ANALYSIS OF RC BRIDGE DECKS FOR SELECTED NATIONAL AND INTERNATIONALSTANDARD LOADINGS USING FINITE ELEMENT METHOD

Transcription

1 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: ANALYSIS F RC BRIDGE DECKS FR SELECTED NATINAL AND INTERNATINALSTANDARD LADINGS USING FINITE ELEMENT METHD Hemalatha A 1, Ashwin K. N 2, Dattatreya J.K 3, S.V.Dinesh 4 1 Post raduate Student, 2 Assistant Professor, 3 Research Professor, 4 Professor and Head, Department of Civil Enineerin, Siddaana Institute of Technoloy, Tumkur. hemacivil1@mail.com, meetashwinkn@yahoo.com, jk.dattatreya@mail.com, dineshsv24@yahoo.com Abstract The paper presents the comparison of the effect of different standard s on a set of reinforced concrete bride s usin the finite-element method. The parameters investiated include the aspect ratio (span/width) and type of. The investiations are conducted on two lane slab bride s of span 5m to 9.5m and two lane T beam bride s of span 7.5m to 2m. A total of 36 bride models were analyzed. The variation of different critical structural response parameters such as deflection, lonitudinal bendin moment, transverse moment, shear force and torsional moments are evaluated for ( Class A and s), (HL93) and standard (LM1). The results shows that the maximum difference in deflection and lonitudinal bendin moment for the two standard ranes from 5 to 15%. While the difference between correspondin values for the in the rane of 5 to 17%. The maximum axle load of euro standard is found to be 2.2 times hiher than maximum axle load hence the values of structural response parameters are increased by 1.7 to 1.8 times. Therefore there is a need for adoptin simplified and more realistic standard loads in the future. Keywords: Brides, Concrete slabs; Finite element method; T-beam bride s; Aspect ratio; Live load, code, code and code *** INTRDUCTIN Vehicular loads constitute the most important type of to be considered in the desin of brides. Many countries have formulated their own standard specification and codes of practice for brides such as, and EUR codes, with a view to establish a common procedure for the desin and construction of brides. Most of the prevailin standard loads includin the bride loads have very little rational basis and lackin relevance to the current vehicular confiuration plyin on the roads and brides. With rowin tendency to overload the vehicle beyond the permitted leal axle load and also increase in vehicular traffic, it has become necessary to have a reappraisal of current bride s of to evaluate the safety of existin brides and for the desin of many new brides for increased manitude of loads and intensity of traffic. Reappraisal of the safety of existin brides and desin of new brides is rather difficult in the Indian context due to complicated load pattern of different classes of load therefore there is a need to simplify the standards and adopt more realistic desin vehicle in similar to that adopted by and EUR code. Also the standards depends on different factors such as type of vehicle plyin, their capacities, the intensity and frequency of traffic and loistic considerations for eneral mobilization in case of national emerencies. They may also have a bearin on the permissible stresses in materials and desin methods in the country concerned. Therefore the comparisons made may not be viewed as strictly quantitative, it will be more reasonable to take them as reflectin the lobal trend of the lobal effects of the s on the bride. Earlier investiation on comparative study of hihway bride s in different countries by Thomas(1975) concluded that there was a wide variation in the hihway bride standards of different countries and also Medhat Kamal Abdullah(213) studied a comparison between different standards such as, Eyptian and code s and concluded that Eypt and code s were much hiher than the s. Also earlier analytical studies on brides shows that modelin of brides usin FEM is easy and it ives accurate values, some of the studies are Maher Qaqish et al. (28) found that the results obtained from s are conservative and Kanchan Sen Gupta et al.(211) carried out the investiations on Simply supported concrete bride slab for vehicle s usin finite element analysis. Reduction factors will be suested to apply to the FEM IC-RICE Conference Issue Nov-213, 59

