beam. The beam was wetted through a crack width of 0.5 mm and by using sensory carbon fibers the occurring changes in resistance were specified.

The paper explores the sensing capabilities of a carbon based textile reinforced concrete (TRC) composite element to monitor its structural mechanisms. The concept is based on continuous carbon rovings knitted into glass textile mesh that simultaneously serve as the structural reinforcement and as the sensory system. The loading procedures which starts from a healthy state, to micro and macro cracked state, and ends with a completely pull-out of the tensioned rovings is strongly affected by the micro-structural mechanism of the carbon rovings within the concrete matrix. It is found that the measured electrical resistance is characterized by this mechanism and can reflect the structural condition. Therefore, it can serve as a structural health monitoring system. The paper demonstrates these sensing capabilities along the entire range of the loading procedure, even up to progressive failure mechanism, where traditional sensing devices usually failed to produce meaningful information.

This paper studies the ability of self-sensory carbon/glass textile reinforced concrete (TRC) beams to distinguish between micro- and macrocracking. In the proposed configuration, continuous carbon rovings knitted into the textile mesh serve both as the structural reinforcement and as the sensory system. The paper faces the challenge of detecting structural damage within the TRC structure. In this study, damage is defined as the formation of macroscopic cracks, which lead to the accumulation of significant irreversible residual deflection and to a reduction of the relative stiffness of the component. We explore experimentally the correlation between the electrical resistance change and the change of the structural properties and suggests crack detection parameters in order to identify, and mainly to distinguish, between micro- and macrostructural phenomena. Carbon rovings are found to provide electromechanical sensing capabilities, having the ability to distinguish between inner micromechanical structural phenomena and macroscopic ones. These observations are a step towards the applications of SHM techniques by intelligent carbon-based TRC elements.

This study examines the feasibility of smart textile reinforced concrete (TRC) elements with self-sensing capabilities that are based on stainless steel yarns knitted in the textile grid. The self-sensory structural element combines the advantages of the glass fiber based TRC technology for thin-walled structural elements with those stemming from the electrical properties of yarns made of stainless steel filaments knitted in the textile fabric. The current study explores the ability of the yarns to sense humidity governed by infiltration of water through cracked zones along the structure. To examine this concept and its potential feasibility, a TRC beam specimen with stainless steel sensory yarns knitted in a glass fiber fabric is tested and monitored under different environmental conditions. The paper looks into the ability of the embedded steel yarns to detect wetting through the comparison of four electrical schemes and four sensing concepts. The results of the tests demonstrate the features of each sensory scheme and reveal its potential use as a basis for functional monitoring in TRC structures.

This article investigates the feasibility of intelligent textile-reinforced concrete structural elements with sensing capabilities. The concept is based on dual use of glass and carbon fiber textiles as reinforcement and, at the same time, as a sensory agent. Experimental investigation demonstrates the feasibility of the concept in two applications: detecting strains in a mechanically loaded textile-reinforced concrete beam and monitoring the interaction of the structural element with a wet environment. By detecting the changes to the integrative electrical resistance of the carbon tow, the ability of the textile to sense strain and exposure to water is demonstrated. For strain sensing, the hybrid reinforcing textile provides electro-mechanical sensing with a gauge factor of the order of 1 and a detectable correlation with the load, strain, and displacement responses. For the detection of wetting, the implementation of the carbon tow in a Wheatstone bridge detects fractional resistance changes in the order of 10^'5, a figure that is effectively detected by monitoring the voltage across the bridge. The response to wetting, which is conditioned by the cracking of the beam and the exposure to ionic conductive solutions, provides a mean to monitor the functionality and the structural health of the textile-reinforced concrete beam.

This paper studies the piezoresistive behavior of self-sensory carbon/glass textile reinforced concrete beams under the effect of loading, unloading, and reloading in the un-cracked region. Continuous carbon tows knitted into the textile serve both as the structural reinforcement and as the structural health sensors. The design eliminates the need for additional sensors by taking advantage of a monitoring system that is an inherent part of the load bearing element. The paper faces the challenge of understanding of the correlation between the piezoresistive change of the electrical properties of the carbon tow and the change of mechanical properties under repeated loading representing the response to service live loads. The paper looks into this correlation and explores it through an experimental investigation. It is found that for the un-cracked stage of the beam, the carbon component of the reinforcing textile provides an electro-mechanical sensing capability with gauge factors of 2.4-5.4 for tensile strain. Since the investigation focuses on flexural elements with at least two layers of textile reinforcement, the experiments also reveal negative gauge factors of -2.7 to -6.5 for compressive strains. These observations take a step towards many applications of sensory carbon based textile reinforced concrete elements.

