As our infrastructure ages and deteriorates, the demand for repairing, strengthening, and rehabilitating existing structures continues to grow. This need is further amplified by our efforts to combat climate change, as extending the lifespan of our infrastructure is now more critical than ever. Demolishing and constructing new structures results in a significant amount of carbon emissions. Consequently, there is a growing focus on research and innovation in the field of repairing and strengthening infrastructure, particularly with the emergence of new environmentally friendly materials and technologies. This evolution in infrastructure management necessitates enhanced approaches for assessing the condition of deficient structures and the performance-based design of new structures, as well as the retrofitting of existing deficient structures. While substantial progress has been made in this domain, numerous challenges remain to be addressed. The primary objective of this special session is to showcase the outcomes of recent research studies encompassing experimental, numerical, and analytical investigations related to retrofitting and repairing structural elements.
Seismic Retrofitting of Reinforced Concrete Beam-Column Joints with Extremely High Eccentricity
Presented By: Bora Gencturk
Affiliation: University of Southern California
Description: Beam-column joints are critical components of the lateral force resisting system in buildings. In properly designed connections, plastic hinging is expected to develop at the beam ends while the columns and the joint region are capacity protected. It is not uncommon to see beam-column joints in exterior frames of buildings where the beam longitudinal axis is eccentric from the transverse axis of the column mid-plane. Previous studies have investigated similar eccentric joints; however, there is very little understanding of the behavior of such connections with extremely high eccentricity where the beam section only partially intersects with the column axis. In this study, four such large-scale connections were tested under simulated seismic loading. One of the specimens was retrofitted with carbon fiber-reinforced polymer (CFRP) composites. The results indicated that joints had sufficient ductility and considerable energy dissipation capacity. The FRP strengthening did not change the failure mode or strength of the connection; however, the energy dissipation capacity was improved. In this presentation, the details of the highly eccentric joints, the experimental program, and the results of the tests will be presented.
Seismic Retrofitting of Reinforced Concrete T-Beams Using Anchored FRP Composites
Presented By: Bora Gencturk
Affiliation: University of Southern California
Description: In this presentation, seismic strengthening of T-shaped reinforced concrete (RC) beams using fiber reinforced polymers (FRP) will be discussed. T-shaped beams are widely used in RC structures. For reasons including increased demands due to change in usage, deterioration, or retrofitting to improve seismic performance, T-beams may need to be strengthened. In this study, six large-scale RC T-beams are strengthened in shear using splay anchored strips of carbon FRP (CFRP) and subjected to simulated earthquake loading. The beams were tested in two groups of concrete strengths. The reference beams failed brittlely due to shear cracking while the FRP strengthened beams failed due to shear cracking followed by FRP delamination. The shear capacity of the beams were increased by up to 40% with the FRP strengthening. In this presentation, the details of the FRP strengthening approach and results from the large-scale testing will be presented along with conclusions of the effectiveness of the retrofitting approach.
Moment Strengthening of Concrete Shear Walls using Carbon Fiber Reinforced Polymers in Seismic Applications
Presented By: Wassim Ghannoum
Affiliation: University of Texas at San Antonio
Description: An experimental study was conducted to investigate the potential for increasing the moment capacity of existing concrete shear walls using anchored Carbon Fiber Reinforced Polymer (CFRP) laminates in seismic applications. The utilization of CFRP composites for moment strengthening of walls in seismic applications presents a unique challenge due to the inherent lack of ductility in FRP materials. The main objective of the study is to explore CFRP layouts that balance moment strength gains and preserve member ductility capacities.
Six reinforced concrete walls with relatively low steel reinforcement ratios and concrete strength, representative of older non seismic construction practices, were retrofitted using CFRP aligned with the longitudinal wall axes. The walls were 6 in. thick and 12 feet high by 6 feet wide. The walls were reinforced with a single matt of reinforcing bars.
Various layouts of CFRP laminates and CFRP anchors were applied to only one wall face. Single-face CFRP layouts were considered as they are more challenging to implement, while considering that both sides of a wall are often not accessible for retrofit in practice due to occupancy and architectural limitations. Test results are presented with emphasis on the effects of amount of CFRP laminates and location of CFRP anchors on behavior.
Retrofitting of Precast Concrete Floors
Presented By: Frank Bueker
Affiliation: The University of Auckland
Description: Precast concrete hollow-core floors have been found susceptible to sudden loss of gravity load-carrying capacity in past earthquakes and seismic testing. The risk of floor collapse in building structures has led to considerable research-industry collaborations in New Zealand towards the development and testing of retrofits.
