Dan Palermo

COMPRESSION FIELD MODELING OF REINFORCED CONCRETE SUBJECTED TO REVERSED LOADING: FORMULATION

Analysis of reinforced concrete (RC) structures subjected to general loading conditions requires realistic constitutive models and analytical procedures to produce reasonably accurate simulations of behavior. However, models reported that have demonstrated successful results under reversed cyclic loading are less common than models applicable to monotonic loading. This paper presents a unified approach to constitutive modeling of RC that can be implemented into finite element analysis procedures to provide accurate simulations of concrete structures subjected to reversed loading. Improved analysis and design can be achieved by modeling the main features of the hysteresis behavior of concrete and by addressing concrete in tension.

EXPERIMENTAL INVESTIGATION OF TSUNAMI IMPACT ON FREE STANDING STRUCTURES

As tsunami waves propagate towards the shoreline, they break where the water depth is approximately equal to the incident wave height. Following breaking, waves run up the shore in form of a hydraulic bore. Video footage of the 26 December 2004 Indian Ocean Tsunami shows that, upon reaching the shoreline, tsunami waves broke and transformed into a hydraulic bore that propagated onshore with considerably high velocity. However, mechanisms of hydraulic bore impact on structures are not yet well understood. Analogies between a tsunami-induced hydraulic bore and a dam-break induced wave have been previously demonstrated and published by various researchers. In order to advance the existing understanding of the complex interaction between hydraulic forces and the impacted structures, an experimental approach was taken where a dam-break induced flow, generated by the fast opening of a gate, impacted various free standing structures of different shapes located downstream of the gate. The pressures exerted on the upstream and lateral sides of a cylindrical structure, together with the bore height and the flow velocities in the flume were measured. In addition, the time history of the total force exerted on the cylindrical structure was also recorded. For the square structure, local forces on the upstream side were recorded. The effects of upstream obstacles and flow constrictions on flow velocities and on local forces exerted on a square structure were also investigated. In addition, to further understand the impact of debris during tsunami-induced flooding, wooden logs were added to the bore in order to act as water-borne missiles, while the structures reaction was measured.

Behavior of Three-Dimensional Reinforced ConcreteShear Walls

Results from two large-scale flanged shear walls tested under static cyclic displacements are presented. The objectives of the tests were to provide insight into the behavior of shear walls under cyclic displacements, and more importantly, to provide data to help corroborate constitutive models for concrete exposed to arbitrary loading conditions. The results indicated that the presence of an axial load, although relatively small, and the stiffness of flange walls have a significant effect on the strength, ductility, and failure mechanisms of the shear walls. Finite element analyses using provisional constitutive models are also provided to show that the procedures employed are stable, compliant, and provide reasonably accurate simulations of behavior. The analyses presented also indicated that two-dimensional analyses capture main features of behavior, but three-dimensional analyses are required to capture some important second-order mechanisms.

Tsunami loading of near-shoreline structures: a primer

The effects and estimation of tsunami-induced loading on near-shoreline structures located within inundation zones have recently gained significant interest from researchers, engineers, and government agencies. Building codes, namely the 2005 National building code of Canada, do not explicitly consider tsunami loading, as it is understood that inland structures can be protected by proper site planning. However, recent catastrophic events (Indian Ocean, 2004; Solomon Islands, 2007) indicate that tsunami loading should be considered in structural design. Presented herein is a review of force components that arise from tsunami-induced hydraulic bores running inland, along with proposed loading combinations and load cases readily applicable for building codes. Test results from a comprehensive experimental program conducted in a large-scale flume are also provided. A comparison of experimental results with force components provided in readily available design documents is presented, and suggestions for improv...

