SEIMIC RETROFIT PROGRAM FOR TAIWAN SCHOOL BUILDINGS AFTER 1999 CHI-CHI EARTHQUAKE

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1 October 1-17, 008, Beijing, China SEIMIC RETROFIT PROGRAM FOR TAIWAN SCHOOL BUILDINGS AFTER 1999 CHI-CHI EARTHQUAKE Keh-Chyuan Tai 1 and Shyh-Jiann Hwang 1 Profeor, Dept. of vil ENG, National Taiwan Univerity, Taipei, Chinee Taiwan Director, National Center for Reearch on Earthquake Engineering, Taipei, Chinee Taiwan Profeor, Dept. of vil ENG, National Taiwan Univerity, Taipei, Chinee Taiwan Diviion Head, National Center for Reearch on Earthquake Engineering, Taipei, Chinee Taiwan kctai@ncree.org, jhwang@ncree.org ABSTRACT : Baed on the obervation made after everal major earthquake occurred in Taiwan, chool building ha been found mot vulnerable to evere earthquake damage among all building type. Although the eimic deign force for chool building ha been 5% higher than the ordinary building, it performance to reit trong earthquake ha been proved inufficient. Seriou caualtie and loe may be reulted from the collape of chool building under trong earthquake. Furthermore, chool building are uually required to erve a emergency helter oon after a major earthquake. The urgent need of eimic performance evaluation and enhancement work i evident. Lack of integral planning, lack of eimic reitance along corridor, effect of hort column, embedded pipeline and lack of lateral reinforcement ha been found the key factor reponible for the collape of chool building. A three-tage trategy for eimic evaluation and retrofit of exiting low-rie reinforced concrete chool building ha been propoed. It i baed on the common tructural type, eimic reitance, poible failure mode and available experimental data. Seimic-deficient chool building are being retrofitted baed on the performance index introduced in thi paper. KEYWORDS: 1. Introduction School building, eimic evaluation, eimic retrofit A number of building in the primary and middle chool in Taiwan have uffered damage of variou degree during the Ruei-Li earthquake (July 17, 1998), Chi-Chi earthquake (September 1, 1999) and Chia-Yi earthquake (October, 1999) in the pat decade. In the diater area of Ruei-Li earthquake, many chool building were everely damaged. The damage mode included the palling of column cover concrete, cracking of core concrete, buckling of longitudinal reinforcement. The eimic reitance of thee building hould have been greatly reduced. Thee chool building were on the brink of collaping. Neverthele many chool building were collaped during Chi-Chi earthquake. According to the report publihed by Minitry of Education, a total of 786 chool (1958 claroom) were damaged in Chi-Chi earthquake. Even in Taipei ty, which i about 150 km far away from the epicenter, there were 67 chool building damaged. The total lo of life reulted from the Chi-Chi earthquake almot reached 500. If Ruei-Li earthquake were not occurred during the ummer break or the Chi-Chi earthquake were not took place in late night, the total caualtie could have been much more. Baed on the damage tatitic, a lack of eimic reitance appear to be a common problem in the exiting primary and econdary chool building in Taiwan. Significant caualtie and property loe could be reulted from the collape of thee chool building under trong earthquake. Furthermore, chool building might have to be aigned a emergency helter immediately after a evere earthquake. For the purpoe of conducting eimic performance evaluation and retrofit of thee noted tructure, a rather imple template ha been developed in NCREE for preliminary eimic evaluation of typical chool building. The propoed template i to evaluate the tructural type, apparent eimic weaknee, potential failure mode and the available experimental data. The complete trategy for eimic evaluation and retrofit of chool building i introduced later in thi paper. Some key factor, among many item, reponible for the poor eimic performance of chool building are dicued hereafter.. Seimic Deficiency.1. Lack of Integral Planning

2 th The 14 World Conference on Earthquake Engineering October 1-17, 008, Beijing, China In Taiwan, a large number of old building in elementary and econdary chool appear lacking of an integral planning in advance. In tead, many old chool building have been contructed and later on expanded in a patchy way. It wa due to the population growth in the chool ditrict and the riing of multifariou branche of teaching, the number of exiting claroom wa no longer enough. Hence the chool authoritie had trived for funding from year to year. When the budget allowed, new claroom were added to the exiting one in the horizontal or vertical direction at different time in order to olve the problem of under-upply of claroom. If the new claroom were added horizontally, the tructural