Wael Zatar

Flexural Behavior of Hybrid Composite Beams

This paper presents the development of composite beams, which consist of hybrid carbon and glass fiber-reinforced polymer (FRP) I-beams and precast, ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs. Hybrid FRPs (HFRPs) provide the advantage of high resistance to corrosion, while UHPFRC has great strength and durability. The combination of these two materials is expected to benefit structures subjected to severe environmental conditions and to respond to the need for accelerated bridge construction. Three full-scale composite beams with varied UHPFRC slab width were tested under four-point flexural loading. Bolt shear connectors with and without epoxy bonding were used in the tested beams. The bolt shear connectors and epoxy were used to resist the horizontal shear flow at the interface between the HFRP I-beam and the UHPFRC slab. The composite action between the HFRP I-beam and UHPFRC slab was investigated. The test results showed that all of the composite beams exhibited significant improvements in stiffness and strength properties, above those of single HFRP I-beams without a UHPFRC slab. A fiber model was developed to predict the strength and stiffness of the composite beam, and the model accuracy was verified. Good agreement was found between the experimental and analytical results. The high tensile strength of a carbon FRP in an HFRP tensile flange could be used effectively, and the delamination failure of an HFRP compressive flange could be prevented through the addition of a UHPFRC slab on the top flange of the HFRP I-beam. The study revealed that HFRP–UHPFRC beams were efficient and could provide a competitive, cost-effective, and sustainable solution to bridge structures.

Hybrid Fiber-Reinforced Polymer Girders Topped with Segmental Precast Concrete Slabs for Accelerated Bridge Construction

The behavior of composite girders made of hybrid fiber-reinforced polymer (HFRP) I-girders, topped with precast ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs is presented in this paper. HFRP I-girders were manufactured under the pultrusion process in which unidirectional carbon fibers and bidirectional fiberglass fabric or continuous strand mat were used. Four large-scale composite girders were tested under four-point flexural loading. In the first composite girder, the HFRP I-girder was topped with a full-length precast UHPFRC slab. Twelve precast UHPFRC segments were used in each slab of the other three composite girders. Either epoxy or mortar connections were used to connect the precast UHPFRC segments. The test results showed that the flexural stiffness of the composite girder with the epoxy-connected segmental precast slabs was similar to that of the full-length precast composite girder. The mortar-connected girder exhibited more ductile behavior than the epoxy-connected girder. All the composite girders exhibited significant improvements in strength and stiffness compared with the HFRP I-girder without the UHPFRC slab. The HFRP–UHPFRC composite girders were shown to provide a promising and sustainable solution for accelerated bridge construction.

Mechanical properties of hybrid polymer composite

Abstract Hybrid composites have unique features that can be used to meet specified design requirements in a more cost-effective way than nonhybrid composites. They offer many advantages over conventional composites including balanced strength and stiffness, enhanced bending and membrane mechanical properties, balanced thermal distortion stability, improved fatigue/impact resistance, improved fracture toughness and/or crack arresting properties, reduced weight and/or cost, and reduced notch sensitivity. “Synergistic” effect of hybrid composites (defined as the difference between the performance of a fiber in a hybrid composite and in a single fiber composite) has gained interest of researchers worldwide. This chapter reviews recent research activities on natural fiber-based hybrid composites with the main focus on their mechanical properties.

Hybrid polymer composites for structural applications

Abstract Hybrid composites have unique features that can be used to meet specified design requirements in a more cost-effective way than nonhybrid composites. They offer many advantages over conventional composites including balanced strength and stiffness, enhanced bending and membrane mechanical properties, balanced thermal distortion stability, improved fatigue/impact resistance, improved fracture toughness and/or crack arresting properties, reduced weight and/or cost, and reduced notch sensitivity. “Synergistic” effect of hybrid composites (defined as the difference between the performance of a fiber in a hybrid composite and in a single fiber composite) has attracted the interest of researchers worldwide. This chapter reviews recent structural applications of hybrid composites for various sectors such as aerospace, automobile, civil engineering, energy, marine, sport, and telecommunication. The development and applications of innovative hybrid FRP–concrete composite structural system for civil infrastructure (e.g., highway bridge decks, girders, columns, and piles) are emphasized.

Characterization of non-stationary properties of vehicle–bridge response for structural health monitoring

Quantifying the non-stationary properties of bridge under passing vehicle has been an important topic in structural health monitoring of bridge. There are many methods of time–frequency representation used for the study of dynamics of bridge under passing vehicle, including spectrogram, wavelet, Hilbert–Huang transform, and so on. This article uses adaptive optimal kernel time–frequency representation to quantify the non-stationary properties of the response of bridge under passing vehicle and illustrates and discusses its advantages over conventional time–frequency methods.

