Publications

Parametric and optimization analyses of a dynamic Trombe wall incorporating PCM to save heating energy under cold climate zones

The Trombe wall system incorporating a dynamic PCM layer (DTWPS) has been recognized as a viable envelope to reduce the energy demand for heating effectively. However, properly selecting PCMs in the DTWPS is complicated and much less studied. Therefore, parametric and optimization analyses of the PCM thermal properties of a DTWPS are carried out for heating energy saving under cold climate zones using a validated CFD model, multiple linear and nonlinear regression models, and the particle swarm optimization (PSO) algorithm. The results show nonlinear relationships between the four critical PCM thermal properties and the energy saving, time lag, and thermal comfort. Moreover, the optimal values of the melting point, latent heat, density, and thermal conductivity of the PCM are 26.4 °C, 200 kJ/kg, 2080 kg/m3, and 1.34 W/(m·K), respectively. Meanwhile, the energy saving for the test room equipped with the DTWPS with optimal thermal properties could reach 100 % compared to that for the traditional reference Trombe wall. With available PCMs, heating energy consumption can be saved by up to 90 % or more. Further, the DTWPS demonstrates a reduced PCM mass compared to other passive walls.

Flexural Behavior of Concrete Beams Reinforced with Carbon Fiber-Reinforced Polymer (CFRP) Prestressed Prisms

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Modifications of standard GFRP sections shape and proportions for improved stiffness and lateral-torsional stability

In this paper the results of a comprehensive numerical investigation regarding the axial–flexural–torsional response of pultruded slender beams is presented. The goal is to propose GFRP standard cross-sections of such proportions and shapes that would possess improved strength, stability and deformational characteristics compared to the corresponding existing sections whose proportions are generally based on standard steel sections. As GFRP sections are thin-walled but are significantly less stiff than similar steel sections, the study focuses on enhancing their appropriate stiffness and buckling strength. The novel and efficient numerical model used in this investigation was developed by the writers and can be used to trace the complete pre-buckling geometrically nonlinear response of any GFRP or steel thin-walled member with open or closed cross-section. The bucking load is computed by the asymptotic value of the load–displacement curve. Members with I-, L-, T- and box sections are analyzed, considering different loading and boundary conditions. It is demonstrated that due to their unsuitable proportions, available standard GFRP sections do not have adequate stiffness and buckling strength. Consequently, recommendations are made for new sectional proportions and modified shapes, and some graphical results are presented to demonstrate how the results of the proposed method could be utilized in practical design situations. The superiority of the proposed sections is quantified by an efficiency factor, defined in terms of ratio of strength gain to material volume increase.

Shear capacity evaluation of steel reinforced recycled concrete (RRC) beams

The applicability of some major concrete design standards and other pertinent methods to calculate the concrete contribution to the shear resistance of reinforced recycled concrete (RRC) beams without stirrups is investigated. Results of a relatively comprehensive experimental program are used to compare the actual shear strength of the tested beams with their corresponding predicted values. The concrete mixes for the RRC beams were proportioned by the so-called Equivalent Mortar Volume (EMV) method. The method is predicated on the fact that recycled concrete aggregate (RCA) is a composite material, comprising mortar and natural aggregate, and the volumetric content and properties of each phase must be quantitatively accounted for when proportioning concrete mixes containing RCA. The test variables included in the test program are shear-span/depth ratio, beam size, RCA source, and coarse aggregate type. The results show that the shear capacity of a RRC beam is comparable, or sometimes superior, to that of a companion beam made of conventional concrete. The analyses performed in the current investigation show, contrary to previous findings, that existing shear design methods, such as the ACI and CSA codes methods, are applicable to RRC beams, provided the EMV method of mix design is used.

A general finite element for beams or beam‐columns with or without an elastic foundation

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.

MINIMIZATION OF REFLECTION CRACKING THROUGH THE USE OF GEOGRID AND BETTER COMPACTION

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.

Experimental investigation of load distribution in a composite girder bridge at elastic versus inelastic states

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.

Mode II interface constitutive law for concrete substrates strengthened with steel reinforced polymers

C-Anchor for Strengthening the Connection between Adhesively Bonded Laminates and Concrete Substrates

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.

