SEISMIC DESIGN OF HIGH PIERS FOR MOUNTAIN BRIDGES

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1 ARPN Journal of Engneerng and Appled Scence SEISMIC DESIGN OF HIGH PIERS FOR MOUNTAIN BRIDGES Qngxang Zheng 1 and Wenhua Lu 2 1 Qufu Normal Unverty, Qufu, Chna 2 Chelb Engneerng Conultant, Inc., Beng, Chna E-Mal: z.q.x.818@163.com ABSTRACT Becaue of complex topography of brdge t, many hgh per brdge wth unconventonal confguraton n wetern mountanou area of Chna are ued n hghway. The damage of the brdge n the Wenchuan earthquake told u that the new concept and meaure hould be ued n mountan brdge degn. The mportance of the emc concept degn, the tructure analy and the detal of emc meaure for brdge wa dcued. Some advce n the emc degn of brdge are gven. eyword: mountan brdge, hgh per, earthquake retant degn, emc meaure. INTRODUCTION In thee year, many hghway are beng bult n the outhwet and northwet of Chna. Becaue of complex topography of brdge t, many hgh per brdge wth unconventonal confguraton n mountanou area are ued. A nvetgaton about hghway brdge, ncludng thoe who have completed and are plannng, how that about 40% brdge, the heght of per, are more than 40-meter hgh. Such a Lancangang brdge of Xaowan nuclear power taton n Yunnan provnce, the hghet per 115-meter hgh, Luohe brdge of Huangyan hghway n Shanx provnce, the hghet per 143-meter hgh, etc. The mountan brdge have everal charactertc. Frt, many mall-radu curved brdge are ued (Fgure-1). Second, the contnuou beam brdge and rgd frame brdge are alway ued n upertructure. Thrd, thn-walled hollow per are alway ued n ubtructure, the heght of per varyng a great deal and the lenderne rato large (Fgure-2). For the evere damage of brdge n the Wenchuan (Schuan provnce, Chna) earthquake, mot degner have pay attenton to the emc degn of hgh per for mountan brdge [10]. The newly reved rule of Gudelne for Semc Degn of Hghway Brdge (JTG/T B , ued by Mntry of Tranport, Chna), for not more than 40m hgh per of the regular brdge, have done a detaled provon [8]. For rregular brdge and pecal brdge, the new rule call for a pecal tudy. It dffcult to repar after the brdge damaged by the earthquake, becaue degner of dometc and foregn lack the degn experence about hgh per under hghntenty earthquake. After ummng up the damage of the maor earthquake and Wenchuan earthquake n the world, the damage of hgh per brdge n mountan manly focue on the followng. Frt, the damage of abutment (Fgure- 3), uch a poton of abutment changed, abutment ettlement, wng-wall damaged and crackng, dlocaton of contructon ont a well a collon and damage of the man beam. Second, the damage of per and ple (Fgure-4), uch a per and ple nclned, breakng and crackng, the teel yelded of lower part of concrete brdge per, etc. Fgure-1. Curve brdge of hghway n Guzhou provnce Fgure-2. Mahuhe brdge (142m hgh of per) Thrd, the damage of upport (Fgure-5), uch a upport nclned, cut, anchor bolt pull-out, roller upport rollng off, upport t own detructon, etc. Forth, the damage of man beam(fgure-6), fallng of the beam the mot common, the reaon are the collape of per, damage of upport, collon of beam and large relatve dplacement between adacent per reulted n lackng of adequate beam devce. In th paper, three apect about emc degn of hgh per brdge, ncludng emc concept degn, 58

2 ARPN Journal of Engneerng and Appled Scence emc computng and detal of emc meaure, are recommended. Fgure-6. Damage of man beam. Fgure-3. Damage of abutment. Fgure-4. Concrete cruher of per. SEISMIC CONCEPT DESIGN OF MOUNTAIN HIGH-PIER BRIDGE Data how that the reaonable form and ucceful emc degn of the tructure can greatly reduce or even avod the occurrence of damage [3, 9]. The arch brdge, rgd-frame Brdge, mply upported Beam Brdge, and contnuou grder brdge ha a dfferent performance n the Wenchuan earthquake. For example, Maozpng Brdge (Fgure-7) ha a better concept of degn n Wenchuan earthquake. The man brdge ue rgd frame brdge, and the member of crong the fault ue the tructure of mply upported beam. Only one beam fallng, and full-brdge collape dd not happen. The reaonable concept degn, ncludng the choce of brdge te, the electon of Brdge-program, the choce of the lower part of the tructure and the upper part of the tructure, the choce of connectng component and the choce of renforcement, and o on, all the member of brdge hould meet the requrement of emc degn. (A) (B) Fgure-7. A. Man brdge of Maozpng. B. Fallng beam of Maozpng auxlary brdge. Fgure-5. Damage of upport. Arrangement of hgh-per about brdge n mountan The dplacement of per-top relatvely large about hgh-per brdge n the earthquake. Ung mply upported beam than ung contnuou beam more ealy fallng beam n the earthquake. The emc force that paed to the upper part of the kew brdge per nteract wth the brdge, whch can make the upper part of the tructure of the brdge rotate n plane. When the emc 59

