Bahram M. Shahrooz

Behavior and Design of Reinforced Concrete, Steel, and Steel‐Concrete Coupling Beams

The efficiency of coupled wall systems to resist lateral loads is well known. In order for the desired behavior of the coupled wall system to be attained, the coupling beams must be sufficiently strong and stiff. The coupling beams, however, must also yield before the wall piers, behave in a ductile manner, and exhibit significant energy-absorbing characteristics. This paper reviews the current state of the art for the design of conventional reinforced concrete, diagonally reinforced concrete, steel, and composite steel-concrete coupling beams. Although not exhaustive, critical aspects of the design of these systems are presented.

Seismic Design of Hybrid Coupled Wall Systems: State of the Art

Hybrid coupled walls (HCWs) are comprised of two or more reinforced concrete wall piers connected with steel coupling beams distributed over the height of the structure. Extensive research over the past several decades suggests that such systems are particularly well suited for use in regions of moderate to high seismic risk. This paper reviews the state of the art in seismic modeling, analysis, and design of HCW systems. Design methodologies are presented in both prescriptive and performance-based design formats and a discussion of alterative types of hybrid wall systems is provided.

Steel-concrete composite coupling beams — behavior and design

Structural steel/composite beams provide a viable alternative for coupling individual reinforced concrete wall piers. Well-established guidelines for shear links in eccentrically braced steel frames form the basis of current design guidelines. However, these provisions ignore the effects of nominally reinforced concrete encasement which typically surrounds the coupling beam, and are based on overly conservative assumed deformation demands. A coordinated analytical and experimental research program at the University of Cincinnati has focused on cyclic response of steel/composite coupling beams, their connections to reinforced concrete walls, and overall behavior of composite coupled wall systems. Using the results from this study, guidelines for proper design and detailing of steel/composite coupling beams and beam-wall connections have been developed. This paper summarizes the research program, and highlights the basic concepts, important findings, and recommendations.

Practical Design of Diagonally Reinforced Concrete Coupling Beams- Critical Review of ACI 318 Requirements

Diagonally reinforced concrete beams coupling reinforced concrete wall piers are a very attractive structural system for resisting lateral loads in medium- to high-rise structures. However, for the design of diagonally reinforced concrete coupling beams (DCBs) to be compliant with AC! 318-05 often necessitates the designer to make inappropriate assumptions or results in unconstructible beam details. A discussion of the design requirements for DCBs is presented along with a number of design examples in an attempt to illustrate the difficulties inherent in designing these elements. Recommendations aimed at simplifying the design of DCBs are presented.

Investigation on Effect of Transverse Reinforcement on Performance of Diagonally Reinforced Coupling Beams

This study investigates the effects of transverse reinforcement ratios on the post-elastic performance of diagonally-reinforced coupling beams in coupled core wall systems. Two coupled wall subassemblages, with two different transverse reinforcement detailings, were designed and tested under cyclic reversed loads. The design philosophy for both specimens is presented and discussed, and the detailing is compared with what is required by ACI 318-05. The experimental results are presented, with attention to the post-elastic performance of the specimens tested. Overall performance comparisons are made. Findings show that providing a higher transverse reinforcement ratio in a diagonally-reinforced coupling beam than that currently required by ACI 318-05 greatly benefits ductility and hysteretic stability.

Toward an improved understanding of shear-friction behavior

Through an in-depth review of previous work complemented by an experimental study, the nature of shear-friction behavior is studied. It is shown that the ACI 318-08 and AASHTO approaches to shear friction do not capture the actual behavior and imply incorrect limit states. A simple explanatory model and modifcations to the form of empirical design equations are proposed. A large number of parameters affect shear-friction performance. This study does not attempt to address them all but rather illustrates the fundamental shear-friction behavior. This study does, however, consider the use of high-yield-strength reinforcing steel (ASTM A1035/A1035M). In doing so, the serious limitations of the design equations are illustrated. Additionally, this study is the only known study of shear-friction behavior to include high-strength steel.