Applications of electrically conductive membranes in water treatment via membrane distillation: Joule heating, membrane fouling/scaling/wetting mitigation and monitoring

Membrane distillation (MD) is a thermally driven separation process that is driven by phase change. The core of this technology is the hydrophobic microporous membrane that prevents mass transfer of the liquid while allowing the vapor phase to pass through the membrane's pores. Currently, MD is challenged by its high energy consumption and membrane degradation due to fouling, scaling and wetting. The use of electrically conductive membranes (ECMs) is a promising alternative method to overcome these challenges by inducing localized Joule heating, as well as mitigating and monitoring membrane fouling/scaling/wetting. The objective of this review is to consolidate recent advances in ECMs from the standpoint of conductive materials, membrane fabrication methodologies, and applications in MD processes. First, the mechanisms of ECMs-based MD processes are reviewed. Then the current trends in conductive materials and membrane fabrication methods are discussed. Thereafter, a comprehensive review of ECMs in MD applications is presented in terms of the different processes using Joule heating and various works related to membrane fouling, scaling, and wetting control and monitoring. Key insights in terms of energy consumption, economic viability and scalability are furnished to provide readers with a holistic perspective of the ECMs potential to achieve better performances and higher efficiencies in MD. Finally, we illustrate our perspectives on the innovative methods to address current challenges and provide insights for advancing new ECMs designs. Overall, this review sums up the current status of ECMs, looking at the wide range of conductive materials and array of fabrication methods used thus far, and putting into perspective strategies to deliver a more competitive ECMs-based MD process in water treatment.

Finite element modeling of coupled heat transfer, moisture transport and carbonation processes in concrete structures

Carbonation is one of the many reasons of reinforcement corrosion in concrete structures. Due to the coupling effects of moisture, heat and carbon dioxide transport in concrete, the modeling of this problem is a rather challenging task. A nonlinear finite element approach is adopted here for tracing the spatial and temporal advancement of the carbonation front in concrete structures with and without cracks. A two-dimensional Windows-based finite element computer program, called CONDUR, is developed and the results obtained from the program are compared with available experimental data. The program is designed to be flexible and comprehensive in its scope.

Response of Arching Unreinforced Concrete Masonry Walls to Blast Loading

New standards for blast protection of buildings are currently being developed in the United States and Canada. In this regard, both standards are considering unreinforced masonry (URM) walls as particularly vulnerable to blast events and may not be used in blast-resisting structural systems. In this paper, the effectiveness of enforcing arching action as a cost-effective hardening technique for vertically spanning one-way URM walls under blast loads is investigated. A total of eight full-scale concrete-block URM walls were subjected to blast loads generated by high explosives. Enforcing URM walls arching between rigid supports significantly enhanced their out-of-plane blast resistance compared to similar nonarching (flexural) URM walls. Moreover, no fragments or debris were observed on the leeward side of the arching walls, indicating the potential of the proposed hardening technique in reducing the hazard level on the occupants of buildings with exterior URM walls. The improved performance is attributed to the formation of hinges at the walls' supports and midheights. This three-hinged arch mechanism allowed the walls to develop large in-plane compressive forces, which subsequently increased their out-of-plane resistances and prevented flying debris due to increased friction forces between the masonry courses. Comparing the observed strength of the arched walls to their strength predicted by existing models showed a significant underestimation of the actual wall strengths. The results of the study clearly demonstrate that, with minimal structural intervention, URM walls can significantly improve the building envelope performance and contribute to the structural resistance of blast loads.

SESSION 2: ANALYSIS AND DESIGN I. SECOND INTERNATIONAL CONFERENCE ON SHORT AND MEDIUM SPAN BRIDGES: AUGUST 17-21, 1986, OTTAWA, CANADA: PROCEEDINGS VOLUMES 1 AND 2

Papers presented at session 2 were as follows: shear lag analysis of concrete box beams using small computer capacity (maisel,bi); staggered shear design of concrete bridge girders (marti,p); ultimate strength evaluation for bridge structures (nowak,as); fatigue design problems in steel bridges (pietraszek,t); hybrid precast concrete girder bridges (harvey,di); forces at the slab-web connections of box-girders (razaqpur,ag). For the covering abstract of the conference see IRRD 291033. (TRRL)

Modeling the Nonlinear Behavior of Concrete Masonry Walls Retrofitted with Steel Studs under Blast Loading