3 ARPN Journal of Engneerng and Appled Scence block of brdge cap can not ret the rotaton of the upper part, the fallng beam damage wll happen. The rotaton of brdge wll ncreae the collon between the man beam, whch can caue the detructon of the man beam, ont and other component. If the per and beam are conoldated, the redundant contrant whch can form platc hnge wll be a large number of energy-conumng member n trong earthquake, whch can mprove the emc performance of brdge. Another reaon that reulted n a large dplacement of the top n hgh-per Brdge the mbalance of qualty and tffne about per. A a reult of the valley on both de of the mountan lope, the heght of the per are often gnfcant dfference and ung non-unform pan. The large dfference n tffne about the per wll lead to large dfference dtrbuton n the level of emc force between the per, and the large tffne of the per wll ubect to large level force, whch can affect the emc capacty of the tructure. If the center of tffne and ma revere the devaton, the upper member of the brdge wll have a rotaton wth an ncreae probablty of the beam fallng, collon and other damage. For the contnuou grder brdge, the tffne of the per n the ame conuncton hould be a cloe a poble. In the "Gudelne for Semc Degn of Hghway Brdge, Chna' newly rule promulgated n 2008, the tffne and ma balance not explctly requeted. But n the "Caltran emc degn crtera of Unted State, the contnuou grder brdge per tffne rato and the bac cycle have done the provon [2]. The ant-puh tffne of any two per and the ant-puh tffne of two adacent per hall meet formula (1) and (2). The fundamental natural vbraton perod of two adacent on hould meet the rato of formula (3) (1) (2) The combnaton of ant-puh tffne a ere connecton tffne of per and upport, whch atfed to the followng formula: = b P + b P Where: a combnaton of ant-puh tffne, that b the level tffne of the per, and the hear p tffne of the upport. The change are gnfcant about the heght of the per n mountan, from the formula (4) we can ee that the brdge hould to enure the balance of qualty and rgdty. Frt, the per hould ue the ame hgh-per, and the pan and the wdth of deck hould be equal a far a poble. The econd to adut the dameter of per and the upport form and o on, whch ued to mprove the tffne balance of the brdge. Choce of per form Mountan Brdge generally Curve Brdge of changng heght, not only the geometry of the curve brdge wll affect t earthquake repone; the type of per alo one of the man factor to affect t earthquake repone. Under the force of earthquake, the combnaton of hgh per and hort per made the force of brdge even more complcated, when hgh-per not coupled wth the hort per, t may lead to hgh per emc dplacement too large, the electon of hgh-per form and degn ha an mportant gnfcance for the emc afety of full-brdge Hghway n mountan, a a reult of retrcton n terran and landform, the rregular brdge that the per heght 40m hgh or more are many. For thoe n the heght of 30m hgh per, grder brdge are often ung double-cylndrcal per. When the heght of per more than 30m hgh, ngle column T-per, hollow thn-wall per and gantry type brdge per and o on, are often ued (Fgure-8). Thee per have ther own type of charactertc. (4) T T 0.7 (3) Where, and, ant-puh tffne of the per No. and repectvely, ; M and M, the equvalent concentrated ma at the top of per No. and repectvely, f the brdge non-wdened, then M = M ; T and T, the frt bac-cycle of on No. and repectvely, T T. (A) (B) (C) (D) Fgure-8. A. Double-cylndrcal per; B. Sngle column T-per ; C. Hollow thn-wall per; D. Double thn-wall per. If the brdge located on the curve, the emc repone of per coupled wth bendng and toronal vbraton. The cro-ecton type of per requre a better bendng rgdty and toronal rgdty. The horzontal 60

