<p dir="ltr">This project looks into the strength capacity and behavior of GFRP rebars compared to steel rebars. Tested with different adhesives and embedded at multiple embedment depths, this research aims to look how those factors influence the overall performance of the rebars.</p>

Post-installed anchoring systems are used extensively in Massachusetts Department of Transportation (MassDOT) projects due their ease of attachment to existing structures. However, recommendations on materials from various manufacturers are currently lacking for certain situations such as long-term tension loading. The purpose of the investigation presented in this thesis was to provide guidance on the use of anchoring systems to MassDOT. This research project evaluated the behavior of adhesive and cementitious bonded anchoring systems per the Stress-versus-Time-to-Failure approach found in the provisional standard AASHTO TP-84 in order to provide recommendations pertaining to the test method. Supplemental short-term anchor pullout tests were conducted using the best performing materials as evaluated by AASHTO TP-84 to study the effects of certain in-service and installation parameters on bond strength. The parameters studied included installation direction and extreme in-service temperatures. Polymer characterization testing of adhesive products were also conducted in order to comment on technique usefulness for field quality assurance/quality control of field installed bonded anchor materials.

This work presents the development of a test program and the results from the final round of testing to better understand the effect a submerged anchor installation has on the pullout strength of epoxy anchors. Two different epoxies were tested at embedment depths of two, four, and six bar diameters. These tests utilized three distinct installation procedures under dry and submerged conditions. The testing program occurred over five phases, with the final round used in analysis consisting of 24 anchor pullout tests. These tests showed that the presence of water did not have an effect on the epoxy bond when anchor holes were cleaned dry and installed underwater, but it did have a significant impact on the ability to consistently clean each anchor when it was submerged.

This thesis describes an experimental study on the long-term creep behaviour of adhesive anchors under sustained tensile loads in combination with different environmental exposures. A comprehensive background and literature review is presented, focusing on various bond stress models for adhesive anchors, factors affecting their bond behavior, and an overview of available testing standards and evaluation criteria. The experimental program comprises of 82 test specimens. The specimens consist of a cylindrical shaped concrete block of 300 mm (12 inch) in diameter and 200mm (8 inch) in depth, with 15M (No. 5) deformed steel bar post-installed to an embedment depth of six times the bar diameter or 125mm (5 inch). Three types of adhesives were used for anchor installation: Type-A a fast setting two component methyl methacrylate adhesive, Type-B a fast setting two part epoxy adhesive, and Type-C a standard set two part epoxy adhesive. The study is divided into four phases. Phase I consists of 27 static pullout tests to determine the yield strength (fy) and the maximum tensile capacity of each anchor system under three exposure conditions. Phase II and Phase III consist of 36 specimens tested under sustained load levels of 40%fy (32kN) and 60%fy (48kN)under normal laboratory conditions (room temperature) and moisture exposure, respectively. Phase IV consists of 9 specimens tested under sustained load with a load level of 40%fy (32kN) with exposure to freeze/thaw cycling. All sustained load tests lasted for a period of at least 90 days. The results of the static pullout testing showed that specimens with epoxy based adhesive exhibited stronger bond strength, forcing the anchor to fail by rupture prior to bond failure. Under sustained load testing, specimens with standard set epoxy based adhesive showed insignificant creep displacement under room conditions, however, when exposed to moisture noticeable creep displacements were recorded. Specimens with both fast setting epoxy and methyl methacrylate based adhesives showed higher creep displacements under environmental exposure (moisture, freeze/thaw) versus those kept at room temperature. Displacement data from creep testing were analysed and projected over a service life span of 50 years for room temperature exposure, and for 10 years for moisture and freeze/thaw exposures. Based on the analysis results, the service life of different anchor systems was estimated. An integrated qualification and testing protocol is proposed for the creep behavior of adhesive anchors under various environmental exposures.

After the 1999 Kocaeli Earthquake, the use of chemically bonded post-installed anchors has seen a great growth for retrofits in Turkey. Currently, chemically bonded post-installed anchors are designed from related tables provided by adhesive manufacturers and a set of equations based on laboratory pullout tests on normal or high strength concretes. Unfortunately, concrete compressive strengths of existing buildings, which need retrofit for earthquake resistance, ranges within 5 to 16 MPa. The determination of tensile strength of chemically bonded anchors in low-strength concretes is an obvious prerequisite for the design and reliability of retrofit projects. Since chemically bonded anchors result in the failure of concrete, adhesive-concrete interface or anchored material, the ultimate resistance of anchor can be predicted through the sum of the contributions of concrete strength, properties of anchored material (which is steel for this work), and anchorage depth. In this work, all three factors and the predictions of current tables and equations related to anchorages are examined throughout site tests.