ytem of the old chool building could be poiled. If the new claroom were built on top of the old one, eimic and gravity load demand on the old claroom would be ignificantly increaed. The new claroom expanded in the horizontal direction are rather cloely adjacent, if it i not connected, to the old one o a to maintain the continuity of activity pace for pupil and teacher. Having contructed at different time, the old and the new claroom could be different in height, weight or tiffne. Thu, the two tructure may poe different fundamental vibration period. When an earthquake occurred, the old and new claroom would vibrate not in-phae. Under thi circumtance, if the adjacent eimic gap were not wide enough, thoe claroom could have pounded each other (Figure 1). The pounding could caue the complete failure and collape of column in the adjacent building. The eimic force of each floor i in direct proportion to it floor weight and acceleration. The eimic hear force undertaken by the old claroom would be the um of inertia force of each floor of the entire chool building. Building new claroom over the old one would increae the tory hear force and the overturning moment, reult in the collape of the entire tructure during a evere earthquake (Figure ). A noted above, building claroom without integral deign are likely to make undeirable change in the mechanical propertie of the tructural ytem. It could reult in ponding or collape of the building. Thu, without proper trengthening of the exiting tructure, adding new claroom to old one i very hazardou. Accordingly, it i recommended that new claroom be properly deigned before it i built on it own foundation baed on an integral plan. Figure 1 Ponding damage due to inufficient eimic gap Figure Earthquake damage due to vertical building expanion Figure 3 Short column damage.. Collape in the Longitudinal Direction Mot chool building in Taiwan were deigned baed upon the tandard floor plan developed in According to the tandard floor plan, claroom have been configured ide by ide in a row. Typically there i a corridor outide of the claroom. The floor or roof above the corridor i often cantilevered without column. Tranvere to the corridor, claroom are typically partitioned by uing brick wall which are continuou in the gravity direction. However, along the direction of the corridor, door and window have been contructed for entrance and natural light. Only mall amount of wall could be continuou. The noted

3 October 1-17, 008, Beijing, China cantilevered corridor may be convenient for tudent activitie on the firt floor. Thu, it often leave only reinforced concrete frame along the corridor direction. Unfortunately, thee two frame typically conit of hort column. Thee hort column are reulted from the concrete or brick windowill contructed between the column. The advere effect of the hort column on the eimic performance of RC frame tructure will be highlighted later in thi article. Baed on the worldwide obervation on chool building damage, there i a trong evidence that chool building tend to collape along the corridor. There eem no cae recorded that chool building collape tranvere to the corridor direction. In 1967, the compulory education in Taiwan wa extended from 6 to 9 year. The tandard claroom floor plan noted above wa to match the tringent requirement in the contruction of claroom. At that time, there wa no concept of eimic reitant deign. If double corridor, upported by column at the free end, are adopted for claroom, there are four column, three pan normal to the corridor. Strength and ductility can be highly enhanced with the increae in the degree of redundancy. Therefore, catatrophic collape can be avoided. Beide, if the amount of wall can be increaed and kept continuou in the gravity direction, the poibility of collape may be decreaed..3. Effect of hort column In order to gain lighting and ventilation, the two exterior ide of the claroom have been built with window and door. At the upper portion of the column, it i often contrained by concrete or brick lintel above the window. At the lower portion of the column, it i typically contrained by the noted infill below the windowill. Thu, the effective length of the column ha been ignificantly hortened. During a earthquake, the hear demand on the hortened column i therefore greatly increaed. Unfortunately, thee column have been contructed with poor concrete and without ufficient hear reinforcement. Conequently, the column have been found frequently failed in the hear mode, with X-hape crack commonly oberved (Figure 3). A a matter of fact, if a eimic gap had been cut between the column and the infill, the effective length of the column would not be hortened. In thi manner, a more deirable flexural failure mode could be achieved. The eimic gap could be filled with