Yahya C. Kurama

Design and measured behavior of a hybrid precast concrete wall specimen for seismic regions

This paper presents the measured behavior from the testing of a 0.4-scale “hybrid” precast concrete wall specimen under reversed-cyclic lateral loading and provides an assessment of the seismic design and analysis of the wall by using the experimental results. The hybrid precast wall system investigated in the paper utilizes a combination of mild (i.e., Grade 400) steel and high-strength unbonded posttensioning (PT) steel for lateral resistance across horizontal joints. A seismic design procedure that conforms to ACI 318 and ACI ITG-5.2 was used for the design of the test specimen based on ACI ITG-5.1. The behavior of the specimen was measured with conventional data acquisition techniques and also full-field digital image correlation of the base panel and the critical joint between the base panel and the foundation, providing unprecedented information on the wall performance. The paper compares these measurements with the design and analytical predictions, focusing specifically on the applied lateral load...

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.

SDOF Demand Index Relationships for Performance-Based Seismic Design

This paper investigates design relationships to estimate the following four seismic demand indices for single-degree-of-freedom (SDOF) systems: (1) the peak displacement ductility demand, μ; (2) the cumulative plastic displacement ductility demand, μp; (3) the residual displacement ductility demand, μr; and (4) the number of yield events, ny. The main objectives of the study are (1) to develop relatively simple regression relationships that can be used to estimate mean values of these demand indices; and (2) to investigate the effects of structure yield strength, hysteretic behavior, fundamental period, site soil characteristics, seismic demand level, site seismicity, and epicentral distance on these relationships. It is shown that the correlation between μ and the other demand indices is usually relatively strong. In some cases, the cross-correlations between the demand indices are weak, indicating that these indices carry independent measures of seismic demand.

Behavior of Precast Concrete Shear Walls for Seismic Regions: Comparison of Hybrid and Emulative Specimens

AbstractThis paper discusses the lateral load behavior of two, 0.40-scale, hybrid, precast concrete shear wall test specimens and the behavior of a third precast specimen designed to emulate monolithic cast-in-place RC shear walls. The walls had identical overall geometry and were constructed by placing rectangular precast panels across horizontal joints. The hybrid walls used mild steel bars [Grade 400 (U.S. Grade 60)] and high-strength unbonded posttensioning (PT) strands for lateral resistance, whereas the emulative wall used only mild steel bars. The mild steel bars crossing the base joint were designed to yield and provide energy dissipation, with the PT steel in the hybrid walls reducing the residual displacements of the structure. The mild steel bars at the base of the emulative wall and one of the hybrid walls used Type II mechanical splices, while the other hybrid wall used continuous bars grouted into the foundation. Because of the lack of PT steel, the emulative wall developed a large residual ...

Analytical Modeling of Medium-Rise Reinforced Concrete Shear Walls

This paper describes the analytical modeling of medium-rise monolithic cast-in-place reinforced concrete (RC) shear walls where nonlinear shear deformations play a significant role in the wall response under lateral loads. The analytical models use a fiber element developed based on a microplane approach to account for combined axial, flexural, and shear effects in the nonlinear range. Low-rise shear-critical walls that fail in shear-dominated failure modes are not within the scope of the paper. The verification of the analytical models is achieved based on comparisons of estimated global (for example, load versus deflection) and local (for example, reinforcement steel strains and limit states) behaviors with experimental measurements of RC wall specimens under reversed-cyclic lateral loading.

SIMPLIFIED SEISMIC DESIGN APPROACH FOR FRICTION-DAMPED UNBONDED POST-TENSIONED PRECAST CONCRETE WALLS

In this paper, the seismic design of unbonded posttensioned precast concrete walls with supplemental friction dampers is addressed. Significant research has been conducted on unbonded posttensioned precast walls because of their simplicity in construction and desirable seismic characteristics. The greatest disadvantage of these walls in seismic regions is an increase in the lateral displacements as a result of small inelastic energy dissipation. This paper shows that these displacements can be greatly reduced by using supplemental friction dampers along vertical joints between 2 walls. A simplified performance-based seismic design approach is introduced to reduce the maximum displacement of the walls below an allowable target displacement. Nonlinear dynamic time-history analyses of 6-, 8-, and 10-story prototype walls show that the design approach is effective in reducing the lateral displacements to prevent significant damage in the walls under maximum credible ground motions.

WWW-based virtual laboratories for reinforced concrete education†

This paper introduces three interactive virtual laboratory modules for undergraduate and graduate level education on the behavior and design of reinforced concrete structures using the World Wide Web (WWW). Users can select and configure module parameters (such as reinforcement) to investigate the design and behavior of a reinforced concrete member or section.

Experimental Evaluation of Posttensioned Precast Concrete Coupling Beams

This paper describes the results from eight half-scale experiments of unbonded posttensioned precast concrete coupling beams under reversed-cyclic lateral loading. Each test specimen includes a coupling beam and the adjacent concrete wall pier regions at a floor level. Under lateral loads, the nonlinear displacements of unbonded posttensioned coupling beams are governed by the opening of gaps at the beam-to-wall joints. Steel top and seat angles are used at the beam ends to yield and provide energy dissipation. The test parameters include the beam posttensioning tendon area and initial stress, initial beam concrete axial stress, angle strength, and beam depth. The results demonstrate the lateral stiffness, strength, and ductility of the coupling beams under cyclic loading, with considerable energy dissipation concentrated in the angles. It is shown that the residual displacements of the structure upon unloading are small due to the restoring effect of the posttensioning force. The sustained chord rotation capacities of the test specimens are compared with those from previous tests of monolithic coupling beams.

Design of Concrete Mixtures with Recycled Concrete Aggregates

This paper investigates the workability, compressive strength, and elastic modulus of normal-strength concrete with recycled concrete aggregate (RCA) as replacement for coarse natural aggregate (for example, crushed stone, gravel). To represent the variability in material quality and properties, 16 different RCA sources are used in the experimental program. Three RCA concrete mixture design methods using varying amounts of direct volume aggregate replacement, direct weight replacement, and equivalent mortar replacement are compared. It is found that these different mixture design methods result in similar compressive strength and elastic modulus of RCA concrete; however, the workability of RCA concrete may be considerably reduced when using the equivalent mortar replacement method. While the effect of increased amounts of RCA on the concrete compressive strength is generally small for all three mixture design methods, the concrete elastic modulus is more significantly affected by RCA. A multiple least-squares regression analysis of the test results is conducted to develop predictive design relationships for the strength and stiffness of RCA concrete. The results suggest that the RCA water absorption and deleterious material content can be used to prequalify the material for selected concrete strength and stiffness performance objectives.

Design of Normal Strength Concrete Mixtures with Recycled Concrete Aggregates

This paper investigates the design of normal strength concrete mixtures that use recycled concrete aggregates as replacement for virgin natural aggregates. Three mix design methods utilizing direct weight replacement, equivalent mortar replacement, and direct volume replacement are compared based on concrete workability, compressive strength, and elastic modulus. A total of 42 mixes were made with different aggregate replacement amounts. It was determined that the concrete workability changes significantly depending on the replacement method used, with the direct volume and equivalent mortar methods resulting in the best and worst workability, respectively. The compressive strength and elastic modulus of the mixes with recycled concrete aggregates showed little variation from concrete with natural aggregates.