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Bridge design and evaluation involve the determination of the internal forces and moments that each bridge element must resist. In slab-on-girder bridges, the moment and shear caused by traffic loads are normally determined using load distribution factors. These factors are derived based on results of analytical models, numerical analyses, as well as actual loading tests, but there appears to be scant experimental data to gauge their accuracy, particularly beyond the elastic limit state. To address the scarcity of the experimental data and to understand how the distribution characteristics of concrete slab on steel girder composite bridges change with the advent of yielding and inelasticity, a 1/3 scale model of a hypothetical composite bridge was tested to failure in this study. Extensive measurements were taken during the test to allow better understanding of the response of slab-on-girder bridges as well as their live load distribution characteristics at all stages of loading up to failure. The experimentally determined distribution factors for the tested bridge model are compared with the calculated values based on the Canadian Highway Bridge Design Standard, and the code values are found to overestimate the maximum moment in the interior loaded girder by about 22% and 33% at the elastic and the inelastic states, respectively.
A commonly observed failure mode in laboratory tests involving surface bonded fiber-reinforced polymer (FRP) laminates or near-surface-mounted (NSM) bars is premature delamination, that is, the separation of the FRP from the substrate well before the FRP reaches its ultimate strain capacity. To delay the onset of delamination and to ensure that the NSM FRP reinforcement continues to contribute to member strength after partial delamination, a new self-anchored carbon fiber-reinforced polymer (CFRP) bar was developed and tested for this investigation. This bar is made with a series of monolithic spikes that can be anchored deep inside the concrete. In addition to cutting grooves into the concrete cover for the placement of the primary reinforcing bar, holes are drilled deep into the concrete to insert the spikes. To test the performance of this bar, six large, simply supported, reinforced, concrete beams were retrofitted with NSM bars and tested in four-point bending. Two beams were strengthened with NSM bars without anchors or spikes but were otherwise similar to the self-anchored bar and served as control specimens (Series B1). Two beams were strengthened in flexure with the new self-anchored NSM bars (Series B2), and the remaining two beams (Series B3) were strengthened in flexure and shear by using the self-anchored NSM bars as partial shear reinforcement. The effect of the proposed strengthening system on the beams' strength, failure mode, deformability, and ductility are discussed on the basis of the experimental results. The anchors delayed delamination and enabled the NSM bar to experience at least a 77% higher strain at failure than the companion bar without anchors. The anchors also increased beam displacement ductility and energy ductility at a 20% strength degradation by at least 34% and 42%, respectively.
Six full-scale concrete masonry walls were tested under free-field blast loading using different charge sizes up to 250 kg of ammonium nitrate/fuel oil (ANFO) and at a constant stand-off distance of 15.0 m to cover a wide range of expected damage levels. Five walls were retrofitted with cold-formed steel studs anchored to the wall backs and were compared to the remaining as-built wall. Significant enhancement to the out-of-plane blast resistance of the retrofitted walls, compared to the as-built wall, was observed. This enhancement is attributed to the development of a tied-arch action in the retrofitted walls in which the masonry forms a compression strut while the steel studs serve as the tie. A simplified single-degree-of-freedom model was used to analyze the experimental results, and the model results agreed well with the observed damage levels and the resistances of the walls. In addition, the effectiveness of the proposed retrofit technique was evaluated in terms of strength enhancement and wall deflection reduction. The test results were also compared with those predicted by available blast damage assessment models for unreinforced masonry walls. However, it was found that available models, which do not account for the tied-arch mechanism, greatly underestimate the actual blast capacity of the retrofitted walls because of the assumption of a tensile flexural failure mode. Additionally, the proposed retrofit technique shifts the mode of failure from flexure to shear.
No abstract is provided for this article.
A new method of mixture proportioning is used for investigating the shear performance of reinforced concrete (RC) beams made with coarse recycled concrete aggregate (RCA). In this method, RCA is treated as a two-phase material comprising mortar and natural aggregate therefore to proportion the concrete mixture with RCA, the relative amount and properties of each phase are considered separately. Using the new mix proportioning method, several beams were designed and tested to study the effect of a number of parameters including the shear span-to-depth ratio and beam size on the serviceability and strength of RCA concrete beams without shear reinforcement. For each beam its load–deflection curve, shear deformations, diagonal cracking load, crack pattern, ultimate shear strength and failure mode were determined. The results showed that the shear performance of RC beams made with RCA can be comparable, or even superior, to that of beams made entirely with natural aggregates at both serviceability and ultimate limit states, provided the proposed mixture proportioning method is used. Furthermore, the simplified methods of ACI and CSA standards as well as Eurocode 2 were found applicable to all reinforced RCA-concrete beams.
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A nonlinear analytical model is presented and used to determine the interfacial shear and normal stresses at the FRP/concrete interface for RC beams externally strengthened with CFRP sheets. The computed stresses can be used to predict intermediate crack-induced debonding near the section of maximum moment. The model is based on composite beam theory with partial slip at the FRP-concrete interface permitted. Nonlinearity in the retrofitted beam is accounted for via consideration of the full moment-strain response of the unretrofitted beam. For model validation, the computed longitudinal strain along the laminate and the debonding load for a number of tested beams are compared with their corresponding experimental values. Furthermore, the shear and normal stresses distribution were also predicted. The theoretical predicted delamination load is in good agreement with the experimental results. The model yielded a reasonable theoretical load for beams with anchors and as predicted using ACI (08) method.