4 ARPN Journal of Engneerng and Appled Scence bendng tffne of ordnary double-cylndrcal per well, but the longtudnal bendng tffne and toronal rgdty poor. When the heght of per more than 30m hgh, t not recommend ung double-cylndrcal per. If the per hgh, the double-column per prone to be damaged for the ntablty under the combned effect of the bendng moment, hear force and axal force. There are many advantage of the ngle column T-per and hollow thn-wall per, that the flexural rgdty n all drecton, and toronal rgdty, overall good. The ngle column T-per General a combnaton type of pretreed cantlever cap beam and per. The characterzed the maller ze horzontal cro-ecton and maller cro-ecton tffne. Generally appled to the per not more than 60 m hgh brdge. The appearance of thn-walled hollow per and ngle column T-per are relatvely cloe. For the croecton ze and the lateral tffne, the thn-walled hollow per larger than the ngle column T-per. The thn-walled hollow per, ued n le than 80 m hgh per, ha obvou advantage. Stffne of gantry per better than the regular double cylndrcal per. Wth the ncreae n heght of brdge per, the two column of gantry per are lnked by the horzontal te beam. The lateral rgdty, the ntegrty, and the toronal rgdty of gantry per are le than thoe of double cylndrcal per, therefore, the gantry per are ued for not more than 90m hgh brdge. If the electon of per form to be condered, ngle T-per and hollow thn-wall per ued n Grder Brdge have a certan advantage. Sngle thn-wall per and double thn-walled per are alway appled to pretre concrete rgd frame brdge. Table-1 how the correpondng relatonhp between the heght of per and the form of per. Table-1. Relatonhp between the heght and the type of per. Supertructure Per heght Per form <30m Double cylndrcal per 30-60m Sngle T-per Beam brdge 60-80m Sngle T-per, hollow thn-wall per >80-100m Hollow thn-wall per, gantry per >100m Hollow thn-wall per, combnaton of per Rgd frame brdge ---- Sngle-thn-wall per, double thn-walled per SEISMIC CALCULATION OF HIGH-PIER BRIDGE For the hgh mountan valley on both de of the mountan lope, the heght of the per are often gnfcant dfference between non-unform pan. Semc force dtrbuton between the per are generally not good enough, o the calculaton of brdge emc mountan ha t dffculte and charactertc [5, 6]. Becaue of the complexty of the terran, the long-pan brdge (> 600m) whch cro-fault, near-fault and large change n terran, need to conder the mpact of mult-upport exctaton. A large number of emc record how that the earthquake at the ame tme, the reacton of the entre urface dfferent, even f the dtance only ten of meter, vbraton ampltude, phae and pectral charactertc are not the ame, and t patal varaton very complcated [1, 4]. Therefore, rregular mountan brdge hould target to conder the mpact of mult-pont earthquake exctaton. The mpact of dynamc nonlnear hould be condered n hgh brdge per. Many hgh-per brdge even under the tatc load wll produce a gnfcantly nonlnear deformaton. The large-pan rgd frame brdge very entve to deformaton. Therefore, the mountan hgh per emc analy of brdge hould be taken nto account the mpact of non-lnear. Semc analy of brdge per hould be taken nto account the mpact of hgher-order vbraton mode. Natural vbraton perod of the hgh per wll be very long and the qualty wll be very large, and two or more platc hnge may be formed under trong earthquake. If the emc analy overlook the contrbuton of hgher-order mode, t dffcult to enure the emc afety of tructure. Accordng to the charactertc of the emc calculaton about hgh-per Brdge, t neceary to tudy the applcablty of emc calculaton method. Under the earthquake exctaton, the changed load of tructure over tme are the dplacement caued by the upport movement. If the conttutve relaton, portng tate, and the mechancal tate of tructure are dentfed, and tme-varyng change of the upport ha a certan velocty and acceleraton, then the non- upport part of the tructure wll produce the ame dplacement, velocty and acceleraton. If the freedom of tructure dvded nto upport freedom and non- upport freedom, the dynamc balance equaton have the followng form: M u& &+ Cu& + u = R (5) Alo can be expreed a M Mb u && C + Cb u & + b u = 0 Mb Mbb u&& b Cb Cbb u& b b bb u b Rb Where, u& &, u&, u are the moton vector of upertructure n the abolute coordnate; u& & b, u& b, ub are the ground moton vector n the abolute coordnate; M,C, are the matrx of ma, dampng and tffne, the meanng of (6) 61