A carbon fiber textile reinforced concrete (TRC) is a preferred construction material for intelligent thin-walled concrete structures. The concept is based on dual use of glass/carbon fiber textiles as reinforcement for structural concrete elements and, at the same time, as a sensory agent. By detecting the changes to the integrative electrical resistance of the carbon roving, the ability of the reinforcing textile to sense the structural health can be achieved. In this study, we aim to investigate the capability of the carbon roving to distinguish between the structural response at the healthy state and at the damaged state. Specifically, we aim to experimentally explore the correlation between the electrical readings of the carbon rovings within the TRC beam before and after damage takes place. Understanding this correlation is essential for the development of intelligent carbon fiber TRC structural elements with inherent SHM capabilities.

A procedure for identifying the bending stiffness distribution in plate-like structures is presented. The algorithm is based on the correlation between a parameter called curvature increased factor (CIF) and the bending stiffness of the plate, D. Accurate correlation can be achieved only by considering the effect of the redistribution of internal forces and moments due to the damage on the curvature distribution. In order to achieve this goal, the study offers an iterative procedure, which eliminates the effect of the moment redistribution from the CIF and eventually correlates accurately between CIF and D. The curvature rate is evaluated from the displacement mode shape using a 2D smoothing technique. The procedure takes into account the presence of random errors and the limited number of measured nodes. The procedure's effectiveness, reliability, and range of applicability are demonstrated using numerical examples.

This study examines and demonstrates the feasibility of a new class of smart textile reinforced concrete (TRC) structural elements with inherent sensing capabilities that are based on embedding metallic yarns in the textile mesh. The new approach combines the advantages of thin walled glass fiber based TRC with the electro-mechanical properties of the stainless steel fibers embedded in the textile matrix. To examine this concept and to demonstrate its potential feasibility, TRC beam specimens are tested and monitored under mechanical and environmental loading condition. The results of the tests demonstrate the features of the sensory/structural system, reveals its potential use as a basis for a combined structural and functional monitoring system, and highlights its spectrum of potential applications.

Brillouin optical time domain reflectometry or analysis (BOTDR/A) is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. Although the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of approximately 1 m. This infers that the technology may lack the ability to identify the exact type and source of damage; that is, different geometrical configurations of cracking within a concrete beam may lead to similar BOTDR/A readings, and hence, the exact nature of cracking might not be resolved. This study suggests different crack indicators and analytically and experimentally examines their correlations with BOTDR/A readings of damaged RC beams. The analytical part entails a finite-element based statistical analysis of hundreds of cracking cases in fractured RC beams and their effects on the simulated BOTDR/A readings. It is found from the analysis that the increase of curvature measured by BOTDR/A is best correlated with the sum of ratios of crack size to the remaining healthy cross section within 1 m. This finding is supported by an experimental study of a cracked RC beam. The correlation, by itself, is only valid when the increase of curvature is associated with the damage and does not involve a curvature increase as a result of redistribution of moments. This, however, would be the case only in statically determinate beams. To facilitate the use of the correlation for statically indeterminate beams, this paper suggests an iterative algorithm that evaluates the different contributors to the increase of the curvature.

An identification procedure is presented for the stiffness distribution of beam elements, under an approach based on changes in a few natural frequencies. The stiffness distribution along the beam is represented by a polynomial function, while its coefficients are the unknown in the identification procedure. Thus, the procedure suits a continuous damage scenario, which in the case of reinforced concrete elements represents an advanced distributed cracked zone.In order to reduce the number of degrees of freedom of the analytical model, the algorithm employs the " exact" element method. The identification procedure constructs a sensitivity matrix using a reference stage of a healthy beam. This matrix is constructed once for each healthy beam. The stiffness distribution function is then obtained using a given set of frequencies in a damage condition. The only modal parameters required are, therefore, a subset of pre- and post-damage vibration frequencies.The presented procedure is validated on single and continuous beams using analytical and varied modal frequencies. In order to demonstrate its practicability, the procedure is validated using experimental data available from the literature.

