188 publications from this institution
A general finite element is derived for beams or beam‐columns with or without a continuous Winkler type elastic foundation. The need to discretize members into shorter elements for convergence towards an ‘exact’ solution is eliminated by employing in the derivation of the element exact shape functions obtained from the equation of the elastic line. Inter‐nodal values of deflections, bending moments and shear forces are obtained using the exact shape functions and trigonometric series. The effect of heavy compressive or tensile axial forces on bending stiffness is treated as a linear problem by considering the axial force as a constant parameter affecting the stiffness. FORTRAN subroutines to compute the stiffness matrix, equivalent nodal forces, deflected shape, bending moments and shear forces are provided and verified by an example.
This paper discusses the issue of redistribution of stresses and moments in continuous FRP reinforced concrete beams. Six 6.5 m long two-span FRP reinforced concrete beams were designed and constructed. While two of the beams were reinforced with steel as control specimens, the other four were longitudinally reinforced with CFRP rods. Analysis of results showed considerable amount of redistribution for FRP over-reinforced concrete beams while the amount of redistribution for FRP under-reinforced concrete beams was negligible.
Red mud (RM) is a hazardous by-product of alumina refining processes. Due to its high alkalinity, large specific surface area, and complex and variable composition, RM is hard to treat or utilize on a large scale. To date, more than 4 billion tons of RM have been stockpiled globally and is still growing by more than 120 million tons annually. Many investigations have focused on the largescale utilization of RM as a construction material, either in its virgin form or after heat treatment. However, the huge differences among the chemical/mineralogical compositions of RMs due to differences among bauxite ores from different sources and/or different refining processes, it is difficult to prescribe a unique process for activating RM cementitious/pozzolanic properties. The present study aims to identify the key chemical and process-dependent factors that influence the cementitious/pozzolanic properties of RM. Two types of RM from different sources are investigated to determine the effects of the chemical/mineralogical composition, the alumina refining process, and calcination on the mineralogical phases and compressive strength of mortar cubes made with ordinary Portland cement (OPC)- RM blended cement. Mortar made with 15 wt.% OPC replaced by one type of virgin RM produced by the Bayer’s process was found to have better strength than a control mortar made with 15% OPC replaced by sand, which indicates that this RM had cementitious/pozzolanic property without requiring heat treatment. On the other hand, the RM produced by the bauxite calcination method needed heat treatment to improve its pozzolanicity, but, despite the improvement, mortar made with its optimally treated form had lower 91-day compressive strength than the companion control mortar made with extra sand as RM replacement. The compressive strength of mortars made with calcined RM was not only affected by the phase changes of the virgin RM properties brought about by calcination but also by changes to its physical.
To utilize effectively passive solar energy for heating buildings, an innovative building envelope is proposed, and its superior performance is for the first time experimentally demonstrated by constructing and testing its full-scale model. The proposed envelope comprises a dynamic Trombe wall incorporating phase change material (PCM). Its salient feature and novelty are its innovative multi-panel solar collector-storage wall and the ability of each panel to independently rotate about its vertical axis. One face of each panel is cladded with PCM, and in a typical 24 h cycle, during sunshine hours, this face is turned towards the incident solar irradiation and the rest of the time towards the conditioned space. The thermal performance of the proposed envelope is compared with that of a companion envelope having a traditional static Trombe wall with the same amount of PCM and wall geometry. The results show that compared to the traditional envelope, the new envelope regulates the thermal load more evenly by preventing large temperature swings, it reduces heat loss during the solidification phase of PCM by 29% and is overall 20% thermally more efficient. These benefits can result in energy saving from non-renewable energy sources over the design life of the building.
