Earthquake Resistant Reinforced Concrete Structures
The Method of Analysis and Design of Earthquake Resistant Reinforced Concrete Structures and Buildings with the Aim of Assessing their Service Reliability
Tech Area / Field
- PHY-STM/Structural Mechanics/Physics
3 Approved without Funding
K.S.Zavriev Institute of Structural Mechanics and Earthquake Engineering, Georgia, Tbilisi
- University of Thessaloniki, Greece, Thessaloniki\nHadjian Consultancy, USA, VA, Alexandria
Project summaryActuality of problem. The territory of Georgia as a part of seismic active region of the Caucasus is referred to the Mediterranean seismic zone. The information of seismic events on the territory of Georgia has been known from time immemorial. In historic past on the territory of Georgia and adjacent to it area occurred a number of large earthquakes, the general parameters of which were described in the catalog of earthquakes of the Caucasus, covering the period of two thousand years. For the past 50 years the mentioned region has been hit by large earthquakes with the intensity of 7-9 degrees. It is necessary to note particularly the earthquake in Spitak, 1988 (2500 lives were lost and earthquakes in Georgia of 1991, 1994, 1997, 2000 and 2002, which caused great fiscal damage to the economy of the country. The seismic hazard of the Caucasus region is indicated at least by the fact, that only in the area of Tbilisi there are 31 zones of possible earthquake focuses, along with two faults in the northern and southern parts of the city area.
The analysis of the above-mentioned devastating earthquakes shows that not only old houses, were damaged due to negligence of building code specifications but also the buildings where such seismic specifications were observed. Houses with bearing walls of natural or artificial stones of low quality and buildings with bearing reinforced concrete frame were subjected to significant destruction. It should be noted, that one of the reasons of destruction reveals inadequacy of analytical model to real picture of work of RC columns during the realization of gravitation mechanism of collapse.
Investigation of peculiarities of real deformation of structures under seismic effect and their consideration under analysis and design is one of the most actual problems of science of seismic resistance. The change of mechanical characteristics of materials, cyclic character and sign-variability of effects, which change character of crack formation and limit states, lead to progressive reduction of stiffness of elements and to change of analytic scheme of buildings, on the whole, influences significantly the deformation of RC structures of buildings under seismic effect.
In spite of the increased interest to the above mentioned problem and considerable amount of investigations carried out in ERD centres of different countries of the world, it has not been studied thoroughly enough. The complex assessment of reliability and stability of RC buildings with consideration of spatial work of System, nonlinear deformations and regional character of seismic effect so far has been absent. Proceeding from this, the recommended by the project the overall evaluation of RC buildings behaviour and constructions under strong earthquake effects using numerical simulation on the basis of deformation method of analysis, considering all states right up to the collapse and ensuring high level of service reliability both of the building on the whole and resisting elements is a highly actual problem of the theory and practice of earthquake engineering.
The State in the scope of investigations. The acquaintance with the present state of investigation of earthquake resistant buildings shows that in practice of ERD analytical and numerical methods of specifying seismic response considering nonlinear deformation of structures have been successfully used. Discrete and discrete-continual two-dimensional design models are widely employed with the aim of mathematical simulation of RC buildings and their elements. The appropriate behaviour of RC structures taking into account the actual work of materials under sign-variable loads are investigated both experimentally and using the methods of nonlinear mechanics.
Due to the fact that mathematical models of collapse mechanism under complex loading have not been thoroughly elaborated the capacity of RC structures to deform at nonlinear stage under seismic effect are taken into consideration in building codes of different countries indirectly by means of empirical coefficient, without differentiation of responsibility and consideration of service life of buildings on the basis of spectral analysis of elastic systems.
The difficulty of the solution to the task of the evaluation of seismic resistance is stipulated by the lack of sufficient statistical information (data) about possible seismic effect on a given site by the change of material properties, statical schemes and dynamic features of building under the condition of non-stationary random effects due to the development of big nonlinear deformation and significant damages at the stage, prior to the collapse of the system.
The conducted survey gives grounds to consider that principles on which analytical models and structural schemes have been based up to now, do not completely reveal the real physical picture of processes developed both in grounds of foundations and in building under intensive seismic effect. Proceeding from this, the development of new principles and methods of analysis and design of seismic resistant RC structures and buildings based on their behaviour during strong earthquakes is urgent.
The aim of project. On the basis of modern achievements in structural mechanics and theory of earthquake resistance to elaborate the method of analysis and design of RC buildings and structures subjected to seismic effect in order to achieve greater conformity of design premises with their real behaviour during earthquake using deformation parameters, limit surfaces of RC elements bearing capacity reflecting cinematically allowable plastic deformations corresponding to various load combinations.
Ensuring in earthquake engineering wide use of the updated (improved) method of analysis and design of buildings on the basis of technical and standard (code) documentation created by the project.
Influence of the project on progress in scope of investigation. The present project creates scientific-theoretical and methodological basis for further improvement of design method for new rational structural solutions of buildings corresponding to requirements of high service reliability and durability under seismic effects.
Competency. Co-authors have elaborated a number of interesting, original and significant techniques for the analysis of RC elements and buildings subjected to static and dynamic effects which were successfully used in Georgia and abroad at different periods while designing RC structures and buildings with various functional purposes.
