The Queensland Department of Transport and Main Roads (TMR) manages over 3300 bridges, and many of these bridges have shearreinforcement levels considerably lessthan the requirements of modern design codes. As a result, the theoretical assessed structural capacities for these PrestressedConcrete (PSC) beam bridges (when assessed to AS5100.7 and TMR’s Tier 1 Bridges Heavy Load Assessment Criteria) are particularly low despite observed satisfactory in-service performance (Moua & al. 2017). This illustrates the increased importance of being able to accurately and safely predict the shear capacities and ductility of bridgebeams, in maintaining network operation and transport productivity given the large increases in the loads since the bridges were constructed.
mm and a span length of 1770 mm, while the simply supported span was 1470 mm. A shear span to effective depth ratio of 3.5 was used. This study was found to be stimulating, as it fixated on something, which was quite different as compared to all other studies in the same scope. An assessment of the ability of crimped and hooked-end steel fibres to be used as minimumshearreinforcement in RC beams prepared with two different grades of concrete was completed. To accomplish this, the control samples were made from the beams, which were believed to be satisfactory. The fibre-reinforced beams also showed fluctuating degrees of multiple cracking at ultimate loads. The shear strength of the FRC beams was found to be more than a low value endorsed in the literature. The grade of concrete was found to be of little importance in this regard. A comparison of the strength of the two types of deformed fibres revealed that the beams reinforced with the hooked-end fibres were found to have up to 38% higher shear strength than the crimped fibres. A simple model for shear strength was also suggested for the calculation of the behaviour of fibre reinforced concrete. The proposed model was tested along with seven other shear strength models. The seven models were selected from the literature. The proposed model predicted fairly good values. However, a model proposed by other researchers from the selected literature was found to be projecting a better approximation. Imam et al. (1995) presented an analytical model for predicting the shear strength of reinforced high-strength concretebeams. The dimensions of all the specimens were constant and valued at 200 mm × 350 mm. All beams had span length of 3600 mm. All specimens were singly reinforced without stirrups. The author classified the beams into four groups based on three factors (a/d, V f , and ) in different levels. These beams
Prestressedconcrete girders are the main superstructure elements in many bridge structures. Shear failures in these girders are undesirable due to brittle failure and little warning time. To prevent shear controlled brittle failure, it is normal practice to increase the amount of transverse reinforcement in flexural members. However, past studies have revealed that even higher transverse reinforcement ratios (i.e. > 4%) may not be able to eliminate shear failure in some cases. Moreover, the increased reinforcement makes it more difficult to place and consolidate the concrete. This research program aimed to investigate the feasibility of replacing traditional shearreinforcement in prestressedconcretebeams with steel fibers. A total of 14 rectangular and 8 I-shaped prestressedconcretebeams were investigated after subjecting them to a two-point loading test. The beams were cast with steel fiber ratios ranging from 0.75% to 2.00%. Experimental results revealed that the inclusion of steel fibers in concrete mix improved the shear strength of rectangular and I shaped prestressedbeams. It was observed that on adding 1% fibers, the shear strength of I-beams enhanced by 23%. Moreover, in some cases, the addition of steel fibers also caused the shear failure mode to shift to flexural failure mode without traditional shearreinforcement. Furthermore, cracking behavior and ultimate strength were also improved. However, at high fiber dosages, balling of the fibers was observed and the load capacity decreased compared to beams with lower fiber contents.
TxDOT currently uses Tx-series of PC girders for highway bridge construction. Tx-series girders have a web thickness of 178 mm and depths ranging from 711 to 1,829 mm. Typically Tx-series girders have a top slab with a thickness 203 mm and the minimum spacing between girders is 2,032 mm. In this research an internal Tx54 was considered with a top slab 2,032 mm wide. The resulting girder cross section was scaled down to 43 % to form the modiﬁed Tx28 girder, Fig. 1, which was used in seven of the tested girders. The other two girders had the same web thickness and effective depth, Fig. 2. Their bottom ﬂange had a higher depth by one inch to accommodate the additional longitu- dinal reinforcement required to increase the ﬂexure capacity and ensure having a shear failure at the ultimate load. Also, their top ﬂange had a reduced width equals to the width of the real top ﬂange scaled down by the same ratio to allow ﬂexure shear failure to happen at the ultimate load. These two modiﬁcations in the cross section should not have any effect on the shear cracking strength of the web.
