Study on Variable Action Value Standard for Harbor Infrastructures

Transcription

1 4 th International Conference on the Durability of Concrete Structure July 2014 Purdue Univerity, Wet Lafayette, IN, USA Study on Variable Action Value Standard for Harbor Infratructure Xiaoping Zhong and Qianyi Zhao College of Civil Science and Engineering of Yangzhou Univerity Xiaoping Zhong and Weiliang Jin Intitute of Structural Engineering, Zhejiang Univerity Abtract To meet with different level of requirement from proprietor and uer and to offer a bai for variable action value to the deigner, aociated with the tandard, thi diertation tudied the value tandard of load effect and environmental effect. For load effect, on the foundation of analyzing variable load effect model, we ued equal exceeding probability principle to calculate the load adjutment coefficient for the cargo loading in harbor and river port under different deigning ervice life. For environmental effect, according to the rank of marine chloride environment in tandard GB/T , after analyzing and comparing the reearch achievement on urface chloride concentration at home and abroad, we obtained the value tandard of chloride ion loading in different rank of chloride environment. 1. INTRODUCTION Whether or not a tructure can meet with the demand of proprietor, uer and ociety in the future are cloely related to the effect level conidered to impoe on it when deigning, that i the magnitude of effect. Uually, we ue the value tandard of variable effect to quantify the magnitude of effect. Uing different tandard of effect in deigning, correpondingly, we get variou performance level for tructure and variou atifaction level for proprietor and uer. Therefore, determination of tructural effect tandard i neceary for performance-baed tructural deign. The main effect impoed on harbor tructure are load effect and environmental effect. Load effect control the afety and applicability of tructure, while environmental effect influence the tructural durability, the inufficient of which may further affect the afety and applicability of tructure. Current harbor tructure deigning mainly value the variable load according to the Code for Load of Port Engineering, in which the value tandard of variable load, wind load, and ice load are provided under the circumtance of 50-year deigning ervice life. When the demand of proprietor and uer differ from the 50-year deigning ervice life, the code give no correponding value tandard. Moreover, the durability problem caued by environmental effect, epecially chloride environment, i particularly eriou in harbor tructure, which directly affect the ervice life of harbor tructure. Hence, we mut take it into eriou conideration. However, to clarify the connection between harbor tructure ervice life and it durability, one of the important tak i to determine the value tandard of environmental load. However, a the code of harbor tructure ha not included the value tandard of environmental load yet, the deigner hand are tied on relative durability deign. In view of the abovementioned factor, it ha a really profound theoretical and practical meaning to carry out the reearch on the value tandard of variable load of harbor tructure under the circumtance of different deigning ervice life and chloride attack. 2. LOAD EFFECT STANDARDS FOR VARIOUS DESIGNING SERVICE LIFE 2.1 relationhip between variable load tandard value and deign reference period In the performance-baed tructural deign, the tandard value of variable load hould be determined firt, according to the requirement of proprietor and uer, then the variou performance indexe of component or the whole tructure can be analyzed and calculated (Jin & Zhong, 2009). Studie howed that with longer deign reference period, it i more poible for the peak load to appear (Wang et al., 2009; Zhang, Gao, & Li, 2000). That i to ay, the variable load tandard value change with the deign reference period. Current code for harbor load provide the variable load tandard value for 50-year deign reference period only. If the proprietor or uer require a deigning ervice life unequal to 50 year, uing a 50-year deign reference period, to determine the variable load tandard value may be either conervative or inecure. Thu, performance-baed 352