Software Agents to Support Structural Health Monitoring (SHM)-Informed Intelligent Transportation System (ITS) for Bridge Condition Assessment

In Structural Health Monitoring (SHM)-informed Intelligent Transportation Systems (ITS) system, SHM sensors can provide data on a bridge health condition for ITS applications. Where ITS uses this bridge health condition information for real-time trafc management and monitoring. Most of the SHM-informed ITS use wireless sensor network (WSN) to allow devices to coordinate and collaborate to effectively measure a structure, whether the goal is to improve spatial resolution, structural resilience, bridge traffic, or perform advanced in-situ analysis. The WSN suffers from high power consumption, yet they are generally equipped with a limited power supply and in most cases AAA batteries. Even under the most stringent power management, the sensor nodes have an unattended life of approximately a few months to a year. Towards this end, the paper proposes a multi-agent based system to augment the life time of WSN supporting SHM-informed ITS systems. The proposed agent based routing (ABR) approach consists of a mobile agent (MA) that is able to traverse the network, i.e., sensor nodes, mounted onto a bridge using multi-hop communication; collecting and aggregate the data, thus eliminating the two major causes of power consumption. These include (a) the direct transmission/broadcast from each sensor node to the sink and (b) redundant sensory data. In addition, ABR reduce much of the communication overhead and hence prolong the operational lifetime of SHM-informed ITS. Our experiment conducted on an open source simulator shows that the proposed ABR is 30% more energy efficient in comparison to the baseline, i.e., direct transmission (DT) to the sink.

Characterization of Nonstationary Mode Interaction of Bridge by Considering Deterioration of Bearing

As all bridges get deteriorated over time, structural health monitoring of these structures has become very important for the damage identification and maintenance work. Evaluating a bridge’s health condition requires the testing of a variety of physical quantities including bridge dynamic responses and the evaluation of the functions of varied bridge subsystems. In this study, both the acceleration of the deck and the dynamic rotational angle of the bearings in a long-span steel girder bridge were measured when the bridge system was excited by passing-by vehicles. The nonstationary dynamical phenomena including vibration mode interactions and coupling are observed in response spectrogram. To elaborate the phenomena, the linear vibration mode properties of the bridge are characterized by finite element analysis and are correlated with the specific modes in test. A theoretical model is presented showing the mechanism of the mode coupling and instability originated from the friction effects in bearing. This study offers some insights into the correlation between complex bridge vibrations and the bearing effects, which lays a foundation for the in situ health monitoring of bridge bearing by using dynamical testing.

Quantification of Dynamic Properties of Pile Using Ensemble Empirical Mode Decomposition

This paper investigated dynamical interactions between pile and frozen ground by using the ensemble empirical mode decomposition (EEMD) method. Unlike the conventional empirical mode decomposition (EMD) method, EEMD is found to be able to separate the mode patterns of pile response signals of different scales without causing mode mixing. The identified dynamic properties using the EEMD method are more accurate than those obtained from conventional methods. EEMD-based results can be used to reliably and accurately characterize pile-frozen soil interactions and help designing infrastructure foundations under permafrost condition.

Tensile Behavior of Pultruded Fiber-Reinforced Polymer Laminates with Bonded and Bolted Splice Joints

This paper presents an experimental investigation on double-lap joints of grit-blasted surface finish fiber-reinforced polymer (FRP) splice plates bonded and bolted to FRP laminates. Eighteen coupon joint specimens were tested under tensile loading with varying types of FRP splice plates and FRP laminates. Four types of bolts were evaluated: FRP bolts, high corrosion-resistant steel (HCRS) bolts, stainless steel (SS) bolts, and SS bolts wrapped with glass FRP (GFRP) (referred to as “SF” bolts). The test results indicated that double-lap splice joints, which incorporated HCRS bolts, epoxy adhesive, and grit-blasted surface finish FRP splice plates, provided strong bonds with FRP laminates. The grit-blasted surface finish of the FRP splice plates and the epoxy adhesive contributed to improving joint stiffness and strength. The specimens with FRP bolts showed brittle behavior and failed at relatively low ultimate load. The failures of those specimens were debonding of epoxy layers followed by shearing of the FRP bolts. The specimens with steel bolts (i.e., HCRS, SS, and SF bolts), however, exhibited ductile behavior and failed at a much higher ultimate load than did the FRP bolt specimens. Typical failure modes of the steel bolt specimens were fracturing of the FRP laminate (resulting from fiber rupture or kink, shear-out, and delamination failure of the GFRP plies and bearing failure of FRP materials near the edge of bolt holes in the load direction), bearing failure of the FRP splice plates, epoxy debonding, and yielding of bolts. Although FRP wraps may enhance the durability of the SS bolts, the use of SF bolts may significantly affect the failure mode of the splice joints.

Upgrading of ductility and shear capacity of reinforced concrete beams of highway bridge bents

Two techniques to upgrade the ductility and shear capacity of reinforced concrete beams of existing highway bridge bents were examined. An experimental program that consisted of 3 scaled models was conducted. The specimens were tested using statically reversed cyclic loading. The first specimen was a control specimen. The beams of the other 2 specimens were upgraded. External steel plates were bonded to the beam in the first upgrading technique and external steel rods were employed in the second upgrading technique. The characteristic behavior of each specimen was experimentally clarified in terms of hysteretic behavior, displacement response ratio, maximum displacement, damage propagation, energy dissipation, equivalent damping factor, and final failure mode. The study revealed that the 2 upgrading techniques could result in enhancement of the overall behavior of the bridge bents. Upgrading the beams utilizing external steel rods, however, was shown to be more effective in resisting future earthquakes. Analytical modeling of the highway frames utilizing FEM was performed. The numerical simulation resulted in a satisfactory accuracy of the predicted behavior. A calibrated baseline FE model was derived and could be employed to quantitatively identify the strengthening effect on resulting behavior of the bridge bents. The study provides an addition to the experimental data for ductility and shear capacity enhancement of bridge bents, and may assist selecting the most appropriate upgrading technique.