2 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: bendin moment results to et the results similar to bendin moments. Critical appraisal of literature shows that most of the studies on comparison of s have adopted simplified method such as rillae analysis and considered only simple brides which are amenable to hand computation. Since analytical modelin usin FEM ive a complete picture of the bride response. Therefore the comparisons of the effect of different standard s on a set of reinforced concrete bride s usin the finiteelement method has been carried out and some FEM results are found underestimated for those modifications are needed. ii. A typical simply supported, sinle span, two lane T beam bride s of span 7.5m to 2m at equal intervals of 2.5mwith constant slab depth of.3 m and beam dimension.4m x 1.6m. The width of each bride is 9.5m in all cases and it includes 1m footpath on both side of carriaeway. Each T beam bride s consist of three lonitudinal T- beams and two diaphrams at ends. The eometric confiuration of slab bride and T beam bride are indicated in Fi.1 and PARAMETRIC STUDY Two types of bride s are considered for the analysis. i. A typical simply supported, sinle span, two lane slab bride s of span 5m, 7.5m and 9.5m with constant slab depth of.75m. Fi.1.Description of Deck slab bride. Fi.2.Description of T beams bride. 3. LAD N BRIDGE DECK MDELS In order to obtain the maximum structural response for the desin, different positions of each type of system as per 6:2, LRFD desin specification and code part 2 are analyzed. For the present study class A and s are selected by seein table 2 of 6:2, HL 93 from code and Load model 1(LM1) from EUR code are considered. 4. FINITE ELEMENT MDELLING The bride s are analyzed usin Finite element method. The 4 nodded flat plate elements are used to model the concrete slabs and the 2 nodded beam elements are used to model the concrete lonitudinal beams and ends diaphrams. The mesh size of plate element is.2m x.2m.the material property of the concrete considered are the compressive strenth (f ck ') = 25 Mpa, the modules of elasticity (E c ) = 25 Gpa, the Poisson's ratio (ν) =.2 and density = 25kN/m RESULTS AND DISCUSSINS The followin observations are made on the basis of the finite element analysis carried out and the results are represented in the followin charts and tables. 5.1 Variation of Important Structural Response Parameters in Slab Bride Decks under Selected Loadins (A) Deflection: It is seen from Fi.7a.thatthe maximum deflection values caused by and wheeled vehicle do not differ by more than 7% for the selected aspect ratios of Slab IC-RICE Conference Issue Nov-213, 6

3 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: Bride s investiated. Althouh the total axle load is less for compared to, closer wheel and axle spacin counteract the effect of decreased axle load and thereby induce the almost same order of deflection. For similar cases the deflection produced by vehicle HL 93 is varyin from -7 to 17% more than that of, althouh the total load of vehicle exceeds 26% of. In case of EUR standard vehicle LM1 there is a substantial increase in deflection from 1.7 to 1.8 times that of due to aainst the maximum wheel load increase of 2.2. For the iven class of the deflection has increased approximate in proportion to the cube of the span in all cases. Deflection in mm Aspect ratio (L/B) Lonitudinal bendin moment in knm class A a. Variation of deflection. b. Variation of lonitudinal bendin moment. Fi.7.Variation of maximum Deflection and lonitudinal bendin moment in Slab Bride s under selected s. (B) Lonitudinal Bendin Moment: It is seen from Fi.7b. that the maximum bendin moment values caused by, and vehicle do not differ by more than 5% which is much less than that of deflection for the selected aspect ratios of the slab bride s. As bendin moment is the second derivative of deflection, the chane in bendin moment will be a fraction of chane in deflection. The order of increase in bendin moment is similar to that of chane in deflection. But the maximum lonitudinal bendin moment caused by EUR is more than 1.71 to 1.77 times that of due to aainst the maximum wheel load increase of 2.2. (C) Transverse Bendin Moment and Torsional Moment It is seen from Fi.8. that the transverse moments and torsional moments show considerable difference for different standard loads and the order of difference ranes from 26 to 46% for class compared to in case of transverse moment and 26 to 85% in case of torsional moments. This is attributed to the considerable difference in wheel spacin and vehicle spacin, for example the spacin between two adjacent is 1.8mwhere as the spacin between two inner wheels of typical axle of class load is.79m. However the transverse moment and torsional moment ranes from 15 to 2% and 3 to 4% respectively of correspondin lonitudinal moment. Further the additional lonitudinal moment computed from the torsional moment is about 5 to 55% of the value of the latter. Therefore in view of considerable width of slab and its thickness the torsional and transverse moment cannot produce any sinificant distortion of and they et further reduced more than 5% of their oriinal value on crackin durin service load stae. The load shows a result almost similar to in respect of transverse moment but slihtly hiher increase of 29 to 31% in torsional moment due to difference in wheel confiuration. The EUR standard load results in enhancement in manitude of transverse and torsional moments in the rane of 1.98 to 2.1 and 1.54 to 2.2 times respectively compared to that of, mainly due to the wheel confiuration chanes. IC-RICE Conference Issue Nov-213, 61

