Jerry Stephens

Performance of 100% Fly Ash Concrete with Recycled Glass Aggregate

Concrete is the most widely used construction material in the world, and with the ever-increasing population the use of concrete is expected to increase substantially. The environmental impacts of using concrete as a construction material are significant, ranging from the CO2 emitted during its production and transportation, to the disturbance of virgin land for the production of aggregates and the extraction of limestone. Therefore, there is a great need for alternative “greener” materials for use in construction. Furthermore, if these “greener” materials are generated from common waste-streams, the environmental benefits are two-fold: reduced impacts from the manufacturing of building materials and reduced need for stockpiling of common waste products. The focus of this project realizes both of these benefits through the use of fly ash as a replacement for 100% of the Portland cement in concrete and the use of recycled pulverized glass as a replacement for traditional aggregate. This paper highlights significant findings from a research effort conducted at Montana State University focused on the use of 100% fly ash concrete with recycled glass aggregate. This material was tested to investigate its suitability in construction applications and the applicability of existing design procedures. The material proved promising with respect to its fundamental engineering properties, durability, and structural performance.

Preservation of Infrastructure by Using Weigh-in-Motion Coordinated Weight Enforcement

The Montana Department of Transportation (DOT) has completed a pilot project in which data from a statewide network of weigh-in-motion (WIM) sensors were used to assist in scheduling weight-enforcement activities of patrol personnel. The purpose of the project was to determine if one of the division’s objectives—reducing infrastructure damage from overweight vehicles—could be better realized by using WIM data when dispatching officers. Data for the project were obtained from Montana’s state truck activities reporting system (STARS), which consists of WIM sites deployed around the state to collect information for a spectrum of Montana DOT activities. In this case, the STARS data were processed to determine the pavement damage caused by overweight vehicles each month during the baseline year. The trends identified from this analysis were used in the subsequent year to direct patrol efforts each month to the five sites that historically had experienced the greatest pavement damage from overweight vehicles. Officers were directed to the specific vehicle configurations historically responsible for the damage, as well as to their direction of travel and time of operation. During this year of WIM-directed enforcement, pavement damage from overweight vehicles decreased by 4.8 million equivalent single-axle load miles, and the percentage of vehicles operating over weight decreased by 20% across all STARS sites (both enforced and unenforced). While changes in loading patterns were observed during the enforcement activities (fewer overweight and more weight-compliant vehicles), the effectiveness of the focused enforcement in producing long-term changes in loading behaviors was uncertain.

Concrete Filled Steel Tube Piles to Concrete Pile-Cap Connections

This paper describes preliminary findings from a Montana Department of Transportation (MDT) funded project focused on testing the seismic performance of concrete filled steel tube (CFT) pile to concrete pile-cap connections. These connections are common/critical components of the support structure for highway bridges in Montana and across the country, and it is essential for these connections to perform well during seismic events. Despite their widespread use, the design and expected performance of these connections are not necessarily well understood. The preferred failure mechanism for this connection is for the pile cap to possess sufficient capacity to force the connection failure into the more ductile CFT piles. Traditional design methods for this connection often lead to congested and complex reinforcing schemes, and this complexity can obscure the true behavior/effectiveness of the elements within the connection. In this research effort, nine half-scale connections were tested under a monotonic pushover load until failure. The piles were then cycled through several load reversals. As a result of this research effort, a new reinforcing scheme was developed that greatly simplifies the design and construction of the connection while increasing the capacity of the cap. This newly developed reinforcing scheme includes U-shaped reinforcing bars that encircle the embedded CFT piles within the cap that counteract the moment related demands introduced by the embedded pile. In particular, this paper presents the details and results of the nine specimens tested during this research effort. Data collected during these tests includes load, deformations, and strains. The structural efficiency of the newly developed reinforcing scheme is discussed and contrasted with conventional reinforcing schemes. Additionally, future directions of this research effort are presented.

Seismic Performance of Concrete-Filled Steel Tube to Concrete Pile-Cap Connections

AbstractThis study investigates the seismic behavior of the connection between concrete-filled steel tube piles and concrete pile caps. This connection is an important component of an accelerated bridge construction technique, which involves driving steel piles to a finished elevation just below the design deck level, forming a pile cap around the ends of the driven piles, reinforcing this cap, and then filling both the piles and formwork with concrete. This cap will then serve as the deck support system. In this research, a total of six connection specimens with various details were tested under lateral loads until failure while monitoring applied loads and lateral displacements. All of the specimens achieved the desired moment capacity, and all but one experienced a typical progression of damage in the concrete cap. This progression initiated with crushing of the concrete (interior and exterior), was followed by yielding of the longitudinal reinforcement, and concluded with yielding of the transverse re...