Experimental investigation on fatigue of concrete cantilever bridge deck slabs subjected to concentrated loads

doi:10.1016/j.engstruct.2015.02.010

Engineering Structures

Volume 89, 15 April 2015, Pages 191-203

https://doi.org/10.1016/j.engstruct.2015.02.010 Get rights and content

Highlights

•
Traffic loads have a repetitive nature that may reduce deck slab strength (fatigue).
•
Eleven tests under concentrated fatigue loads + four static reference tests presented.
•
Cantilever bridge deck slabs are less sensitive to shear-fatigue failures than beams.
•
Slabs with rebar fractures have significant remaining life after first rupture.
•
Test results are compared to shear-fatigue provisions of Model Code 2010 and the CSCT.

Abstract

Shear has been observed to be often the governing failure mode of RC cantilever deck slabs of bridges without shear reinforcement subjected to concentrated loads when tested under a quasi-static application of the load. However, concentrated loads of heavy vehicles have a repetitive nature, causing loss of stiffness and potential strength reductions due to fatigue phenomena.

In this paper, the fatigue behavior of cantilever bridge deck slabs is investigated. A specific experimental programme consisting on eleven tests under concentrated fatigue loads and four static tests (reference specimens) is presented. The results show that cantilever bridge deck slabs are significantly less sensitive to shear-fatigue failures than beams without shear reinforcement. Some slabs failed due to rebar fractures. They presented significant remaining life after first rebar failure occurred and eventually failed due to shear. The test results are finally compared to the shear-fatigue provisions of the fib-Model Code 2010 and the Critical Shear Crack Theory to discuss their suitability.

Introduction

Design of reinforced concrete cantilever bridge deck slabs without shear reinforcement is generally governed by the action of concentrated loads of heavy vehicles (Fig. 1), which may cause shear, punching shear or flexural failures. Amongst these potential failure modes, shear is the most common governing failure mode under quasi-static application of concentrated loads [1], [2], [3], [4]. The concentrated loads resulting from heavy vehicles have a repetitive nature and may cause potential stiffness and strength reductions due to fatigue effects [5]. Fatigue failure modes are the same as the static ones and can be due to rebar fracture and/or failure of concrete.

Investigation of fatigue behavior in shear has mainly focused in the past on three and four-point bending tests on reinforced concrete beams without shear reinforcement (Fig. 2a). An extensive summary on this topic can be found in Ref. [6]. Beams can fail in bending or shear in both static and fatigue tests (bending failures being associated to rebar fracture or concrete crushing). Shear-fatigue failures were first studied by Chang and Kesler [7], [8]. They observed two potential failure modes: diagonal-cracking failures (where failure takes place by development of a diagonal shear crack) and the shear-compression failures (where failure takes place when the propagation of the shear crack reduces the depth of the compression zone to an extent such that it can no longer resist the acting compressive forces).

However, it should be noted that the results obtained for beams and one-way slabs are not directly applicable to cantilever slabs subjected to concentrated loads. This is justified as beams do not exhibit a two-way action and consequently cannot redistribute their internal forces due to bending and shear cracking [4]. Moreover, the ratio between the maximum acting moment $m_{\max}$ and the maximum acting shear force $v_{\max}$ in cantilever slabs at the support is lower than for cantilever beams with the same shear span [2].

With respect to fatigue testing of reinforced concrete slabs without shear reinforcement under concentrated loads, previous research has mainly focused on simply supported or inner slabs [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19] supported on two or four edges, refer to Fig. 2b and c. Table 1 presents some geometric properties of available experimental evidence. With respect to typical deck slabs of concrete bridges, it can be observed that several specimens have relatively low thicknesses ( $< 100$ mm) and others have low reinforcement ratios ρ ( $⩽ 0.2 %$ , including specimens even with no flexural reinforcement) or fairly large ones ( $> 1.5 %$ ).