This thesis describes part of the work associated with Project 0-6719 sponsored by the Texas Department of Transportation (TxDOT). The primary objective of the project is to examine the feasibility of strengthening older continuous multi-span steel girder bridges through the use of post-installed shear connectors. Bridges potentially eligible for retrofit have noncomposite floor systems, where the concrete slab is not attached to the steel girders with shear connectors. Many of these bridges were designed in the 1950's and 1960's for loads smaller than the standard design loads used today. A secondary objective of the project, and the main focus of this thesis, is to examine the design of post-installed shear connectors for fatigue. Of particular interest in this study is the adhesive anchor, given its convenient installation procedure but relatively poor fatigue performance in previous tests. The objectives of this thesis were to quantify the fatigue strength of the adhesive anchor, as well as quantify the shear force and slip demands on adhesive anchors in realistic bridge conditions. In regards to the first objective, twenty-six direct shear fatigue tests were performed on adhesive anchors. Each test was conducted on a single adhesive anchor in order to capture its individual cyclic load-slip behavior. Results indicate that adhesive anchors have considerably higher fatigue strength than conventional welded shear studs, making partial composite design feasible in the strengthening of older steel bridges. In regards to the second objective, analytical and computational studies were conducted on composite beams with adhesive anchors. Results show that the shear force and slip demands are typically smaller than the endurance limits determined from direct-shear testing. This suggests that fatigue failure of adhesive anchors under service loads may not be a primary concern. Based on the results, preliminary recommendations for the design of adhesive anchors for fatigue are provided. / text

This thesis describes an experimental study on the long-term creep behaviour of adhesive anchors under sustained tensile loads in combination with different environmental exposures. A comprehensive background and literature review is presented, focusing on various bond stress models for adhesive anchors, factors affecting their bond behavior, and an overview of available testing standards and evaluation criteria. The experimental program comprises of 82 test specimens. The specimens consist of a cylindrical shaped concrete block of 300 mm (12 inch) in diameter and 200mm (8 inch) in depth, with 15M (No. 5) deformed steel bar post-installed to an embedment depth of six times the bar diameter or 125mm (5 inch). Three types of adhesives were used for anchor installation: Type-A a fast setting two component methyl methacrylate adhesive, Type-B a fast setting two part epoxy adhesive, and Type-C a standard set two part epoxy adhesive. The study is divided into four phases. Phase I consists of 27 static pullout tests to determine the yield strength (fy) and the maximum tensile capacity of each anchor system under three exposure conditions. Phase II and Phase III consist of 36 specimens tested under sustained load levels of 40%fy (32kN) and 60%fy (48kN)under normal laboratory conditions (room temperature) and moisture exposure, respectively. Phase IV consists of 9 specimens tested under sustained load with a load level of 40%fy (32kN) with exposure to freeze/thaw cycling. All sustained load tests lasted for a period of at least 90 days. The results of the static pullout testing showed that specimens with epoxy based adhesive exhibited stronger bond strength, forcing the anchor to fail by rupture prior to bond failure. Under sustained load testing, specimens with standard set epoxy based adhesive showed insignificant creep displacement under room conditions, however, when exposed to moisture noticeable creep displacements were recorded. Specimens with both fast setting epoxy and methyl methacrylate based adhesives showed higher creep displacements under environmental exposure (moisture, freeze/thaw) versus those kept at room temperature. Displacement data from creep testing were analysed and projected over a service life span of 50 years for room temperature exposure, and for 10 years for moisture and freeze/thaw exposures. Based on the analysis results, the service life of different anchor systems was estimated. An integrated qualification and testing protocol is proposed for the creep behavior of adhesive anchors under various environmental exposures.

<p>  </p> <p>Glass Fiber Reinforced Polymer (GFRP) rebars are frequently used to construct offshore structures, bridges, and airport terminals due to their high tensile strength, lightweight, and non-corrosive nature. GFRP rebars are also non-magnetic, electrically non-conductive, and have a higher strength-to-weight ratio than steel rebars. Consequently, many studies have been conducted to investigate the bond behavior of cast-in GFRP rebars, leading to the formulation of ACI 440. </p> <p>Post-installed rebar technology has become increasingly popular due to its flexibility in retrofitting and extending existing structures. Given the growing demand for post-installed technology and the superior qualities of GFRP rebars, there is a keen interest in understanding the behavior of post-installed GFRP rebars. Post-installed connections involve inserting a rebar in a pre-drilled hole in hardened concrete using an injectable epoxy. The post-installed system allows for construction between existing and new concrete for structural extension and rehabilitation purposes.</p> <p>Currently, only limited work has been performed on post-installed GFRP rebars at relatively small embedment depths. The adhesive mortars used for post-installation generally have a high bond strength. Most of the connections with post-installed rebars are made close to the edges of the members. Due to edge proximity, concrete-related failure modes (concrete splitting) govern, and the high bond strength of the post-installed system is not utilized. </p> <p>This study aims to understand the bond-splitting behavior of GFRP rebars post-installed using epoxy-based adhesive (DeWalt Pure200+). Experimental and Numerical investigations were conducted with various parameters that influence the bond-splitting. These parameters include but are not limited to, concrete cover, embedment depth, concrete strength, rebar diameter, and transverse confinement. </p> <p>An optimal experimental program was designed to test the minimum concrete cover, relative concrete cover, rebar diameter, rebar surface characteristics, and rebar embedment depth. The experimental investigation was carried out in two phases to determine the local bond strength by conducting confined pullout tests away from the edges at shallow embedment depths and the bond-splitting tests at varying parameters. Due to its low transverse strength, a unique grip using a steel pipe grouted with epoxy grout was used for the pullout tests. A new test specimen and test setup were designed to execute the experimental program at deeper embedment depths successfully.</p> <p>Numerical simulations were then performed using the macroscopic space analysis (MASA) program to investigate additional parameters and cases. The numerical models were first validated using results obtained from experimental investigation. Solid tetrahedral elements were used for modeling concrete elements with microplane models to simulate the damage in concrete. GFRP rebars were modeled using solid hexahedral elements with linear elastic material properties. The connection between concrete-to-GFRP rebar was modeled using 2-node bar elements embedded in the contact layer. The bond-slip curve gives the characteristic properties of the bar elements.</p> <p>The influence of individual parameters on the bond strength of the post-installed GFRP rebars was calculated, and comparisons were made with existing bond-splitting models for post-installed steel rebars. This thesis presents the details of the experimental program, the test specimen, the test setup, numerical modeling, and the results obtained on the GFRP bars post-installed with different sets of parameters. The studies prove the feasibility of using GFRP bars as post-installed for structural extensions/retrofitting and highlight certain aspects that must be considered while designing such connections.</p>

