live load distribution factor of hybrid frp-uhpc …

The 12th International Symposium on Fiber Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-12) & The 5th Asia-Pacific Conference on Fiber Reinforced Polymers in Structures (APFIS-2015)

Joint Conference, 14-16 December 2015, Nanjing, China

LIVE LOAD DISTRIBUTION FACTOR OF HYBRID FRP-UHPC BRIDGE: EXPERIMENTAL COMPARISON WITH CSA S6-06

Donna Chen1 and Raafat El-Hacha2

1 ISL Engineering and Land Services (formerly PhD Student at University of Calgary) 6325 12 Street S.E., Calgary, Alberta, T2H 2K1 Canada

Email: [email protected]

2 Department of Civil Engineering, University of Calgary 2500 University Drive N.W, Calgary, Alberta, T2N 1N4 Canada

Email: [email protected]

Keywords: Bridge, Hybrid, High performance, Live load distribution factor

ABSTRACT

This paper details the comparison of key design parameter, the live load distribution factor (LLDF), for bridge deck systems made up using high performance materials. The comparison was conducted using experimental test results from multiple concentric and eccentric transverse loading configuration, which were then compared with code-stipulated values from the Canadian Highway Bridge Design Code. Overall, conservative values for the shear and moment LLDFs were calculated using code guidelines. The one exception was in the case of highly eccentric transverse load configurations, where the moment LLDF achieved experimentally was approximately 30% higher than the code-stipulated value. Further testing and analysis is recommended for a thorough understanding towards the applicability of the Canadian code in the design of high performance material bridge deck systems. 1 INTRODUCTION

The use of high performance materials such as Fibre Reinforced Polymers (FRPs) and Ultra-High Performance Concrete (UHPC), for structural applications has grown in recent years [1, 2]. To further its use in future applications, restructuring of the results achieved through academic research into design guidelines, standards and codes, is required to facilitate its practical usage. This paper will discuss the experimental performance of a specially design hybrid bridge deck system, made up from high performance materials without the presence of steel components, and evaluate its performance with regards to the live load distribution factor (LLDF). The LLDF is one of the main tools used in bridge design to ascertain the expected transverse distribution of load in a bridge system, in lieu of extensive experimental testing and analytical modelling. Comparison between the experimental and code recommended values for the LLDF would aid in assessing whether the current Canadian Highway Bridge Design Code (CHBDC) [3], typically used for bridge design using conventional materials, is applicable for the design of high performance bridge deck systems. 2 HYBRID BRIDGE DECK SYSTEM

2.1 Design Details

The developed hybrid bridge deck system consists of only high performance material; this includes a combination of Glass Fibre Reinforced Polymer (GFRP), Carbon FRP (CFRP) and Ultra-High Performance Concrete (UHPC). Due to the linear-elastic properties of these high performance materials, design optimization of the developed hybrid bridge deck system had to be conducted to include pseudo-ductility in the global system response in order to prevent abrupt failure at ultimate condition. The completed design of the hybrid bridge deck system consists of four parallel longitudinal GFRP hollow box beams, spaced evenly apart, acting as the main structural girders. CFRP laminate sheets are bonded to the bottom exposed surface of the GFRP beams to provide further

Donna Chen and Raafat El-Hacha

flexural strength. A series of horizontal and diagonal GFRP rods positioned within the inter-girder space perform as the transverse composite action system. A cast-in-place UHPC slab is placed overtop of the multi-girder FRP bridge deck base. Connection between the FRP bridge deck base and the UHPC slab is provided through a two-part bond system. The two-part bond system consists of a layer of epoxy bonded coarse silica sand layer (aggregate interlock system) on the top surface of the GFRP top flange along with full-depth GFRP rods (rod clamping system). The hybrid FRP-UHPC bridge deck structural system been studied extensively experimentally and analytically by the authors [4-10]. A diagram of the design dimensions of the quarter-scale prototype fabricated for experimental testing is provided in Figure 1.

