Strategies for Teaching the Reinforced Concrete Structures Course in Engineering Majors

The cultivation of engineering capabilities aims to equip engineering professionals with high-level expertise to meet the demands of society and industry development,thereby enhancing their competitiveness and career potential.This article focuses on engineering capability development,exploring teaching strategies for the Reinforced Concrete Structure course.It aims to provide insights for educators in engineering programs at universities and vocational colleges in China.By doing so,teaching plans that meet the needs of engineering capability development,laying a solid educational foundation for the healthy growth of engineering professionals in the new era,and enhancing their application of knowledge and skills can be developed.

Durability design of prestressed concrete structures

Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reliability mathematics and stochastic processes areconstructed, and the pure theoretical formulae of failure probability of prestressed concretestructures are analyzed. In addition, a simple durability design method for carbonation ofstructures is put forward. According to the analysis, the durability of prestressed concretestructures is superior to that of traditional structures. The research also indicates that theconcrete cover prescribed in the current code (GB 50010-2002) is not adequate. The rational coverthickness should notbe less than 35 or 45 mm according to carbonation or chloride ion attack,respectively.

The States-of-arts and Key Scientific Issues on Durability Research of Concrete Structures

Concrete has traditionally been regarded as a durable material requiring little or no maintenance. However, over the past several decades, a number of durability related problems have emerged and stimulated research into the factors relating to concrete durability globally. The challenge now facing practicing engineers is how to design and build structures that not only satisfy the specified structural requirements, but also achieve the performance levels required from a durability standpoint. Research works on concrete structural durability have been widely reported in the literature over the last several decades. In this paper, reviews of four stages of research work on durability, i e, environments, materials, components, and structures, were presented. Afterwards, the key scientific issues in this field were also pointed out.

Corrosion risk assessment of chloride-contaminated concrete structures using embeddable multi-cell sensor system

Monitoring the service condition of concrete structures requires the quantitative assessment of properties and corrosion rate of structural steels surrounded by concrete.A multi-cell sensor system that included a reference electrode,a chloride content sensor,a macrocell current unit and an electrical resistance measurement unit was developed.This system provided the following important electrochemical data in the cover-zone concrete on site:open circuit potential,macrocell current from anodes to cathode,chloride profile,concrete resistance and corrosion rate of built-in anodes.The experimental results show that the macrocell current increases when the chloride content in concrete is higher.Thus,monitoring the chloride content is a good method for monitoring the corrosion state.The chloride ion content and cover depth are the key factors that affect the electrical resistance of concrete.Without considering the temperature and time,a simplified model of the instantaneous corrosion rate of steel rebar in a concrete structure based on the measured chloride contents and concrete resistance was proposed.The test results further prove the reliability of this simplified predicting model.

Piezoelectric-based Crack Detection Techniques of Concrete Structures:Experimental Study

Feasibility of a wave propagation-based active crack detection technique for nondestructive evaluations （NDE） of concrete structures with surface bonded and embedded piezoelectric-ceramic （PZT） patches was studied. At first, the wave propagation mechanisms in concrete were analyzed. Then, an active sensing system with integrated actuators/sensors was constructed. One PZT patch was used as an actuator to generate high frequency waves, and the other PZT patches were used as sensors to detect the propagating wave. Scattered wave signals from the damage can be obtained by subtracting the baseline signal of the intact structure from the recorded signal of the damaged structure. In the experimental study, progressive cracked damage inflicted artificially on the plain concrete beam is assessed by using both lateral and thickness modes of the PZT patches. The results indicate that with the increasing number and severity of cracks, the magnitude of the sensor output decreases for the surface bonded PZT patches, and increases for the embedded PZT patches.

DAMAGE LOCATION DUE TO CORROSION IN REINFORCED CONCRETE STRUCTURES

An investigation on damage location due to the corrosion in reinforced concrete structures is conducted. The frequency change square ratio is used as a parameter for the damage. It is theoretically verified that the parameter is a function of the damage location. Experimental results of the corrosion in reinforced concrete structures show that the predicted damage location is in agreement with the real damage location. The modal parameters are used to detect the damages in structural concrete elements, and so they are useful for structural appraisal.

