Abstract

Sustainability is a primary concern that needs to be addressed since infrastructure development requires significant natural resources. Using Recycled Concrete Aggregates (RCA) for road construction has numerous benefits in saving natural resources and the environment. In the present investigation, the demolition waste is being used for road construction, partially/fully replacing natural aggregates. The Cement Treated Recycled Concrete Aggregate (CTRCA) specimens were prepared at 3%, 5%, and 7% cement with various blends of RCA and Natural Coarse Aggregates (NCA) ranging from 0 to 100%. The strength characteristics in terms of Unconfined Compressive Strength (UCS), Flexural Strength (FS), Elastic Modulus, Indirect Tensile Strength (ITS) and durability tests were conducted on cured samples. Microstructural analysis using Scanning Electronic Microscope (SEM) revealed that the pores and cracks in the old mortar have a detrimental influence on the mechanical properties of CTRCA mixes. However, Energy Dispersive Spectroscopy (EDS) and durability tests have shown positive results. The Response Surface Method (RSM) was utilised to optimise the RCA and cement content in CTRCA mixes. The research resulted in the maximum possible RCA of up to 70% with a cement content of 5.8%, which met the Indian Road Congress (IRC) specifications for Cement Treated Bases (CTB).

Introduction

The demolition waste generated from old structures is inevitable due to economic development and technological advancement. More than half of global demolition waste comes from China, India, and the United States of America, with concrete waste accounting for up to 67% of total demolition waste (Chung and Lo 2003, Akhtar and Sarmah 2018). Every year, more than 6 billion tonnes of concrete is produced worldwide (Ä et al. 2012). This waste is disposed of in dumping yards, water bodies, drain trenches, and untilled grounds around human habitations.

Furthermore, accumulating demolition waste in landfills tends to inhabit vacant land that could have been used for other purposes. These waste materials have become vital resources increasingly in road construction due to the scarcity of natural resources. Recycling aggregates from construction and demolition waste is the sole solution to conserve traditional aggregates and safeguard the environment. The potential application of RCA in base and sub-base pavement courses will solve disposal problems and conserve natural resources (Leite et al. 2011, Arulrajah et al. 2014). It is necessary to characterise RCA before its use in pavements. A crucial factor influencing the performance of pavements is the particle size distribution. Different crushing techniques and the concrete’s strength are responsible for the variances in the particle size distribution of RCA (Aydilek.pdf n.d., Arulrajah et al. 2012, Gabr and Cameron 2012). The density of RCA is lower than NCA because of the attached mortar content on its surface (Tang et al. 2018).

Conclusions

In this study, the optimisation and characterisation of the CTRCA mixes were carried out. The RSM was employed to study the effect of individual and combined factors on CTRCA mixtures. Based on test results, RCA can be used in cement-treated base and sub-base courses in Pavements. The following conclusions are drawn based on the present investigation in the laboratory.

. The mix with NCA could get the required strength in UCS, FS, ITS and Elastic Modulus at 5 per cent Cement content after seven days of curing. It also passes the durability test.

. The CTRCA mix with 30 per cent NCA and 70 per cent RCA could get the required strength with 5.8 per cent cement after seven days of curing in terms of UCS, FS, ITS and Elastic Modulus. All the samples satisfy the durability test.

Abstract

Corrosivity category of the atmosphere in coastal regions is usually very high. Reinforced structures frequently show short service life if adequate measures are not applied. Determination of time-to-corrosion-initiation (ti) and time to corrosion with induced cracking (tcc) to calculate the service life in buildings located in coastal cities is not usually performed. Changes in ti and tcc, depending on the w/c ratio, and concrete covering thickness, were determined in extremely aggressive coastal outdoor exposure site located within 10 m of the shoreline in Havana, one of the most aggressive coastal sites in the world. The electrochemical corrosion rate was determined in the reinforced concrete specimens. It is a very important parameter to follow environmental degradation of concrete. Environmental parameters were determined at the site. Calculated Chloride deposition rate is over the maximum level established in ISO 9223 standard (S3). Effective capillary porosity, compressive strength and ultrasonic pulse velocity were determined for all specimens. An acceptable service life was obtained for w/c ratio 0.4. However, effective capillary porosity is an important parameter to determine the concrete quality assessment before building reinforced structures exposed to extreme corrosivity. It is recommended to consider this parameter to predict a service life in very aggressive coastal sites.

