Experimental Study on RC Beams Strengthened with Carbon and Glass Fiber Sheets

This study investigates the effects of the two types of fiber sheets, namely, carbon and glass fiber sheets, on the flexural behaviors of reinforced concrete (RC) beams when they are bonded to the tension zones of the beams. A total of eight full-scale beams were tested in the experiments. The flexural strength and stiffness of RC beams were found to increase significantly after the installation of fiber sheets. An analytical model based on the principle of virtual work was developed to predict the load-deflection relationship of the hybrid beams. The paper also highlights the characteristics of debonding problem which limits the effective use of fiber materials

Optimum Design of Steel Structures in Accordance with AISC 2010 Specification Using Heuristic Algorithm

This paper proposes a heuristic algorithm (HA) for the optimum design of steel structures in accordance with all three methods specified in the ANSI/AISC 360-10 "Specification for Structural Steel Buildings". These methods include the direct analysis method (DAM), and two alternative methods, namely, the first-order analysis method (FAM), and the effective length method (ELM). The objective of the design algorithm is to obtain the least weight for the designed steel sections. The optimum design combines the SAP2000 structural analysis program and the heuristic algorithm that is written in Microsoft Visual Basic program. The rigorous second-order analysis was performed in both DAM and ELM, while the first-order analysis was used in the FAM. Three design examples of planar steel frames are used to illustrate the application. Among the three design methods, the FAM results in lower bound solutions, while the EFM results in upper bound solutions

Flexural Response of CFRP-Strengthened Steel Beams with Initial Bond Defects

This paper presents the flexural behavior of steel beams strengthened with partial-length adhesive-bonded carbon fiber-reinforced polymer (CFRP) plates under static four-point bending. An initial bond defect was intentionally introduced in the constant moment region of the CFRP-strengthened steel beams. In the experimental program, the test variables included the size of the initial bond defect, FRP modulus, FRP plate length, and condition of the steel beam before installation of the FRP plate (undamaged and pre-yielded conditions). Based on the test results, the presence of the initial bond defect changed the failure mode of FRP-strengthened steel beam from the fiber rupture to intermediate plate debonding. With the initial bond defect, the effectiveness of the FRP strengthening scheme decreased as FRP modulus increased. The stiffness, strength, and ductility index of the CFRP-strengthened beam with the initial bond defect decreased as the defect size increased. However, the initial bond defect had no detrimental effect on the maximum load capacity and ductility index of the strengthened beams. The strengthening effectiveness in terms of stiffness, strength, and ductility enhancement was more pronounced in the case of the pre-damaged steel beam, of which the bottom flange had already yielded before installation of the CFRP plate, than the undamaged steel beam

Finite Element Modelling of Concrete-Encased Steel Columns Subjected to Eccentric Loadings

This paper presents the 3D finite element (FE) analysis of the concrete-encased steel (CES) columns subjected to concentric or eccentric loadings. A new simplified technique of FE modelling that incorporates the concrete confinement behavior of the composite columns is proposed. This technique eliminates the need of predefining zones and constitutive properties of the confined concrete. After validated with past experimental data, the FE analysis is conducted to construct the strength interaction diagrams of the short CES columns. The effects of material properties including the compressive strength of concrete and yield strength of structural steel on the strength interaction diagrams of CES columns are numerically investigated. The FE results show that the concrete strength only has a significant effect on the column strength under combined compression and bending (compression phase) of the interaction diagram, while the yield strength of structural steel has a significant effect on both compression and tension phases. A comparison between the strength interaction diagrams predicted by FE analysis and the plastic stress distribution method specified in AISC360-16 “Specification for Structural Steel Buildings” shows that the design provision underestimates the strength of the short CES columns subjected to concentric or eccentric loadings. Such underestimation reduces as the compressive strength of concrete decreases or yield strength of structural steel increases

Thermoporoelastic Effects of Drilling Fluid Temperature on Rock Drillability at Bit/Formation Interface

A drilling operation leads to thermal disturbances in the near-wellbore stress, which is an important cause of many undesired incidents in well drilling. A major cause of this thermal disturbance is the temperature difference between the drilling fluid and the downhole formation. It is critical for drilling engineers to understand this thermal impact to optimize their drilling plans. This thesis develops a numerical model using partially coupled thermoporoelasticity to study the effects of the temperature difference between the drilling fluid and formation in a drilling operation. This study focuses on the thermal impacts at the bit/formation interface. The model applies the finite-difference method for the pore pressure and temperature solutions, and the finite-element method for the deformation and stress solutions. However, the model also provides the thermoporoelastic effects at the wellbore wall, which involves wellbore fractures and wellbore instability. The simulation results show pronounced effects of the drilling fluid temperature on near-wellbore stresses. At the bottomhole area, a cool drilling fluid reduces the radial and tangential effective stresses in formation, whereas the vertical effective stress increases. The outcome is a possible enhancement in the drilling rate of the drill bit. At the wellbore wall, the cool drilling fluid reduces the vertical and tangential effective stresses but raises the radial effective stress. The result is a lower wellbore fracture gradient; however, it benefits formation stability and prevents wellbore collapse. Conversely, the simulation gives opposite induced stress results to the cooling cases when the drilling fluid is hotter than the formation

Systematic Approaches towards the Development of Host-Directed Antiviral Therapeutics

Since the onset of antiviral therapy, viral resistance has compromised the clinical value of small-molecule drugs targeting pathogen components. As intracellular parasites, viruses complete their life cycle by hijacking a multitude of host-factors. Aiming at the latter rather than the pathogen directly, host-directed antiviral therapy has emerged as a concept to counteract evolution of viral resistance and develop broad-spectrum drug classes. This approach is propelled by bioinformatics analysis of genome-wide screens that greatly enhance insights into the complex network of host-pathogen interactions and generate a shortlist of potential gene targets from a multitude of candidates, thus setting the stage for a new era of rational identification of drug targets for host-directed antiviral therapies. With particular emphasis on human immunodeficiency virus and influenza virus, two major human pathogens, we review screens employed to elucidate host-pathogen interactions and discuss the state of database ontology approaches applicable to defining a therapeutic endpoint. The value of this strategy for drug discovery is evaluated, and perspectives for bioinformatics-driven hit identification are outlined

A Fracture-Based Criterion for Debonding Strength of Adhesive-Bonded Double-Strap Steel Joints

This paper addresses the debonding strength of adhesive-bonded double-strap steel joints. A fracture-based criterion was formulated in terms of a stress singularity parameter, i.e., the stress intensity factor, which governs the magnitude of a singular stress field near the joint ends. No existing crack was assumed. A total of 24 steel joint specimens were tested under constant amplitude fatigue loadings at stress ratio of 0.2 and frequency of 2 Hz. The joint stiffness ratio was slightly less than one to control the maximum adhesive stresses at the joint ends. To detect the debonding, a simple and practical technique was developed. The test results showed that the interfacial failure near the steel/adhesive corner was a dominant failure mode. The failure was brittle and the debonding life was governed by the crack initiation stage. The finite element analysis was employed to calculate the stress intensity factors and investigate the effects of the adhesive layer thickness, lap length and joint stiffness ratio on the debonding strength