Research

Current Research Projects

 

Automated pin-dot marking effects on A709-Gr50 Steel Plate Fatigue Capacity:

with Michael Noernberg

Supported by W&W|AFCO Steel

pin-dot pic

During fabrication of multi-piece steel assemblies, markings are often made on the steel surface to identify/track individual pieces or to provide reference for later erection. While these markings can be made by various manual methods (crayons, tags, die stamps, etc.) automated marking methods offer potential fabrication efficiencies by creating rapid computer controlled indentations in the steel surface through the repeated impact of hardened steel pins. For marked steel sections subjected to frequent or repeated loading (i.e. bridge girders, machinery components, etc.) surface indentations from these automated markings have the potential to alter component fatigue capacity. To account for marking effects, specifications often require additional experimental verification to ensure adequate fatigue performance. This research study experimentally investigates the effects of piece markings on bridge steel fatigue performance and compares capacities with existing AASHTO fatigue detail categories for compliance with AREMA specifications. Effects of the pin-dot marking frequency on fatigue susceptibility is also considered.

 

Pre-Stressed CFRP Fatigue Retrofits for Improved Waterway Lock Reliability:

with Christine Lozano and Maggie Langston

Funded by the Maritime Transportation Research and Education Center (MarTREC)

Lock-Gate

Locks are essential to waterway transport for many river and canal systems, allowing passage of ships through areas of differing water elevation. Over 23M cargo tons passed US Army Corps locks in January of 2015 alone, and 19 locks aid water transport throughout Arkansas, Louisiana, and Mississippi. These waterway locks typically consist of large steel gates that are subject to large alternating forces as water levels are changed, and as lock gates open/close. Repeated loads, corrosive waterway environments, and component geometry can all contribute to fatigue/fracture issues that can limit lock gate service and inhibit the overall reliability of waterway transport. Unfortunately, fatigue issues within steel lock gate components are often only evident once the gates are emptied for routine service, or once serviceability is interrupted by structural failures. Lock service interruptions/repairs are costly (temporary repairs to the Montgomery Lock & Dam =$3.5M) but manageable from a fatigue perspective. Research into cheap, corrosion-tolerant fatigue retrofit solutions are needed. The following project addresses fatigue issues within lock gates, identifying critical components and exploring methods for preventing fatigue cracks for the entire gate component service life. The use of carbon fiber reinforced polymer (CFRP) plates will be explored along with innovative pre-stress and bonding strategies to fine-tune component stresses and improve fatigue life.

 
Fatigue of Welded Shear Connectors in Composite Steel Bridge Beams:

with Brianna Ovuoba

Funded by W&W|AFCO Steel

Shear Stud

Fatigue often governs in the design of composite steel bridge girders, and a large number of shear connectors are often required. With the current AASHTO fatigue requirements assuming a lower shear-connector fatigue capacity than comparable specifications throughout the world, the current research project re-evaluates existing fatigue test data using a more quantifiable probabilistic approach. In addition, double-sided push-out fatigue tests are conducted to add to the existing S-N curve data sets. (Photo credit: Grady Harvell, W&W | AFCO Steel)

Click HERE for update on experimental testing currently underway

 

Towards a Fast Reconstruction Paradigm for Urban Environments
in Developing Regions Affected by Natural Disasters:

with Chris Maestri and Julian Fairey

Funded by the UofA Engineering Research & Innovation Seed Fund

http://www.ssrl-uark.com/wp-content/uploads/2015/08/Tent-City.png

Disasters in developing regions often destroy homes and contribute to unstable economic conditions that force people to live in temporary shelters for extended periods of time. This ERISF research project aims to gather preliminary data to support a novel fast rebuilding paradigm for urban environments in developing regions affected by natural disasters. The focus of the project is on multi-story, multi-purpose element, urban shelter concepts, having fully integrated simple water collection (SWAC) systems. A multi-purpose structural element is one that is locally produced in the affected area for an application not related to the shelter construction, but whose mechanical properties are well suited for carrying structural loads. In general, the multi-purpose shelter elements must be low-cost, lightweight, quickly and easily fabricated at an industrial scale, durable, and have good structural properties to allow construction of multiple stories. Example multi-purpose elements include: light-gauge steel tubing from ventilation ducts, signposts, discarded drill-piping, roadway guardrails, drain gutters, etc.

