Joseph M. Bracci

Seismic Response and Fragility of Deteriorated Reinforced Concrete Bridges

One of the greatest challenges in the United States today is overcoming the deterioration of an aging infrastructure system. In particular, the highway/bridge infrastructure system has traditionally been neglected of maintenance and repair. One of the most concerning degrading mechanisms in the bridge infrastructure is corrosion, and it is compounded by the fact that much of the older infrastructure is not consistent with current seismic code requirements. The research presented here determines the effects of corrosion on the seismic response of a typical reinforced concrete bridge designed according to recent standards, predominantly governed by flexural deformations, and based on realistic lifetime deteriorations in strength due to the reduction in cross-sectional area of the reinforcement and in stiffness due to concrete cover spalling. The findings of the research, given the noted modeling assumptions, are that the losses in strength and stiffness only marginally influence the seismic fragility of the selected bridge.

Inelastic Response of R/C Structures with Viscoelastic Braces

The addition of viscoelastic braces in structures for vibration reduction has been proposed and implemented in the past decade in metal scaled models of full-scale structures. Viscoelastic braces can provide energy dissipation, while the structure remains elastic. In reinforced concrete structures, the seismic response is usually inelastic, which is often accompanied by permanent deformations and damage. The addition of viscoelastic dampers can dissipate energy at the early stages of cracking of the concrete elements and reduce the development of damage. With proper selection of dampers, this damage can be substantially reduced or even eliminated. However the addition of viscoelastic dampers may stiffen the structure unnecessarily producing increased inertial forces and base shears when subjected to seismic motion. The quantification of the influence of viscous damping and elastic stiffness properties of dampers during the inelastic response of reinforced concrete structures is the subject of this investigation. Models for analysis of inelastic response with damage indexing for reinforced concrete structures that include viscoelastic braces are developed and calibrated using experimental data produced by shaking table tests. These models are then used to determine the variation of expected damage in the presence of damping and quantify the hysteretic energy dissipation along with the damping energy.

Compatibility Strut-and-Tie Modeling: Part I—Formulation

A compatibility-based strut-and-tie model (C-STM) intended for analyzing the nonlinear force-deformation behavior of disturbed regions and structural concrete deep beams is presented. In addition to the normal strut-and-tie force equilibrium requirements, the proposed C-STM accounts for nonlinear behavior using nonlinear constitutive relations for cracked reinforced concrete. The model is implemented using commercially available structural analysis software, SAP2000. To assess C-STM accuracy, convergence studies using different truss representations are explored. Particular emphasis is placed on investigating the behavior of deep cantilevered beams to provide insight into the progression of nonlinear response leading to the ultimate shear failure. New developments for modeling the nonlinear behavior of concrete compression chord members and compression-softening effects of diagonal concrete struts are proposed. The implementation is presented in the companion paper.

Performance of RC Columns Affected by ASR. II: Experiments and Assessment

AbstractThis paper describes the structural performance and analytical methodology for large-scale column specimens with a lap splice and concentric axial loading affected by varying levels of alkali-silica reaction (ASR) under displacement-controlled monotonic loading. The lap-splice length in the specimens is typical of the Texas DOT practice for the bar size used and is conservative by code standards. The specimens with varying degrees of ASR showed no evidence of bond deterioration within the splice; had similar initial stiffness and behavior up to the first cracking; had a 25–35% increase in postcracking stiffness up to yielding; had a 5–15% increase in yield strength; and showed no overall detrimental effects on the structural response when compared with control specimens without ASR deterioration. This improved behavior can be explained by the resulting volumetric expansion of the concrete because of the ASR that engaged the longitudinal and transverse reinforcement—this is believed to have resulte...

Performance of RC Columns Affected by ASR. I: Accelerated Exposure and Damage

AbstractIn Texas, a number of RC bridges have developed early cracking. Most of this deterioration has been identified or suspected to be from alkali-silica reaction (ASR), and in some cases from delayed ettringite formation (DEF). An area of concern for the Texas DOT is the performance of columns, and specifically their lap-splice regions, which have varying levels of cracking primarily from ASR but also possibly from DEF. Therefore, a research program was carried out (1) to evaluate the experimental behavior of a typical column using large-scale specimens under varying levels of premature concrete deterioration and (2) to develop an analytical model that can evaluate the behavior of the column based on calibration with the experimental behavior. This paper provides a brief overview of ASR and DEF; documents the design, construction, curing conditions, and instrumentation of 16 large-scale specimens; and presents the findings on the specimen dimensional changes and cracking that occurred during the deter...