Figure 1 – Dimensions for quarter-scale prototype of hybrid FRP-UHPC bridge deck system [4]

2.2 Experimental test results and system performance metrics

Testing of the quarter-scale prototype bridge deck system was conducted using seven wheel load configurations based off of axles 3 and 4 of the standard CL-625 kN truck [3]. Repeat tests were performed for a select number of wheel load configurations, with a total of twelve test conducted. With the exception of the final test, loading was applied within the service conditions, in order to remain within the elastic global performance range of the hybrid bridge deck system. Wheel placement in all loading configurations was concentric about the mid-span of the hybrid bridge deck system, with a quarter-scaled longitudinal spacing of 300 mm in all tests except Test #10, which used had a longitudinal spacing of 600 mm. Two-dimensional diagrams showing the transverse position of the wheel loads for each load configuration tested in shown in Table 1. Table 1. Transverse wheel load configurations [4]

C1 (a, b, c) C2 C3

E1a E2a E3

E1b E2b E4



The hybrid bridge deck system confirmed linear-elastic performance during the tests conducted within the service load condition range. Similarly, load-deflection and load-strain response exhibited linear-elastic behaviour prior to reaching peak load condition during the final ultimate load condition test. A full discussion of the experimental results is provided in associated publications [4]. For the investigation in this publication, in order to determine the shear and moment live load distribution factors, the relevant data are the load cell readings and longitudinal strain data at mid-span in the CFRP laminate, respectively.

The shear live load distribution factor was determined based on the portion of the total vertical applied load carried by the individual longitudinal GFRP girders, as represented by the load cell readings at the support. Due to the symmetry in both the bridge deck system geometry as well as the applied loading, load cells were positioned at only one end of the simply supported specimen. The moment live load distribution factor was likewise calculated based on the portion of the total moment load carried by the individual GFRP girders. To determine the portion of total moment resistance provided by the individual girders, the relative values of tensile strain detected at the base of the girders, on the CFRP sheet, were used. Averaged values for the shear and moment live load distribution factors, taken at six increments during service loading testing, were obtained for each test; they are summarized in Table 2. Table 2. Experimental live load distribution factor for hybrid bridge deck system [4]

Test Configuration ID Shear LLDF per girder Moment LLDF per girder A B C D A B C D

C1a 0.200 0.285 0.305 0.210 0.244 0.294 0.297 0.262 C1b 0.197 0.284 0.306 0.213 0.248 0.288 0.290 0.263 E1a 0.303 0.305 0.258 0.133 0.371 0.317 0.248 0.169 E2a 0.443 0.322 0.170 0.065 0.514 0.312 0.179 0.085 E1b 0.111 0.227 0.306 0.355 0.139 0.211 0.318 0.396 E2b 0.036 0.162 0.320 0.481 0.076 0.142 0.321 0.502 E3 0.130 0.218 0.293 0.359 0.180 0.216 0.274 0.401 E4 0.196 0.242 0.294 0.268 0.208 0.245 0.290 0.333

C1c 0.197 0.281 0.307 0.216 0.256 0.280 0.285 0.267 C2 0.188 0.298 0.316 0.198 0.256 0.257 0.293 0.267 C3 0.238 0.240 0.270 0.251 0.279 0.227 0.258 0.302

4 EXISTING LITERATURE ON LIVE LOAD DISTRIBUTION FACTOR

4.1 Overview of Canadian Highway Bridge Design Code Simplified Method

The Canadian Highway Bridge Design Code [3] contains clauses with guidelines for calculating the proper shear and moment live load distribution factors. The simplified method is provided in Chapter 5 [3]. Bridges are first divided into the following types, based on the predominant structural system used and thus the expected structural response. The 10 primary types (Type A – K) are as follows:

A. Slab; B. Voided slab; C. Deck-on-girder; D. Shear-connected beam, with and without continuity of transverse flexural rigidity across

the cross-section; E. Truss members and floor systems; F. Arch members and floor systems; G. Rigid frame and integral abutment; H. Incorporating wood beams; I. Box girder – single cell; J. Box girder – multi-cell; and, K. Box girder – multi-spine.


In addition to these classifications, the bridge types and the analysis procedures are also determined based upon the following aspects:

• superstructure category, whether considered with a shallow superstructure or multi-spine bridge;

• traffic volumes, as determined by the highway class; and • overall bridge length.