 

Recent Research Projects

 
Isolation of Carbide/Sulfide Inclusion Effects on Structural Steel
Ductile Fracture Processes:

with Qian Lin

FIB fabricated micro-specimen

Based on the underlying knowledge that metallic fractures initiate through a process of void growth around existing hard-phase particle (carbide/sulfide) inclusions, this exploratory research project focuses on an experimental approach to spatially characterize inclusion locations and measure steel alloy fracture characteristics at the micro- and macro-levels. This will leverage existing technology for a new purpose, and generate novel steel alloy fracture data at length scales not previously attempted. To better understand the fundamental processes driving ductile fracture within steel alloy materials, continuum properties and the local constitutive and damage response (which may contribute to fracture at larger scales) are measured from micro-steel specimens (diameters ranging from ~0.5 – 2microns in diameter) and macro-steel specimens (~3-4mm in diameter). These micro-specimens are fabricated through a series of focused ion beam (FIB) milling procedures, and are tested using modified nano-indentation devices capable of measuring applied forces and displacements at the micro level.

 
Evaluation and Repair of Existing Bridges in Extreme Environments:

with Korey Pough and Royce Floyd

Funded by the Southern Planes Transportation Center (SPTC)

Shear Stud

Aging or deterioration of our nation’s bridge infrastructure is a significant problem that requires attention. In general this infrastructure deterioration can be attributed to two main factors, 1) corrosion, and 2) metallic fatigue, both of which work together to reduce structural capacity over time. Many of the bridges currently in service in Oklahoma, Arkansas, and throughout the southern plains region are reaching the end of their design lives or have been labeled structurally deficient either due to deterioration or differences between past and current code requirements. The goal of the proposed project is to produce comprehensive strategies for evaluation and resilient repair of prestressed concrete and steel bridge girders subjected to extreme environments in order to increase the longevity of existing structures. The effect of end region steel corrosion on capacity of prestressed concrete girders will be examined, with the objective of producing rating procedures related to corrosion level and repair designs incorporating residual strength. Innovative design strategies for corrosion resistant steel bridge fatigue retrofits will also be explored, to protect against environmental extremes and extend bridge fatigue life under increased levels of freight/truck traffic.

 
Steel Special Moment Frame Connections with Out-of-Plane Skew:

with Paul W. Richards and Clovis Desrochers

Skewed MRF png2

Steel special moment resisting frames (SMRFs) are a popular lateral force resisting system for steel buildings because of their architectural flexibility, providing brace-free spaces.  Unusual building designs however, may require skewed moment connections. The most common SMRF connection (the reduced beam section, RBS) has never been tested with out-of-plane skew.  Our research uses numerical methods to quantify SMRF skewed connection demands and help practicing engineers determine acceptable levels of skew wherein current RBS designs are still applicable.

 

 

Effect of Radial Base-Plate Welds on the ULCF Performance of Tank Shell-to-Base Connections:

with Alain Nussbaumer

Tank Fabrication MethodDuring severe earthquakes, the base connection region of large steel tanks is subjected to large inelastic rotations and possible ultra low-cycle fatigue (ULCF) damage. Because these large steel tanks are typically constructed by welding together much smaller steel plate sections, similar to construction of a patchwork quilt, there are two base connection scenarios to consider: 1) connections contained within an entire base-plate section, having only circumferential welds, and 2) connections at the junction of two base-plate sections, having both circumferential and radial welds.  The Figure to the left  shows a typical tank assembly, with the tank base having multiple pentagonal sections near the tank edge, forming a ring for connection of the tank shell. Connections having only circumferential welds have been tested in two recent studies by Dr. Prinz; however connections with both radial and circumferential welds have not been tested.  Our research aims to experimentally quantify connection ULCF capacities for configurations having both transverse and radial welds and justify modifications to the current Eurocode standards.

 

Effect of Concrete Slabs on the Seismic Performance of Eccentrically Braced Frame Systems:

with Albano de Castro e Sousa

EBF Slab EffectsExperimental testing of steel lateral force resisting systems or components often neglects interactions with the concrete slab.  However, neglecting the concrete slab may have particular impact on predicting the performance of eccentrically braced frame (EBF) systems. In EBF systems, the in-plane slab stiffness could prevent relative column deformations, improving performance by somewhat inhibiting rotations within the link region.  Additionally, the out-of-plane stiffness in the slab and slab-to-frame interactions may have restorative (self-centering) effects, reducing residual frame drifts.  Our research aims to quantify slab contributions in EBFs with particular effort spent investigating the accumulation of ultra low-cycle fatigue damage within the link regions during dynamic loading.