Fibre Optic Protection System for Concrete Structures

The design concepts, modelling and implementation of various fibre optic sensor protection systems for development in concrete structures were investigated. Design concepts and on-site requirements for surface-mounted and embedded optical fibre sensor in concrete were addressed. Finite element （FE） modelling of selected sensor protection systems in strain-transfer efficiency from the structure to the sensing region was also studied. And experimental validation of specified sensor protection system was reported. Results obtained indicate that the protection system for the sensors performs adequately in concrete environment and there is very good correlation between results obtained by the protected fibre optic sensors and conventional electrical resistance strain gauges.

Sensitivity Study on Durability Variables of Marine Concrete Structures

In order to study the influence of parameters on durability of marine concrete structures, the parameter＇s sensitivity analysis was studied in this paper. With the Fick＇s 2nd law of diffusion and the deterministic sensitivity analysis method （DSA）, the sensitivity factors of apparent surface chloride content, apparent chloride diffusion coefficient and its time dependent attenuation factor were analyzed. The results of the analysis show that the impact of design variables on concrete durability was different. The values of sensitivity factor of chloride diffusion coefficient and its time dependent attenuation factor were higher than others. Relative less error in chloride diffusion coefficient and its time dependent attenuation coefficient induces a bigger error in concrete durability design and life prediction. According to probability sensitivity analysis （PSA）, the influence of mean value and variance of concrete durability design variables on the durability failure probability was studied. The results of the study provide quantitative measures of the importance of concrete durability design and life prediction variables. It was concluded that the chloride diffusion coefficient and its time dependent attenuation factor have more influence on the reliability of marine concrete structural durability. In durability design and life prediction of marine concrete structures, it was very important to reduce the measure and statistic error of durability design variables.

Reliability-based service life prediction of existing concrete structures under marine environment

Chloride-induced corrosion of the reinforcement is considered as one of the major mechanisms resulting in the reduction of structural resistance of reinforced concrete structural elements located in marine and other aggressive environments. A study of reinforced concrete structures located at the Fangcheng dock in the Beibu Gulf port, China, was present. The result from field survey indicates that the concrete cover depth and chloride diffusion coefficient fit best normal distribution and lognormal distribution, respectively. The service life of structure is about 55 a, while initiation time is 45 a. Sensitivity analysis indicates that the most influential factor of the structure service life prediction is concrete cover, followed by diffusion coefficient, diffusion decay index, critical chloride concentration, surface chloride concentration, current density and localized pitting corrosion. Finally, the effects of diffusion decay index and critical chloride concentration on structure service life prediction are discussed.

Introduction of a Japan Concrete Institute Guideline： Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures

There are many cracked concrete structures worldwide. Although there have been numerous efforts to eliminate cracks, some cracks are very harmful and should be repaired as soon as possible. On the other hand, some cracks are almost harmless. So, a good guideline regarding how to deal with cracks in concrete structures is needed. In this guideline, the practical investigation, repair and strengthening method of cracked concrete structures is discussed. And the detecting subjects are cracks generated immediately after casting and during the service time. This guideline targets on the owners （including managers） of concrete structure and the engineers working for the maintenance of concrete structure. JCI （Japan Concrete Institute） published first version of ＂Practical Guideline for Investigation and Repair of Cracked Concrete Structures＂ in 1980, and then the fourth version titled ＂Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures--2009＂ was published. This guideline is very practical when cracks are observed in existing concrete structures, in any other countries as well as in Japan. These three authors led the establishment of this guideline.

Introduction of a JCl Guideline： Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures

There are many cracked concrete structures, although there have been numerous efforts to eliminate cracks. Some cracks are very harmful and should be repaired as soon as possible. On the other hand, the other cracks are almost harmless. So, a good guideline about how to deal with cracks in concrete structures had been needed. JCI （Japan Concrete Institute） published the first version of ＂Practical Guideline for Investigation and Repair of Cracked Concrete Structures＂ in 1980, the second version in 1987, the third version in 2003, and then the fourth version titled ＂Practical Guideline for Investigation, Repair and Strengthening of Cracked Concrete Structures-2009＂ was published. This Guideline is very practical, when cracks are observed in existed concrete structures, in any other countries as well as in Japan.