compreible but watertight material..4. Imbedded Pipeline Utility line, including water upply, drainage and electricity have been embedded inide the column. Conequently, the effective area of the column i ubtantially reduced. The cro-ectional area of the column i typically about 5 to 30 cm quare. After a 5-cm diameter minimum drainage pipe i embedded, the column cro-ectional area i greatly reduced. The trength of the column ha been evidently reduced and wa never carefully taken into account. It i obviou that a complete eparate pace for running the utility line i needed..5. Lack of Lateral Reinforcement The pacing of column tranvere teel reinforcement in many old building ha been found exceeding 0 cm. Tranvere teel reinforcement i eential in confining core concrete, prolonging buckling of longitudinal reinforcement and prohibiting hear failure. The lack of lateral reinforcement hould help to explain why the chool building column have often been failed in a brittle hear failure mode. The ductility of thi kind of column can be effectively enhanced by eimic retrofit uing teel or carbon fiber jacketing. 3. Strategy In order to effectively tackle the eimic deficiency problem for chool building in Taiwan, three tage have been propoed for creening, including imple urvey, preliminary evaluation and detailed evaluation. The imple urvey i conducted by chool adminitrator. In a imple urvey, a chart ha been developed for collecting chool data and building data. School data include treet addre of the chool, the number and the identification of chool building. Building data include the number of torie, the year of deign or contruction, condition of the building, floor dimenion, number of column and the cro-ectional dimenion of the typical column in each frame, number of wall and the cro-ectional dimenion of the typical wall in each frame. After the urvey chart i filled, data entrie are ubmitted through internet. Before the extenive imple urvey wa launched acro all chool ditrict, workhop ha been held to train chool

4 October 1-17, 008, Beijing, China adminitrator reponible for conducting the urvey. The econd tage of creening, preliminary evaluation i conducted by profeional. In a preliminary evaluation, a chart ha been developed for the profeional to carry out the evaluation. In addition to the identification of the chool and the building, the data include deign ground acceleration, number of torie, floor area above the firt tory, cro-ectional area of column, reinforced-concrete wall, four-ide and three-ide bounded brick wall, and condition of the building. The third tage of creening i the detailed evaluation conducted by profeional engineer. Three method have been adopted in Taiwan. It include (1) trength and ductility method, () puh-over method uing commercial computer program uch a ETABS, and (3) implified puh-over method. Seimic retrofit deign i conducted by profeional engineer. Three eimic retrofit technique for chool building have been verified experimentally in NCREE. It include reinforced concrete jacketing of column, teel jacketing of column and wing wall addition adjacent to column. The propoed trategy of eimic evaluation and retrofit of thee chool building ha been accepted and implemented by the Taiwan Minitry of Education. It ha been recommended by NCREE reearch team that detailed evaluation and retrofit deign of a chool building be conducted by the ame profeional engineer o that the reponibility can be clearly defined. Moreover, it i alo uggeted that the detailed evaluation and retrofit deign mut be reviewed by a panel o that the engineering work quality can be guaranteed. In the final tage of retrofit contruction, inpection ha been precribed Simple Survey The eimic performance of chool building can be evaluated from it eimic capacity to demand ratio. The eimic capacity of the chool building i computed by uperimpoing the hear trength of variou vertical member uch a wall and column. The eimic demand i determined from the weight and location of chool building. The eimic performance i further modified according to the condition of the building. Simple urvey ha been conducted by chool adminitrator uch a director of general affair, ection chief of general ervice, or teacher with knowledge on civil engineering or building maintenance. The information of the urvey ha been ubmitted to the computer erver in NCREE through internet. 