Reinforced Concrete Structure Basic Earthquake Resistance ThoughtReinforced Concrete Structure Basic Earthquake Resistance ThoughtReinforced Concrete Structure Basic Earthquake Resistance Thought
钢筋混凝土结构基抗震思想
The structure mainly depends on the ductility to resist under the big earthquake function the inelastic distortion therefore under the earthquake function the structure ductility and the structure intensity has the equally important significance The seismic force stepdown ratio reduced to the defended intensity earthquake function whole had in fact decided the structure submitted the standard and to the structure ductility demand size At present ability design law generally has accepted for the various countries traffic capacity design law forms reasonably consumes energy the mechanism causes the plastic hinge to appear the spot which easy to guarantee in the ductility Guarantees the structure in not to achieve needs in front of the ductility as for does not have the cutting expiration And guarantees the ductility through the detail structure measure full display
The earthquake disaster is one of serious natural disasters which the humanity faces The earthquake has the burst characteristics characteristic until now the predictability very was still low The strong earthquake often creates the person and the property heavy loss Our country is the earthquake to send the country needs to consider the earthquake resistance fortification the vast in territory therefore the research structure earthquake resistance performance has the full necessity in our country
Our country's modern earthquake resistance design theory is starts from the 50's develops in under the international earthquake resistance theory impetus and has formed own characteristic gradually In accumulated the suitable research results and in the experience foundation has formulated 74 one after another 78 89 standard and the new revision 2001 earthquake resistance design standard (GB5001122001) presses in 2001 the standard design the building earthquake resistance ability 89 standards to be possible to enhance 10~15 its technical content achieves the international advanced level But as a result of the state economy strength limit the security margin of safety establishment is still lower than US and so on the developed country
Must want better to carry out the standard to have to be clear about the earthquake resistance standard formulation the basic thought is clear about the earthquake resistance design the basic principle Below does emphatically from following several aspects elaborated
1 under the earthquake function pursues the structure the intensity not to be possible constantly to take the structure ductility is the extremely important
earthquake divides into slightly shakes shakes with the big quake Socalled slightly shakes refers often meets the earthquake 50 years appear the probability probably is 63 the return period is 50 years Shakes is refers to the probability which 50 years appear is approximately 10 the return period is 475 years But the big quake refers meets the earthquake rarely 50 years appear the probability is 2~3 the return period is 1641~2475 years Regarding fortuitous and the random very big earthquake load needs to want to cause the structural strength certainly to be bigger than the structure to respond that is nearly not impossible moreover is extremely uneconomical Is withstood the sacrifice the society ability and the economical restriction factor we only can embark from the probability angle enable the structure normally to play the role safely under certain probability guarantee This had decided the earthquake resistance design basic principle slightly shakes does not go bad shakes may repair big quake which namely usually said in our country not but actually
In slightly shakes under the function the request structure is not damaged or does not have to repair still may continue to use From the structure earthquake resistance analysis angle is requests the structure in slightly to shake under the function to maintain the accurate elastic reaction condition but does not enter causes the building interrupt to use and to have the inelasticity reactive state which the nonstructural unit destroys Simultaneously the structure lateral deformation should control in the reasonable limit scope the goal is enable the structure to have the enough antiside force rigidity
Shakes is probably equal to ours defended intensity earthquake when shook the function the bitter experience to the structure may have certain degree damage or still could not continue after the repair after the repair to use From the economical angle the maintenance cost cannot too be high
To had the probability minimum met the big quake rarely (big quake intensity to be approximately higher than defended intensity once about)Requests to work as structure when bitter experience big quake function should not collapse the serious destruction which or occur endangers life
This kind of earthquake resistance fortification goal is extremely economical reasonable Because the earthquake occurrence too is accidental supposing we pursue the structure the intensity to guarantee constantly shakes even is under the big quake function the structure does not go bad this will be able to cause the enormous quantity the material in the major part time even will all be at in the entire average life cannot play the role fully the condition will do this will be wise
Under the above principle of design instruction the request structure is in this kind of kind of condition When slightly shakes approaches should guarantee all structural unit when the resistance earthquake action has the enough intensity causes its to be at the elastic condition basically And slightly shakes under the function through the checking calculation the elastic displacement to guarantee together the structure does not go bad Is at this stage the structural unit not to be able to have the obvious nonlinear distortion also does not need to need to take the special structure measure Shakes under the function in structure certain essential spots surpass the elastic strength enters submits occurs distorts greatly achieved the nonlinear stage by now we on proposed specially the ductility request (the ductility refers when the earthquake forces the structure has the big nonlinear distortion the structure still can maintain its initial intensity ability was the structure surpasses the elastic stage distortion ability it is the structure earthquake resistance ability strong and the weak symbol It and depends on including withstanding enormous distortion ability stagnates the characteristic absorbed energy ability it is resists earthquakes middle the design an extremely important characteristic)Middle shakes approaches because the structure has the inelastic characteristic certain essential spots surpass its ball
