The current market of utility poles is growing rapidly. The dominant materials that are used for this purpose are generally wood, steel, concrete, and fiber-reinforced polymers (FRP). FRP poles are gaining wide acceptance for what they provide in terms of strength and durability, lack of maintenance and a high strength to weight ratio. Hybrid structures can combine the best properties of the materials used, where each part enhances the structure to provide a balanced structure. This study evaluates a hybrid structure composed of three main layers, an outer FRP shell, a hollow concrete core and an inner hollow steel tube, this whole system is to be utilized as a tapered utility pole. The outer FRP shell provides protection and enhances the strength of the pole, the concrete core provides stiffness, and the inner steel tube enhances the flexural performance while reducing the volume in consequence the weight of the structure compared to a fully filled pole. A new design for a 12-feet long hybrid FRP pole using finite element is presented in this paper. The design was based on a parametric study evaluating the effect of key-design parameters (i.e., the thickness of FRP, the volume and strength of the concrete, the thickness and diameter of the steel tube). Concrete strength affected the general performance of the pole, the decrease in concrete strength due to utilizing lightweight concrete was compensated with increasing the FRP pole thickness. For the same pole configuration, with incremental variation of the FRP thickness values from 3 mm to 7 mm up to the initial concrete cracking load, no significant variation of the pole top deflection was observed. However, at failure load the increase of FRP thickness from 3 mm to 7 mm decreased the ultimate tip deflection by 50%. New hybrid utility poles have the potential to be an interesting alternative solution to the conventional poles as they can provide better durability and mechanical performances.

Due to a dynamic development of infrastructure, engineers around the world are looking for new materials and structural solutions, which could be more durable, cheaper in the life cycle management, and built quickly. One of prospective solutions for building small-span bridges can be precast lightweight concrete reinforced with glass fiber-reinforced polymer (GFRP) rebars. Thanks to prefabrication, it is possible to shorten the construction time. Using lightweight concrete affects structure weight as well as transportation costs. GFRP rebars can make the structure more durable and also cheaper in terms of life cycle management costs. The paper focuses on the fatigue performance of a real-scale arch (10.0 m (33 ft) long, 1.0 m (3.3 ft) wide, and 2.4 m (7.9 ft) high) made of lightweight concrete and GFRP rebars (LWC/GFRP) in comparison with an arch made of normal weight concrete and typical steel reinforcement (NWC/steel). The fatigue loads ranging from 12 to 120 kN (2.7 to 27 kip) were applied in a sinusoidal variable manner with a frequency of 1.5 Hz. This research revealed that the NWC/steel arch exhibited significantly better fatigue resistance when compared to the LWC/GFRP arch. Differences in the behavior of the NWC/steel and LWC/GFRP models under fatigue load were visible from the beginning of the research. The LWC/GFRP model was exposed to fatigue loads, resulting in gradual deterioration at an early stage. This degradation was evident through stiffness being progressively reduced, leading to increased displacements and strains as the number of load cycles increased. The model did not withstand the fatigue load and was destroyed after approximately 390 thousand load cycles, in contrast to the NWC/steel model, which withstood all 2 million load cycles without significant damages or the stiffness being decreased. However, the prefabricated lightweight concrete arches with composite reinforcement seem to be an interesting alternative of load-bearing elements in infrastructure construction.

Fiber-reinforced polymer (FRP) bars can serve as an appropriate substitute for steel rebar due to their lightweight, high strength, and good corrosion resistance. Nevertheless, the long-term success of FRP bars as promising reinforcement in concrete depends on understanding the bond between FRP bars and concrete. ACI 440.1R-15 recommends utilizing CSA S806-12 Annex S ‘‘Test Method for Determining the Bond-Dependent Coefficient of FRP Rods” for estimating the design value of the bond-dependent coefficient (kb). However, this testing method requires a four-point loaded 3.0-meter-long beam with continuous assessment of developed crack width. Due to the complexity of the test, studies were scarce in assessing the factors affecting the kb. Therefore, this study aimed to relate the experimental kb obtained from large-scale testing to a relatively simpler bond strength value, τu , obtained from smaller-scale FRP pull-out test. The relation was established utilizing data collection for both tests from experimental studies. Three machine learning techniques (Ensembled Trees Artificial Neural Network and Gaussian Process Machines) were then applied to mimic and understand the complex bond-behaviour at varying FRP and concrete properties. The results have shown promising relation (R2>0.8) between kb and τu for different surface textures and fibre types.