3.. Fundamental Aumption Tranvere to the corridor, claroom are typically partitioned by wall, which are continuou in the gravity direction. However, along the corridor, there are window and door for entrance and natural light. Thee wall are eldom continuou in the gravity direction. Damage and collape of chool building have been found occurred only along the corridor. Thu, eimic performance i evaluated along the corridor direction only. Since eimic hear force at the firt tory i larger than other tory, and the chool building are quite regular from tory to tory, thu, eimic reitance of the firt tory i mot critical. Therefore eimic vulnerability of the firt tory need to be evaluated. Due to the preence of the concrete lab and the lintel above the window, the beam became tronger than the column. The chool building were often damaged or collaped due to the failure of vertical member. Therefore, only column and wall are taken into account for the eimic reitance of the chool building. From the tatitic of 30 chool building urveyed in Tainan area in outhern Taiwan, the mean of the dead load per unit area i 913kg m and the tandard deviation i 10 kg m. Since the dead load at the roof floor i lower than typical claroom floor, the average dead load per unit area above the firt tory i aumed to be 900 kg m for implicity. Moreover, from tatitical data, the compreive trength of concrete and the yielding trength of teel reinforcement are, repectively, 160 kg cm and 800 kg cm for the exiting chool building Shear Strength of Vertical Member In the imple urvey, all wall are conidered a three-ide bounded brick wall. Thee wall are bounded between the top and bottom beam, and bounded one ide by a column. When the brick wall i three-ide bounded, the width varie from 0 to 180 cm and the height 60 to 80 cm. The average modulu of rupture for brick i 18.5kg cm. Baed on the empirical formula, the hear trength of three-ided bounded brick

5 October 1-17, 008, Beijing, China wall, τ W i about 1.5kg cm. The weighting factor for the hear trength of the wall i aigned a 0.5. Along the corridor of the chool building, the depth of column varie from 5 to 35cm and the pacing of tranvere reinforcement varie from 0 to 30 cm. In thi paper, the depth and width of the column are aumed to be 30 cm and 40 cm, repectively. The tranvere reinforcement i #3 rebar with a pacing of 5 cm. The hear trength of a reinforced-concrete column i contributed by concrete and lateral reinforcement. The averaged hear trength of a typical reinforced concrete column τ C ha been found about 15 kg cm. The weighting factor for the hear trength of the reinforced-concrete column i aigned a Fundamental Seimic Performance In a typical chool building, there are at mot four frame along the corridor. The chool adminitrator i aked to record the number of wall and the dimenion of the typical wall in each frame. From the data, the cro ectional area of the wall on the firt floor can be computed a: 4 A = N B D (1) W i= 1 where N i the number of wall; B i the breath of the typical wall; and D i the width of the typical wall in the i-th frame. From the data of the column, the cro ectional area of the column on the firt floor can be computed a: 4 i= 1 A = N B D () C where N i the number of column; B i the breath of the typical column; and D i the depth of the typical wall in the i-th frame. From the data of the chool building, the total floor area above the firt tory can be computed a: A f = NSLS BS (3) where N S i the number of torie; L S i the length of the floor; and B S i the width of the floor in the chool building. The deigned peak ground acceleration factor, Z aociated with a pecific eimic zone can be determined from the location of the building. Baed on the capacity veru demand ratio, the eimic performance of chool building can be conveniently evaluated a: 0.5AW + 5AC E = (4) 10ZAf Additional modification factor noted below may apply to further improve the reult of the evaluation Modification Factor Corroion of reinforcement: If the reinforcement corroion or concrete palling i found in the column or beam, the modification factor i q = Crack and leakage: If the beam or column crack or leakage of water i found, the modification factor i q = Differential ettlement and inclination: If ubtantial deformation of the chool building i found induced by differential ettlement, the modification factor i q = Redundancy: If the corridor i cantilever and no column i found at the exterior edge of the corridor, the modification factor i q = If column exit at the exterior edge of the corridor, the modification factor i q = Seimic gap: If the eimic gap from an adjacent building i le than 7 cm multiplied by the number of torie, the modification factor for irregularity i q = Short column: Since the preence of hort column i very common in typical chool building, the