The natural intensity enters the plastic state Because it has certain ductility its nonlinearity can undertake the plastic deformation enables it to consume and to absorb the earthquake energy in the distortion The price is possibly causes the wide crack the concrete epidermis to get up the shell falls off possibly has certain remaining distortion but as for does not cause the safe expiration achieved shakes the defended goal which may repair Is at this stage the structure can set the corresponding request to the ductility but the ductility must depend on the careful design the detail structure measure to guarantee When the big quake approaches the structure nonlinearity distorts extremely in a big way also possibly has the destruction which cannot be repaired Is at this stage the structure to need through to calculate its elastoplasticity distortion to guarantee the structure does not send the collapse
Therefore usually we only need according to slightly to shake the function effect and other load effect basic combination checking calculation component section earthquake resistance supporting capacity and structure elastic deformation But shakes the function effect to need the structure to depend on certain plastic deformation ability (ie ductility) to resist Therefore the structure ductility to the construction earthquake resistance is extremely important
2 seismic force stepdown ratio size has decided the design seismic force value size thus has decided to the ductility request size
States from on uses in the supporting capacity design the earthquake function being possible to take slightly shakes the level when a bigger earthquake approaches then depends on the structure the ductility to resist Therefore we do not use the defended intensity earthquake action to carry on the structure supporting capacity design but needs to reduce the defended intensity seismic force a coefficient is called the seismic force stepdown ratio
The seismic force stepdown ratio obtains in a big way the design earthquake function obtains slightly The seismic force stepdown ratio obtains slightly the design earthquake function obtains in a big way Under the identical defended intensity the seismic force stepdown ratio obtains in a big way the earthquake function is smaller then presses the structure which this small earthquake function designs to submit the standard to be lower meant structure the inelasticity which forms under the corresponding intense degree earthquake distorts is bigger this request structure has the big ductility to guarantee it big inelasticity distorts realization thus proposed to the ductility the request is higher This ductility rank structure namely for low design seismic force value 2 high ductility requests high ductility rank structure The seismic force stepdown ratio obtains
Smaller the earthquake function is bigger then presses the structure which this big earthquake function designs to submit the standard to be higher meant structure the inelasticity which forms under the corresponding intense degree earthquake distorts is smaller this only needs to request the structure to have the small ductility to guarantee it small inelasticity distorts realization thus proposed to the ductility the request is lower This ductility rank structure namely for high design seismic force value 2 low ductility requests low ductility rank structure Likewise under the identical defended intensity the seismic force stepdown ratio takes for medium earthquake function also for medium thus proposed to the ductility request also for medium This ductility rank structure namely for medium design seismic force value 2 medium ductility requests medium ductility rank structure Thus the seismic force stepdown ratio size has in fact decided the design seismic force value size thus has decided to the ductility request size
The Chinese standard stipulated reduces the defended intensity earthquake function 3 times to carry on approximately the supporting capacity design namely defended intensity earthquake function response spectrum dividing earthquake supporting capacity stepdown ratio 3 but obtains the response spectrum which the design uses And the Chinese standard decrease proposed according to the defended intensity to the structure ductility from high to low request concrete is indicated with the earthquake resistance rank altogether divides into the level two levels of three level of four level of four ranks
The preliminary impression is China's seismic force stepdown ratio value is somewhat low This as if explained China's seismic force value is high thus does not need to set the high ductility request to the structure Be in effect it is not so after has contrasted Chinese and the Western country defended earthquake function response spectrum curve we discovered in the long period scope the West must be higher than China in other words China reduces 3 times under the low response spectrum level reduces 5 times with the West under the high response spectrum level even the more after function level is the difference not many this explained China to the antiseismic structure should propose is equal is equal to 5 in the Western seismic force stepdown ratio even high scale high ductility request
3 ability design law has accepted generally for the various countries
Traffic capacity design law chooses the nature different main antilateral force component has in the big distortion situation in the earthquake function influence can form well consumes energy the mechanism
In order to cause the reinforced concrete structure causes at the earthquake in the dynamic response process displays the essential ductility must the traffic capacity design law cause the plastic deformation many to concentrate quite easily in to guarantee the good ductility performance or has on certain ductility ability component The ability design method concrete mentality has three steps
(1) first step chooses the plastic deformation organization which may accept Chooses the organization the displacement ductility to be supposed to depend on the plastic hinge place smallest nonlinearity rotation to achieve Once had designated the appropriate plastic deformation organization may determine the energy aerodynamic spot precisely Ability design law has two kind of different plans in the choice plastic deformation organization choice