A two steps sub-structuring strategy is proposed for possible implementation in identification procedure. In the first step- the most important modes for a chosen master are defined with the aid of the OMR technique. In the second step - the optimal set of DoFs in the slave sub-structure is evaluated, with respect to the modal responses of the main sub-structure for the obtainable set of modes. Identification procedure, based on GA, demonstrate the efficiency of the proposed procedure by numerical example.

Brillouin Optical Time Domain Reflectometry (BOTDR) is a promising candidate for static damage evaluation in large structures as it allows continuous distribution of strain along the structure. In previous works, it was found that even though the inherent limitation of spatial resolution of approximately 1m, a quantified parameter for very localized damage as cracks and an equivalent bending stiffness distribution can be found in RC beam. To use this concept in plate-like structures, estimation of the curvature distributions along x and y directions with respect to the capability of the BOTDR technology should be considered, as well as, consideration to the influence of the redistribution of the internal forces and moments on the curvature distributions. Therefore, the aim of this study is to investigate these issues in details and to suggest a tailored identification procedure for plate-like structures based on the BOTDR technology.

The purpose of damage identification procedures in large structures is to assess the stiffness distribution in a specific zone (master), while minimizing the number of measurements on the other zones of the structure (slaves). In order to achieve this goal a sub-structuring strategy is usually adopted. The reduction in the measurement and the computational efforts is achieved by replacing the slave substructures with other ones with a much smaller number of sensors and Degrees of Freedom (DoFs), respectively. Since the reliability of the identified damage, involved in such condensation, is strongly dependent on the sensors location in the slave substructures, this study offers to use the Optimal Modal Reduction (OMR) technique The OMR technique minimizes the error of the modal parameters (frequencies and mode shapes) of the master structure, in such a way that the DoFs obtained from this technique indicate the optimum sensors location in the slave sub-structures. The identification procedure is then applied only to the unknown parameters of the master structure. This study demonstrates the efficiency of the OMR in damage identification procedure through multi-story shear building model. A Genetic Algorithm (GA), based optimization procedure, is applied for minimizing the differences between the simulated measured modal dynamic properties and the analytical one. In order to simulate field conditions the effect of noisy signals and limited number of sensors are considered.

A mixed formulation has been proposed to simplify the calculation of initial postbuckling behavior and Koiter's b parameter for laminated shells. According to Koiter's general theory of elastic stability, the imperfection sensitivity of a structure is closely related to its initial postbuckling behavior, and the theory is exact in the asymptotic sense. The nonlinear equilibrium equations and the appropriate boundary conditions are derived on the basis of the potential-energy approach. The classical buckling load of a perfect structure is denoted which is the load at which a nonaxisymmetric bifurcation from the prebuckling state occurs. This method's advantages include direct involvement of the stiffness matrices, without their derivatives, exclusive linear and quadratic operators in the governing equations, and the first derivatives in the axial direction of the unknown functions the highest. These features make for a much simpler and more accurate analysis of the shell's behavior, which can be applied to any shells of revolution for the analysis of both initial postbuckling and full nonlinear behavior.

An identification procedure is presented for cracks along a plane frame element. The cracks are modeled locally as mass less rotational springs that are characterized by their equivalent depth. Using the dynamic stiffness method for the structural model, it is possible to obtain a condensed reduced order system of equations without the loss of accuracy due to size reduction, which is essential in an identification procedure of a full scale structure. The identification procedure is based on changes in natural frequencies and an optimization procedure is used to detect and assess the damage from changes in natural frequencies using Genetic Algorithm (GA). In order to study the efficiency and to examine the reliability of the presented procedure, it has been applied to a two bar plane frame. It was found that the reliability of the procedure is strongly dependent on the chosen size of the initial population, in order to enable accurate identification of the location and severity of the damage.

BOTDR is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. While the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of about 1 m. In a previous work, it was found that curvature increase along the beam can be related to the crack configuration. This, however, only appropriate to statically determinate beams, where no redistribution of internal forces is induced by the damage. Consequently, the use of the previously suggested relation to statically indeterminate beams may result in inaccurate estimation of the damage. In order to overcome this problem the current paper suggests an iterative identification algorithm which deals with statically indeterminate beams.

BOTDR is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. While the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of about 1m. This infers that the technology may lack the ability to identify the exact type and source of damage; that is, different geometrical configurations of cracking within a concrete beam may lead to similar BOTDR readings, and hence the exact nature of cracking might not be resolved by the BOTDR. This study suggests different crack indicators, and examines, both analytically and experimentally, their correlation with BOTDR readings of damaged reinforced concrete beams. The analytical part entails statistical analysis of hundreds of cracking cases in fractured reinforced concrete beams and their effect on the simulated BOTDR readings. The analysis is conducted within COMSOL-Multiphysics, and is aimed to understand the correlation between different crack indicators and the beam curvature as would be obtained by the BOTDR. The experimental part consists of a controlled load test of a reinforced beam instrumented by BOTDR fibers, and is aimed to support the analytical findings.