5 ARPN Journal of Engneerng and Appled Scence lower Fgure, bb, b are the freedom of upertructure, bae and ther couple tem; R b reacton of bae (If the repone of tructure have been got, the R b can be calculated by the econd equaton of formula (6) ) So the dynamc equaton about u& &, &u, u can be got from the frt equaton of formula(6) a M u& + C u& + u = M u&& + C u& + u ) (7) ( b b b b b b If the lumped ma model of tructure ued, the M b equal to zero; the dampng matrx dffcult to be calculated, and the dampng force C b u& b alway neglected; o the equaton (7) can be wrtten a M b b u& + C u& + u = u (8) Where, u b the vector of ground moton; - b u b the force of upertructure for the ground moton n the abolute coordnate. Equaton (8) the bac formula of analy tructure under ground moton. A can be een from the equaton, tudyng on dynamc repone of the brdge under earthquake actually a tudy of equaton (8). From the above formula, four common emc analytcal method can be got; they are repone pectrum method, random vbraton method, puhover analy method and tme htory analy method. Repone pectrum method: In emc analy of brdge tructure, the repone pectrum method the mot fundamental and mot wdely ued analytcal method. But the repone pectrum method can t conder the mpact of mult-upport exctaton. Th method aume that all the upport are n accordance wth the law of the ame movement. Reearch how that when the pan of the tructure meet or exceed the emc wavelength 1/4, the movement of the urface upport can t be condered a a content. Vbraton mode uperpoton method baed on the repone pectrum method a lnear method. For non-lnear analy, t may lead to large error. Random vbraton method: Earthquake ground moton a non-tatonary random proce. Random vbraton method take full account of the probablty charactertc of the earthquake. It generally agreed that the random vbraton method a reaonable analy method. The hortcomng of random vbraton method are the large ze of calculaton and for non-lnear problem may lead to large error. Peudo-exctaton method [7] olve the problem of large ze of calculaton. Peudo-exctaton method n ome apect make up the defcence of repone pectrum method. However, the method n dealng wth the trongly nonlnear problem of hgh per under rare earthquake ha t lmtaton. Puhover analy method: Puh-over method ha a certan value for mlar nonlnear emc analy, and t manly ued for the deformaton analy of tructure. However, t ung tatc analy method to tudy the dynamc repone of the tructure, and the mechancal model of telf ha t lmtaton. Tme htory analy method: The tudy howed that the hgh brdge per may enter a tate of erou non-lnear elatc-platc under a trong earthquake. At th pont, the tme htory analy method more adaptve than the repone pectrum method and random vbraton method. It wll be a very good contact of the charactertc of the earthquake and the nherent charactertc of the tructure, epecally lnked wth the elatc-platc emc repone of tructure. However, the large ze of the calculaton tll a hortcomng of the tme-htory analy method. To conduct mult-upport exctaton tme-htory analy, Space earthquake ground alo need to be generated. A can be een from the above, wth the undertandng of ground moton n depth and the development of computer technology, although the tmehtory analy method ha a certan defect, t one of the bet oluton to calculate the non-lnear repone of hgh-per rregular brdge n mountan under mult-upport exctaton. In th paper, the repone pectrum method, random vbraton method, tatc puhover analy and tme htory analy are propoed n lnear analy of hgh per brdge. The tme-htory analy method one of the bet choce for the nonlnear analy and the mult-upport exctaton analy. DETAILS OF SEISMIC MEASURES ABOUT HIGH PIER In Wenchuan earthquake, many brdge there have the damage of fallng beam and detructon of per, abutment and upport. At th pont, th paper ummarze ome detal of emc meaure, whch can be appled to hgh-per brdge emc degn of mountan. The effectve detal of emc meaure have the followng: The ung of lmt-dplacement apparatu n per and abutment. The emc code of Unted State and Japan recommend that the lmt devce hould be ntalled n ont to lmt the relatve dplacement, and the degn method of lmt devce alo pecfed. Japanee brdge