One kind is the Liang articulation organization Its specific measures are artificial great scope increase column end anticurved ability causes besides the first floor base of cylinder various columns end under the strong earthquake function after in principle does not enter submits the condition namely does not appear the plastic hinge Because the column end in principle does not enter submits the curvature is small therefore to eliminates the first floor base of cylinder other various story posts end not to need to propose the strict axis presses compared to the control condition namely did not need certainly to have to leave in a big way the column end stressful condition control the small eccentric compression boundary condition still has certain distance ductility good greatly eccentric compression condition This kind of organization mainly depends on the Liang end to leave the articulation to come the diffusion earthquake energy
Another kind is the beam column articulation organization Its specific measures were only to a certain extent artificial increase the column anticurved ability therefore generally speaking column end although looks carefully relatively compared to with Liang strong but under strong and very strong earthquake function the column end still had the possibility to enter submits the Liang end appeared the plastic hinge the opportunity to be many early the plastic rotation was big The column end plastic hinge appears relatively late plastic rotation relative small So long as the paired columns axis presses the control is stricter than causes the column end not to appear the small eccentric compression and to big the small bias dividing line condition excessively near greatly eccentric compression situation again through the enhancement paired columns end plastic hinge area restraint may cause the not extremely harsh plastic rotation ability which the column end has needs (ductility ability) also does not send bruising This kind of organization mainly depends on the beam column to leave the articulation to come the diffusion earthquake energy together
Contrasts above two kind of plans the former in fact enhanced the column intensity strengthened the column elastic deformation ability Matches in the middle of the muscle in the reality vertical muscle amount used relative many stirrup amount used relative few The latter in fact sharpened the column plastic deformation ability matches in the middle of the muscle in the reality vertical muscle amount used relative few stirrup amount used relative many
The Chinese standard has chosen the second plan namely beam column articulation organization This is strong column weak Liang who we usually said In order to realize in ability design method strong column weak Liang organization our usual procedure is the paired columns section combination bending moment is multiplied by increases the coefficient Also may to match the muscle by the Liang end instead to figure out Liang Duanke actually to resist the bending moment namely really matches the bending moment to be multiplied by increases the coefficient the method to realize and with increases after the bending moment value to carry on the column end control section the supporting capacity design
(2) second step is must through artificial increase each kind of component antito cut ability causes it not to send under the strong earthquake function has not displayed in the structure ductility before appears the nonductility shearing failure This is which we usually said cuts weakly curved The usual procedure is increases the coefficient with the shearing force to increase the summer beam end the column end the shearing force wall end shearing force wall opening Lian Liang Duan as well as the beam column node place combination shearing force value and with increases after the shearing force design value to carry on is cut the control section control condition carries on the checking calculation and the design The specific measures also have two kinds
One kind is directly clockwise or the counterclockwise direction combination bending moment does a tour of duty to a cross Liang both sides section increases the coefficient again a vertical gravity load generation of tabular value which affects with Liang on together from the balance relations obtains the Liang end shear
Another kind is obtains a cross Liang both sides section along clockwise or the counterclockwise direction to match the bending moment according to the reality which the muscle can resist is multiplied by to it increases the coefficient again a vertical gravity load generation of tabular value which affects with Liang on together from the balance relations obtains the Liang end shear
(3) third step is through the corresponding structure measure guaranteed possibly appears the plastic rotation ability and the plasticity which the plastic hinge the spot has needs consumes energy ability Usually through the stirrup encryption the limit axis pressure compares and so on the measures to give the guarantee
The above three steps adopt the measure is the interdependence The second step measure is the first step measure realization premise and the safeguard Because only then the plastic hinge area did not send has cutting to expire ahead of time only then could have the beam column plastic hinge area plastic rotation The first step measure request is strict then third step may relative weak Otherwise the first step measure is loose then is strict to the third step request If because the column bending moment enhancement coefficient is very big big enough to can guarantee other column end all does not appear the plastic hinge besides the first floor then does not need the countershaft to press compared to with the restraint stirrup proposed the strict limit namely does not need to cause the column to be at the ductility good big bias condition and enable the column to have the very strong rotation ability This forms the Liang articulation organization But if controls the column the bending moment enhancement coefficient enable the Liang end to leave the articulation to compare the column end to leave the articulation many the rotation is early big the column end leaves the articulation then relative few the rotation is late small This is the beam column articulation organization This time needs to press to the axis of a cylinder compared to proposed certain limit causes the column end the stressful condition to be in the big bias simultaneously strengthens to the plastic hinge area stirrup restraint enhances the plastic hinge rotation ability like this sharpened the column end ductility ability causes it in under the plastic rotation which needs as for not to crush Therefore the column bending moment increases the coefficient to be bigger the countershaft presses the limit and the stirrup restraint request is lower than The bending moment increases the coefficient to be smaller the countershaft presses the limit and the stirrup restraint request is higher than
4 several kind of basic earthquake resistance system performance