Fiber reinforced polymer (FRP) composite rebar is a non-metallic concrete reinforcement alternative that has been successfully deployed in hundreds of structural applications globally. The increasing demand for FRP rebar as a metal alternative is driven by its unique value proposition, including lightweight, high strength, magnetic transparency, and most significantly, corrosion resistance. FRP rebar is fabricated through pultrusion, a high throughput composite fabrication process in which, resin-impregnated fiber undergoes rapid cure when pulled through a heated furnace. Considering the open nature of the open pultrusion process, expansion of production capacity for FRP rebar manufacturing demands the use of advanced resins that are free from Volatile Organic Compounds (VOCs), enable high throughput production, and deliver an outstanding translation of fiber properties following cure. In this work, we will present an epoxy system that is inherently VOC Free and is tailored to enable high throughput manufacturing of glass fiber reinforced polymer (GFRP) rebar at scale. Furthermore, the rapid formation of highly crosslinked structures achieved with this resin system during pultrusion is found to enable outstanding fiber property translation resulting in high modulus (>70 GPa) and corrosion resistance (>80 % tensile strength retention without load) that exceeds existing standards such as ASTM D7957.

With the aging and deterioration of infrastructure, the need for repair, strengthening, and rehabilitation of existing structures continues to increase. Climate change makes extending the service life of our infrastructure critical since any demolition and new construction will trigger substantial amounts of carbon emissions. Research related to repairing and strengthening existing infrastructure is seeing major developments as new green materials and technologies become available. Improved assessment and retrofit of deficient structures, and performance-based design of new structures are also in high demand. Despite the progress, there are many challenges yet to be addressed. The main objective of this Special Publication is to present results from recent research studies (experimental/numerical/analytical) on the retrofit and repair of structural elements along with the assessment, analysis, and design of structures. Several of these papers were presented at the ACI Fall Convention “Seismic Repair/Retrofit/Strengthening of Bridges at the Element or System Level: Parts 1 and 2.” The presented studies cover various aspects of structural retrofitting and strengthening techniques including the use of rubberized engineered cementitious composite for enhancing the properties of lightweight concrete elements, high-performance concrete jacketing to strengthen reinforced concrete piers/columns, and the behavior of fiber-reinforced-polymer-wrapped concrete cylinders under different environmental conditions. Additionally, the research explores the behavior of concrete-filled FRP tubes under axial compression, innovative bridge retrofit technologies, and retrofit techniques for deficient reinforced concrete columns. There is also a focus on evaluating the seismic response of retrofitted structures, designing guidelines for seismic retrofitting using tension-hardening fiber-reinforced concrete, strengthening unreinforced masonry walls with ferrocement overlays, and developing seismically resilient concrete piers reinforced with titanium alloy bars. The seismic response of a retrofitted curved bridge was also presented where elastomeric bearings of the as-built bridge were replaced by high damping rubber bearings as a part of the seismic retrofit. Recommendations for nonlinear finite element analysis of reinforced concrete columns under seismic loading are also presented to simulate their behavior up to collapse. Overall, the presented studies in this Special Publication demonstrate the potential of new materials, methods, and technologies to improve the performance of various structural elements under different loading conditions, including seismic and environmental loads. These studies are expected to help our practitioners and researchers not only develop more effective and sustainable methods for repairing and strengthening of structures but also improve their analysis and design skills.