Post-installed anchors for civil construction are elements that ensure the integrity of building structures even under the most severe static, seismic and shock loadings. Despite the high popularity of this technology in construction sites all over the world, the current state of knowledge is limited and there is still a great potential for significant improvements. Specifically, expansion anchors’ mechanism relies purely on friction, therefore being able to manipulate and optimize their tribological behavior is key to meet strict safety regulations and develop outperforming and outlasting design solutions. This research project, conducted at Hilti Corporation in Schaan (Liechtenstein), presents an investigation of several antifriction coating solutions. Laboratory-scale tests have been performed to quantify the different coefficient of friction while, with full-scale standardized tests (anchor set in concrete), it has been possible to evaluate the overall mechanical performances of the specimens. Afterwards, the obtained data have been analyzed with numerical software and the samples have been further investigated with optical microscopy. The outcome of this thesis work is crucial for the development of the next generation of expansion fasteners and gives additional insights for a deeper understanding in the tribology of functional coatings. / Eftermonterade fästankare i byggnader säkerställer byggnadsstrukturernas integritet, även under de mest allvarliga statiska, seismiska och chockbelastningar. Trots stor användning och popularitet  på byggarbetsplatser över hela världen är det nuvarande kunskapsläget av denna teknik begränsat och det finns en stor potential för betydande förbättringar. Specifikt bygger expansionsankringsmekanismen på ren friktion. Därför är möjligheten att manipulera och optimera fästankarnas tribologiska beteende nyckeln till att uppfylla strikta säkerhetsbestämmelser och kunna utveckla bättre prestanda och designlösningar. Detta forskningsprojekt har utförts på Hilti Corporation i Schaan (Liechtenstein) och presenterar en undersökning av flera antifriktionsbeläggningslösningar. Laboratorieprov har utförts för att kvantifiera olika friktionskoefficienter, och efter fullskaliga standardiserade tester (med fästankare i betong) har det varit möjligt att utvärdera de övergripande mekaniska prestationerna av dessa. Erhållna data har analyserats numerisk och proverna har undersökts ytterligare med optisk mikroskopi. Resultatet av detta examensarbete är viktigt för utvecklingen av nästa generation expansionsfästen och ger även ytterligare insikt och en djupare förståelse av tribologin av funktionella beläggningar.

The increased amount of traffic combined with higher traffic loads leads to many existing bridges needing strengthening in the future to ensure their expected lifespan. This means the bridge owners will be focusing more on strengthening projects and smart solutions will be crucial for preserving a healthy bridge stock. When strengthening existing non-composite bridges (with steel girder and concrete deck) one potential method is to achieve composite action by installing shear connectors. The post-installed shear connectors prevent slip between the steel girders and the concrete. The composite action will reduce bending stresses and deflection of the bridge, due to the increase in moment of inertia and relocation of the neutral axis. Different types of shear connectors can be used for achieving composite action and each type of connector has its own installation method. The biggest distinction between the methods is how the connectors gain access to the steel girder for installation and what technique is used when installing them. This thesis presents the theory behind composite action, the current methods used for achieving composite action on existing bridges and to what extent a bridge can be strengthened by composite action. The thesis also provides a status of the existing road bridge stock around the world. The four case studies examined in this thesis have used different post-installed shear connectors to manage different strengthening problems like weight restriction, fatigue life of shear connectors and a unique problem on the Pitsund Bridge where loud bangs appeared from the bridge when truck passed in the morning. For the case study on the Pitsund Bridge an interview was conducted that explains the entire procedure of the project, from the noise problem to how the installation of coiled spring pins was performed. The bridge over Lule River at Akkatsfallen consists of two steel girders and a concrete deck. This bridge is chosen as a real case study to determine to what extent a bridge can increase its capacity by achieving composite action. The calculations are performed in accordance with the Eurocodes on both non- and full-composite action and the result is compared to the other case studies.