(1) portal frame construction system According to the above ability design mentality through the reasonable design may make the portal frame construction the ductility frame The ductility frame under the big quake function after appears Liang Jiao first appears the column articulation such one kind to consume energy the organization diffusion massive earthquake energy the structure can withstand certain lateral deformation Therefore the pure portal frame construction is one kind of earthquake resistance performance very good structure But we simultaneously also saw is small as a result of the pure frame antiside rigidity the side which creates moves the value quite to be big therefore the constructive height is not suitable too high Nonstructural unit for instance infilled wall under earthquake function also possibly appears the crack and the destruction Between the frame and the infilled wall rigid joint creates the rigidity increases the effect also possibly to create designs on had not considered increases side force If is half high infilled wall but also can cause to form the short stump the rigidity increases the withstanding very big shearing force creates the pillar the shearing failure
(2) shearing force wall structure system The shearing force wall structure supporting capacity and the rigidity very are all big the side moves distorts slightly therefore its use scope may be higher than the pure portal frame construction Is suitable also may use in the shearing force wall as a whole in the portal frame construction component nonlinear earthquake resistance performance principle also may design into the shearing force wall the ductility shearing force wall also may come the diffusion earthquake energy by the stable way But in shearing force wall no matter is the wall extremity or Lian Liang its section characteristic is short and is high this kind of component is quite sensitive to the detrusion easy to appear the crack easy to appear the brittle shearing failure Therefore must carry on the careful reasonable design only then can enable the shearing force wall to have the good earthquake resistance performance and the good ductility ability If the shearing force wall destruction shape cuts steps compared to has the very big relations to cuts steps compared to the very small low wall the shearing failure shape primarily plastic deformation ability is very bad therefore should avoid in the antiseismic structure using the low wall Regarding the bracket wall energy aerodynamic mainly is leaves the articulation through the wall bottom to carry on But regarding the joint extremity wall passes through designs the hole position reasonably enable its energy aerodynamic mechanism with to have the strong column weak Liang's Liang articulation organization to be similar forms strong wall weak Liang namely LianLiang the Liang end leaves the articulation the wall bottom leaves the articulation but the wall other places do not appear the plastic hinge Otherwise if Lian Liang Qiangyu wall extremity then can appear with the column articulation organization same level distortion organization Regarding the long bracket wall usually through artificial opens the hole to cause it to turn the joint extremity wall because the bracket wall takes the statically determinate structure once has a section destruction to expire can cause the structure expiration and the collapse but unites the extremity wall to be possible to design Cheng Qiangqiang weak Liang leaves the articulation number to be many consumes energy in a big way Cuts weakly with frame design is curved same Lian Liang Jiqiang the extremity also needs to pass strongly cuts weakly curved enhances its anticuts the bearing capacity the postpone shearing failure thus improves its ductility But its own section characteristic influence the component still cannot guarantee does not have the shearing failure specially Lian Liang in the ordinary circumstances ordinary matches when muscle Lian Liang Hennan realizes the high ductility the design must specially take the measure to change its performance
(3) frame 2 shearing force wall structure system Is the frame and the shearing force wall unifies in together together resists vertical and the horizontal load one kind of system it uses the shearing force wall the high antilateral force rigidity and the supporting capacity the atonement portal frame construction antiside rigidity is bad distortion big weakness As a result of the shearing force wall and the frame joint operation improved the pure frame and the pure shear wall distortion performance always distorts reduces the level distorts reduces moreover about tends to evenly about the frame various story posts stress quite is also even Moreover under the earthquake function the shearing force wall undertook the majority of shearing force the frame has only undertaken very small part of shearing force usually all was the shearing force wall submits first after the shearing force wall will submit has the endogenic force redistribution the frame assignment shearing force can increase if the earthquake function continued to increase the portal frame construction also could submit causes it to form the curve distribution to tally well
From the office building nonlinear earthquake responded the time interval analysis as well as under three kind of side force distribution pattern static elastoplasticity analysis final plastic hinge distribution map may see the office building satisfies the strong column weak Liang's earthquake resistance request The time interval analysis (under EL2CENTRO earthquake wave input) as well as under three kind of side force distribution pattern static elastoplasticity analysis obtains during the biggest level the angle of displacement respectively is 170114311171118 is smaller than the reinforced concrete portal frame construction elastoplasticity angle of displacement limiting value which the standard gives [θp] 150 therefore this office building satisfies meets under the earthquake function rarely the distortion request
5 conclusions
(1) compare with the conventional structure static elastoplasticity analysis method considered the earth 2 structures affect mutually the structure static elastoplasticity analysis method has its particularity in the structure static elastoplasticity analysis side force distribution pattern the goal displacement definite method must determine
(2) pair of comparison rule highlevel portal frame construction carries on the consideration earth 2 structures to affect the nonlinear earthquake resistance analysis mutually also may use the nonlinear earthquake to respond the time interval analytic method also may use the static elastoplasticity analysis method two methods both can carry on the earthquake resistance performance appraisal to the structure
(3) pair of highrise construction structure carries on when mutually the consideration earth 2 structures affect the static elastoplasticity analysis considered the higher order inspires the influence the side force distribution pattern is best selects the curve distributed pattern