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For the first time, the feasibility of adhesively bonded connections in FRP frame structures is explored as an alternative to bolted connections. Eight full-scale GFRP beam-column connections are tested and their failure mode, strength and rotational stiffness are investigated. A single pultruded GFRP I-profile is used for the two members. In four of the specimens the beam and the column are connected by epoxy adhesive and GFRP seat angles, similar to the so-called “standard bolted connection”. In the remaining four specimens, the seat angles are supplemented by additional GFRP angles and stiffeners to strengthen the column flange and web. The beam-column assembly forms an inverted L-shape frame, with the column being fixed at the bottom and attached to the beam near the top. The beam, acting as a cantilever, is loaded by a point load near its free end, which subjects the connection to bending and shear. The current standard connection failed by debonding within the column flange while the improved/strengthened connection failed within the adhesive or at the adhesive-column flange interface. The test results reveal that both the standard and improved connection can have at least the same strength as the corresponding bolted connection, irrespective of whether GFRP or steel bolts are used to make the connection. Hence, the current restrictions against the use of adhesive beam-column connections in GFRP frame structures may be unjustified. In making this comparison, the observed failure load of each connection is normalized by the ultimate moment capacity of the GFRP profile in the beam-column assembly.
Due to the assumption of uniform bond stress, the development length of fibre reinforced polymer (FRP) bars by design standards can be unnecessarily long and difficult to provide in practice. Hence, the bond stress distribution and required development length of a glass fibre reinforced polymer (GFRP) rebar is investigated. Four beam-bond specimens, two following RILEM specifications and two based on a procedure by ACI are tested to evaluate the effect of test method on bond strength. Ten pullout tests are also performed using the same bar. The two test methods yield similar results, but the ACI test is easier to perform. The bond stress distribution in the beams is highly nonlinear but in the pullout tests approaches uniformity. The actual development length is found to be 50% to 250% less than that required by the aforementioned standards. Consequently, a new equation is proposed based on the logistic growth function to model the non-uniform bond stress distribution and estimate the required development length.
No abstract is provided for this article.
This study is concerned with the determination of the effects of shear span-to-depth ratio (a/d) and beam depth, or size, on the concrete contribution to the shear resistance of beams longitudinally reinforced with carbon fiber-reinforced polymer (CFRP) bars. One of the distinguishing features of the study is the unsymmetrical nature of the applied load, which creates two distinct a/d ratios in the same beam and allows the effect of the a/d ratio on shear strength to be clearly seen. Six simply supported large size CFRP reinforced concrete beams without shear reinforcement were tested, each under a single concentrated load. The test variables were the a/d ratio, varying from 1.0–11.5, and the beam depth varying from 200–500 mm. All the beams failed in shear, but the failure load and location for some of these beams could not be predicted by the shear design recommendations of American Concrete Institute (ACI) Committee 440. The reason is that these recommendations do not account for the effects of a/d and beam size on shear strength. Suggestions are made for the inclusion of these parameters in the shear design equations.
In this paper, the spectrum and power requirements of an indoor pico-cell radio system at different operating frequencies in a building are studied. Based on measurement results obtained in other studies on losses due to walls, floors, etc., a picocell radio system with frequency reuse capability is considered for a typical high-rise office building. the amount of spectrum required by the pico-cell system is evaluated based on operating frequency, dase station olcations and cell configurations, vertical reuse distance, outage probilities, and floor layout, in addition to traffic demand and blocking probalility.
A new carbon fiber reinforced polymer (CFRP) anchor is developed and tested to delay debonding in reinforced concrete (RC) beams externally strengthened with FRP laminate/sheet. The C-shape anchor is made from a commercially available CFRP grid. The anchors legs are 95 mm long while the spacing between the legs is adjustable, depending on FRP laminate and beam widths. Nine full scale RC beams, 3.0 m long, 250 mm wide and 400 mm deep, were strengthened with CFRP laminate/sheet, with and without the C-anchor. The main test parameters were the type and amount of FRP laminate and the presence/absence of the anchor. Test results showed that beams with the anchor had generally 5%–10% higher debonding and failure load, and they reached higher deflection at failure than the companion beams without anchors. Although complete separation of the FRP laminate from the concrete was not observed in any of the beams with anchors, there was noticeable slip at failure at one end of the laminate. A significant outcome of the study is that anchors are effective in limiting the extent of debonding along the laminate, thus contributing to the flexural stiffness of the beam by reducing the extent of cracking and limiting the crack width along the beam. Finally, the anchor allowed the FRP to reach or exceed its theoretically allowable strain computed based on the American Concrete Institute (ACI) Committee 440 recommendation while in none of the beams without anchors, the FRP reached its theoretically allowable strain.