An identification procedure is presented for assessment of the stiffness distribution in structures with the aid of an inverse-problem algorithm, based on an FE model of the structure with an unknown stiffness distribution and a subset of measured vibration frequencies and vibration modes. Two independent stiffness indicators-axial and flexural-are used, determined by means of the axial strain and the curvature mode shapes, respectively. The procedure permits simultaneous location of damaged elements, with accurate quantification of damage severity. Furthermore, it is applicable to a variety of structure types, including frames, beams and trusses. The effects of random measurement noise and of realistic joints are taken into consideration. The effectiveness, reliability, and range of application of the procedure are demonstrated in a numerical study.

Most of the previous research on buckling and stability of shell structures is confined to u-v-w or w-F formulation, which are limited either by accuracy or by the chosen kinematic theory. In this work, an alternative mixed formulation is proposed for general laminated shells of revolution and calculated for different shell theories. Its principle consists in choosing the set of unknown functions as the obtainable boundary conditions from the variational formulation. The main advantage of the mixed formulation is direct involvement of the stiffness matrices, without their derivatives. This quality is most important in complicated woven-fabric procedures when the derivative functions of the fiber orientations are not available or the constitutive functions have discontinuities. The proposed formulation is validated and demonstrated for filament-wound laminated conical shells with variable material properties.

The stability pattern of shells is governed by a set of nonlinear partial differential equations. The solution procedure can be simplified, and fast and accurate predictions of the critical buckling load obtained, with the aid of a multilevel approach. Under this approach the lower levels are implemented by means of the perturbation technique, with the nonlinear prebuckling deformation disregarded, and a linear set of equations solved for each state. It turns out, however, that in these circumstances the prediction may differ depending on the chosen formulation. In an attempt to find the reasons for these differences, the linear bifurcation buckling behavior of laminated cylindrical shells was examined via two well-known formulations, with u-v-w and w-F as the unknowns. A third, mixed formulation, was found the most reliable in predicting the buckling behavior.

An identification procedure is presented for the stiffness distribution in statically indeterminate structures. The proposed procedure analogous to direct calculation of the dynamic stiffness, the inverse-problem algorithm used in it is based on a finite element (FE) model of the damaged structure with unknown stiffness distribution and on a subset of measured vibration frequencies and vibration modes. The bending stiffness is updated for each element in the FE-model by an iterative procedure. In order to improve its practicability, the effect of random measurement noise is taken into consideration. A numerical study of statically indeterminate beams shows that it is able to locate both localized and multiple damage and determine its severity with a high level of reliability.

The sensitivity of stiffened conical shells to imperfection is considered, via the initial postbuckling analysis. Unlike stiffened cylindrical shells, in the case of stiffened conical shells the stiffeners' inclination and the distance between the stiffeners vary with the shell coordinates, which complicates the problem considerably. The main objective of the study is to investigate the influence of the stiffeners on the buckling load and on the imperfection sensitivity. It is felt that by finding the various parameters that influence the shell's imperfection sensitivity, it is possible to improve the behavior of the whole structure. A special computer code had been developed to calculate the classical buckling load and the imperfection sensitivity via Koiter's theory of generally stiffened conical shells with consideration to the variation of the material properties in the shell's coordinates. In the present work the shell is assumed to be closely stiffened and a smeared approach is adopted. Therefore, only global buckling behavior is considered.

The sensitivity of laminated conical shells to imperfection is considered, via the initial post-buckling analysis, on the basis of three different shell theories: Donnell's, Sanders', and Timoshenko's. Unlike isotropic conical shells or laminated cylindrical shells, in the case of laminated conical shells the thickness and the material properties vary with the shell coordinates, which complicates the problem considerably. The main objective of the study is to investigate the influence of the variation of the stiffness coefficients on the buckling behavior and on the imperfection sensitivity of laminated conical shells. It is felt that by finding the various parameters that influence the shell's imperfection sensitivity, it is possible to improve the behavior of the whole structure. A special Level-1 computer code ISOLCS (Imperfection Sensitivity of Laminated Conical Shells) had been developed. ISOLCS calculates the classical buckling load and the imperfection sensitivity via Koiter's theory of laminated conical shells with consideration to the variation of the material properties in the shell's coordinates. The range of validity of the Level-1 predictions by ISOLCS is verified by the Level-3 code STAGS-A.