2 Study on Variable Action Value Standard for Harbor Infratructure 353 deign hould conider the variable load value under the circumtance of different deigning ervice life. Thi diertation ued the cargo loading in harbor a an example to tudy it variable load value tandard for different deign reference period. 2.2 Model for variable load effect Determining variable load value tandard according to different deigning ervice life i equivalent to ranking the variable load into different level, and load for each level can be determined on the bai of exiting model of variable load. According to the tationary binomial random proce model { Qt (), t [0, T] } and relative hypothei, the probability ditribution function of peak load Q T in the deign reference period T i F ( x) = [ F ( x)] m. (1) QT Q In thi function, m = pr i the average appearing time of load in deign reference period; p i the probability for the load appearance on each period. If the probability ditribution at any given time follow the extreme I ditribution: F ( x) = exp[ exp( ( x u))] Q. (2) u = /. (3) = 1. 6 (4) In which, u mean mode; a i the cale parameter. Variable load tandard value i equal to ome fractile on the peak load probability ditribution for deign reference period. The relationhip among the peak load ditribution, at any given time, the peak load ditribution for deign reference period, and the load tandard value i hown in Figure 1. Figure 1. Relationhip between any time point and deign reference period of the bigget live load ditribution. Therefore, there i a relationhip lied between the average value and tandard deviation of load ditribution in a certain deign reference period T and of load ditribution at any given time: 6 lnr Q (5) QT Q = QT Q. (6) The relationhip between the tandard value of load and the auring rate in deign reference period T i a follow: p = F ( Q ) = exp[ exp( ( Q u))] k QT KT KT. (7) Q = u 1 ln( ln( p )) KT k. (8) which can be further implified a the following: ln(ln(1/ p )) k Q = 0.45 KT QT QT QT (9) ln(ln(1/ p )) k = QT QT In thi function, Q KT i the correponding load tandard value to deign reference period T; QT, QT are the average value and tandard deviation of load ditribution in reference period T; Q, Q are the average value and tandard deviation of load ditribution at any given time; r i the average change time of load in deign reference period T. 2.3 Determination of cargo loading tandard value for different deigning ervice life From the April of 1984 to the October of 1988, China ha invetigated and analyzed the cargo loading of three harbor in Shanghai, Tianjin, Dalian, and eight river port in Changha, Wuxi, Nanjing, Harbin, and o on. The tatitical reult how that the cargo loading follow the extreme I ditribution (Drafting Group of Standard, 1992). In the current Code for Load of Port Engineering (JTS ), the deign reference period for harbor cargo loading i 50 year. Cargo variable loading tandard value i determined by Q = Suppoe that KT QT QT the ditribution of Q KT alo follow the extreme I ditribution, the auring rate for thi i 95.8%. To keep the load auring rate or the rik rate for different deigning ervice life accord with current code, thi diertation ued an identical auring rate 98.5% a the etting level (alo known a equal exceeding probability). According to the tatitical information (Drafting Group of Standard, 1992), for different harbor type, under normal handing technology, the cargo loading tandard value for different deigning ervice life can be calculated by function (5), (6), and (9). Conidering that cargo loading tandard value in the code hould not change with the deigning ervice life; thu, a loading adjutment coefficient T i ued

3 354 Structural Performance to amplify the effect of deigned value of load. T i determined a follow: = Q KT. T (10) Q K50, In thi function, Q K, 50 i the load tandard value that correpond to 50-year deign reference period. Uing function (9) and (10) can calculate the load adjutment coefficient for harbor and river port in different deigning ervice life. The calculation reult are provided in Table 1. The value not hown in the table can be calculated by linear interpolation. Table 1. Load adjutment coefficient of harbor/river port loading dock good load baed on conidering tructure deign ervice life. Deigning ervice life/year Harbor T River port Deigning ervice Life/Year Harbor T River port The effect level for chloride environment differ among the code of countrie. For example, the Eurocode2 (Britih Standard Intitution [BSI], 2004) for Europe make three effect level for two kind of chloride environment eparately; the American Concrete Intitute [ACI] Committee 318 (2008) for America divided the effect level into three kind according to the requirement of protection of teel corroion. Although variou countrie had their rank of chloride environment, they did not provide the eigenvalue of environmental load correponded to different environmental effect level. Thu, the relationhip between tructure performance and the demand of proprietor i not clear enough. The deigner can only obtain the durability performance requirement of material according to the correponding chloride environment effect level and the deigning ervice life and then provide the contruction meaure, concluding minimum concrete cover, maximum water cement ratio, and o on., that i to aure the durability of harbor tructure from contruction meaure, which prevent the proprietor and uer from preciely knowing how long can the tructure lat in the future. To build the quantitative relation for the performancebaed harbor concrete tructure durability ultimate limit tate deign, it i neceary to tudy the value tandard of chloride corroion load. In tructural deigning, the load effect for different deigning ervice life can be obtained by multiplying the load effect calculated according to the code (50-year reference period) by the adjutment coefficient T, a howed in function (11): S = ( S + S ) d 0 G Gk Q T Qk. (11) In the function, G, Q are the partial factor of permanent load and variable load; 0 i the tructural importance factor. 