Introduction

Many reinforced concrete (RC) structures located in coastal cities and exposed to the direct influence of marine aerosols present generally a severe deterioration, indicative of short service life (Sl), caused mainly by atmospheric corrosion of the reinforcement steel [1–4]. The RC structures are often built using very permeable concretes with low quality.

Different softwares (Life-365, Eucon, and Duracon/fib MC SLD) have already been developed to calculate the Sl of RC structures in coastal cities [5]. Some input basic parameters as cement type, concrete constituents, water/cement (w/c) ratio, additions, air content, concrete covering thicknesses, and protective systems, play a fundamental role in the determination of Sl. However, some input basic parameters depending on concrete quality as effective capillarity porosity, compressive strength, ultrasonic pulse velocity, and behavior of electrochemical corrosion rate in the reinforcement steel are not included in the software. Atmospheric transitory processes such as chloride deposition rate, relative humidity, and wind speed influencing in the corrosivity category of the atmosphere, and in the electrochemical corrosion rate in the reinforcement steel, neither are included in the software as input basic parameters [6, 7].

Conclusions

The Sl of RC structures in extremely coastal site of a city like Havana, considered one of the most aggressive environments of the Ibero-American region, depends on concrete quality, and atmospheric corrosion of reinforcement steel. Changes in the w/c ratio and concrete cover thickness, determined significant changes in the atmospheric corrosion rate of reinforcement steel in RC specimens exposed to extreme (CX) corrosivity categories of the atmosphere. The role of concrete cover thickness with respect to the Sl in RC structures become important for 0.4 w/c ratio.

Prediction and determination of the Ic, as indicator of atmospheric corrosion of reinforcement steel bars in RC specimens exposed in a coastal outdoor exposure site, can be used to obtain ti plus tcc. The importance of obtaining ti from the prediction and determination of Ic in the reinforcement steel is confirmed in the research work.

Abstract

The marine environments reduce the working life of the concrete structures owing to the severe exposure to the chemical ingress, and continuous contact with the humid air, and saline soil conditions. A scientific investigation and the conditional assessment of the existing structures may be helpful to learn the damage mechanism. This article represents the scientific conditional assessment of some existing old concrete structures in the coastal areas of Jamnagar and Dwarka of Gujarat. The objective of the study was to collect information on the types and severity of the damagesin the existing structures and preparing an assessment rubric mentioning the significance of modes of marine environment resulting in a specific damage type. To evaluate the severity of the damages, the parametric approach and a root cause analysis including the experimental investigations on the collected samples has been utilized. The outcomes revealed several interesting observations those have been classified into three major attributes namely material limitations, structural design and third as the gross environmental impacts. The study encouraged the authors to dig deeper in the area of work and showed potential of the methodology to understand the damages caused by the marine environments to the on-shore concrete structures.

Introduction

The marine exposure condition imposes a challenging environment on concrete as a material, structures and member. The long-term performance of concrete in marine environment is observed to be subjected on a complex integrated physical and chemical mechanisms [1]. The marine environment is not always regarded as the sea water, but it is the combination of the marine sand /ground, air and temperature at and around the coastal regions and the shallow as well as deep sea water together. In such cases, the damage occurred on the concrete structures needs to be evaluated or assessed for the damage with a systematic approach. Therefore, conditional assessment of the marine structures is merely not similar to the other structures. In fact, how to assess the damages of concrete in marine environments is a challenge because the nature of degradation and skill of damage varies with the location of marine structure. The concrete in the marine environment along with the reinforcements of steel bars shows damages namely corrosion, efflorescence, staining, erosion, cracking, mortar spalling and surface losses, lump mass losses, and many others. Regarding reinforced concrete in particular, chloride ingress by diffusion is probably the most important mechanism of deterioration, leading to corrosion of the embedded reinforcing steel. However, the overall situation is complicated by concomitant deterioration of the material itself by sulfate attack and physical effects such as salt crystallization and mechanical action of the waves.There are references available to refer on the topic of assessment of damage in marine environments. Use of common methods of assessment includes use of rebound hammers, porosity meters, carbonation tests on the samples [1] providing preliminary damage information, use of non-destructive tests methods and visual inspections [2], [3], on site assessment of the strength parameters of the concrete [4], use of permeability apparatus for fluid ingress, destructive tests on samples at the site and chemical analysis of the samples in laboratories [5], [6], assessment of the degree of the distresses in the concrete due to marine environment by visual and analytical inspections of the sites [7], applications of electromagnetic methods on the existing structures [8], the corrosion detection of the damages structures in the repaired structures by.