A hierarchical high-fidelity analysis procedure is adopted for predicting the critical buckling load of filament wound laminated conical shells. This hierarchical procedure includes three levels of fidelity for the analysis. Level-1 assumes that the shell buckling load can be predicted by using simply supported boundary condition with a linear membrane prebuckling solution. Level-2 includes the effects of a nonlinear prebuckling solution and the effects of different boundary conditions. Level-3 includes the nonlinear interaction between nearly simultaneous buckling modes and the effects of boundary imperfections. For the Level-1 analysis a computer code BOLCS had been developed. BOLCS calculates the buckling load of laminated conical shells by a linear bifurcation analysis. The buckling behavior obtained by BOLCS is compared for various load cases with Level-3 solutions calculated by the two-dimensional nonlinear code STAGS-A. The effects of the assumptions and approximations used for the two solutions are discussed. In addition, the influence of the in-plane boundary condition on the buckling behavior of laminated conical shells under axial compression is investigated. It is found that the in-plane boundary condition at the large end of the shell has a major effect on the buckling behavior.

The sensitivity of stiffened conical shells to imperfection is considered, via the initial post-buckling analysis. Unlike stiffened cylindrical shells, in the case of generally stiffened conical shells the stiffeners inclination and the distance between the stiffeners vary with the shell coordinates, which complicates the problem considerably. The main objective of the study is to investigate the influence of the stiffeners on the budding load and on the imperfection sensitivity. Thus, by finding the parameters that influence the shell's imperfection sensitivity, it is possible to improve the behavior of the whole structure.

Optimum laminate configuration for minimum weight of filament-wound laminated conical shells is investigated subject to a buckling load constraint. In the case of a composite laminated conical shell, due to the manufacturing process, the thickness and the ply orientation are functions of the shell coordinates, which ultimately results in coordinate dependence of the stiffness matrices (A,B,D). These effects influence both the buckling load and the weight of the structure and complicate the optimization problem considerably. High computational cost is involved in calculating the buckling load by means of a high-fidelity analysis, e.g. using the computer code STAGS-A. In order to simplify the optimization procedure, a low-fidelity model based on the assumption of constant material properties throughout the shell is adopted, and buckling loads are calculated by means of a low-fidelity analysis, e.g. using the computer code BOCS. This work proposes combining the high-fidelity analysis model (based on exact material properties) with the low-fidelity model (based on nominal material properties) by using correction response surfaces, which approximate the discrepancy between buckling loads determined from different fidelity analyses. The results indicate that the proposed multi-fidelity approaches using correction response surfaces can be used to improve the computational efficiency of structural optimization problems.

Optimum laminate configuration for the maximum buckling load of filament-wound laminated conical shells is investigated. In the case of a laminated conical shell, the thickness and the ply orientation (the design variables) are functions of the shell coordinates, influencing both the buckling load and the weight of the structure. Thus, optimization can be performed by maximization of the buckling load for a specific weight, or by minimization of the weight of the structure under the constraint of applied buckling load. Due to the complex nature of the problem a preliminary investigation is made into the characteristic behavior of the buckling load with respect to the volume as a function of the ply orientation. The exact buckling load is calculated by means of the computer code STAGS-A (Structural Analysis of General Shells [Almroth BO, Brogan FA, Meller E, Zele F, Petersen HT. Collapse analysis for shells of general shape, user's manual for STAGS-A computer code. Technical report AFFDL TR-71-8; 1973]) by adding a user written subroutine WALL, see Ref. [Goldfeld Y, Arbocz J. Buckling of laminated conical shells taking into account the variations of the stiffness coefficients. AIAA J 2004; 42(3):642-649]. The optimization problem is solved using response surface methodology.

The discontinuity in the sensitivity of laminated cylindrical shells is investigated via the initial post-buckling analysis. A general procedure for sensitivity, based on Roller's parameters and using the Donnell and Sanders shell theories, is developed and used for parametric study of the discontinuity phenomenon. It was found that the discontinuity occurs at points of change of the circumferential wave number.