Yao, W., Li, J. & Wu, K. (2003). Mechanical properties of hybrid fiber-reinforced concrete at low fiber volume fraction. Cement & Concrete Research, 33(1), 27-30. Yoo, D. Y., Yuan, T., Yang, J. M., & Yoon, Y. S. (2017). Feasibility of replacing minimumshearreinforcement with steel fibers for sustainable high-strength concretebeams. Engineering Structures, 147, 207-222.
A simplified mechanical model for the shear strength prediction of reinforced and prestressedconcrete members with and without transverse reinforcement, with I, T or rectangular cross section is presented. The model, derived after further simplifications of a previous one developed by the authors, incorporates in a compact formulation, the contributions of the concrete compression chord, the cracked web, the dowel action and the shearreinforcement. The mechanical character of the model provides valuable information about the physics of the problem and incorporates the most relevant parameters governing the shear strength of structural concrete members. The predictions of the model fit very well the experimental results collected in the ACI-DAfStb databases of shear tests on slender reinforced and prestressedconcretebeams with and without stirrups. Due to this fact and the simplicity of the derived equations it may become a very useful tool for structural design and assessment in engineering practice.
(iii) Fiber dosage should also be limited to a minimum to ensure the correct structural behaviour of FRC element. When considering the global beam behaviour, a higher fiber dosage obviously contributes to a higher ultimate resistance, although its beneficial effect is clearly inferior than the one produced by passive shearreinforcement. Additionally, it was verified that an increase on the ultimate load and associated ductility is manifested more intensively for FRC presenting a higher fibers’ dosage. It seems therefore legit to prescribe a minimum limit of fibers dosage, in order to preclude the occurrence of brittle and dangerous failures.
In this study, the failure modes of BSM are governs by steel yielding before the concrete strain at the compression area reached the maximum permissible value of 0.0035 . For shearreinforcement, 2-legged steel stirrups of 8 mm diameter (mild steel) were spaced at 50 mm and 150 mm centre to centre at the shear region. These two kinds of spacing were calculated based on BS8110 code provisions in order to investigate the shear performance of the beams with minimum and adequate amount of stirrups. In each specimen, strain gauges were position at selected locations at longitudinal bars, stirrups and concrete which were labelled as X (see Fig. 1). The deflection of the beam was measured by at mid-span and two loading points.
Safety, durability and cost are the main objectives the designers consider in the design of reinforced concrete members. Sudden failure due to shear low strength is not desirable mode of failure. The reinforced concretebeams are designed primarily for flexural strength and shear strength. Beams are structural members used to carry loads primarily by internal moments and shears. In the design of a reinforced concrete member, flexure is usually considered first, leading to the size of the section and the arrangement of reinforcement to provide the necessary resistance for moments. For safety reasons, limits are placed on the amounts of flexural reinforcement to ensure ductile type of failure. Beams are then designed for shear. Since shear failure is frequently sudden with little or no advanced warning, the design for shear must ensure that the shear strength for every member in the structure exceeds the flexural strength. The shear failure mechanism varies depending upon the cross-sectional dimensions, the geometry, the types of loading, and the properties of the member.
Three-dimensional finite element models were created using Abaqus/Standard 6.11 (Dassault Systèmes 2010) and were used to model the elastic tension and compression behavior of prestressedconcrete girder bridges. The Abaqus bridge superstructures were divided into five parts, including: neoprene bearing pads, traffic barriers, end or intermediate diaphragms, bridge deck, and girders. The geometry of each part was adequately subdivided using partitions for two reasons. First, prior to meshing, individual surfaces were defined to ensure that surface-to-surface constraints were easy to create and to ensure that applied loads could be placed at the correct locations. Second, subdividing each part allowed for use of hexahedral elements and the structured meshing technique in Abaqus, which was preferred because it was more efficient. The mesh for each part was constructed independently using automatic seeding and mesh generation in Abaqus. All parts for non-skewed bridges were meshed using element type C3D8R which is an eight node three-dimensional linear continuum element with reduced integration. Skewed bridge decks utilized a sweep meshing technique with hex-dominated elements. Generally, the majority of skewed bridge deck elements were hexahedral shaped, however select elements were six noded three-dimensional linear triangular prism wedge elements (element type C3D6) used to complete the meshing in areas of unusual geometry.