The conventional membrane distillation (MD) process is accompanied by large energy consumption, low thermal efficiency and inevitable requirements of centralized infrastructures, which impede its practical applications, especially in the offshore and remote off-grid areas. Thanks to the rapid development of efficient photothermal materials over the last decade, a new photothermal membrane distillation (PMD) process has emerged to harness abundant solar energy and localize heating on the membrane-feed water interface via photothermal effects. Driven by the temperature difference across the PMD membrane, water vapor can be generated on the membrane-feed surface, transported through membrane pores and condensed at permeate side to obtain freshwater, thus tackling the challenge of obtaining clean water using green energy. The PMD process avoids heating the entire bulk feed water and feed transportation from heat units to membrane modules, which save substantial amounts of energy. The interfacial localized heating intrinsically mitigates the temperature polarization across the membrane. The latent heat from vapor condensation can be effectively recovered via multi-level PMD configurations. As great efforts have been made to exploit PMD process, it is imperative to review the state-of-the-art progress of PMD and shed light on its future trend. Here, we briefly illustrate PMD mechanisms and membrane requirements, photothermal materials feasible for developing PMD membranes along with their light-to-heat mechanisms. This is followed by reviewing diverse approaches to prepare PMD membranes, which are classified into one-step fabrication and multi-step modification methods. Comprehensive discussion about PMD membrane performance in different configurations and their small pilot-scaled applications are provided. The effects of operational parameters and module designs are discussed in Section 6. Finally, the current challenges and future perspectives of PMD process are emphasized with the aim of providing guidance for future works.
The mechanisms of shear transfer in fiber-reinforced polymer (FRP) reinforced concrete members with shear reinforcement are discussed, and it is explained how these were used to derive the shear design provisions of the Canadian standard for design and construction of building structures with FRPs. Subsequently, the accuracy of these provisions and the validity of their underlying assumptions are assessed by comparing the predicted shear strengths of over three hundred FRP-reinforced beams with their corresponding experimental values. Although the focus of the paper is mainly on beams with FRP shear reinforcement, for completeness beams with and without shear reinforcement are analyzed. It is determined that the mean and standard deviation of the ratio of the test to predicted shear strength of the beams without shear reinforcement are 1.16 and 0.24, respectively, whereas those of beams with shear reinforcement are 1.15 and 0.23. The strengths of these beams are also computed using the recommendations and it is shown that overall recently proposed Canadian method yields more accurate and consistent results.
Traditionally, the slump test has been used to measure concrete consistency. However, many researchers contend that the slump alone is not a sufficient measure of consistency and that other quantifiable rheological properties such as shear yield stress and plastic viscosity are more representative and should be considered. A SLump Rate Machine (SLRM) was adapted and calibrated, to consistently measure the plastic properties for a number of concrete mixes, namely slump rate and slump flow. Furthermore, a theoretical model was developed to correlate the slump flow and slump rate with the shear yield stress and plastic viscosity of fresh concrete, respectively. Employing the SLRM and the theoretical model has resulted in an efficient new approach to adequately predict the rheological behaviour of fresh concrete as well as to provide reasonably accurate values for shear yield stress and plastic viscosity.
Standard methods for blast testing of structural materials and components are not currently available, but the designer must have a sense about the accuracy of the analytical and numerical methods used in blast analysis and the justification for accepting the results of different models. The objective of this chapter is to present the results of field tests conducted by the writers on full scale reinforced concrete and structural steel beams and columns. Extensive data captured during the test, including incident and reflective pressure, member displacements and strains, will be compared with results of some empirical and numerical models. The relative accuracy of the models will be gauged and the validity of certain assumptions in these models will be examined. Finally, recommendations regarding the suitability of each model and the need for standardizing test methods to assess the blast resistance of structures and the properties of materials under high strain rates will be highlighted.
Every year, large amounts of pavement deicing chemicals are used for snow and ice control on Canadian highways and airports. Until recently, urea had been the only pavement deicing chemical in use at Canadian airports, but due to recent concerns about the impact of this deicer on the environment, consideration has been given to replacing it with more environmentally friendly deicers. Concerns have also been expressed regarding the impact of road salts, which are used exclusively on highways but not airfields, on the environment. However, before substituting these conventional deicers with new ones, the potential deleterious effects of the new deicers on the pavement need to be quantified and compared with those of the conventional deicers. This paper presents an investigation to compare the destructive effect of newly introduced deicing chemicals such as potassium acetate and sodium formate, with urea and ordinary road salts on the durability of pavement construction aggregates and asphalt concrete when subjected to freeze-thaw cycles while submerged in solutions of different concentrations. The destructive effect of each deicer on aggregates was determined in terms of percent weight loss due to breakdown. For pavement samples, it was quantified in terms of weight and density loss, change in mechanical properties, variation in the penetration of recovered asphalt, and variation in the gradation of recovered aggregates. The test results showed that for all deicers the critical concentration, the one that caused the greatest damage to the aggregate, was in the 1–2% range, and for all deicers the quartzite aggregate suffered more damage than the limestone. It was also found that the road salt produced comparable damage to that caused by other deicers to quartzite, while the damage was significantly less for limestone aggregates. In case of asphalt concrete samples, it was found that conditioning asphalt samples using freeze-thaw cycles in the presence of a deicer solution caused a decrease in the indirect tensile strength and modulus of elasticity and an increase in the penetration values of the recovered asphalt cement. In addition, the test results showed that the maximum damage was caused by urea, while the damage due to the other deicers was comparable to that of distilled water.