Conclusion

From the case study and the proposed systematic assessment methodology, the authors have observed that the conditional assessment of a marine structure requires a panoramic perspective on the investigations. The site survey remains the key factor for obtaining the exact details of the structural conditions, however the pre-assessment survey and related inquiries supports the process significantly. The laboratory tests and results contributed to a significant extent in ascertaining the scientific reasons for the damage. The study encouraged the authors to propose an overall severity rubric based on the systematic assessment process suggested in the present study. Table 4 indicates the overall rating to be utilized for declaring the damage scenario of the structures impacted by the marine environment.

Abstract

Concrete exposed to splash zone in partially submerged concrete structures deteriorates rapidly due to reasons such as wetting-drying cycles, the impact of waterborne materials, bio-deterioration, chloride and sulphate attacks. Existing condition assessment and rating systems do not adhere to the interrelation between different performance attributes of splash zones and these models are extremely subjective to the performance of the evaluator. The objectives of this study are to evaluate the effectiveness of parameters that deteriorate marine concrete structures and to develop a new model to predict the rate of deterioration of splash zone in marine concrete structures. The fuzzy Analytical Hierarchy Process (FAHP) was used to develop the model to predict the rate of deterioration. Here, local factors were grouped under five primary parameters as visual inspection, water quality, casual factors, Non-Destructive Tests (NDTs) and crack details. Data relevant to 15 structures were gathered by visual inspection, laboratory and field experiments to validate the proposed model. Attributes of water quality achieved the highest priority for the deterioration of the slash zone of marine concrete structures. Further, numerical values were assigned to this rating model to avoid ambiguity and vagueness of linguistic descriptors in existing rating systems. Finally, the model developed in this study can be used to evaluate the deterioration percentage of the splash zone in structures and according to that appropriate retrofitting and repair work can be done.

Introduction

At the present, reinforced concrete has been widely used in coastal and underwater structures in order to construct bridges, jetties, breakwaters and floating structures. However, concrete is more prone to deteriorate due to the aggressive environmental conditions in the atmospheric and splash zone due to chloride content in water, sulphate attacks, abrasion erosion caused by slit, sand and gravel, wetting and drying cycles and due to presence of waste and chemicals in water [13], [5]. These environmental parameters will cause cracking, spalling and corrosion which leads to incurring an enormous amount of money on repairing purposes and also this will reduce the structural health and safety of structures [23].

According to researchers, deterioration of concrete structures due to chloride induced reinforcement corrosion is a major problem around the world and reinforcement in partially submerged concrete structures is mainly corroded due to the ingress of chloride ions [18], [39]. According to Neville [20], a protective oxide layer that consists of γ-Fe2O3 is formed on steel which is generated soon after the hydration of concrete has started. Chloride ions that ingress inside concrete can be dissolved in pore solution (free chloride) or bound to the cement hydrates (bounded chloride) and only free chloride contributes to breaking this passive layer which results in corrosion [17]. When the concentration of chloride ions in the pore solution around the steel surface reaches the threshold value this film will be destroyed [4].

Conclusions

In this study, a rating model was developed to predict the rate of deterioration of the splash zone of marine concrete structures and the model was validated by assessing the current condition of 15 existing marine concrete structures. The model was developed based on FAHP and numerical definitions were used to avoid subjectivity of evaluators. According to the model, water quality has the highest priority for the deterioration of the splash zone of the structure and visual inspection, causal factors, crack detail and NDT have priority weights in the decreasing order. The proposed method can be used to rate the deterioration percentage of existing marine concrete structures in tropical countries and according to the results obtained from the model, proper remediation can be done. As future research work in this domain, freeze-thaw action can be taken into consideration in order to modify this model.

Abstract

     Concrete exposed to splash zone in partially submerged concrete structures deteriorates rapidly due to reasons such as wetting-drying cycles, the impact of waterborne materials, bio-deterioration, chloride and sulphate attacks. Existing condition assessment and rating systems do not adhere to the interrelation between different performance attributes of splash zones and these models are extremely subjective to the performance of the evaluator. The objectives of this study are to evaluate the effectiveness of parameters that deteriorate marine concrete structures and to develop a new model to predict the rate of deterioration of splash zone in marine concrete structures. The fuzzy Analytical Hierarchy Process (FAHP) was used to develop the model to predict the rate of deterioration. Here, local factors were grouped under five primary parameters as visual inspection, water quality, casual factors, Non-Destructive Tests (NDTs) and crack details. Data relevant to 15 structures were gathered by visual inspection, laboratory and field experiments to validate the proposed model. Attributes of water quality achieved the highest priority for the deterioration of the slash zone of marine concrete structures. Further, numerical values were assigned to this rating model to avoid ambiguity and vagueness of linguistic descriptors in existing rating systems. Finally, the model developed in this study can be used to evaluate the deterioration percentage of the splash zone in structures and according to that appropriate retrofitting and repair work can be done.