The authors of the project are licensed experts on the problems of reliability assessment of both existing buildings and those which are still under construction. Competency of the participants has not been repeatedly confirmed at international symposiums and conferences on earthquake resistance, composite materials. Some of the authors of the project participated in the work of international conferences at different time.
The authors of the project published a lot of scientific papers regarding the given topic.
Expected results. The project belongs to the sphere of applied investigations as a result of which the following significant data will be obtained:
1. Define more precisely reduction coefficient (or behaviour) for design of RC buildings in seismic regions.
2. Dependence of seismic stability upon the value of plastic deformations of RC structures under strong seismic effects.
3. Hysteresis model for the evaluation of damages and degradation (decrease) of RC elements’ strength under low-cycle loading.
4. Method for the evaluation of RC buildings’ reliability considering nonlinear character of deformation and seismic regime of the area.
5. New principles for optimal reinforcing of RC structures with the aim of prevention of their brittle collapse.
The scope of application. The results of the project will serve as a basis of new specifications of ERD, will be used for the evaluation of seismic reliability of experimental and existing buildings, for their reconstruction, will promote fur their development and application of nonlinear analysis of RC structures under the conditions of strong seismic effect and permit to reveal rational structural schemes of buildings, expedient to use in specific seismic prone regions.
Realization of aims and tasks of ISTC. The Georgian scientists and experts will be mainly involved in the project. They used to carry out military orders of the Ministry of Defense of the USSR. Support of the project will allow to direct scientific potential of these scientists for the elaboration of both applied and fundamental tasks, thus contributing to the solution of one of the most basic problems, also will promote the association of scientists connected with construction into international scientific society. The aims and tasks of the project completely conform to the national program of 1998-2005 on seismic protection of Georgia, as well as foreign countries concerned about the problem of struggle against seismic hazard both of natural and artificial origin.
Scope of activity. The project includes the conduction of research and experimental work on the following tasks:
1. Systematization and specification of deformation characteristics of employed concrete and reinforcement of various classes within the range of strength effect and RC members under various kinds of complex loading.
2. Definition of the role of plastic deformations in loss of stability of complex strained RC structures under seismic effects.
3. Definition of RC buildings’ reliability taking into consideration nonlinear character of deformation and seismic regime of the area (site).
4. Optimization of reinforcement ensuring plastic deformation and stability of buildings with the given degree of reliability.
5. Revision of a number of provisions of acting codes on design in seismic region with the following introduction of improvement in the part of design provisions RC structures design.
The role of foreign collaborators. Corresponding to the scope of activity within framework of the submitted project, the role of foreign collaborators (according to their abilities) can be rather essential and prolific and it is revealed in the following:
- Submission of comments to technical reports (quarter, annual, total etc.) presented by the participants of the project in ISTC;
- Cross-examination of the results obtained during realization of the project;
- Participation in technical verification of the project activity executed by ISTC experts;
- Conducting of joint symposiums and workshops;
Technical approach. Technical approach implies execution of work on research and programming thus including:
- Selection, analysis, systematization and specification of existing and new obtained results of theoretical and experimental investigations of RC elements under various types of strained states (systematization and specification of these data are executed using method of statistic theory).
- Conduction of experiments with the aim of extension of bank of experimental data while testing under central compression and tension, bending, compression, torsion, torsion with bending, shear of concrete and RC elements of construction, as well as steel reinforcement. On the basis of their analysis and generalizations there were created analytical relationships “s-e’’ (stress-strain), “M–q” (moment-curvature) and “F–u” (shearing force - displacement) with acceptable precision of approximating data of experiment.
- Construction of physically reliable conceptual analytical models, describing the strained states of normal and sloping cross-sections, suitable for the definition of curvatures, displacements and angles of rotation, permitting regulation of stiffness, moments and shearing forces taking into consideration redistribution of inner and outer force due to the development of plastic deformations of concrete and reinforcement.
- Elaboration of algorithm and program of original analytical approach, which on the basis of a series of computer experiments permits to find optimal solution, effective cross-sections of bearing elements of structures, most profitable and ensure reliable work due to rational reinforcement.
- Plotting analytical diagrams of deformation of shearing of structural joints under monotonous statical and low-cycle sign-variable loading taking into consideration degradation of stiffness and strength.
- Definition of parameters of analytical seismic effect for the territory of Tbilisi area.
- Elaboration of algorithms and programs of design of RC buildings under real seismic effect taking into consideration nonlinear deformation of structural members.
Methodology. On the basis of formed in project problem and separate tasks for its solution there has been offered methodology, based on the following:
- Using as analytical parameters standard relations “s-e’’ (stress-strain), “M–q” (moment-curvature) for concrete and steel, and “F–u” (shearing force - displacement) for structural joints;
- Deformation criterion of bearing capacity of RC structures of buildings;
- Combination of super-element modification of finite element method with the idea of plastic hinges;
- Elaboration of the method of definition of the criterion of stability using limit surfaces of deformation of RC elements, subjected to complex loading;
- Definition of parameters of damages of structural elements, which are the function of cumulative cyclic plastic deformation under shear;
- Development of reliability model for structural systems taking into consideration specific features of elements and regional character of seismic effect;
- Definition of analytical parameters of seismic response of RC buildings using the method of statistical tests;
- Definition of parameters of optimal reinforcement of seismic resistant RC structures.
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.