Performance of Five-Span Steel Bridge with Fiber-Reinforced Polymer Composite Deck Panels

To better understand the performance of bridges with fiber-reinforced polymer (FRP) composite decks, the short-term and long-term responses of a 207-m, five-span bridge retrofitted with four different FRP panel systems were monitored through controlled truck load and modal tests at various stages and through long-term monitoring of key load-transfer mechanisms and panel responses. The overall aspects of the panel systems, connection details, construction techniques, and experimental program are presented followed by presentation of the measured responses. Key design issues (impact factors, girder distribution factors, level of composite action, and overall structural stiffness) for FRP and reinforced concrete decks are evaluated and compared against published design provisions. Performance of panel-to-panel connections and panel-to-girder connections is also discussed.

STRENGTH OF SHORT AND LONG CONCRETE-FILLED TUBULAR COLUMNS

Using experimental data from previous tests and detailed analytical studies, the applicability of American Concrete Institute (ACI) standard techniques for analysis of concrete-filled tubular columns is evaluated. Both short and slender columns are considered. The focus of the reported research is on rectangular and square normal or high-strength steel tubes filled with normal or high-strength concrete. Capacity of short concrete-filled tubular columns is predicted reasonably well by the ACI method as long as normal strength tubes are used. However, this procedure tends to significantly underestimate the capacity for cases with high-strength tubes. In lieu of fiber analysis, the ACI method should be revised to incorporate full yielding of the steel tube. The results, as obtained by ACI or its revised method, are fairly close to those obtained from more refined fiber analysis. Capacity of slender concrete-filled tubular columns is also computed reasonably well by the ACI moment magnifier method. The results correspond to those obtained from second-order analysis in which material and geometric nonlinearities are incorporated. Therefore, the ACI procedure provides a simple yet reliable method for analysis of short and slender concrete-filled tubular columns if appropriate measures are made for cases with high-strength tubes.

A Performance-Based Design Approach for Coupled Core Wall Systems with Diagonally Reinforced Concrete Coupling Beams

Coupled core wall systems (CCWs) are lateral force resisting systems that can provide remarkable lateral stiffness for mid- to high-rise buildings, exceeding the lateral stiffness of isolated walls while providing the redundancy and force redistribution capabilities of framed systems. The lateral stiffness provided by CCWs largely depends on the type of coupling beams used to transfer forces between wall piers. Diagonally-reinforced concrete coupling beams are one of the more common details although composite alternatives (e.g., those using structural steel W-shapes, hollow structural steel sections, or embedded steel plates) or beams with rhombic reinforcement are increasingly being selected as viable alternatives. Despite the favorable behavior exhibited by diagonally-reinforced coupling beams in experimental studies, designing and constructing diagonally-reinforced coupling beams having practical span-to-depth ratios presents significant difficulties, impacting the use of CCWs as a viable lateral force resisting system. This paper presents a performance-based design (PBD) approach that allows the designer to successfully proportion a code-compliant CCW system that addresses the shortcomings related to the traditional strength-based design approach. A prototype building is designed following both approaches, and is analyzed both statically and dynamically. Results show that the PBD approach produces a code-compliant structure that satisfies the most pressing constructability constraints.

Flexural Crack Widths in Concrete Girders with High-Strength Reinforcement

AbstractThe introduction of steel reinforcing bars having yield strengths exceeding 517 MPa (75 ksi) and often approaching 827 MPa (120 ksi) may allow for significant economies to be realized, particularly when used in conjunction with high-strength concrete. One implication of the adoption of higher-strength reinforcing steel is that reinforcing bar stresses (and therefore strains and consequently crack widths) at service load levels are expected to be greater than when conventional bars [having a yield of 414 MPa (60 ksi)] are used. A study of flexural crack widths of beams reinforced with high-strength ASTM A1035 reinforcing steel is presented. Discussion focuses on the behavior at loads corresponding to longitudinal reinforcing bar stresses of 248, 414, and 496 MPa (36, 60, and 72 ksi), representing service load levels (i.e., 0.6fy) for steel having fy = 414,690, and 827 MPa (60, 100, and 120 ksi), respectively. Average measured crack widths obtained from a series of flexural beams having reinforcing ...