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In an arch dam, adjacent monoliths separated by vertical contraction joints may move relative to each other during an earthquake, resulting in the gradual opening and closing and possible shear movement at the joint surfaces. This paper presents the formulation of a joint constitutive model for a zero-thickness joint element that can simulate both the opening and closing and shear sliding behaviour, as well as the non-linear shear key effects of the joint. The proposed joint element has been implemented in the concrete arch dam finite element analysis program ADAP-88. The response of a typical arch dam subjected to earthquake ground motion is presented to demonstrate the capability of the proposed joint model. Results from a parametric study carried out to study the sensitivity of the response to the joint properties are discussed. The joint parameters considered in the parametric study include apparent cohesion, friction coefficient, and whether the joint has beveled or unbeveled shear key, or the joint is unrestrained in shear sliding. The analysis results show that joint opening and shear slippage at the contraction joints can have significant effects on the response of an arch dam. © 1998 John Wiley & Sons, Ltd.
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.
Four large scale concrete beams of 4.2 m length and 200 x 500 mm cross-section were built and tested under four-point bending. Two beams were used as control beams and were reinforced with mild steel for both shear and flexure. The flexural and shear reinforcement for the remaining two beams were provided by externally bonded carbon fibre (CFRP) sheet. In addition, to achieve ductility in the CFRP reinforced beams, a low modulus high strain high density polypropylene grid (HDPP) was placed within them. The primary focus of this study was to achieve ductility via the provision of HDPP but it was also intended to prevent delamination of bonded CFRP sheets by attaching some of the laminae to the sides of the beam rather than attaching them all to the beam soffit. Finally, the magnitude of shear that could be resisted by externally bonded CFRP U stirrups was investigated. The hybrid reinforced beams achieved their design capacity and initial failure occurred due to rupture of CFRP sheet in the maximum moment region, followed by some delamination. The CFRP stirrups reached 70% of their ultimate strain capacity. After the rupture of CFRP, the HDPP provided the beams with residual strength, but due to the low modulus of HDPP, the deformations of the beams increased substantially. (A) For the covering abstract see ITRD E104933.