Introduction

     At the present, reinforced concrete has been widely used in coastal and underwater structures in order to construct bridges, jetties, breakwaters and floating structures. However, concrete is more prone to deteriorate due to the aggressive environmental conditions in the atmospheric and splash zone due to chloride content in water, sulphate attacks, abrasion erosion caused by slit, sand and gravel, wetting and drying cycles and due to presence of waste and chemicals in water [13], [5]. These environmental parameters will cause cracking, spalling and corrosion which leads to incurring an enormous amount of money on repairing purposes and also this will reduce the structural health and safety of structures [23].

     According to researchers, deterioration of concrete structures due to chloride induced reinforcement corrosion is a major problem around the world and reinforcement in partially submerged concrete structures is mainly corroded due to the ingress of chloride ions [18], [39]. According to Neville [20], a protective oxide layer that consists of γ-Fe2O3 is formed on steel which is generated soon after the hydration of concrete has started. Chloride ions that ingress inside concrete can be dissolved in pore solution (free chloride) or bound to the cement hydrates (bounded chloride) and only free chloride contributes to breaking this passive layer which results in corrosion [17]. When the concentration of chloride ions in the pore solution around the steel surface reaches the threshold value this film will be destroyed [4].

Conclusions

     In this study, a rating model was developed to predict the rate of deterioration of the splash zone of marine concrete structures and the model was validated by assessing the current condition of 15 existing marine concrete structures. The model was developed based on FAHP and numerical definitions were used to avoid subjectivity of evaluators. According to the model, water quality has the highest priority for the deterioration of the splash zone of the structure and visual inspection, causal factors, crack detail and NDT have priority weights in the decreasing order. The proposed method can be used to rate the deterioration percentage of existing marine concrete structures in tropical countries and according to the results obtained from the model, proper remediation can be done. As future research work in this domain, freeze-thaw action can be taken into consideration in order to modify this model.

1. Introduction

2. Test methodology

3. Corrosion rate analysis

4. Corrosion potential measurements

5. Mass loss measurements

6. Models and statistical analysis

7. Conclusions

References

Abstract

Corrosion of steel in reinforced concrete is a serious concern for owners and asset managers of various concrete structures and infrastructure. Literature suggests there is limited research on long-term corrosion behaviour of various types of reinforced concretes under similar conditions of chloride and surrounding temperature environments. This paper presents results of a comprehensive experimental program designed to investigate the long term corrosion resistance of various types of reinforced concretes in the coupled effect of varying chloride and temperature conditions. Large size specimens (slabs) made of ordinary concrete (OC), lightweight concrete (LWC) and self-compacting concrete (SCC) were developed. The specimens were subjected to 365 days of corrosion under varying levels of chlorides and three temperature exposures respectively. The test results indicated that the corrosion rates of the rebars in LWC are the lowest compared to those of OC and SCC. Relations were developed for corrosion rates as a function of percentage chloride, temperature and time for different types of concretes. The current research can serve as a benchmark for adequate selection of type of concrete for construction in aggressive environments.

Introduction

Corrosion-induced deterioration of structures and infrastructure accounts for 2.5 trillion dollars per annum globally [1]. Significant efforts have been devoted to the development of new materials to enhance the service life of reinforced concrete structures and infrastructure against corrosion. Chloride attacks are the most detrimental to steel/rebar in any type of concrete, including ordinary, self-compacting or lightweight concrete [2–4].

Recently, the use of lightweight concrete in construction has increased in the last 10 to 15 years [5–10]. New techniques have been developed for construction with LWC, which are simple [11–13], cost-effective and environmentally friendly [14,15]. Moreover, several studies on the structural performance of LWC have been undertaken over the last 20 years [16–20]. However, research on the durability of LWC, and specifically on chlorideinduced corrosion of the rebars is scarce [4,21]. Furthermore, there are limited comparisons between chloride-induced corrosion of LWC and other types of reinforced concrete. Moreover, long-term chloride attacks, which may prove to be detrimental to the service life of various types of reinforced concrete in hot climatic conditions, have not been adequately investigated.

