implementation of the aashto lrfd bridge design specifications for bridge superstructure design

International Journal of Applied Sciences, Engineering and Management ISSN 2320 – 3439, Vol. 02, No. 02, March 2013, pp. 37 - 40

IJAEM 020203 Copyright @ 2013 SRC. All rights reserved.

Traffic Flow from phase 4

Implementation of the AASHTO LRFD Bridge Design Specifications for Bridge Superstructure Design

ADIL RAFIQ

1, AKHTER NAEEM KHAN2 , KHAN SHAHZADA

2, SYED SHAHAN ALI SHAH3,

SYED AZMAT ALI SHAH3, ZAIGHAM ALI

4 1Assistant District Monitoring Officer, Monitoring Department KPK, Peshawar Pakistan

2 Faculty member, University of Engineering and Technology, Peshawar Pakistan 3Faculty member, Iqra National University, Peshawar Pakistan

4 Faculty member, Gandhara Institute of Science & Technology, Peshawar Pakistan Email: [email protected]

Abstract: This research paper presents the procedure of redesign of an existing bridge. Hayatabad Medical complex (HMC) bridge Peshawar Pakistan was early designed in 1970’s according to the old bridge code of Pakistan 1967. In this project the bridge was redesigned according to the AASHTO LRFD bridge design specification 2005. Only superstructure was considered in the design. Using HL-93 Vehicle loading, influence lines were developed and distribution factors were calculated. Then these Influence lines functions were used to calculate the shear force and bending moment of the above stated bridge. After the design, recommendation were given to Peshawar development Authority. Keywords: AASHTO, LRFD bridge design specification, HL-93 Vehicle loading, influence lines, Distribution factors Introduction: The provisions of AASHTO LRFD bridge design Specifications are intended for the design, evaluation, and rehabilitation bridges. These Specifications employ the Load and Resistance Factor Design (LRFD) methodology using factors developing from current statistical knowledge of loads and structural performance. Seismic design shall be in accordance with either the provisions in these Specifications or those given in the AASHTO Guide Specifications for LRFD Seismic Bridge Design. Construction specifications consistent with these design specifications are the AASHTO LRFD Bridge Construction Specifications(3). The bridge studied in this project was located at the entry of phase 4, Hayatabad Peshawar Pakistan. There were two roadways each having a three span bridge over the Nullah, one for entrance and one for exit. Some of the girders in the bridge at the exit roadway were found cracked. These Cracks didn’t reflect any serious damage for normal traffic. But we can also expect extreme conditions of traffic because the bridge is located in the place through which heavily loaded traffic goes to Afghanistan. This bridge was constructed somewhere in 1970’s. Methods of design were based on the codes of that time. After the new AASHTO LRFD bridge design specification 2005 it was thought to recheck the design of bridge using th above stated specifications. Methodology: The influence functions: Each of our girder was 42ft long, The influence functions for our girders are given in figure 1,

Figure 1: Influence line functions Distribution factor – Case study: The distribution factors found out for the girders are as follows(1), Girder width, b = 18in = 1.5ft Girder Spacing, S = 72in = 6ft Span Length, L = 504in = 42ft Deck Thickness, ts = 8in = 0.667ft Deck Modulus of Elasticity, Ec = 3600ksi = 518400ksf

Location of Cracks

ADIL RAFIQ, AKHTER NAEEM KHAN , KHAN SHAHZADA , SYED SHAHAN ALI SHAH, SYED AZMAT ALI SHAH, ZAIGHAM ALI


Load Placement for R200 - Single Lane Loaded6'6'6'6'3'-6"

6'16kips 16kips

404 501.4301.4

301.4

6'

3'-6" 6' 6' 6' 6'

16kips

Load Placement for M204 - Single Lane Loaded

204

6'16kips 16kips16kips

16kips

204


16kips

6'6'6'6'3'-6"

6'

Girder Modulus of Elasticity, Ec = 3600ksi = 518400ksf Applying the formulas we get the following summary of distribution factors tabulated in table 1. Table 1: Summary of distribution factors