Cracking in reinforced concrete bent caps

This paper presents findings from an experimental investigation into the causes of unexpected cracking in reinforced concrete bent caps at outside column locations during service load conditions. 16 full-scale bent cap specimens were constructed and tested under quasistatic monotonic loading. Several bent cap parameters were evaluated with regard to their influence on cracking. Cracks were measured and reinforcement strain data was recorded throughout the load history. The experimental program confirmed that flexural crack widths during service loading are directly proportional to the level of stress in the longitudinal reinforcement, and that the allowable service stress limit should be lowered to reduce such cracking. In addition, increasing the shear strength of the bent cap led to reduced inclined flexure-shear crack widths.

Compatibility Strut-and-Tie Modeling: Part II—Implementation

This paper presents the implementation and computational validation of a compatibility-based strut-and-tie model (C-STM) presented in a companion paper intended for analyzing the nonlinear force-deformation behavior of disturbed regions and structural concrete deep beams. The C-STM is used to predict the force-deformation response and internal nonlinear strain behavior of previously conducted large-scale reinforced concrete bridge bent-cap experiments. Additionally, the experimental results are compared with current code-based approaches to illustrate how the C-STM can be used as a minimalist computational analysis tool to provide an accurate prediction of the structures force-displacement response. A comprehensive description of how the C-STM is implemented into structural analysis software SAP2000TM is given to provide a step-by-step modeling procedure that can be replicated by practicing engineers seeking to apply this modeling procedure to other facets of research and design.

Performance of D-Regions Affected by Alkali-Silica Reaction: Accelerated Exposure and Damage

In Texas, a number of reinforced concrete (RC) bridge structures have developed early cracking that has been attributed to, or at least suspected to be from, alkali-silica reaction (ASR) and possibly delayed ettringite formation (DEF). An area of concern is the structural performance of D-regions in RC bridge bents that have varying levels of cracking from ASR and/or DEF. A research program was carried out to assess the experimental behavior of D-regions using large-scale specimens under varying levels of premature concrete deterioration, and to perform conventional code-based analyses and three-dimensional nonlinear finite element analyses to evaluate the behavior of the D-region. This paper, documenting part of the research program, provides a brief overview of ASR and DEF; documents the design, construction, curing conditions, and instrumentation of four large-scale specimens used to assess the structural performance of D-regions in RC bridge bents; and presents the findings during the specimen exposure phase, which includes the effects of forces from gravity loading, propagation of crack directions and widths, and resulting expansions, both that are internal and those at the surface of the specimens.

Behavior of Reinforced Concrete Members Prone to Shear Deformations: Part II-Effect of Interfacial Bond Stress-Slip

An experimental program was conducted at Texas A&M University to evaluate the effect of reinforcement details on the structural performance of reinforced concrete (RC) bent caps where shear was considered to be the dominant action in the load transfer mechanism. This article, the second of two in a series, reports on the behavior of RC members prone to shear deformations, focusing on the effect of interfacial bond stress-slip. Interfacial bond stress-slip between the concrete and longitudinal reinforcement always occurs in reinforced concrete (RC) members. The companion paper showed that the direct application of the Modified Compression Field Theory (MCFT) led to an overestimation of the post-cracking stiffness of the RC bent cap members. The authors hypothesize that this may be attributed to the inadequate representation of bond-slip using tension-stiffening in MCFT. They present a parametric study on the effect of interfacial bond-slip modeling in shear-dominated RC members. Results from the analytical investigation are compared with experimental results on RC bent caps. The authors conclude by proposing a new bond-slip model for RC members prone to shear deformations with lumped longitudinal reinforcement.

Behavior of Reinforced Concrete Members Prone to Shear Deformations: Part I—Effect of Confinement

An experimental program was conducted at Texas AM this concern is addressed in the companion paper.