Liquefaction potential analysis is a required task in the foundation design process of offshore wind turbine in Taiwan. The standard penetration test (SPT) is mostly used in the preliminary soil investigation of the pilot offshore wind farm in Chang-Bin, Taiwan. Due to the different experimental conditions and operating conditions, the N value (SPT-N) of SPT varies greatly. This study applies statistical methods in conjunction with the New Japan Road Association simplified-empirical method (NJRA method) to incorporate the uncertainty of SPT-N values into the offshore liquefaction potential assessment to quantify the risk of seabed liquefaction. The study statistics the field experimental geotechnical parameters SPT-N and determines the probability density function of the SPT-N distribution of each layer of soil in the offshore wind farm. In order to quantify the risk of seabed soil liquefaction potential, the Monte Carlo random sampling method is used, and by the NJRA method to carry out the seabed liquefaction potential in Changhua, Taiwan. After comparing, the results obtained by the current SPT-based soil liquefaction potential assessment by deterministic approach are conservative. In the ground investigation of offshore wind farm development, the method proposed in this paper can access the thickness of liquefiable soil layers under any given probability for optimizing offshore wind turbine foundation design.

Introduction

The Chang-Bin offshore wind farm of Taiwan Power Company is located in the offshore area of Changhua. The preliminary geotechnical investigation results show that the seabed of Chang-Bin offshore wind farm in Taiwan is mainly composed of silty sand (SM) and low plasticity clay (CL), it contains a small number of low plasticity silt (ML) and silty poorly graded sand (SP-SM) [CSC (2017), Hai-Shia Offshore Wind Energy Co., LtD. (2017a, 2017b), Chien at al. (2014), TORI (2012), TPC (2012, 2018)].. The soil within 80 meters below the seabed can be roughly divided into three layers. The uppermost layer is mainly loose to medium dense sand (SPT-N<30) and the depth is about 25 meters. The soil conditions of Taiwan’s offshore wind farm are very different from the offshore wind farm in the North Sea [Le at al. (2014)]. For a sandy soil within 20 meters of the surface depth, it is highly likely that soil liquefaction will occur when an earthquake occurs [Seed and Idriss (1971)]. The soil liquefaction potential can assess by deterministic approach in Taiwan, which the SPT-N based soil liquefaction potential semi-empirical analysis method is the common adopted in the engineering design in Taiwan [JRA (1996), CPA (2011)], However, soil liquefaction can be affected by soil layer distribution, soil properties, seismic wave transmission, stress conditions, etc. Therefore, quantifying the risk of soil liquefaction in highly seismic region is essential for the development of offshore wind farms.

1- Introduction

2- Case-study application

3- Results and discussion

4- Conclusions

References

Abstract

Many coastal regions lying on subduction zones are likely to experience the catastrophic effects of cascading earthquake and tsunami observed in recent events, e.g., 2011 Tohoku Earthquake and Tsunami. The influence of earthquake on the response of the structure to tsunami is difficult to quantify through damage observations from past events, since they only provide information on the combined effects of both perils. Hence, the use of analytical methodologies is fundamental. This paper investigates the response of a reinforced concrete frame subjected to realistic ground motion and tsunami inundation time histories that have been simulated considering a seismic source representative of the M9 2011 Tohoku earthquake event. The structure is analysed via nonlinear time-history analyses under (a) tsunami inundation only and (b) earthquake ground motion and tsunami inundation in sequence. Comparison of these analyses shows that there is a small impact of the preceding earthquake ground shaking on the tsunami fragility. The fragility curves constructed for the cascading hazards show less than 15% reduction in the median estimate of tsunami capacity compared to the fragility functions for tsunami only. This outcome reflects the fundamentally different response of the structure to the two perils: while the ground motion response of the structure is governed by its strength, ductility and stiffness, the tsunami performance of the structure is dominated by its strength. It is found that the ground shaking influences the tsunami displacement response of the considered structure due to the stiffness degradation induced in the ground motion cyclic response, but this effect decreases with increasing tsunami force.

