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

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

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

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

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