Predict Reinforced Concrete Structure Life Time (Part I)

One can find that the predicting the life time of the structure is very complicated subject. As after collecting all the required data about the strength and loads still the time of the structure failure is varies from structure to another depending on many factors.

According to many researchers are interesting to focus about the buildings life time as they found that there are some materials and structures have a longer life time than the other.
Throughout history, service-life predictions of structures, equipment, and other components were generally qualitative and empirical. The first step it is required to understand the causes of many degradation processes and identifying the reasons is the main step  for making quantitative predictions of the service life of concrete structures and its components. In addition to actual or potential structural failure, many other factors can govern the service life of a concrete structure, for example, excessive operating costs or major repair cost can lead to a structure's replacement.

In most text books usually used expression durability and service life as the terms "durability" and "service life" are often erroneously interchanged. The distinction between the two terms is evident when their definitions, as given in ASTM E 632, are compared and defined the durability as, its capability of maintaining the serviceability of a building, component, assembly, or construction over a specified time. Serviceability is viewed as the capacity of the above to perform the function(s) for which they are de­signed and constructed.

The definition of Service life  is defined by by three types of service life have been defined which are:

·         Technical service life is the time in which the building in service until shown  unacceptable state is reached, such as spalling of concrete, safety level below acceptable, or failure of elements.
·         Functional service life is the time in service until the structure no longer fulfills the functional requirements or becomes obsolete due to change in functional requirements, such as the needs for increase clearance, higher axle and wheel loads, or road widening in case of bridges.
·         Economic service life is the time in service until replacement of the structure (or part of it) is economically more advantageous than keeping it in service or repairing or strengthening it.

The service-life methodologies have been included  in the design stage of a structure-where certain parameters  are established and this is clear in EC2. The some of the parameters that affect by defining the service life of the structure as selection of water-cementitious materials ratios (w/c), concrete cover, and admixtures-and in the operation phase where inspection and maintenance strategies can be developed in support of life-cycle cost analyses.

According to  CEBIRILEM 1986 service-life design includes the architectural and structural design, selection and design of materials, maintenance plans, and quality assurance and quality control plans for a future structure. Based on mixture proportioning, including selection of concrete components, known material properties, expected service environment, structural detailing such as concrete cover, construction methods, the loading history, and the definition of end-of-life, the service life can be predicted and concrete with a reasonable assurance can achieve the design service life as discussed by Elreedy MA (2012).

There are many trials to develop a method to predict the service life of existing concrete structures. To predict the service life of existing concrete structures, information is required on the present condition of concrete, rates of degradation, past and future loading, and definition of the end-of-life as mention that Clifton (1991). Based on remaining life predictions, economic decisions which is usually the responsibility to the owner to take the decision  on whether or not a structure should be repaired, rehabilitated, or replaced.

It is worth to mention that, all decisions concerning the definition of end of-life are combined with human safety and economic considerations. In most cases, the condition, appearance, or capacity of a structure can be upgraded to an acceptable level; however, costs associated with the upgrade can be prohibitive.

The service life of new and existing concrete structures is influenced by measures taken during design and construction to resist degradation from imposed loads and environmental conditions (for example, the degree of durability). Durability brings the time element into the design of reinforced concrete structures and should be given equal importance to that given to strength. It is worth to mention that, design and construction currently consist of seven which are as follow:

1) Design loads and actions;

2) Performance criteria;

3) Factors of safety, or reliability;

4) Design and detailing;

5) Material specifications;

6) Workmanship and construction practices

7) Minimum levels of maintenance.

Provisions for durability in the past have primarily been addressed under Items 5 and 6. It is important to mention that the design for durability requires essentially an improved understanding of the degradation mechanisms, improved characterization of service environments, data on materials, the development of advanced models, and the development of standards and guidelines for the use of design methods and acceptance for durability predictions.

To predict the concrete structure life time, it needs a complete evaluation for the whole building by visual inspection, collecting data and provide some experimental test if needed.

The data which will be collect and evaluate will be in three directions which are the loads, the environmental condition surrounding the building and the structural strength.

When start to predict the life time of the structure it is very important to know the loads that have been affect the building from its construction until the time of evaluation and the expecting loads that affecting the structure for upcoming years.

The most important design parameter is the definition of structural loads. Minimum design loads and load combinations are prescribed by legally adopted building codes for example, ACI 318, or ASCE7. There is a balance between selection of a design to meet minimum loading conditions and the design responsibility is to provide a conservative design that results in higher initial price but can provide lower life-cycle cost.