Introduction

Tsunami have contributed to 250,125 deaths between 1994 and 2013 [1]. They are the deadliest natural hazard, with an average of 79 deaths for every 1000 people affected, compared to four deaths per 1000 for other natural hazards. Past tsunami have caused widespread damage and economic losses, with a direct loss of US$211 billion being estimated for the 2011 Tohoku event alone [2]. Exposure to this hazard is high, as 6 out of the 10 most populous megacities are at risk of being severely affected by storm surge and tsunami [3]. Moreover, regions at highest risk lie on subduction zones around the Pacific “Ring of Fire” (e.g., Japan, Indonesia, Pacific Northwest), and hence are likely to experience strong ground shaking as well as tsunami inundation [4]. An important component in the evaluation of tsunami impact or risk is the estimation of building response due to tsunami onshore flow. To date the majority of research on this topic has focussed on the development of fragility functions based on post-tsunami damage observed at a given location, so-called “empirical fragility functions”, e.g. Suppasri et al. [5] among many others. Empirical tsunami fragility functions are by their nature specific to the event represented in the post-event damage data as well as the local building stock, and are limited by the typical absence of locally recorded tsunami intensity measures, such as the flow velocity. They commonly adopt building damage observations from locations that have been affected by both earthquake and tsunami hazards, implicitly including the response of buildings to the combined hazards. Assessment of structural performance through numerical analyses is therefore essential to overcome these limitations. Analytical fragility functions are therefore needed to complement empirical assessments for a physical understanding of structural behaviour under cascading earthquake and tsunami.

The performance of the ship hull deteriorates randomly over time under corrosion attacks. To ensure the safe operation of a ship, dry-docking inspections are carried out on a regular basis to inspect, recoat, and renew structural members. The convention “at least two inspections every five years”, implemented in the shipping industry, is empirically determined without much numerical evidence. Considering the expensive cost of drydocking inspections, it is crucial to study the optimal inspection interval in the presence of uncertainty. This paper proposes a risk-based maintenance decision-making framework for ships to address the optimal drydocking inspection. The minimum expected cost rule is used to explore the economically optimal inspection interval. Monte Carlo simulations are employed to obtain the probability distribution of the life-cycle cost. The costs considered include the cost of dry-docking and member renewal as well as monetary consequences of hull failure. A ship hull is utilized to illustrate the application of the proposed framework.

Introduction

The loss of a ship has significant implications in terms of environmental impact, economic loss, and crew casualties. Metal loss corrosion is a primary concern for the safety of aging ships [1,2]. By decreasing the modulus of the hull cross-section, growing corrosion reduces the ultimate strength against external loadings. To maintain the satisfactory integrity of the hull, ships are dry-docked for inspection at a minimum twice in a 5-year period [3]. During the inspection, the thickness of the structural members of the hull is measured using non-destructive tools (e.g., ultrasound inspection), structural renewal is performed for the critical members and new protective coatings are applied to the hull surface to protect against corrosion [4]. Dry-docking is an expensive process and accounts for the largest maintenance cost throughout the ship service life. The cost of one dry-docking can be as high as $0.2 M to $0.7 M [4]. Dry-docking can also adversely affect the flexibility of operational schedules by taking a ship out of service. It is of paramount importance to explore a cost-effective inspection schedule that allows the ship to stay longer in water while guaranteeing an acceptable level of safety. Determining the optimal inspection is not a simple task. Various uncertainties are associated with the performance of the hull. Specifically, the bending moment induced by still water and sea waves experienced during one voyage is uncertain; the spatial variability of geometric and material properties associated with different structural members, the uncertainty associated with the prediction of bendingresistant capacity, and the stochastic corrosion growth result in the uncertain structural performance of the hull.

To investigate the seismic performance of railway bridge piers with round-ended hollow section, five 1/6-scale specimens were tested under low-cyclic loading. The two variable parameters were the volumetric stirrup ratio and axial load level. The damage evolution, strain response, and plastic hinge behavior were meticulously explored. The load-drift relationship, displacement ductility, strength/stiffness degradation, dissipated energy, and viscous damping were analyzed in depth. The quantification of seismic performance objectives was implemented by displacement ductility based on damage assessment. The relationships among the ductility and strength/ stiffness degradation and equivalent damping ratio were regressed using the test data. The experiment and analysis results showed that all specimens suffered flexural failure, with flexural cracks covering nearly twothirds of the pier height. The plastic hinge region lengthened and moved upwards along the column due to the existence of solid segment, internal chamfer and variable section. The displacement ductility capacity enhanced noticeably with increasing stirrup ratio. The increasing axial compression ratio led to higher initial stiffness and seismic capacity to some extent, but excessive axial load would decrease ductility with premature concrete crushing. Furthermore, the seismic safety of the piers were ensured under a ductility factor limitation of 4.8 required by the current seismic code for railway engineering of China.

