Master of Science / Department of Architectural Engineering / Don Phillippi / Concrete anchors represent an important transition for both the design and construction of a project. Anchors are produced in two main categories: cast-in-place and post-installed. For designers, anchors are used to attach steel members to supporting concrete members. The anchors are designed using the provisions outlined in Building Code Requirements for Structural Concrete, ACI 318-11, Appendix D. These anchors are used to transmit tension and shear forces by using an individual anchor or a multiple anchor group. For contractors, anchor installation marks the transition between concrete and steel construction. Various types of anchors are produced by manufacturers, requiring contractors to be familiar with many installation methods. Careful planning and coordination is necessary to layout and place anchors into their correct location. Once anchors are installed, they must be protected from damage resulting from moving machinery and material. The purpose of this report is to introduce the basics to design concrete anchors by outlining the provisions in ACI 318-11 Appendix D and demonstrating these provisions with design examples. Anchor types, applications and common construction issues important to the structural engineer are also discussed.

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Shallow embedded column connections are widely used for columns resisting gravity loads in current design methods. These connections are usually considered “pinned” for structural analysis. In reality these connections fall in between a fixed and a pinned condition. Although methods exist to estimate the stiffness and strength of exposed columns or embedded columns under lateral loads, little research has been done to determine the strength of shallow embedded columns. An experimental study was carried out to investigate the strength of these connections. A total of 12 specimens with varying orientation, embedment depth, and column size were loaded laterally until failure or significant loss in strength. The results showed that shallow embedded connections are 86%-144% stronger in yielding and 32%-64% stronger in ultimate strength than current design methods would predict. This strength comes from a combination of the embedment depth and the resistance from the base plate and anchor rods. A model is proposed to explain the strength of the specimens and to conservatively estimate the strength of specimens with different variables. The specimens also exhibited stiffness ranging from 50%-75% of what would be expected from fully embedded columns.

Ancillary structures are highway support structures such as traffic signals, sign structures, luminaires, and high-mast light towers which are typically fastened to a concrete foundation using embedded anchor rods and anchor nuts. The inventory of ancillary structures across the United States is huge, and these structures vary dramatically in type, age, size, and material. There have been reported cases of anchor nut loosening on ancillary structures in the past few decades, but the cause of loosening is still unknown. Ancillary structures are susceptible to vibrations due to different wind loadings like natural gusts, vortex shedding, galloping, and truck-induced gusts. Wind-induced vibrations are believed to be one of the potential causes of anchor nut loosening. Previous research also suggests that vibrations can lead to loosening of nuts in structural and mechanical connections. There is concern regarding the current tightening procedures specified in the various federal and state specifications. Improper tightening can potentially lead to anchor nut loosening under the effect of wind-induced vibrations. In ancillary structures, the anchor rods and nuts are first snug-tightened using a wrench before fully pretensioning them as per the current specifications. The snug-tight condition is vaguely defined at present and needs revisions to avoid any under-tightening or over-tightening. Galvanization and overtapping of the anchor nuts also pose a potential concern. Anchor nuts are tapped oversize after galvanization to ensure the nuts fit well on the galvanized rod. American Society for Testing and Materials (ASTM) standards provide specific allowable tolerances on the thread parameters of the anchor rod and nut after galvanization and overtapping. Any deviation from the allowable tolerances can lead to gaps between the mating threads, which can contribute to the loosening of nuts under vibrations. This study focuses on investigating the following potential causes of loosening: improper tightening, wind-induced vibrations, snug-tight condition, and thread fabrication tolerance. Current tightening procedures for double-nut and single-nut connections on ancillary structures were verified using a tightening study as part of the investigation. New revisions to the specified nut rotation values for double-nut connections and a draft for proposed new specifications on single-nut connections has been provided as a result of discrepancies and inconsistencies in the current specifications. Vibration testing of a full-scale traffic signal was conducted on the basis of results from a four-month field monitoring program in order to investigate the effects of wind-induced vibrations on anchor nut loosening. It was concluded from testing that improper tightening (pretension < 5ksi) can lead to loosening of anchor nuts under wind-induced vibrations. A small-scale testing was also conducted to verify the results from the large-scale vibration testing. Snug-tight pretension in grade 55, 1-inch and 2-inch anchor rods was found to be highly variable due to different wrench lengths and personnel strength. Thread parameters of galvanized anchor rods and nuts procured from 3 different regional suppliers were found to be within specified tolerances. Various recommendations were then made as a result of the above tightening, vibration, and thread tolerance studies in an effort to reduce the cases related to anchor nut loosening in the future. / Doctor of Philosophy / Ancillary structures like traffic signals, sign structures, and light poles are typically connected to the ground using anchor rods and anchor nuts. There is a very large number of ancillary structures throughout the United States and vary in type, age, size, and material. There have been reported cases of anchor nut loosening on ancillary structures in the past few decades, but the cause of loosening is still unknown. Different types of wind loadings like natural gusts, vortex shedding, galloping, and truck-induced gusts vibrate the ancillary structures. These vibrations due to the wind are believed to be one of the potential causes of anchor nut loosening. Vibrations in the past have been shown to cause loosening of nuts in other structural and mechanical connections. There is also concern that the anchor rods and anchor nuts are not tightened properly as per the specifications, which can lead to loosening of nuts when the ancillary structures vibrate due to wind loadings. In ancillary structures, the anchor nuts are first made tight using a wrench with the full effort of a worker, also known as the snug-tight condition. The snug-tight condition is not properly defined at present and needs to be changed to prevent any under-tightening or over-tightening of the anchor nuts. Also, the anchor rods and nuts are generally coated with a hot zinc layer to prevent their corrosion when exposed to environmental effects like ice, snow, humidity, and rain. This process is called galvanization. The American Society for Testing and Materials (ASTM) provides some guidelines on the amount of coating allowed on the threads of the anchor rods and nuts. Any deviation from the allowable tolerances can lead to gaps between the threads of the anchor rod and nut, which can contribute to the loosening of nuts during vibrations of ancillary structures due to wind. This study focuses on investigating the following potential causes of loosening: improper tightening, vibrations of ancillary structures due to wind, snug-tight condition, and allowable tolerances for the amount of galvanization. Current tightening procedures for anchor rods and nut on ancillary structures were verified using a tightening study as part of the investigation. New revisions to the current tightening procedures have been provided as a result of discrepancies and inconsistencies observed in the current specifications. A traffic signal and a light pole were instrumented with sensors for four months to measure wind-related forces acting on these structures. Further, a full-scale traffic signal was vibrated in the laboratory using an electric motor to simulate the vibrations due to the measured wind forces. It was determined from the testing that if the anchor nuts were not properly tightened, they could become loose during vibrations due to wind. A small-scale testing was also conducted to check the results from the full-scale vibration testing. The snug-tight force in the anchor rods was also found to be dependent on the length of the wrench and the worker tightening it. The amount of galvanization on the rods and nuts procured from 3 different suppliers were found to be within allowable tolerances. Various recommendations were then made as a result of the conclusions in an effort to reduce the cases related to anchor nut loosening in the future.