To the author’s knowledge no tests are available on cantilever deck slabs (Fig. 2d), whose mechanical behavior may significantly differ from simply supported slabs [4]. In order to provide such experimental evidence, an experimental programme has been performed at the Ecole Polytechnique Fédérale de Lausanne (Switzerland). The specimens are full-scale slabs (3.00 m × 3.00 m × 0.25 m) with a central line support and subjected to a single concentrated load on both sides of the support. Four static tests were performed on two slabs (two tests per slab and load location) and eleven fatigue tests on eight slabs (four slabs per load location).

Other topics as the influence of moving loads [14], [15], [19] or the influence of impact loading on shear strength [20] are not investigated within this paper.

Section snippets

Test specimens

Ten slabs (FN1-FN10) were tested. The slabs had the dimensions of 3.00 m × 3.00 m × 0.25 m and contained only flexural reinforcement.

The geometry and reinforcement layout were the same for all slabs. The bending top reinforcement in the x-transverse direction (perpendicular to the support) consisted of 20 mm diameter bars spaced 150 mm with a nominal effective depth $d_{xt} = 210$ mm (nominal reinforcement ratio $ρ_{xt} = 1.00$ %), and the bottom one 16 mm diameter bars spaced 150 mm with a nominal effective depth $d_{xb} = 212$

Static reference tests

The quasi-statically tested slabs (reference specimens) failed in shear, in a similar manner as the tests reported in [4]. Table 4 presents the maximum loads for all static tests. For both loading locations, once the maximum load was attained, the slabs presented a softening behavior, with a significant decrease of the applied load for increasing displacements (refer to Fig. 7a and c).

The crack pattern on the top surfaces developed parallel to the linear support in the central region, while on

Analysis of the test results

In the following, the results of the tests will be compared with the fib-Model Code 2010 [23] shear-fatigue provisions that depend on the static shear strength. To that aim, the static shear strength will be calculated based on the fib-Model Code 2010 as well as using the Critical Shear Crack Theory (CSCT), as they are both based on mechanical models and allow a physical understanding of the observed phenomena [4].

First, a number of test results on statically determinate beams will be presented

Conclusions

This paper presents the results of an experimental programme on the fatigue behavior of reinforced concrete cantilever slabs subjected to concentrated loads near linear supports. The results are investigated and finally compared to the strength predictions of the fib-Model Code 2010 and the Critical Shear Crack Theory (CSCT). The main conclusions of this paper are:

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Fatigue loading of cantilever slabs with two-way action exhibits a similar influence on the shear strength as in beams (one-way

Acknowledgements

The authors would like to gratefully acknowledge the support and funding of the Swiss Federal Road Authority and Dr. Juan Manuel Gallego for the kind permission to use his shear-fatigue database on beams without shear reinforcement.

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Experimental investigation on fatigue of concrete cantilever bridge deck slabs subjected to concentrated loads

Highlights

Abstract

Introduction

Section snippets

Test specimens

Static reference tests

Analysis of the test results

Conclusions

Acknowledgements

Eng Struct

Eng Struct

Eng Struct

Eng Struct

Int J Impact Eng

Shear resistance of bridge decks without transverse reinforcement (in German)

Beton Stahlbetonbau

Experimental investigations on the shear-bearing behavior of bridge deck cantilever slabs under wheel loads (in German)

Beton Stahlbetonbau

Static and fatigue strength in shear of beams with tensile reinforcement

ACI J

Fatigue behavior of reinforced concrete beams

ACI J Proc

Effect of fatigue on ultimate load behavior of concrete bridge decks

ACI J Proc SP

Fatigue design considerations for reinforcement in concrete bridge decks

ACI J

An investigation of the fatigue strength of deck slabs of composite steel/concrete bridges

Transp Res Rec

Fatigue mechanism of reinforced concrete bridge deck slabs

Transp Res Rec

Fatigue strength of reinforced concrete slabs under moving loads

Fatigue Steel Concr Struct

RC bridge decks under pulsating and moving load

J Struct Eng

Slab continuity effect on ultimate and fatigue strength of reinforced concrete bridge deck models

ACI Struct J

Behavior of composite bridge deck slabs subjected to static and fatigue loading

ACI Struct J