Experimental Modeling of Extreme Hydrodynamic Forces on Structural Models

This paper presents the results of a comprehensive experimental program focused on the impact of extreme hydrodynamic forces on structural models generated by a turbulent hydraulic bore. The parameters investigated include: (1) bore depth-time history; (2) initial flume-bed conditions (dry bed versus wet); and (3) damping effect of mitigation walls on the hydrodynamic forces. At impact, the maximum inundation (bore) depths varied between 250 mm and 450 mm and the bore front velocity ranged from 2.6 m/s to 5.0 m/s. High-speed video recordings of the bore-structural model interaction were captured simultaneously with the base shear force-, pressure-, base overturning moment-, and top lateral displacement-time histories experienced by the structural models. Three force components were identified in the bore-induced force-time histories: impulsive, run-up (transient hydrodynamic force), and quasi-steady hydrodynamic. The impulsive or run-up force was the maximum force component experienced by the structural models under initial dry-bed flume conditions; while for the initial wet-bed flume condition, the run-up force component was the maximum force. The effect of 100 mm and 150 mm low-height mitigation walls inclined at angles of 45° or 90°, which were installed at distances of 305 mm or 915 mm upstream from the structural model, was also investigated. The angle of inclination of the mitigation walls, its location relative to the structural model, and its cross-sectional shape all influence the base shear force- and base overturning moment-time histories. The base shear forces in the direction of the flow measured during experimental testing were greater than those estimated using the Federal Emergency Management Agency (FEMA) document P646, while the Structural Design Method of Buildings for Tsunami Resistance (SMBTR) overestimated the base shear forces.

Modeling of RC Shear Walls Retrofitted with Steel Plates or FRP Sheets

AbstractAdvancements in the nonlinear finite-element method have resulted in reliable simulations of response for reinforced concrete (RC) structures, provided that an analysis program with comprehensive models for material and structural behavior is employed. However, a need to provide simple, yet adaptive modeling guidelines for engineers and researchers using these tools exists, specifically for structures retrofitted with external materials for which bond behavior with the existing concrete surface is critical. Nonlinear analyses were conducted in this study to provide modeling procedures that can satisfactorily replicate the response of retrofitted RC shear walls. The retrofitting strategies included bolting of steel plates, bonding of external steel plates and fiber-reinforced polymer (FRP) sheets, and addition of steel plates with delay mechanisms. The modeling used simple rectangular and triangular membrane elements for concrete with smeared internal reinforcement, truss bar elements for external ...

BEHAVIOR OF REPAIRED CYCLICALLY LOADED SHEARWALLS

This paper describes a test program in which large-scale, 3-D wall systems were severely damaged under reversed cyclic loading conditions, and were then repaired and reloaded. The main aim was to present data that will be useful in calibration studies. The paper also shows that a proper repair can largely restore the strength, stiffness, and energy dissipation characteristics of a severely damaged wall. Lastly, it is shown that a proper account of previous loading and damage is essential if one is aiming to accurately model the response of a repaired wall.

Seismic Retrofit of Concrete Shear Walls with SMA Tension Braces

AbstractA bracing system consisting of tension-only superelastic nickel-titanium shape-memory alloy (SMA) was developed and implemented as a retrofitting methodology for seismically deficient squat...

GFRP-Retrofitted Reinforced Concrete Columns Subjected to Simulated Blast Loading

AbstractThis paper presents experimental results of one as-built and three glass-fiber-reinforced polymer (GFRP)-retrofitted reinforced concrete columns subjected to simulated blast loading. Retrofitting involved various configurations of longitudinal and transverse GFRP layers to enhance flexural and shear capacity. The objective was to study the performance and level of protection of the retrofitted columns to mitigate blast effects. The results demonstrated that retrofitting can significantly increase the strength and stiffness of reinforced concrete flexural members and greatly improve blast response. Furthermore, the addition of transverse GFRP wraps can lead to enhancements in the debonding strain and behavior of longitudinal GFRP, as well as an increase in postpeak ductility of concrete. A complementary analytical study based on the single-degree-of-freedom (SDOF) dynamic analysis method was conducted to predict the displacement response of the columns. The load–deformation relationships of the col...

Post-Tsunami Engineering Forensics

This chapter presents results from comprehensive tsunami forensic field surveys conducted by the authors immediately following three major tsunami events: 2004 Indian Ocean (Indonesia and Thailand), 2010 Chile, and 2011 Tohoku, Japan. Coastal and inland nonengineered structures located in coastal communities suffered extreme damage, many of which were completely destroyed. The Japan event also resulted in heavy damage to engineering structures. These reconnaissance field investigations were conducted within 4 weeks after the tsunamis hit the above affected areas. While tsunami surveys typically focus on determining the spatial extent of the coastal flooding, these three surveys focused on investigating the behavior of structures impacted by extreme loading due to inland flooding generated by the tsunamis. Therefore, a comprehensive review and analysis of the damage induced by the tsunamis on a variety of structures with various functions (industrial, residential, and community uses) and characteristics (geometry, type of construction material, etc.) is presented herein. In addition, this chapter also presents a concise comparison between the types of tsunami damage observed during these surveys.