The sensitivity of laminated cylindrical shell to imperfection is considered, via the initial post-buckling analysis, on the bases of Sanders' theory. A general code is developed and used in studying the effect of the stretching-bending coupling (B) and the flexural (D) stiffness matrices on the buckling and the post-buckling behavior of the shell, thereby improving its behavior.

The buckling behavior of filament-wound laminated conical shell is thoroughly investigated by consideration of the variation of the stiffness coefficients. To date, all analyses of laminated conical shells have been undertaken with constant stiffness coefficients in the laminate constitutive relations, usually under the assumption of nominal material properties taken from the midlength of the cone. The main object of the study is to investigate the influence of the variation of the stiffness coefficients on the buckling behavior of laminated conical shells. An analytical and computational model was developed to calculate the variation of the stiffness coefficients under the assumption that, in the case of filament-wound truncated conical shells, the fiber orientation changes using a geodesic path. The model was added to the computer code STAGS-A to calculate the buckling behavior of the laminated conical shell.

The shell theory accuracy with regard to initial postbuckling behavior of cylindrical shell was described. The nonlinear equilibrium differential equations for the three theories were derived on the basis of the kinematic approach by the use of the displacement components as the unknown dependent variables. An algorithm was developed and used for examination of the accuracy of each theory. The dimensional buckling loads were plotted against the circumferential wave number for several length-to-radius (l/r) ratios.

Optimum laminate configuration for minimum weight of filament-wound laminated conical shells subject to buckling load constraint is investigated. In the case of a laminated conical shell the thickness and the ply orientation (the design variables) are functions of the shell coordinates, influencing both the buckling load and its weight. These effects complicate the optimization problem considerably. The first level of complexity is attributed to the correlation between the volume and the buckling load and their dependence on the fiber configuration. The second level of complexity is associated with the high computational cost involved in the calculation of the buckling load. Thus, the main objective of this study is to solve the optimization problem as well as to reduce the computational cost associated with it. Based on the characteristic buckling behavior of laminated conical shells an adaptive response surface technique is developed.

The imperfection sensitivity of laminated cylindrical shells is considered-via the initial postbuckling analysis-on the basis of three different shell theories: Donnell in 1933; Sanders in 1963; and Timoshenko in 1961. The procedure involves nonlinear partial differential equations, which are converted into a sequence of three linear sets. The equations are solved with the variables expanded in Fourier series in the circumferential direction and in finite differences in the axial directions. A general code is developed and used in studying the effect of higher exactness of the shell theory on the sensitivity behavior, and in a parametric study of the sensitivity of anisotropic angle-ply cylindrical shells.

The sensitivity of isotropic conical shells to imperfection is considered, via the initial postbuckling analysis, on the basis of three different shell theories: Donnell's, Sanders's, and Timoshenko's. The conical shell was chosen as a representative case exhibiting the entire range of imperfection sensitivity. The procedure involves nonlinear partial differential equations, which are converted into a sequence of three linear sets. The latter are solved with the variables expanded in Fourier series in the circumferential direction and in finite differences in the axial directions. A general code is developed and used in studying the effect of higher exactness of the shell theory on the sensitivity behavior and in parametric analyses of the sensitivity of conical shells, especially with respect to the cone semivertex angle.

Bifurcation buckling analysis of laminated cylindrical shells is presented on the basis of three different shell theories: Donnell's (Donnell, L. H., "Stability of Thin-Walled Tubes under Torsion," NACA TR-479, 1933), Sanders's (Sanders, J. L.,Jr., "Nonlinear Theories of Thin Shells," Quarterly Journal on Applied Mathematics, Vol. 21, No. 1, 1963, pp. 21-36), and Timoshenko's (Timoshenko, S., Theory of Elastic Stability, McGraw-Hill, New York, 1961). Formulations in terms of the displacement components and of the Airy stress function and normal displacement are examined. The partial differential equations are derived via the variational principle and solved with variables expanded in Fourier series in the circumferential direction and presented as finite differences in the axial direction. The buckling behavior of an angle-ply laminated cylindrical shell under different modes of loading was investigated parametrically, showing-in contrast to its isotropic counterparts-a discrepancy be tween the two formulations.

The influence of shell theory in analyzing the sensitivity of laminated cylindrical shells to imperfection is analyzed. The characteristic sensitivity behavior with reference to the laminate stacking combination and orientation is investigated. The asymptotic technique is used to convert the non-linear equations into three linear sets. These equations are solved through expansion of the dependent variables in Fourier series in the circumferential direction and in finite differences in the axial direction.