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钢筋混凝土结构基抗震思想
The structure mainly depends on the ductility to resist under the big earthquake function the inelastic distortion therefore under the earthquake function the structure ductility and the structure intensity has the equally important significance The seismic force stepdown ratio reduced to the defended intensity earthquake function whole had in fact decided the structure submitted the standard and to the structure ductility demand size At present ability design law generally has accepted for the various countries traffic capacity design law forms reasonably consumes energy the mechanism causes the plastic hinge to appear the spot which easy to guarantee in the ductility Guarantees the structure in not to achieve needs in front of the ductility as for does not have the cutting expiration And guarantees the ductility through the detail structure measure full display
The earthquake disaster is one of serious natural disasters which the humanity faces The earthquake has the burst characteristics characteristic until now the predictability very was still low The strong earthquake often creates the person and the property heavy loss Our country is the earthquake to send the country needs to consider the earthquake resistance fortification the vast in territory therefore the research structure earthquake resistance performance has the full necessity in our country
Our country's modern earthquake resistance design theory is starts from the 50's develops in under the international earthquake resistance theory impetus and has formed own characteristic gradually In accumulated the suitable research results and in the experience foundation has formulated 74 one after another 78 89 standard and the new revision 2001 earthquake resistance design standard (GB5001122001) presses in 2001 the standard design the building earthquake resistance ability 89 standards to be possible to enhance 10~15 its technical content achieves the international advanced level But as a result of the state economy strength limit the security margin of safety establishment is still lower than US and so on the developed country
Must want better to carry out the standard to have to be clear about the earthquake resistance standard formulation the basic thought is clear about the earthquake resistance design the basic principle Below does emphatically from following several aspects elaborated
1 under the earthquake function pursues the structure the intensity not to be possible constantly to take the structure ductility is the extremely important
earthquake divides into slightly shakes shakes with the big quake Socalled slightly shakes refers often meets the earthquake 50 years appear the probability probably is 63 the return period is 50 years Shakes is refers to the probability which 50 years appear is approximately 10 the return period is 475 years But the big quake refers meets the earthquake rarely 50 years appear the probability is 2~3 the return period is 1641~2475 years Regarding fortuitous and the random very big earthquake load needs to want to cause the structural strength certainly to be bigger than the structure to respond that is nearly not impossible moreover is extremely uneconomical Is withstood the sacrifice the society ability and the economical restriction factor we only can embark from the probability angle enable the structure normally to play the role safely under certain probability guarantee This had decided the earthquake resistance design basic principle slightly shakes does not go bad shakes may repair big quake which namely usually said in our country not but actually
In slightly shakes under the function the request structure is not damaged or does not have to repair still may continue to use From the structure earthquake resistance analysis angle is requests the structure in slightly to shake under the function to maintain the accurate elastic reaction condition but does not enter causes the building interrupt to use and to have the inelasticity reactive state which the nonstructural unit destroys Simultaneously the structure lateral deformation should control in the reasonable limit scope the goal is enable the structure to have the enough antiside force rigidity
Shakes is probably equal to ours defended intensity earthquake when shook the function the bitter experience to the structure may have certain degree damage or still could not continue after the repair after the repair to use From the economical angle the maintenance cost cannot too be high
To had the probability minimum met the big quake rarely (big quake intensity to be approximately higher than defended intensity once about)Requests to work as structure when bitter experience big quake function should not collapse the serious destruction which or occur endangers life
This kind of earthquake resistance fortification goal is extremely economical reasonable Because the earthquake occurrence too is accidental supposing we pursue the structure the intensity to guarantee constantly shakes even is under the big quake function the structure does not go bad this will be able to cause the enormous quantity the material in the major part time even will all be at in the entire average life cannot play the role fully the condition will do this will be wise
Under the above principle of design instruction the request structure is in this kind of kind of condition When slightly shakes approaches should guarantee all structural unit when the resistance earthquake action has the enough intensity causes its to be at the elastic condition basically And slightly shakes under the function through the checking calculation the elastic displacement to guarantee together the structure does not go bad Is at this stage the structural unit not to be able to have the obvious nonlinear distortion also does not need to need to take the special structure measure Shakes under the function in structure certain essential spots surpass the elastic strength enters submits occurs distorts greatly achieved the nonlinear stage by now we on proposed specially the ductility request (the ductility refers when the earthquake forces the structure has the big nonlinear distortion the structure still can maintain its initial intensity ability was the structure surpasses the elastic stage distortion ability it is the structure earthquake resistance ability strong and the weak symbol It and depends on including withstanding enormous distortion ability stagnates the characteristic absorbed energy ability it is resists earthquakes middle the design an extremely important characteristic)Middle shakes approaches because the structure has the inelastic characteristic certain essential spots surpass its ball