Analysis and design – Deck Slab Deck thickness We assumed, hs = 8in Weights of Components Slab 8in thick ws = (0.15/123)*8 = 0.0006944ksi Future Wearing Surface 3in thick wDW =(0.141/123)*3 = 0.0002448ksi Cantilever Overhang Attatchments 9in thick wo = (0.14/123)*9 = 0.0007292ksi Dead Load Moments and Shear: R200 = w (Net Area w/o cantilever) S M200 = w (Net Area w/o cantilever) S2 Deck Slab R200 =0.01964k/in, M200 =0k in/in, M204 =0.27792k in/in, M300 =-0.38556k in/in Future Wearing Surface R200 =0.024154k/in M200 =0k in/in M204 =0.097967k in/in M300 =-0.1359k in/in Cantilever Overhang Slab R200 =0.03997k/in M200 =-0.6125k in/in M204 =-0.30135k in/in M300 =0.165375k in/in Cantilever Overhang Attachments R200 = 0.041969 k/in M200 = -0.64313 k in/in M204 = -0.31642 k in/in M300 = 0.173644 k in/in

Live Load Moments & Shear: The width of equivalent transverse strips

over which the wheel loads can be considered distriuted longitudinally in CIP concrete decks is given as: Overhang. 1140 + 0.833X Positive Moment. 660 + 0.55S Negative Moment. 1220 + 0.25S Where, (X = 0) is the distance b/w wheel load & centre line of the support. (S= 72in) is the spacing of the T-beam. No. of Design Lanes NL = INT(24ft/12ft) = 2 For analysis Loads are placed at various positions

shown in figure 2, 3 and 4.

Figure 2: Load placement for R200

Figure 3: Load placement for M204

Figure 4: Load placement for M 300

Tire load P = 16kips Maximum Positive Live Load Moment Transverse strip width =1650mm = 66in Single loaded lane R200 =0.12541k/in M204 =3.61309k in/in Two loaded lane R200 =0.12963k/in M204 =3.73667k in/in Maximum Negative Live Load Moment Transverse strip width =1670mm=66.8in M300 =-3.60293k in/in Maximum Live Load Reaction at Exterior Girder

Interior Exterior

Lane loaded

Single Multi Single Multi

Moment 0.46965 0.60457 0.6 0.60457

Shear 0.59684 0.6717 0.6 0.40302

305

16kips

205


16kips

6'6'6'6'3'-6"

6'

Implementation of the AASHTO LRFD Bridge Design Specifications for Bridge Superstructure Design


Transverse strip width =1140mm45.6in R200 =0.42105k/in Girder: Develop Typical Section Standards of AASHTO LRFD: According to AASHTO LRFD , for #14 bar, bmin = 2(cover for main steel ) = 2")+3(db=1.75")+2(1.5* (db=1.75")) = 14.5" hmin = 0.065 x L =0.065 x 42ft = 2.73ft Dimensions we observed: total depth H = 44in = 3.667ft Deck Slab Thickness hs = 8in = 0.667ft Web Width bw = 18in = 1.5ft Beam Stem Height = 36in = 3ft Cover for bars = 3in Effective Depth d= 41in = 3.4167ft Dead Load Calculation: Interior Girder:

(bi)eff = ( )ftspaneffective 4221 =

=

114in

(bi)eff = ws bt +12 = 126in

(bi)eff =Average spacing of adjacent beams = 72in governs DC Slab Strip = 0.05k/in DC Girder Stem = 0.05625k/in DW Future Wearing Surface = .017625k/in By adding we get, DC = 0.10625k/in DW= 0.017625k/in Exterior Girder: (be)eff=

( ) ( )effibftspaneffective += 4281

= 99in

(be)eff = ( )effiws bbt ++2

16 = 93in

(be)eff =Width of overhang + (bi)eff = 78in governs DC Deck Slab = 0.01964k/in DC Overhang Slab = 0.039970486k/in DC Overhang Attachments’= 04196901k/in DC Girder Stem = 0.05625k/in DW Future Wearing Surface = 0.024153594k/in By adding we get, DC = 0.157829497k/in DW = 0.024153594k/in Live Load Calculation: The distributed live load moments and shears will be,

( )( )[ ]LNTaTrIMLL MorMMmgM +=+ 33.1

( )( )[ ]LNTaTrIMLL VorVVmgV +=+ 33.1 Max Positive Moments @ 105 Design Truck =5632.8(k.in) Design Tandem =5700(k.in) Design Lane =1693.44(k.in) Interior Girder

