Ronald A. Cook

BEHAVIOR AND DESIGN OF SINGLE ADHESIVE ANCHORS UNDER TENSILE LOAD IN UNCRACKED CONCRETE

A user-friendly model for the design of single adhesive anchors subjected to tension loading in uncracked concrete is presented. Descriptions of the various types of adhesive anchor systems is included as well as a summary of previously published design models. The development of the user-friendly design model includes a comparison of the model and previously published models to a database including 888 European and American tests. The comparison shows that the simple user-friendly model provides a better fit to the database than more complicated design models previously presented. Although the model is limited to anchors located away from free edges, it provides the basis for development of models that account for the effect of edges, anchor groups, and other design conditions.

Behavior and design of adhesive bonded anchors

Post-installed bonded anchors are used extensively in practice but have not yet been incorporated into the design provisions of ACI 318-05, Appendix D. This paper presents a behavioral model that provides the basis for developing design provisions for anchorages to concrete using adhesive bonded anchors. The model is based on results of extensive numerical and experimental work. The behavioral model is compared with a worldwide database containing 415 tests on adhesive anchor groups, 133 tests of adhesive anchors located near a free edge, and accompanying baseline single anchor tests used to establish the relationship between the results of the group and edge tests and the behavior of isolated single anchors. The proposed model agrees very well with the tests on adhesive anchor groups, but is conservative compared to the tests with single anchors close to the edge.

FACTORS INFLUENCING BOND STRENGTH OF ADHESIVE ANCHORS

This paper presents results of a comprehensive test program that investigated various factors with the potential to influence the bond strength of polymer-based adhesive anchors. 20 products from 12 manufacturers were included in the program for a total of 765 tests. To establish a reference bond strength, baseline tests were performed at room temperature for anchors installed in cleaned, dry holes. Individual factors were isolated through separate test series that maintained baseline conditions, except for the variable under consideration. The variables that were investigated included those that could be anticipated to occur during and after installation. Factors occurring during installation included the condition of the drilled hole, differences in the concrete strength, and differences in concrete aggregate. Factors occurring after installation included a short-term adhesive curing period and loading at an elevated temperature. This research demonstrates that reliable predictions of adhesive anchor performance are only practical by product-specific and condition-specific testing.

Bond Stress Model for Design of Adhesive Anchors

Adhesive (chemical) anchors are used frequently in both new construction and repair/retrofit projects. Current design codes do not contain rational design procedures for these anchors. An experimental program was undertaken to determine the behavior of these anchors and to develop a rational procedure for their design. The experimental program described in this study involved 97 tensile tests of 6 adhesive products on the following types of 5/8-in. diameter threaded anchors; fully bonded single anchors; partially bonded single anchors; and fully bonded anchor pairs. A behavioral model based on an elastic formulation is developed and assessed. Design recommendations for single and multiple adhesive anchors are presented in the paper.

LOAD-DEFLECTION BEHAVIOR OF CAST-IN-PLACE AND RETROFIT CONCRETE ANCHORS

The purpose of this study was to investigate the design and behavior of single cast-in-place and retrofit concrete anchors under static, fatigue, and impact tensile loads. The following types of anchors were tested: (1) Cast-in-place anchor bolts and embeds; and (2) Retrofit anchors--(a) adhesive anchors (epoxy, polyester, and vinylester); (b) grouted anchors; (c) expansion anchors (torque-controlled); and (d) undercut anchors. The study described in this report involved 178 tests. Load-deflection behavior was recorded for each test. Behavior of adhesive anchors was studied with respect to variations in installation, orientation (vertical, horizontal, and overhead), and in hole cleaning techniques. Most anchors had a 5/8-in. nominal diameter. Required embedment lengths for the cast-in-place anchors were estimated using the criteria of ACI 349 Appendix B. Embedment lengths for the embeds, expansion, undercut, and some adhesive anchors were determined by the individual anchor manufacturer, and some anchors were only available in fixed lengths. Behavior modes of anchors were identified under static, fatigue, and impact tensile loads, and anchor types were categorized according to these behavior modes. Recommendations are given for embedment depths and installation techniques for anchors of each type. Recommendations are made for further research, some of which will be addressed in future reports produced by this project.

Full-Scale Experimental Measurement of Barge Impact Loads on Bridge Piers

Bridges that span navigable waterways must be designed to resist potential impact loads associated with barge or ship collisions. Despite this fact, few experimental data have been collected about the magnitude and nature of such loads. Vessel-impact components of bridge design specifications, such as the AASHTO bridge design provisions, are therefore based on limited experimental data. Recently, a bridge in the United States (Florida) was replaced with a new structure and thus afforded a unique opportunity to conduct full-scale barge impact tests on piers of the preexisting structure before it was demolished. Tests were conducted on two piers with fundamentally different types of foundation systems. Tests on one pier also were repeated in two structural configurations (with the superstructure present and then with it removed). In each test, instrumentation and high-speed data acquisition systems were used to quantify the dynamic loads generated during controlled collision events. Experimental procedures used during the tests are described, and selected test results are presented, including experimentally measured dynamic impact loads and associated barge deformations. Comparisons are then presented between experimentally collected data and the current AASHTO barge impact bridge design provisions.

