Sriram Aaleti

Cyclic response of reinforced concrete walls with different anchorage details: Experimental investigation

Previoustestsofstructuralwallshaveroutinelyusedcontinuousreinforcementextendingfromthefoundationtothetopofthespec- imen. This detailing is consistently different from that of multistory walls in the field, which incorporate splices in the wall longitudinal rein- forcement above the wall-foundation interface. As a result, the performance of walls incorporating continuous reinforcement in the laboratory may not be representative of walls in the field that use lap splices or mechanical couplers near the wall base. This paper investigates lateral load behavior of three nominally identical structural walls with continuous reinforcement, lap splices, and mechanical couplers in the plastic hinge region, and quantifies the differences in their responses using force-displacement response, lateral deformation components, and energy dissipation estimated using equivalent viscous damping. DOI: 10.1061/(ASCE)ST.1943-541X.0000732.

Concept and Finite-Element Modeling of New Steel Shear Connectors for Self-Centering Wall Systems

Self-centering precast concrete walls have been found to provide excellent seismic resistance. Such systems typically exhibit low energy dissipation, requiring supplementary dissipating components to improve their seismic performance. Mild steel shear connectors can provide an economical energy dissipating element. The design and analysis of steel shear connectors for a new precast wall system has been undertaken. A series of finite-element analyses were conducted to investigate the behavior of different types of connectors. Emerged from these analyses is a oval-shaped connector (O-connector) that provided satisfactory force-displacement behavior and appeared well suited for the new wall system in high seismic regions. An extensive experimental test program was then conducted to verify the performance of the chosen O-connector, which confirmed the expected response with sufficient energy dissipation. The experimental data demonstrated good correlation with the finite-element model developed, providing satisfactory confidence in the finite-element technique used for the development of the different connectors.

Structural Behavior of Waffle Bridge Deck Panels and Connections of Precast Ultra-High-Performance Concrete: Experimental Evaluation

The AASHTO strategic plan in 2005 identified extending the service life of bridges and accelerating bridge construction as two of the grand challenges in bridge engineering. Previous studies have shown that using a prefabricated full-depth precast concrete deck system not only accelerated the bridge deck rehabilitation process but also extended its service life with reduced user delays and lower life-cycle costs. The recent use of ultra-high-performance concrete (UHPC) in the United States for bridge applications has proved efficient and economical because of its superior structural and durability characteristics. On the basis of the advantages of UHPC and precast systems, a design for a full-depth UHPC waffle deck panel system was developed. A full-scale, single-span, 60-ft long by 33-ft wide prototype bridge with full-depth prefabricated UHPC waffle deck panels has been planned as a replacement bridge in Wapello County, Iowa. In support of this project, structural performance and constructability of the UHPC waffle deck system and its critical connections were studied through an experimental program at Iowa State University. Two prefabricated, full-depth, UHPC waffle deck panels were connected to two 24-ft long precast prestressed girders, and the system was tested under service, fatigue, and ultimate loads. On the basis of the test observations and results and the experience gained from fabrication of deck panels and casting of UHPC infill joints (transverse and longitudinal), the prefabricated UHPC waffle deck system concept was found to be a viable option to achieve the goals of the AASHTO strategic plan.

Design of Ultrahigh-Performance Concrete Waffle Deck for Accelerated Bridge Construction

As part of an innovation project funded by the FHWA Highways for LIFE program, a full-depth precast, ultrahigh-performance concrete (UHPC) waffle deck panel and appropriate connections suitable for field implementation of waffle decks were developed. After a successful full-scale validation test on a unit consisting of two panels with three types of connections under laboratory conditions, the waffle deck was installed on a replacement bridge in Wapello County, Iowa. The subsequent load testing confirmed the desirable performance of the UHPC waffle deck bridge. With lessons from the completed project and outcomes from a series of simple and detailed finite element analyses of waffle decks, a design guide was developed to help broaden the design and installation of the UHPC waffle deck panel cost-effectively in new and existing bridges. This paper describes the waffle deck design introduced in the guide as it is applied to new bridges. To minimize the cost of this new bridge deck system, information on maximum rib spacing and simplified connections, along with the design of the deck panel for positive and negative moments, is presented.

Hybrid System of Unbonded Post-Tensioned CLT Panels and Light-Frame Wood Shear Walls

AbstractCross-laminated timber (CLT) is a relatively new type of massive timber system that has shown to possess excellent mechanical properties and structural behavior in building construction. When post-tensioned with high-strength tendons, CLT panels perform well under cyclic loadings because of two key characteristics: their rocking behavior and self-centering capacity. Although post-tensioned rocking CLT panels can carry heavy gravity loads, resist lateral loads, and self-center after a seismic event, they are heavy and form a pinched hysteresis, thereby limiting energy dissipation. Conversely, conventional light-frame wood shear walls (LiFS) provide a large amount of energy dissipation from fastener slip and, as their name implies, are lightweight, thereby reducing inertial forces during earthquakes. The combination of these different lateral behaviors can help improve the performance of buildings during strong ground shaking, but issues of deformation compatibility exist. This study presents the re...

Tests of structural walls to determine deformation contributions of interest for performance-based design

A collaborative research project is underway at the University of Minnesota Multi-Axial Subassemblage Testing (MAST) Laboratory regarding the behavior of structural wall systems. The investigation included tests and numerical simulations of three rectangular reinforced concrete wall systems to investigate the effect of continuous, spliced, and mechanically connected longitudinal reinforcement at the wall-foundation interface. It was anticipated that the different reinforcement details would have an effect on the plastic hinge length, local strain demands, and consequent flexural (deformation) response including the damage state of the wall systems. The walls were instrumented to investigate the overall behavior and to isolate the individual deformation components attributed to flexure and shear. Understanding the sources of deformation and correlation of the results with models that can be used to predict the behavior is important for development of performance-based seismic design procedures. The project was funded by the National Science Foundation (NSF) grants CMS0324504 and CMS0324559. BACKGROUND

Bridge Decks with Precast UHPC Waffle Panels: A Field Evaluation and Design Optimization

AbstractThe first full-depth precast ultrahigh-performance concrete (UHPC) waffle panels have been designed and implemented in a bridge replacement project to use accelerated bridge construction and increase bridge deck longevity. This paper first evaluates the structural performance of this bridge using a combination of field live-load testing and analytical modeling. The collected data for vertical deflections and strains at discrete critical locations on the bridge deck, subjected to static and dynamic truck loads, demonstrated satisfactory performance of the bridge deck and correlated well with the results obtained from the analytical model. Thereupon, options to optimize the bridge deck are examined to minimize the UHPC volume and associated labor costs. Using the analytical model, an optimization of the waffle panels was undertaken by varying the number of ribs as well as spacing between the ribs. An optimized panel was achieved by reducing the interior ribs per panel from four to two, or zero, in t...