To delay or prevent debonding of externally bonded fiber-reinforced polymer (FRP) laminate from concrete substrate, a new carbon FRP (CFRP) anchor is developed. The monolithically built anchor comprises two legs and a wide head plate, with the legs inserted into adhesive-filled drilled holes in the concrete and the head plate bonded to the surface of the FRP laminate and the adjacent concrete. Full-scale reinforced concrete T-beams were strengthened in flexure with different amounts of CFRP laminate and tested in four-point bending. The anchor number and spacing were varied to find the most effective configuration. It was determined that the configuration involving nearly uniform spacing of the anchors along the laminate and the placement of the laminate strips between the anchor legs were most effective to allow beams with up to eight plies of the laminate to fail by rupture of FRP rather than debonding. When comparing the efficiency factor of the proposed anchor with those of other anchors reported in the literature, it was found to have the highest efficiency factor.
Compaction of asphalt mix has been recognized as one of the most important factors that affect the long-term performance of the pavement. Problems experienced in compacting asphalt mixes have generally been ascribed to the mix. Roller "checking," the result of compaction with steel rollers, has been disregarded or considered as irrelevant. Compaction based on a new concept, using a soft plate, avoids roller checking, as demonstrated by a series of side-by-side field tests with steel and pneumatic rollers. The surface cracks initiated by the steel wheel roller may provide an explanation for the often reported phenomenon of early deterioration of asphalt pavements. Finite element analyses of pavement structures with roller-induced cracks have shown significantly higher tensile stresses than the corresponding stresses in otherwise identical uncracked pavements. The analytical findings are supported by indirect tensile and stress fatigue tests results obtained in the laboratory from asphalt samples compacted in the field. The test samples were recovered from pavements compacted either by existing compaction equipment and technique or by the new soft plate method. Key words: asphalt, crack, compaction, fatigue, finite element, tensile strength testing, pavement.
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Results from finite element analyses and laboratory tests are presented which suggest that in the presence of construction induced cracks in new asphalt overlays, geogrid reinforcement will be ineffective in preventing reflective cracking. As is customary, the reinforcement layer was placed at the interface of the overlay and the existing pavement surface. However, when through improved compaction, by means of a newly developed compactor, called AMIR, construction induced cracks were minimized, the same reinforcement proved to be effective in controlling reflective cracking. (A) For the covering abstract see IRRD 857794.
An experimental investigation was carried out to evaluate the seismic behaviour of 200 × 200 mm2 reinforced-concrete columns with an embedded drain pipe subjected to monotonic and reversed cyclic loading. Nine full-scale specimens were prepared, including two control specimens without an embedded pipe and seven specimens with a pipe embedded in the column core. Among the latter seven columns, two were highly confined using 8 mm dia. ties with 80 mm spacing, while a 200 mm spacing was used in the other columns. The test results indicated that the pipe adversely affected the column's load-carrying capacity, load–displacement response and ductility. The extent of the adverse effect was found to depend on the level of axial load, the degree of confinement and the distance of the pipe exit from the column base. Due to local stress concentration, some local damage was observed in the vicinity of the pipe exit, but the provision of high confinement in the pipe exit region significantly improved the overall behaviour of the column under reversed cyclic loading.
Vlasov's thin walled box beam theory, which accounts for the distortion of the cross section, is combined with special shear lag warping functions to derive a box girder finite elenent model with exact shape functions. The governing differential equations are used to derive the exact shape functions and the stiffness matrix and nodal load vector are developed based on these. The paper describes the computer program in which the proposed procedures are implemented, and two numerical examples are presented which compare the proposed method with facet shell finite element analyses.