Probabilistic Assessment of Pitting Corrosion Effect on Flexural Strength of Partial Prestressed Concrete Structures in a Chloride Environment

Like reinforced concrete （RC） structure, Prestressed concrete （PC） structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride environment. The corrosion of PC and RC structures can take place if the concrete quality is not adequate, the concrete cover is less than that specified in the design, poor detailing during design and construction. For RC structures, corrosion in the reinforcing steel generally leads to serviceability problems （staining, cracking and spalling of concrete）. By contrast, for PC structures, corrosion of prestressing strands may initiate structural collapse due to higher stress levels in the steel and smaller diameter of the prestressing steel. Research on corrosion effect on concrete structure has mainly considered the effect of corrosion have on reinforced and full prestressed concrete structure. In this study, a structural framework will be developed to predict the flexural strength of partial prestressed concrete structures in a chloride environment. The corrosion model previously developed for reinforced and prestressed concrete structures will be combined to predict the effect of corrosion has on partial prestressed concrete structures. Note that in partial prestressed concrete structures, both non prestressing steel （passive） and prestressing （active） reinforcement are utilized to carry the load. The framework developed will be combined with probability analysis to take into account the variability of parameters influencing the corrosion process. This approach allows more accurate prediction of service life of partial prestressed concrete structures in a chloride environment.

Crack detection for wading-concrete structures using water irrigation and electric heating

Cracking in wading-concrete structures has a worse impact on structural safety compared with conventional concrete structures.The accurate and timely monitoring of crack development plays a significant role in the safety of wading-concrete engineering.The heat-transfer rate near a crack is related to the flow velocity of the fluid in the crack.Based on this,a novel crack-identification method for underwater concrete structures is presented.This method uses water irrigation to generate seepage at the interface of a crack;then,the heat-dissipation rate in the crack area will increase because of the convective heat-transfer effect near the crack.Crack information can be identified by monitoring the cooling law and leakage flow near cracks.The proposed mobile crack-monitoring system consists of a heating system,temperature-measurement system,and irrigation system.A series of tests was conducted on a reinforcedconcrete beam using this system.The crack-discrimination indexψwas defined,according to the subsection characteristics of the heat-source cooling curve.The effects of the crack width,leakage flow,and relative positions of the heat source and crack onψwere studied.The results showed that the distribution characteristics ofψalong the monitoring line could accurately locate the crack,but not quantify the crack width.However,the leakage flow is sensitive to the crack width and can be used to identify it.

Research on the Course of Principles of Concrete Structure Design

Nowadays,education and teaching have become a hot topic,and teaching in colleges and universities is facing a brand-new development direction.Principles of Concrete Structure Design,as one of the main courses,transmits professional knowledge for students,enhances the students’professional ability,and further carries out in-depth research on the course to bring a better teaching effect for students.The article mainly focuses on the research of the principles of concrete structure design course,conducts an analysis of the teaching characteristics of the principles of concrete structure design course,and reasonably sets the teaching content from the optimization of the course teaching objectives;innovative course teaching methods can deepen the effect of knowledge understanding;reform of experimental practice teaching can lay down the effect of the internalization of knowledge,etc.The in-depth description and discussion of the relevant aspects of the research aim to provide guidelines for related research.

Self-centering seismic retrofit scheme for reinforced concrete frame structures:SDOF system study

This paper presents the results of a parametric study of self-centering seismic retrofit schemes for reinforced concrete (RC) frame buildings. The self-centering retrofit system features flag-shaped hysteresis and minimal residual deformation. For comparison purpose,an alternate seismic retrofit scheme that uses a bilinear-hysteresis retrofit system such as buckling-restrained braces (BRB) is also considered in this paper. The parametric study was carried out in a single-degree-of-freedom (SDOF) system framework since a multi-story building structure may be idealized as an equivalent SDOF system and investigation of the performance of this equivalent SDOF system can provide insight into the seismic response of the multi-story building. A peak-oriented hysteresis model which can consider the strength and stiffness degradation is used to describe the hysteretic behavior of RC structures. The parametric study involves two key parameters -the strength ratio and elastic stiffness ratio between the seismic retrofit system and the original RC frame. An ensemble of 172 earthquake ground motion records scaled to the design basis earthquake in California with a probability of exceedance of 10% in 50 years was constructed for the simulation-based parametric study. The effectiveness of the two seismic retrofit schemes considered in this study is evaluated in terms of peak displacement ratio,peak acceleration ratio,energy dissipation demand ratio and residual displacement ratio between the SDOF systems with and without retrofit. It is found from this parametric study that RC structures retrofitted with the self-centering retrofit scheme (SCRS) can achieve a seismic performance level comparable to the bilinear-hysteresis retrofit scheme (BHRS) in terms of peak displacement and energy dissipation demand ratio while having negligible residual displacement after earthquake.