3. ENVIRONMENTAL EFFECT LEVEL AND EFFECT STANDARD 3.1 Environmental effect level The factor that can caue tructure deterioration are of multiapect. According to the corroion mechanim of teel and concrete, Code for Durability Deign of Concrete Structure (GB/T ) of China divided the environment into five level: normal environment, freeze thaw environment, marine chloride environment, deicing alt and other chloride environment, and chemical corroion environment. On the bai of environmental level, the marine chloride environment i divided into four effect level: C medium, D evere, E very evere, and F extreme evere. Detailed decription are alo provided. 3.2 Determination of chloride corroion load tandard For the harbor tructure in chloride environment, the diffuion of chloride ion i caued by the chloride concentration difference. The higher the urface chloride concentration i, the bigger the concentration difference i in and out, and more chloride ion will get into the concrete, teel will get corroded more eaily, which will reult in the deterioration of tructural performance. Hence, the urface chloride concentration of concrete C can be taken a the environmental load. The urface chloride concentration i mainly determined by local environmental condition, a well a the concrete quality, hape of the tructure, and the expoed part. A Fluge reported (Fluge, 2001), chloride ion maximum concentration decreae with the rie of altitude above ea level. Part with lower chloride concentration are mainly thoe who are expoed to the prevailing wind direction or be wahed by ea water all the time. Chloride ion at thee part will be occaionally wahed away by water and ettle down omewhere ecluded. The dicretene and variability of urface chloride concentration for all the concrete tructure are big (Odd, 2009). For newly built harbor concrete tructure, when evaluating and chooing the chloride ion concentration, it i better to ue the

4 Study on Variable Action Value Standard for Harbor Infratructure 355 field invetigation data of imilar tructure in imilar environment condition. When there i no field urvey information, the normal experience in reference can be ued to chooe an adequate chloride load. Baed on the immene invetigation information on the concrete tructure at Norway eahore, Odd (2009) gave a guidance of the dicreet value of tructure chloride concentration in evere marine environment. The data are howed in Table 2. Table 2. Chloride ion load-etimated value of concrete tructure in propoed evere ocean environment by odd.e.gj rv. Chloride load C (%, for cement ma) Average Standard deviation High 5.5 (0.96) 1.3 Average 3.5 (0.61) 0.8 Medium 3.5 (0.61) 0.3 The value in bracket are the percentage of concrete ma. In the converion, the ma of each cubic meter of concrete i 2300 and 400 kg for the binding material. According to the 4600 chloride ion ampling analye of Bridge Gim y Straumen in Norway and other 35 eahore bridge, Fluge (2009) divided four zone for chloride concentration, a howed in Table 3, in which the eigenvalue of urface chloride concentration C n = C + 1.3σ. Table 3. Propoed urface chloride ion concentration value by fluge (%, for concrete ma). Altitude above ea level/m Average value C Standard deviation σ Eigenvalue C n > Val and Stewart (2003) uggeted that the urface chloride load C in different environmental condition hould value according to Table 4 and take logarithmic normal ditribution a the probability ditribution. Table 4. Propoed urface chloride ion concentration value by tewart (unit: kg/m 3 ). Environmental condition Average value Variable coefficient Splah zone 7.35 (1.28) 0.70 Offhore atmopheric environment 2.95 (0.51) km 1 km Ditant from eahore 1.15 (0.20) 0.50 The value in bracket are the percentage of concrete ma. In the converion, the ma of each cubic meter of concrete i 2300 and 400 kg for the binding material. Baed on the expoure tet and invetigation at engineering work, Wang, Tian, and Fan (2010) dicovered that uing fly ah and lag will increae urface chloride concentration. After tatitical analyi, the concrete maximum urface chloride concentration i provided in Table 5. Table 5. Propoed bigget urface chloride ion concentration value by Wang Shengnian and o on (%, for concrete ma). Zone Atmopheric zone Splah zone/tidal range zone Portland cement Fly ah cement/ Slag cement North Eatern China Southern China In the concrete tandard