The natural intensity enters the plastic state Because it has certain ductility its nonlinearity can undertake the plastic deformation enables it to consume and to absorb the earthquake energy in the distortion The price is possibly causes the wide crack the concrete epidermis to get up the shell falls off possibly has certain remaining distortion but as for does not cause the safe expiration achieved shakes the defended goal which may repair Is at this stage the structure can set the corresponding request to the ductility but the ductility must depend on the careful design the detail structure measure to guarantee When the big quake approaches the structure nonlinearity distorts extremely in a big way also possibly has the destruction which cannot be repaired Is at this stage the structure to need through to calculate its elastoplasticity distortion to guarantee the structure does not send the collapse
Therefore usually we only need according to slightly to shake the function effect and other load effect basic combination checking calculation component section earthquake resistance supporting capacity and structure elastic deformation But shakes the function effect to need the structure to depend on certain plastic deformation ability (ie ductility) to resist Therefore the structure ductility to the construction earthquake resistance is extremely important
2 seismic force stepdown ratio size has decided the design seismic force value size thus has decided to the ductility request size
States from on uses in the supporting capacity design the earthquake function being possible to take slightly shakes the level when a bigger earthquake approaches then depends on the structure the ductility to resist Therefore we do not use the defended intensity earthquake action to carry on the structure supporting capacity design but needs to reduce the defended intensity seismic force a coefficient is called the seismic force stepdown ratio
The seismic force stepdown ratio obtains in a big way the design earthquake function obtains slightly The seismic force stepdown ratio obtains slightly the design earthquake function obtains in a big way Under the identical defended intensity the seismic force stepdown ratio obtains in a big way the earthquake function is smaller then presses the structure which this small earthquake function designs to submit the standard to be lower meant structure the inelasticity which forms under the corresponding intense degree earthquake distorts is bigger this request structure has the big ductility to guarantee it big inelasticity distorts realization thus proposed to the ductility the request is higher This ductility rank structure namely for low design seismic force value 2 high ductility requests high ductility rank structure The seismic force stepdown ratio obtains
Smaller the earthquake function is bigger then presses the structure which this big earthquake function designs to submit the standard to be higher meant structure the inelasticity which forms under the corresponding intense degree earthquake distorts is smaller this only needs to request the structure to have the small ductility to guarantee it small inelasticity distorts realization thus proposed to the ductility the request is lower This ductility rank structure namely for high design seismic force value 2 low ductility requests low ductility rank structure Likewise under the identical defended intensity the seismic force stepdown ratio takes for medium earthquake function also for medium thus proposed to the ductility request also for medium This ductility rank structure namely for medium design seismic force value 2 medium ductility requests medium ductility rank structure Thus the seismic force stepdown ratio size has in fact decided the design seismic force value size thus has decided to the ductility request size
The Chinese standard stipulated reduces the defended intensity earthquake function 3 times to carry on approximately the supporting capacity design namely defended intensity earthquake function response spectrum dividing earthquake supporting capacity stepdown ratio 3 but obtains the response spectrum which the design uses And the Chinese standard decrease proposed according to the defended intensity to the structure ductility from high to low request concrete is indicated with the earthquake resistance rank altogether divides into the level two levels of three level of four level of four ranks
The preliminary impression is China's seismic force stepdown ratio value is somewhat low This as if explained China's seismic force value is high thus does not need to set the high ductility request to the structure Be in effect it is not so after has contrasted Chinese and the Western country defended earthquake function response spectrum curve we discovered in the long period scope the West must be higher than China in other words China reduces 3 times under the low response spectrum level reduces 5 times with the West under the high response spectrum level even the more after function level is the difference not many this explained China to the antiseismic structure should propose is equal is equal to 5 in the Western seismic force stepdown ratio even high scale high ductility request
3 ability design law has accepted generally for the various countries
Traffic capacity design law chooses the nature different main antilateral force component has in the big distortion situation in the earthquake function influence can form well consumes energy the mechanism
In order to cause the reinforced concrete structure causes at the earthquake in the dynamic response process displays the essential ductility must the traffic capacity design law cause the plastic deformation many to concentrate quite easily in to guarantee the good ductility performance or has on certain ductility ability component The ability design method concrete mentality has three steps
(1) first step chooses the plastic deformation organization which may accept Chooses the organization the displacement ductility to be supposed to depend on the plastic hinge place smallest nonlinearity rotation to achieve Once had designated the appropriate plastic deformation organization may determine the energy aerodynamic spot precisely Ability design law has two kind of different plans in the choice plastic deformation organization choice
One kind is the Liang articulation organization Its specific measures are artificial great scope increase column end anticurved ability causes besides the first floor base of cylinder various columns end under the strong earthquake function after in principle does not enter submits the condition namely does not appear the plastic hinge Because the column end in principle does not enter submits the curvature is small therefore to eliminates the first floor base of cylinder other various story posts end not to need to propose the strict axis presses compared to the control condition namely did not need certainly to have to leave in a big way the column end stressful condition control the small eccentric compression boundary condition still has certain distance ductility good greatly eccentric compression condition This kind of organization mainly depends on the Liang end to leave the articulation to come the diffusion earthquake energy
