Tension-hardening fiber-reinforced concrete (THFRC) is characterized by ductile response in tension and a significant tensile strength that can be sustained to large levels of tensile strain. The strain ductility imparted by the dense network of fibers presents an opportunity in seismic design and retrofit, whereas the significant durability enabled by the low porosity of the cementitious matrix makes this class of materials ideal for bridge retrofits since they can mitigate many of the limitations of the existing approaches. However, no design provisions exist regarding the application of THFRC in seismic design and retrofit. A summary of a pertinent framework of design guidelines is presented, which are needed for determination of both seismic demands and criteria for performance-based design of THFRC based retrofits. To this end, stress-strain relationships are formulated considering the confinement effect imparted by the fiber reinforcement. Strain limits are established by reference to test data from various studies of THFRC.

This research investigates the High Performance Concrete (HPC) jacketing method to strengthen reinforced circular concrete piers/columns. Four different types of HPC jackets such as Self-Consolidating Concrete (SCC), Engineered Cementitious Composites (ECC) and two types of Ultra-High Performance Concrete (UHPC) with three jacket thicknesses of 25 mm, 38 mm and 51 mm, with same reinforcement configuration were used to strengthen reinforced SCC core piers and analyze behavior. Thirteen pier specimens were tested to failure under concentric axial load applied through the SCC core. Test results indicated performance enhancement of piers strengthened with UHPC and ECC jackets, which not only prevented brittle failure but also improved the ductility and energy absorbing capacity by achieving a superior ultimate axial load capacity increase by more than 90% with a jacket thickness of 33% of the core diameter. Existing Code and analytical equations with reduction factors can be used for predicting axial load capacity of the strengthened piers/columns but choice of equations should be based on types of jacket concrete to ensure safe design.

Recently, a new generation of concrete sandwich panels (CSPs) comprising ultra-high performance concrete (UHPC) wythes and glass fiber reinforced polymer (GFRP) as reinforcement and shear connectors was developed and evaluated experimentally. In this study, a non-linear finite element model is presented to study the detailed behavior of these panels under bending. The model included detailed features such as a constitutive material law that considers the post-crack stiffening of UHPC, failure of GFRP material, wythe-to-insulation contact and slipping, and stability failure. Compared with eight previously tested panels, the model predictions of ultimate load, general load-deflection behavior, and failure modes matched those from experiments. The composite degree of each panel, a key design parameter frequently used in characterizing the structural and thermal efficiencies of CSPs, was determined from the ultimate load of the tested panel and that of two additional numerically-based non and fully composite ones and ranged between 3 to 34%. The structural performance of the GFRP connector was deemed satisfactory for the range of composite degrees proposed for the panels. The validated model will be deployed in a large parametric analysis studying different material and geometric variables and assisting in developing a design tool to estimate the strength and composite degree of UHPC CSPs with GFRP reinforcement.

This paper investigates the use of glass fiber reinforced polymer (GFRP) bars to reinforce the jointed precast bridge deck slabs built integrally with steel I-girders. In addition to a cast-in-place slab, three full-size, GFRPreinforced, precast concrete slabs were erected to perform static and fatigue tests under a truck wheel load. Each slab had 200 mm (7.9 in) thickness, 2500 mm (98.4 in) width normal to traffic, and 3500 mm (137.8 in) length in the direction of traffic and was supported over a braced twin-steel girder system. The closure strip between connected precast slabs has a width of 125 mm (4.9 in) with a vertical shear key, filled with ultra-high-performance concrete (UHPC). Sand-coated GFRP bars in the precast slab project into the closure strip with a headed end to provide a 100 mm (3.9 in) embedment length. A static test and two fatigue tests were performed, namely: (i) accelerated variable amplitude cyclic loading and (ii) constant amplitude cyclic loading, followed by static loading to collapse. Test results demonstrated excellent fatigue performance of the developed closure strip details, with the ultimate load-carrying capacity of the slab far greater than the demand. While the failure in the cast-in-place slab was purely punching shear, the failure mode in the jointed precast slabs was punching shear failure with incomplete cone-shape peroration through the UHPC closure strip, combined with a major transverse flexural crack in the UHPC strip. This may be attributed to the fact that the UHPC joint diverted the load distribution pattern towards a flexural mode in the UHPC strip itself close to failure.

Fiber-reinforced polymer (FRP) reinforcements for concrete structures and civil engineering applications have become one of the innovative and fast-growing technologies to stop the rapid degradation of conventional steel-reinforced concrete infrastructure. FRP reinforcements for construction can be divided into three main types: 1. External sheets or plates to rehabilitate and repair existing concrete and masonry structures, and in some cases steel and wood structures; 2. Internal FRP bars or tendons for new and existing reinforced concrete structures, and 3. FRP stay-in-place forms to be filled with unreinforced or reinforced concrete. A considerable and valuable development and application’s work has been accomplished during the last three decades, leading to the development of numerous design guidelines and codes around the world, making the FRP-reinforcement technology one of the fast-growing markets in the construction industry. During the ACI Concrete Convention, Fall 2021, four full sessions were sponsored and organized by ACI Committee 440. Session S1 was focused on the bond and durability of internal FRP bars; Session S2 on codes, design examples, and applications of FRP internal reinforcements; Session S3 on external FRP reinforcements; and Session S4 on new systems and applications of FRP reinforcements, such as CFFT post-tensioned beams, GFRP-reinforced concrete sandwich panels, FRP-reinforced masonry walls, CFFT under impact lateral loading, near-surface mounted FRP-bars, and GFRP-reinforced-UHPC bridge deck joints.