of JSCE publihed in 2002, the concrete urface chloride concentration value in offhore atmopheric zone were raied, a hown in Table 6 (CCES01, 2004). And the value ued in American Life-365 (2000) tandard deign procedure were given in Table 7. Table 6. Surface chloride ion concentration of concrete in inhore atmopheric zone (japan ociety civil engineer; %, for concrete ma). Splah zone Ditance from eahore/km Around coatline Concentration in the table i the relative ratio to the ma of each cubic meter of concrete (about 2300 kg). Table 7. Adopted urface chloride ion concentration of harbor engineering concrete in life-365 deign (%, for concrete ma). Zone Accumulation peed of urface chloride/%/year Maximum urface chloride concentration/% Tidal range zone Intant 0.8 Salt fog zone m within eahore 1500 m within eahore Concentration in the table i the relative ratio to the ma of each cubic meter of concrete (about 2300 kg). Bamforth (1994) uggeted that the urface chloride concentration C ued for deign can take the value in Table 8 a reference.

5 356 Structural Performance Table 8. Propoed urface chloride Ion concentration C for deign by Bamforth (%, for concrete ma). Environment Portland cement Cement concrete with admixture Splah zone 0.75 (4.5) 0.9 (5.4) Salt fog zone 0.5 (3.0) 0.6 (3.6) Atmopheric zone 0.25 (1.5) 0.3 (1.8) Value in bracket are the ratio for occupying the ma of binding material, approximately 400 kg binding material for each cubic meter of concrete. Vu and Stewart tudied about 1158 bridge and achieved the reult that the urface chloride concentration C (kg/m 3 ) of concrete in eahore atmopheric environment i connected with it ditance from coatline d (km), the value of which can be calculated by function (12): C ( d) = 2.95, d < 0.1 C ( d) = lg d, 0.1< d < (12) = > C ( d) 0.03, d 2.84 Dura Crete of Europe thought that urface chloride concentration ha a relationhip with environmental condition, water cement ratio of concrete, and binding material type, of which the average value ue function (13) to calculate, and the deign value determined by function (14): C = A ( W B) c. (13) C = A ( W B). c c (14) In thee function, A c i the regreion parameter decribing the relationhip between urface chloride concentration and water cement ratio, whoe value i provided in Duracrete (2000); c i the partial coefficient of urface chloride concentration. According to the ratio between the expene ued to contain teel corroion and the tructure repairing expene, the partial coefficient i determined a 1.70, 1.40, and 1.20, repectively correponding to a higher, equal, and lower rate. According to the maximum water cement ratio requirement of concrete in chloride environment from our tandard GB/T50476 (2008) and the calculation method given by Dura Crete, we ued the condition of water cement ratio at 0.35 and 0.4 a two example, to calculate the average value and deign value of chloride concentration in different zone. The reult are howed in Table 9. Taken the tudie of Odd (2009), Val and Stewart (2003), Wang et al. (2010), CCES01 (2004), Life- 365 (2000), Banforth (1994), Vv and Stewart (2000), and Duracrete (2000) together, there are mainly two direction. One i to divide region along the altitude above ea level, o that underwater zone, tidal range zone, plah zone, atmopheric zone are partitioned; the other i to divide region along the horizontal direction, according to the ditance from coatline. Difference exit among the uggeted value of urface chloride concentration from different reference. But they hare accordance with each other in the general trend, that i, the more corroive the environment i, the higher urface chloride concentration will be a tructure get. Surface chloride concentration in plah zone, tidal range zone i higher than atmopheric zone. With the increae of ditance from coatline, urface chloride concentration decreae. To determine the tandard value of chloride concentration in different level of chloride environment, thi diertation ued the environmental level in Code for Durability Deign of Concrete Structure of China (GB/t ) a tandard. According to the detailed decription of different zone, combining the reult of Odd (2009), Val and Stewart (2003), Wang et al. (2010), CCES01 (2004), Life-365 (2000), Banforth (1994), Vv and Stewart (2000), and Duracrete (2000), conidering that the urface chloride concentration i a kind of environmental effect, which hould maintain a certain aurance rate, we ugget Table 9. Calculated urface chloride ion concentration by adopting dura crete method in thi article. W/C Environment C (% for concrete ma) Average value Deign value Portland cement Fly ah Slag Silica fume Portland cement Fly ah Slag Silica fume 0.35 Underwater zone Splah/tidal range zone Atmopheric zone Underwater zone Splah/tidal range zone Atmopheric zone Ma of each cubic meter of concrete i 2300 kg, for binding material i 400 kg. The partial coefficient c = 1.4.