Another kind is the beam column articulation organization Its specific measures were only to a certain extent artificial increase the column anticurved ability therefore generally speaking column end although looks carefully relatively compared to with Liang strong but under strong and very strong earthquake function the column end still had the possibility to enter submits the Liang end appeared the plastic hinge the opportunity to be many early the plastic rotation was big The column end plastic hinge appears relatively late plastic rotation relative small So long as the paired columns axis presses the control is stricter than causes the column end not to appear the small eccentric compression and to big the small bias dividing line condition excessively near greatly eccentric compression situation again through the enhancement paired columns end plastic hinge area restraint may cause the not extremely harsh plastic rotation ability which the column end has needs (ductility ability) also does not send bruising This kind of organization mainly depends on the beam column to leave the articulation to come the diffusion earthquake energy together
Contrasts above two kind of plans the former in fact enhanced the column intensity strengthened the column elastic deformation ability Matches in the middle of the muscle in the reality vertical muscle amount used relative many stirrup amount used relative few The latter in fact sharpened the column plastic deformation ability matches in the middle of the muscle in the reality vertical muscle amount used relative few stirrup amount used relative many
The Chinese standard has chosen the second plan namely beam column articulation organization This is strong column weak Liang who we usually said In order to realize in ability design method strong column weak Liang organization our usual procedure is the paired columns section combination bending moment is multiplied by increases the coefficient Also may to match the muscle by the Liang end instead to figure out Liang Duanke actually to resist the bending moment namely really matches the bending moment to be multiplied by increases the coefficient the method to realize and with increases after the bending moment value to carry on the column end control section the supporting capacity design
(2) second step is must through artificial increase each kind of component antito cut ability causes it not to send under the strong earthquake function has not displayed in the structure ductility before appears the nonductility shearing failure This is which we usually said cuts weakly curved The usual procedure is increases the coefficient with the shearing force to increase the summer beam end the column end the shearing force wall end shearing force wall opening Lian Liang Duan as well as the beam column node place combination shearing force value and with increases after the shearing force design value to carry on is cut the control section control condition carries on the checking calculation and the design The specific measures also have two kinds
One kind is directly clockwise or the counterclockwise direction combination bending moment does a tour of duty to a cross Liang both sides section increases the coefficient again a vertical gravity load generation of tabular value which affects with Liang on together from the balance relations obtains the Liang end shear
Another kind is obtains a cross Liang both sides section along clockwise or the counterclockwise direction to match the bending moment according to the reality which the muscle can resist is multiplied by to it increases the coefficient again a vertical gravity load generation of tabular value which affects with Liang on together from the balance relations obtains the Liang end shear
(3) third step is through the corresponding structure measure guaranteed possibly appears the plastic rotation ability and the plasticity which the plastic hinge the spot has needs consumes energy ability Usually through the stirrup encryption the limit axis pressure compares and so on the measures to give the guarantee
The above three steps adopt the measure is the interdependence The second step measure is the first step measure realization premise and the safeguard Because only then the plastic hinge area did not send has cutting to expire ahead of time only then could have the beam column plastic hinge area plastic rotation The first step measure request is strict then third step may relative weak Otherwise the first step measure is loose then is strict to the third step request If because the column bending moment enhancement coefficient is very big big enough to can guarantee other column end all does not appear the plastic hinge besides the first floor then does not need the countershaft to press compared to with the restraint stirrup proposed the strict limit namely does not need to cause the column to be at the ductility good big bias condition and enable the column to have the very strong rotation ability This forms the Liang articulation organization But if controls the column the bending moment enhancement coefficient enable the Liang end to leave the articulation to compare the column end to leave the articulation many the rotation is early big the column end leaves the articulation then relative few the rotation is late small This is the beam column articulation organization This time needs to press to the axis of a cylinder compared to proposed certain limit causes the column end the stressful condition to be in the big bias simultaneously strengthens to the plastic hinge area stirrup restraint enhances the plastic hinge rotation ability like this sharpened the column end ductility ability causes it in under the plastic rotation which needs as for not to crush Therefore the column bending moment increases the coefficient to be bigger the countershaft presses the limit and the stirrup restraint request is lower than The bending moment increases the coefficient to be smaller the countershaft presses the limit and the stirrup restraint request is higher than
4 several kind of basic earthquake resistance system performance