If the design is go through another approach by provide the least cost building with minimum load mention in the codes but this can design approach will need a higher life cycle cost and this can be more susceptible to degradation than the more conservative design approach.

Predicting service life of new concrete , in most cases the selection of the concrete materials and design mix of the concrete based o the laboratory test and its expectation for its behavior after pouring on site. But this approach is based on the concrete is durable materials regardless the surrounded environmental condition and it has a service life according to the codes which in most cases around 25 years. Now a days due to enhanced the materials of concrete and there are a new materials developed in the market such as additives, silica fume , slag , fly ash and others so we have the opportunity to choose the materials additives that will enhance the properties of concrete in harsh environment and as a result of that the concrete can reach the required service life  without maintenance cost during its life time.

There are many service-life prediction methods focus on the effect of one degradation process. Experience, however, has shown that degradation results when one or more degradation processes are operative or if there is a combination between the environmental condition and the loads.

• Predictions based on experience-Semiquantitative predictions
• Comparison performance approach
• Accelerated testing
• Mathematical models-Mathematical

This combination effect complicates the prediction of the new concrete structures service-life prediction for both new concrete structures where environmental factors and loads may have not been well defined, and existing structures where the contribution to degradation by various influences is difficult to assess. The main factors that affect the service life of reinforced concrete structures include the presence of chlorides, carbonation, aggressive chemicals, such as acids and sulfates, freezing-and thawing cycling, and mechanical loads, such as fatigue, vibration, and local overloads. Typically, only one primary factor limits the service life and is the focus of service-life prediction. As limited information is available on the synergistic effect when more than one factor is operative.

Mohamed A. El-Reedy, Ph.D

www.elreedyman.com

Industrial Projects Charactristics

The development of any country depends on the rate of industrial growth. Currently, there is a race in industrial projects worldwide. The development of the industry depends on the development of the energy reserve by investment in projects of oil and gas exploration, onshore and offshore, which require new facilities or rehabilitation of existing facilities. At the same time, there are projects that are running in parallel to deliver electricity from electrical power stations or through nuclear power plants.

The term industrial structures means all the reinforced concrete and steel structures from a small factory to a nuclear plant. My book (www.amazon.com/author/elreedyma) provides  an overview of industrial project management, design, construction, and eventually providing a maintenance plan. Industrial projects, in most cases, are huge and can cost a billion dollars for one project, so the client, engineering firm, and contractor are in the same boat until they achieve project success through a strong management system and technical competence.

In these types of projects, all the engineering disciplines are working together, but, unfortunately, the structural or civil engineers are usually the last ones to obtain the exact data from the other disciplines and the first ones to start on site. Therefore, it is a challenge for the structural engineers to work fast and efficiently in this type of project. So it is required a strategy plan and professionalism in dealing with these projects.

It is important to regular familiar ourselves with up-to-date methodology and industry technical practice and guidelines to design, construct, and maintain the reinforced concrete and steel structures in these industrial projects. The other challenge that faces structural engineers is that most of the undergraduate courses they studied in college focused mainly on real estate projects and housing. However, the characteristics of industrial projects are different, as it needs from the project and construction manager to lead the project and to successfully achieve the owner’s requirements.

On the other hand, the structure engineer should be  familiar with the codes and standards that are usually used in industrial projects which is really few and is not famous rather normal building codes and standard and the most applicable methods used in the design of the steel and reinforced concrete structures that serve the static equipment, tanks and towers, and vibrating equipment.

Dr. Mohamed A. El-Reedy

www.elreedyman.com

Can We Predict Concrete Structure Life?

Most of the structure engineers are focusing on design a safe structure by following the parameters and factors in the code and standard that requested in the project specifications. After finishing the design stage the structure engineers who work on site receive the drawings and the specifications from the designer and start their role by performing the project construction. Then their colleagues who are on the operations and maintenance phase will start monitoring and maintain the structure performance along its life time. So around this project life cycle all the structure engineers are focusing on the same target that the structure is working safely along its service life according to the design code. The main objective of this book  to cover the methods that enable us to have a reliable structure along its life time during all the project phases and also presenting the up to date methods to  predict the  structure remaining life time from practical point of view.

The structure engineers have a famous  statement  called a “factor of safety” and some engineers thinking that they can satisfy and sleep well as their structure design has a factor of safety  by following a partial factors as in British Standard  or reduction factor as in American code for strength and another factors for load, so the reliability book for concrete structure (www.amazon.com/author/elreedyma )  will assist us to understand from where these factors  come from to provide us the sense about the problems that we may face in case of deviating  from these factors and to be sure that, this factor of safety will not guarantee to let us sleep peacefully until following some precaution to avoid the potential mistakes and errors.