Introduction

With the robust expansion of high-speed rail (HSR) network in recent years, a large number of standard short-span bridges (including simply supported beam bridges and a few continuous beam bridges) have been constructed or are being built in the southwest region of China [1,2]. To accommodate the rugged topography of mountainous areas, the height of these piers is usually over 30 m [3]. For slender railway bridge columns, the round-ended hollow piers are usually selected as the substructure [4], which not only saves material, lowers self-weight and reduces seismic inertial forces compared with traditional solid piers, but also meets with the stiffness requirement for HSR bridges. However, the Southwest China is known for frequent intensive earthquakes (such as the Wenchuan Earthquake in 2008 and the Lushan Earthquake in 2013). The railway bridges with thin-walled slender columns are vulnerable to seismic damage, so their seismic performance need to be studied in depth. To date, numerous experiments have been finished on rectangular (e.g., [5–10]) and circular (e.g., [11,12]) hollow columns. Mander et al. [5] concentrated on the seismic performance of rectangular hollow columns via semi-static tests of four reduce-scaled models. A series of experiments on full or reduce-scaled rectangular hollow columns were conducted by Yeh and Mo [6–8] since 2000. Furthermore, biaxial quasistatic tests were also performed on rectangular hollow pier specimens [9,10]. For circular hollow piers, Zahn [11] and Yeh [12] studied the flexural strength and ductility behavior respectively.

Life line structures such as elevated flyovers and rail over bridges should remain functional after an earthquake event to avoid possible traffic delays and risk to general public. Generally, restraining the structure by reducing the degrees of freedom often cause serious damages that occurs during a seismic event through yielding of the structural components. By allowing the structure to rock through uplift using suitable arrangements can be a plausible seismic resilient technique. In this context, this article proposes a novel seismic resilient pile supported bridge pier foundation, which uses elastomeric pads installed at top of pile cap. The effect of pile soil interaction along with ground response analysis is also incorporated in the full bridge model adopted for the study. One dimensional equivalent linear site response analyses were performed to arrive at the amplified/attenuated ground motions along the depth of soil.The seismic performance of the proposed bridge with new rocking isolation concept is compared with existing bridge located in medium seismic zone of India. With the help of non-linear dynamic time history analysis and nonlinear static pushover analysis, the bridge modelled using the proposed novel rocking isolation technique shows good re-centering capability during earthquakes with negligible residual drifts and uniform distribution of ductility demand along the piers of the bridge considered in this study.

Introduction

Bridges and flyovers are major assets of any country and failure of such structures during seismic event leads to economic loss to the country and traffic disruptions to the general public. Despite their importance, these key infrastructure assets have been designed for many years, neglecting the fact that loads and geo-hazards may change drastically and thus significant upgrades may be required during their service life. Societies expect accelerated constructions, minimal damage and rapid upgrading for bridges which are sources of transportation and thus must be designed to face very strong earthquake in order to avoid permanent drift which are beyond repairs. Collapse of whole bridge caused by extended damage of the piers and/or unseating of the superstructure caused by insufficient deformation capacity of the bearing and other destruction of bridge structure often occurs in an earthquake [1].The concept of ductility is used in the conventional design of bridge pier wherein the pier reinforcement is detailed to develop flexural plastic hinges at the base and top of pier [2]. Although bridges designed in this manner may undergo damages due to severe earthquake excitations as observed in Fig. 1(a)–(d). Rocking isolation in the form of structural rocking or geotechnical rocking of the bridge pier experience far less damage when subjected to high intensity earthquake ground motion with added bonus of pier that recenter due to the increased period of vibration owing to the flexibility of the resilient pier [3,4]. The design of South Rangitikei Railway Bridge in New Zealand in 1981 used structural rocking by adopting the concept of dissipative rocking at the pier-to-foundation interface by means of prestressing tendons which had more rocking sections contributing to dissipation of energy and thus less prone to heavy damages when subjected to severe earthquakes [5,6].