(1) portal frame construction system According to the above ability design mentality through the reasonable design may make the portal frame construction the ductility frame The ductility frame under the big quake function after appears Liang Jiao first appears the column articulation such one kind to consume energy the organization diffusion massive earthquake energy the structure can withstand certain lateral deformation Therefore the pure portal frame construction is one kind of earthquake resistance performance very good structure But we simultaneously also saw is small as a result of the pure frame antiside rigidity the side which creates moves the value quite to be big therefore the constructive height is not suitable too high Nonstructural unit for instance infilled wall under earthquake function also possibly appears the crack and the destruction Between the frame and the infilled wall rigid joint creates the rigidity increases the effect also possibly to create designs on had not considered increases side force If is half high infilled wall but also can cause to form the short stump the rigidity increases the withstanding very big shearing force creates the pillar the shearing failure
(2) shearing force wall structure system The shearing force wall structure supporting capacity and the rigidity very are all big the side moves distorts slightly therefore its use scope may be higher than the pure portal frame construction Is suitable also may use in the shearing force wall as a whole in the portal frame construction component nonlinear earthquake resistance performance principle also may design into the shearing force wall the ductility shearing force wall also may come the diffusion earthquake energy by the stable way But in shearing force wall no matter is the wall extremity or Lian Liang its section characteristic is short and is high this kind of component is quite sensitive to the detrusion easy to appear the crack easy to appear the brittle shearing failure Therefore must carry on the careful reasonable design only then can enable the shearing force wall to have the good earthquake resistance performance and the good ductility ability If the shearing force wall destruction shape cuts steps compared to has the very big relations to cuts steps compared to the very small low wall the shearing failure shape primarily plastic deformation ability is very bad therefore should avoid in the antiseismic structure using the low wall Regarding the bracket wall energy aerodynamic mainly is leaves the articulation through the wall bottom to carry on But regarding the joint extremity wall passes through designs the hole position reasonably enable its energy aerodynamic mechanism with to have the strong column weak Liang's Liang articulation organization to be similar forms strong wall weak Liang namely LianLiang the Liang end leaves the articulation the wall bottom leaves the articulation but the wall other places do not appear the plastic hinge Otherwise if Lian Liang Qiangyu wall extremity then can appear with the column articulation organization same level distortion organization Regarding the long bracket wall usually through artificial opens the hole to cause it to turn the joint extremity wall because the bracket wall takes the statically determinate structure once has a section destruction to expire can cause the structure expiration and the collapse but unites the extremity wall to be possible to design Cheng Qiangqiang weak Liang leaves the articulation number to be many consumes energy in a big way Cuts weakly with frame design is curved same Lian Liang Jiqiang the extremity also needs to pass strongly cuts weakly curved enhances its anticuts the bearing capacity the postpone shearing failure thus improves its ductility But its own section characteristic influence the component still cannot guarantee does not have the shearing failure specially Lian Liang in the ordinary circumstances ordinary matches when muscle Lian Liang Hennan realizes the high ductility the design must specially take the measure to change its performance
(3) frame 2 shearing force wall structure system Is the frame and the shearing force wall unifies in together together resists vertical and the horizontal load one kind of system it uses the shearing force wall the high antilateral force rigidity and the supporting capacity the atonement portal frame construction antiside rigidity is bad distortion big weakness As a result of the shearing force wall and the frame joint operation improved the pure frame and the pure shear wall distortion performance always distorts reduces the level distorts reduces moreover about tends to evenly about the frame various story posts stress quite is also even Moreover under the earthquake function the shearing force wall undertook the majority of shearing force the frame has only undertaken very small part of shearing force usually all was the shearing force wall submits first after the shearing force wall will submit has the endogenic force redistribution the frame assignment shearing force can increase if the earthquake function continued to increase the portal frame construction also could submit causes it to form the curve distribution to tally well
From the office building nonlinear earthquake responded the time interval analysis as well as under three kind of side force distribution pattern static elastoplasticity analysis final plastic hinge distribution map may see the office building satisfies the strong column weak Liang's earthquake resistance request The time interval analysis (under EL2CENTRO earthquake wave input) as well as under three kind of side force distribution pattern static elastoplasticity analysis obtains during the biggest level the angle of displacement respectively is 170114311171118 is smaller than the reinforced concrete portal frame construction elastoplasticity angle of displacement limiting value which the standard gives [θp] 150 therefore this office building satisfies meets under the earthquake function rarely the distortion request
5 conclusions
(1) compare with the conventional structure static elastoplasticity analysis method considered the earth 2 structures affect mutually the structure static elastoplasticity analysis method has its particularity in the structure static elastoplasticity analysis side force distribution pattern the goal displacement definite method must determine
(2) pair of comparison rule highlevel portal frame construction carries on the consideration earth 2 structures to affect the nonlinear earthquake resistance analysis mutually also may use the nonlinear earthquake to respond the time interval analytic method also may use the static elastoplasticity analysis method two methods both can carry on the earthquake resistance performance appraisal to the structure
(3) pair of highrise construction structure carries on when mutually the consideration earth 2 structures affect the static elastoplasticity analysis considered the higher order inspires the influence the side force distribution pattern is best selects the curve distributed pattern
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