All the beams failed in shear. The references deep beams are failed by one of the following mode; shear compression failure, strut compression failure and diagonal splitting failure between the load point and support point in shear-span, as can be seen in Figure 4a and listed in Table 2. While the retrofitted deep beams are failed either by separate of CFRP from concrete or concrete crushing, as can be seen in Figure 4b and listed in Table 2. According to test results listed in Table 2, deep beams DB6, which has a minimum horizontal web reinforcement of ratio 0.3% and retrofitted by CFRP sheets, failed at a load 161% of ultimate loading. This beam appears a highest percentage of repair enhancement in comparison with others beams. While the ultimate strength of this beam before retrofit was closely to the strength of beam without shearreinforcement, DB1. The second highest percentage of enhancement 121% is appeared in the beam without shearreinforcement, DB1. So, one can conclude the importance of minimum horizontal reinforcement is more obviously in retrofitted beams. And generally, the horizontally reinforced deep beams (DB6 and DB7) appearance good retrofit enhancement in comparison with vertically reinforced deep beams (DB4 and DB5) for the same steel ratio (0.3% and 0.5%) as mentioned in Table 2.
Upon examination of the slender members within the uniform load database, there is an obvious lack of full scale specimens that are more commonly encountered in practice. The majority of the test results have small effective depths (d) with high longitudinal reinforcement ratios (ρ), and the few larger test results have very low longitudinal reinforcement ratios. Based upon the preceding discussed parameters, ACI- DAfStb uniform load data is likely to vastly over or under predict shear capacity. The University of Texas test results represent specimens likely to be found in field structures with a larger specimen depth (d = 21.3 in. (541 mm)) and longitudinal reinforcement ratio of 1.02%. Thus, the test results obtained work toward addressing the visible gap within the ACI-DAfStb slender uniform database.
Since the beams were prepared with different shear span length, significant influence can be seen from two types of failure mode. It is clearly shown that the beams with lesser a/d ratio (i.e.; BSM-01 to BSM-04) experienced higher capacity compared to beams which have greater a/d ratios (i.e.; BSM-05 to BSM-08). Similar results was found in beams which reinforced with GFRP bars i.e.; BGM-01 with 1.6 a/d ratios exhibit high capacity up to 233.2 kN rather than BGM-05 with a/d=3.1 that only reached 99.0 kN when it failed. It is shown that the ultimate capacity increases as the shear span-to-depth ratios decreases. In addition, two modes of failure, shear and flexure were observed from the test results. Sudden formation of diagonal crack can be found in the shear span zone followed by beam failure (BSM-03, BSM-04, BGM-03 and BGM-04). Additionally, the inclination of shear cracks growth rapidly as the load increase. While, beam failed in flexure experienced by one of the following condition i.e.; rupture of tensile longitudinal reinforcement for beam BGM-01, BGM-05, BGM-06, BGM-07 and BGM-08 and also concrete crushing on the top of
Figure 1 shows the shear force vs. midspan deflection response of specimens C12N3 and C12N4 together with the crack diagrams of the beams at shear failure. The two specimens behaved very similarly even though they exhibited significantly different shear strengths. The initial response was linear until the propagation of the first flexural cracks in the pure-bending region between the applied loads. Further loading caused the propagation of more flexural and flexural-shear cracks in the two symmetrical shear spans, and the stiffness of the beam decreased gradually. The last major cracks propagated from the inner edge of the supports towards the loading points across the shear spans (diagonal shear cracks). Following the propagation of these cracks, the beams were able to sustain a load increment of about one third of the load at diagonal cracking. The diagonal cracks widened and eventually a shear failure occurred along one of these cracks with crushing of the concrete in the vicinity of the point load. Qualitatively, this behaviour is very similar to the behaviour of steel- reinforced deep beams described in many experimental studies (i.e. Mihaylov et al. 2010).