Many researches are discussing the reliability analysis which provides the same meaning as calculation of the structure probability of failure and this calculation depends mainly on the statistics and theory of probability.

The book dedicated a whole chapter is discussing all the statistics methods,  tools and probability theory which are  used in structural and civil engineering field from practical point of view and away from complicated approach that bother us and don’t benefit us in a real practical life. It is worth to mention that, there is an increase in researches about structure reliability as we have a lot of data worldwide from which we can calculate the concrete structure reliability.

Due to the fast development of communication, any engineer can work on any project worldwide so one will  find that some  countries follow ACI code and the another countries follow British standard, in addition to Eurocode and another local code for different countries. Hence, it is usually raise a question in mind what is the best code or standard to follow, I try to answer this question on the reliability book..    

You can find that the code and standard should be specific for each country but in some specific projects which financing through international assistance. As the country which provides the financial usually requests to work by their code, so you can work by this code but should considering the different conditions surrounding the structure. The best code which comes from the country itself depends on the country economics, society behavior, laws that govern the country. Therefore, the design factors should be extracted from the country statistics of loads and resistance and the way of obtaining these factors will be discussed in detail in this book to be a practical guide to differentiate between different code and standard and assist the structure engineers to understand the philosophy of every code and standard that can help them to work in any international codes and standard around the world.

For the mature structure, there is a change in concrete structure resistance capacity with time depending on the surrounding environmental condition and also the loads that affecting the structure along its life time so all these factors should be considered  to assess the old structure and calculate its probability of failure.

The effect of the steel bars corrosion on the structure’s probability of failure will be discussed for different concrete members you can see the book in http://www.amaazon.com/author/elreedyma. By going through the methods of reliability assessment will present also the precaution to be considered to have a design for durable concrete structure.

The column is considered the most critical member in the building as it affects the structure probability of failure, so will concentrated about it and considering the effect of corrosion on the column probability of failure and the precautions and guide for column design to follow to obtain a durable concrete structure.

The book provides a guidelines and tools to evaluate the existing concrete structure by professional way and also assess the new structures.  So  all the available methods and test that enable us to evaluate the structure and focusing on the visual inspection technique, nondestructive testing for concrete strength and also corrosion test to know the status of the corrosion in the steel reinforcement.

So It is helpful for junior and senior engineers who are working in any phase of concrete structure projects from the design until the maintenance phase by increasing the sense of the structure behavior and the feeling about the codes and standards factors, and the allowable limits in the construction phase and its effect on the concrete structure probability of failure and provide the practical way to evaluate and predict the remaining service life of the existing buildings. We have a webinars about it for register. http://www.elreedyman.com

Offshore structure Careers and Challenges

When a structural engineer starts work on offshore structure design, construction
or maintenance, the offshore structure may appear to be a black box to him. Most
engineering faculties, especially those in structural or civil engineering, focus on
the design of residential, administrative, hospital and other domestic buildings
from concrete or steel, while other faculty focus on harbor design.
The design of offshore structure platforms is a combination of steel structure design methods and loads applied in harbors, such as waves, current and other parameters. On the other hand, offshore platform design depends on technical practice, which depends on the experience of the engineering company itself.
While the construction of steel structures is familiar to the structural engineer, as anyone can observe construction of a new steel building, the construction and installation of an offshore structure platform are very rarely seen unless one has a direct role in the project, especially because the installation will be in the sea or ocean. There are far fewer offshore structures world-wide than there are steel structures for normal buildings on land, and the major design guidance for offshore structures lies in research and development, which is growing very fast to keep pace with development in the global oil and gas business. 

Therefore, all the major oil and gas exploration and production companies support and sponsor research to enhance the design and reliability of offshore structures, in order to improve revenues from their petroleum projects and their assets.
My online seminars (www.elreedyman.com) and my book aims (www.amazon.com/author/elreedyma) to cover the design, construction and maintenance of offshore platforms in detail, with comprehensive focus on the critical issues in design that
the designer usually faces. I try to provides the simplest design tools, based on the most popular codes (such as API and ISO) and the other technical standards and practices that are usually used in offshore structure design. 
In addition, it is important to focus on methods for controlling and reviewing the design
that most engineers will face in the review cycle, so this book covers the whole
range of the offshore structure engineer’s activities.

Mohamed A. El-Reedy, Ph.D.
elreedyma@elreedyman.com

my new website

YOU CAN VISIT MY NEW WEBSITE : www.elreedyman.com and there is alot of different seminars such as SACS , ONSHORE STRUCTURES AND OFFSHORE STRUCTURES 

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