These techniques, however, are based upon experimental testing, analysis and previous field experience obtained from bridge structures constructed using conventional materials. These materials are, namely, reinforced concrete, structural steel and prestressed concrete. Other limitations include restrictions on overall dimension ratios, regularity in cross-sectional dimensions through the full length of the bridge, as well as degree of rotation, curving and skew in the bridge alignment.

4.2 Moment live load distribution factor

The technique presented in Clause 5.7.1.2 of CSA S6-06 [3], intended for the characterization of shallow superstructures, was used to derive the moment LLDF using the following equation:

avggmg MFM ,= (1)

The moment LLDF (Mg) is determined by multiplying the amplitude factor intended to account for transverse variations in load distribution (Fm) and the average moment per girder determine as if all girder shared the applied load equally (Mg,avg). The follow factors are used to calculate Mg, using Equation 1.

Girder spacing (S) m 1.8m45.04 =×=S (2) Deck width (Wc) m 6 m5.14 =×=cW (3)

Effective lane width (We) 1m 6 =→== nnWW c

e (4)

Width dimension (F) ⎪⎩

⎪⎨⎧

=−=−

=−=−=

(interior) 15.42464.4640.4

(exterior) 42.32425.3250.3

L

LF (5)

Percentage correction factor (Cf) 5.424125125 =−=−= LC f (6)

Lane width correction factor (µ) 0.1 0.1

5.46.0

3.366.0

3.3=

⎪⎩

⎪⎨

⎧ =−

=−

≤eW

µ (7)

Number of girders (N) 4=N (8) Number of lanes (n) 4=n (9)

Multi-lane modification factor (RL) 1=LR (10)

Using the factors and parameters derived using Equations 2 – 10, the required components (Fm and Mg,avg) can be calculated as shown in Equation 11 and Equation 12, followed by the calculation of Mg.

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

=

⎥⎦

⎤⎢⎣

⎡ ×++

×

=

⎥⎦

⎤⎢⎣

⎡ ×++

×

=

⎥⎦

⎤⎢⎣

⎡++

=(interior) 39.1

1005.40.1115.4

40.1

(exterior) 61.1

1005.40.1142.3

40.1

1001 f

m CF

SNFµ

(11)

TLTLT

avgg MRMNRnMM 25.0

41

, =××

== (12)



⎩⎨⎧

=×

=×==

(interior) 3475.025.039.1(exterior) 4025.025.06.1

,TT

TTavggmg MM

MMMFM 12(a)

4.3 Shear live load distribution factor

Similarly, the shear LLDF is calculated based upon the simplified method, as described in Section 5.7.1.4 of CSA S6-06 [3]. The approach is the same as that used for calculating the moment LLDF, where the shear LLDF is calculated using the equation below:

avggvg VFV ,= (13)

All of the parameters used for the calculation of Mg can be applied directly towards determining the value of Vg, except for F. The width dimension, F, is a value that depends on the type of load applied as well as the limit state under consideration. In the case of determining F for longitudinal vertical shear load under ultimate limit state, its value is 3.50. The calculations for Vg are as follows:

06.25.348.1=

×==

FSNFv (14)

TLTLT

avgg VRVNRnVV 25.0

41

, =××

== (15)

514.025.006.2, =×== Tavggvg VVFV (13a)

4 COMPARISON BETWEEN EXPERIMENTAL AND CODE LLDF

Comparison of the results for shear and moment LLDFs, between those obtained experimentally against those stipulated by the code is summarized in Figure 2.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

A B C D

Shea

r LLD

F

Girder Location

C1aC1bC1cC2C3

S6-06 Shear LLDF

0.000

0.100

0.200

0.300

0.400

0.500

0.600

A B C D

Shea

r LLD

F

Girder Location

E1aE2aE1bE2bE3E4

S6-06 Shear LLDF

0.000

0.100

0.200

0.300

0.400

0.500

0.600

A B C D

Mom

ent L

LDF

Girder Location

C1aC1bC1cC2C3

S6-06 Moment LLDF (Internal Girders)

S6-06 Moment LLDF (External Girders)

0.000

0.100

0.200

0.300

0.400

0.500

0.600

A B C D

Mom

ent L

LDF

Girder Location

E1aE2aE1bE2bE3E4

S6-06 Moment LLDF (Internal Girders)