Part 2: Design of Foundations and Structures: Full-Scale Experimental Measurement of Barge Impact Loads on Bridge Piers

Bridges that span navigable waterways must be designed to resist potential impact loads associated with barge or ship collisions. Despite this fact, few experimental data have been collected about the magnitude and nature of such loads. Vessel-impact components of bridge design specifications, such as the AASHTO bridge design provisions, are therefore based on limited experimental data. Recently, a bridge in the United States (Florida) was replaced with a new structure and thus afforded a unique opportunity to conduct full-scale barge impact tests on piers of the preexisting structure before it was demolished. Tests were conducted on two piers with fundamentally different types of foundation systems. Tests on one pier also were repeated in two structural configurations (with the superstructure present and then with it removed). In each test, instrumentation and high-speed data acquisition systems were used to quantify the dynamic loads generated during controlled collision events. Experimental procedures ...

Anchor Bolt Steel Strength in Annular Stand-Off Base Plate Connections

Anchor bolts in annular stand-off base plates connecting cantilever sign and signal structures to concrete foundations may experience high shear from base plate torsion and direct shear forces. A three-phase experimental study evaluated the steel shear strength of anchor bolts in grouted and ungrouted annular stand-off base plate connections to concrete. Phase 1 included flush-mounted and ungrouted stand-off base plates with ⅝- and 1-in.-diameter bolts loaded in direct shear. Phase 2 employed a novel torsion test approach on 10 circular groups of six ⅝-in.-diameter bolts installed in flush-mounted, ungrouted stand-off, and grouted stand-off base plates, along with three ungrouted groups of three 1-in.-diameter bolts. Phase 3 comprised one ungrouted and three grouted full-scale annular base plate tests of six 1.25-in.-diameter bolts under predominantly torsion loading. Results from this study suggest that AASHTOs provisions allowing bolt bending stresses to be ignored for anchor bolts with an exposed length of less than one bolt diameter overestimate ultimate strength. The beam model suggested by AASHTO accounting for anchor bolt bending fits experimental data well and is recommended for all ungrouted annular stand-off base plates. The American Concrete Institutes 0.8 reduction factor for steel shear strength of anchor bolts in grouted connections was found to be conservative and is also recommended.

Long-Term Performance of Epoxy Adhesive Anchor Systems

Adhesive anchor systems are used to anchor both threaded rods and reinforcing bars into hardened concrete. Common transportation structure applications for adhesive anchor systems include bridge widening, structure-mounted signs and appurtenances, luminaires and light poles, concrete repair and rehabilitation, barrier retrofitting, utility installation on existing structures, and tunneling finishing. The objective of National Cooperative Highway Research Project 4-37, “Long-Term Performance of Epoxy Adhesive Anchor Systems,” was to develop proposed standard test methods, materials specifications, design specifications and guidelines, construction specifications and guidelines, and quality assurance guidelines for the use of adhesive anchor systems in transportation structure applications. Development of these standards was founded on the results of a comprehensive program of laboratory experiments to determine, predict, and verify the long-term performance of adhesive anchors under sustained load in their typical service applications and environments. The research investigated the effects of various parameters on the long-term bond strength of adhesive anchors in hardened concrete. Testing was conducted on three adhesives of different chemistries that had passed current product evaluation criteria requiring sustained load testing at 110°F. A stress versus time-to-failure approach was used to evaluate the effects of various parameters on the sustained load performance of adhesive anchors. Within the range of parameters studied, only elevated service temperature (>120°F) and manufacturer’s minimum cure time were shown to influence the sustained load performance beyond that predicted by short-term tests of fully cured adhesive. Rheological analysis of the adhesives alone was conducted to investigate any correlation with anchor testing in concrete, but no consistent relationships were discovered that applied to all three adhesives investigated. Additionally the effect of early-age concrete on the bond strength of adhesive anchors was investigated. This report, along with thirteen appendixes printed here and seven appendixes available to download from the NCHRP Project 04-37 web page at http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=2495, fully document the research.

An integrated technique for the analysis of traffic lights and signs supported by the dual cable system

Abstract Due to failures of cable-supported traffic lights and signs under wind loading during Hurricane Andrew, a need for a comprehensive analysis method was identified. The computer program ATLAS satisfies this need and utilizes an integrated technique that consists of the extended force density method and the nonlinear direct stiffness method for large displacements. The integration of the two methods is essential for the analysis of such systems because of the numerical instabilities developed when using the direct stiffness method alone. The resulting analysis procedure proved to be stable. This paper provides a description as to how the two methods were integrated and implemented in ATLAS.