1、 附 录 Seismology Civil Engineering SEISMIC RESISTANT REINFORCED CONCRETE STRUCTURES-DESIGN PRINCIPLES SUMMARY:Earthquakes cause considerable economic losses.It is possible to minimize the economic loses by proper seismic design.In this paper basic principles for seismic design are summarized.There ar
2、e three basic requirements to be satisfied；(a)strength,(b)ductility and(c)stiffness.In the paper these are briefly discussed. In the second part of the paper the author summarizes his views on the damages observed in the past earthquakes.He concludes that most of the damages have been due to,(a)bad
3、configuration,(b)inadequate detailing and(c)inadequate supervision.In the paper these are discussed,pointing out the common mistakes made and damages observed as a result of these mistakes.In the last part of the paper some simple recommendations are made for producing seismic resistant reinforced c
4、oncrete structures,emphasizing on detailing and proportioning. Key Words:Seismicresistance,reinforced concrete. 1.INTRODUCTION Every year more than 300 000 earthquakes occur on the earth.Many of these are of small intensity and do not cause any damage to our structures.However,earthquakes of larger
5、intensity in the vicinity of populated areas cause considerable damage and loss of life.It is estimated that on the average 15000 people have been killed each year throughout the world because of earthquakes. Since ancient times mankind has sought ways and means of minimizing the damage caused by ea
6、rthquakes.The great masters of the art of building have been able to build structures which have withstood many severe earthquakes for centuries.Magnificent mosques and bridges in the Middle East built by our ancestors are still in service,These masters did not know seismic analysis,but were able to
7、 evaluate past experience with their excellent engineering intuition and judgement.Mosques,bridges and schools(Medrese)built by Sinan in Istanbul and Edirne are not only beautiful,but are also engineering masterpieces. Today we have great advantages as compared to our ancestors.We have more experien
8、ce,we have highly developed analytical tools and considerable experimental data.It should also be noted that computers enable us to consider more variables and several alternatives in the analysis. The main objective of this paper is to lay down some basic principles for producing earthquake resista
9、nt reinforced concrete structures.These are simple principles and easy to apply.They have been developed in the light of analytical and experimental research done and on observations made from past earthquakes. 2.BASIC PHILOSOPHY AND REQUIREMENTS Design principles cannot be laid down unless there is
10、 a well defined design philosophy.The design philosophy generally accepted is summarized below: -Buildings should suffer no structural damage in minor, frequent earthquakes. Normally there should be no nonstructural damage either. - Buildings should suffer none of minor structural damage (repairable
11、) in occasional moderate earthquakes. - Buildings should not collapse in rarely occurring major earthquakes. During such earthquakes structures are not expected to remain in the elastic range. Yielding of reinforcing stellweill lead to plastic hinges at critical sections. The general design philosop
12、hy will not have much practical use unless design requirements are developed in parallel with this philosophy.The author believes that the design requirements can be summarized in three groups. a.Strength requirements b.Ductility requirements c.Stiffness requirements(or drift control). These three r
13、equirements will be briefly discussed in the following paragraphs. 2.1.Strength Requirements Members in the structure should have adequate strength to carry the design loads safely.Since the designers are well acquainted with this requirement,it will not be discussed in detail.However,it should be p
14、ointed out that the designer should avoid brittle type of failure,by making a capacity design(1).The basic principles in capacity design are illustrated for a beam in Figure 1.If the design shear is computed by placing the ultimate moment capacities at each end of the beam,the designer can make sure
15、 that ductile flexural failure will take place prior to shear failure. 2.2.Ductility Requirements In general it is not economical to design R/C structures to remain elastic during a major earthquake.It has been demonstrated that structures designed for horizontal loads recommended in the codes can o
16、nly survive strong earthquakes if they can have the ability to dissipate considerable amount of energy.The energy dissipation is provided mainly by large rotations at plastic hinges.The energy dissipation by inelastic deformations requires the members of the structure and their connections to posses
17、s adequateductility”.Ductility is the ability to dissipate a significant amount of energy through inelastic action under large amplitude deformations,without substantial reduction of strength. Adequate ductility can be accomplished by specifying minimum requirements and by proper detailing(2). 2.3.S
18、tiffness Requirements In designing a building for gravity loads,the designer should consider serviceability in addition to ultimate strength.In seismic design,drift limitations imposed might be considered to be some kind of a serviceability requirement.However,the drift limitation in seismic design
19、is more important than the serviceability requirement. The limiting drift is usually expressed as the ratio of the relative storey displacement to the storey height(interstorey drift).Excessive interstorey drift leads to considerable damage in nonstructural elements.In many cases the cost of replaci
20、ng or repairing of such elements is very high.Excessiveinterstorey drift can also lead to very large second order moments(P-effect)which can endanger the safety and stability of the structure.Thereforeinterstorey drift control is considered to be one of the most important requirements in seismic des
21、ign.The recent Mexico and Chile earthquakes have demonstrated the importance of this requirement(1).In Turkish Code the interstorey drift is limited to 0.0025h,where h is the storey height. 3.LESSONS LEARNED FROM PAST EARTHQUAKES Our knowledge in seismic design has developed has developed as a resul
22、t of analytical and experimental research and experience gained from past earthquakes.The author believes that lessons learned from past earthquakes have been the most important source among all others,because earthquakes perform the most realistic laboratory tests on the buildings. The author has r
23、eevaluated the damages observed in earthquakes during the past 30 years in Turkey.This reevaluation has revealed that more than 90%of the damages can be attributed to one of the following causes or combinations of these: a.Mistakes made in choosing the building configuration(general configuration or
24、 the structural system chosen). b.Inadequatedetaling and proportioning or errors made in detailing. c.Poor construction quality caused by inadequate supervision. It is interesting to note that causes of damage grouped into the above three categories seem to apply to earthquake damages observed in ot
25、her countries also.These three causes will be discussed briefly in the paragraphs to follow. 3.1.Building Configuration Seismic resistance should be initiated at the architectural design stage.If the general configuration chosen by the architect is wrong,it is very difficult and expensive for the st
26、ructural engineer to make the building seismic resistant.As a general principle the floor plan should be as symmetrical as possible.The length of wings(T,L,.cross shaped buildings)causing re-entrant corners should not be large.If the length of the wings is not short,then these should be separated fr
27、om the main building by an expansion Joint.Symmetry about the elevational axis is not as significant as the plan symmetry.However,abrupt changes in building plan along the height of the building are not desirable from the seismic resistance point of view.Setbacks are common vertical irregularities i
28、n building geometry.Setbacks cause discontinuities and abrupt changes in strength and stiffness.The seriousness of the setback effect depends on the relative proportions and absolute size of separate parts of the building. In general the designer should try to make changes in strength and stiffness
29、along the building height as small as possible. As far as the structural system is concerned,one can set out some basic rules for better seismic resistance.Before setting out these rules,it would be appropriate to remind the engineers that nonstructural infill walls will influence the frame behaviour significantly unless separated from the frame. Sudden changes in stiffness along the height of the building should be avoided.If the stiffness of one storey is significantly smaller than the others(soft