S6-06 Moment LLDF (External Girders)

Figure 2 – Comparison between experimental and code calculated values of: a) shear LLDF for C1-C3, b) shear LLDF for E1-E4, c) moment LLDF for C1-C3 and, d) moment LLDF for E1-E4.

a) b)

c) d)


5 DISCUSSION ON LIVE LOAD DISTRIBUTION FACTOR

The comparison presented in Figure 2 clearly shows that the code calculated values for the LLDF are higher than experimental values in three of the four cases. The sole exclusion is the case of the most highly eccentric loading configuration (E2a and E2b) for moment distribution (Figure 2d). From this investigation, it appears that the Canadian standard underestimates the required design moment resistance allotted to exterior girders when highly eccentric transverse loading is applied to a bridge structure made up of high performance materials. Whereas the code stipulates a moment LLDF equal to 0.4025, the experimental results indicate a higher value, equal to approximately 0.52. This is equal to a 29% increase in required moment resistance for exterior girders. 6 CONCLUSIONS

The work summarized in this paper demonstrates the overall suitability of live load distribution factor calculations provided through the CHBDC when implemented for bridge deck system composed solely of high performance materials. Nevertheless, in the case of extreme transverse loading configuration, where highly eccentric loading is applied at the edge of the bridge cross-section, the code-stipulated moment LLDF underestimates the required design moment resistance by approximately 30%. This result shows that the hybrid bridge deck system displays a lesser degree of load distribution transversely between the longitudinal girders than proposed by the CHBDC. Due to the limited scope of this study, based on one design configuration to represent a high performance bridge deck system, further testing and analysis is recommended to achieve a comprehensive conclusion.

ACKNOWLEDGEMENTS

We would like to thank the following companies for their generous donation of materials used in this research project: Lafarge Canada, Pultrall Inc., and Sika Canada Inc. Additionally, we would like to acknowledge the National Sciences and Research Council (NSERC) of Canada and the University of Calgary for their financial support.

REFERENCES

[1] C. Bakis, L. Bank, V. Brown, E. Cosenza, J. Davalos, J. Lesko, A. Machida, S. Rizkalla, T. Triantafillou, Fiber-Reinforced polymer composites for construction, Journal of Composites for Construction, 2002, 6(2): 73-87

[2] L. Cheng, V. Karbhari, New bridge systems using FRP composites and concrete: a state-of-the-art review, 2006, 8:143-154

[3] Canadian Standards Association, Canadian highway bridge design code (CSA-S6-06), 2006. [4] D. Chen, Development of innovative hybrid steel-free multi-girder bridge deck system (Ph.D.

dissertation). Calgary, AB: University of Calgary, 2015. [5] D. Chen, R. El-Hacha, Investigation of hybrid FRP-UHPC beams under flexural loading using

finite element methods. Proceedings of the ACI Special Publications SP-301—1 Modeling of FRP Strengthening Techniques in Concrete Infrastructure, 2015.

[6] D. Chen, R. El-Hacha, Cohesive fracture study of a bonded coarse silica sand aggregate bond interface subjected to mixed-mode bending conditions. Polymers Journal, Special Issue: Fiber-Reinforced Polymer Composites in Structural Engineering, 2014, 6(1): 12-38.

[7] D. Chen, R. El-Hacha, Damage tolerance and residual strength of hybrid FRP-UHPC beam. Elsevier Engineering Structures, April 2013, 49: 275–283.

[8] R. El-Hacha, D. Chen, Behaviour of hybrid FRP-UHPC beams subjected to static flexural loading. Elsevier Journal of Composite Part B: Engineering, March 2012, 43(2): 582–593

[9] D. Chen, R. El-Hacha, Investigation of bond behavior between cast-in-place UHPC and GFRP plates using coarse silica sand bonded with different epoxy adhesives - Experimental study using shear and tension tests. Journal of ASTM International, March 2012, 9(3): 3-25.

[10] D. Chen, R. El-Hacha, Behaviour of hybrid FRP-UHPC beams in flexure under fatigue loading”, Elsevier Journal of Composite Structures, December 2011, 94(1): 253–266.

live load distribution factor of hybrid frp-uhpc …

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