The effects of ageing on the microstructure and dynamic rheological properties of three modified asphalt binders are investigated. The asphalt modifiers used comprise crumb rubber (CR), styrene–butadiene–styrene (SBS) block copolymer and a blend or combination of CR and SBS (CCR). To investigate the modified asphalts microstructure, scanning electron microscopy is applied, while for assessing rheological properties at a wide range of temperature, Bending Beam Rheometry and Dynamic Shear Rheometry are employed. Ageing of asphalt during construction and under service conditions is simulated using the rolling thin film oven test and the Pressurised Ageing Vessel procedures. It is observed that ageing makes all three modified asphalts harder, increases their resistance to deformation under high temperatures, and decreases their fatigue and cracking resistance at low temperatures. Comparatively, the CR maintains its bond with the asphalt better than the SBS and the CR-modified asphalt exhibits lower stiffness and lower degree of ageing under cold temperature, while it shows the highest resistance to high-temperature deformation and fatigue. On the contrary, the SBS-modified asphalt exhibits the worst performance in practically every respect compared to the CR- and CCR-modified asphalts.
A Single-Degree-of-Freedom (SDOF) model is used to determine the effect of axial load on column strength and stability during a blast event. The model, which accounts for the axial load–bending interaction (P–δ effect) and strain rate effect on the column dynamic response, is validated by comparing its results with experimental data from blast tests on full scale steel columns and with the results of the finite element software LS-DYNA. Maximum displacements and moments obtained from SDOF analysis are also compared with the results of the interaction formulas recommended by the Unified Facilities Criteria (UFC 3-340-02) design manual for steel structures. It is shown that the UFC method overestimates the column capacity for ductility ratios μ greater than one, irrespective of the axial load to Euler elastic buckling load ratio (P/P e ). Also for P/P e >0.5, even if μ <1.0, the UFC method still overestimates the actual column capacity. For dealing with this problem in practical applications, non-dimensional beam column curves are developed to include the effects of the blast load and column properties on both its strength and stability.
Discussions 835 The authors are to be commended for attempting to pro- vide a refined, yet simple, flexural analysis tool for rein - forced concrete beams strengthened with composite laminates. Although there is much merit in the paper, there are also some aspects of the work that need careful examina- tion before anyone begins to apply it to any real structure. The purpose of this discussion is to point out the danger that is inherent in analyses that (i) assume perfect bond between the FRP laminate and the concrete and (ii) assume the shear and normal stresses at the interface of the laminate and the substrate to be governed by classical beam theory. The writer is confident that the authors know about these dan- gers, but have forgotten to mention them in the paper. Both experiments (Tumialan et al. 1999) and theory (e.g., Rabinovitch and Frostig 1999) have shown that the shear and normal stresses at the interface of the laminate-epoxy and epoxy-concrete have a complex distribution which can- not be found by using the simple beam theory. In fact, beam theory erroneously gives the normal stresses perpendicular to the interface to be zero, but more refined analyses based on theory of elasticity indicate significant tensile stresses de - veloping at the interface. The beam theory also leads one to believe that the interfacial longitudinal shear stresses can be calculated using the elementary shear stress equations given in strength of material books. In reality these stresses have a much more complex distribution. Furthermore, when a con- crete beam cracks, the stresses at the interface in the vicinity of the crack greatly deviate from the distribution predicted by simple beam theory or by any other theory that ignores the presence of cracks. The experimentally observed delamination of either the substrate concrete or the FRP laminate is caused by the combined effect of these high in- terfacial stresses. Given that premature delamination will cause a strength- ened reinforced concrete beam to fail at a load lower than predicted by the program described in the paper, the results of the program could lead to unsafe design. This is the dan- ger that users of the program must be aware of. Figure 6 of the paper illustrates this point where the predicted and the actual load differ significantly. Note that the measures taken to prevent delamination, namely, the use of the U-shaped composite anchors, cannot be modelled by the program as described. The program is unable to quantify the effect of the end anchors and thus unless it can be shown by some other method that delamination cannot occur, it may overes- timate the actual capacity of a member with or without an- chors.
The capacity provisions of conventional Reinforced Concrete (RC) and Prestressed Concrete (PC) beams subjected to combined action of torsion, shear and flexure are well known and stated by international/national codes.Similar provisions lack for concrete members containing Fibre Reinforced Polymer (FRP) reinforcements.In general, there is paucity of research on the treatment of torsion combined with other stress resultants for FRP-RC/PC members.In this paper, the theoretical method proposed by the Canadian standard CSA S806 for FRP-RC/PC structures is presented.The critical issues, related to this topic, such as the appropriate strength and inclination of the diagonal struts and failure criteria are critically analyzed and addressed.In order to assess the reliability of this study a comparison between available experimental data regarding FRP-RC/PC beams subjected to combined actions and their corresponding theoretical provisions derived by the CSA S806 standard is shown.Furthermore, another approach, available in literature, which is based on the space truss model, is examined and used for comparison in order to evaluate the theoretical provisions offered by this model against the tests value of the set of the beams analyzed in this study.Based on the critical analysis of the results, it can be highlighted that the CSA method is able to conservatively predict the capacity of these beams.
