188 publications from this institution
Five rheological models for conventional concrete are modified to make them suitable for application to recycled aggregate concrete (RAC). The modification involves the inclusion of the effects of the quantity and properties of residual mortar on creep of RAC. The accuracy of the modified models is assessed by comparing their predictions with measured creep strain data from 150 x 300 mm (6 x 12 in.) concrete cylinders made of RAC, proportioned either by the conventional concrete mixture design method or by the Equivalent Mortar Volume (EMV) Method developed by the authors. It is demonstrated that the modified rheological models can be used to obtain reasonable estimates of the creep of RAC, irrespective of the mixture proportioning method and the aggregate type. It is also shown that, for practical applications, the existing ACI Method for calculating the creep of concrete can be applied to RAC via the introduction of a recycled concrete aggregate (RCA) coefficient.
A comprehensive model is presented for predicting the rate of steel corrosion in concrete structures and the consequent formation and propagation of cracks around the steel reinforcement. The corrosion model considers both the initiation and the propagation stages of corrosion. Processes commencing in the initiation stage, such as the transport of chloride ions and oxygen within the concrete and variation in temperature and moisture, are assumed to continue in the propagation stage while active corrosion is occurring contemporaneously. This allows the model to include the effects of changes in exposure conditions on the corrosion rate and the effects of the corrosion reactions on the transport properties of concrete. The corrosion rates are calculated by applying the finite-element solution of the Laplace equation for electrochemical potential, with appropriate boundary conditions. Because these boundary conditions are nonlinear, a nonlinear solution algorithm is used. The results of the analysis are compared with available test data, and the comparison is found to be satisfactory. Key words: reinforced concrete, steel corrosion, finite-element modelling, durability.
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 primary objective of this study was to demonstrate that a significant degree of anisotropy may occur in particulate materials that have nearly spherical aggregates (i.e., are typically considered as isotropic) provided there is a bias in the distribution of pore space as a result of the initial densification process. The study included both an experimental and a theoretical component. An experimental program was conducted on dynamically compacted samples of Ottawa standard sand (C109) and incorporated a series of tests performed at different orientations of the specimens. Following the experimental part, a plasticity formulation based on the critical-plane approach was presented. A systematic procedure for identification of material parameters was outlined, and some numerical simulations of a series of triaxial tests were conducted. The last part of this work dealt with a much weaker load-induced anisotropy. Here, the mathematical framework was enhanced by an evolution law for the material fabric. Again, some numerical simulations were conducted, and it was demonstrated that the proposed framework can, at least in a qualitative manner, account for various manifestations of induced anisotropy.
To ensure public safety, existing bridges are often evaluated for their load-bearing capacity. Realistic evaluation must take into account the actual nonlinear stress–strain characteristics of the ...
Due to the large carbon footprint of ordinary Portland cement (OPC) and the rapid corrosion of steel rebars in certain environments, the search for greener, sustainable and more durable reinforced concrete structures is ongoing. In this study, the alkali resistance of basalt- and glass-fibre reinforced polymer (BFRP/GFRP) bars in sulfoaluminate cement (SAC) concrete made with seawater and sea sand is investigated for the first time. Production of SAC involves lower energy consumption and greenhouse gas emission compared to OPC while SAC concrete provides a lower pH environment, which favors the durability of FRP bars. Following ASTM D 7705-D7705M-12 Procedure A, the bars were immersed for three months in simulated pore solution of concrete made with SAC, river sand and fresh water, termed Solution A, and compared their durability to that of companion bars immersed in simulated pore solution of concrete made with SAC, seawater, and sea sand, termed Solution B. Both solutions had the same pH, and their temperature was maintained at 60℃ for the duration of the test. The post-immersion or retained tensile strength of GFRP bars in Solution A and B was 83.0% and 73.6%, respectively, while the corresponding values for the BFRP bars were 52.5% and 67.9%, respectively. It appears that due to the presence of sea salt, Solution B is less damaging to BFRP than Solution A while the opposite is true in the case of GFRP. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results are utilized to explain the damage mechanisms. Based on image analysis, it is shown that the deteriorated zone within the bar cross-section is not a uniform ring, but its cross-sectional area correlates with the reduction in tensile strength.
The effect of loading and geometric parameters on the transverse and longitudinal redistribution of moments in continuous composite bridges, comprising a concrete slab on parallel steel girders, is investigated with the nonlinear finite element method. Fifty bridges are analyzed over their entire range of loading up to failure, and their moment redistribution factors are determined and compared with the relevant predictions of the Canadian Highway Bridge Design Code (CHBDC) and the AASHTO LRFD Bridge Design Specifications. The parameters studied included truck position along the bridge, number of loaded lanes, bridge width, number of girders, slab thickness, degree of composite action, and presence of diaphragms. The study reveals that among the preceding parameters only the number of loaded lanes and the bridge width significantly affect transverse redistribution of moments at ultimate limit state (ULS). However, most of the preceding parameters affect longitudinal redistribution at ULS. Finally, it is demonstrated that plastic analysis of composite multi-girder continuous bridges, treated as an equivalent beam, provides a reasonable estimate of their longitudinal moment redistribution capacity at ULS. It is demonstrated that the actual load-carrying capacity of a composite bridge may be more than 50% higher than that predicted by the CHBDC or AASHTO code. Such higher predicted capacity may obviate the need for retrofit in some cases.Key words: analysis, bridge, composite, concrete, distribution, finite element, inelastic, load, steel.
Results of an experimental study on the bond performance of deformed steel rebars in concrete made with coarse recycled concrete aggregate (RCA) are presented. The distinctive feature of the study ...