After a summary of the seismic vulnerabilities of hollow-core floors, this presentation focuses on the key considerations for the development of floor retrofit guidance based on lessons learned from large-scale test-ing. Main discussion points include the alignment of retrofit design procedures with existing assessment ap-proaches, as well as the formulation of strength and deformation compatibility requirements. Construction and performance challenges identified during the design and testing of two full-scale frame specimens with retrofitted hollow-core floors will be shared. Furthermore, various retrofit options will be showcased, includ-ing a novel comprehensive retrofit solution that can also serve as a gravity load repair option for hollow-core floors.
Attendees will gain valuable insights into the latest advances in precast floor retrofit development and the practical implications of implementing these solutions to strengthen the seismic performance of building structures.
Experimental Study on Strengthening a Brick Wall with Openings Using Steel Frames
Presented By: Tsung-chih Chiou
Affiliation:
Description: Many historic buildings are of masonry construction. Existing masonry walls may be required an opening when the building usage is changed. A police station, for example, was turned into a museum. To provide constant tempera-ture and humidity for treasures, the brick walls were required openings for air conditioning pipelines.
In order to protect the corners of the opening wall from cracking due to stress concentration, a retrofitted scheme using two steel frames with L-shaped sections was proposed. The two steel frames were installed along the edges of the openings. High-strength bolts were anchored through the steel plates and brick walls.
The study conducted cyclic loading tests in the laboratory of National Center for Research on Earthquake Engi-neering to verify the strengthening effects. Two specimens were fabricated in the experiment, namely brick-filled RC frame with openings, and brick-filled RC frame with openings strengthened by steel frames. Experimental stud-ies indicate that the proposed retrofitting scheme can perform very good seismic behavior, even better than that of brick walls without openings.
A simulation model for brick wall with openings is proposed and verified by the experimental results.
Cyclic Response of RC Beams Strengthened and Anchored Using CFRP with and without Steel Fuse
Presented By: Hayder Rasheed
Affiliation: Kansas State University
Description: CFRP strengthening with fiber anchors has been recently proven to be an effective technique for seismic upgrades. However, the use of multiple layers of thick CFRP sheet may pose limitations in strengthening due to the limited ductility and energy dissipation characteristics of this solution. A recent patent suggests the use of a small steel plate as a ductility fuse by sandwiching it in between two layers of FRP at the critical plastic hinge region. This study applies the proposed technique in cyclic testing of RC beams to allow for more ductile seismic response. This work was compared with an identical control strengthened beam without the steel fuse to highlight the benefit of this solution. Comparisons are performed experimentally for low and high concrete strength with low and moderate steel ratios. The results are comparatively discussed.
Seismic Retrofitting of Reinforced Concrete Bridge Elements with Sliding Isolation
Presented By: Ronald Watson
Affiliation: R J Watson Inc
Description: Developed in the 1990’s sliding Isolation bearings (SIB) with a polyurethane recentering mechanism have been used on hundreds of structures around the world. This design is based on a convential multi-directional sliding disk bearing that is outfitted with orthogonal polyurethane springs. Energy dissipation is provided by the sliding surface which during dynamic testing offers beneficial damping. With this design the spring stiffness for service loads can be adjusted by changing the quantity and shape factor. In addition, the damping levels can be modified by the use of different sliding materials. The result is a fine-tuned design for the level of seismicity and type of structure. This paper will focus on the development of SIB and how they are being used to seismically protect reinforced concrete bridge elements. Several case histories will be presented along with shake table and full scale bearing testing results.
Lateral Cyclic Response Repaired Hybrid RC Bridge Piers
Presented By: Sherif Osman
Affiliation: University of British Columbia
Description: This study examines the lateral cyclic response of a repaired damaged bridge pier originally reinforced with Fiber-Reinforced Polymer (FRP) bars, particularly Glass FRP (GFRP), as a corrosion-resistant and durable alternative to traditional steel. As-built large-scale hybrid (GFRP-steel) reinforced concrete (RC) column was built where the outer cage is reinforced with GFRP bars and the inner cage with steel rebars. The column was tested under cyclic lateral loads exhibiting adequate ductility and energy dissipation capacity when compared to a conventional single layered steel RC column. Both as-built tested columns were then repaired with GFRP mesh reinforcements and tested under cyclic lateral loads comparing the effectiveness of single-layer and hybrid reinforcement designs. Enhanced structural integrity and energy dissipation underscore the success of innovative repair techniques in seismic engineering, offering a blueprint for resilient infrastructure in earthquake-prone areas, crucial for advancing bridge design and repair strategies.