4 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: Transverse bendin moment in knm class A Trsional moment knm a. Variation of transverse bendin moment. b. Variation of torsional moment. Fi.8.Variation of maximum Transverse moment and maximum Torsional moments in slab brides under selected s. 4.2 Variation of Important Structural Response Parameters in T Beam Bride Deck Slabs under Selected Loadins It is seen from Fi.1. that the effect of standard on T beam bride slab is found to follow a pattern similar to that slab bride s in respect of deflection, lonitudinal moment with a difference of -3 to 11% in deflection, -29 to - 82% in lonitudinal bendin moment and -13 to -25% in transverse bendin moment in case of and with a difference of -14 to -44% in deflection, -19 to -25% in lonitudinal bendin moment and -23 to -37% in transverse bendin moment in case of. It is seen that the order of increase in maximum values of deflection, lonitudinal bendin moment and transverse bendin moment of T beam bride s due to standard is about 1.3 to 2.2 times that of, which is much less than that of slab bride. In case torsional moment the increase is hiher for compared to the class A primarily due to closed wheel spacin in the transverse direction and in case of EUR torsional moment ranes from 1.6 to 3.2 times. Deflection in mm Lonitudinal bendin moment in knm class A IC-RICE Conference Issue Nov-213, 62

5 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: Transverse bendin moment in knm class A Torsional moment in knm class A Fi.1.Variation of maximum Deflection, maximum lonitudinal moment, maximum Transverse moment and maximum Torsional moments in slab of T beam brides under selected s. 4.3 Variation of Important Structural Response Parameters in the Lonitudinal Girders of T Beam Bride Deck under Selected Loadin:- The variation of maximum deflection, maximum shear force, maximum lonitudinal bendin moment and maximum torsional moments in the lonitudinal irders of T beam bride s are tabulated in the followin tables 1 to 4.The effect of standard on T beam bride s is found to follow a pattern similar to that slab bride s in respect of deflection, lonitudinal moment with a difference of 17 to 37% in deflection and -1 to -27% in lonitudinal bendin moment in case. The correspondin differences in case of are 8 to -22% in deflection and -4 to -15% in lonitudinal bendin moment. It is seen that the order of increase in maximum values of deflection, lonitudinal bendin moment and transverse bendin moment of T beam bride s due to standard is about 1.7 to 1.9 times that of. In case of torsional moment the increase is hihest for compared to the primarily due to closed wheel spacin in the transverse direction. The variation in torsional moment is much less compared to a slab because the presence of irders in both direction and also reduce the distortion and warpin caused by torsion. The maximum shear force in beams mainly depends on the manitude of, since wheel load of, is more compared to, the maximum shear force values produced by, increased by -71 to 52% and.5 to 1.8 times respectively compared to that of. Althouh the class wheel load is small compared to wheel load due to the closed wheel spacin the maximum shear force values decreased by -1 to 91%. IC-RICE Conference Issue Nov-213, 63

6 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: Table.1. Variation of Deflection in lonitudinal irders Aspec t ratio (L/B) Deflection in beam 1 in mm Deflection in beam 2 in mm Deflection in beam 3 in mm Table.2. Variation of Shear force in lonitudinal irders Aspec t ratio (L/B) Shear force in beam 1 in kn Shear force in beam 2 in kn Shear force in beam 3 in kn Table.3. Variation of Lonitudinal bendin moments in lonitudinal irders Aspec t ratio (L/B) Bendin moment in beam 1 in knm Bendin moment in beam 2 in knm Bendin moment in beam 3 in knm class A IC-RICE Conference Issue Nov-213, 64