Glass Fiber Reinforced Polymer (GFRP) I-beam-column adhesively bonded connections are tested under combined bending and shear. The special feature of the novel connection is the wrapping of the seat angles at the connection by a carbon fiber reinforced polymer (CFRP) fabric wrap. The wrap is primarily intended to alter the connection failure mode from brittle to pseudo-ductile, thus providing adequate warning of impending failure. Four moment resisting connection configurations are tested, including the reference configuration without the wrap. It is observed that the connection failure is initiated by the fracture of the adhesive, but the provision of the wrap, together with a steel seat angle, alters the failure mode from brittle to pseudo-ductile. The post-peak load deformation is achieved without a large drop in the resistance of the connection. On other hand, the connection with the wrapping and a GFRP seat angle can also change the failure mode to pseudo-ductile, but it could not be done without a large reduction in the connection resistance after the peak load.
A thin‐walled‐box‐girder finite element that can model extension, flexure, torsion, torsional warping, distortion, distortional warping, and shear lag effects was developed using an extended version of Vlasov's thin‐walled beam theory. The element has two end nodes, but it has besides the six nodal degrees of freedom of a conventional beam element, additional degrees of freedom to account for torsional warping, distortion, distortional warping, and shear lag. The governing differential equation pertaining to each action was used to derive the exact shape functions and the stiffness matrix and nodal load vector of the element. An orthogonalization procedure was employed to uncouple the various distortional and shear lag modes. A numerical example was solved that compared the proposed method with the facet‐shell finite element analysis, with good agreement between the two sets of results.
An experimental study is conducted to investigate the shear behaviour and strength of concrete beams made with coarse recycled concrete aggregate. The distinguishing feature of the beams is the manner in which their concrete mixture is proportioned. A new method of concrete mixture proportioning is used wherein recycled concrete aggregate is treated as a two-phase material comprising residual mortar and natural aggregate, and the relative amount and properties of each phase are considered. Using this method, several beams are made of recycled concrete aggregate-concrete and tested to study their serviceability and shear strength. For each beam its load–deflection curve, shear deformations, diagonal cracking load, crack pattern, ultimate shear strength, and failure mode are determined. The results show that the shear performance of reinforced recycled concrete aggregate-concrete beams is comparable, or even superior, to that of beams made entirely with natural aggregates at both the serviceability and ultimate limit states, and the current Canadian Standards Association, American Concrete Institute and Eurocode provisions for shear design can be used without any modification to design recycled concrete aggregate-concrete beams, provided the aforementioned mixture proportioning method is used.
Sustainability is now a high priority goal in the construction industry. One way of achieving this aim is to use recycled concrete aggregate (RCA) for base courses and other purposes. However, RCA is not widely used in new concrete mixtures largely because RCA concrete has been reported to be of inferior quality relative to concretes produced with virgin aggregates. In this article, a new mixture proportioning method for RCA concrete is outlined, and it is demonstrated that the method results in RCA concrete mixtures suitable for structural applications, with predictable short- and long-term properties, and requiring less cement than a concrete mixture of comparable quality made with only virgin aggregates.
One of the most urgent problems related to highway infrastructure is that the cost of maintaining a network of bridges with an acceptable level of service is more than the available budgeted funds. Low prioritization of the available resources allocated to bridge projects exacerbates the situation. About 42 percent of the 574,000 highway bridges in the United States were reported by FHWA to be structurally deficient or functionally obsolete. Traditional management practices have become inadequate as ways to face this serious problem. Priority-setting schemes for bridge projects range from those done on a subjective basis in which engineering judgment is used to those that use very complex optimization models. However, currently used priority-setting schemes do not have the ability to optimize the system's benefits to obtain optimal solutions. The present objective is to show how artificial neural networks (ANNs) can be used to optimize the system's resources to generate the group of bridge improvements that minimizes the loss of the network benefits. ANNs are algorithms with characteristics that are able to solve certain classes of optimization problems. The advantages of using ANNs include improvements in the speed of operation by parallel implementation either in hardware or in software. It is also possible to implement ANNs by optical devices that operate at higher speeds than traditional electronic chips.
A rigorous and relatively efficient algorithm based on the non-orthogonal smeared crack approach is coded in a special finite element program to study the seismic response of arch dams. The formulation is briefly presented. The 130 m high Shahid Rajaee arch dam in Iran subjected to the Friuli-Tolmezzo earthquake is selected to present a practical application of the technique. Under the same geometry and loading conditions, six nonlinear analyses with different parameters are performed, and the results are compared with each other and a linear case. The varied parameters include secant and elastic unloadingreloading options, threshold angle, and tensile strength of the material. It is concluded that the non-orthogonal smeared crack approach can redistribute the state of stresses and produces a more realistic profile of stresses in the dam. A drift in the crest displacements forms the prominent characteristics of the cracking behavior. The results also suggest that the dam can suffer significant cracking during a strong earthquake and still remain stable. Moreover, the influences of the mentioned parameters in the seismic response of the dam are comprehensively discussed.Key words: nonlinear dynamic analysis, concrete arch dam, smeared crack approach.
Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of each component are individually considered. The test variables include the mixture proportioning method, and the aggregate type. The results show that the amounts of creep and shrinkage in concretes made with coarse RCA, and proportioned by the new method, are comparable to, or even lower than, those in similar concretes made entirely with natural aggregates. Furthermore, it is demonstrated that by applying the proposed “residual mortar factor” to the existing ACI and CEB methods for calculating creep or shrinkage of conventional concrete, these methods could be also applied to predict the creep and shrinkage of RCA-concrete.