6 Study on Variable Action Value Standard for Harbor Infratructure 357 Table 10. Propoed urface chloride ion load characteritic value in thi article (%, occupying ma of concrete). Environment Effect level Environmental condition Average value C Marine chloride environment Standard deviation n σ Eigenvalue C n = C +1.3σ III-C Underwater and underearth zone: urrounded by ea water or buried in the ground forever III-D Atmopheric zone (light alt fog): atmopheric zone more than 15 m above the average water level; outdoor onhore environment more than m away from the tide coatline III-E Atmopheric zone (evere alt fog): atmopheric zone above the average water level within 15 m; outdoor onhore environment away from the tide coatline within 100 m and above the ea level within 15 m Tidal zone and plah zone, nonhot region III-F Tidal zone and plah zone, hot region that the eigenvalue of concrete urface chloride load i C n = C (90% aurance rate). In the meantime, the diertation provided the eigenvalue of chloride load correponding to different chloride environment level in Table 10. Since the urface chloride concentration ha a large dicretene and variability, the uggeted chloride load value hould get further modification according to the future accumulation of tatitical information for pecific cae in our country. Anyhow, uggeted value in the table provide the deigner a foundation for the environment load value in performance-baed durability deign. 4. CONCLUSION (1) Thi diertation uing the equal exceeding probability principle, combining with current tandard, baed on the analyi of the relationhip between variable load and deign reference period and the model of variable load effect, gave the load adjutment coefficient T for harbor and river port in conideration of the tructure deigning ervice life. Thi adjutment coefficient enable the proprietor and uer to get a value tandard of load correponding to their requirement. With a imple form, it i eay to undertand and apply. (2) On the bai of exiting reearch achievement, combining with the level diviion of chloride environment in GB/T , we provided the uggetion value tandard of chloride load correponding to different chloride environment level. Thi value tandard can be ued a the foundation of environment load value in performance-baed durability deign. (3) The accuracy of urface chloride concentration value depend on immene actual urvey data. We ugget that the value tandard of chloride load correponding to different chloride environment effect hould better get further modification on the bai of future urvey information. Acknowledgment Thi work wa upported by the National Natural Science Fund Program ( ) and Technology Project of Minitry of Tranport ( ). REFERENCES American Concrete Intitute (ACI) Committee 318. (2008). Building code requirement for tructural concrete (ACI ) and commentary (ACI318R-08). Detroit, MI: ACI. Britih Standard Intitution (BSI). (2004). Eurocode2 (EN1992): Part 1 1: General rule and rule for building. London: Author. Banforth, P. B. (1994). Specification and deign of concrete for the protection of reinforcement in chloride contaminated environment (pp ). Bournemouth: UK Corroion and Eurocorr 94. CCES01. (2004). Durability deign and contruction guideline of concrete tructure. Beijing: China Architecture & Building Pre. Drafting Group of Standard. (1992). Reliability of port engineering tructure. Beijing: China Communication Pre. DuraCrete. (2000). General guideline for durability deign and redeign. The European Union Brite EuRam III, Reearch Project No. BE Probabilitic performance baed durability deign of concrete tructure. Document Report 15:109. Fluge, F. (2001). Marine chloride: A probabilitic approach to derive proviion for EN In Proceeding, third workhop on ervice life deign of concrete tructure: From theory to tandardiation, DuraNet, Trom (pp ).

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