7 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: Aspe ct ratio( L/B) Table.4. Variation of Torsional moments in lonitudinal irders Torsional moment in beam 1 in knm Torsional moment in beam 2 in knm Torsional moment in beam 3 in knm class A class A class A Comparison of important structural response parameters in selected slab bride and T beam bride slab of aspect ratio.789 under selected :- The comparison of important structural parameters in slab bride and T beam bride slab of aspect ratio.789 is shown in the Table.9. The maximum deflection in T beam bride slab is reduced by 25 to 3 % in case of class A, and EUR compared to slab bride but in case of maximum deflection increases by 1.95% because of less wheel spacin. In case of lonitudinal bendin moment in T beam bride slab is decreased by 76 to 81% compared to slab bride for all selected cases. Similarly the transverse bendin moment and tosional moment in T beam bride slab is reduced by 33 to 65% compared to slab bride for all selected cases. This reduction in important structural parameters in T beam bride slab compared to slab bride is due to the provision beams in both direction of slab. Table.5. Comparison of important structural response parameters in selected slab bride and T beam bride slab of aspect ratio.789 under selected Loadin Loadin Loadin Loadin EUR Loadin Bride type Slab T beam Slab T beam Slab T beam Slab T beam Deflection in mm Lonitudinal bendin moment in knm Transverse bendin moment in knm Torsion in knm IC-RICE Conference Issue Nov-213, 65

8 IJRET: International Journal of Research in Enineerin and Technoloy eissn: pissn: CNCLUSINS a. The maximum values of deflection and lonitudinal bendin moment caused by and wheeled vehicle do not differ by more than 7% for the selected aspect ratios of Slab Bride s investiated.the correspondin difference in case of T beam s is -22 to 37%. b. causes -7 to 17% hiher deflection and less than 5% in case of lonitudinal bendin moment compared to. While the correspondin rane is 1.7 to 1.8 times for EUR. c. In eneral maximum transverse and maximum torsional moments are more pronounced in case of slab bride s compared to T beam s and are found to be in the rane of 15 to 2% and 3 to 4% respectively of correspondin lonitudinal moment in case slab bride s and less than 5% of correspondin lonitudinal moment in case of T beam s because of hiher transverse moment of inertia and torsional riidity. d. Because of their lower manitude and thick solid sections are adopted for the members the maximum torsional moment and maximum transverse bendin moments may not have any major sinificance on the desin of slab bride and T beam bride. e. The provision of T beam bride s instead of solid bride s of same aspect ratio is found to reduce in maximum deflection values by 25 to 3% and the maximum lonitudinal bendin moment values are reduced by 76 to 81%. Another major advantae is the reduction in maximum torsional and maximum transverse moments by 33 to 65%. f. The study shows that there is a wide variation in the hihway bride standards of different countries. However the chanes in critical response parameters are not very sinificant. has adopted 6 standard s with widely varyin manitude of wheel and wheel and axle spacin. However the investiations indicate that there is no appreciable difference in structural response parameters for the different s. It is suested that may also adopt the sinle desin vehicle with simple confiuration for standard similar to and EUR standard which have only 2 to 3 axles. Element Method and Specification KMITL Sci. Journal. Vol.8 No.1 January June, 28. [4] KanchanSen Gupta and SomnathKarmakar Investiations on Simply supported concrete bride slab for vehicle s usin finite element analysis Journal of Earth Sciences and Enineerin, Volume 4, No 6 SPL, ctober 211, PP [5] 6:2 Standard Specifications and Code of Practice for Road Brides, Section-II Loads and Stresses, Indian Road Conress, New Delhi. [6] American Association of State and Hihway Transportation fficials () specifications. [7] code 1 Part 2 - pren [8] 21:2 Standard Specifications and Code of Practice for Road Brides, Section-III Cement Concrete (Plain and Reinforced),Indian Road Conress, New Delhi. REFERENCES [1] P.K. Thomas A Comparative Study of Hihway Bride Loadins in Different Countries supplementary report 135UC, Transport and road research laboratory. [2] Medhat Kamal Abdullah Comparison between Hihway Codes for Traffic Loads on Brides Life Science Journal 213: PP [3] Dr.MaherQaqish, Dr.EyadFaddaand Dr.EmadAkawwi Desin of T-beam Bride by Finite IC-RICE Conference Issue Nov-213, 66