David I. McLean

Performance of Existing Bridge Columns under Cyclic Loading—Part 1: Experimental Results and Observed Behavior

This study was conducted to investigate the flexural and shear performance of older columns for purposes of seismic assessment and retrofit design, particularly with regard to assessing the residual strengths present in degraded hinge regions. In this first of a two-part paper, experimental observations and results of tests on eight reduced-scale specimens that incorporated deficiencies present in older bridge columns are presented. The columns were fixed against rotation at both the top and bottom to enable shear transfer, even after a flexural hinging region degrades. Test variables included columns aspect ratio, longitudinal reinforcing ratio, lap splice length, and retrofitting detail. Shear failures were observed both outside and within the plastic hinge regions.

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...

A comparison of current computer analysis methods for seismic performance of reinforced concrete members

In this paper, an evaluation of current capabilities in the area of cyclic analysis of reinforced concrete components is presented through the application of several analysis methods to a benchmark problem. Data from experimental tests involving the flexural and shear performance of a reinforced concrete column was used for comparison. Analyses for cyclic and monotonic load cases were performed using a degrading plastic hinge model, a fiber beam model, and a three-dimensional finite element model. Details of the data preparation and analysis results are presented and evaluated. Recommendations are made regarding the relative effectiveness of the methods for practical dynamic analysis.

Displacement-Based Seismic Design for Reinforced Masonry Shear-Wall Structures, Part 2: Validation with Shake-Table Tests

This paper provides a comprehensive validation of a displacement-based seismic design procedure proposed in a companion paper for reinforced masonry shear-wall structures. For this purpose, a full-scale, two-story reinforced masonry specimen was tested on a shake table to examine the global and local behaviors of a low-rise reinforced masonry building designed by the proposed displacement-based procedure, and to validate the analytical tool used in the design process. This specimen successfully resisted repeated ground motions with intensities up to the maximum considered earthquake (MCE). Its performance on the shake-table demonstrates that a reinforced masonry structure designed, detailed, and constructed according to the proposed displacement-based design procedure can resist MCE earthquakes without collapse even though it may suffer severe damage. In critical regions of this specimen, elements detailed in accordance with displacement-based requirements showed more inelastic deformation capacity than the deformation limits imposed by the displacement-based design provisions proposed here. The proposed procedure produces structures that behave according to design expectations, even though severely damaged.

Effects of blast loading on prestressed girder bridges

Since the events of September 11th, increased attention has been given to the effects of blast loading on structures. Bridges are especially important due to their potentially critical role in the economy and for emergency response. Prestressed concrete highway bridges are very common, representing 11 percent of state bridges nationwide. Yet, very little is known about how prestressed concrete bridges respond to blast loading.

Seismic Retrofitting of Bridge Foundations

An experimental study investigated retrofitting measures for improving the seismic performance of the foundations of existing bridges. Retrofit measures for both pile-supported and spread footings were investigated. Tests were conducted on 1/3-scale footing and column assemblages that incorporated details selected to represent deficiencies common in older bridges. Tests on the as-built specimens resulted in a brittle failure because of insufficient joint shear strength in the column-footing connection. An added reinforced concrete overlay provided an effective retrofit for the as-built footings. In specimens that were overturning critical, increased overturning resistance was achieved by enlarging the footing plan size, by providing additional piles, or by providing tie-downs through the footing.

Displacement-Based Seismic Design for Reinforced Masonry Shear-Wall Structures, Part 1: Background and Trial Application

In this paper, a displacement-based seismic design procedure is presented for reinforced masonry shear-wall structures, with the objective of being more consistent, transparent, and practical than current force-based seismic design procedures. The procedure anticipates the formation of a plastic mechanism at specified target displacements, calculates the local deformation demands associated with that mechanism, and ensures that those local deformation demands remain below deformation capacities for flexure-dominated and shear-dominated wall segments. Guidelines to determine the target displacements and effective damping properties for reinforced masonry wall structures are provided. The proposed procedure and guidelines are used in a trial application to design a full-scale, two-story reinforced masonry shear-wall system.

Performance of Existing Bridge Columns under Cyclic Loading--Part 2: Analysis and Comparison with Theory

This study was conducted to investigate the flexural and shear performance of existing columns for purposes of seismic assessment and retrofit design, particularly with regard to assessing the residual strengths present in degraded hinge regions. In this, the second part of a two-part paper, observed experimental results from a series of column tests are evaluated and compared with various predictive models of column shear and flexural behavior. Both current design approaches and proposed assessment behavioral models are evaluated. Based on the comparisons with test results from this and other studies, recommendations are made for assessing the flexural and shear capacities of existing bridge columns.

Performance of lightly confined reinforced concrete columns in long-duration subduction zone earthquakes

The main goals of this research were to evaluate typical 1950s and 1960s as-built bridge columns in western Washington State in large subduction zone earthquakes and to investigate the dependency of failure mechanisms on loading history. Eight displacement histories were applied to eight nominally identical, half-scale, circular reinforced concrete columns expected to respond primarily in flexure (flexure-dominated). The main design deficiencies were a short longitudinal reinforcement lap splice at the base of the column (35db) and inadequate transverse reinforcement. Test results showed that the failure mode of reinforced concrete columns was controlled by the column loading history. Three distinct failure mechanisms were observed for columns with an aspect ratio of approximately 4.2, assuming symmetric, double-curvature behavior. Large initial displacements greater than six times the effective yield displacement (Δ y ) were likely to result in shear failures. Columns experiencing many displacements less than 4Δ y were likely to fail because of longitudinal reinforcement buckling. Columns subjected to several displacement excursions less than 4Δ y followed by an excursion greater than 6Δ y were likely to fail by longitudinal reinforcement slipping within the splice region. Despite the deficiencies present in circular reinforced concrete bridge columns built before 1975 in western Washington State, this study showed that flexure-dominated columns with a 35db lap splice in multiple-column bent, three-or four-span bridges were not likely to experience significant damage in the predicted Cascadia Subduction Zone earthquake. However, other components of the bridge need to be assessed to determine whether the global bridge response is acceptable under the predicted Cascadia Subduction Zone earthquake.

Seismic Performance of Low-Rise Wood-Framed and Reinforced Masonry Buildings with Clay Masonry Veneer

AbstractThis paper describes a coordinated experimental and analytical study that investigated the seismic performance of wood-stud construction with clay masonry veneer and of RC masonry construction with clay masonry veneer designed according to current U.S. building codes. As part of this study, two 1-story buildings were tested on a shaking table. Both had clay veneer on the outside. One had wood-frame walls for the backing and load-resisting system, whereas the other had RC masonry walls. With one exception, the behavior of the veneer in the wood-framed building was satisfactory up to levels of shaking consistent with the design level earthquake. That exception was related to the relatively low pullout strength in wet wood of the conventional nails used to attach the veneer connectors to the wood-stud wall. On the basis of this study, code changes have been implemented to require the use of higher-capacity fasteners for such applications. The wood-frame building specimen itself did not collapse under...