6 October 1-17, 008, Beijing, China hort-column modification factor i required for all chool building a q = The effect of all thee modification factor, Q i defined a: Q = q1qq3q 4q5q6 (5) 3.5. Seimic Performance Index The eimic performance index I i defined a: ( 0.5AW + 5AC I = EQ = q1q q3q4q5q6 ) (6) 10ZAf Since chool building are public, the eimic demand i increaed uing an importance factor I = Therefore, if the eimic performance index of a chool building i I < 80, the chool building i likely to collape when ubjected to an earthquake of 475 year return period. If the performance index i 80 I 100, the chool building i likely to be damaged when ubjected to the ame deign earthquake. If the performance index i I > 100, the chool building hould not be eriouly damaged when ubjected to the noted level of earthquake. The chool building are not required to go through the preliminary evaluation if it performance index I i greater than 100. Higher priority for preliminary evaluation ha been given to chool building having I index maller than Preliminary Evaluation The fundamental aumption for the preliminary evaluation are the ame a thoe for imple urvey. Since preliminary evaluation i conducted by profeional from academic or engineering community, the reult hould be more meaningful. The reult of the preliminary evaluation have been ubmitted to the computer erver in NCREE through internet Shear Strength of Vertical Member In the chool building, when the brick wall i four-ide bounded, the width typically varie from 500 to 700cm and the height 60 to 80cm. Baed on the empirical formula, the hear trength of four-ided bounded brick wall, τ BW 4, i about 3.0kg cm. The weighting factor i aigned a 1.0. A mentioned previouly, the hear trength of three-ided brick wall τ BW 3 and reinforced-concrete column are about 1.5kg cm and 15 kg cm, repectively. The correponding weighting factor τ C are 0.5 and 5.0, repectively. From the experiment conducted at NCREE on reinforced concrete frame with and without in-filled reinforced concrete wall, it i found that the hear trength of reinforced concrete wall i about 4.0kg cm by the regreion analyi. The weighting factor i aigned a Fundamental Seimic Performance Baed on the demand veru capacity ratio for eimic performance evaluation of chool building, the fundamental eimic performance of the chool building E i computed a: 0.5ABW 3 + ABW 4 + 5AC + 8ARCW E = (7) 10ZA where A BW 3, A BW 4, A C and RCW f A are the cro-ectional area in cm of three-ide bounded brick wall, four-ide bounded brick wall, reinforced-concrete column and reinforced-concrete wall in the firt floor along the corridor, repectively. Additional modification factor noted below may apply to further improve the reult of the evaluation Modification Factor Regularity: If the dimenion of convexity in both direction are larger than 15% of the dimenion of chool

7 October 1-17, 008, Beijing, China building in the correponding direction, the modification factor for regularity i q = If the chool building i regular both in elevation and plan, the modification factor for regularity i q = For any other condition, the modification factor for regularity i q = Soft and weak tory: If more than /3 of the wall of any tory are not extended continuouly to the lower tory, the modification factor for oft and weak tory i q = If 1/3 to /3 of the wall of any tory are not extended continuouly to the lower tory, the modification factor for oft and weak tory i q = If le than 1/3 of the wall of any tory are not extended continuouly to the lower tory, the modification factor for oft and weak tory i q = Crack, corroion and leakage: If the degree of crack, corroion and leakage i eriou, the modification factor i q = If there i no crack, corroion and leakage, the modification factor i q = For any other condition, the modification factor for crack, corroion and leakage i q = Differential ettlement: If ubtantial deformation of the chool building i induced by differential ettlement, the modification factor i q = Otherwie, the modification i q = Redundancy: If the floor above the firt tory corridor i cantilever and no column at the exterior edge of the corridor, the modification for redundancy i q = If there i only one corridor at one ide of the chool building and column exit at the exterior edge of the corridor, or there i a corridor at the middle of the chool building, the modification for redundancy i q = If there are two corridor at both ide of the chool building and column exit at the exterior edge of the corridor, the modification factor for redundancy i q = Short column: If more than 50% of the column are confined by infill under the windowill, the modification factor for hort column i q = Otherwie the modification factor i q = The effect of all thee modification factor, Q can be computed a tated in Equation (5) Seimic Performance Index The eimic performance index I i defined a: 0.5ABW 3 + ABW 4 + 5AC + 8ARCW I = EQ = q1qq3q 4q5q6 ( ) (8) 10ZAf If the eimic performance index of a chool building i I < 80, the chool building i likely to collape when it i ubjected to an earthquake of 475 year return period. If the performance index i 80 I 100, the chool building i likely to be damaged when ubjected to the ame deign earthquake. If the performance index i I > 100, the chool building hould not be eriouly damaged when ubjected to the noted level of earthquake. The chool building are not required to go further through the detailed evaluation if it performance index I i greater than 100. Higher priority for detailed evaluation ha been given to chool building having I index maller than 80. It ha been recommended by the NCREE reearch team that the eimic retrofit deign work, when it i found neceary, be conducted by the ame engineer perform the detailed evaluation. 