Richard E. Klingner

LATERAL LOAD RESPONSE OF STRENGTHENED AND REPAIRED REINFORCED CONCRETE COLUMNS.

The effectiveness of three different repair and/or strengthening techniques in enhancing the lateral load response of identical reinforced conrete short columns was studied. Based on an 18 in. square prototype, three column test specimens were constructed to two-thirds scale, using identical geometry and reinforcement. The test specimens representing existing columns had a 12 in. square cross section reinforced with eight No.6 longitudinal bars, 6-mm ties spaced at 8 in., and a 1-in. cover. Spacing of the tranverse reinforcement, while greater than current design requirements, was intended to represent typical practice of column design in seismic regions of the U.S. in the 1950s and early 1960s. One of the specimens was tested, repaired by jacketing, and then retested. The remaining two specimens were strengthened by jacketing prior to testing. A single lateral displacement history and constant axial load were used for all tests. Both the strengthened and the repaired columns performed better than the original column. Columns strengthened by jacketing, both with and without suppementary crossties, were much stiffer and stronger laterally than the original, unstrengthened column. The column repaired by jacketing was also much stiffer and stronger laterally than the original column and performed almost as well as the strengthened columns.

Experimental Behavior of Bridge Beams Retrofitted with Postinstalled Shear Connectors

A number of older bridges were constructed with floor systems consisting of a noncomposite concrete slab over steel girders. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders with postinstalled shear connectors to permit the development of composite action. This paper presents the results of an experimental investigation of this concept. Five large-scale noncomposite beams were constructed, and four of these were retrofitted with postinstalled shear connectors and tested under static load. The retrofitted composite beams were designed as partially composite with a 30% shear connection ratio. A noncomposite beam was also tested as a baseline specimen. Test results showed that the strength and stiffness of existing noncomposite bridge girders can be increased significantly. Further, excellent ductility of the strengthened partially composite girders was achieved by placing the postinstalled shear connectors near zero-moment regions to reduce slip demand on the connectors. The test results also showed that current simplified design approaches commonly used for partially composite beams in buildings provide good predictions of the strength and stiffness of partially composite bridge girders strengthened using postinstalled shear connectors.

Punching-Shear Behavior of Bridge Decks underFatigue Loading

In this research, the punching-shear behavior of bridge decks under fatigue loading is studied experimentally and analytically, including the effect of arching action. The study includes static and pulsating fatigue tests on full-scale, cast-in-place and precast, and prestressed panel specimens. Failure modes, loads, and test specimen behaviors observed during the experimental tests are discussed and compared with analytical predictions. Finite-element models developed for a full-scale bridge and for test specimens are discussed, and results obtained from them are compared with test results. A method is proposed that includes effects of membrane compression in calculations of punching-shear capacity, giving reasonable agreement with test results. S-N curves are proposed for pulsating fatigue design and assessment.

Seismic Evaluation of Low-Rise Reinforced Masonry Buildings with Flexible Diaphragms: I. Seismic and Quasi-Static Testing

This and a companion paper compare the results from shaking-table testing, quasi-static testing, and analytical predictions, to provide a coherent description of the seismic response of low-rise reinforced masonry buildings with flexible roof diaphragms. Two half-scale, low-rise reinforced masonry buildings with flexible roof diaphragms are subjected to earthquake ground motions on the Tri-axial Earthquake and Shock Simulator at the United States Army Construction Engineering Research Laboratory, Engineer Research and Development Center. Following the shaking-table tests, diaphragms and top four courses of attached masonry walls are salvaged from the half-scale structures and tested quasi-statically in their own plane. In contrast to what is usually assumed in design, the half-scale specimens do not behave as systems with a single degree of freedom associated with the in-plane response of the shear walls, but rather a system with a dominant degree of freedom associated with the in-plane response of the roof diaphragm. A new index describing the potential for diaphragm damage is introduced, the diaphragm drift ratio. A companion paper, Part II: Analytical Modeling, presents analytical work intended to corroborate and extend results from experimental testing.

Seismic Testing of Autoclaved Aerated Concrete Shearwalls: A Comprehensive Review

Autoclaved aerated concrete (AAC) is a lightweight cementitious material that has recently been introduced into the United States construction market. This article reports on the first phase of a comprehensive research program that has recently been carried out to propose design provisions for autoclaved aerated concrete (AAC) and to develop the technical basis for those provisions. The first phase of the program addressed extensive testing on AAC shearwalls, which are the fundamental lateral force-resisting elements of AAC structural systems. The 19 shearwall specimens were made of a variety of AAC elements, including masonry-type units and reinforced panels, laid either horizontally or vertically. The aspect ratio of the specimens (ratio of height to base length) varied from 0.6 to 3, and each specimen was designed to fail in either shear or flexure. Based on the test results obtained at The University of Texas at Austin and elsewhere, the authors developed reliable procedures and corresponding provisions for the design behavior of AAC shearwalls as governed by flexure, shear, and other limit states. Flexural cracking was observed in two directions in 15 shearwall specimens, with a resulting limiting value of tensile bond strength between leveling bed mortar and AAC of 50 psi based on a lower 20% fractile. Flexure-shear cracking was observed in seven shearwall specimens, and web-shear cracking was observed in 13 shearwalls.