Full－range nonlinear analysis of fatigue behaviors of reinforced concrete structures by finite element method

The offshore reinforced concrete structures are always subject to cyclic load, such as wave load.In this paper a new finite element analysis model is developed to analyze the stress and strain state of reinforced concrete structures including offshore concrete structures, subject to any number of the cyclic load. On the basis of the anal ysis of the experimental data,this model simplifies the number of cycles-total cyclic strain curve of concrete as three straight line segments,and it is assumed that the stress-strain curves of different cycles in each segment are the same, thus the elastoplastic analysis is only needed for the first cycle of each segment, and the stress or strain corresponding to any number of cycles can be obtained by superposition of stress or strain obtained by the above e lastoplastic analysis based on the cyclic numbers in each segment.This model spends less computer time,and can obtain the stress and strain states of the structures after any number of cycles.The endochronic-damage and ideal offshore concrete platform subject to cyclic loading are experimented and analyzed by the finite element method based on the model proposed in this paper. The results between the experiment and the finite element analysis are in good agreement,which demonstrates the validity and accuracy of the proposed model.

Progressive collapse resisting capacity of reinforced concrete load bearing wall structures

Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthquakes, but also more economical. The effect of progressive collapse caused by removal of load bearing elements, in various positions in plan and stories of the RC load bearing wall system was evaluated by nonlinear dynamic and static analyses. For this purpose, three-dimensional model of 10-story structure was selected. The analysis results indicated stability, strength and stiffness of the RC load-bearing wall system against progressive collapse. It was observed that the most critical condition for removal of load bearing walls was the instantaneous removal of the surrounding walls located at the corners of the building where the sections of the load bearing elements were changed. In this case, the maximum vertical displacement was limited to 6.3 mm and the structure failed after applying the load of 10 times the axial load bored by removed elements. Comparison between the results of the nonlinear dynamic and static analyses demonstrated that the "load factor" parameter was a reasonable criterion to evaluate the progressive collapse potential of the structure.

Effects of Temperature Variations on Safety of Reinforced Concrete Structures During Construction

Since 1960s, many research works on the reinforced concrete structure have been published and some concise and practical calculation methods for safety control during construction have been achieved. The reinforced concrete structure during construction is a time-dependent structure which consists of a partly completed structure and a formwork-shore system. Experience shows that the most critical condition of the time-dependent structure may happen when the formwork-shore system is partly removed or reset and accidents may occur. In the present paper, effect of ambient temperature variation between day and night is considered, new structural models for reinforced concrete frames, slab-column systems and shear wall structures are proposed, and a new software named Safety Analysis During Construction Considering Temperature(SACT) is also introduced. Compared with on-site measurements, the software SACT is validated for application on construction site.

Service Life Prediction and Management of Concrete Bridge Structures Due to Corrosion

The increasing stocks of public infrastructure and serious deterioration of infrastructure systems due to corrosion present great financial, safety, technical and operational challenges to government organizations in charge of public infrastructure development and management. To meet those challenges, a performance-based life-cycle management model for reinforced concrete structures was proposed in this paper. This model predicts the life-cycle performance of infrastructure based on the corrosion-induced deterioration mechanism： condition index as well as performance limit states. A case study is provided to demonstrate the use of the proposed performance-based life-cycle cost management model.

Research on the Reform of the Course“Reading of Concrete Structure Plan and Construction Drawings”Under the Background of“Promoting Teaching and Learning Through Competitions”

The inherent teaching approach can no longer meet the demands of society.In this paper,current issues within the teaching landscape of architectural engineering technology in higher vocational colleges as well as the policies and teaching demands that formed the basis of this model were analyzed.The study shows the importance of the implementation of the teaching model“promoting teaching and learning through competitions.”This model puts emphasis on the curriculum and teaching resources,while also integrating the teaching process and evaluation with competition.These efforts aim to drive education reform in order to better align with the objectives of vocational education personnel training,while also acting as a reference for similar courses.