degn pecfcaton alo take nto account the mpact of collon, and relatve dplacement repone pectrum alo ued n the degn to prevent the occurrence of beam fallng. Semc degn of Chna only pay attenton to the trength and deformaton capacty of brdge. Lmt devce have been adopted by ome of the brdge n Chna, but t alo a lack of ytematc tudy ndepth. Ratonal degn of block about per and abutment mportant. The current code for the detal emc degn of brdge hould be mproved n Chna. A large number of brdge damage took place n the block n Wenchuan earthquake, and the damage phenomenon cuttng block or the hear crack of block. Th how that the reaonable emc degn and contructon of block very mportant. Block degn hould pay attenton to the followng area: The rato of the tffne about block and man beam hould be reaonable; the extent of hear crack about block hould be moderate; dfferent pan and type of brdge hould ue dfferent ze of block. 62

6 ARPN Journal of Engneerng and Appled Scence The ung of emc olaton upport, th nclude the ung of lamnated rubber upport, PTFE upport, LRB, etc. To ncreae the flexble n the beam body and ncreae the dampng of connectng part about per and abutment, whch can reduce the emc repone of brdge. The ung of emc olaton upport and damper combnaton ytem, n thee 20 year, the Unted State, New Zealand and Japan and other countre, about the brdge emc olaton and ductlty degn are ncluded n the correpondng norm. Chnee pecfcaton alo not pecfc enough. The ung of ductlty dampng per, ductlty dampng member, whch have uffcent ductlty enable brdge form a table platc hnge under trong earthquake, degned to be ome part. The elatc-platc deformaton of tructure can extend the natural cycle of tructure, and conume emc energy. Development and utlzaton of new materal to make a brdge olate, aborb and dpate emc energy and reduce the emc repone of brdge, and the deformaton of the brdge lmted n a cope to avod the redual damage and permanent deformaton caued by accumulaton of platc deformaton. For example, concrete-flled teel tube tructure and teel renforced concrete, etc. are effectvely mprovng the emc capacty of brdge. Mot of Japan' new brdge on the ue of teel how the trend of th development. CONCLUSIONS Ground moton telf a complex random proce. The rregular nature of the hgh per brdge n mountan area make the emc degn of brdge to be dffcult. The followng concluon can be adopted n th paper: To trengthen the emc concept degn of the hgh-per brdge n mountan, t preferred to elect the form of per to ret large bendng moment, hear force and torque. It mportant to adut the tffne balance of the component, and enhance the ntegrty of the upper tructure. For the complexty of the tuaton n mountanou terran, the non-lnear analy of hgh per hould to be trengthened, and the mult-pont emc analy and patal emc analy hould to be taken targeted. The hgh per brdge n the mountan hould take full account of the detal of emc meaure. The type of tructure hould be elected accordng to dfferent emc program. It ndpenable to attend the detal of meaure and the tffne balance of tructure. [2] Caltran Semc Degn Crtera, Veron I.2. [3] Chen H Semc conceptual degn for brdge (n Chnee). Scence and Technology of Overea Buldng Materal. 25(2): [4] Chong Y.L Brdge repone due to multple upport exctaton. 7 th ymp. on earthquake engneerng. Unverty of Rookee. [5] L Q., Wang. and We H Semc repone analy for Grder Brdge wth hgh per (n Chnee). Earthquake Engneerng and Engneerng Vbraton. 26(3): [6] L R., Nng X. and Ye L Earthquake repone analy of Grder Brdge wth hgh per (n Chnee). Journal of unmng Unverty of Scence and Technology (Scence and Technology). 26(10): [7] Ln J., Zhang W. and Zhong W Stochatc earthquake repone of long pan tructure (n Chnee). Acta Mechanca Solda Snca. 12(4): [8] Mntry of Tranport, Chna, (JTG/T B ) Gudelne for Semc Degn of Hghway Brdge (n Chnee). [9] Song X.D. and L J.Z Semc Conceptual Degn for Mountan Brdge (n Chnee), Earthquake Engneerng and Engneerng Vbraton. 24(1): [10] Wang.H. and Sun Y.H Comment on Semc Strengthenng for Structural Engneerng n Chna after Wenchuan Earthquake (n Chnee). Journal of Hghway and Tranportaton Reearch and Development. 25(11): REFERENCES [1] Bonganoff J.L., Goldberg J.E. and Schff A.J The effect of ground tranmon tme on the repone of long tructure. Bulletn of the Semologcal Socety of Amerca. 55: