Tommy Cousins

High-Performance/High-Strength Lightweight Concrete for Bridge Girders and Decks

This report presents proposed changes to the AASHTO LRFD bridge design and construction specifications to address the use of lightweight concrete in bridge girders and decks. These modified specifications will provide highway agencies with the information necessary to develop comparable designs of lightweight and normal weight concrete bridge elements for use in evaluating alternatives and selecting the alternative that will yield economic benefits. The material contained in the report should be of immediate interest to state bridge engineers and others involved in the design and construction of concrete bridges.

Field Verification of Simplified Analysis Procedures for Segmental Concrete Bridges

Load tests on segmental bridges are uncommon in the literature given their relatively short history and comparatively smaller presence in the national bridge inventory. This paper presents results from two segmental concrete bridge field tests and compares them with common simplified longitudinal and transverse analysis procedures. These single-cell structures, built with balanced cantilever construction, represent two significantly different segmental concrete bridges. Designers frequently use a beamline model for longitudinal analysis. When compared with the load test results, this simple method produces conservative predictions of longitudinal behavior within 20%, which is also reflected in the literature. Conversely, little information exists in the literature on transverse bending analysis. When analyzing the localized transverse bending from concentrated wheel loads, designers commonly use an equivalent frame model. Most frequently, designers use influence surfaces to estimate the scaled loads to apply to these two-dimensional frame models. This simplified approach is shown to be conservative overall but cannot always predict bending sense and frequently overpredicts demand in excess of 100%.

Full-Scale Investigation of Differential Settlements Beneath a Geosynthetic-Reinforced Soil Bridge Abutment

Geosynthetic-reinforced soil bridge abutments can be constructed quickly and at lower cost than traditional alternatives. However, the lack of deep foundation elements contributes to a perceived vulnerability to differential settlements at the foundation level, either because of scour undermining or compressible soils beneath the foundation. A full-scale abutment was constructed, instrumented, and subjected to carefully controlled differential settlements. Data collected during construction indicate that the abutment adequately supported the surcharge load. Subsequent large differential settlements imposed at the foundation level resulted in small surface expression of differential settlements, redistribution of stresses within the reinforced fill, and adequate support at the level of the superstructure. However, the facing units appeared vulnerable to removal, potentially exposing the reinforced fill to erosion. Three measures to help mitigate this risk are discussed: pinning the concrete masonry units (CMUs) near the corner of the abutment, adding a protective wrap behind the CMUs to encapsulate the fill, and increasing the reinforcement length at the base of the abutment.

First Use of Lightweight High-Performance Concrete Beams in Virginia

The paper describes an experimental program to demonstrate the feasibility of using lightweight high performance concrete (LWHPC) bridge beams and decks. These prestressed beams had a minimum 28-day compressive strength of 8,000 psi and the deck concrete had 4,000 psi. The beams had maximum permeability of 1500 coulombs, and the deck concrete had 2500 coulombs. The beams were required for an LWHPC demostration bridge being built in Charles City County-New Kent County border line in Virginia.

Investigation of the Effects of Transverse Bending in a Composite Inverted T-Slab Bridge System

AbstractThe composite inverted T-slab bridge system provides an accelerated bridge construction alternative for short- to medium-span bridges with spans ranging from 6.1 to 20 m. The system consists of adjacent precast inverted T-slabs with a cast-in-place (CIP) concrete topping. Such a composite bridge system offers a shallow superstructure depth ideal for sites with stringent vertical clearance requirements. When concentrated loads are applied to a bridge of this type, the bridge deforms as a two-way flat plate. This paper presents an analytical and experimental investigation to study the relationship between transverse bending and reflective cracking. Transverse bending moment demands were quantified using a finite-element model and compared with tested transverse bending moment capacities provided by several subassemblage specimens, which feature two precast cross-sectional shapes and three transverse connections. It was concluded that all tested specimens performed well at service load levels. The de...

Flexural Lateral Load Distribution Characteristics of Sandwich Plate System Bridges: Parametric Investigation

The sandwich plate system (SPS) is a relatively new bridge deck system that consists of steel face plates bonded to a rigid polyurethane core. The decks are thin, lightweight, and modular in design and can be tailored to numerous applications. This system provides an excellent alternative for the rapid construction and rehabilitation of bridge decks. With any new system, there exists some uncertainty in the design procedures as a result of the limited population for comparison. This paper presents the results of a finite-element parametric investigation of the lateral load distribution characteristics of SPS bridges. The parametric study primarily focuses on the influence of deck thickness on distribution behavior as compared to conventional reinforced concrete decks. Results from the study demonstrate that the inherent flexibility of a thin SPS deck yields larger distribution factors (up to 20%) than a typical reinforced concrete deck, but these distribution factors can still be conservatively estimated with current AASHTO LRFD methods. Additional comparisons indicate that the distribution behavior of SPS bridges can also be estimated with the equations proposed by the NCHRP 12-62 project.

Full-Scale Investigation of Differential Settlements beneath a GRS Bridge Abutment: An Overview

Geosynthetic-reinforced soil bridge abutments can be constructed rapidly, at low cost, and with relatively low environmental impact. However, like all shallow foundations, they can be vulnerable to differential settlements. A full-scale abutment was constructed, instrumented, and subjected to carefully controlled differential settlements. The abutment performed well with respect to providing support at the level of the superstructure. However, the facing blocks (concrete masonry units, or CMUs) demonstrated susceptibility to removal following settlement of the abutment, and the backfill was exposed through gaps between adjacent CMUs. Three potential measures to mitigate this risk include pinning the CMUs near the corner of the abutment, adding a protective wrap behind the CMUs to encapsulate the fill, and increasing the base width of the abutment.