This paper presents the results of an analytical investigation of one-way unreinforced masonry (URM) walls retrofitted with externally anchored steel studs and subjected to blast loads. Using the wall geometrical and material properties, deflected shape, and crack pattern as input, a nonlinear model is developed to predict the inward force-displacement relationship of the retrofitted walls. In addition, using a rigid body analysis, a simple bilinear force-displacement relationship is developed to model the outward force-displacement relationship of the walls. Utilizing these two force-displacement relationships (resistance functions), a generalized single-degree-of-freedom (SDOF) model is developed to capture the nonlinear out-of-plane dynamic response of the retrofitted walls under blast loads. The SDOF model captured the experimentally observed displacement responses of the tested walls with reasonable accuracy. The model was also used to investigate the influence of block thickness, wall slenderness ratio, blast load intensity, and blast pulse shape on the out-of-plane dynamic response of retrofitted walls. The results demonstrated that anchored steel-stud systems could significantly enhance the out-of-plane capacity of the retrofitted walls by increasing their out-of-plane capacity and reducing their displacement.

Estimation of global land surface evapotranspiration and its trends in past two decades using a hybrid deep learning and physical process-based model

Nonlinear analytical procedure for predicting debonding of laminate from substrate subjected to monotonic or cyclic load

The bonding of steel/fiber-reinforced polymer (SRP/FRP) laminate strips to concrete/masonry elements has been found to be an effective and efficient technology for improving the elements’ strength and stiffness. However, premature laminate–substrate debonding is commonly observed in laboratory tests, which prevents the laminate from reaching its ultimate strength, and this creates uncertainty with respect to the level of strengthening that can be achieved. Therefore, for the safe and effective application of this technology, a close estimate of the debonding load is necessary. Towards this end, in this paper, a new, relatively simple, semi-analytic model is presented to determine the debonding load and the laminate stress and deformation, as well as the interfacial slip, for concrete substrates bonded to SRP/FRP and subjected to monotonic or cyclic loading. In the model, a bond-slip law with a linearly softening branch is combined with an elasto-plastic stress-strain relationship for SRP. The model results are compared with available experimental data from single-lap shear tests, with good agreement between them.

Effect of key parameters on the transient thermal performance of a building envelope with Trombe wall containing phase change material

The thermal behavior of a building envelope having a Trombe wall incorporating phase change material (PCM) is investigated during heating season, using experimentally validated 3D computational fluid dynamics (CFD) simulations. The effects of transient versus steady-state ambient irradiation and temperature, presence of PCM and different solar irradiation intensities on the spatial and temporal variation of temperature and airflow rate in the conditioned room are investigated. The results show that the flow transition and temperature rise mainly happen in the near-wall regions close to the room ceiling and in the air channel. They also indicate that the Trombe wall with PCM tends to prevent large fluctuations in room temperature and airflow rate. More importantly, it is determined that under constant radiation flux and ambient temperature, the PCM significantly improves the thermal performance of the envelope and effectively shifts the heating load, but under diurnally transient solar radiation flux and ambient temperature, these benefits seem less evident. Accordingly, caution must be exercised in extrapolating results obtained under constant ambient conditions to situations involving transient

New Mixture Proportioning Method for Concrete Made with Coarse Recycled Concrete Aggregate

New method of mixture proportioning is proposed for concrete made with coarse recycled concrete aggregates (RCA). The proposed method, dubbed the "equivalent mortar volume" method, is predicated on the fact that RCA is a two-phase material comprising mortar and natural aggregate; therefore, when proportioning a concrete mixture involving RCA, one must account for the quantity and quality of each phase and adjust both the coarse aggregate and fresh paste content of the mix accordingly to achieve the same total mortar volume as a companion mix with the same specified properties but made entirely with coarse natural aggregates of similar properties to the coarse natural aggregate contained in RCA. Using the proposed method and the conventional aggregate replacement method, a large number of mixes was made with RCA obtained from two demolition waste recycling plants. For each mix, its slump, fresh and hardened densities, compressive strength, and elastic moduli were measured. The results showed that using the proposed method, unlike the conventional method, yields concrete mixes with consistent, predictable, and comparable properties to those of similar mixes made with natural aggregates.