Seismic Performance of Cantilever-Reinforced Concrete Masonry Shear Walls

AbstractThis paper describes an experimental study of the seismic performance of cantilever-reinforced concrete masonry shear walls. As part of a research project on displacement-based design of masonry structures, 30 cantilever shear-wall specimens, made of fully grouted reinforced concrete masonry, were tested under reversed cyclic loading at the University of Texas at Austin and at Washington State University. Based on test results, the relationship between key design parameters and the nonlinear hysteretic response of the specimens was evaluated. The specimens exhibited predominantly flexural behavior, as intended, and their behavior was generally in good agreement with that reported in previous research work. Specimens constructed with masonry units containing recycled materials behaved similarly to otherwise identical specimens constructed with ordinary units, indicating the structural equivalence of those two types of units. Lap splices in the longitudinal reinforcement caused a reduction in wall p...

Development of Seismic Force Reduction and Displacement Amplification Factors for Autoclaved Aerated Concrete Structures

This paper addresses the development and application of a rational procedure to select the seismic force reduction factor (R) and the displacement amplification factor ( Cd ) for the design of autoclaved aerated concrete (AAC) structures. The values of R and Cd are proposed based on a combination of laboratory test results and numerical simulation. The test results are obtained from 14 AAC shear-wall specimens tested under simulated gravity and quasi-static reversed cyclic lateral loads. Analytical responses are predicted using nonlinear analysis models whose hysteretic characteristics are based on the experimentally observed responses. Using an iterative procedure, typical AAC structures are designed using successively larger trial values of the factor, R, until the structures response (either ductility or drift) exceeds the experimentally determined capacity. A lower fractile of those critical values, modified for probable structural overstrength, is taken as a reasonable value of 3 for R. Using an analogous procedure, a reasonable value of Cd is determined as 3. These values will undoubtedly be refined based on field experience, just as they have been for other structural systems.

Seismic Evaluation of Low-Rise Reinforced Masonry Buildings with Flexible Diaphragms: II. Analytical Modeling

This and a companion paper compare the results from shaking-table testing, quasi-static testing, and analytical predictions to provide a coherent description of the seismic response of low-rise reinforced masonry buildings with flexible roof diaphragms. This paper presents the development, implementation, and results of coordinated analytical modeling intended to corroborate and extend the results of experimental work discussed in a companion paper, Part I: Seismic and Quasi-Static Testing, and more important, examine the efficacy and accuracy of different analytical modeling approaches. Specifically, linear elastic finite-element models, simplified two-degree-of-freedom models, and nonlinear lumped-parameter models are created and all agree well with measured responses. Based on these, a simple design tool for the analysis of low-rise reinforced masonry buildings with flexible diaphragms is developed and verified.

Seismic Design Factors for Steel Moment Frames with Masonry Infills: Part 2

In this two-part work, seismic behavior and design of steel moment frames with masonry infills are investigated systematically. In this first part, the “infill strength ratio” (the ratio of the story shear strength of infills to the story shear strength of the bare frame) is shown to have a fundamental effect on the seismic behavior of an infilled frame. This fundamental effect is demonstrated using pushover analysis of an example steel moment frame with masonry infills in uniformly infilled and open ground story configurations. In general, infill strength ratios greater than about 0.35 are associated with progressive deterioration of seismic performance, leading to story mechanisms concentrated in the lower stories. Greater infill strength ratios can also lead to local shear failures in frame members.

EFFECTS OF ENVIRONMENTAL EXPOSURE ON THE PERFORMANCE OF CAST-IN-PLACE AND RETROFIT ANCHORS IN CONCRETE

Single cast-in-place anchors and retrofit anchors (expansion, undercut, and adhesive) were exposed to five simulated environmental exposure conditions: ultraviolet light, freezing and thawing, corrosion in a pH-neutral salt solution, wetting and drying with simulated acid rain, and combined freezing and thawing, corrosion in a pH-neutral salt solution, and wetting and drying. To evaluate the effects of different environmental exposures, the tensile load-deflection behavior of the exposed anchors was compared with that of otherwise identical unexposed anchors. Ultraviolet light exposure did not affect the anchors studied. Freeze-thaw exposure reduced the preload and decreased the initial stiffness of torque-controlled expansion anchors. Salt (corrosion) exposure did not adversely affect the behavior of expansion anchors. Wetting and drying exposure to simulated acid rain did not significantly affect the anchors studied. The combination exposure reduced the stiffness of some torque-controlled expansion anchors. These results show that when expansion anchors are used in concrete subjected to cycles of freezing and thawing, their preload should be checked regularly. The results also imply that in concrete subject to cycles of freezing and thawing while wet, water should be prevented from entering the drilled holes of mechanical anchors.