 # Exploration of classroom teaching of reinforced concrete structural design principles

Principles of reinforced concrete structure design is an important major course for civil engineering majors, which mainly studies some mechanical properties, design methods, construction requirements and damage characteristics of typical members such as beams, slabs and columns, etc. Its task is to teach students the force properties, calculation principles and design methods of concrete structural members, and to lay the foundation for concrete structure design.

However, the design principles of reinforced concrete structures are characterized by many concepts, contents and symbols, coupled with the binding nature of codes, the empirical nature of formulas and the multi-solution nature of problems, which bring certain difficulties to students’ learning. In order to change this situation and improve the teaching effect, this paper combines the author’s years of teaching experience and makes some discussions from the perspective of classroom teaching.

## 1 Course characteristics

### (1) The course is very comprehensive, requiring students to have a solid basic knowledge of mathematics and mechanics.

The teaching content of reinforced concrete structural design principles starts from the mechanical properties of materials, and then studies the load-bearing properties and damage characteristics of basic members. Since concrete is formed by mixing cement, aggregates and water by setting and hardening, the concrete material is discrete, the mechanical properties are more complex and the corresponding material parameters are uncertain. In order to obtain the strength design values of concrete materials and their components, students need to master the mathematical knowledge related to probability theory and mathematical statistics and understand the limit state design method. In the process of analyzing the basic forces of the members, although the concrete material is not homogeneous and non-isotropic, the method of analyzing the problems of material mechanics is still used. Therefore, students need to have a solid foundation in mathematics and mechanics.

### (2) The combination of theory and engineering practice requires the cultivation of students’ engineering quality.

The basic principles of reinforced concrete structure is a subject that transforms from theory to engineering practice, and it is also the first time that students are exposed to a course with strong theory and engineering practice. During the teaching process, students often have the confusion of why the result of problem solving is not the only one. Therefore, students need to be made to understand that there are many parameters that affect a practical project. Under the prerequisite of meeting the Code for Design of Reinforced Concrete Structures, the selection of many parameters is somewhat subjective and empirical. Therefore, it is necessary to establish students’ engineering concept and cultivate their engineering quality in the course teaching.

### (3) involves a lot of content and wide knowledge coverage.

The content of basic principles of reinforced concrete mainly includes four parts: material properties, load-bearing properties of members, theoretical analysis, and design calculation of members. In the material properties, not only to master the mechanical properties of concrete, but also to master its non-mechanical properties, such as shrinkage and creep. The load-bearing properties of the members are affected by the discrete and brittle characteristics of the concrete, the ratio of the 2 materials of reinforcement and concrete, and the loading method of the load. By analyzing the load-bearing properties of the members, a reasonable mechanical calculation model is established, theoretical analysis is performed, and the design calculation theory of the members is deduced. And compare with the experimental results, and consider the safety and comfort of the project, and finally implement into the engineering practice. Therefore, the basic principle of reinforced concrete involves a lot of contents and a complicated system.

## 2 Classroom teaching exploration

### (1) Adopt the case method to sort out the content of concrete structural design principles.

The case teaching method is characterized by students’ use and discussion of cases to help students master the method of analyzing and reflecting on practical problems, with emphasis on improving students’ level of understanding and problem-solving ability. Its teaching method is based on the needs of teaching objectives, taking cases as basic materials, bringing students into specific event scenarios, and then identifying problems, analyzing them and solving them, and its most fundamental content is the selection and use of cases, which is the key to distinguish case teaching from other methods. Its characteristics are: authenticity, typicality, normality, inspiration and practicality.

### (2) Establish the correct design concept and cultivate engineering literacy.

At the beginning of the course on basic principles of reinforced concrete structure design, the students’ concept is still that there is only one exact theoretical solution to any problem, and they will only answer problems with strictly given conditions, but when the conditions are not completely set, students often cannot start. When faced with the basic principles of reinforced concrete structures, students will always try to find the uniqueness and exactness of the design results. This requires the instructor to answer the right design concepts. Design is from the unknown to the known, including the collection of information, comparison of solutions, calculation and analysis, evaluation of results, and iterative revision. In the process of data collection, the properties of the materials used can only be estimated; in the analysis of structural solutions, only an approximate analysis of the structure can be performed; the external loads applied on the building structures are not accurately known. Therefore, design is also a comprehensive and creative work, and design is not a one-time success. It is a process of seeking the best solution. The discrete nature of material properties and the uncertainty of external loads, among other factors, make the design result not a unique answer, but a good or bad one. By explaining the design concept, students can understand the difference between designing an engineering project and doing a mathematical problem, so as to develop their engineering literacy.

### (3) Systematic introduction of research ideas to help students understand the scientific nature of experimental results.

Compared with the mechanics of materials course, the basic theory of reinforced concrete structures is based on a large amount of experimental data curve fitting, and the design and calculation contents of members are based on experimental and engineering practice, so there are many empirical coefficients and empirical formulas. This may make students doubt the scientific nature of this subject and make it difficult for them to find a way to learn this subject. Therefore, there is a need for teachers to systematically introduce theoretical approaches to design based on probability theory. For an unknown field, the main idea of problem solving is divided into the following steps: ① firstly, through a large number of experiments, observe the experimental phenomena and find the main influencing factors of the problem; ② establish a reasonable mathematical mechanics calculation model; ③ establish the corresponding design calculation method based on the relevant mechanics theory; ④ compare and analyze the theoretical results with the experimental results carefully to find the reasons for the difference in results; ⑤ take the (5) to take the actual needs of the project as the goal and make corrections to the design calculation method. Then the design calculation theory of a member (such as torsional member) is used as an example to explain the design method. This makes it easy for students to understand the relevant structural requirements in the code, as well as the upper and lower limits of design parameters (such as minimum and maximum reinforcement rates).

### (4) Focus on summarization to enhance the logic of teaching

Many symbols are a feature of the basic principles of reinforced concrete structures, and students often confuse the symbols in the learning process. Therefore, teachers need to explain to students the laws of symbols in the teaching process. The subscript of the symbol is usually the beginning letter of the English word. For example: εe, εp, εsh, εcr are elastic strain, plastic strain, shrinkage strain and creep in that order. In order to facilitate the students to remember these symbols well, the English words of the specialized terms are given in the textbook. In addition, the textbook has many prescriptive things in the construction part, and the content is fragmented and lacks logic; sometimes, a provision, in different places, appears several times.

## 3 Conclusion

Reinforced concrete structure is a course closely related to theory and practice, with strong engineering concept and systematic scientific theory. During the teaching process, the actual needs of engineering should be the goal, the scientific research methods should be introduced systematically, and the logic of reinforced concrete structure knowledge should be enhanced by summarizing the regular knowledge inductively. Ultimately, the effect of classroom teaching is improved.