Chadd LaneJian Zhao Assistant Professor WisCamp Undergraduate ResearchSummer 2009University of Wisconsin Milwaukee

Motivation:Structural safetyCracks in the cement, broken anchors, or shifting of the beams. Maximize structural safetySaving time and money

Behavior of anchor connections

Concrete cracking in tension

Current design regulations

Limited guidance

How does one maximize structural safety with the number of anchors, anchor design, and location?

How does one disperse the weight of a large beam evenly among all the anchors?

Concrete Spall Cone

Steel Breakage

Anchor Pullout

Bond Failure

Edge Distance and Spacing Reduction

Spalled concrete split, chip, or to break into smaller pieces

A material can be loaded in:

a) compression b) tension c) shear

Computer simulation failure rate of cement and anchors Real life seismic loading simulation. Confirm computer simulationsHow the cement and anchors should look when they fail. Understand the full nature of cement and anchors. CalculationsHow to disperse the weight of the large beam evenly amongst all anchors evenly

One of the anchor bolts was fractured

The other bent under a combined tension and shear action.

The top layer of concrete spalled such that the hairpin, with an intention to help the anchor connection to resist shear, was displaced outside the anchor connection. Note that the failure of the anchor connection might have contributed to the total collapse of the industrial building.

The experimental tests include the ongoing single-anchor tests at UWM and the anchor group tests (to be conducted at Illinois in 2010). Anchors in every test group are subjected to these loadings: tension and shearThe loading frame shown right are set for the various loading patterns. Meanwhilehttp://www.youtube.com/watch?v=3z4YLUqOysI

The anchor position is chosen to enable concrete breakout failure. The same configurations will be cast and tested with various anchor reinforcements to explore practical and effective reinforcement details that can prevent the concrete breakout failure modes. Headed bars and reinforcement cages are under consideration.

The single anchor tests will be simulated using finite element models to optimize the anchor reinforcement details. The proposed design procedures will be incorporated in the MathCAD programs.

Using the NEES facility at the University of Illinois. Obtain detailed experimental - cyclic shear and combined tension-shear. Evaluate current seismic anchor design provisions and develop new design methodologies and the use of anchor reinforcements. Create fiber-based connection interface models. Promote a timely transfer of knowledge

This UWM project is being led by Dr. ZhaoTwo graduate students Joshua Johnston and Derek Petersen from UWM and one graduate student from UC are working on the project. Two undergraduate students Alice Muehlbauer and Chadd Lane.

Seismic behavior and design of cast-in-place anchors/studs using NSF NEES facility and local resources. Anchor tests that simulate a combination of concrete breakout failure under shear and/or tension. The focus will be also on the improvement of anchor behavior through using anchor reinforcements. The research program will generate critical knowledge that advances the seismic design of anchor connections, as well as providing essential information for future revision of anchorage design regulations.

Dr. Zhao and his teamWisCamp and McNair Staff and studentsAll other people that played a roll in this great experience.

*Throughout history there have been many problems with the structural safety of cement, beams, and anchors. Whether it be cracks in the cement, broken anchors, or shifting of the beams. Engineers have been trying to figure out how to maximize structural safety, while saving time and money with computer simulation and real life testing. Through multiple types of testing it will be easier to understand the behavior and design of cast-in-place anchors under simulated seismic loading. Also the issues of number of anchors, anchor design, and location will be addressed and easier to understand with new computer simulations and a real life demonstration of anchor failures.Cast-in-place anchors/headed studs are used in connecting steel members with concrete. The behavior of anchor connections directly affects the behavior of the structure in regions of moderate or high seismic risk. The current design regulations, represented by the American Concrete Institute (ACI) Committee 318 document (Appendix D), are largely based on monotonic tests of anchor bolts and anchor groups. Consequently, these documents provide limited guidance for the seismic design of connections between steel members (e.g., steel braces, columns, or girders) to concrete, where anchors are subjected to substantial cyclic loading. Concrete cracking in tension in most cases controls the design of anchor connections. Although steel reinforcements have been proposed to prevent concrete failure modes and to increase the ductility of anchor connections, there is very limited supporting data in the literature.