1. Introduction

2. Flexible pipe design

3. Reliability approach to flexible pipe design

4. Project application and associated sensitivity analysis

5. Conclusion and perspectives

References

Flexible riser systems offer operators a robust method of producing oil and gas fields in harsh environments. Systems are currently designed using a mixture of local and international standards such that they can withstand conditions with a sufficient margin of safety. Flexible pipes have been installed for water depth exceeding 2500m. The application of reliability methods to determine the design of offshore systems such as jackets and ship hulls is well developed and has a long and successful track record. Flexible risers are subjected to the same random environmental loads. While probabilistic methods have been explored, they have yet to be applied in any meaningful manner to the fatigue limit state. How to account in the most robust manner for uncertainties within the loading has become critical for deriving cost effective and robust design rules for flexible risers. Especially the layer of the flexible riser bearing the tensile load, named tensile armours, is critical in the design in many of the deep-water developments. In this paper, multiple structures designed for west of Africa and the North Sea are investigated through a reliability method. Typical Uncertainties within the global riser motions, the local stress computations and in the stress-life curve resistance are accounted for. Demonstration is made that for the same uncertainties the variables influencing the reliability of the structure differ. Finally, the comparison with actual international design rules is made through the value of the safety factor applied on the design life.

Introduction

Flexible riser systems are a robust method of producing oil and gas fields in a range of locations. Often, these locations are most economically developed using a floating production vessel with flexible risers linked to the subsea infrastructure. Many applications are in locations which experience harsh environments and high seas like West-of-Shetland, South Atlantic or Offshore Canada. Designing flexible riser systems to withstand these conditions with a sufficient margin of safety while still making them economically viable remains a challenge. Flexible riser systems are currently designed using a mixture of local and international standards [1, 2]. Once an initial geometry has been determined, fatigue dynamic analysis using proprietary finite element analysis codes and models (e.g. [3]) is performed. An agreed, between operator and manufacturer, deterministic load case matrix over the scatter diagram is used. For this specific failure mode, uncertainties in the resistance side are accounted for using validated fatigue curves established based on international standards such as ASTM E739-10 [4]. The low frequency, wave induced, fatigue limit state may govern the design of flexible pipe for harsh environments or accidental loading conditions (e.g. flooded annulus).

1- Introduction

2- Modeling, limit states, and analysis setup

3- Results

4- Summary and conclusions

References

Abstract

The number of offshore wind turbine farms in seismic regions has been increasing globally. The seismic performance of steel monopile-supported wind turbines, which are the most popular among viable structural systems, has not been investigated thoroughly and more studies are needed to understand the potential vulnerability of these structures during extreme seismic events and to develop more reliable design and assessment procedures. This study investigates the structural performance assessment of a typical offshore wind turbine subjected to strong ground motions. Finite element models of an offshore wind turbine are developed and subjected to unscaled natural seismic records. For the first time, the sensitivity to earthquake types (i.e. crustal, inslab, and interface) and the influence of soil deformability and modeling details are investigated through cloud-based seismic fragility analysis. It is observed that monopile-supported offshore wind turbines are particularly vulnerable to extreme crustal and interface earthquakes, and the vulnerability increases when the structure is supported by soft soils. Moreover, a refined structural modeling is generally necessary to avoid overestimation of the seismic capacity of offshore wind turbines.

Introduction

Wind energy production from offshore wind farms is a reality nowadays around the world. Fig. 1 shows main countries that are developing and investing in offshore wind power according to the Global Wind Energy Council [1]. The same figure shows a global seismic hazard map in terms of peak ground acceleration (PGA) with probability of exceedance of 10% in 50 years [2]. Several countries are in high seismic regions, including the USA, China, India, and South East Asia, and are adjacent to subduction zones (blue lines in Fig. 1), where magnitude M9-class megathrust earthquakes can occur. This highlights that earthquake risk for newly built offshore wind farms can be potentially high and that reliable design and assessment methods for these structures against intense ground excitations need to be developed. In fact, current international standards and national codes (e.g., GL [3], DNV [4], IEC [5]) suggest considering seismic actions but without explaining in detail how to evaluate the seismic performance (e.g. suitable analysis methods). The lack of basic research that underpins codes’ requirements may be related to the limited number of wind turbines that were actually damaged during major earthquakes [6,7]. Moreover, structural damage to wind turbines was mainly reported for onshore wind turbines, thus contributing to common misperception that seismic loading is not critical for offshore wind turbine structures [8]. On the other hand, the global development of such structures in active seismic regions makes imperative to understand to which extent structural demand on offshore wind turbines is increased by earthquake loads, and whether numerical results may be affected by modeling details or by the implementation of the soil-structure interaction (SSI) that has been recognized playing a very important role on the structural performance.