7) The derived formulae have been applied to predict the results of 112 shear tests on FRP reinforced concretebeams with FRP stirrups. Predictions made by other existing formulations and some provisions of current guidelines have been also compared with the experimental results. The results obtained by the proposed method are very good, in terms of mean value (1 .08 ) and coefficient of variation (19.5%) of the ratio between the experimental and the predicted values, V exp/Vpred . The coefficient of variation (COV) obtained is the lowest of all the methods studied. This fact is relevant, since the model with similar results  is based on genetic algorithms while the proposed method has been rationally derived, without any adjustment to the database.
Reinforcement corrosion in concrete structures is the biggest durability problem facing the UK at present. In a survey of 200 randomly selected concrete bridges, corrosion was found in 72% of the sample. It has been suggested that 10 to 25 percent reduction in steel bar section due to corrosion results in servi- ceability failure (Comite Euro-International du Be- ton 1983). It is estimated that the direct cost of rein- forcement corrosion to the UK economy is around £550m per year (Webster and Clark, 2000). A recent analytical survey for the Highways Agency in the UK (Parsons Brinckerhoff Ltd. 2003) showed that the most common deteriorated elements in the 294 sub-standard bridges analysed on the motorway and trunk road network were slabs, main beams and piers, deck cantilevers and parapets. Within these elements, the most common modes of failure were longitudinal flexure, transverse flexure and general shear. The use of overly conservative or inappro- priate methods of analysis was reported to be re- sponsible for the majority of the failures. This may suggest that engineers are attempting to model struc- tural performance with insufficient knowledge of corrosion effects.
Concrete is the most common material for construction. The demand for concrete as a construction material l eads t o the increase of demand for Portland cement. Concrete is known as a significant contributor to the emission of greenhouse gases. The cement industry is the second largest producer of the greenhouse gas. The environmental problems caused by cement production can be reduced by finding an alternate material. One of potential material to substitute for conventional concrete is geopolymer concrete. Geopolymer concrete is an inorganic alumino-silicate polymer synthesized from predominantly silicon, aluminium and by product materials such as fly ash, GGBS (ground granulated blast furnace slag). Geopolymer concrete does not contain cement. Hybrid fibres were used in this study. Hybrid fibre is the combination of steel fibre and basalt fibre with different volume fractions. When these fibres are added to this special concrete it improves the ductile behaviour and energy absorption capacity. This is due to the property of steel and basalt fibre to bridge the crack development inside the concrete. The main objective of the study is to look into the shearbehaviour of hybrid fibre reinforced geopolymer concretebeams.
As discussed previously, the distribution of strains in the end region of a prestressedconcretebridge girder is quite complex. The end region is defined as a discontinuity region due to the concentrated force at the support and the development of the prestressing stands. The main purpose of this appendix is to describe and demonstrate the ability of tools that have been developed to post-process data acquired by the Krypton System. This information will be used in conjunction with data from concrete surface strain gages and strain data from the reinforcing steel to gain a deeper understanding of specific factors affecting the behavior of end regions. Additionally, finite element analysis of the girders has been completed using Vector2; the information gained from this analysis can be used to determine the elastic strain distributions prior to loading that are not captured by the instrumentation and aid in the interpretation of experimental test data. The information presented in this chapter is intended to demonstrate the ability to post-process the data obtained from the tests in a significant way that can contribute to achieving the objectives of this research.
The experimental program is also intended to observe the bond mechanism between the CFRP sheet and the concrete. All experi- mental beams are specially designed to fail in shear in order to bet- ter study the interaction between the concrete and the externally applied CFRP sheets. Results obtained from the experimental pro- gram do not only expand the relatively small database currently available on CFRP shear-strengthening, but also help improve existing analytical models by evaluating and identifying new key parameters. Understanding the interaction between CFRP and concrete helps improve existing analytical models and obtain a better estimation of the shear strength added by the CFRP. Consid- ering the current database of CFRP strengthened beams, more data derived from large-scale specimen testing are needed in order to account for the scale effect and provide a better prediction of the behavior of externally applied CFRP sheets. Specific experiments designed to capture bond and anchorage issues are also needed to better predict the added shear capacity of the CFRP.