When anchors are loaded to their maximum capacity, several different types (modes) of failure are possible depending on the type of anchor, strength of the base material, embedment depth, location of the anchor, etc. Common modes of failure include: Concrete Spall Cone Occurs at shallow embedments where the resistance of the base material is less than the resistance of the anchor and the base material fails. Steel BreakageThe capacity of the anchorage exceeds the tensile or shear strength of the steel anchor or rod material.Anchor PulloutBase material adjacent to the extension portion of an anchor crushes, resulting in the anchor pulling out of the hole until the capacity of the spall cone is reached, at which point the concrete will spall. This type of failure happens more commonly when anchors are set with deep embedment depths. Bond FailureShear failure of the adhesive at rod-adhesive interface or adhesive-base material interface. Occurs more commonly in deep embedments using high strength steel rods. Edge Distance and Spacing ReductionReduces the holding values, when anchors are placed too close to the edge. This also occurs when two or more anchors are spaced closely together. See suggested edge distance, anchor spacing distances and reduction values in the product sections.

Definition: Spalling is a result of water entering brick, concrete or natural stone and forcing the surface to peel, pop out or flake off. This is because there is salt in water. Salt pushes outward from the inside. Eventually, spalling can cause crumbling and destruction of a structure*Through a newly created computer simulation one can figure out the failure rate of cement and anchors, how the cement and anchors should look when they fail. One can confirm computer simulated results with a real life seismic loading simulation. Through simulations and careful calculations one will be able to figure out the full nature of cement and anchors which will make is easier to understand how the weight of a large beam will disperse among the anchors. It is critical that one understands the full construction and error to insure maximum performance of the anchors.An anchor connection failure is shown left. One of the two anchor bolts was fractured and the other bent under a combined tension and shear action. The top layer of concrete spalled such that the hairpin, with an intention to help the anchor connection to resist shear, was displaced outside the anchor connection. In addition, the cracking under the shear action enabled the anchor pull-out failure despite the vertical supplemental reinforcements. Note that the failure of the anchor connection might have contributed to the total collapse of the industrial building.

*The failure modes of an anchor with certain diameter (e.g., 1 inch as shown below) are controlled by its embedment length and the edge distance in the shear direction. The anchor position is chosen to enable concrete breakout failure. The anchor specimens with the same configurations will be cast and tested with various anchor reinforcements to explore practical and effective reinforcement details that can prevent the concrete breakout failure modes. Headed bars and reinforcement cages are under considerationThe single anchor tests will be simulated using finite element models to optimize the anchor reinforcement details. The proposed design procedures will be incorporated in the MathCAD programs. Programs have been developed per ACI Committee 318 document, PCI design handbook, and the European standards to facilitate the implementation.

*Objectives NEES-Anchor project targets at the seismic behavior and design of cast-in-place anchors and headed studs using the NEES facility at the University of Illinois at Urbana-Champaign. The objectives of the project are: Obtain detailed experimental data for cast-in-place anchors/studs under simulated seismic loadings with a focus on cyclic shear and combined tension-shear. Evaluate the limitations of current seismic anchor design provisions and develop new design methodologies and equations focusing on the use of anchor reinforcements. Evaluate proposed design methods and details by testing anchor connections between steel girders and concrete walls. Create fiber-based connection interface models to improve analysis tools for advancing performance-based engineering. Promote a timely transfer of knowledge generated as part of the proposed research to engineers, students, and underrepresented groups for a broader impact.

*NEES-Anchor is a project targeting at the seismic behavior and design of cast-in-place anchors/studs using NSF NEES facility and local resources. The experimental program includes anchor tests that simulate a combination of concrete breakout failure under shear and/or tension. The focus will be also on the improvement of anchor behavior through using anchor reinforcements, which would eliminate concrete breakout failure (under shear, tension, and combined actions). The research program will generate critical knowledge that advances the seismic design of anchor connections. The research results will provide essential information for future revision of anchorage design regulations.

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