MLL+IM =5607.06(k.in) Exterior Girder

MLL+IM =5607.06(k.in) Max Shear @ 100 Design Truck =55.62(kips) Design Tandem =47.62kips) Design Lane =13.44(kips) Interior Girder

VLL+IM =58.71644kips)

Exterior Girder VLL+IM =35.22986(kips)

From strength limit state, we get, From strength limit state, we get, Skin Reinforcements – Interior & Exterior Girder: Since the depth of the girder is 36in so according ACI we will provide skin reinforcements (2). d =39.875in Maximum area of skin required by ACI : Main Fluxure Reinforcements = 7.938414in2 (we take the area of interior girder)

Askin, max = As /2 = 3.969207 in2 Rang upto which Skin Reinforcement is provided

d/2 =19.9375in For #6 bars

Ab =0.44in2 ssk = 6in Askin = 6 x 0.44 in2 = 2.64 in2 < Askin,max = 3.97in2, O.K we can use this reinforcement for both internal and external girders. Diaphragm: Dimensions: total depth H = 37in Deck Slab Thickness hs = 8in Web Width bw = 12in Beam Stem Height hw = 29in Effective Depth d = 34.5in Span length S = 6ft By using the same beff equations as for internal girders, we get, beff

= 108in 18in governs

M105 =

19793.86 k/in

V100 =

136.7048 kips

M105 = 17158.59 k in

V100 = 167.5339 kips

ADIL RAFIQ, AKHTER NAEEM KHAN , KHAN SHAHZADA , SYED SHAHAN ALI SHAH, SYED AZMAT ALI SHAH, ZAIGHAM ALI


n/a Load Calculation: Dead Loads:

DC Slab Strip = 0.0125 k/in

DC Daiphram Stem = 0.030208333 k/in

DW FWS = 0.00440625 k/in

DC = 0.042708333 k/in

DW = 0.00440625 k/in Live Loads:

Tire load P =16kips

V100 =19.2kips

M104 =2.50176k in

M200 =-3.34272k in (calculated through same method as done before) By using the table of influense function for deck analysis we get the following summary of moments and shear, Applying limit state, we get,

(M104)+ive = 28.27054401 k in

(M200)-ive = 38.93760147 k in

V100 = 43.99514897 Kips

V200 = 45.50850609 Kips Flexure Design:

Figure 5: Diaphram reinforcement

Applying the previous formulas, we can find, Asmax = 8.5284in2 Asmin = 1.3248in2 Assume a = hf = 8in For (M104)

+ive =28.27054401k in As =0.017164872in2 < Asmin = 1.3248in2 For (M200)

-ive =38.93760147k in As =0.02322276in2 < Asmin = 1.3248in2 So we can use Asmin for both positive and negative moments, Use #8 bars, db =1in Ab =0.79in2

No. of Bars = As/Ab = 1.676962025 = 2 bars Shear Design: The maximum shear at a support is,

V200 = 45.50850609kips While the shear which Diaphragm can bear is,

ΦVc = 47.13058625 kips Since, ΦVc > V200 So there is no need to calculate stirrup spacing, but it would be a good approach to provide #3 Stirrups @ 9in c/c distance. Conclusions & Recommendations Our transport system is such that there is no proper check and balance for the heavy loaded vehicles by the authorities. The vehicles that pass through this bridge were supposed to be checked for the loads it was designed which was an unjust behavior. From all this situation we concluded that first of all some alternative route must be provided for the heavy traffic. The authority must check the trolleys, loaded with big container for loads and must stop the heavy loaded traffic exceeding its strength limit. The cracks must be repaired, if not possible than it has to be replaced by new girders, designed for heavy loading such as HS 20, HL 93, Class A, and Class AA. Prestressed girders would be good practice for carrying such loads, but it may cost more. We have designed these girders for new loadings and prepared fresh details of the structure, as the details were missing from the record. The detailed structural drawings are provided at the end of this thesis.

Referrences

[1] Design of Highway Bridges, Based on AASHTO LRFD Bridge Design Specifications,(R.M. Barker – J.A. Puckett)

[2] Standard Specifications for Highway Bridges – AASHTO

[3] https://bookstore.transportation.org/collection_detail.aspx?id=112

implementation of the aashto lrfd bridge design specifications for bridge superstructure design

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