5. Seimic Retrofit Reearch Before the full implementation of the cot-effective eimic retrofit cheme for improving eimic performance of exiting chool building, an extenive reearch program wa launched in 003. Since then, a great number of large cale pecimen have been teted in NCREE (Tu et al. 006). In addition, everal in-itu collape tet of chool building were conducted in recent year (Hwang et al. 007). More detailed information can be found in the link of the web ite:

8 October 1-17, 008, Beijing, China 6. Concluion Among many type of governmental building, primary and middle chool have been found the mot paciou and uniformly ditributed according to the ditribution of population. Therefore, chool building are likely to play a very important role for emergency repone purpoe immediately after a natural diater. Hence, the tructural afety of chool building i evident. Thi explain why the eimic deign force for chool building tructure ha alway been 5% higher than ordinary building. However, according to the obervation made from the Ruei-Li, Chi-Chi and Chai-Yi earthquake, damage of chool building ha been the mot eriou one among all building type. The pecific feature of the chool building tructure noted above hould help to explain why it had uffered the mot during a evere earthquake. Baed on the NCREE propoed trategy for the eimic evaluation and retrofit of chool building noted in thi paper, the Taiwan Minitry of Education ha implemented an extenive program for improving the eimic performance of elementary and econdary chool. A ignificant number of chool building are being retrofitted for a higher eimic reitance. A different trategy ha been formulated by NCREE for eimic evaluation and retrofit of building for police and fire department. Acknowledgement The author would like to acknowledge the upport from the National Science Council, the National Applied Reearch Laboratorie, the National Center for Reearch on Earthquake Engineering, and the Miniter of Education. In particular, many reearch taff, including Dr. Lap-Loi Chung, Wen-Yu Chien and Yeong-Kae Yeh actively participated in the reearch work and coordination with variou agencie. Reference Chiou, T.C. (00), Seimic Retrofit of Reinforced-Concrete Wall by FRP, Mater Thei, National Taiwan Univerity of Science and Technology, Taipei, Taiwan. (in Chinee) Chung, L.L., and Hu, T.Y. (000), 'Seimic damage of chool building in Taiwan', Proceeding of Firt International Conference on Structural Stability and Dynamic, Taipei, Taiwan, pp Chung, L.L., Sheu, D.Y., Jean, W.Y., Liao, W.I., Chiu, C.K., and Chow, T.K. (004), 'Preliminary eimic evaluation of primary and econdary chool building', International Conference in Commemoration of 5 th Anniverary of the 1999 Chi-Chi Earthquake, Taiwan, pp Hwang, S.J. et al. (1996), Common Damage and Retrofit Planning of School Building, Building Reearch Intitute, Taipei, Taiwan. (in Chinee) Liao, W.I., and Yeh, Y.H. (003), Seimic Tet of Two-Story Frame with Non-Structural Wall, Technical Report, National Center for Reearch on Earthquake Engineering, Taipei, Taiwan. (in Chinee) National Center for Reearch on Earthquake Engineering (000), Seimic Evaluation and Retrofit of Primary and Secondary School Building, Workhop on Seimic Evaluation and Retrofit of Primary and Secondary Building, Taipei, Taiwan. (in Chinee) Tai, I.C. et al. (000), Detailed eimic evaluation of chool building, Seimic Evaluation and Retrofit of Primary and Secondary School Building, Workhop on Seimic Evaluation and retrofit of Primary and Secondary Building, Taipei, Taiwan. (in Chinee) Yeh, Y.H. (001), Seimic Retrofit of Reinforced-Concrete Wall by FRP, Mater Thei, National Taiwan Univerity of Science and Technology, Taipei, Taiwan. (in Chinee) Tu, Y.H., Hwang, S.J., Yi-Huan Tu and Chiou, T.C. (006), In-Site Puh Over Tet and Seimic Aement on School Building in Taiwan, 4th International Conference on Earthquake Engineering, paper No. 147, Taipei, Taiwan, October Hwang, S.J., Chiou, T.C. and Weng, Y.T. (007), Experimental and Analytical Performance Aement of In-Situ Puhover Tet of Reui-Pu Elementary School Building in Taiwan, APRU/AEARU' 3rd Reearch Sympoium in Jakarta, Indoneia, for the period of June1-.